| 1. |
- MacDougall, Andrew S., et al.
(författare)
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Context-dependent interactions and the regulation of species richness in freshwater fish
- 2018
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Species richness is regulated by a complex network of scale-dependent processes. This complexity can obscure the influence of limiting species interactions, making it difficult to determine if abiotic or biotic drivers are more predominant regulators of richness. Using integrative modeling of freshwater fish richness from 721 lakes along an 11 degrees latitudinal gradient, we find negative interactions to be a relatively minor independent predictor of species richness in lakes despite the widespread presence of predators. Instead, interaction effects, when detectable among major functional groups and 231 species pairs, were strong, often positive, but contextually dependent on environment. These results are consistent with the idea that negative interactions internally structure lake communities but do not consistently 'scale-up' to regulate richness independently of the environment. The importance of environment for interaction outcomes and its role in the regulation of species richness highlights the potential sensitivity of fish communities to the environmental changes affecting lakes globally.
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| 2. |
- Cazelles, Kevin, et al.
(författare)
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Homogenization of freshwater lakes : Recent compositional shifts in fish communities are explained by gamefish movement and not climate change
- 2019
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Ingår i: Global Change Biology. - : John Wiley & Sons. - 1354-1013 .- 1365-2486. ; 25:12, s. 4222-4233
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Tidskriftsartikel (refereegranskat)abstract
- Globally, lake fish communities are being subjected to a range of scale-dependent anthropogenic pressures, from climate change to eutrophication, and from overexploitation to species introductions. As a consequence, the composition of these communities is being reshuffled, in most cases leading to a surge in taxonomic similarity at the regional scale termed homogenization. The drivers of homogenization remain unclear, which may be a reflection of interactions between various environmental changes. In this study, we investigate two potential drivers of the recent changes in the composition of freshwater fish communities: recreational fishing and climate change. Our results, derived from 524 lakes of Ontario, Canada sampled in two periods (1965-1982 and 2008-2012), demonstrate that the main contributors to homogenization are the dispersal of gamefish species, most of which are large predators. Alternative explanations relating to lake habitat (e.g., area, phosphorus) or variations in climate have limited explanatory power. Our analysis suggests that human-assisted migration is the primary driver of the observed compositional shifts, homogenizing freshwater fish community among Ontario lakes and generating food webs dominated by gamefish species.
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| 3. |
- Gilbert, Benjamin, et al.
(författare)
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A bioenergetic framework for the temperature dependence of trophic interactions
- 2014
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 17:8, s. 902-914
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Tidskriftsartikel (refereegranskat)abstract
- Changing temperature can substantially shift ecological communities by altering the strength and stability of trophic interactions. Because many ecological rates are constrained by temperature, new approaches are required to understand how simultaneous changes in multiple rates alter the relative performance of species and their trophic interactions. We develop an energetic approach to identify the relationship between biomass fluxes and standing biomass across trophic levels. Our approach links ecological rates and trophic dynamics to measure temperature-dependent changes to the strength of trophic interactions and determine how these changes alter food web stability. It accomplishes this by using biomass as a common energetic currency and isolating three temperature-dependent processes that are common to all consumer-resource interactions: biomass accumulation of the resource, resource consumption and consumer mortality. Using this framework, we clarify when and how temperature alters consumer to resource biomass ratios, equilibrium resilience, consumer variability, extinction risk and transient vs. equilibrium dynamics. Finally, we characterise key asymmetries in species responses to temperature that produce these distinct dynamic behaviours and identify when they are likely to emerge. Overall, our framework provides a mechanistic and more unified understanding of the temperature dependence of trophic dynamics in terms of ecological rates, biomass ratios and stability.
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| 4. |
- Nilsson, Karin A., 1977-, et al.
(författare)
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Interaction strength and stability in stage‐structured food web modules
- 2018
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Ingår i: Oikos. - : John Wiley & Sons. - 0030-1299 .- 1600-0706. ; 127:10, s. 1494-1505
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Tidskriftsartikel (refereegranskat)abstract
- There has been a long‐standing debate on what creates stability in food webs. One major finding is that weak interactions can mute the destabilizing potential of strong interactions. Considering that stage structure is common in nature, that existing studies on stability that include population stage structure point in different directions, and the recent theoretical developments in the area of stage structure, there is a need to address the effects of population stage structure in this context. Using simple food web modules, with stage structure in an intermediate consumer, we here begin to theoretically investigate the effects of stage structure on food web stability. We found a general correspondence to previous results such that strong interactions had destabilizing effects and weak interactions that result in decreased energy flux had stabilizing effects. However, we also found a number of novel results connected to stage structure. Interestingly, weak interactions can be destabilizing when they excite other interactions. We also found that cohort cycles and predator–prey cycles did not respond in the same way to increasing interactions strength. We found that the combined effects of two predators feeding on the same prey can strongly destabilize a system. Consistent with previous studies, we also found that stage‐specific feeding can create a refuge effect that leads to a lack of strong destabilization at high interaction strength. Overall, stage structure had both stabilizing and destabilizing aspects. Some effects could be explained by our current understanding of energetic processes; others need additional consideration. Additional aspects such as shunting of energy between stages, control of biomass fluxes, and interactions between lags and energy flux, should be considered.
