| 1. |
- Agrell, Jep, et al.
(author)
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Effects of CO2 and light on tree phytochemistry and insect performance
- 2000
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In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 88:2, s. 259-272
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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.
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| 2. |
- Ahlgren, Johan, et al.
(author)
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Fleeing towards death - leech-induced behavioural defences increase freshwater snail susceptibility to predatory fish
- 2012
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In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 121:9, s. 1501-1506
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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.
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| 3. |
- Alerstam, Thomas, et al.
(author)
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Long-distance migration: evolution and determinants
- 2003
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In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 103:2, s. 247-260
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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.
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| 4. |
- Andersson, Petter, et al.
(author)
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How insects sense olfactory patches : the spatial scaling of olfactory information
- 2013
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In: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 122:7, s. 1009-1016
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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.
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| 5. |
- Attayde, J L, et al.
(author)
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Press perturbation experiments and the indeterminacy of ecological interactions: effects of taxonomic resolution and experimental duration
- 2001
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In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 92:2, s. 235-244
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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.
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| 6. |
- Birkhofer, Klaus, et al.
(author)
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Density-dependent and -independent effects on the joint use of space by predators and prey in terrestrial arthropod food-webs
- 2011
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In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 120:11, s. 1705-1711
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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.
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| 7. |
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| 8. |
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| 9. |
- Caplat, Paul, et al.
(author)
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Sophia Title
- 2013
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In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 122:9, s. 1265-1274
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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.
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| 10. |
- Chapman, Ben, et al.
(author)
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Partial migration: an introduction
- 2011
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In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 120:12, s. 1761-1763
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Journal article (other academic/artistic)
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