The ranging behaviour of a large sexually dimorphic herbivore in response to seasonal and annual environmental variation GRAEME SHANNON, 1 * BRUCE R. PAGE, 1 KEVIN J. DUFFY 2 AND ROB SLOTOW 1 1 Amarula Elephant Research Programme, School of Biological and Conservation Sciences, University of KwaZulu-Natal,Westville Campus, University of KwaZulu-Natal, Private Bag X54001, Durban 4000, South Africa (Email: shannongraeme@gmail.com), and 2 Centre for Systems Research, Durban University of Technology, Durban, South Africa Abstract The allometric relationships of body size play a principle role in determining how large herbivores respond to the marked spatial and temporal heterogeneity of the savanna biome. Using location data collected over an 8-year period from five distinct study sites, we investigated the influence of environmental variation (using phenological and rainfall data) on the ranging behaviour of the African elephant (Loxodonta africana), a species that exhibits pronounced sexual dimorphism. Both sexes expanded their annual ranges during years of high rainfall and contracted their ranges during periods of resource scarcity, concurring with the hypothesis that abiotic factors dictate the distribution of large generalist herbivores at the landscape scale. However, female elephant did not exhibit the same consistent response to rainfall at the seasonal scale. Furthermore, male elephant demonstrated a reduction in their daily displacement distances during the dry winter season, and altered their movement rates on the basis of seasonal rainfall.These results suggest that male elephant are able to consistently adapt their movement behaviour according to forage quality and abundance. Smaller-bodied female elephant on the other hand, are unlikely to exhibit the same flexibility in their ranging behaviour because of their higher relative nutritional demands, lower tolerance to fibrous forage and the social and energetic constraints of group living with juveniles. Our study highlights the major role that body size and sociality plays in the decision making of sexually dimorphic herbivores.These differences can have important implications for effective conservation and management, particu- larly with regard to demographic (e.g. survival) and ecological (e.g. habitat use) factors. Key words: elephant (Loxodonta africana), movement, plant phenology, rainfall, savanna. INTRODUCTION Large herbivores experience wide scale temporal fluctuations in forage availability and quality (Owen- Smith 1994; Illius & O’Connor 2000). This is particu- larly apparent in the savanna biome where primary productivity is determined by the two distinct seasons (wet summer and dry winter) and annual rainfall (McNaughton & Georgiadis 1986). Furthermore, there is pronounced spatial heterogeneity in resource distribution and quality from the landscape to the plant scale (Pickett & Cadenasso 1995; Skarpe et al. 2000). In order to maximize nutritional return and adapt to variable forage availability and quality, herbivores make a series of hierarchical decisions that are nested across a range of spatial and temporal scales, from the selection of individual plant parts to seasonal move- ment patterns (Senft et al. 1987; Ward & Saltz 1994; Searle et al. 2005). Therefore, as plant biomass and quality changes between seasons and years, an indi- vidual herbivore is predicted to adapt its ranging and foraging behaviour optimally (Stephens & Krebs 1986). Effective decision making becomes particularly important during periods of resource scarcity as poor strategies can lead to a reduction in individual fitness, resulting in lower reproductive output and even death (McNaughton & Georgiadis 1986; Mysterud et al. 2001a). Body size is a key determinant in the effective deci- sion making of large herbivores as it directly influences a range of physiological and behavioural processes, including metabolism (Demment & Van Soest 1985), movement (Jetz et al. 2004; Carbone et al. 2005), tem- perature regulation (Calder 1984) and reproduc- tion (McElligott et al. 2001). Furthermore, as body size increases, the energy required per unit mass scales with a factor of 0.75M (M = body mass), because of greater muscle efficiency and lower heat loss (Kleiber 1975; Demment & Van Soest 1985). Larger bodied herbivores are therefore predicted to have lower rela- tive energy demands (per kg) and are also able to tolerate lower quality diets because of their increased *Corresponding author. Accepted for publication September 2009 Austral Ecology (2010) 35, 731–742 © 2009 The Authors doi:10.1111/j.1442-9993.2009.02080.x Journal compilation © 2009 Ecological Society of Australia