| 1. |
- Öhlund, Gunnar, et al.
(författare)
-
Apex predator induces predator-rich ecosystem state innorthern lakes
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Large predators are disappearing from ecosystems around the world. If predator speciesfacilitate each other’s existence through niche construction, this development could causecascading predator collapses and reduce ecosystem resilience. However, the importance offacilitation for the assembly and function of predator communities remains poorly understood.Here, we show that a large piscivorous fish, the northern pike (Esox lucius), enables theformation of a numerous and diverse predator community by inducing a dwarf ecotype ofEuropean whitefish (Coregonus lavaretus). Pike increases the standing biomass of prey-sized(<200mm) whitefish with a factor of 12.6, allowing small-gaped fish species (Percafluviatilis, Lota lota, Salvelinus alpinus and Salmo trutta) to go from small-growinggeneralists, to large-growing piscivores. Similarly, a guild of piscivorous birds (Gavia arctica,G. stellata, Sterna paradisaea, S. hirundo, Mergus serrator and M. merganser) shift from amixed diet to relying mainly on whitefish prey in presence of pike. Through this regime shift,the functional piscivore biomass in the non-pike fish community increases with a factor of14.2, and the density- and species richness of piscivorous birds increase with factors of 2.08and 2.16, respectively. Our results demonstrate how feedbacks between presence/absence ofimportant predators and the phenotype of prey may keep complex ecosystems in predator-richor predator-depleted states.
|
|
| 2. |
- Öhlund, Gunnar, 1977-, et al.
(författare)
-
Ecological speciation in European whitefish is driven by a large‐gaped predator
- 2020
-
Ingår i: Evolution Letters. - : John Wiley & Sons. - 2056-3744. ; 4:3, s. 243-256
-
Tidskriftsartikel (refereegranskat)abstract
- Lake‐dwelling fish that form species pairs/flocks characterized by body size divergence are important model systems for speciation research. Although several sources of divergent selection have been identified in these systems, their importance for driving the speciation process remains elusive. A major problem is that in retrospect, we cannot distinguish selection pressures that initiated divergence from those acting later in the process. To address this issue, we studied the initial stages of speciation in European whitefish (Coregonus lavaretus) using data from 358 populations of varying age (26–10,000 years). We find that whitefish speciation is driven by a large‐growing predator, the northern pike (Esox lucius). Pike initiates divergence by causing a largely plastic differentiation into benthic giants and pelagic dwarfs: ecotypes that will subsequently develop partial reproductive isolation and heritable differences in gill raker number. Using an eco‐evolutionary model, we demonstrate how pike's habitat specificity and large gape size are critical for imposing a between‐habitat trade‐off, causing prey to mature in a safer place or at a safer size. Thereby, we propose a novel mechanism for how predators may cause dwarf/giant speciation in lake‐dwelling fish species.
|
|
| 3. |
|
|
| 4. |
|
|
| 5. |
- Abrahamsen, Håkon B, et al.
(författare)
-
Simulation-based training and assessment of non-technical skills in the Norwegian Helicopter Emergency Medical Services : a cross-sectional survey
- 2015
-
Ingår i: Emergency Medicine Journal. - : BMJ. - 1472-0205 .- 1472-0213. ; 32:8, s. 647-653
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Human error and deficient non-technical skills (NTSs) among providers of ALS in helicopter emergency medical services (HEMS) is a threat to patient and operational safety. Skills can be improved through simulation-based training and assessment. Objective: To document the current level of simulation-based training and assessment of seven generic NTSs in crew members in the Norwegian HEMS. Methods: A cross-sectional survey, either electronic or paper-based, of all 207 physicians, HEMS crew members (HCMs) and pilots working in the civilian Norwegian HEMS (11 bases), between 8 May and 25 July 2012. Results: The response rate was 82% (n=193). A large proportion of each of the professional groups lacked simulation-based training and assessment of their NTSs. Compared with pilots and HCMs, physicians undergo statistically significantly less frequent simulation-based training and assessment of their NTSs. Fifty out of 82 (61%) physicians were on call for more than 72 consecutive hours on a regular basis. Of these, 79% did not have any training in coping with fatigue. In contrast, 72 out of 73 (99%) pilots and HCMs were on call for more than 3 days in a row. Of these, 54% did not have any training in coping with fatigue. Conclusions: Our study indicates a lack of simulation-based training and assessment. Pilots and HCMs train and are assessed more frequently than physicians. All professional groups are on call for extended hours, but receive limited training in how to cope with fatigue.
|
|
| 6. |
- Englund, Göran, 1957-, et al.
