### 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.

Original language | English (US) |
---|---|

Pages (from-to) | 1402-1414 |

Number of pages | 13 |

Journal | Ecological Applications |

Volume | 15 |

Issue number | 4 |

State | Published - Aug 2005 |

### Fingerprint

### Keywords

- Density dependence
- Diffusion approximation
- Disease
- Epidemic
- Epidemiology
- Extinction risk
- Host-pathogen interactions
- Parasite
- Pathogen
- Population viability analysis
- PVA
- Reservoir host

### ASJC Scopus subject areas

- Ecology

### Cite this

*Ecological Applications*,

*15*(4), 1402-1414.

**Exposing extinction risk analysis to pathogens : Is disease just another form of density dependence?** / Gerber, Leah; McCallum, Hamish; Lafferty, Kevin D.; Sabo, John; Dobson, Andy.

Research output: Contribution to journal › Article

*Ecological Applications*, vol. 15, no. 4, pp. 1402-1414.

}

TY - JOUR

T1 - Exposing extinction risk analysis to pathogens

T2 - Is disease just another form of density dependence?

AU - Gerber, Leah

AU - McCallum, Hamish

AU - Lafferty, Kevin D.

AU - Sabo, John

AU - Dobson, Andy

PY - 2005/8

Y1 - 2005/8

N2 - 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.

AB - 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.

KW - Density dependence

KW - Diffusion approximation

KW - Disease

KW - Epidemic

KW - Epidemiology

KW - Extinction risk

KW - Host-pathogen interactions

KW - Parasite

KW - Pathogen

KW - Population viability analysis

KW - PVA

KW - Reservoir host

UR - http://www.scopus.com/inward/record.url?scp=23044509952&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=23044509952&partnerID=8YFLogxK

M3 - Article

VL - 15

SP - 1402

EP - 1414

JO - Ecological Appplications

JF - Ecological Appplications

SN - 1051-0761

IS - 4

ER -