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1.	Agrell, Jep, et al. (author) Effects of CO2 and light on tree phytochemistry and insect performance 2000 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 88:2, s. 259-272 Journal article (peer-reviewed)abstract Direct and interactive effects of CO2 and light on tree phytochemistry and insect fitness parameters were examined through experimental manipulations of plant growth conditions and performance of insect bioassays. Three species of deciduous trees (quaking aspen, Populus tremuloides: paper birch, Betula papyrifera; sugar maple, Acer saccharum) were grown under ambient (387 +/- 8 mu L/L) and elevated (696 +/- 2 mu L/L) levels of atmospheric CO2, with low and high light availability (375 and 855 mu mol x m(-2) x s(-1) at solar noon). Effects on the population and individual performance of a generalist phytophagous insect, the white-marked tussock moth (Orgyia leucostigma) were evaluated. Caterpillars were reared on experimental trees for the duration of the larval stage; and complementary short-term (fourth instar) Feeding trials were conducted with insects fed detached leaves. Phytochemical analyses demonstrated strong effects of both CO2 and light on all foliar nutritional variables (water. starch and nitrogen). For all species. enriched CO2 decreased water content and increased starch content, especially under high light conditions. High CO2 availability reduced levels of foliar nitrogen. but effects were species specific and most pronounced for high light aspen and birch. Analyses of secondary plant compounds revealed that levels of phenolic glycosides (salicortin and tremulacin) in aspen and condensed tannins in birch and maple were positively influenced by levels of both CO2 and light. In contrast, levels of condensed tannins in aspen were primarily affected by light, whereas levels of ellagitannins and gallotannins in maple responded to light and CO2, respectively. The lone-term bioassays showed strong treatment effects on survival, development time, and pupal mass. In general. CO2 effects were pronounced in high light and decreased along the gradient aspen > birch > maple. For larvae reared on high light aspen, enriched CO2 resulted in 62% fewer survivors. with increased development time, and reduced pupal mass. For maple-fed insects, elevated CO2 levels had negative effects on survival and pupal mass in low light. For birch, the only negative CO2 effects were observed in high light, where female larvae showed prolonged development. Fourth instar feeding trials demonstrated that low food conversion efficiency reduced insect performance. Elevated levels of CO2 significantly reduced total consumption, especially by insects on high light aspen and loa: light maple. This research demonstrates that effects of CO2 on phytochemistry and insect performance can be strongly light-dependent, and that plant responses to these two environmental variables differ among species. Overall, increased CO2 availability appeared to increase the defensive capacity of early-successional species primarily under high light conditions, and of late successional species under low light conditions. Due to the interactive effects of tree species, light, CO2, and herbivory, community composition of forests may change in the future.
2.	Agrell, Jep, et al. (author) Elevated CO2 levels and herbivore damage alter host plant preferences 2006 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 112:1, s. 63-72 Journal article (peer-reviewed)abstract Interactions between the moth Spodoptera littoralis and two of its host plants, alfalfa (Medicago sativa) and cotton (Gossypium hirsutum) were examined, using plants grown under ambient (350 ppm) and elevated (700 ppm) CO2 conditions. To determine strength and effects of herbivore-induced responses assays were performed with both undamaged (control) and herbivore damaged plants. CO2 and damage effects on larval host plant preferences were determined through dual-choice bioassays. In addition, larvae were reared from hatching to pupation on experimental foliage to examine effects on larval growth and development. When undamaged plants were used S. littoralis larvae in consumed more cotton than alfalfa, and CO2 enrichment caused a reduction in the preference for cotton. With damaged plants larvae consumed equal amounts of the two plant species (ambient CO2 conditions), but CO2 enrichment strongly shifted preferences towards cotton, which was then consumed three times more than alfalfa. Complementary assays showed that elevated CO2 levels had no effect on the herbivore-induced responses of cotton, whereas those of alfalfa were significantly increased. Larval growth was highest for larvae fed undamaged cotton irrespectively of CO2 level, and lowest for larvae on damaged alfalfa from the high CO2 treatment. Development time increased on damaged cotton irrespectively of CO2 treatment, and on damaged alfalfa in the elevated CO2 treatment. These results demonstrate that elevated CO2 levels can cause insect herbivores to alter host plant preferences, and that effects on herbivore-induced responses may be a key mechanism behind these processes. Furthermore, since the insects were shown to avoid foliage that reduced their physiological performance, our data suggest that behavioural host plant shifts result in partial escape from negative consequences of feeding on high CO2 foliage. Thus, CO2 enrichment can alter both physiology and behaviour of important insect herbivores, which in turn may to impact plant biodiver
3.	Ahlgren, Johan, et al. (author) Fleeing towards death - leech-induced behavioural defences increase freshwater snail susceptibility to predatory fish 2012 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 121:9, s. 1501-1506 Journal article (peer-reviewed)abstract Prey species are often exposed to multiple predators, which presents several difficulties to prey species. This is especially true when the response to one predator influences the preys susceptibility to other predators. Predator-induced defences have evolved in a wide range of prey species, and experiments involving predators with different hunting strategies allow researchers to evaluate how prey respond to multiple threats. Freshwater snails are known to respond to a variety of predators with both morphological and behavioural defences. Here we studied how freshwater snails Radix balthica responded behaviourally to fish and leech predators, both separately and together. Our aim was to explore whether conflicting predator-induced responses existed and, if so, what effect they had on snail survival when both predatory fish and leeches were present. We found that although R. balthica increased refuge use when exposed to predatory fish, they decreased refuge use when exposed to predatory leeches. When both predators were present, snails showed a stronger response towards leech than fish and responded by leaving the refuge. This response made the snails more susceptible to fish predation, which increased snail mortality when exposed to both fish and leech compared to fish only. We show that predators that have a relatively low predation rate can substantially increase mortality rates by indirect effects. By forcing snails out of refuges such as rock and macrophyte habitats, leeches can indirectly increase predation from molluscivorous fish and may thus affect snail densities.
4.	Albrectsen, Benedicte R., 1960-, et al. (author) Nutrient addition extends flowering display, which gets tracked by seed predators, but not by their parasitoids 2008 In: Oikos. - : Wiley-Blackwell. - 0030-1299 .- 1600-0706. ; 117, s. 473-480 Journal article (peer-reviewed)abstract Although phenological matching between two and three trophic interactions has received some attention, it has largely been disregarded in explaining the lack of strong cascade dynamics in terrestrial systems. We studied the response of the specialist seed predator, Paroxyna plantaginis (Tephritidae) and associated generalist parasitoids (Chalcidoidea) to controlled fertilisation of individuals of naturally growing Tripolium vulgare (Asteraceae) on four island populations (Skeppsvik Archipelago, Sweden). We consistently found evidence of nutrient limitation: fertilised plants increased their biomass, produced more capitula (the oviposition units for tephritid flies), were more at risk of attack by the tephritids, and puparia were heavier in fertilised plants. During some parts of the season tephritids became more heavily parasitized, supporting the presence of cascade dynamics, however net parasitism over season decreased in response to nutrient addition. We found no evidence that capitulum size complicated parasitoid access to the tephritids, however the extended bud production prolonged the flowering season. Thus, tephritids utilized the surplus production of capitula throughout the entire season, while parasitoids did not expand their oviposition time window accordingly. Implications for top down regulation and cascade dynamics in the system are discussed.
5.	Alerstam, Thomas, et al. (author) Long-distance migration: evolution and determinants 2003 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 103:2, s. 247-260 Journal article (peer-reviewed)abstract Long distance migration has evolved in many organisms moving through different media and using various modes of locomotion and transport. Migration continues to evolve or become suppressed as shown by ongoing dynamic and rapid changes of migration patterns. This great evolutionary flexibility may seem surprising for such a complex attribute as migration. Even if migration in most cases has evolved basically as a strategy to maximise fitness in a seasonal environment, its occurrence and extent depend on a multitude of factors. We give a brief overview of different factors (e.g. physical, geographical, historical, ecological) likely to facilitate and/or constrain the evolution of long distance migration and discuss how they are likely to affect migration. The basic driving forces for migration are ecological and biogeographic factors like seasonality, spatiotemporal distributions of resources, habitats, predation and competition. The benefit of increased resource availability will be balanced by costs associated with the migratory process in terms of time (incl. losses of prior occupancy advantages), energy and mortality (incl. increased exposure to parasites). Furthermore, migration requires genetic instructions (allowing substantial room for learning in some of the traits) about timing, duration and distance of migration as well as about behavioural and physiological adaptations (fuelling, organ flexibility, locomotion, use of environmental transport etc) and control of orientation and navigation. To what degree these costs and requirements put constraints on migration often depends on body size according to different scaling relationships. From this expos it is clear that research on migration warrants a multitude of techniques and approaches for a complete as possible understanding of a very complex evolutionary syndrome. In addition, we also present examples of migratory distances in a variety of taxons. In recent years new techniques, especially satellite radio telemetry, provide new information of unprecedented accuracy about journeys of individual animals, allowing re-evaluation of migration, locomotion and navigation theories.
