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Evaluating the efficacy of predator removal in a conflict-prone world

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Predators shape ecosystem structure and function through their direct and indirect effects on prey, which permeate through ecological communities. Predators are often perceived as competitors or threats to human values or well-being. This conflict has persisted for centuries, often resulting in predator removal (i.e. killing) via targeted culling, trapping, poisoning, and/or public hunts. Predator removal persists as a management strategy but requires scientific evaluation to assess the impacts of these actions, and to develop a way forward in a world where human-predator conflict may intensify due to predator reintroduction and rewilding, alongside an expanding human population. We reviewed literature investigating predator removal and focused on identifying instances of successes and failures. We found that predator removal was generally intended to protect domestic animals from depredation, to preserve prey species, or to mitigate risks of direct human conflict, corresponding to being conducted in farmland, wild land, or urban areas. Because of the different motivations for predator removal, there was no consistent definition of what success entailed so we developed one with which to assess studies we reviewed. Research tended to be retrospective and correlative and there were few controlled experimental approaches that evaluated whether predator removal met our definition of success, making formal meta-analysis impossible. Predator removal appeared to only be effective for the short-term, failing in the absence of sustained predator suppression. This means predator removal was typically an ineffective and costly approach to conflicts between humans and predators. Management must consider the role of the predator within the ecosystem and the potential consequences of removal on competitors and prey. Simulations or models can be generated to predict responses prior to removing predators. We also suggest that alternatives to predator removal be further developed and researched. Ultimately, humans must coexist with predators and learning how best to do so may resolve many conflicts.
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Biological Conservation
journal homepage: www.elsevier.com/locate/biocon
Review
Evaluating the ecacy of predator removal in a conict-prone world
Robert J. Lennox
a,
, Austin J. Gallagher
a,b,c
, Euan G. Ritchie
d
, Steven J. Cooke
a
a
Fish Ecology and Conservation Physiology Laboratory, Department of Biology, Carleton University, Ottawa, Ontario K1S 5B6, Canada
b
Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL 33149, USA
c
Beneath the Waves, Inc., Miami, FL 33133, USA
d
Centre for Integrative Ecology, School of Life and Environmental Sciences, Deakin University, Burwood, Victoria 3125 Australia
ARTICLE INFO
Keywords:
Conservation and wildlife management
Fisheries and agriculture
Human-wildlife conict
Predator-prey interactions
Rewilding
Trophic cascade
ABSTRACT
Predators shape ecosystem structure and function through their direct and indirect eects on prey, which
permeate through ecological communities. Predators are often perceived as competitors or threats to human
values or well-being. This conict has persisted for centuries, often resulting in predator removal (i.e. killing) via
targeted culling, trapping, poisoning, and/or public hunts. Predator removal persists as a management strategy
but requires scientic evaluation to assess the impacts of these actions, and to develop a way forward in a world
where human-predator conict may intensify due to predator reintroduction and rewilding, alongside an ex-
panding human population. We reviewed literature investigating predator removal and focused on identifying
instances of successes and failures. We found that predator removal was generally intended to protect domestic
animals from depredation, to preserve prey species, or to mitigate risks of direct human conict, corresponding
to being conducted in farmland, wild land, or urban areas. Because of the dierent motivations for predator
removal, there was no consistent denition of what success entailed so we developed one with which to assess
studies we reviewed. Research tended to be retrospective and correlative and there were few controlled ex-
perimental approaches that evaluated whether predator removal met our denition of success, making formal
meta-analysis impossible. Predator removal appeared to only be eective for the short-term, failing in the ab-
sence of sustained predator suppression. This means predator removal was typically an ineective and costly
approach to conicts between humans and predators. Management must consider the role of the predator within
the ecosystem and the potential consequences of removal on competitors and prey. Simulations or models can be
generated to predict responses prior to removing predators. We also suggest that alternatives to predator re-
moval be further developed and researched. Ultimately, humans must coexist with predators and learning how
best to do so may resolve many conicts.
