Rhino Poaching May Cause Atypical Trophic Cascades

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Write Back WRITE BACK WRITE BACK WRITE BACK Smith 1988 ), adult rhinos have neg- Local superstition dictates that carry- 65 ligible trophic interactions with ing a body part from a lion will Rhino poaching may cause lions or spotted hyenas ( Crocuta provide a hunter with luck on a dan- atypical trophic cascades crocuta ) (Clements et al . 2014 ). gerous hunt, including the ability to Current anthropogenic pressures However, both these apex-predator avoid capture by rangers (Els 2002 ). drive the widespread loss of apex species readily scavenge (Estes The killing of lions, for the local consumers where the effects of their 1992 ), are able to open pachyderm demand for body parts, threatens the removal from a system may cascade carcasses (White and Diedrich population of lions in Limpopo through lower trophic levels, with 2012 ), and can take advantage of (Everatt 2015 ). unanticipated impacts (Estes et al. this rich resource subsidy. Predator This link between rhino poaching 2011 ; Ripple et al . 2014 ). Similarly, abundance is positively correlated and lion poaching suggests that an the observed global decline in large with prey resources (Carbone and increase in the perceived risk to herbivores has complex outcomes for Gittleman 2002 ), and lion pride rhino poachers, from intensifying ecosystem functioning (Ripple et al. sizes are known to increase incre- anti-rhino- poaching efforts in 2015 ). Key to predicting and under- mentally following resource aug- Kruger, could lead to increased pres- standing the consequences of mentations (Packer et al. 2005 ). sure on Limpopo ’ s lion population. declines in both these guilds has Because carcass occurrence has been Furthermore, reduced lion densities been the concept of ecological predictable on the landscape and in Limpopo may make the landscape cascades. Thus, hypothesizing has been steadily increasing (cur- appear more attractive to African ecological pathways and species’ rently about two per day) ( www. wild dogs seeking refugia from the interactions is an important first step environment.gov.za ), this increase (already) higher lion densities in forecasting ecological responses to in food resources may likely lead to encountered in Kruger (van der changes in the abundance and distri- an increase in predator numbers Meer et al . 2014 ). Unfortunately, bution of both apex predators and (Oro et al. 2013; Ripple et al. 2013 ). African wild dogs are particularly large herbivores. This hypothesis is in line with the vulnerable to mortality from snares We raise the question of whether findings that the provision of set for herbivores (Becker et al. the recent surge in poaching of white trophy-hunted elephant (Loxodonta 2013 ), and illegal snaring for bush- rhinoceros (Ceratotherium simum) africana ) carcasses in Botswana rep- meat is widespread and common in and, to a lesser extent, the less abun- resented a substantial and valuable Limpopo (Everatt et al. 2014 ). It is dant black rhinoceros ( Diceros bicor- resource for spotted hyena (Cozzi therefore reasonable to predict that nis) in the Kruger National Park, et al . 2015), changing their foraging a greater disparity in the density of South Africa, is providing the ingre- behavior and possible clan sizes. lions between Kruger and Limpopo, dients for an atypical cascade – one A numerical increase in the abun- combined with the high threat of in which the mechanisms include an dance of lions and hyenas in Kruger snares in Limpopo, could result in an artificial enhancement rather than may have widespread and undesira- ecological trap that will be detri- reduction of apex predators ble impacts on predator-limited prey mental to the region’ s African wild (Figure 1 ). We further hypothesize species. For example, higher numbers dogs. that this atypical trophic cascade of lions in Kruger may imperil the Moreover, the loss of primary could act synergistically with another park’ s small population of roan ante- consumers, whose massive body size anthropogenic pressure, the related lopes ( Hippotragus equinus) already typically safeguards them from preda- poaching of lions ( Panthera leo ) for restricted to low numbers due to tion (Clements et al. 2014 ), may also body parts coveted by rhino poach- predation pressure (McLoughlin and induce trophic cascades. For ers, and subsistence poaching of wild Owen- Smith 2003 ). Additionally, instance, the removal of white rhinos meat in the adjoining Limpopo increasing numbers of lions and hyenas from the Kruger ecosystem leads to National Park, Mozambique, leading in Kruger could enhance intraguild the loss of “grazing lawns”, areas of to the creation of an “ecological competition. Competitively inferior short grass (roughly 4 m 2 ) main- trap” (where species mistakenly predators, including endangered tained by rhinos but potentially respond to environmental cues that African wild dogs ( Lycaon pictus ) benefiting insects, birds, small mam- no longer match habitat quality) for (Creel and Creel 1996 ) and cheetahs mals, and ungulates (Ripple et al. an endangered species. (Acinonyx jubatus) (Durant 1998 ), 2015 ). The reduction of rhino- In Kruger National Park poachers may no longer be able to find suffi- maintained short grass areas also have slaughtered 1670 rhinos over cient competition refugia in the coincides with changes in fire the past 3 years (2012–2014) (http:// park. regimes, with larger, hotter fires bit.ly/1PELXMm), taking the horns The rhino poachers entering occurring where rhinos have been and leaving the (~1900-kg) car- Kruger largely come from communi- removed. These intense fires increase casses. As a mega- herbivore not ties within the adjoining Limpopo the homogenous nature of the normally predated upon (Owen- National Park (Oosthuizen 2014 ). savanna, creating a positive feedback

66 Kruger Nat. Park Limpopo Nat. Park

Lions and spotted hyenas Rhino poachers

Lions

Roan Bushmeat poachers Wild dogs

Rhinoceros

Cheetahs Wild dogs

Figure 1 . Conceptual diagram showing a hypothetical atypical trophic cascade induced by rhino poaching in the Kruger National Park, South Africa. Poachers decrease abundance (black arrow) of mega-herbivores (www.environment.gov.za ), leaving carcasses that provide a resource subsidy, supporting an increase in abundance (red arrow) of apex predators (lions and spotted hyenas) in Kruger (Carbone and Gittleman 2002 ; Packer et al. 2005 ). Increased apex predators in Kruger suppress (black arrows) competitively inferior, endangered African wild dogs (Creel and Creel 1996 ) and cheetah (Durant 1998 ) and predator- limited roan antelope (McLoughlin and Owen-Smith 2003 ). Simultaneously, lions are killed in adjoining Limpopo Park (black arrow) to acquire body parts coveted by rhino poachers (Els 2002 ; Everatt 2015 ). African wild dogs select habitat (dashed arrow) with lower lion densities (van der Meer et al. 2014 ), moving from Kruger to Limpopo, where they then suffer high mortalities (black arrow) in snares set for bushmeat (Becker et al. 2013 ). Other important pathways not shown include the indirect effects following the loss of the rhinos, including the loss of rhino- maintained “grazing lawns”: a distinct micro- habitat that could support species of birds and lizards and encourage smaller grazers, and that alters fire patterns (Cromsigt and te Beest 2014 ).

loop toward a fire- dominated system herbivores. We hypothesize that Although we describe untested (Cromsigt and te Beest 2014 ). such cascades could result not only hypotheses in this letter, each path- The current rhino poaching cri- in the loss of other populations of way has been observed and the pre- sis of Kruger has the ingredients for endangered species but also in dicted end results are important widespread ecological degradation. changes in vegetation structure enough to justify prudence among We suggest the possible pathways and fire regimes; in addition, these natural resource managers tasked of atypical trophic cascades origi- cascades may interact with the with mitigating the impacts of poach- nating with the increases, rather actions of local poachers to create ing as well as further investigations by than loss, of apex predators, and an ecological trap for an endan- ecologists into unanticipated dynam- the associated loss of mega- gered species. ics in systems affected by poaching.

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