6.	Andersson, Petter, et al. (author) How insects sense olfactory patches : the spatial scaling of olfactory information 2013 In: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 122:7, s. 1009-1016 Journal article (peer-reviewed)abstract When searching for resources in heterogeneous environments, animals must rely on their abilities to detect the resources via their sensory systems. However, variation in the strength of the sensory cue may be mediated by the physical size of the resource patch. Patch detection of insects are often predicted by the scaling of sensory cues to patch size, where visual cues has been proposed to scale proportional to the diameter of the patch. The scaling properties of olfactory cues are, however, virtually unknown. Here, we investigated scaling rules for olfactory information in a gradient of numbers of odour sources, relevant to odour-mediated attraction under field conditions. We recorded moth antennal responses to sex pheromones downwind from pheromone patches and estimated the slope in the scaling relationship between the effective length of the odour plumes and the number of odour sources. These measurements showed that the effective plume length increased proportional to the square root of the number of odour sources. The scaling relationship, as estimated in the field experiment, was then evaluated against field data of the slope in the relationship between trap catch and release rate of chemical attractants for a wide range of insects. This meta-analysis revealed an average slope largely consistent with the estimated scaling relationship between the effective plume length and the number of odour sources. This study is the first to estimate the scaling properties of olfactory cues empirically and has implications for understanding and predicting the spatial distributions of insects searching by means of olfactory cues in heterogeneous environments.
7.	Attayde, J L, et al. (author) Press perturbation experiments and the indeterminacy of ecological interactions: effects of taxonomic resolution and experimental duration 2001 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 92:2, s. 235-244 Journal article (peer-reviewed)abstract The outcomes of press perturbation experiments on community dynamics are difficult to predict because there is a high degree of indeterminacy in the strength and direction of ecological interactions. Ecologists need to quantify uncertainties in estimates of interaction strength, by determining all the possible values a given interaction strength could take and the relative likelihood of each value. In this study, we assess the degree to which fish effects on zooplankton and phytoplankton are indeterminate in direction using a combination of experimental data and Monte Carlo simulations. Based on probability distributions of interaction strength (i.e. effect magnitude), we estimated the probability of each fish interaction being negative, positive or undetermined in direction. We then investigated how interaction strength and its predictability might vary with experimental duration and the taxonomic resolution of food web data. Results show that most effects of fish on phyto- and zooplankton were indeed indeterminate, and that the effects of fish were more predictable in direction as the taxonomic resolution of food web data decreased and the experimental duration increased. Results also show that most distributions of interaction strength were not normal, suggesting that normal based statistical procedures for testing hypothesis about interaction strength may be misleading, as well as predictions of food web models assuming normal distributions of interaction strength. By considering the probability distributions and confidence intervals of interaction parameters, ecologists would better understand the outcomes of species interactions and make more realistic predictions about our perturbations in natural food webs.
8.	Barta, Z, et al. (author) Annual routines of non-migratory birds: optimal moult strategies 2006 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 112:3, s. 580-593 Journal article (peer-reviewed)abstract In a periodically changing environment it is important for animals to properly time the major events of their life in order to maximise their lifetime fitness. For a non-migratory bird the timing of breeding and moult are thought to be the most crucial. We develop a state-dependent optimal annual routine model that incorporates explicit density dependence in the food supply. In the model the birds' decisions depend on the time of year, their energy reserves, breeding status, experience, and the quality of two types of feathers (outer and inner primaries). Our model predicts that, under a seasonal environment, feathers with large effects on flight ability, higher abrasion rate and lower energetic cost of moult should be moulted closer to the winter (i.e. later) than those with the opposite attributes. Therefore, we argue that the sequence of moult may be an adaptive response to the problem of optimal timing of moult of differing feathers within the same feather tract. The model also predicts that environmental seasonality greatly affects optimal annual routines. Under high seasonality birds breed first then immediately moult, whereas under low seasonality an alternation occurs between breeding and moulting some of the feathers in one year and having a complete moult but no breeding in the other year. Increasing food abundance has a similar effect.
9.	Bengtson, Per, et al. (author) Relieving substrate limitation-soil moisture and temperature determine gross N transformation rates 2005 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 111:1, s. 81-90 Journal article (peer-reviewed)abstract A field experiment was designed with the objective to reveal the interactions between soil moisture, temperature, total, dissolved, and phosphate buffer extractable C and N, and microbial activity in the control of in situ gross N mineralization and immobilization rates in a deciduous forest. We had three alternative hypotheses to explain variations of the gross N transformations: 1) microorganisms are C limited, 2) microorganisms are N limited, or 3) neither C nor N limit the microorganisms but moisture and temperature conditions. Each hypothesis had specific criteria to be fulfilled for its acceptance. The results demonstrated that gross N transformation rates were more dependent on and variable with soil moisture and temperature than the size of the different C and N pools. The immobilization of N was dependent on the gross mineralization rate, suggesting that the production of enzymes for mineralization of organic N and the immobilization of N from the surrounding soil is disconfirmed when the intracellular N content of the microorganisms is sufficiently high. If the microorganisms are starved for N, enzyme systems involved in both the assimilation and mineralization of N are activated. The mean in situ gross N mineralization rate was two orders of magnitude higher than the natural N deposition in the area and the N addition in the NITREX experiments, meaning that a reduction in the gross N mineralization rate of about 1% would be enough to compensate for the addition of inorganic N. This decrease would hardly be detectable given the great spatial and temporal variability of N transformation rates.
10.	Birkhofer, Klaus, et al. (author) Density-dependent and -independent effects on the joint use of space by predators and prey in terrestrial arthropod food-webs 2011 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 120:11, s. 1705-1711 Journal article (peer-reviewed)abstract The spatial distribution of predators and their prey is affected by their joint use of space. While the formation of such spatial patterns may be driven by density-dependent and -independent factors our knowledge on the contribution of different land-use activities on the formation of spatial patterns between predators and prey remains very limited. Agriculture is one of the most prevailing land-use activities with strong effects on invertebrate densities and structural habitat conditions. Here, we used replicated conventionally and organically managed winter wheat fields to investigate the effects of agricultural land-use on the spatial patterns of generalist predators and decomposer prey. We then identified the explanatory power of density-dependent (prey and predator activity density) and density-independent (vegetation structure) predictors for the observed spatial patterns. Generalist predators were regularly distributed only in conventionally managed fields and this pattern intensified with decreasing Collembola prey availability and increasing spider activity density. Segregation between carabid and spider predators was strongest in fields with lowest wheat plant height, suggesting more intense intraguild interactions in structurally less complex habitats. Collembola were aggregated independent of management and aggregation was strongest in fields with highest Collembola and carabid activity density. Spiders and Collembola prey were associated, but higher aphid densities under conventional management weakened or interrupted this spatial relationship. We conclude that active control of crop plant physiognomy by growth hormones and herbicides in conventionally managed fields promotes predator–predator segregation and that a high availability of aphid prey seems to decouple predator–Collembola prey associations. Our results emphasise the need for a more mechanistic understanding of the effects of land-use on the formation of spatial patterns and species interactions, especially under scenarios of environmental change and an ongoing loss of biodiversity.