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| 5. |
- Nilsson, Karin A., et al.
(författare)
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Interaction strength revisited-clarifying the role of energy flux for food web stability
- 2016
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Ingår i: Theoretical Ecology. - : Springer. - 1874-1738 .- 1874-1746. ; 9:1, s. 59-71
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Tidskriftsartikel (refereegranskat)abstract
- Interaction strength (IS) has been theoretically shown to play a major role in governing the stability and dynamics of food webs. Nonetheless, its definition has been varied and problematic, including a range of recent definitions based on biological rates associated with model parameters (e.g., attack rate). Results from food web theory have been used to argue that IS metrics based on energy flux ought to have a clear relationship with stability. Here, we use simple models to elucidate the actual relationship between local stability and a number of common IS metrics (total flux and per capita fluxes) as well as a more recently suggested metric. We find that the classical IS metrics map to stability in a more complex way than suggested by existing food web theory and that the new IS metric has a much clearer, and biologically interpretable, relationship with local stability. The total energy flux metric falls off existing theoretical predictions when the total resource productivity available to the consumer is reduced despite increased consumer attack rates. The density of a consumer can hence decrease when its attack rate increases. This effect, called the paradox of attack rate, is similar to the well-known hydra effect and can even cascade up a food chain to exclude a predator when consumer attack rate is increased.
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| 6. |
- Ripa, Jörgen, et al.
(författare)
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Interaction assessments in correlated and autocorrelated environments
- 2007
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Ingår i: The impact of environmental variability on ecological systems. The Peter Yodzis Fundamental Ecology Series Vol. 2. - 9781402058509 ; 2, s. 111-131
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Natural food webs are embedded in a variable environment, which causes population densities to fluctuate, despite a potential stable equilibrium. Population interactions as well as the characteristics of the environmental fluctuations determine the resulting population dynamics. Populations sensitive to the same kind of environmental disturbances will show correlated responses in their respective growth rates. Such 'environmental correlation' between species can have profound effects on the populations' dynamics, e.g. generating a positive correlation between the abundances of two competitors, which makes a direct correlation a highly inappropriate measure of population interactions. However, multivariate time series analysis will still identify and quantify population interactions correctly. The picture is more complicated if the environmental fluctuations are correlated over time – environmental autocorrelation causes biases in interaction assessments and possibly falsely identified delayed interactions. We present approximate expressions for the estimation bias, which show that the bias is the weakest when food web dynamics are close to unstable. In the absence of close to unstable dynamics the only way avoid this estimation error is to incorporate the most important environmental drivers as covariates in the time series analysis.
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| 7. |
- van Rheenen, Wouter, et al.
(författare)
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Genome-wide association analyses identify new risk variants and the genetic architecture of amyotrophic lateral sclerosis
- 2016
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Ingår i: Nature Genetics. - : Springer Science and Business Media LLC. - 1061-4036 .- 1546-1718. ; 48:9, s. 1043-1048
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Tidskriftsartikel (refereegranskat)abstract
- To elucidate the genetic architecture of amyotrophic lateral sclerosis (ALS) and find associated loci, we assembled a custom imputation reference panel from whole-genome-sequenced patients with ALS and matched controls (n = 1,861). Through imputation and mixed-model association analysis in 12,577 cases and 23,475 controls, combined with 2,579 cases and 2,767 controls in an independent replication cohort, we fine-mapped a new risk locus on chromosome 21 and identified C21orf2 as a gene associated with ALS risk. In addition, we identified MOBP and SCFD1 as new associated risk loci. We established evidence of ALS being a complex genetic trait with a polygenic architecture. Furthermore, we estimated the SNP-based heritability at 8.5%, with a distinct and important role for low-frequency variants (frequency 1-10%). This study motivates the interrogation of larger samples with full genome coverage to identify rare causal variants that underpin ALS risk.
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