(författare)
-
Holocene extinctions of a top predator : effects of time, habitat area and habitat subdivision
- 2020
-
Ingår i: Journal of Animal Ecology. - : John Wiley & Sons. - 0021-8790 .- 1365-2656. ; 89:5, s. 1202-1215
-
Tidskriftsartikel (refereegranskat)abstract
- Loss of habitat and changes in the spatial configuration of habitats are major drivers of species extinctions, but the responses to these drivers differ between organisms. To advance theory on how extinction risk from different types of habitat alteration relates to species-specific traits, there is a need for studies of the long-term extinction dynamic of individual species. The goal of this study was to quantify how habitat area and the spatial configuration of habitats affect extinction rate of an aquatic top predator, the northern pike Esox lucius L. We recorded the presence/absence of northern pike in 398 isolated habitat fragments, each one consisting of a number of interconnected lakes. Time since isolation of the habitat fragments, caused by cut-off from the main dispersal source in the Baltic Sea, varied between 0 and 10,000 years. Using survival regression, we analysed how pike population survival was affected by time since isolation, habitat size and habitat subdivision. The approach builds on the assumptions that pike colonized all fragments before isolation and that current absences result from extinctions. We verified these assumptions by testing (a) if pike was present in the region throughout the entire time period when the lakes formed and (b) if pike typically colonize lakes that are formed today. We also addressed the likelihood that unrecorded anthropogenic introductions could bias our estimates of extinction rate. Our results supported the interpretation that current patterns of presence/absence in our study system are shaped by extinctions. Further, we found that time since isolation and fragment area had strong effects on pike population survival. In contrast, spatial habitat subdivision (i.e. if a fragment contained few large lakes or many small lakes) and other environmental covariates describing climate and productivity were unrelated to pike survival. Over all, extinction rate was high in young fragments and decreased sharply with increasing fragment age. Our study demonstrates how the link between extinction rate and habitat size and spatial structure can be quantified. More similar studies may help us find generalizations that can guide management of habitat size and connectivity.
|
|
| 7. |
- Englund, Göran, 1957-, et al.
(författare)
-
Temperature dependence of the functional response
- 2011
-
Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 14:9, s. 914-21
-
Tidskriftsartikel (refereegranskat)abstract
- The Arrhenius equation has emerged as the favoured model for describing the temperature dependence of consumption in predator-prey models. To examine the relevance of this equation, we undertook a meta-analysis of published relationships between functional response parameters and temperature. We show that, when plotted in lin-log space, temperature dependence of both attack rate and maximal ingestion rate exhibits a hump-shaped relationship and not a linear one as predicted by the Arrhenius equation. The relationship remains significantly downward concave even when data from temperatures above the peak of the hump are discarded. Temperature dependence is stronger for attack rate than for maximal ingestion rate, but the thermal optima are not different. We conclude that the use of the Arrhenius equation to describe consumption in predator-prey models requires the assumption that temperatures above thermal optima are unimportant for population and community dynamics, an assumption that is untenable given the available data.
|
|
| 8. |
- Hansson, Lena, 1967-, et al.
(författare)
-
Vitamin D, liver-related biomarkers, and distribution of fat and lean mass in young patients with Fontan circulation
- 2022
-
Ingår i: Cardiology in the Young. - : Cambridge University Press. - 1047-9511 .- 1467-1107. ; 32:6, s. 861-868
-
Tidskriftsartikel (refereegranskat)abstract
- Introduction/aim: Young patients with Fontan circulation may have low serum 25-hydroxyvitamin D levels, an affected liver, and unhealthy body compositions. This study aimed to explore the association between vitamin D intake/levels, liver biomarkers, and body composition in young Fontan patients.Method: We collected prospective data in 2017 to 2018, obtained with food-frequency questionnaires, biochemical analyses of liver biomarkers, and dual-energy X-ray absorptiometry scans in 44 children with Fontan circulation. Body compositions were compared to matched controls (n = 38). Linear regression analyses were used to investigate associations of biomarkers, leg pain, and lean mass on serum levels of 25-hydroxyvitamin D. Biomarkers were converted to z scores and differences were evaluated within the Fontan patients.Results: Our Fontan patients had a daily mean vitamin D intake of 9.9 µg and a mean serum 25-hydroxyvitamin D of 56 nmol/L. These factors were not associated with fat or lean mass, leg pain, or biomarkers of liver status. The Fontan patients had significantly less lean mass, but higher fat mass than controls. Male adolescents with Fontan circulation had a greater mean abdominal fat mass than male controls and higher cholesterol levels than females with Fontan circulation.Conclusion: Vitamin D intake and serum levels were not associated with body composition or liver biomarkers in the Fontan group, but the Fontan group had lower lean mass and higher fat mass than controls. The more pronounced abdominal fat mass in male adolescents with Fontan circulation might increase metabolic risks later in life.
|
|
| 9. |
- Hein, Catherine L, et al.
