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Ecology, management and conservation in natural and modified habitats
RESEARCH ARTICLE

Population dynamics of large and small mammals: Graeme Caughley’s grand vision

Charles J. Krebs
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Institute for Applied Ecology, University of Canberra, Canberra, ACT 2601, Australia. Email: charles.krebs@canberra.edu.au or krebs@zoology.ubc.ca

Wildlife Research 36(1) 1-7 https://doi.org/10.1071/WR08004
Submitted: 11 January 2008  Accepted: 16 May 2008   Published: 21 January 2009

Abstract

Ecologists that study the population dynamics of large and small herbivorous mammals operate in two worlds that overlap only partly, and in this paper I address whether the conjecture that these worlds represent two distinct and valid paradigms is currently justified. I argue that large mammals fall into three groups depending on whether they have effective predators or not, and whether they are harvested by humans. Because of human persecution of large predators, more and more large herbivorous mammals are effectively predator-free and are controlled bottom-up by food. But in less disturbed systems, large herbivorous mammals should be controlled top-down by effective predators, and this can lead to a trophic cascade. Small herbivorous mammals have been suggested to be controlled top-down by predators but some experimental evidence has challenged this idea and replaced it with the notion that predation is one of several factors that may affect rates of population increase. Intrinsic control (territoriality, infanticide, social inhibition of breeding) appears to be common in small herbivorous mammals with altricial young but is absent in species with precocial young, in ecosystems with strong stochastic weather variation (deserts) and in areas of human-induced habitat fragmentation in agricultural monocultures. The extrinsic control of large herbivores with precocial young validates part of Graeme Caughley’s Grand Vision, but the relative role of intrinsic and extrinsic mechanisms for small herbivores with altricial young is still controversial. An improved knowledge of population control mechanisms for large and small herbivores is essential for natural resource management.


Acknowledgements

I thank the Australasian Wildlife Management Society and the Australian Academy of Science for the invitation to address the Fenner Conference in Canberra in December 2007. I acknowledge a debt to the late Graeme Caughley for his many insights into population dynamics. I thank Jim Hone and Dennis Chitty for their comments. Three referees were most helpful in suggesting revisions to the original manuscript.


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