11.	Birkhofer, Klaus, et al. (author) Subsidy from the Detrital Food Web, but Not Microhabitat Complexity, Affects the Role of Generalist Predators in an Aboveground Herbivore Food Web 2008 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 117:4, s. 494-500 Journal article (peer-reviewed)abstract The activity and density of generalist predators, such as carabid beedes, rove beedes and spiders, may increase in response to: (1) increased availability of prey from the belowground subsystem and/ or (2) enhanced complexity of aboveground vegetation. Organic farming practices support decomposer populations and enhance habitat complexity due to an increased weed density. A response by generalist predators to such below-or aboveground changes could affect predation rates on herbivores in the aboveground food web. We tested this hypothesis in a replicated field experiment conducted in a winter wheat field, where increased predator activity could lead to improved control of herbivorous pests. In a crossed design, we increased and lowered densities of decomposer prey, and manipulated vegetation complexity using artificial plants in order to examine the effect of structural complexity in isolation from effects of plant-attracted additional prey. Isotomid Collembola exhibited lowest activity-densities (AD) in plots treated with soil insecticide and had gradually increasing AD in untreated plots and plots receiving detrital subsidies. Carabid beedes and cursorial spiders did not respond to increased availability of isotomid prey, and they unexpectedly displayed higher AD in the structurally less-complex plots. Aphid density mirrored the positive response of isotomids to detrital subsidies, suggesting that aphids benefited from reduced predation due to predators switching to abundant prey in the decomposer subsystem. The absence of a numerical response by surface-active predators apparendy strengthened this indirect effect of isotomids on aphids. Our results suggest that indirect predator-mediated prey-prey interactions can reduce beneficial effects of detrital subsidies on pest suppression. We further demonstrated that generalist predators may not per se benefit from structural complexity. Both results document the challenges associated with management practices that support generalist predators, as these measures may not necessarily improve herbivore suppression.
12.	Brodersen, Jakob, et al. (author) Ecosystem effects of partial fish migration in lakes 2008 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 117:1, s. 40-46 Journal article (peer-reviewed)abstract Migration is a widespread phenomenon in many ecosystems. Most often, studies on migration have focused on how migration strategies are dependent on ecological parameters, but little attention has been paid to the top-down effect of migration on ecosystem processes. Cyprinid fish in many European lakes undergo partial migration, where a part of the population leaves the lake and enters streams for the winter. In this study, we model the effect of partial migration by fish on lower trophic levels in a lake ecosystem. Our results suggest that spring phyto- and zooplankton dynamics, including occurrences of clear-water phases, can be related to the timing and magnitude of partial migration of planktivorous fish. From our results we conclude that partial migration can influence the dynamics of lower trophic levels in the ecosystem. Furthermore, we hypothesize that partial migration may affect the stability of alternative stable states and transitions between them.
13.	Brodersen, Jakob, et al. (author) Interplay between temperature, fish partial migration and trophic dynamics 2011 In: Oikos. - : Wiley-Blackwell. - 0030-1299 .- 1600-0706. ; 120, s. 1838-1846 Journal article (peer-reviewed)
14.	Bruun, Hans Henrik, et al. (author) Community-level birth rate: a missing link between ecology, evolution and diversity 2006 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 113:1, s. 185-191 Journal article (peer-reviewed)abstract We propose a conceptual model to explain the variation in species richness in local communities and in build-up of regional species pools over time. The idea is that the opportunity for new species to enter a community (its invasibility) determines the present richness of that community as well as the long-term build-up of a species pool by speciation and migration. We propose that a community's invasibility is determined by the turnover rate of reproductive genets in the community, which we call the 'community-level birth rate'. The faster the turn-over, the more species will accumulate per unit time and per unit community size (number of genets) at a given per-birth rate of immigration and speciation. Spatially discrete communities inhabiting similar environments sum up to metacommunities, whose inhabitant species constitute the regional species pool. We propose that the size of a regional species pool is determined by the aggregate community-level birth rate, the size of the metacommunity through time and age of the metacommunity. Thus, the novel contribution is our proposal of a direct effect of local environment on the build-up rate of species pools. The relative importance of immigrating species and neospecies originating locally will change with the temporal and spatial scale under consideration. We propose that the diversification rate specific to evolutionary lineages and the build-up rate of species pools are two sides of the same coin, and that they are both depending on mean generation time. The proposed model offers a reconciliation of two contrasting paradigms in current community ecology, viz. one focussing on present-time ecological processes and one focussing on historical events governing the size of species pools which in turn determines local richness
15.	Bruun, Hans Henrik, et al. (author) Why are small seeds dispersed through animal guts: large numbers or seed size per se? 2006 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 113:3, s. 402-411 Journal article (peer-reviewed)abstract Long-distance dispersal of seeds is an important process in metapopulation dynamics and in plant migrations, but at the same time extremely difficult to observe or quantify directly. If seed dispersal ability were related to attributes of seeds or motherplants, long-distance seed dispersal would be predictable by indirect approximation using easy-to-measure traits. Seed size has been suggested to be such a key trait in seed dispersal ability. However, having smaller seeds also implies having more numerous seeds per plant individual (given equal reproductive effort), and consequently increases the probability of seeds being ingested accidentally. The question is whether small-seeded species are more abundant in herbivore dung because smaller seed size increases survival rate during gut passage or because they are produced (and ingested) in greater numbers than larger seeds. We investigated endozoochorous seed dispersal via cattle grazing a meadow, and related seed abundance in dung samples to seed attributes. We found that seeds were ingested and passed through the bovine intestinal tract in proportion to the numbers produced per unit area in the grazed vegetation. In contrast, no relationship could be found between endozoochorous dispersal potential (measured as abundance of seeds in dung samples corrected for seed output in the grazed vegetation) and seed attributes such as seed mass, seed shape (roundness), and thickness of the seed coat. This finding underlines the importance of seed number in plant dispersal ability. In addition, it shows that grazing mammals may constitute an important dispersal vector for many plant species conventionally classified as 'unspecialised'.
16.	Bråthen, KA, et al. (author) Intraclonal variation in defence substances and palatability: a study on Carex and lemmings 2004 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 105:3, s. 461-470 Journal article (peer-reviewed)abstract Clonal sedges consist of integrated ramets at different development stages. Many of these sedges are important food for herbivores, yet differences in herbivore preferences and defence allocation between ramet development stages have not previously been evaluated. In this study we investigated intraclonal ramet variation in level of plant defence and nutrient compounds and intraclonal ramet preferences by lemmings (Lemmus trimucronatus) in field samples of a rhizomatous sedge (Carex stans). Plant defence was measured as the level of proteinase inhibitor activity (PIA) and the ratio of PIA to soluble plant proteins (SPP), whereas plant nutrients were measured as the level of soluble plant sugars (SPS) and SPP. Flowering ramets generally had a higher content of defence compared to vegetative ramets, which is consistent with the optimal defence theory predicting that defence compounds are allocated to the ramet stage of the highest fitness value. Compared to vegetative ramets, the flowering ramets had a lower content of SPP and a higher content of SPS. The lemmings showed preference differences between the ramet development stages, and to a large extent the ramet content of defence compounds and nutrient compounds covaried with these preferences in the predicted way. This study shows that defence allocation between ramet development stages of the clonal sedge Carex conforms to predictions of the optimal defence theory.
17.	Brönmark, Christer, et al. (author) Chemical communication in aquatic systems: an introduction 2000 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 88:1, s. 103-109 Journal article (peer-reviewed)
18.	Caplat, Paul, et al. (author) Sophia Title 2013 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 122:9, s. 1265-1274 Journal article (peer-reviewed)abstract Synthesis Prediction and management of species responses to climate change is an urgent but relatively young research field. Therefore, climate change ecology must by necessity borrow from other fields. Invasion ecology is particularly well-suited to informing climate change ecology because both invasion ecology and climate change ecology address the trajectories of rapidly changing novel systems. Here we outline the broad range of active research questions in climate change ecology where research from invasion ecology can stimulate advances. We present ideas for how concepts, case-studies and methodology from invasion ecology can be adapted to improve prediction and management of species responses to climate change. A major challenge in this era of rapid climate change is to predict changes in species distributions and their impacts on ecosystems, and, if necessary, to recommend management strategies for maintenance of biodiversity or ecosystem services. Biological invasions, studied in most biomes of the world, can provide useful analogs for some of the ecological consequences of species distribution shifts in response to climate change. Invasions illustrate the adaptive and interactive responses that can occur when species are confronted with new environmental conditions. Invasion ecology complements climate change research and provides insights into the following questions: 1) how will species distributions respond to climate change? 2) how will species movement affect recipient ecosystems? And 3) should we, and if so how can we, manage species and ecosystems in the face of climate change? Invasion ecology demonstrates that a trait-based approach can help to predict spread speeds and impacts on ecosystems, and has the potential to predict climate change impacts on species ranges and recipient ecosystems. However, there is a need to analyse traits in the context of life-history and demography, the stage in the colonisation process (e.g. spread, establishment or impact), the distribution of suitable habitats in the landscape, and the novel abiotic and biotic conditions under which those traits are expressed. As is the case with climate change, invasion ecology is embedded within complex societal goals. Both disciplines converge on similar questions of when to intervene? and what to do? which call for a better understanding of the ecological processes and social values associated with changing ecosystems.