(författare)
-
Dispersal through stream networks : modelling climate-driven range expansions of fishes
- 2011
-
Ingår i: Diversity & distributions. - : Wiley. - 1366-9516 .- 1472-4642. ; 17:4, s. 641-651
-
Tidskriftsartikel (refereegranskat)abstract
- Aim To incorporate dispersal through stream networks into models predicting the future distribution of a native, freshwater fish given climate change scenarios. Location Sweden. Methods We used logistic regression to fit climate and habitat data to observed pike (Esox lucius Linnaeus) distributions in 13,476 lakes. We used GIS to map dispersal pathways through streams. Lakes either (1) contained pike or were downstream from pike lakes, (2) were upstream from pike lakes, but downstream from natural dispersal barriers, or (3) were isolated from streams or were upstream from natural dispersal barriers. We then used climate projections to model future distributions of pike and compared our results with and without including dispersal. Results Given climate and habitat, pike were predicted present in all of 99,249 Swedish lakes by 2100. After accounting for dispersal barriers, we only predicted pike presence in 31,538 lakes. Dispersal barriers most strongly limited pike invasion in mountainous regions, but low connectivity also characterized some relatively flat regions. Main conclusions The dendritic network structure of streams and interconnected lakes makes a two-dimensional representation of the landscape unsuitable for predicting range shifts of many freshwater organisms. If dispersal through stream networks is not accounted for, predictions of future fish distributions in a warmer climate might grossly overestimate range expansions of warm and cool-water fishes and underestimate range contractions of cold-water fishes. Dispersal through stream networks can be modelled in any region for which a digital elevation model and species occurrence data are available.
|
|
| 10. |
- Hein, Catherine L., et al.
(författare)
-
Fish introductions reveal the temperature dependence of species interactions
- 2014
-
Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 281:1775, s. 20132641-
-
Tidskriftsartikel (refereegranskat)abstract
- A major area of current research is to understand how climate change will impact species interactions and ultimately biodiversity. A variety of environmental conditions are rapidly changing owing to climate warming, and these conditions often affect both the strength and outcome of species interactions. We used fish distributions and replicated fish introductions to investigate environmental conditions influencing the coexistence of two fishes in Swedish lakes: brown trout (Salmo trutta) and pike (Esox lucius). A logistic regression model of brown trout and pike coexistence showed that these species coexist in large lakes (more than 4.5 km(2)), but not in small, warm lakes (annual air temperature more than 0.9-1.5 degrees C). We then explored how climate change will alter coexistence by substituting climate scenarios for 2091-2100 into our model. The model predicts that brown trout will be extirpated from approximately half of the lakes where they presently coexist with pike and from nearly all 9100 lakes where pike are predicted to invade. Context dependency was critical for understanding pike-brown trout interactions, and, given the widespread occurrence of context-dependent species interactions, this aspect will probably be critical for accurately predicting climate impacts on biodiversity.
|
|
| 11. |
- Hein, Catherine L., et al.
(författare)
-
Future distribution of Arctic Char Salvelinus alpinus in Sweden under climate change : Effects of temperature, lake size and species interactions
- 2012
-
Ingår i: Ambio. - : Springer Netherlands. - 0044-7447 .- 1654-7209. ; 41:3, s. 303-312
-
Tidskriftsartikel (refereegranskat)abstract
- Novel communities will be formed as species with a variety of dispersal abilities and environmental tolerances respond individually to climate change. Thus, models projecting future species distributions must account for species interactions and differential dispersal abilities. We developed a species distribution model for Arctic char Salvelinus alpinus, a freshwater fish that is sensitive both to warm temperatures and to species interactions. A logistic regression model using lake area, mean annual air temperature (1961-1990), pike Esox lucius and brown trout Salmo trutta occurrence correctly classified 95 % of 467 Swedish lakes. We predicted that Arctic char will lose 73 % of its range in Sweden by 2100. Predicted extinctions could be attributed both to simulated temperature increases and to projected pike invasions. The Swedish mountains will continue to provide refugia for Arctic char in the future and should be the focus of conservation efforts for this highly valued fish.
|
|
| 12. |
- Olajos, Fredrik, et al.
