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Rhino poaching may cause
atypical trophic cascades
Current anthropogenic pressures
drive the widespread loss of apex
consumers where the effects of their
removal from a system may cascade
through lower trophic levels, with
unanticipated impacts (Estes et al .
2011 ; Ripple et al . 2014 ). Similarly,
the observed global decline in large
herbivores has complex outcomes for
ecosystem functioning (Ripple et al .
2015 ). Key to predicting and under-
standing the consequences of
declines in both these guilds has
been the concept of ecological
cascades. Thus, hypothesizing
ecological pathways and species’
interactions is an important first step
in forecasting ecological responses to
changes in the abundance and distri-
bution of both apex predators and
large herbivores.
We raise the question of whether
the recent surge in poaching of white
rhinoceros ( Ceratotherium simum )
and, to a lesser extent, the less abun-
dant black rhinoceros ( Diceros bicor-
nis ) in the Kruger National Park,
South Africa, is providing the ingre-
dients for an atypical cascade – one
in which the mechanisms include an
artificial enhancement rather than
reduction of apex predators
(Figure 1 ). We further hypothesize
that this atypical trophic cascade
could act synergistically with another
anthropogenic pressure, the related
poaching of lions ( Panthera leo ) for
body parts coveted by rhino poach-
ers, and subsistence poaching of wild
meat in the adjoining Limpopo
National Park, Mozambique, leading
to the creation of an “ecological
trap” (where species mistakenly
respond to environmental cues that
no longer match habitat quality) for
an endangered species.
In Kruger National Park poachers
have slaughtered 1670 rhinos over
the past 3 years (2012–2014) ( http://
bit.ly/1PELXMm ), taking the horns
and leaving the (~1900- kg) car-
casses. As a mega- herbivore not
normally predated upon (Owen-
Smith 1988 ), adult rhinos have neg-
ligible trophic interactions with
lions or spotted hyenas ( Crocuta
crocuta ) (Clements et al . 2014 ).
However, both these apex- predator
species readily scavenge (Estes
1992 ), are able to open pachyderm
carcasses (White and Diedrich
2012 ), and can take advantage of
this rich resource subsidy. Predator
abundance is positively correlated
with prey resources (Carbone and
Gittleman 2002 ), and lion pride
sizes are known to increase incre-
mentally following resource aug-
mentations (Packer et al . 2005 ).
Because carcass occurrence has been
predictable on the landscape and
has been steadily increasing (cur-
rently about two per day) ( www.
environment.gov.za ), this increase
in food resources may likely lead to
an increase in predator numbers
(Oro et al. 2013; Ripple et al. 2013 ).
This hypothesis is in line with the
findings that the provision of
trophy- hunted elephant ( Loxodonta
africana ) carcasses in Botswana rep-
resented a substantial and valuable
resource for spotted hyena (Cozzi
et al . 2015), changing their foraging
behavior and possible clan sizes.
A numerical increase in the abun-
dance of lions and hyenas in Kruger
may have widespread and undesira-
ble impacts on predator- limited prey
species. For example, higher numbers
of lions in Kruger may imperil the
park s small population of roan ante-
lopes ( Hippotragus equinus ) already
restricted to low numbers due to
predation pressure (McLoughlin and
Owen- Smith 2003 ). Additionally,
increasing numbers of lions and hyenas
in Kruger could enhance intraguild
competition. Competitively inferior
predators, including endangered
African wild dogs ( Lycaon pictus )
(Creel and Creel 1996 ) and cheetahs
( Acinonyx jubatus ) (Durant 1998 ),
may no longer be able to find suffi-
cient competition refugia in the
park.
The rhino poachers entering
Kruger largely come from communi-
ties within the adjoining Limpopo
National Park (Oosthuizen 2014 ).
Local superstition dictates that carry-
ing a body part from a lion will
provide a hunter with luck on a dan-
gerous hunt, including the ability to
avoid capture by rangers (Els 2002 ).
The killing of lions, for the local
demand for body parts, threatens the
population of lions in Limpopo
(Everatt 2015 ).
This link between rhino poaching
and lion poaching suggests that an
increase in the perceived risk to
rhino poachers, from intensifying
anti- rhino- poaching efforts in
Kruger, could lead to increased pres-
sure on Limpopo s lion population.
Furthermore, reduced lion densities
in Limpopo may make the landscape
appear more attractive to African
wild dogs seeking refugia from the
(already) higher lion densities
encountered in Kruger (van der
Meer et al . 2014 ). Unfortunately,
African wild dogs are particularly
vulnerable to mortality from snares
set for herbivores (Becker et al.
2013 ), and illegal snaring for bush-
meat is widespread and common in
Limpopo (Everatt et al. 2014 ). It is
therefore reasonable to predict that
a greater disparity in the density of
lions between Kruger and Limpopo,
combined with the high threat of
snares in Limpopo, could result in an
ecological trap that will be detri-
mental to the region s African wild
dogs.
Moreover, the loss of primary
consumers, whose massive body size
typically safeguards them from preda-
tion (Clements et al. 2014 ), may also
induce trophic cascades. For
instance, the removal of white rhinos
from the Kruger ecosystem leads to
the loss of “grazing lawns”, areas of
short grass (roughly 4 m
2
) main-
tained by rhinos but potentially
benefiting insects, birds, small mam-
mals, and ungulates (Ripple et al .
2015 ). The reduction of rhino-
maintained short grass areas also
coincides with changes in fire
regimes, with larger, hotter fires
occurring where rhinos have been
removed. These intense fires increase
the homogenous nature of the
savanna, creating a positive feedback
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loop toward a fire- dominated system
(Cromsigt and te Beest 2014 ).