19.	Chapman, Ben, et al. (author) Partial migration: an introduction 2011 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 120:12, s. 1761-1763 Journal article (other academic/artistic)
20.	Chapman, Ben, et al. (author) The ecology and evolution of partial migration 2011 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 120:12, s. 1764-1775 Journal article (peer-reviewed)abstract Partial migration, where populations of animals are composed of a mixture of resident and migratory individuals, is a widespread phenomenon in nature. It has been reported to occur in all major vertebrate groups, and can have significant ecological consequences. Here we give an overview of the ecology and evolution of partial migration in animals. We firstly review the different types of partial migration, and assess the ecological drivers responsible for driving individual differences in migratory tendency within populations. A variety of factors can be important in promoting the evolution of partial migration, including competition for resources or breeding opportunities, predation risk and intraspecific niche diversity. Often various factors act synergistically to create complex patterns of movement polymorphism within populations. The question of how partial migration is maintained over evolutionary timescales is also addressed. Whilst many theoretical considerations of partial migration utilise an evolutionary stable state (ESS) paradigm, empirical evidence for this is lacking. Rather the evidence suggests that partial migration is mostly condition dependent, and the optimum outcome for an individual is dependent upon its phenotype. What determines whether an individual follows a migratory or resident strategy is discussed in light of new theory and empirical data which supports the idea that environmentally responsive genetic thresholds are important across a range of species, from birds to fish, in proximately shaping migratory tendency. Finally we espouse our vision of how partial migration research will develop in the future, and suggest a number of exciting directions that studies into migratory dimorphism may take in the coming years.
21.	Clausen, P, et al. (author) Energy limitations for spring migration and breeding: the case of brent geese Branta bernicla tracked by satellite telemetry to Svalbard and Greenland 2003 In: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 103:2, s. 426-445 Conference paper (peer-reviewed)abstract Brent geese were tracked by satellite telemetry from spring staging areas in Denmark to Arctic breeding areas in Svalbard and Greenland in 1997 and 2001. From estimated departure masses and carcass analysis we used flight mechnical theory to estimate maximum flight ranges of both sexes, and remaining stores of fat and protein upon arrival in females. Model predictions suggested that all birds but one exceptionally thin male could easily reach Svalbard, but that approximately one third of the males and half of the females would have problems with flying to Greenland. Nevertheless, some birds even flew longer than the models predicted. In addition, females predicted to be capable of making the flight to Greenland, were predicted to arrive almost lean of fat. This contradicts our expectation that these birds are capital breeders - that they depend on endogenous stores of fat and protein when initiating and incubating their eggs. We discuss how the Greenland breeding sub-population during 1985-1998 has been able to grow at the same rate as the sub-population breeding in Svalbard, despite the added flight distance of 700-1000 km, and despite the birds predicted shortage of fat stores on arrival. We suggest four hypotheses that alone or in combination could explain the discrepancy between model predictions and observations. These are that most birds: (1) refuel on stop-overs in Spitsbergen en route to Greenland; (2) pick favourable tail-winds enabling them to reduce flight costs; (3) fly in formation and thereby save energy; and/or (4) undergo gut atrophy immediately prior to departure, and use the nutrients mobilised by catabolism of the digestive system to build larger pectoral muscles. The latter option would both reduce their airframe fraction, and increase their fat and flight-muscle fractions, enabling them to fly longer. We conclude that the latter option seems less likely to operate in brent geese.
22.	Drent, R, et al. (author) Pay-offs and penalties of competing migratory schedules 2003 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 103:2, s. 274-292 Journal article (peer-reviewed)abstract We relate variation in the timing of arrival by migrating birds breeding at northerly latitudes to individual differences in the prior accumulation of energy stores. Balancing starvation risks early in the season against the almost universal declining trend in reproductive prospects with advancing date is seen as an individual decision with fitness consequences. We review three studies implicating events at the staging sites or in winter in setting the individual migratory schedule. Climate change influences the timetable of a pied flycatcher (Ficedula hypoleuca) population breeding in The Netherlands and wintering in West Africa, followed since 1960. Mean air temperature in the period mid April-mid May (arrival and laying) increased and laying date advanced by 10 days. Still, in recent years most birds did not lay early enough to maximise fitness (determined by recruitment and parental survival) whereas many parents achieved this goal in 1980-1985. As the flycatchers have not started to arrive earlier, some ecological constraint further upstream is postulated (possibly the hurdle of the crossing of Sahara and Mediterranean). The ability to follow individual migrants provides a second avenue to assess the fitness implications of migratory schedules. Thus, brightly coloured male bar-tailed godwits (Limosa lapponica) captured in the Dutch Wadden Sea (the intermediate staging site linking a West African wintering area with breeding sites in arctic Russia) and traced with miniature radio-transmitters did not depart early. The 'best' males (with bright breeding plumage) were picked up by the listening stations in Sweden 650 km further along the migratory route ten days later than the paler individuals. If early arrival confers the competitive advantage of prior occupancy but increases mortality, the 'best' males may be able to afford arriving later and thus avoid some of the survival costs. Return rate of the 'bright' males to the staging site in later seasons was indeed higher than for the 'pale', early males. Intensive observation of pink-footed geese (Anser brachyrhynchus) fitted with coded neck-collars substantiate the tight relationship between energy stores (fat) accumulated up to final departure from the final staging site (Vesteralen, N. Norway) en route to the nesting grounds (Spitsbergen) and subsequent success. The breeding outcome of individual parents (accompanied by juveniles or not) could be related to observations of body condition before departure (visual 'abdominal profile index'). Recently, perceived conflicts with agriculture have resulted in widespread harassment by humans. The geese have: drastically shortened their stay on the Vesteralen, fail to achieve the body condition usual a decade ago and reproductive output has fallen. Although the geese are currently pioneering new staging sites, an adequate alternative has not materialised, underlining the critical role of the final take-off site.
23.	Dänhardt, Juliana, et al. (author) Farmland as stopover habitat for migrating birds - effects of organic farming and landscape structure 2010 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 119:7, s. 1114-1125 Journal article (peer-reviewed)abstract Agricultural intensification in Europe has affected farmland bird populations negatively, both during summer and winter. Although the migratory period poses separate challenges on birds than breeding and wintering, the consequences of farming practices for birds during migration remain poorly investigated. We monitored abundance and species richness of migratory birds in autumn at matched pairs of organic and conventional farms situated either in intensively farmed open plains (homogeneous landscapes) or in small-scale farming landscapes (heterogeneous landscapes) in southern Sweden. Total bird density did not differ between landscape types but was marginally higher on organic compared to conventional farms. When including taxonomic status in the model (passerines vs non-passerines), we found significantly more birds on organic farms, and more non-passerines in the homogeneous landscapes. The effect of farming practice and landscape type on density differed between functional groups. Omnivore density was higher in the homogeneous landscapes, and invertebrate feeders were marginally more abundant on organic farms. The effects of farming practice on the overall species richness and on the density of granivorous birds were landscape dependent. In the homogeneous landscapes, organic farms held a higher number of species and density of granivorous birds than conventional farms, but there was no such difference in the heterogeneous landscapes. Thus, organic farming can enhance abundance and species richness of farmland birds during migration, but the effect differs between landscape types and species. The effectiveness of organic farming was highest in the homogeneous landscape making it important to promote organic farming there. However, for some species during migration, increased heterogeneity in homogeneous landscapes may have negative effects. We propose that migratory bird diversity in homogeneous landscapes may be best preserved by keeping the landscape open, but that a reduced agricultural intensity, such as organic farming, should be encouraged.
24.	Griffiths, B S, et al. (author) Ecosystem response of pasture soil communities to fumigation-induced microbial diversity reductions: an examination of the biodiversity-ecosystem function relationship 2000 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 90:2, s. 279-294 Journal article (peer-reviewed)abstract A technique based on progressive fumigation was used to reduce soil microbial biodiversity, and the effects of such reductions upon the stability of key soil processes were measured. Mineral soil samples from a grassland were fumigated with chloroform for up to 24 h and then incubated for 5 months to allow recolonisation by surviving organisms. The diversity of cultivable and non-cultivable bacteria, protozoa and nematodes was progressively reduced by increasing fumigation times, as was the number of trophic groups, phyla within trophic groups, and taxa within phyla. Total microbial biomass was similar within fumigated soils, but lower than for unfumigated soil. There was no direct relationship between biodiversity and function. Some broad-scale functional parameters increased as biodiversity decreased, e.g. thymidine incorporation, growth on added nutrients, and the decomposition rate of plant residues. Other more specific parameters decreased as biodiversity decreased, e.g. nitrification, denitrification and methane oxidation. Thus specific Functional parameters may be a more sensitive indicator of environmental change than general parameters. Although fumigation reduced soil microbial biodiversity, there was evidence to suggest that it selected for organisms with particular physiological characteristics. The consequences of this for interpreting biodiversity - function relationships are discussed. The stability of the resulting communities to perturbation was further examined by imposing a transient (brief healing to 40 degrees C) or a persistent (addition of CuSO4) stress. Decomposition of grass residues was determined on three occasions after such perturbations. The soils clearly demonstrated resilience to the transient stress; decomposition rates were initially depressed by the stress and recovered over time. Resilience was reduced in the soils with decreasing biodiversity. Soils were not resilient to the persistent stress, there was no recovery in decomposition rate over time, but the soils with the highest biodiversity were more resistant to the stress than soils with impaired biodiversity. The study of functional stability under applied perturbation is a powerful means of examining the effects of biodiversity.