(författare)
-
Consistent findings from ddPCR and metabarcoding analyses of piscivorous bird diets
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The diet of apex predators is crucial for addressing fundamental ecological questions. The diets ofpiscivorous birds have traditionally been studied using invasive methods that may be harmful.Consequently, researchers have been compelled to explore alternative options. Molecular toolshave proven effective in discerning dietary preferences of piscivorous birds. In this study, a totalof 151 faecal samples were collected from 6 bird species of lacustrine piscivorous birds occupying36 lakes from 2018 to 2022. Faecal samples were analysed using two molecular methods todetermine the proportion of fish DNA using 1) high-throughput sequencing metabarcoding withthe teleo-2 universal fish primer and 2) a digital droplet PCR array with 7 species-specific newlydesigned primers targeting the most common prey fish species in Scandinavian freshwaterecosystems. The dominant prey species identified by both methods were: whitefish (Coregonuslavaretus), Eurasian perch (Perca fluviatilis) and Eurasian minnow (Phoxinus phoxinus). The twomethods showed a high degree of agreement, suggesting that they both provide accurateassessments of the dietary compositions of bird diets.
|
|
| 13. |
- Olajos, Fredrik, et al.
(författare)
-
Estimating species colonization dates using DNA in lake sediment
- 2018
-
Ingår i: Methods in Ecology and Evolution. - : British Ecological Society. - 2041-210X. ; 9:3, s. 535-543
-
Tidskriftsartikel (refereegranskat)abstract
- Detection of DNA in lake sediments holds promise as a tool to study processes like extinction, colonization, adaptation and evolutionary divergence. However, low concentrations make sediment DNA difficult to detect, leading to high false negative rates. Additionally, contamination could potentially lead to high false positive rates. Careful laboratory procedures can reduce false positive and negative rates, but should not be assumed to completely eliminate them. Therefore, methods are needed that identify potential false positive and negative results, and use this information to judge the plausibility of different interpretations of DNA data from natural archives.We developed a Bayesian algorithm to infer the colonization history of a species using records of DNA from lake-sediment cores, explicitly labelling some observations as false positive or false negative. We illustrate the method by analysing DNA of whitefish (Coregonus lavaretus L.) from sediment cores covering the past 10,000 years from two central Swedish lakes. We provide the algorithm as an R-script, and the data from this study as example input files.In one lake, Stora Lögdasjön, where connectivity with the proto-Baltic Sea and the degree of whitefish ecotype differentiation suggested colonization immediately after deglaciation, DNA was indeed successfully recovered and amplified throughout the post-glacial sediment. For this lake, we found no loss of detection probability over time, but a high false negative rate. In the other lake, Hotagen, where connectivity and ecotype differentiation suggested colonization long after deglaciation, DNA was amplified only in the upper part of the sediment, and colonization was estimated at 2,200 bp based on the assumption that successful amplicons represent whitefish presence. Here the earliest amplification represents a false positive with a posterior probability of 41%, which increases the uncertainty in the estimated time of colonization.Complementing careful laboratory procedures aimed at preventing contamination, our method estimates contamination rates from the data. By combining these results with estimates of false negative rates, our models facilitate unbiased interpretation of data from natural DNA archives.
|
|
| 14. |
- Olajos, Fredrik, et al.