1. Introduction
Predators can inuence ecosystems through top-down control of the
distribution and abundance of other species (Estes et al., 2011;Mills
et al., 1993;Newsome et al., 2017;Pace et al., 1999). The loss of pre-
dators can therefore have profound ecological eects in certain con-
texts, including disease outbreaks, biodiversity loss, and ecosystem
state changes (Myers et al., 2007;Ripple et al., 2014). There is evidence
to suggest that ecological communities can exhibit dramatic shifts fol-
lowing the loss of predators (Crooks and Soulé, 1999;Pech et al., 1992;
Ritchie and Johnson, 2009;Wallach et al., 2010), including changes at
other trophic levels (Anthony et al., 2008;Atwood et al., 2015;Suraci
et al., 2016). Although predators occur among diverse animal taxa (e.g.,
arthropods, molluscs, teleosts, raptors, canids, mustelids, etc.), verte-
brate predators frequently conict with humans, and many species are
threatened (Ripple et al., 2014); they are therefore the focus of this
paper.
Many predatory vertebrates are vulnerable to disturbances because
they generally have slower life histories, higher investment in parental
care, lower abundances, and patchy distributions (Purvis et al., 2000).
Yet, predators are challenged by a perception of being a threat to
human interests or safety. Indeed, predators can be considered ha-
zardous to domesticated animals (Gusset et al., 2009;Mishra, 1997;Oli
et al., 1994), prey species of economic importance (Dalla Rosa and
Secchi, 2007;Henschel et al., 2011;Weise and Harvey, 2005), or
human safety via direct conict (Dickman, 2010;Gore et al., 2005;Löe
and Röskaft, 2004;Penteriani et al., 2016). Consequently, predators are
often negatively perceived and persecution of vertebrate predators has
a long a history (Bergstrom et al., 2014;Kruuk, 2002;Reynolds and
Tapper, 1996;Treves and Naughton-Treves, 1999). Competition with
https://doi.org/10.1016/j.biocon.2018.05.003
Received 12 June 2017; Received in revised form 30 April 2018; Accepted 7 May 2018
Corresponding author.
E-mail address: robert.lennox@carleton.ca (R.J. Lennox).
Biological Conservation 224 (2018) 277–289
0006-3207/ © 2018 Elsevier Ltd. All rights reserved.
T
predators yielded many institutionalized campaigns against them
dating back to ancient Greece and Rome, a trend that pervaded through
medieval Europe and was exported to North America with emigrants in
the 1700s (Reynolds and Tapper, 1996 and references therein). Today,
state, regional, and agency-led programs to systematically control
predator populations exist. Predator removal is carried out system-
atically via a number of methods and across various geographic scales
(Bergstrom et al., 2014;Reynolds and Tapper, 1996), including poison
baiting, trapping, hunting, and culling or via bounty or reward systems
in public hunting or shing events, but may also be more haphazard as
retaliation for encroachment or interaction with humans or their
property (e.g., farmer killing a wolf encroaching on their herds; e.g.
Bergstrom et al., 2014;Treves and Karanth, 2003).
