Time to competitive exclusion

Kramer, Andrew M.; Drake, John M.

doi:10.1890/es14-00054.1

Cited by 15 publications

(24 citation statements)

References 75 publications

(109 reference statements)

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“…One lesson from our results for such studies is that ecologists may need to account for the effects of demographic stochasticity and individual variation on predicted dynamics. Indeed, recent theoretical work formally includes extinction risk as a consequence of stochasticity into assessments of species coexistence, which is more consistent with empirical realities (Turelli 1980;Tilman 2004;Adler & Drake 2008;Gravel et al 2011;Kramer & Drake 2014).…”

Section: Limitations and Extensionsmentioning

confidence: 57%

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How variation between individuals affects species coexistence

2016

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Although the effects of variation between individuals within species are traditionally ignored in studies of species coexistence, the magnitude of intraspecific variation in nature is forcing ecologists to reconsider. Compelling intuitive arguments suggest that individual variation may provide a previously unrecognised route to diversity maintenance by blurring species-level competitive differences or substituting for species-level niche differences. These arguments, which are motivating a large body of empirical work, have rarely been evaluated with quantitative theory. Here we incorporate intraspecific variation into a common model of competition and identify three pathways by which this variation affects coexistence: (1) changes in competitive dynamics because of nonlinear averaging, (2) changes in species' mean interaction strengths because of variation in underlying traits (also via nonlinear averaging) and (3) effects on stochastic demography. As a consequence of the first two mechanisms, we find that intraspecific variation in competitive ability increases the dominance of superior competitors, and intraspecific niche variation reduces species-level niche differentiation, both of which make coexistence more difficult. In addition, individual variation can exacerbate the effects of demographic stochasticity, and this further destabilises coexistence. Our work provides a theoretical foundation for emerging empirical interests in the effects of intraspecific variation on species diversity.

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Section: Limitations and Extensionsmentioning

confidence: 57%

“…Indeed, recent theoretical work formally includes extinction risk as a consequence of stochasticity into assessments of species coexistence, which is more consistent with empirical realities (Turelli ; Tilman ; Adler & Drake ; Gravel et al . ; Kramer & Drake ).…”

Section: Discussionmentioning

confidence: 99%

How variation between individuals affects species coexistence

2016

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“…If a community is neutral such that species fitnesses are identical, demographic stochasticity is expected to be the primary driver of compositional variation. Thus, neutral models incorporating demographic stochasticity and no fitness differences between species are frequently applied to empirical datasets to determine whether they can reproduce observed community patterns (Volkov et al , Chave , Tilman , Adler et al 2007, Chase and Myers , Rosindell et al , Vellend et al , Wang et al ). However, while the importance of demographic stochasticity in neutral communities is well recognized, there is little appreciation for the idea that it can have effects on communities that are not neutral.…”

Section: Introductionmentioning

confidence: 99%

“…Of the few studies that do consider finer‐scale outcomes such as abundances over time, most examine the effects of demographic stochasticity alongside other factors such as dispersal (Alexander et al ), priority effects (Mertz et al 1976, Fukami ) or density manipulations (Svensson et al 2018). These approaches are incomplete because even with fine experimental control, the effects of demographic stochasticity are difficult to isolate from other drivers of variability without ample time‐series data (Vellend et al , Engen et al ), and the application of detailed stochastic population models (Melbourne and Hastings ).…”

Section: Introductionmentioning

confidence: 99%

“…The small number of theoretical and simulation studies on the role of demographic stochasticity in non-neutral communities have largely focused on how it affects coexistence, showing a range of impacts, including both higher and lower probabilities of coexistence (Orrock and Fletcher 2005, Orrock and Watling 2010, Kramer and Drake 2014, Capitán et al 2015, Okuyama 2015, Pedruski et al 2015. Several theoretical analyses suggest that the importance of stochasticity for coexistence appears to depend on the magnitude of fitness differences between co-occurring species (Orrock and Fletcher 2005, Orrock and Watling 2010, Pedruski et al 2015.…”

Section: Introductionmentioning

confidence: 99%

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Demographic stochasticity alters expected outcomes in experimental and simulated non‐neutral communities

Legault

Fox

Melbourne

2019

Oikos

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Theory has shown that the effects of demographic stochasticity on communities may depend on the magnitude of fitness differences between species. In particular, it has been suggested that demographic stochasticity has the potential to significantly alter competitive outcomes when fitness differences are small (nearly neutral), but that it has negligible effects when fitness differences are large (highly non‐neutral). Here we test such theory experimentally and extend it to examine how demographic stochasticity affects exclusion frequency and mean densities of consumers in simple, but non‐neutral, consumer–resource communities. We used experimental microcosms of protists and rotifers feeding on a bacterial resource to test how varying absolute population sizes (a driver of demographic stochasticity) affected the probability of competitive exclusion of the weakest competitor. To explore whether demographic stochasticity could explain our experimental results, and to generalize beyond our experiment, we paired the experiment with a continuous‐time stochastic model of resource competition, which we simulated for 11 different fitness inequalities between competiting consumers. Consistent with theory, in both our experiments and our simulations we found that demographic stochasticity altered competitive outcomes in communities where fitness differences were small. However, we also found that demographic stochasticity alone could affect communities in other ways, even when fitness differences between competitors were large. Specifically, demographic stochasticity altered mean densities of both weak and strong competitors in experimental and simulated communities. These findings highlight how demographic stochasticity can change both competitive outcomes in non‐neutral communities and the processes underlying overall community dynamics.

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The effects of demographic stochasticity and parameter uncertainty on predicting the establishment of introduced species

Palamara

Carrara

Smith

et al. 2016

Ecology and Evolution

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Invasive species are a serious threat to biodiversity worldwide and predicting whether an introduced species will first establish and then become invasive can be useful to preserve ecosystem services. Establishment is influenced by multiple factors, such as the interactions between the introduced individuals and the resident community, and demographic and environmental stochasticity. Field observations are often incomplete or biased. This, together with an imperfect knowledge of the ecological traits of the introduced species, makes the prediction of establishment challenging. Methods that consider the combined effects of these factors on our ability to predict the establishment of an introduced species are currently lacking. We develop an inference framework to assess the combined effects of demographic stochasticity and parameter uncertainty on our ability to predict the probability of establishment following the introduction of a small number of individuals. We find that even moderate levels of demographic stochasticity influence both the probability of establishment, and, crucially, our ability to correctly predict that probability. We also find that estimation of the demographic parameters of an introduced species is fundamental to obtain precise estimates of the interaction parameters. For typical values of demographic stochasticity, the drop in our ability to predict an establishment can be 30% when having priors on the demographic parameters compared to having their accurate values. The results from our study illustrate how demographic stochasticity may bias the prediction of the probability of establishment. Our method can be applied to estimate probability of establishment of introduced species in field scenarios, where time series data and prior information on the demographic traits of the introduced species are available.

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Time to competitive exclusion

Cited by 15 publications

References 75 publications

How variation between individuals affects species coexistence

How variation between individuals affects species coexistence

Demographic stochasticity alters expected outcomes in experimental and simulated non‐neutral communities

The effects of demographic stochasticity and parameter uncertainty on predicting the establishment of introduced species

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