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Reconstructing local population dynamics in noisy metapopulations--the role of random catastrophes and Allee effects.

Hart EM, Avilés L - PLoS ONE (2014)

Bottom Line: Catastrophes also generally increased extinction risk, in particular when endogenous Allee effects were large.Using social spider colonies (Anelosimus spp.) as models for populations, we show that after known or suspected catastrophes are accounted for, reconstructed growth parameters are consistent with intrinsic dynamical instability and substantial Allee effects.Our results are applicable to metapopulation or time series data and are relevant for predicting extinction in conservation applications or the management of invasive species.

View Article: PubMed Central - PubMed

Affiliation: Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada.

ABSTRACT
Reconstructing the dynamics of populations is complicated by the different types of stochasticity experienced by populations, in particular if some forms of stochasticity introduce bias in parameter estimation in addition to error. Identification of systematic biases is critical when determining whether the intrinsic dynamics of populations are stable or unstable and whether or not populations exhibit an Allee effect, i.e., a minimum size below which deterministic extinction should follow. Using a simulation model that allows for Allee effects and a range of intrinsic dynamics, we investigated how three types of stochasticity--demographic, environmental, and random catastrophes--affect our ability to reconstruct the intrinsic dynamics of populations. Demographic stochasticity aside, which is only problematic in small populations, we find that environmental stochasticity--positive and negative environmental fluctuations--caused increased error in parameter estimation, but bias was rarely problematic, except at the highest levels of noise. Random catastrophes, events causing large-scale mortality and likely to be more common than usually recognized, caused immediate bias in parameter estimates, in particular when Allee effects were large. In the latter case, population stability was predicted when endogenous dynamics were actually unstable and the minimum viable population size was overestimated in populations with small or non-existent Allee effects. Catastrophes also generally increased extinction risk, in particular when endogenous Allee effects were large. We propose a method for identifying data points likely resulting from catastrophic events when such events have not been recorded. Using social spider colonies (Anelosimus spp.) as models for populations, we show that after known or suspected catastrophes are accounted for, reconstructed growth parameters are consistent with intrinsic dynamical instability and substantial Allee effects. Our results are applicable to metapopulation or time series data and are relevant for predicting extinction in conservation applications or the management of invasive species.

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The percent increase in local extinctions for our smallest (0.5) and highest (0.9) catastrophe levels, over a scenario with no catastrophes.Generally this decreases with increasing environmental noise because the background extinction rate increases with increasing noise. Both small and large populations with small Allee effects have almost no difference at the 0.5 catastrophe level, whereas high Allee effect populations show an increase in extinction rate with either catastrophe level.
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pone-0110049-g005: The percent increase in local extinctions for our smallest (0.5) and highest (0.9) catastrophe levels, over a scenario with no catastrophes.Generally this decreases with increasing environmental noise because the background extinction rate increases with increasing noise. Both small and large populations with small Allee effects have almost no difference at the 0.5 catastrophe level, whereas high Allee effect populations show an increase in extinction rate with either catastrophe level.

Mentions: Finally, the presence of random catastrophes interacted with Allee effect size to determine the extinction probability of the local populations. Thus, the probability of a local population going extinct was greatly increased, relative to a no catastrophe scenario, when catastrophe severity and Allee effect size were large (Figure 5).


Reconstructing local population dynamics in noisy metapopulations--the role of random catastrophes and Allee effects.

Hart EM, Avilés L - PLoS ONE (2014)

The percent increase in local extinctions for our smallest (0.5) and highest (0.9) catastrophe levels, over a scenario with no catastrophes.Generally this decreases with increasing environmental noise because the background extinction rate increases with increasing noise. Both small and large populations with small Allee effects have almost no difference at the 0.5 catastrophe level, whereas high Allee effect populations show an increase in extinction rate with either catastrophe level.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4216000&req=5

pone-0110049-g005: The percent increase in local extinctions for our smallest (0.5) and highest (0.9) catastrophe levels, over a scenario with no catastrophes.Generally this decreases with increasing environmental noise because the background extinction rate increases with increasing noise. Both small and large populations with small Allee effects have almost no difference at the 0.5 catastrophe level, whereas high Allee effect populations show an increase in extinction rate with either catastrophe level.
Mentions: Finally, the presence of random catastrophes interacted with Allee effect size to determine the extinction probability of the local populations. Thus, the probability of a local population going extinct was greatly increased, relative to a no catastrophe scenario, when catastrophe severity and Allee effect size were large (Figure 5).

Bottom Line: Catastrophes also generally increased extinction risk, in particular when endogenous Allee effects were large.Using social spider colonies (Anelosimus spp.) as models for populations, we show that after known or suspected catastrophes are accounted for, reconstructed growth parameters are consistent with intrinsic dynamical instability and substantial Allee effects.Our results are applicable to metapopulation or time series data and are relevant for predicting extinction in conservation applications or the management of invasive species.

View Article: PubMed Central - PubMed

Affiliation: Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada.

ABSTRACT
Reconstructing the dynamics of populations is complicated by the different types of stochasticity experienced by populations, in particular if some forms of stochasticity introduce bias in parameter estimation in addition to error. Identification of systematic biases is critical when determining whether the intrinsic dynamics of populations are stable or unstable and whether or not populations exhibit an Allee effect, i.e., a minimum size below which deterministic extinction should follow. Using a simulation model that allows for Allee effects and a range of intrinsic dynamics, we investigated how three types of stochasticity--demographic, environmental, and random catastrophes--affect our ability to reconstruct the intrinsic dynamics of populations. Demographic stochasticity aside, which is only problematic in small populations, we find that environmental stochasticity--positive and negative environmental fluctuations--caused increased error in parameter estimation, but bias was rarely problematic, except at the highest levels of noise. Random catastrophes, events causing large-scale mortality and likely to be more common than usually recognized, caused immediate bias in parameter estimates, in particular when Allee effects were large. In the latter case, population stability was predicted when endogenous dynamics were actually unstable and the minimum viable population size was overestimated in populations with small or non-existent Allee effects. Catastrophes also generally increased extinction risk, in particular when endogenous Allee effects were large. We propose a method for identifying data points likely resulting from catastrophic events when such events have not been recorded. Using social spider colonies (Anelosimus spp.) as models for populations, we show that after known or suspected catastrophes are accounted for, reconstructed growth parameters are consistent with intrinsic dynamical instability and substantial Allee effects. Our results are applicable to metapopulation or time series data and are relevant for predicting extinction in conservation applications or the management of invasive species.

Show MeSH
Related in: MedlinePlus