DENSITY-DEPENDENT GROWTH, BODY CONDITION, AND DEMOGRAPHY IN FERAL DONKEYS - TESTING THE FOOD HYPOTHESIS

The food hypothesis of population regulation was tested using two predation-free populations of feral donkeys in tropical northern Australia. Growth, body condition, and age-specific rates of fecundity and mortality were compared between the two populations. One of the populations was roughly one-half the density of the other, following an experimental reduction 3-4 yr previously. Fecundity was high and independent of density, with > 70% of mature females pregnant in both populations. Age at maturity and juvenile mortality displayed some density dependence. Populations conformed to predictions of the food hypothesis, abundance being ultimately regulated by food-related juvenile mortality. At high density, juvenile mortality was there times as great as at low density, and was associated with poorer juvenile body condition and slower growth. Differences in rates of juvenile mortality are associated with nutritional status of lactating females, which is in turn determined by density-dependent competition for quality forage. The effects of competition for forage upon juvenile mortality synchronize lactation with an annual flush of quality forage at the onset of the monsoonal wet season.