WHY FORESTS NO LONGER EXIST WITHOUT THE CARNIVORES

[Reproduced from  Science 10 January 2014: 

Vol. 343 no. 6167 ]

DOI: 10.1126/science.1241484

• Review

Status and Ecological Effects of the World’s Largest Carnivores

Structured Abstract

Background

The largest terrestrial species in the order Carnivora are wide-ranging and rarebecause of their positions at the top of food webs. They are some of the world’s most admired mammalsand, ironically, some of the most imperiled. Most have experienced substantial populationdeclines and range contractions throughout the world during the past two centuries. Because of thehigh metabolic demands that come with endothermy and large body size, these carnivores oftenrequire large prey and expansive habitats. These food requirements and wide-ranging behavioroften bring them into confl ict with humans and livestock. This, in addition to human intolerance,renders them vulnerable to extinction. Large carnivores face enormous threats that have causedmassive declines in their populations and geographic ranges, including habitat loss and degradation,persecution, utilization, and depletion of prey. We highlight how these threats can affect theconservation status and ecological roles of this planet’s 31 largest carnivores.

Ecologically important carnivores. Seven species oflarge carnivores with documented ecological effectsinvolving (A) “tri-trophic cascades” from large carnivoresto prey to plants, (B) “mesopredator cascades”from large carnivores to mesopredators to prey ofmesopredators, and (C) both tri-trophic and mesopredatorcascades. [Photo credits: sea otter (N. Smith),puma (W. Ripple), lion (K. Abley), leopard (A. Dey), Eurasianlynx (B. Elmhagen), dingo (A. McNab), gray wolf(D. Mclaughlin)]Ecologically important carnivores. Seven species oflarge carnivores with documented ecological effectsinvolving (A) “tri-trophic cascades” from large carnivoresto prey to plants, (B) “mesopredator cascades”from large carnivores to mesopredators to prey ofmesopredators, and (C) both tri-trophic and mesopredatorcascades. [Photo credits: sea otter (N. Smith),puma (W. Ripple), lion (K. Abley), leopard (A. Dey), Eurasianlynx (B. Elmhagen), dingo (A. McNab), gray wolf(D. Mclaughlin)]

Advances

Based on empirical studies, trophic cascades have been documented for 7 of the 31 largestmammalian carnivores (not including pinnipeds). For each of these species (see fi gure), humanactions have both caused declines and contributed to recovery, providing “natural experiments” forquantifying their effects on food-web and community structure. Large carnivores deliver economicand ecosystem services via direct and indirect pathways that help maintain mammal, avian, invertebrate,and herpetofauna abundance or richness. Further, they affect other ecosystem processes andconditions, such as scavenger subsidies, disease dynamics, carbon storage, stream morphology, andcrop production. The maintenance or recovery of ecologically effective densities of large carnivoresis an important tool for maintaining the structure and function of diverse ecosystems.

Outlook

Current ecological knowledge indicates that large carnivores are necessary for the maintenanceof biodiversity and ecosystem function. Human actions cannot fully replace the role of largecarnivores. Additionally, the future of increasing human resource demands and changing climate willaffect biodiversity and ecosystem resiliency. These facts, combined with the importance of resilientecosystems, indicate that large carnivores and their habitats should be maintained and restored whereverpossible. Preventing the extinction of these species and the loss of their irreplaceable ecologicalfunction and importance will require novel, bold, and deliberate actions. We propose a Global LargeCarnivore Initiative to coordinate local, national, and international research, conservation, and policy.

Preserving Predators

Large-bodied animals play essential roles in ecosystem structuring and stability through both indirect and direct trophic effects. In recent times, humans have disrupted this trophic structure through both habitat destruction and active extirpation of large predators, resulting in large declines in numbers and vast contractions in their geographic ranges. Ripple et al. (10.1126/science.1241484; see the Perspective byRoberts) review the status, threats, and ecological importance of the 31 largest mammalian carnivores globally. These species are responsible for a suite of direct and indirect stabilizing effects in ecosystems. Current levels of decline are likely to result in ecologically ineffective population densities and can lead to ecosystem instability. The preservation of large carnivores can be challenging because of their need for large ranges and their potential for human conflict. However, the authors demonstrate that the preservation of large carnivores is ecologically important and that the need for conservation action is immediate, given the severity of the threats they face.

Abstract

Large carnivores face serious threats and are experiencing massive declines in their populations and geographic ranges around the world. We highlight how these threats have affected the conservation status and ecological functioning of the 31 largest mammalian carnivores on Earth. Consistent with theory, empirical studies increasingly show that large carnivores have substantial effects on the structure and function of diverse ecosystems. Significant cascading trophic interactions, mediated by their prey or sympatric mesopredators, arise when some of these carnivores are extirpated from or repatriated to ecosystems. Unexpected effects of trophic cascades on various taxa and processes include changes to bird, mammal, invertebrate, and herpetofauna abundance or richness; subsidies to scavengers; altered disease dynamics; carbon sequestration; modified stream morphology; and crop damage. Promoting tolerance and coexistence with large carnivores is a crucial societal challenge that will ultimately determine the fate of Earth’s largest carnivores and all that depends upon them, including humans.