Effects of wet season mineral nutrition on chital deer distribution in northern Queensland

Abstract

Context: To predict the success of an invasive species, it is important to understand the habitat factors that influence its distribution and abundance. In northern Queensland, chital deer (Axis axis) is an introduced ungulate that occupies specific areas over periods of several decades.Aims: The aim was to compare mineral concentrations in the soil and food plants of areas that chital occupy in high and low densities, and to assess mineral levels in blood sera.Methods: Faecal counts were used to identify areas of high and low chital density. Samples of soil and food plants were analysed from high- and low-density areas to determine the concentrations of 10 minerals from 32 collection sites. Laboratory examination was conducted on serum collected from 46 culled chital to evaluate mineral concentrations.Key results: Chital density varied markedly, with higher mineral concentrations found in soil and food plants in areas of high chital density compared with low-density locations. Average-ranked analyses indicated soil phosphorus levels were significantly (1.5×) higher in areas of high chital density, together with levels of Na (3.4×), Mg (2.3×), Mn (2.1×) and Fe (1.3×) in grasses that comprise more than 90% of the wet season (November to March) diet. Based on minimum requirements for ruminants, the concentrations of Na and Zn in grasses were suboptimal for chital. Serum Zn concentrations suggest a marginal deficiency in most of the animals sampled.Conclusions: Mineral requirements of ungulates are such that deficiencies in availability of key nutrients may be sufficient to influence density and distribution. If there are deficiencies, the principal determinants of habitat selection are likely to be P in soil, and Na and Zn in food plants. Deficiencies of both Na and Zn in the diet may limit growth and reproductive output.Implications: Mineral adequacy in the diet of chital may be a determinant of their current distribution and a predictor of the habitats they may successfully colonise in the future. Recognition of mineral nutrition as a habitat predictor may aid in the management of chital as a keystone species where it is native on the Indian subcontinent, and as an invasive species where it has become naturalised.