M. J. Dawson previously published as M. J. Walter.
Demography and dynamics of three wild horse populations in the Australian Alps
Article first published online: 27 APR 2011
© 2011 The Authors. Journal compilation © 2011 Ecological Society of Australia
Volume 37, Issue 1, pages 97–109, February 2012
How to Cite
DAWSON, M. J. and HONE, J. (2012), Demography and dynamics of three wild horse populations in the Australian Alps. Austral Ecology, 37: 97–109. doi: 10.1111/j.1442-9993.2011.02247.x
- Issue published online: 30 JAN 2012
- Article first published online: 27 APR 2011
- Accepted for publication 23 December 2010.
- demographic rate;
- Equus caballus;
- feral horse;
- numerical response;
- population growth rate;
- wild horse
Wild horses (Equus caballus) are a non-native species occupying over 2800 km2 of the nationally significant Australian Alps National Parks. We estimated key demographic parameters (fecundity, adult and juvenile survival and annual finite population growth rate) over 3 years and related these to horse body condition and available food for three populations under natural conditions, and found a trend consistent with food limitation. The populations were independent, with different site characteristics and occupied areas, identified by land managers, as areas of concern about possible conservation impacts. Annual fecundity and juvenile survival varied across sites averaging between 0.21 and 0.31 female young per adult female, and 0.83 and 0.90 per annum, respectively, and annual adult survival was consistent across sites averaging 0.91 per annum. One population was increasing (λ = 1.09 year−1; 95% CI 1.04–1.14) and two populations were stable (λ ∼ 1.0 year−1). Mean body condition of horses was positively correlated with mean pasture biomass rank. Across the three populations, fecundity, recruitment, body condition and annual finite population growth rate were lowest when mean pasture biomass rank was lowest and conversely highest when pasture rank was highest. We conclude that food limitation appears to be operating across these three sites. We used our results to assess the sensitivity of annual finite rate of increase (λ) to changes in key demographic parameters and found that λ was most sensitive to a change in adult survival, with the second most sensitive parameter being fecundity. Thus, if the aim of management is to reduce the size of the wild horse population then targeting adult survival is most important, followed by fecundity. Finally, we estimated the linear, negative, numerical response for wild horses between annual λ and horses per unit pasture biomass.