| 1. |
- Brännström, Åke, 1975-, et al.
(author)
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Emergence and maintenance of biodiversity in an evolutionary food-web model
- 2011
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In: Theoretical Ecology. - : Springer Science+Business Media B.V.. - 1874-1738 .- 1874-1746. ; 4:4, s. 467-478
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Journal article (peer-reviewed)abstract
- Ecological communities emerge as a consequence of gradual evolution, speciation, and immigration. In this study, we explore how these processes and the structure of the evolved food webs are affected by species-level properties. Using a model of biodiversity formation that is based on body size as the evolving trait and incorporates gradual evolution and adaptive radiation, we investigate how conditions for initial diversification relate to the eventual diversity of a food web. We also study how trophic interactions, interference competition, and energy availability affect a food web’s maximum trophic level and contrast this with conditions for high diversity. We find that there is not always a positive relationship between conditions that promote initial diversification and eventual diversity, and that the most diverse food webs often do not have the highest trophic levels.
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| 2. |
- Eklöf, Anna, et al.
(author)
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The phylogenetic component of food web structure and intervality
- 2016
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In: Theoretical Ecology. - : Springer Publishing Company. - 1874-1738 .- 1874-1746. ; 9:1, s. 107-115
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Journal article (peer-reviewed)abstract
- Despite the exceptional complexity formed byspecies and their interactions in ecological networks, such asfood webs, regularities in the network structures are repeat-edly demonstrated. The interactions are determined by thecharacteristics of a species. The characteristics are in turndetermined by the species’ phylogenetic relationships, butalso by factors not related to evolutionary history. Here, wetest whether species’ phylogenetic relationships provides asignificant proxy for food web intervality. We thereafterquantify the degree to which different species traits remainvaluable predictors of food web structure after the base-line effect of species’ relatedness has been removed. Wefind that the phylogenetic relationships provide a significantbackground from which to estimate food web intervalityand thereby structure. However, we also find that thereis an important, non-negligible part of some traits, e.g.,body size, in food webs that is not accounted for by thephylogenetic relationships. Additionally, both these rela-tionships differ depending if a predator or a prey perspectiveis adopted. Clearly, species’ evolutionary history as well astraits not determined by phylogenetic relationships shapes predator-prey interactions in food webs, and the underly-ing evolutionary processes take place on slightly differenttime scales depending on the direction of predator-preyadaptations.
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| 3. |
- Elias Wolff, Federico, et al.
(author)
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How Levins’ dynamics emerges from a Ricker metapopulation model
- 2016
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In: Theoretical Ecology. - : Springer Science and Business Media LLC. - 1874-1738 .- 1874-1746. ; 9:2, s. 173-183
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Journal article (peer-reviewed)abstract
- Understanding the dynamics of metapopulations close to extinction is of vital importance for management. Levins-like models, in which local patches are treated as either occupied or empty, have been used extensively to explore the extinction dynamics of metapopulations, but they ignore the important role of local population dynamics. In this paper, we consider a stochastic metapopulation model where local populations follow a stochastic, density-dependent dynamics (the Ricker model), and use this framework to investigate the behaviour of the metapopulation on the brink of extinction. We determine under which circumstances the metapopulation follows a time evolution consistent with Levins’ dynamics. We derive analytical expressions for the colonisation and extinction rates (c and e) in Levins-type models in terms of reproduction, survival and dispersal parameters of the local populations, providing an avenue to parameterising Levins-like models from the type of information on local demography that is available for a number of species. To facilitate applying our results, we provide a numerical algorithm for computing c and e.
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| 4. |
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| 5. |
- Jonsson, Annie
(author)
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Robustness of life histories to environmental variability in complex versus simple life cycles
- 2021
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In: Theoretical Ecology. - : Springer. - 1874-1738 .- 1874-1746. ; 14:2, s. 335-344
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Journal article (peer-reviewed)abstract
- Most animal species have a complex life cycle (CLC) with metamorphosis. It is thus of interest to examine possible benefits of such life histories. The prevailing view is that CLC represents an adaptation for genetic decoupling of juvenile and adult traits, thereby allowing life stages to respond independently to different selective forces. Here I propose an additional potential advantage of CLCs that is, decreased variance in population growth rate due to habitat separation of life stages. Habitat separation of pre- and post-metamorphic stages means that the stages will experience different regimes of environmental variability. This is in contrast to species with simple life cycles (SLC) whose life stages often occupy one and the same habitat. The correlation in the fluctuations of the vital rates of life stages is therefore likely to be weaker in complex than in simple life cycles. By a theoretical framework using an analytical approach, I have (1) derived the relative advantage, in terms of long-run growth rate, of CLC over SLC phenotypes for a broad spectrum of life histories, and (2) explored which life histories that benefit most by a CLC, that is avoid correlation in vital rates between life stages. The direction and magnitude of gain depended on life history type and fluctuating vital rate. One implication of our study is that species with CLCs should, on average, be more robust to increased environmental variability caused by global warming than species with SLCs.
