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RESEARCH ARTICLE
Contents Vol 32(6)

An experimental study of declining populations

Jim Hone A C , the late Graeme Caughley B and David Grice B
+ Author Affiliations
- Author Affiliations

A Applied Ecology Research Group, University of Canberra, Canberra, ACT 2601, Australia.

B CSIRO Sustainable Ecosystems, GPO Box 284, Canberra, ACT 2601, Australia.

C Corresponding author. Email: Jim.Hone@canberra.edu.au

Wildlife Research 32(6) 481-488 https://doi.org/10.1071/WR04092
Submitted: 15 October 2004  Accepted: 3 June 2005   Published: 18 October 2005

Abstract

Wildlife population declines have been attributed to predation, habitat change, and other agents of decline. An experimental study applied predation (at three levels) and habitat (at two levels) treatments over two years and measured the patterns of decline of populations of a medium-sized mammal (European rabbits). A model of population dynamics and effects of the treatments predicted negative effects of both treatments and an interaction of the treatments. All populations declined during the study including the experimental controls. During the first seven months (first phase of the study) the rate of decline, as estimated by the observed monthly instantaneous rate of increase (r), was more negative (P < 0.05) with increasing predation levels but there was no effect (P > 0.05) of habitat manipulation on r. There were no significant effects of treatments on rabbit abundance, or density, during the first phase of the study. During the second phase of the study, of 12 months’ duration, there were no significant (P > 0.05) effects of treatments on rabbit abundance, density, or r. There were no significant (P > 0.05) interactions of treatments on any response variable during either phase of the study. The interaction predicted by the theoretical model was not supported. Estimated abundance at the end of the study was not related (P > 0.05) to initial abundance (correlation = 0.023). The implications of the results are that such experimental studies can be used to evaluate theoretical models, though such studies may require a larger number of treatment replicates, and treatments at more extreme levels, to more clearly detect the effects of agents of population decline and their interactions.


Acknowledgments

The many colleagues who assisted with the design, establishment, execution and analysis of this study are thanked. The study was initiated by the late Dr Graeme Caughley. Financial support was provided by CSIRO. B. Walker supported the project, and A. Nicholls, S. Morton and R. Edmundson assisted with the study in numerous ways. C. Krebs, R. Pech, A. R. E. Sinclair, D. Freudenberger and A. Nicholls commented on a draft manuscript. Two anonymous referees provided useful comments on an earlier version of the manuscript. A. Chao kindly provided the bias-corrected estimator for the mark–recapture analysis.


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