The current rhino poaching cri-
sis of Kruger has the ingredients for
widespread ecological degradation.
We suggest the possible pathways
of atypical trophic cascades origi-
nating with the increases, rather
than loss, of apex predators, and
the associated loss of mega-
herbivores. We hypothesize that
such cascades could result not only
in the loss of other populations of
endangered species but also in
changes in vegetation structure
and fire regimes; in addition, these
cascades may interact with the
actions of local poachers to create
an ecological trap for an endan-
gered species.
Although we describe untested
hypotheses in this letter, each path-
way has been observed and the pre-
dicted end results are important
enough to justify prudence among
natural resource managers tasked
with mitigating the impacts of poach-
ing as well as further investigations by
ecologists into unanticipated dynam-
ics in systems affected by poaching.
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 ).
Kruger Nat. Park Limpopo Nat. Park
Lions
Bushmeat
poachers
Wild dogs
Wild dogs
Cheetahs
Roan
Rhino poachers
Lions and spotted hyenas
Rhinoceros
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doi:10.1002/fee.1202
The moral basis for
conservation – refl ections
on Dickman et al .
Dickman et al . (2015; Front Ecol
Environ 13[6] : 325–31) suggested
that “moral relativism” and “mis-
guided respect” for cultural practices
impede biological conservation.
They favor a world in which
conservation scientists armed with
universal norms will more readily
implement their solutions without
the consent of local stakeholders.
While we acknowledge their con-
cerns, their vision, however tenta-
tive, appears misguided. Here we
highlight some objections.
The authors suggest their inter-
ventions are justified by universal
values and scientific rationality.
But society also protects cultural
diversity and human rights on the
basis of philosophy and universal
values (Maffi 2005 ; Elliott 2014 ).
Sen, whose non- relativist views
were mentioned, actually proposed
universal human capacities and
freedoms that he wanted to see
protected, not undermined, though
he acknowledged these principles
do not readily yield a practical
means to make choices by calcula-
tion (Sen 1988 ). Human rights
related to conservation actions
enjoy widespread, often legal, rec-
ognition (Elliott 2014 ) and have
motivated various international
agreements (eg www.unccd.int ,
http://undesadspd.org , www.cbd.
int , and www.ilo.org ). “Free, prior,
and informed consent” is a princi-
ple emphasized in these agree-
ments and others (Hanna and
Vanclay 2013 ).
Dickman et al . fail to recognize that
conservation serves a plurality of peo-
ple and principles. Furthermore, con-
servation represents one set of soci-
etal goals among many; choices are
necessary to allocate resources and
manage trade- offs. The challenge is
how to reconcile competing values
and human rights.
We propose that the route to legiti-
macy lies in respecting democratic
and legal principles. Such principles
acknowledge different views and per-
spectives. Scientists should draw on
their knowledge to inform choices,
but scientific utility is no excuse for
tyranny by scientists (Sheil and
Meijaard 2010 ). The ends and means
of science represent one subset of the
ends and means of society as a whole.
Relativism takes many forms. In
conservation, “relativism” emphasizes
inclusive and respectful approaches.
This is a guiding principle, not a fun-
damental doctrine. Such relativism
reflects the diversity of perspectives
that occur even within science.
Scientific views are seldom mono-
lithic. Applied science is often con-
troversial, even among scientists,
and normative assessments differ
(Vedeld 1994 ). Perceptions, fram-
ing, and preferred outcomes vary
among stakeholders, including sci-
Kristoffer T Everatt
1 * , Leah Andresen
1
,
William J Ripple
2
, and Graham IH
Kerley
1
1 Centre for African Conservation
Ecology , Department of Zoology ,
Nelson Mandela Metropolitan
University , Port Elizabeth , South
Africa *(kteveratt@gmail.com);
2 Global Trophic Cascades Program ,
Department of Forest Ecosystems and
Society , Oregon State University ,
Corvallis , OR
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The African lion (Panthera Leo) has suffered drastic population and range declines over the last few decades and is listed by the IUCN as vulnerable to extinction. Conservation management requires reliable population estimates, however these data are lacking for many of the continent's remaining populations. It is possible to estimate lion abundance using a trophic scaling approach. However, such inferences assume that a predator population is subject only to bottom-up regulation, and are thus likely to produce biased estimates in systems experiencing top-down anthropogenic pressures. Here we provide baseline data on the status of lions in a developing National Park in Mozambique that is impacted by humans and livestock. We compare a direct density estimate with an estimate derived from trophic scaling. We then use replicated detection/non-detection surveys to estimate the proportion of area occupied by lions, and hierarchical ranking of covariates to provide inferences on the relative contribution of prey resources and anthropogenic factors influencing lion occurrence. The direct density estimate was less than 1/3 of the estimate derived from prey resources (0.99 lions/100 km2 vs. 3.05 lions/100 km2). The proportion of area occupied by lions was Ψ = 0.439 (SE = 0.121), or approximately 44% of a 2 400 km2 sample of potential habitat. Although lions were strongly predicted by a greater probability of encountering prey resources, the greatest contributing factor to lion occurrence was a strong negative association with settlements. Finally, our empirical abundance estimate is approximately 1/3 of a published abundance estimate derived from opinion surveys. Altogether, our results describe a lion population held below resource-based carrying capacity by anthropogenic factors and highlight the limitations of trophic scaling and opinion surveys for estimating predator populations exposed to anthropogenic pressures. Our study provides the first empirical quantification of a population that future change can be measured against.
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