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| 6. |
- Lade, Steven J., et al.
(author)
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Regime shifts in a social-ecological system
- 2013
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In: Theoretical Ecology. - : Springer Science and Business Media LLC. - 1874-1738 .- 1874-1746. ; 6:3, s. 359-372
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Journal article (peer-reviewed)abstract
- Ecological regime shifts are rarely purely ecological. Not only is the regime shift frequently triggered by human activity, but the responses of relevant actors to ecological dynamics are often crucial to the development and even existence of the regime shift. Here, we show that the dynamics of human behaviour in response to ecological changes can be crucial in determining the overall dynamics of the system. We find a social-ecological regime shift in a model of harvesters of a common-pool resource who avoid over-exploitation of the resource by social ostracism of non-complying harvesters. The regime shift, which can be triggered by several different drivers individually or also in combination, consists of a breakdown of the social norm, sudden collapse of co-operation and an over-exploitation of the resource. We use the approach of generalized modeling to study the robustness of the regime shift to uncertainty over the specific forms of model components such as the ostracism norm and the resource dynamics. Importantly, the regime shift in our model does not occur if the dynamics of harvester behaviour are not included in the model. Finally, we sketch some possible early warning signals for the social-ecological regime shifts we observe in the models.
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| 7. |
- Lögdberg, Frida, et al.
(author)
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Spectral Color, Synchrony and Extinction Risk
- 2012
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In: THEORETICAL ECOLOGY. - : Springer. - 1874-1738 .- 1874-1746. ; 5:4, s. 545-554
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Journal article (peer-reviewed)abstract
- The autocorrelation of environmental variation, also called noise color, influences the population dynamics and the probability of extinction risk. Increasing the distance, the variations over time for two sites will become more unsynchronized. Thus, both degree of synchrony and noise color are parts of the same environmental variation affecting population dynamics in a spatial setting. We present a novel method of generating environmental noise controlling for its noise color and synchrony. We apply these time series to carrying capacity (K) or (indirectly) to growth rate (r), and altered the population regulation response between over- and under-compensatory. A novel finding is that the qualitative effects of noise color on extinction risk do not differ with degree of synchrony. Our results for highly responsive dynamics (large growth rates and overcompensatory dynamics) agree with previous non-spatial studies by showing that the redder the noise, the lower the extinction risk. The results for less responsive dynamics are more complex, indicating that intermediate noise color causes a larger extinction risk compared to whiter or redder color. To explain this hump-shaped response, we use classical descriptions of how means and variances of population density depend on noise color. These results allow a new straightforward interpretation of how extinction risk depends on population dynamics, noise color, and synchrony.
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| 8. |
- Menden-Deuer, S., et al.
(author)
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The theory of games and microbe ecology
- 2019
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In: Theoretical Ecology. - : Springer Science and Business Media LLC. - 1874-1738 .- 1874-1746. ; 12:1, s. 1-15
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Journal article (peer-reviewed)abstract
- Using game theory, we provide mathematical proof that if a species of asexually reproducing microbes is not characterized by maximum variability in competitive abilities among its individual organisms, then that species is vulnerable to replacement by competitors. Furthermore, we prove that such maximally variable species are neutral towards each other in competition for limited resources; they coexist. Our proof is constructive: given one species which does not possess maximum variability, we construct a second species with the same (or lower) mean competitive ability which can outcompete the first, in the sense that its expected value in competition is positive, whereas the expected value of the non-maximally variable species is negative. Our results point towards the mechanistic underpinnings for the frequent observations that (1) microbes are characterized by large intra-specific variability and that (2) the number of extant microbe species is very large.
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| 9. |
- Nilsson, Karin A., et al.
(author)
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Interaction strength revisited-clarifying the role of energy flux for food web stability
- 2016
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In: Theoretical Ecology. - : Springer. - 1874-1738 .- 1874-1746. ; 9:1, s. 59-71
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Journal article (peer-reviewed)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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| 10. |
- Rossberg, Axel, et al.
(author)
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How trophic interaction strength depends on traits : A conceptual framework for representing multidimensional trophic niche spaces
- 2010
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In: Theoretical Ecology. - : Springer Netrherlands. - 1874-1738 .- 1874-1746. ; 3:1, s. 13-24
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Journal article (peer-reviewed)abstract
- A key problem in community ecology is to understand how individual-level traits give rise to population-level trophic interactions. Here, we propose a synthetic framework based on ecological considerations to address this question systematically. We derive a general functional form for the dependence of trophic interaction coefficients on trophically relevant quantitative traits of consumers and resources. The derived expression encompasses—and thus allows a unified comparison of—several functional forms previously proposed in the literature. Furthermore, we show how a community’s, potentially low-dimens ional, effective trophic niche space is related to its higher-dimensional phenotypic trait space. In this manner, we give ecological meaning to the notion of the “dimensionality of trophic niche space.” Our framework implies a method for directly measuring this dimensionality. We suggest a procedure for estimating the relevant parameters from empirical data and for verifying that such data matches the assumptions underlying our derivation.
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