Reproductive ecology of wild tammar wallabies in natural and developed habitats on Garden Island, Western Australia Lisa E. Schwanz A,B,E and Kylie A. Robert C,D A Institute for Applied Ecology, University of Canberra, Canberra, ACT 2601, Australia. B School of Tropical and Marine Biology, James Cook University, Townsville, Qld 4811, Australia. C School of Animal Biology, University of Western Australia, Perth, WA 6009, Australia. D Department of Zoology, La Trobe University, Bundoora, Vic. 3086, Australia. E Corresponding author. Email: lisa.schwanz@gmail.com Abstract. Reproduction may be influenced by major environmental changes experienced by an entire population as well as variation within a population in maternal resource availability or quality. We examined relationships between body condition and reproductive traits in two wild populations of the seasonally breeding tammar wallaby (Macropus eugenii) on Garden Island, Western Australia, that differed in access to supplemental food resources. Body condition changed predictably over the year, with females losing condition over the dry summer and gaining condition over the winters, when lactation occurs and most annual precipitation falls. Body condition influenced reproduction, with females of greater body condition more likely to have a pouch young, and to have a larger pouch young, early in the reproductive season. This intrapopulation pattern was opposite to that seen across populations – females in a native bushland were in poorer condition yet were more likely to have pouch young, and had larger pouch young, in March than did females living in a water-supplemented habitat on a naval base. Body condition did not influence the probability of weaning a pouch young in a year, nor did reproductive success influence changes in body condition across seasons. Instead, annual variation in precipitation had a dramatic effect on population weaning success in the native bushland, but not on the naval base. In summary, individual variation in body condition as well as large climatic variation influenced the reproduction of tammar wallabies on Garden Island, but the nature of the effect depended on the different habitats experienced by the two study populations. Additional keywords: income and capital breeding, Macropodidae, somatic reserves. Received 6 March 2012, accepted 27 July 2012, published online 26 September 2012 Introduction Reproduction in marsupials, as in many mammals, is often tied to large-scale fluctuations in environmental conditions (e.g. Dickman 1988; Rhind and Bradley 2002; Parrott et al. 2007; Sale et al. 2009). One extreme can be seen in red kangaroos, where production and survival of pouch young (PY) is strongly determined by rainfall and vegetative growth (Newsome 1964, 1965, 1966). This pattern results from the tendency to use energy immediately derived from consumption to fuel the energetic demands of reproduction (i.e. ‘income breeding’). Many aspects of marsupial reproductive physiology and ecology are associated with the ability to utilise low resource availability or resource booms to fuel reproduction. Embryonic diapause in red kangaroos allows rapid reproductive response to sudden increases in resource availability by circumventing the delays associated with mating (Newsome 1965). Peak energetic investment via lactation in marsupials occurs late in lactation and has a more prolonged and shallower peak compared with similar- sized eutherians, suggesting that marsupials minimise energy expenditure and risk early during lactation and can take advantage of low-density resources to complete lactation (Low 1978; Cork and Dove 1989; Tyndale-Biscoe 2005). Finally, early birth of highly altricial neonates and offspring accessibility to mothers (in the pouch) may additionally facilitate easy abandonment of reproduction if resource availability plummets, at least in macropods (Low 1978; but see Morton et al. 1982; Russell 1982). Whereas much focus has been spent examining how marsupial populations respond to large-scale variation in resources, less is known about the importance of among-individual variation in reproduction. Individual strategies of reproductive investment trade-off energetic contribution to a current offspring at the expense of maternal survival or the production of future offspring, and the optimal current investment may vary according to factors such as maternal age, somatic reserves or territory quality (e.g. Johnson 1986; Fisher and Blomberg 2011). For example, maternal body condition, mass loss during lactation, or increased maternal mortality are related to increased reproductive output in many marsupials (e.g. Fisher 1999; Isaac and Johnson 2005; Isaac et al. 2005; Foster and Taggart 2008; Fisher and Blomberg 2011). These results suggest that either (1) somatic energetic reserves are Journal compilation Ó CSIRO 2012 www.publish.csiro.au/journals/ajz CSIRO PUBLISHING Australian Journal of Zoology, 2012, 60, 111–119 http://dx.doi.org/10.1071/ZO12024