(författare)
-
Fish colonization patterns in central Sweden from dropletdigital PCR and shotgun sequencing of sedimentary DNA
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The natural establishment of Scandinavian fish populations took place following the lastdeglaciation 9,000 to 12,000 years ago when the retreating ice exposed new habitats. Accessibilityof lakes from the Proto-Baltic sea and the southern freshwater habitats was influenced by theirelevation relative to the post-glacial coastline, with some lakes being unreachable due to migrationbarriers. Long standing hypotheses regarding colonization routes have been formulated based onmodern distribution patterns, knowledge of historic climate variations, and species’ tolerances toenvironmental conditions. These hypotheses have not been tested with other forms of evidencebecause long-term data on past fish histories are limited. In this study, the colonization history ofseveral fish species was investigated using historical data combined with analyses of sedimentaryDNA from Lake Hotagen in central Sweden which is located above the post-glacial coastline.DNA was analyzed with droplet digital PCR (ddPCR) and metagenomic shotgun sequencingapproaches. The ddPCR array used specific primers of seven species known to have beenhistorically present at the lake, and successfully detected 5/7 species in the top 80 cm (~3000 years)of the sediment core where DNA was best preserved. Metagenomics however detected 6/8expected genera in all sediment samples dating back 7000 years. Based on our findings, we inferthat 1) (dd)PCR based methods had too low sensitivity to allow consistent detection of fish inancient samples and 2) metagenomics, while sufficiently sensitive, require expanded databases toincrease granularity across species, especially those who are currently underrepresented. 3) Mostfish species likely colonized lake Hotagen soon after the last deglaciation despite the presence ofmigration barriers.
|
|
| 15. |
- Olajos, Fredrik, 1987-
(författare)
-
Using environmental DNA to unravel aquatic ecosystem dynamics
- 2024
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Human-induced climate change has led to unprecedented declines in Earth's biodiversity and significant habitat loss. Aquatic ecosystems areespecially at risk, facing pollution, overexploitation, and destruction. Consequently, monitoring biodiversity is critical. Traditional monitoring methods are often low in detection rates, time-consuming, invasive, and harmful to species, which hampers comprehensive biodiversity assessments. Environmental DNA (eDNA) offers a rapid alternative fortaxonomic identification, extracting genetic material from soil, sediments, or water without capturing living organisms, proving useful where traditional methods fall short. However, its integration into aquatic ecology is hampered by unresolved methodological issues.This thesis demonstrates how eDNA can help reconstruct fish colonization histories in lakes post-glacial retreat. I employed species-specific primers with digital droplet PCR and metagenomic shotgun sequencing on ancient DNA from Holocene lake sediments. My findings show the detectability of DNA from ancient fish populations. However, each method exhibited technical limitations that led to varying degrees offalse negatives and false positive results. Additionally, I examined how Northern pike (Esox Lucius) affects ecological speciation in Europeanwhitefish (Coregonus lavaretus), promoting a shift from insectivorous to piscivorous states, enhancing predator biodiversity and biomass. Dietan alyses of piscivorous birds through digital droplet PCR revealed that smaller whitefish support a larger, more diverse bird community. Finally, I compared two molecular techniques for quantifying bird diets from fecal DNA, finding that metabarcoding with a universal fish primer and digital droplet PCR yielded similar results. This research enhances ourunderstanding of the potential and limitations of molecular tools forspecies identification and aids the integration of eDNA into aquatic ecology.
|
|
| 16. |
- Skulason, Skuli, et al.
(författare)
-
A way forward with eco evo devo : an extended theory of resource polymorphism with postglacial fishes as model systems
- 2019
-
Ingår i: Biological Reviews. - : John Wiley & Sons. - 1464-7931 .- 1469-185X. ; 94:5, s. 1786-1808
-
Forskningsöversikt (refereegranskat)abstract
- A major goal of evolutionary science is to understand how biological diversity is generated and altered. Despite considerable advances, we still have limited insight into how phenotypic variation arises and is sorted by natural selection. Here we argue that an integrated view, which merges ecology, evolution and developmental biology (eco evo devo) on an equal footing, is needed to understand the multifaceted role of the environment in simultaneously determining the development of the phenotype and the nature of the selective environment, and how organisms in turn affect the environment through eco evo and eco devo feedbacks. To illustrate the usefulness of an integrated eco evo devo perspective, we connect it with the theory of resource polymorphism (i.e. the phenotypic and genetic diversification that occurs in response to variation in available resources). In so doing, we highlight fishes from recently glaciated freshwater systems as exceptionally well‐suited model systems for testing predictions of an eco evo devo framework in studies of diversification. Studies on these fishes show that intraspecific diversity can evolve rapidly, and that this process is jointly facilitated by (i) the availability of diverse environments promoting divergent natural selection; (ii) dynamic developmental processes sensitive to environmental and genetic signals; and (iii) eco evo and eco devo feedbacks influencing the selective and developmental environments of the phenotype. We highlight empirical examples and present a conceptual model for the generation of resource polymorphism – emphasizing eco evo devo, and identify current gaps in knowledge.