25.	Hagberg, Jacob, et al. (author) Uncertain biotic and abiotic interactions in benthic communities 2003 In: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 100:2, s. 353-361 Journal article (peer-reviewed)abstract We analyze marine benthic communities at different sites in Skagerrak with the purpose of understanding the role of exogenous and endogenous factors in explaining the species' temporal dynamics. The previous finding that the dynamics of these species communities are mainly driven and synchronized by environmental (temperature) forcing was only weakly supported when analyzing single-species dynamics at five sites where four of the species were present every year. There was no consistent pattern in how the temperature affected the realized per capita growth rate, either across species at a given site, or among sites for a given species. Furthermore, there was no net-interaction from the community on a given species strong enough to give rise to second-order dynamics. However, when implementing a Multi Dimensional Scaling (MDS) analysis and incorporating all sampling sites and species -we found that the different communities clustered in relation to depth, hence, communities at the same depth were more "similar" than communities at different depth. Revealing the underlying interactions shaping these marine benthic communities is a challenge that calls for an array of various and complementary approaches.
26.	Hake, M, et al. (author) Age-dependent migration strategy in honey buzzards Pernis apivorus tracked by satellite 2003 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 103:2, s. 385-396 Journal article (peer-reviewed)abstract Six adult and three juvenile honey buzzards Pernis apivorus were radio-tracked by satellite during autumn migration from southwestern Sweden. All adults crossed the Mediterranean Sea at the Strait of Gibraltar and continued across the Sahara desert to winter in West Africa, from Sierra Leone to Cameroon. Analysing three main steps of the migration, (1) from the breeding site to the southern Mediterranean region, (2) across the Sahara and (3) from the southern Sahara to the wintering sites, the adults changed direction significantly between these steps, and migrated along a distinct large-scale detour. In contrast, the juveniles travelled in more southerly directions, crossed the Mediterranean Sea at various places, but still ended up in the same wintering areas as the adults. Average speeds maintained on travelling days were similar for the two age groups, about 170 km/day in Europe, 270 km/day across Sahara and 125 km/day in Africa south of Sahara. However, as the adults used fewer stopover days en route, they maintained higher mean overall speeds and completed migration in a shorter time (42 days) than the juveniles (64 days). Although the juveniles set out on more direct courses towards the wintering grounds, they did not cover significantly shorter distances than the adults, as they tended to show a larger directional scatter between shorter flight segments. The results corroborate previous suggestions that adult and juvenile honey buzzards follow different routes during autumn migration, and that the birds change migration strategy during their lifetime. While juveniles may use individual vector orientation, social influences and learning may be of great importance for the detour migration of adults. The remarkable and distinct age-dependent shift in migratory route and orientation of the honey buzzard provides a challenging evolutionary problem.
27.	Hansson, Bengt, et al. (author) The quality and the timing hypotheses evaluated using data on great reed warblers 2000 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 90:3, s. 575-581 Journal article (peer-reviewed)abstract The seasonal decline in reproductive success observed in many animal species may be caused by timing per se (timing hypothesis) or by variation in phenotypic quality between early and late breeding females (quality hypothesis). To distinguish between these two hypotheses, several studies of birds have used clutch removal experiments to manipulate breeding date. However; removal experiments also increase the females' previous reproductive effort due to the production of an extra clutch and a longer incubation period. According to life-history theory an increase in reproductive effort lowers future reproduction. Hence, life-history theory predicts lowered success of replacement broods for other reasons than expected from the timing hypothesis. Female great reed warblers, Acrocephalus ni arundinaceus, studied in Sweden are frequently exposed to nest predation, after which many lay replacement clutches. In order to examine possible effects of previous reproductive effort on different fitness components, we analysed the re-laying frequency and the reproductive success of replacement broods in relation to time of the season and previous reproductive effort (measured as the length of the previous breeding attempt, LPB). In clutches of re-laying females both the number of fledglings and the proportion of recruits were negatively correlated with LPB, whereas re-laying frequency and clutch size were not related to LPB. We expect such relationships to be present also among other species. Consequently, the use of replacement clutches, as for example in clutch removal experiments, in evaluations of the cause of the often observed seasonal decline in various fitness components, might exaggerate the importance of the timing hypothesis over the quality hypothesis.
28.	Hargeby, Anders, et al. (author) Does a long-term oscillation in nitrogen concentration reflect climate impact on submerged vegetation and vulnerability to state shifts in a shallow lake? 2006 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 115:2, s. 334-348 Journal article (peer-reviewed)abstract Various ecosystems, including shallow lakes, are suggested to possess alternative stable state dynamics. The response of such systems to environmental change is non-linear and not fully reversible, which calls for identification of feedback mechanisms and subtle changes connected to structural stability. Here, we used a 25-year data series on water chemistry to make inferences on processes prior to a recent shift from a clear to a turbid state in Lake Takern, Sweden. Before the shift, annual concentration of total organic nitrogen (TON) described a cyclic pattern, with a periodicity of eight years. Annual TON was negatively correlated with the magnitude of a summer decline in calcium carbonate, treated as a proxy of the seasonal production of submerged vegetation. Cross-correlations of TON and the north Atlantic oscillation (NAO) indicated a possible connection to climate. The strongest correlation was obtained by a three-year lag of the NAO index. Using a set of linear time series models, the most parsimonious model was a 3(rd) order autoregressive model with NAO, delayed three years, as a covariate. Analyses of seasonality indicated that the delayed NAO signal was strongly correlated with summer TON. Also, the autocorrelation function was very similar for these two time series, and autoregressive models including NAO as a covariate were strongly supported (sum of Akaike weights = 0.93). These results indicate that climate may have contributed to the regime shift through lowered macrophyte production at the time of the shift, and therefore most likely also a depleted resilience of the clear water state. The delayed effect of climate is suggested to result from indirect and inter-year dependent response of submerged vegetation to fish kills during harsh winters.
29.	Harris, Sanna, et al. (author) Picking personalities apart: estimating the influence of predation, sex and body size on boldness in the guppy Poecilia reticulata 2010 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 119:11, s. 1711-1718 Journal article (peer-reviewed)abstract Predation is a strong selective force in most natural systems, potentially fueling evolutionary changes in prey morphology, life history and behaviour. Recent work has suggested that contrasting predation pressures may lead to population differentiation in personality traits. However, there are indications that these personality traits also differ between sexes and not necessarily in a consistent way between populations. We used an integrative approach to quantify boldness (latency to emerge from a shelter) in wild-caught guppies in relation to predation pressure, population origin, sex and size. In addition we quantified the repeatability of these personality traits. We show that predation regime had significant effects on emergence time. In general, fish from high predation localities emerged sooner from the shelter compared to those from low predation localities. We found strong sex differences; males were significantly bolder than females. The relationship between emergence time and body size was non-significant in all populations. We discuss what responses to expect from predator-nave versus predator-experienced individuals and how this can be linked to the shyness-boldness continuum.
