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Robustness to secondary extinctions: Comparing trait-based sequential deletions in static and dynamic food webs
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
J.F. Blumenbach Institute of Zoology and Anthropology, Georg-August University, Göttingen, Germany.
J.F. Blumenbach Institute of Zoology and Anthropology, Georg-August University, Göttingen, Germany.
Department of Ecology and Ecological Modelling, University of Potsdam, Germany.
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2011 (English)In: Basic and Applied Ecology, ISSN 1439-1791, Vol. 12, no 7, 571-580 p.Article in journal (Refereed) Published
Abstract [en]

The loss of species from ecological communities can unleash a cascade of secondary extinctions, the risk and extent ofwhich are likely to depend on the traits of the species that are lost from the community. To identify species traits that have thegreatest impact on food web robustness to species loss we here subject allometrically scaled, dynamical food web models toseveral deletion sequences based on species’ connectivity, generality, vulnerability or body mass. Further, to evaluate the relativeimportance of dynamical to topological effects we compare robustness between dynamical and purely topological models. Thiscomparison reveals that the topological approach overestimates robustness in general and for certain sequences in particular.Top-down directed sequences have no or very low impact on robustness in topological analyses, while the dynamical analysisreveals that they may be as important as high-impact bottom-up directed sequences. Moreover, there are no deletion sequencesthat result, on average, in no or very fewsecondary extinctions in the dynamical approach. Instead, the least detrimental sequencein the dynamical approach yields an average robustness similar to the most detrimental (non-basal) deletion sequence in thetopological approach. Hence, a topological analysis may lead to erroneous conclusions concerning both the relative and theabsolute importance of different species traits for robustness. The dynamical sequential deletion analysis shows that food websare least robust to the loss of species that have many trophic links or that occupy low trophic levels. In contrast to previousstudies we can infer, albeit indirectly, that secondary extinctions were triggered by both bottom-up and top-down cascades.

Place, publisher, year, edition, pages
Elsevier, 2011. Vol. 12, no 7, 571-580 p.
National Category
Natural Sciences
URN: urn:nbn:se:liu:diva-73611DOI: 10.1016/j.baae.2011.09.008ISI: 000299149700003OAI: diva2:475021
funding agencies|European Science Foundation||German Research Foundation| BR 2315/11-1 |Available from: 2012-01-10 Created: 2012-01-10 Last updated: 2014-07-11
In thesis
1. Extinctions in Ecological Communities: direct and indirect effects of perturbation on biodiversity
Open this publication in new window or tab >>Extinctions in Ecological Communities: direct and indirect effects of perturbation on biodiversity
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the dawning of what may become Earth’s 6th mass extinction the topic of this thesis, understanding extinction processes and what determines the magnitude of species loss, has become only too relevant. The number of known extinctions (~850) during the last centuries translates to extinction rates elevated above the background rate, matching those of previous mass extinction events. The main drivers of these extinctions have been human land use, introduction of exotic species and overexploitation. Under continued anthropogenic pressure and climate change, the current extinction rates are predicted to increase tenfold.

Large perturbations, such as the extinction drivers mentioned above, affects species directly, causing a change in their abundance. As species are not isolated, but connected to each other through a multitude of interactions, the change in abundance of one species can in turn affect others. Thus, in addition to the direct effect, a perturbation can affect a species indirectly through the ecological network in which the species is embedded. With this thesis, I wish to contribute to our basic understanding of these indirect effects and the role they play in determining the magnitude of species loss. All the studies included here are so called in silico experiments, using mathematical models to describe ecological communities and computer simulations to observe the response of these communities to perturbation.

When a perturbation is severe enough, a species will be driven to extinction. The loss of a species from a system is in itself a large perturbation, and may result in further extinctions, so called secondary extinctions. The traits of the species initially lost, can be a potential predictor of the magnitude of secondary species loss. In Paper I of this thesis, I show that when making such predictions, it is important to incorporate temporally dynamic species interactions and abundances, in order not to underestimate the importance of certain species, such as top predators.

I further show that species traits alone are not particularly good predictors of secondary extinction risk (Paper I), but that in combination with community level properties they are (Paper II). Indeed, there seems to be an interaction such that the specific property making a community prone to secondary species loss, depends on what kind of species was lost in the primary extinction. As different types of perturbation put different types of species at risk of (primary) extinction, this means that the specific property making a community prone to secondary species loss, will depend on the type of perturbation the community is subjected to.

One of the predicted main drivers of future species extinction is climate change. If the local climate becomes adverse, a species can either migrate to new and better areas or stay and evolve. Both these processes will be important in determining the magnitude of species loss under climate change. However, migration and evolution do not occur in vacuum – the biotic community in which these processes play out may modulate their effect on biodiversity. In paper III, I show that the strength of competition between species modulates the effect of both dispersal and evolution on the magnitude of species loss under climate change. The three-way interaction between interspecific competition, evolution and dispersal, creates a complex pattern of biodiversity responses, in which both evolution and dispersal can either increase or decrease the magnitude of species loss. Thus, when species interactions are incorporated, it is clear that even though migration and evolution may alleviate the impact of climate change for some species, they may indirectly aggravate the situation for others.

In Paper III, the aspect of climate change incorporated in the model is an increase in mean annual temperature. But climate change is also predicted to increase environmental variability. Paper IV shows that species-rich communities are more sensitive to high environmental variability than species-poor ones. The smaller population sizes in the species-rich communities increased the extinction risk connected to population fluctuations driven by the variable environment. Hence, systems such as tropical forests and coral reefs are predicted to be particularly sensitive to the increased variability that may follow with climate change.

In Paper IV, primary extinctions of primary producers result in extinction cascades of consumer species, when they lose their prey. However, in reality a consumer species might be able to switch to another prey, and such flexibility has both been observed and suggested as a potential rescue mechanism. But what is beneficial for an individual predator in the short-term can become detrimental to the ecological community in the long-term. Paper V shows that consumer flexibility often led to consumers continuously overexploiting their new prey, in the worst case to the point of system collapse. Thus, the suggested rescue mechanism aggravated the effect of initial species loss, rather than ameliorating it.

Overall, the research presented here, underscores the importance of including population dynamics and biotic interactions when studying the effects of perturbation on biodiversity. Many of the results are complex, hard to foresee or even counter-intuitive, arising from the indirect effects of the perturbation being translated through the living web of species interactions.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. 60 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1609
National Category
Other Natural Sciences
urn:nbn:se:liu:diva-108906 (URN)10.3384/diss.diva-108906 (DOI)978-91-7519-278-9 (print) (ISBN)
Public defence
2014-08-29, Schrödinger, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Available from: 2014-07-11 Created: 2014-07-11 Last updated: 2014-07-11Bibliographically approved

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