Elephants in Africa: Big, grey biodiversity thieves?

The conservation of biological diversity is one of the greatest challenges facing humanity today.1,2 Addressing this challenge must inevitably involve the maintenance of the composition, structure and functioning of multi-species ecosystems.2-4 While preventing the loss of particular species is an obvious strategy, a second goal might be to manage for local species diversity and the heterogeneity of habitats.5 A further objective may be the restoration of damaged ecosystems.6 Large herbivore assemblages form an important component of many diverse ecosystems and are of distinct ecological, and hence conservation, value.7-9 On the other hand, herbivores managed at unnaturally high densities may drive detrimental changes in the structural heterogeneity of habitats.10-12 Thus, decision-makers are faced with the challenge of balancing the needs of populations of large herbivores with the preservation of vegetation and ecosystem diversity.9 In light of these considerations, conclusions as to whether large herbivores are 'good' or 'bad' for biological diversity are both contentious and elusive. Nonetheless, we seek to explore this question with particular reference to African savannah elephants (Loxodonta africana). We discuss whether or not the elephant should be considered a biodiversity thief - a species that upsets the natural diversity of life in the habitat in which it lives. The African elephant has been driven to local extinction over much of its former range, with hunting for meat and ivory and the conversion of elephant habitat to agriculture constituting the major drivers.5 Given the historical decline in elephant numbers, the conservation of this species appears to be a sensible objective.9,13 However, the protection afforded to elephants in confined (usually fenced) reserves across Africa has distinct implications for the management of local species diversity and the heterogeneity of habitats.14,15 Elephants have been shown to have clear impacts on the structure of vegetation, particularly in woodland habitats12,16,17, and these changes may have knock-on effects for sympatric species10,18,19. The effects of elephants on biological diversity in protected areas are of particular concern in light of how expansion in human populations, and the land-use change that follows, places increasing pressure on reserves to preserve biological diversity.9,10. Change within ecosystems is natural and inevitable and large herbivores have been living in an ever-changing environment for millions of years.20 Changes brought on by elephants, therefore, should not automatically be categorised as undesirable, and short-term changes may be part of an overarching trend of long-term stability.8,21 Furthermore, current elephant impacts can only be adequately assessed in the light of historical (on the scale of centuries) benchmarks, for which accurate information is notoriously scant.10,21 The current impacts of elephant populations on vegetation dynamics in some regions may in fact represent a shift towards a more natural historical state.8,21 Finally, much of the detrimental impacts of elephants on habitat structure and diversity, particularly at smaller scales, has resulted from human interventions (such as the erection of fences and the establishment of artificial water points) that have unnaturally confined elephants to localised areas, disrupted seasonal movements and disturbed the natural dynamics of population processes.5,13,22