30.	Haubert, Dominique, et al. (author) Trophic structure and major trophic links in conventional vs organic farming systems as indicated by carbon stable isotope ratios of fatty acids 2009 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 118:10, s. 1579-1589 Journal article (peer-reviewed)abstract Using bulk tissue and fatty acid 13C analysis we investigated major trophic pathways from soil microorganisms to microbial consumers to predators in conventional versus organic farming systems planted for the first time with maize. Organic farming led to an increase in microbial biomass in particular that of fungi as indicated by phospholipid fatty acids (PLFAs). Microbial PLFAs reflected the conversion from C3 to C4 plants by a shift in δ13C of 2‰, whereas the isotopic signal in fatty acids (FAs) of Collembola was much more pronounced. In the euedaphic Protaphorura fimata the δ13C values in maize fields exceeded that in C3 (soybean) fields by up to 10‰, indicating a close relationship between diet and vegetation cover. In the epedaphic Orchesella villosaδ13C values shifted by 4‰, suggesting a wider food spectrum including carbon of former C3 crop residues. Differences in δ13C of corresponding FAs in consumers and resources were assessed to assign food web links. P. fimata was suggested as root and fungal feeder in soybean fields, fungal feeder in conventional and leaf consumer in organically managed maize fields. O. villosa likely fed on root and bacteria under soybean, and bacteria and fungi under maize. Comparison of δ13C values in FAs of the cursorial spider Pardosaagrestis and O. villosa implied the latter as important prey species in soybean fields. In contrast, the web-building spider Mangora acalypha showed no predator–prey relationship with Collembola. The determination of δ13C values in trophic biomarker FAs allowed detailed insight into the structure of the decomposer food web and identified diet-shifts in both consumers at the base of the food web and in top predators in organic versus conventional agricultural systems. The results indicate changes in major trophic links and therefore carbon flux through the food web by conversion of conventional into organic farming systems.
31.	Hedenström, Anders, et al. (author) Ecology of long-distance movements: migration and orientation performance 2003 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 103:2, s. 243-245 Journal article (peer-reviewed)abstract Abstract is not available
32.	Hedlund, Katarina, et al. (author) Plant species diversity, plant biomass and responses of the soil community on abandoned land across Europe: idiosyncracy or above-belowground time lags 2003 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 103:1, s. 45-58 Journal article (peer-reviewed)abstract We examined the relationship between plant species diversity, productivity and the development of the soil community during early secondary succession on former arable land across Europe. We tested the hypothesis that increasing the initial plant species diversity enhances the biomass production and consequently stimulates soil microbial biomass and abundance of soil invertebrates. We performed five identical field experiments on abandoned arable land in five European countries (CZ, NL, SE, SP and UK) which allowed us to test our hypothesis in a range of climate, soil and other environmental factors that varied between the experimental sites. The initial plant diversity was altered by sowing seed mixtures of mid-successional grassland species with two or five grass species, one or five legumes and one or five forbs. The results of low and high sown diversity treatments were compared with plots that were naturally colonized by species present in the seed bank. In three out of the five field sites, there was no correlation between plant species number and plant biomass production, one site had a positive and the other a negative relation. Treatments with a high diversity seed mixture had a higher biomass than the naturally colonized plots. However, there was no significant difference between high and low sown diversity plots at four out of five sites. The three-year study did not give any evidence of a general bottom-up effect from increased plant biomass on biomass of bacteria, saprophytic fungi or abundance of microarthropods. The biomass of arbuscular mycorrhizal was negatively related to plant biomass. The abundance of nematodes increased after abandonment and was related to plant biomass at four sites. Our results support the hypothesis that plant species diversity may have idiosyncratic effects on soil communities, even though studies on a longer term could reveal time lags in the response to changes in composition and biomass production of plant communities.
33.	Hedlund, Katarina, et al. (author) Tritrophic interactions in a soil community enhance decomposition rates 2000 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 88:3, s. 585-591 Journal article (peer-reviewed)abstract Microbivorous soil fauna can influence decomposition rates by regulating biomass and composition of the microbial community. The idea that predators at higher trophic levels regulate population densities of microbivorous fauna and thus indirectly increase microbial growth and activity has often been suggested but rarely examined in soil ecosystems. In this paper the effects of tritrophic interactions on decomposition processes in the soil are studied and expressed as soil respiration, hyphal lengths, cellulase and chitinase activities. The experiments were carried out in soil microcosms in a factorial design with three fungal species (Alternaria alternata, Fusarium oxysporum, Trichoderma viride), the fungivorous collembolan Folsomia fimetaria and the predatory mite Hypoaspis aculeifer. The respiration rate was significantly higher with three trophic levels than in those with two and lowest in those with only fungi present. This indicates that a low level of grazing stimulates microbial respiration more than a high level or no grazing at ail. The effect was similar for all three fungal species but most pronounced in microcosms with the fungus A. alternata which was a preferred food source by the collembolans. Hyphal lengths were in all cases but with T, viride reduced in the presence of collembolans and predatory mites. T. viride had a slightly higher chitinase activity than the other fungi but increased numbers of trophic levels did not affect the enzymatic activities of any of the fungi.
34.	Henningsson, Sara, et al. (author) The role of migration for spatial turnover of arctic bird species in a circumpolar perspective 2008 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 117:11, s. 1619-1628 Journal article (peer-reviewed)abstract Several different factors may determine where species range limits are located within regions of otherwise continuously available habitat and suitable climate. Within the Arctic tundra biome many bird species are migratory and their breeding distributions are affected by migration routes that are in turn limited by factors such as suitable winter habitat, migratory stopover sites, geographical barriers and historical routes of colonization. We identified longitudinal zones in the circumpolar Arctic of pronounced changes in the avian species composition (high species spatial turnover; 'species divides'). We tested for the association between migratory status and the geographical location and numbers of such species divides for species with non-breeding habitats mainly within terrestrial, pelagic and coastal ecosystems. Our results demonstrate that migration is of profound importance for both the number and locations of species divides in the Arctic. Long-distance migration is associated with a large number of divides among terrestrial and coastal arctic birds but with a reduced number of divides among pelagic birds. We suggest that long-distance migration permits pelagic but not terrestrial and coastal birds to colonize large winter ranges, which in turn causes expansion of breeding ranges, with more homogenous communities and reduction of species divides as consequences, among the long-distance migrants of pelagic but not of terrestrial and coastal birds. Furthermore, the divides among long-distance migrants are situated in two main regions, the Beringia and Greenland zones, while divides among short-distance migrants are more evenly spaced throughout the circumpolar Arctic. The Beringia and Greenland divides result largely from inter-continental colonization of new breeding ranges but retainment of original winter quarters in a process of evolution through extension of migration routes, leading to aggregated divides in the meeting zones of major global flyways.
35.	Hyvärinen, M, et al. (author) Cyanobacterial lichen symbiosis: the fungal partner as an optimal harvester 2002 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 98:3, s. 498-504 Journal article (peer-reviewed)abstract Lichen symbiosis has been traditionally treated as a model case of mutualism in which both partners, the fungus and the photobiont. gain benefits reciprocally. Some recent evidence, however, supports an alternative view that lichen symbiosis may represent an association largely controlled by the commensal or even parasitic fungal partner. The latter gains photosynthates from the photobiont (algae and/or cyanobacteria) which may not always substantially benefit from the symbiosis. We analyze from this perspective how a lichen fungus may maximize photosynthetic gains in bipartite and tripartite associations. We treat the frequency of nitrogen-fixing cells called heterocysts in cyanobacteria and the relative proportion of green algal cells vs. that of cyanobacteria per unit fungus as the variables to be manipulated for maximal carbon gain. The model predicts that even with a negligible cost of cephalodia (compartments containing cyanobacteria) it is in the interest of the tripartite lichen, first, to increase the heterocyst frequency, and second, keep the relative number of cyanobacteria considerably lower than that of green algae. Hence, the lichen fungus achieves higher fitness by making the cyanobacterial partner to specialize on N fixation. The available empirical data support these predictions as the reported heterocyst frequencies in bipartite lichens range from 2 to 8%, and in tripartite lichens between 10 and 55%. It is concluded that interaction asymmetry (i.e. commensalism or parasitism rather than mutualism) provides a sound basis to understand the high phenotypic plasticity expressed by fungi-forming bipartite and tripartite associations with cyanobacteria and green algae.
36.	Härdling, Roger, et al. (author) A model of triploid endosperm evolution driven by parent-offspring conflict 2001 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 92:3, s. 417-423 Journal article (peer-reviewed)abstract The parental investment in angiosperms comprises the endosperm, a nutrient reserve that is used during seed development. The endosperm contains genes from both parents. The most common endosperm form is the 3n Polygonum-type with more maternal genetic influence than paternal, i.e. with two maternal nuclei and one paternal nucleus. The evolutionary original state is thought to be a diploid endosperm with equal influence of the parents. We focus on the evolution of the triploid endosperm and show that a gene for triploid endosperm would have an initial advantage in a population of diploid endosperm type plants, and increase to fixation. We assume that endosperm amount is controlled by endosperm genes. Then a gene causing triploid endosperm will increase the influence of the mother plant on parental investment. The production of endosperm with two copies of the maternal genes will modify the inheritance of endosperm amount and cause an increased production of seeds.
