DOI: 10.1111/j.1472-4642.2007.00388.x © 2007 The Authors 752 Journal compilation © 2007 Blackwell Publishing Ltd www.blackwellpublishing.com/ddi Diversity and Distributions, (Diversity Distrib.) (2007) 13, 752–760 BIODIVERSITY RESEARCH ABSTRACT Mounting evidence indicates large-scale climatic phenomena such as El Niño Southern Oscillation (ENSO) can overwhelm endogenous factors that govern the population dynamics of wild species. We add to this evidence by documenting an ENSO-related decline of large mammals in the Kumbhalgarh Wildlife Sanctuary, in Rajasthan, India. This event coincided with the drought of 2000, following two consecutive monsoon failures. Time series of biennial counts (1991–2005) shared a common feature: all 13 species declined in abundance from 1999 to 2001, with 11 species experiencing an apparent decline exceeding 25%. An ENSO index explained much of the variability in population size, apparently reflecting mass mortality and/or recruitment failure caused by the major 1998–2000 La Niña event, followed by a rapid rebound. ENSO apparently overwhelmed endogenous factors and synchronized the dynamics of the mammalian community. Our findings may prove to be symptomatic of geographically broad impacts of large-scale climate on the dynamics of terrestrial vertebrate communities, even in protected areas. Our findings reinforce the growing recognition that we should not overlook global-scale causal agents of ecological change. Keywords Drought, El Niño Southern Oscillation, ENSO, extinction threat, India, mammals, population dynamics. INTRODUCTION The ongoing global extinction crisis has spurred countries with intact natural areas to set aside land to protect their natural capital and prevent further loss (Balmford & Bond, 2005). This response reflects the belief that habitat loss and human persecution are the primary extinction drivers (Cardillo et al ., 2005, 2006; Gaston, 2005). Unfortunately, protected areas are often small and surrounded by large human populations (Cardillo et al ., 2004; Luck et al ., 2004; Karanth et al ., 2006), leaving them vulnerable to impacts of humans and their domestic livestock. Collection of fuel wood and assorted plant parts can directly affect food availability for wild species, and can indirectly influence it through reduced plant survival, regeneration, and recruitment. Hunting can alter trophic interactions and even drive populations to extinction (Brashares et al ., 2001; Costa et al ., 2005). Grazing by livestock can decrease food resources for wild herbivores and lead to local extinction or emigration (Madhusudan, 2004; Mishra et al ., 2006). Thus, whenever populations of wild species decline within nominally protected areas, some conservationists find it all too tempting to suspect that local people and their domestic animals might have played a causative role. However, we should also recognize that large-scale climatic phenomena such as the El Niño Southern Oscillation (ENSO) have the capacity to overwhelm endogenous factors that ordinarily regulate population dynamics (Letnic et al ., 2005; Anders & Post, 2006) even within protected areas with no human encroachment (Vucetich et al ., 2005; Wilmers et al ., 2006). This recognition raises the possibility that ENSO may be partly responsible for population and even community-wide crashes within protected areas, especially in arid and semiarid ecosystems where precipitation can have pronounced bottom-up effects (Holmgren et al ., 2006). ENSO fluctuates every few years between El Niño events that, in India, trigger monsoon rains and La Niña events that, in India, trigger monsoon failure. An initial increase in plant productivity following monsoon rains may induce population increases in herbivores and subsequently carnivores. Human activities, including grazing, may alter availability of water and food resources in both positive and negative directions, potentially altering ecosystem dynamics (Gaston, 2005). Plant regeneration provides abundant resources for wild herbivores and domestic animals, so overgrazing may become problematic during drought (Holmgren & Scheffer, 2001; de Beer et al ., 2006). La Niña events can cause resource limitation, population crashes, loss of genetic 1 Department of Evolution, Ecology, and Organismal Biology, Ohio State University, Columbus, Ohio 43210, USA, 2 The School of Desert Sciences, 109, Nehru Park, Jodhpur, India, 3 Department of Geography and Regional Development, University of Arizona, Tucson, Arizona 85721, USA *Correspondence: Tom Waite, Department of Evolution, Ecology and Organismal Biology, Ohio State University, Columbus, Ohio 43210, USA. E-mail: waite.1@osu.edu Blackwell Publishing Ltd La Niña’s signature: synchronous decline of the mammal community in a ‘protected’ area in India T. A. Waite 1 *, L. G. Campbell 1 , A. K. Chhangani 2 and P. Robbins 3