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Of sheep and rain: large-scale population dynamics of the red kangaroo
Article first published online: 20 JAN 2005
DOI: 10.1111/j.1365-2656.2005.00915.x
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How to Cite
JONZÉN, N., POPLE, A. R., GRIGG, G. C. and POSSINGHAM, H. P. (2005), Of sheep and rain: large-scale population dynamics of the red kangaroo. Journal of Animal Ecology, 74: 22–30. doi: 10.1111/j.1365-2656.2005.00915.x
Publication History
- Issue published online: 20 JAN 2005
- Article first published online: 20 JAN 2005
- Received 18 February 2004; revision received 14 May 2004
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Keywords:
- consumer-resource dynamics;
- environmental stochasticity;
- herbivores;
- population dynamics spatial correlation;
- herbivores;
- time-series analyses;
- environmental stochasticity;
- spatial correlation
Summary
- 1We analysed time-series data from populations of red kangaroos (Macropus rufus, Desmarest) inhabiting four areas in the pastoral zone of South Australia. We formulated a set of a priori models to disentangle the relative effects of the covariates: rainfall, harvesting, intraspecific competition, and domestic herbivores, on kangaroo population-growth rate.
- 2The statistical framework allowed for spatial variation in the growth-rate parameters, response to covariates, and environmental variability, as well as spatially correlated error terms due to shared environment.
- 3The most parsimonious model included all covariates but no area-specific parameter values, suggesting that kangaroo densities respond in the same way to the covariates across the areas.
- 4The temporal dynamics were spatially correlated, even after taking into account the potentially synchronizing effect of rainfall, harvesting and domestic herbivores.
- 5Counter-intuitively, we found a positive rather than negative effect of domestic herbivore density on the population-growth rate of kangaroos. We hypothesize that this effect is caused by sheep and cattle acting as a surrogate for resource availability beyond rainfall.
- 6Even though our system is well studied, we must conclude that approximating resources by surrogates such as rainfall is more difficult than previously thought. This is an important message for studies of consumer-resource systems and highlights the need to be explicit about population processes when analysing population patterns.