Biol. Rev. (2012), 87, pp. 390–413. 390 doi: 10.1111/j.1469-185X.2011.00203.x Top predators as biodiversity regulators: the dingo Canis lupus dingo as a case study Mike Letnic1,2,∗, Euan G. Ritchie3 and Christopher R. Dickman2 1 Hawkesbury Institute for the Environment, University of Western Sydney, Locked Bag 1797, Penrith, NSW, Australia, 2751 2 Institute of Wildlife Research, School of Biological Sciences, University of Sydney, NSW 2006, Australia 3 School of Life and Environmental Sciences, Deakin University, Burwood, Victoria, 3125, Australia ABSTRACT Top-order predators often have positive effects on biological diversity owing to their key functional roles in regulating trophic cascades and other ecological processes. Their loss has been identified as a major factor contributing to the decline of biodiversity in both aquatic and terrestrial systems. Consequently, restoring and maintaining the ecological function of top predators is a critical global imperative. Here we review studies of the ecological effects of the dingo Canis lupus dingo, Australia’s largest land predator, using this as a case study to explore the influence of a top predator on biodiversity at a continental scale. The dingo was introduced to Australia by people at least 3500 years ago and has an ambiguous status owing to its brief history on the continent, its adverse impacts on livestock production and its role as an ecosystem architect. A large body of research now indicates that dingoes regulate ecological cascades, particularly in arid Australia, and that the removal of dingoes results in an increase in the abundances and impacts of herbivores and invasive mesopredators, most notably the red fox Vulpes vulpes. The loss of dingoes has been linked to widespread losses of small and medium-sized native mammals, the depletion of plant biomass due to the effects of irrupting herbivore populations and increased predation rates by red foxes. We outline a suite of conceptual models to describe the effects of dingoes on vertebrate populations across different Australian environments. Finally, we discuss key issues that require consideration or warrant research before the ecological effects of dingoes can be incorporated formally into biodiversity conservation programs. Key words: biodiversity, conservation, dingo, Canis lupus dingo, intra-guild predation, trophic cascade, mesopredator, top predator, red fox, Vulpes vulpes, competition. CONTENTS I. Introduction ................................................................................................ 391 II. Natural history of the dingo ................................................................................ 392 (1) Taxonomic status ...................................................................................... 392 (2) Diet .................................................................................................... 392 III. Impacts of the dingo on other animals and plants .......................................................... 393 (1) Early impacts .......................................................................................... 393 (2) Effects of dingoes on large prey (>10 kg) ............................................................... 393 (3) Effects of dingoes on mesopredators (1–7 kg) .......................................................... 397 (4) Effects of dingoes on small and medium-sized prey (<10 kg) ........................................... 400 (5) Effects of dingoes on vegetation ........................................................................ 401 (6) Trophic effects of dingoes and the human economy ................................................... 401 (7) Experimental considerations ........................................................................... 402 IV. The ecological interactions of dingoes: a conceptual model ................................................ 402 (1) Element 1: the effects of dingoes on other species scale with body size ................................. 402 (2) Element 2: the influence of resource pulses and prey switching on dingo interactions .................. 403 (3) Element 3: large predators induce trophic cascades .................................................... 404 (4) Synthesis and application of the model ................................................................ 405 * Address for correspondence (E-mail: [email protected]). Biological Reviews 87 (2012) 390–413 © 2011 The Authors. Biological Reviews © 2011 Cambridge Philosophical Society Top predators as biodiversity regulators 391 V. Dingo interactions: from conceptual model to a practical conservation tool ................................ 406 (1) Native species adversely affected by dingoes ........................................................... 406 (2) Functionally effective dingo populations ............................................................... 406 (3) The effects of dingoes on livestock production ......................................................... 407 (4) Hybridisation .......................................................................................... 407 (5) The role of artificial water ............................................................................. 408 (6) Simulation of the effects of dingoes .................................................................... 408 VI. Conclusions ................................................................................................ 408 VII. Acknowledgements ......................................................................................... 409 VIII. References .................................................................................................. 409 I. INTRODUCTION While these studies demonstrate that top predators can exert strong effects on ecosystems (Beyer et al., 2007; Ripple & The loss of top-order predators has been identified as a Beschta, 2007; Berger & Conner, 2008; Berger et al., 2008), key factor contributing to continuing species extinctions and we still have a poor understanding of the extent to which these the global biodiversity-loss crisis (Duffy, 2003; Ray, 2005). predators can structure ecosystems at larger spatial scales and Consequently, restoring and maintaining the ecological how their effects filter through trophic webs (Schmidt, 2003). function of top predators is a critical goal in many systems This is particularly true in human-modified systems, where (Heithaus et al., 2008; Hayward & Somers, 2009). Top the return of a top predator can threaten native species with predators typically exert top–down control on ecosystems which they coexisted in the pre-disturbance state (Lovari through their direct predatory and competitive interactions et al., 2009). Hence, understanding predator function is of with herbivores and smaller predators (Frank et al., 2005; fundamental importance for biodiversity conservation and Frank, 2008; Ritchie & Johnson, 2009). The disruption or pest control at regional, national and even continental scales cessation of these interactions can have cascading effects on as it considers the ecological role that top predators have in lower trophic groups, and result in declines in small species maintaining functional and biodiverse ecosystems. of animal prey (Crooks & Soule,´ 1999) and the depletion In Australia, the role and historical importance of top of plant species diversity and biomass (Estes & Duggins, terrestrial predators has been controversial. Flannery (1994) 1995; Terborgh et al., 2001). The dramatic reorganisation of proposed that large reptilian predators may have dominated ecosystems and losses of biodiversity that frequently follow terrestrial systems over much of the Quaternary, but there the loss of top predators have provided insight into the were also many species of large carnivorous marsupials pivotal role they can play in maintaining healthy ecosystems over this period (Wroe, Argot & Dickman, 2004). The in marine, aquatic and terrestrial environments (Soule´ largest carnivorous marsupial of recent times, the thylacine et al., 2003). Increasingly, ecologists are realising that top Thylacinus cynocephalus (∼30 kg), became extinct in Tasmania predators shape the ecosystems around them and that their in the early twentieth century (Paddle, 2000), leaving the effects have the potential to be harnessed to manipulate Tasmanian devil Sarcophilus harrisii (10 kg) as the largest living ecological processes and species abundances for the benefit predatory marsupial. On the Australian mainland the largest of biodiversity conservation (Soule´ et al., 2003). of the extant marsupial predators, the spotted-tailed quoll Due to the widespread loss of top-order predators, frequent Dasyurus maculatus, is smaller still and seldom achieves a mass opposition to their reintroduction and sometimes even of more than 5 kg. However, the continent’s largest, most indifference about maintaining existing populations (Coman widespread and important terrestrial predator is no longer a & Evans, 2007), there are relatively few opportunities to marsupial, but a canid—the dingo Canis lupus dingo.Asfor evaluate the role that true top predators have in structuring Canis spp. generally (Vanak & Gompper, 2009), the dingo ecosystems, particularly at large geographical scales. This is appears to be a strongly interactive species with pervasive especially so in terrestrial ecosystems where top predators effects on trophic cascades and other ecological processes can conflict strongly with livestock production