Exposing extinction risk analysis to pathogens: Is disease just another form of density dependence?

Gerber, Leah R., McCallum, Hamish, Lafferty, Kevin D., Sabo, John L. and Dobson, Andy (2005) Exposing extinction risk analysis to pathogens: Is disease just another form of density dependence?. Ecological Applications, 15 4: 1402-1414. doi:10.1890/04-0880

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Author Gerber, Leah R.
McCallum, Hamish
Lafferty, Kevin D.
Sabo, John L.
Dobson, Andy
Title Exposing extinction risk analysis to pathogens: Is disease just another form of density dependence?
Journal name Ecological Applications   Check publisher's open access policy
ISSN 1051-0761
Publication date 2005
Sub-type Article (original research)
DOI 10.1890/04-0880
Open Access Status File (Publisher version)
Volume 15
Issue 4
Start page 1402
End page 1414
Total pages 13
Editor L. F. Pitelka
Place of publication Washington, DC, United States
Publisher Ecological Society of America
Collection year 2005
Language eng
Abstract In the United States and several other countries., the development of population viability analyses (PVA) is a legal requirement of any species survival plan developed for threatened and endangered species. Despite the importance of pathogens in natural populations, little attention has been given to host-pathogen dynamics in PVA. To study the effect of infectious pathogens on extinction risk estimates generated from PVA, we review and synthesize the relevance of host-pathogen dynamics in analyses of extinction risk. We then develop a stochastic, density-dependent host-parasite model to investigate the effects of disease on the persistence of endangered populations. We show that this model converges on a Ricker model of density dependence under a suite of limiting assumptions, including. a high probability that epidemics will arrive and occur. Using this modeling framework, we then quantify: (1) dynamic differences between time series generated by disease and Ricker processes with the same parameters; (2) observed probabilities of quasi-extinction for populations exposed to disease or self-limitation; and (3) bias in probabilities of quasi-extinction estimated by density-independent PVAs when populations experience either form of density dependence. Our results suggest two generalities about the relationships among disease, PVA, and the management of endangered species. First, disease more strongly increases variability in host abundance and, thus, the probability of quasi-extinction, than does self-limitation. This result stems from the fact that the effects and the probability of occurrence of disease are both density dependent. Second, estimates of quasi-extinction are more often overly optimistic for populations experiencing disease than for those subject to self-limitation. Thus, although the results of density-independent PVAs may be relatively robust to some particular assumptions about density dependence, they are less robust when endangered populations are known to be susceptible to disease. If potential management actions involve manipulating pathogens, then it may be useful to. model disease explicitly.
Keyword Ecology
Density Dependence
Diffusion Approximation
Extinction Risk
Host-pathogen Interactions
Population Viability Analysis
Reservoir Host
Q-Index Code C1

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Created: Wed, 15 Aug 2007, 05:24:34 EST