37.	Jackson, A L, et al. (author) Consumer-resource matching in a food chain when both predators and prey are free to move 2004 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 106:3, s. 445-450 Journal article (peer-reviewed)abstract The classical theory of the ideal free distribution (IFD) predicts that the spatial distribution of consumers should follow the distribution of the resources they depend on. Here, we study consumer-resource matching in a community context. Our model for the community is a food chain with three levels. We study whether the primary consumers are able to match resources both under predation risk and in its absence. Both prey and predators have varying degrees of knowledge of the global and local resource distribution. We present two versions of the model. In the "resource maximising" model, the consumers consider the availability of their resource only. In the "balancing" model, individual consumers minimise predation risk per unit of resource that they can gain access to. We show that both models can lead to perfect matching of consumers on resources and predators on consumers, assuming that individuals have full knowledge of the whole environment. However, when the consumers' information and freedom of movement are greater than those of the predators, then the predators generally undermatch the consumers. In the opposite case, we observe overmatching and high consumer movement rates. Furthermore, undermatching of predators on consumers tends to induce overmatching of consumers on resources.
38.	Johansson, Jonas, et al. (author) Active selection for large guppies, Poecilia reticulata, by the pike cichlid, Crenicichla saxatilis 2004 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 105:3, s. 595-605 Journal article (peer-reviewed)abstract Size-selective predation has been proposed to be one important evolutionary force shaping life-history traits in guppies (Poecilia reticulata). Populations living in the presence of the ring-tailed pike cichlid (Crenicichlasaxatilis) are smaller, mature earlier, allocate more energy to offspring and get more and smaller young than guppies in localities without Crenicichla. We investigated if Crenicichlasaxatilis is a size-selective predator, if the selectivity is a result of active choice and if the optimal prey size can be explained according to an optimal foraging model. In single-prey experiments we quantified the predators' pre-capture costs (time), capture success, and post-capture costs (time) for four different prey sizes spanning from 10 to 40 mm total length. To see which of the components of the prey cycle the predator takes into account for its choice, we then predicted prey values and optimal prey size with 6 different models that included one or more of the prey cycle components. In two multiple prey experiments, the cichlids were given the choice of the two and four different prey sizes simultaneously. Crenicichlasaxatilis actively selected the largest guppies in both cases. The three prey-value functions that included handling time (post-capture cost) did not accurately predict the prey choice. Instead the prey-value functions that took into account pre-capture cost (approach and attack time) were able to correctly predict the choice of the largest guppy size, suggesting that pre-capture costs may be more important than post-capture costs for prey choice in Crenicichlasaxatilis. The study confirms that Crenicichlasaxatilis is a size-selective predator selecting large guppies, while earlier evidence for selectivity for large prey in Crenicichla cichlids has been weak and equivocal. Our result strengthen the possibility that size-selective predation is a mechanism in life-history evolution in guppies.
39.	Jonzén, Niclas, et al. (author) Climate patterns and the stochastic dynamics of migratory birds 2002 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 97:3, s. 329-336 Journal article (peer-reviewed)abstract We analyse time series data of 17 bird species trapped at Ottenby Bird Observatory, Sweden, during spring migration 1972-1999. The species have similar demography but respond differently to variation in the North Atlantic Oscillation (NAO) - a strong determinant of winter climate in the northern Hemisphere. Species wintering in northern Europe, compared to species having winter quarters in the Mediterranean area, tend to respond positively to variation in NAO. The variation within each group is high due to wide-ranging winter-distribution in many species, probably smoothing out the effect of spatial variation in NAO. Whereas mild winters (high NAO) are benign for many - but not all - birds wintering in northern Europe, the effect of drier-than-normal conditions in the Mediterranean area during high NAO index winters is uncertain. The work presented here goes beyond simple correlative studies and help identifying which species that are most affected by variation in winter climate. This is a first important step that calls for a more mechanistic approach when analysing possible changes to climate change.
40.	Jönsson, Mikael, et al. (author) Temporal clumping of prey and coexistence of unequal interferers: experiments on social forager groups of brown trout feeding on invertebrate drift 2008 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 117:12, s. 1782-1787 Journal article (peer-reviewed)abstract Environmental fluctuations have been proposed to enhance the coexistence of competing phenotypes. Evaluations are here presented on the effects of prey density and short-term temporal clumping of prey availability on the relative foraging success of unequal interferers in social forager groups of juvenile brown trout Salmo trutta feeding on drifting invertebrate prey (frozen chironomids). Groups of three trout with established linear dominance hierarchies (dominant, intermediate and subordinate) were subjected to three different total numbers of prey, combined with three different levels of temporal clumping of prey arrival, resulting in nine treatment combinations. Higher total number of prey increased the consumption for all dominance ranks, while higher temporal clumping decreased the consumption for the dominant individuals and increased the consumption for the subordinate individuals. The proportion of prey eaten was smaller at high prey numbers. Similarly, there was a trend that increased temporal clumping also decreased the proportion of prey eaten. We conclude that density and temporal clumping of prey contribute to the coexistence of unequal interferers, and that there is a potential positive feedback between prey behaviour and phenotypic coexistence through decreased per capita predation risk for prey that drift synchronously in high densities.
41.	Knape, Jonas, et al. (author) An analysis of hatching success in the great reed warbler Acrocephalus arundinaceus 2008 In: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; :117, s. 430-438 Journal article (peer-reviewed)abstract Hatching success is a potentially important fitness component for avian species. Previous studies of hatching success in natural populations have primarily focused on effects of inbreeding but a general understanding of variation in hatching success is lacking. We analyse data on hatching success in a population of great reed warblers Acrocephalus arundinaceus in Lake Kvismaren in south central Sweden. The effects of a range of covariates, including three measures of inbreeding as well as effects of classifications in the data (such as identities of individuals), on hatching success are analysed simultaneously. This is done by means of fitting Bayesian binomial mixed models using Markov chain Monte Carlo methods. Using random effects for each individual parent we check for unexplained variation in hatching success among male and female individuals and compare it to effects of covariates such as degree of inbreeding. Model selection showed that there was a significant amount of unexplained variation in hatching probability between females. This was manifested by a few females laying eggs with a substantially lower hatching success than the majority of the females. The deviations were of the same order of magnitude as the significant effect of parent relatedness on hatching success. Whereas the negative effect of parent relatedness on hatchability is an expression of inbreeding, the female individual effect is not due to inbreeding and could reflect maternal effects, that females differ in fertilisation and/or incubation ability, or an over representation of genetic components from the female acting on the early developing embryo.
42.	Kvist, Anders, et al. (author) Gluttony in migratory waders - unprecedented energy assimilation rates in vertebrates 2003 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 103:2, s. 397-402 Journal article (peer-reviewed)abstract Maximum energy assimilation rate has been implicated as a constraint on maximal sustained energy expenditure, on biomass production, and in various behavioural and life history models. Data on the upper limit to energy assimilation rate are scarce, and the factors that set the limit remain poorly known. We studied migratory waders in captivity, given unlimited food supply around the clock. Many of these waders assimilated energy at rates of seven to ten times basal metabolism, exceeding maximum rates reported for vertebrates during periods of high energy demand, for example during reproduction and in extreme cold. One factor allowing the high energy assimilation rates may be that much of the assimilated energy is stored and not concomitantly expended by muscles or other organs. The remarkable digestive capacity in waders is probably an adaptation to long and rapid migrations, putting a premium on high energy deposition rates. The upper limit to daily energy assimilation in vertebrates is clearly higher than hitherto believed, and food availability, total daily feeding time and, possibly, the fate of assimilated energy may be important factors to take into account when estimating limits to energy budgets in animals.
43.	Lankinen, Åsa, et al. (author) Allocation to pollen competitive ability versus seed production in Viola tricoloras an effect of plant size, soil nutrients and presence of a root competitor 2012 In: Oikos. - : John Wiley & Sons. - 0030-1299 .- 1600-0706. ; 122:5, s. 779-789 Journal article (peer-reviewed)abstract In hermaphroditic plants, the effect of a social environment on sex allocation has not been studied to our knowledge, while in hermaphroditic animals such effects are known to be common. In recent years, studies on root competition beyond the effects of nutrients have shown that plants can respond to their conspecific root competitors (social environment), making it interesting to ask if these effects could also influence sex allocation in addition to more commonly studied factors, such as plant size or resources. In this study on hermaphroditic Viola tricolor, we investigated how plant size, soil nutrients and presence of a root competitor influenced allocation to pollen competitive ability versus seed production, i.e. male and female reproductive functions. We allowed plants to grow in pairs with partly intermingled or separate roots in the same amount of soil. In additional treatments with intermingled roots (as part of the same experiment) one of the two competitors was given combinations of nitrogen (N), phosphorous (P) and micro nutrients. We found that pollen performance but not seed production increased when plants were in contact in the soil. Additionally, pollen performance was negatively correlated to plant size across fertilisation treatments. For seed production, the opposite relation to plant size was seen, indicating that large, fertilized plants invest relatively more in the female function. In conclusion, in violets, sex allocation appears to be size-dependent and influenced by both the presence of a root competitor and by nutrients. These results suggest that social environment can influence sex allocation in plants as well as in animals, indicating that such effects are important to consider in sex allocation studies across taxa.