|
|
| 17. |
- Öhlund, Gunnar, 1977-
(författare)
-
Ecological and evolutionary effects of predation in environmental gradients
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Understanding species interactions and how they affect densities and distributions of organisms is a central theme in ecological research. Studying such interactions in an ecosystem context is challenging as they often depend on species-specific characteristics and rates that not only change during the ontogeny of an organism, but also are affected by the surrounding environment. This thesis focuses on two separate questions and study systems that highlight different aspects of how effects of predation can depend on environmental conditions. In the first part of the thesis, we studied how temperature affects attack rate and handling time, two ecological rates with profound importance for predator-prey dynamics. Using a metaanalysis, we first show that the currently dominating model for temperature dependence in predator-prey interactions, i.e. the Arrhenius equation, has weak support in available empirical literature. This suggests that we need new rules for how and when we can generalize on the temperature-dependence of intake rates. We then use a simple model and a series of experiments to demonstrate that differences in the relative physiological capacity between predator and prey can impose strong non-linear effects on temperature-response curves of attack rate. In the second part of the thesis, we study the role of predation along a benthic-pelagic habitat gradient in promoting divergence and resource polymorphism among prey. We show that presence of a large piscivorous predator, the northern pike (Esox lucius), induces dwarfs, giants or divergence into both ecotypes in populations of European whitefish (Coregonus lavaretus) depending on lake characteristics. Using dated introductions of whitefish as controlled natural experiments, we show that pike presence induces rapid life history divergence between pelagic and littoral habitat use strategies, and that this divergence can translate into partial reproductive isolation in a matter of decades. Our results demonstrate the potential for thresholds in a crucial ecological rate, setting the stage for tipping points with potentially far reaching implications for effects of warming on predator prey dynamics and ecosystem stability. Moreover, they illustrate the potentially drastic consequences of such tipping points by demonstrating the importance of a single predator species as a driving force behind the creation and maintenance of biodiversity in a natural system.
|
|
| 18. |
- Öhlund, Gunnar, et al.
(författare)
-
Life history and large-scale habitat use of brown trout (salmo trutta) and brook trout (salvelinus fontinalis) - implications for species replacement patterns
- 2008
-
Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. ; 65, s. 633-644
-
Tidskriftsartikel (refereegranskat)abstract
- Simple models of temperature-mediated interference competition have generally failed to explain salmonid species replacement patterns along altitudinal gradients, a fact that emphasizes the need to link individual features and their relation to habitat characteristics to population-level dynamics. We compared life history parameters in stream resident populations of brook trout (/Salvelinus fontinalis/) and brown trout (/Salmo trutta/) in eight boreal streams. By use of electro-fishing data from 1000 sites, we analyzed and related differences in life history traits to habitat- and interaction-related patterns of growth and densities of brook and brown trout, respectively. Brown trout were competitively dominant throughout the size span of sampled sympatric sites and lowered growth rates in sympatry were mainly caused by environmental factors, revealing a link between brook trout invasions and habitat-related limitations on brown trout performance. Still, the frequency of allopatric brook trout sites increased in the smallest watersheds, indicating that localities with a high degree of brook trout dominance rarely sustain brown trout over time. Brook trout populations had higher turn-over rates and proportions of mature females than brown trout populations. Our results suggest growth potential and its effect on population fecundity as a critical factor limiting competitive ability and distribution of brown trout in Swedish brook trout dominated headwaters.
|
|
| 19. |
|
|
| 20. |
- Öhlund, Gunnar, et al.
(författare)
-
Temperature dependence of predation depends on the relative performance of predators and prey
- 2015
-
Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 282:1799
-
Tidskriftsartikel (refereegranskat)abstract
- The temperature dependence of predation rates is a key issue for understanding and predicting the responses of ecosystems to climate change. Using a simple mechanistic model, we demonstrate that differences in the relative performances of predator and prey can cause strong threshold effects in the temperature dependence of attack rates. Empirical data on the attack rate of northern pike (Esox lucius) feeding on brown trout (Salmo trutta) confirm this result. Attack rates fell sharply below a threshold temperature of +11 degrees C, which corresponded to a shift in relative performance of pike and brown trout with respect to maximum attack and escape swimming speeds. The average attack speed of pike was an order of magnitude lower than the escape speed of brown trout at 5 degrees C, but approximately equal at temperatures above 11 degrees C. Thresholds in the temperature dependence of ecological rates can create tipping points in the responses of ecosystems to increasing temperatures. Thus, identifying thresholds is crucial when predicting future effects of climate warming.
|
|
