Measuring the Strength of Demographic Stochasticity

Kokko, Hanna; Ebenhard, Torbjörn

doi:10.1006/jtbi.1996.0210

Cited by 47 publications

(30 citation statements)

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“…It is noteworthy that we did not take into account demographic stochasticity in the model. Even though it is said to be less important than environmental stochasticity and random catastrophes (Sha¡er 1987), it is not to be neglected (Kokko & Ebenhard 1996), meaning that this simpli¢cation underestimates the risk that a group of a given size will be driven below the lower threshold. The results here can therefore be considered as optimistic, since environmental and demographic stochasticity will increase the risk of extinction and, therefore, the constraint of cooperative breeding.…”

Section: Discussionmentioning

confidence: 99%

Population dynamics of obligate cooperators

Courchamp

Grenfell

Clutton‐Brock

1999

Proc. R. Soc. Lond. B

137

121

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Obligate cooperative breeding species demonstrate a high rate of group extinction, which may be due to the existence of a critical number of helpers below which the group cannot subsist. Through a simple model, we study the population dynamics of obligate cooperative breeding species, taking into account the existence of a lower threshold below which the instantaneous growth rate becomes negative. The model successively incorporates (i) a distinction between species that need helpers for reproduction, survival or both, (ii) the existence of a migration rate accounting for dispersal, and (iii) stochastic mortality to simulate the e¡ects of random catastrophic events. Our results suggest that the need for a minimum number of helpers increases the risk of extinction for obligate cooperative breeding species. The constraint imposed by this threshold is higher when helpers are needed for reproduction only or for both reproduction and survival. By driving them below this lower threshold, stochastic mortality of lower amplitude and/or lower frequency than for non-cooperative breeders may be su¤cient to cause the extinction of obligate cooperative breeding groups. Migration may have a bu¡ering e¡ect only for groups where immigration is higher than emigration; otherwise (when immigrants from nearby groups are not available) it lowers the di¡erence between actual group size and critical threshold, thereby constituting a higher constraint.

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Section: Discussionmentioning

confidence: 99%

Population dynamics of obligate cooperators

Courchamp

Grenfell

Clutton‐Brock

1999

Proc. R. Soc. Lond. B

137

121

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“…In case the population is spatially structured, the risk of local extinctions can increase as a result of demographic stochasticity (Kokko and Ebenhard 1996). Spatially structured populations might be better modelled with spatially explicit models (Lande 1993, Kokko et al 1999), when such data are available.…”

Section: Checklistmentioning

confidence: 99%

Status of Baltic grey seals: Population assessment and extinction risk

et al. 2007

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The grey seal (Halichoerus grypus) population in the Baltic Sea is recovering after a century of bounty hunting and 3 decades of low fertility rates caused by environmental pollution. A conservative estimate of the population size in 2003 was 19,400 animals, and available data suggest an annual rate of increase of 7.5% since 1990. The growing population has led to increased interactions with the fishery, and demands are being raised for the re-introduction of the hunt. We provide a demographic analysis and a risk assessment of the population, and make recommendations on how to decrease the risk of overexploitation. Although hunting increases the risk of quasi-extinction, the risk can be significantly reduced by the choice of a cautious hunting regime. The least hazardous regimes allow no hunting below a 'security level' in population size. Obviously, to implement such a hunting regime detailed knowledge of the population size and growth rate is required. It is not possible to estimate "true" risks for quasi-extinction, but we used an approach where the relative difference for different scenarios can be compared. With a security level at 5,000 females, the population quasi-extinction risk increases 50 fold at an annual hunt of 500 females compared with a scenario with no hunting. The risk of quasi-extinction is very sensitive to declines in the mean growth rate and to increased variance in growth rate. The variance in the population estimates over the last 14 years imply that it would take 9 years to detect a decline from 1.075 to 1.027 in the rate of population increase. We also show how the age composition of killed animals influences the impact of the hunt. The overall recommendation is that hunting should be kept to a minimum, carefully documented and accompanied by close population monitoring.Harding, K.C., Härkönen, T., Helander, B. and Karlsson, O. 2007. Status of Baltic grey seals: Population assessment and extinction risk. NAMMCO

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“…The life history of a species, defined as the time, duration and magnitude of important life cycle processes such as growth, reproduction and mortality (Stearns ), greatly influences vulnerability to demographic stochasticity (Kokko & Ebenhard ; Jeppsson & Forslund ), as well as transient dynamics (Koons et al . ; Koons, Grand & Arnold ; Stott et al .…”

Section: Introductionmentioning

confidence: 99%

Linking transient dynamics and life history to biological invasion success

et al. 2015

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1. Upon arriving in a novel environment, invading populations are likely to be small and far from a stable stage structure. This unstable stage structure can cause transient (short-term) population dynamics to differ greatly from asymptotic (long-term) dynamics. Because the persistence of small populations depends heavily on population growth rate, short-term dynamics may strongly influence the viability of invading populations. 2. We used published matrix population models to study the dynamics of small 'invading' populations for 105 plant species spanning a range of life histories, including species classified as both invasive and non-invasive. We simulated the matrix population models to estimate the effect of transient dynamics on population viability (i.e. potential invasiveness) after a hypothetical seed dispersal event into a novel environment. We then evaluated the predictive power of transient and long-term population growth rates to explain variation in population viability and identified the life-history correlates of population dynamics that best explained establishment success. 3. Transient and long-term population growth rates were positively but independently correlated with population viability across species. Minimum transient density (minimum population density attained en route to a stable stage structure) was the best transient predictor of population viability. This suggests that avoidance of severe short-term population declines is more important during establishment than either the rate of decline or transient ability to increase in density following a decline. 4. Despite a negative correlation between transient density and fecundity, species with high fecundity had disproportionately favourable transient dynamics and higher long-term population growth rates, resulting in higher population viability. Together, these results suggest that highly fecund species are better equipped to overcome the early effects of demographic stochasticity in the establishment phase than less fecund species and help explain the common empirical finding that species invasiveness is correlated with fecundity. 5. Synthesis. Transient and long-term population dynamics are independent predictors of demographic performance that influence the viability of invading (i.e. small, unstable) populations subjected to strong effects of demographic stochasticity. Greater long-term population growth rates and disproportionately favourable transient dynamics may account for the commonly observed invasiveness of highly fecund species. Given the strong dependence of population viability on population growth and the wide range of transient responses among species, transient analysis may provide critical insights into the demographic correlates of biological invasion potential.

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Measuring the Strength of Demographic Stochasticity

Cited by 47 publications

References 0 publications

Population dynamics of obligate cooperators

Population dynamics of obligate cooperators

Status of Baltic grey seals: Population assessment and extinction risk

Linking transient dynamics and life history to biological invasion success

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