44.	Lankinen, Åsa, et al. (author) Evolution of pistil length as a choice mechanism for pollen quality 2001 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 92:1, s. 81-90 Journal article (peer-reviewed)abstract During the fertilisation process in plants, pollen tube growth rate may be selected as a trait important in male to male competition. Since female morphology provides the necessary selective arena for such competition. we investigate if sexual selection theory can be used to explain the evolution of pistil length as a female choice mechanism. This choice is performed by direct interference with male to male competition. Furthermore, the sessile nature of plants limits the number of mates a female can choose between, which could limit the benefit a female can gain from distinguishing between donors. To mirror these circumstances, we model a situation when there are only two competitors at a time. Using a game theoretical approach we show that if pollen tube growth rate can be used as an indication of heritable quality, pistil length can be selected in response to variation of this trait. We further find that length of the pistil affects selection of pollen tube growth rate. Thus female preference and male competitive ability co-evolve, but this does not necessarily lead to a positive relationship between the two. Under certain circumstances we find a negative relation instead. Given realistic differences in male quality, the model indicates that there is a potential for evolution of female morphology as a choice mechanism for pollen quality.
45.	Lankinen, Åsa, et al. (author) The effect of pollen competition on maintenance of variation in fertilisation ability 2001 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 93:3, s. 459-469 Journal article (peer-reviewed)abstract Pollen competition in the pistil does not only give flowering plants the possibility to reduce inbreeding but also provides an opportunity for selection of pollen traits that increase male reproductive success. An objection to the existence of selection on pollen competitive ability is that individual variation should quickly vanish if selection is strong. A balance between selection for local adaptation of sporophytes within sites and pollen flow between sites could maintain variation in pollen competitive ability. A prerequisite is that variation in male competitive ability is condition dependent, i.e., influenced by sporophytic adaptation to a parch. This further means that selection on pollen competitive ability can occur both directly on the gamethophytic level and indirectly on the sporophytic level. Our dynamic model shows that maintenance of variation in male competitive ability is more probable when: differences in pollen competitive ability influence male fitness, i.e., in cases with pollen competition, than when differences in this trait only is a side effect of selection for more viable individuals. Since there is a connection between the gamethophytic and sporophytic life-phases, the incidence of pollen competition between donors should make it more probable that variability also in sporophyte fitness is preserved.
46.	Lardner, Björn (author) Morphological and life history responses to predators in larvae of seven anurans 2000 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 88:1, s. 169-180 Journal article (peer-reviewed)abstract Amphibian larvae often face two major sources of mortality: pond desiccation and predation. Tadpoles of seven anuran species with different preferences for type of breeding habitat, on a hydroperiod scale, were tested for responses to the presence of predators by raising them experimentally in the presence and absence of a separately caged invertebrate predator that was fed on conspecific tadpoles. The species typically breeding in temporary or semi-permanent ponds (Rana temporaria, Rana arvalis, Rana dalmatina and Hyla arborea) - where invertebrate predator populations are predicted to vary considerably spatiotemporally - all showed marked induced increases in tail fin depth in response to predator presence. These species also tended to respond by reduced growth rates. The representative of the most ephemeral habitats, Bufo calamita, did not respond in any of these traits. Its congeneric, Bufo bufo, a toxic inhabitant of permanent ponds and lakes, tended to respond to predator presence by reducing its growth rate, though not by a tail depth increase. I argue that the rather poor swimming performance in Bufo tadpoles may opt for defences other than locomotor ability. The palatable, permanent pond species Pelobates fuscus did not alter either its growth rate or tail morphology. Possible explanations for this result are discussed.
47.	Leps, J, et al. (author) Separating the chance effect from other diversity effects in the functioning of plant communities 2001 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 92:1, s. 123-134 Journal article (peer-reviewed)abstract The effect of plant species diversity on productivity and competitive ability was studied in an experiment carried out simultaneously in five European countries: Czech Republic (CZ), the Netherlands (NL), Sweden (SE), Spain (SP), and United Kingdom (UK). The aim was to separate the 'chance' or 'sampling effect' (increasing the number of sown species increases the probability that a species able 'to do a job' will be included) from the complementarity effect (species-rich communities are better able to exploit resources and to take care of ecosystem functions than species-poor communities). In the experiment, low diversity (LD) and high diversity (HD) mixtures of grassland species were sown into fields taken out of arable cultivation. The HD mixture consisted of five grass species, five legumes and five other forbs. The LD mixtures consisted of two grasses, one legume and one other forb, with different plant species combinations in each replicate block. The design of the experiment was constructed in such a way that the total number of seeds of each species over all the replications was exactly the same in HD and LD treatments, and the total number of grass seeds, leguminous seeds and other forb seeds were the same in both LD and HD. The responses measured were the total above-ground biomass las a measure of productivity) and the average number of naturally establishing species in a plot las a measure of the competitive ability of the mixture), both measured in the third year of the experiment. The results show that, on average, the HD plots performed better (i.e., attained higher biomass, had better weed suppression), but that the best LD mixture was as good as the best HD mixture. On the contrary, the worst LD mixture was always less successful than the worst HD replicate. The performance of particular species in the HD mixtures was a good predictor of the success of a certain species combination in a LD mixture (explaining 61% of variability between particular LD mixtures). In all sites, the LD mixture composed of species which were the most abundant in HD mixtures was as efficient in suppressing weeds as the HD mixture itself. It is argued that the performance of a species assemblage is influenced mostly by the identity of species and the diversity effect is mainly due to the 'chance' or 'sampling' effect with increasing number of species the probability that an important species will be included in the mixture increases. Caution is urged in interpreting experiments with manipulated diversity and the possible limitations of such experiments are discussed.
48.	Linden, Andreas, et al. (author) Estimating environmental effects on population dynamics: consequences of observation error 2009 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 118:5, s. 675-680 Journal article (peer-reviewed)abstract Within the paradigm of population dynamics a central task is to identify environmental factors affecting population change and to estimate the strength of these effects. We here investigate the impact of observation errors in measurements of population densities on estimates of environmental effects. Adding observation errors may change the autocorrelation of a population time series with potential consequences for estimates of effects of autocorrelated environmental covariates. Using Monte Carlo simulations, we compare the performance of maximum likelihood estimates from three stochastic versions of the Gompertz model (log-linear first order autoregressive model), assuming 1) process error only, 2) observation error only, and 3) both process and observation error (the linear state-space model on log-scale). We also simulated population dynamics using the Ricker model, and evaluated the corresponding maximum likelihood estimates for process error models. When there is observation error in the data and the considered environmental variable is strongly autocorrelated, its estimated effect is likely to be biased when using process error models. The environmental effect is overestimated when the sign of the autocorrelations of the intrinsic dynamics and the environment are the same and underestimated when the signs differ. With non-autocorrelated environmental covariates, process error models produce fairly exact point estimates as well as reliable confidence intervals for environmental effects. In all scenarios, observation error models produce unbiased estimates with reasonable precision, but confidence intervals derived from the likelihood profiles are far too optimistic if there is process error present. The safest approach is to use state-space models in presence of observation error. These are factors worthwhile to consider when interpreting earlier empirical results on population time series, and in future studies, we recommend choosing carefully the modelling approach with respect to intrinsic population dynamics and covariate autocorrelation.
49.	Lindström, Åke, et al. (author) Density-dependent reproductive output in relation to a drastically varying food supply: getting the density measure right 2005 In: Oikos - Copenhagen. - : Wiley. - 0030-1299 .- 1600-0706. ; 110, s. 155-163 Journal article (peer-reviewed)
50.	Lundberg, Per, et al. (author) Visibility of demography-Modulating noise in population dynamics 2002 In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 96:2, s. 379-382 Journal article (peer-reviewed)

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