Wildlife Research Wildlife Research Society
Ecology, management and conservation in natural and modified habitats

Effective population size of koala populations under different population management regimes including contraception

Mark M. Tanaka A C , Romane Cristescu B and Desmond W. Cooper B
+ Author Affiliations
- Author Affiliations

A Evolution & Ecology Research Centre and School of Biotechnology and Biomolecular Sciences, University of New South Wales, Australia.

B Evolution & Ecology Research Centre and School of Biological, Earth and Environmental Sciences, University of New South Wales, Australia.

C Corresponding author. Email: m.tanaka@unsw.edu.au

Wildlife Research 36(7) 601-609 https://doi.org/10.1071/WR08160
Submitted: 5 November 2008  Accepted: 30 July 2009   Published: 28 October 2009


Context. The management of wildlife populations aiming to control population size should also consider the preservation of genetic diversity. Some overabundant koala populations, for example, have low genetic variation. Different management strategies will affect population genetic variation differently.

Aims. Here, we compare four strategies with respect to their effects on the effective population size, Ne , and therefore on genetic variation.

Methods. The four strategies of interest are: (1) sterilisation or culling (which have the same effect on genetic variation); (2) random contraception of females with replacement; (3) random contraception of females without replacement; and (4) regular contraception, giving every female equal opportunity to reproduce. We develop mathematical models of these alternative schemes to evaluate their impact on Ne . We also consider the effect of changing population sizes by investigating a model with geometric population growth in which females are removed by sterilisation or culling.

Key results. We find that sterilisation/culling at sexual maturity has the most detrimental effect on Ne , whereas regular contraception has no impact on Ne . Random contraception lies between these two extremes, leading to a moderate reduction in Ne . Removal of females from a growing population results in a higher Ne than the removal of females from a static population.

Conclusions. Different strategies for controlling a population lead to different effective population sizes.

Implications. To preserve genetic diversity in a wildlife population under control, the effective population size should be kept as large as possible. We suggest that a suitable approach in managing koala populations may be to prevent reproduction by all females older than a particular age.

Additional keywords: conservation genetics, effective population size, genetic variation, hormonal implant, wildlife management.


We thank John Sved and Cathy Herbert for helpful discussions. This work was supported by the Australian Research Council (ARC Linkage Grant LPO560344).


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