Dynamics of large herbivore populations in changing environments

DYNAMICS OF LARGE HERBIVORE POPULATIONS IN CHANGING ENVIRONMENTS TOWARDS APPROPRIATE MODELS Edited by Norman Owen-Smith Preface This book originated from aworking group established at the National Center for Ecological Analysis and Synthesis (NCEAS) at the University of California, Santa Barbara. The problem confronted was the contrasting dynamics shown by populations of large mammalian herbivores in recent decades. Some of these populations had declined abruptly in abundance, most notably in certain protected areas in Africa. Others had become so abundant as to threaten plant populations and forest regeneration, especially in parts of Europe and North America. Conventional models emphasizing population regulation around some steady state seemed inadequate to explain these divergent trends. Hence the specific aims of the group were to challengethe prevalent models using existing data sets, and develop alternative modelscapable of accommodating the complexity of environmental influences operatingat different spatial and temporal scales. The group met annually over three years, 2001-2003. Much shared understanding was gained, and several joint-authored publications have appeared in journals. During the subsequent period many other papers have also been published on aspects of the dynamics of large ungulate populations. At the same time, population ecology has been undergoing a phase of theory maturation, evidenced by the appearance of several books (e. g.Lande, Engen and Saether 2003, Turchin 2003, Cuddington and Beisner 2005) as well as numerous papers in ecological journals. A balance of nature perspective is no longer the prevalent paradigm (Cooper 2003), and new approaches provide greater recognition of disequilibrium processes, non-linear responses, and the consequences of spatial structure, enabled by expanded computational capacity to accommodate this complexity (Owen-Smith 2002, Ellner and Guckenheimer 2006, Clark 2007). Studies on large herbivores are making an increasing contribution to this theoretical reassessment. New insights have been provided by the opportunities to follow changes in certain ungulate populations in demographicor even individual detail, revealing response mechanisms that generally remain cryptic for small mammal or insect populations. Being directly dependent on vegetation as a food resource, herbivore populations respond sensitively to patterns of plant growth, and hence to changing climatic and human influences onvegetation dynamics. Complications arise from the additional effects of predation and hunting on some of these populations, as well as from fragmentation of the spatial context within which they exist. It is time to take stock of thenew knowledge that has been gained from these large herbivore studies. In particular, there is a need to assess the revision of theory, as expressed through models of population dynamics, required to explain the causes of change, looking beyond the density-dependent processes counteracting change that have apparently become ineffective in some circumstances. Accordingly, this book is aimed at filling this need through (1) reconciling theoretical models with empirical findings on the population dynamics of large mammalian herbivores, and (2) developing appropriate models for identifying the factors and processes causing changes in abundance. It is structured as follows. Chapter 1 outlines the suite of modeling approaches representing prevalent theory and concepts. Chapter 2 summarizes findings from a set of long-term studies on herbivore populations that have been especially revealing of the processes contributing to changes in abundance. The following chapters then explore particular aspects more comprehensively. Chapter 3 is concerned with identifying local and broad-scale climatic influences on population dynamics, as well as the modifying effects of predation and hunting, structured as a temperate-tropical comparison. Chapter 4 considers the demographic processes that generate changes in abundance, asilluminated by individual-based studies. Chapter 5 identifies circumstances that may lead to irruptive oscillations in abundance. Chapter 6 examines how spatial heterogeneity modifies the influences of temporal variation in conditions on population processes. Finally, Chapter 7 outlines of alternative paradigmfor accommodating the effects of spatial and temporal variability in resources and conditions on population dynamics. While certain authors have taken leador subsidiary responsibility for particular chapters, other members of the NCEAS group, and some people outside this group, have contributed in various ways. I thank everyone for their varied inputs. We are indebted to the National Center for Ecological Analysis and Synthesis, University of California, Santa Barbara, for providing the funding that enabled the working group Dynamics of large mammalian herbivores in changing environments: alternative modeling approaches to meet and share our experiences and expertise.

• ISBN: 978-1-4051-9894-3
• Editorial: Wiley-Blackwell
• Encuadernacion: Cartoné
• Páginas: 216
• Fecha Publicación: 12/02/2010
• Nº Volúmenes: 1
• Idioma: Inglés