The signicance of predators in ecosystems is well established yet
their removal remains a component of the management toolbox. Owing
to a lack of clarity pertaining to how and when removal can be expected
to be successful, it may be dicult for management agencies to decide
whether to proceed with predator removal when confronted with a
problem. Furthermore, there is mounting opposition from advocacy
groups (especially animal rights) and conservation-aware citizens that
provide social inertia and pressure on animal control (van Eeden et al.,
2017), which may complicate and inuence decision-making (see
Wallach et al., 2015). The science of predator removal therefore could
benet from an objective evaluation to identify successes and failures to
both inform decision-making and identify lingering research gaps
across multiple taxa (Treves et al., 2016;Eklund et al., 2017). Syntheses
of this topic have focused on using meta-analysis, particularly for
nesting birds (Côté and Sutherland, 1997;Smith et al., 2010, 2011), but
it is challenging to apply such an approach across taxa and research
paradigms (i.e., motivations). In this review, we evaluated these two
competing hypotheses by considering of the available evidence for
predator removal to determine whether predator removal is successful
for wildlife conservation and management. We reviewed relevant lit-
erature and evaluated outcomes. In doing so, we propose a denition of
success that can be applied to predator removal programs and we
provide examples of success and failure in predator removals based on
the following motivations 1) protection of domestic species, 2) pre-
servation of prey species (e.g. economically important species or species
at risk), and 3) mitigating risks of direct human-wildlife conict. We
conclude by considering evidence for the costs of failure in predator
removal and a discussion of alternatives to predator removal. Although
there are social and economic motivations associated with predator
removal (Reynolds and Tapper, 1996;Engeman et al., 2002;Eklund
et al., 2017;Swan et al., 2017), we focus on the ecological motivations
aiming to synthesize perspectives on this practice. In this context, we
refer to removal interchangeably with killing or lethal control. Removal
may also refer to translocation, however, translocating predators has
generally been demonstrated as ineective for reducing conicts
(Athreya et al., 2011;Linnell et al., 1997; but see Hazin and Afonso,
2014). We focus on examples of aquatic and terrestrial vertebrate
predators and ecosystems that include urban and rural areas. Moreover,
we restrict the scope of this review to native predators. Invasive species
are a global threat to biodiversity (Doherty et al., 2016) and the pro-
blems associated with biological invasions, although not necessarily
unique or distinct from the problems that create nuisance predator
conict, are suciently dierent from a conservation and management
perspective (see Doherty and Ritchie, 2016). Specically, we in-
corporated evidence from published and gray literature on a variety of
predatory taxa and from studies with varied predator removal moti-
vations.
2. Approach
Based on preliminary searches and our perceptions regarding the
quality of the evidence base (i.e., most studies had replication or in-
cluded appropriate controls) we opted to conduct a qualitative
literature review rather than a systematic review. Because the scope of
our paper was broad, we used general search terms of the title, key-
words, and abstract of papers in the Scopus search engine: predator
remov*,cull, and predator controlto identify relevant literature
(asterisks are wildcards in the Scopus search engine). Reference lists in
identied literature were consulted for additional resources and sear-
ches were repeated in Google Scholar. Articles were appraised at the
title and then abstract level for inclusion in a synthetic table. Referring
to our denition of success (see below), we sorted literature into suc-
cessful and failed applications of predator removal and by the objective
of the study in removing predators. All searches, ltering and analysis
were conducted by the same individual (RJL) following input from co-
authors. Bibliometric analyses were conducted in R (R Core Team,
2017). Figure plotted using the ggplot2 package (Wickham, 2009).
Included studies were stored in a table (Supplementary material) with
the predator species, motivation for removal, study duration, experi-
mental method, our evaluation of success or failure (or equivocality),
the removal method, a description of the study, and a citation (if not
included in main text).
2.1. Dening successful predator removal
Success is a dicult outcome to dene in predator removal because
the motivations may be variable and idiosyncratic. Although we dene
success in the context of ecological responses, we acknowledge that
successful predator removal must also consider the socioeconomic di-
mensions. For governments, the decision to implement predator re-
moval may be a balance between satisfying demands of constituents for
safety or prosperity against national or international agreements to
protect species and economic externalities associated with wildlife,
particularly ecological integrity. Nonetheless, we approach it from a
conservation perspective insofar as removal must not cause long-term
change or damage to the ecosystem while demonstrably beneting the
prey species, be they domestic animals (e.g. reduced rates of depreda-
tion), species at risk (e.g. increased local abundance or population
growth rate) or of economic concern (e.g. increased harvest yield), or
humans (e.g. reduced conict or fear from predators). From an ecolo-
gical and management perspective, we propose that successful predator
removal would reduce predator population to a size (or demographic state)
that would not negatively impact the persistence of that population or its
competitive status relative to mesopredators, but still provide demonstrable
benets to the prey species following predator removal (Table 2).
Correlative methods used to evaluate success broadly match popu-
lation trends of predator and prey species and ascribe outcomes (in
terms of predator or prey densities) to the removal. Correlative ap-
proaches may lack the power to identify mechanisms (at least in the
short term) driving population dynamics (Grubbs et al., 2016;
Marcström et al., 1988) but can still provide insight into processes
underlying prey population dynamics, particularly where experiments
are infeasible. This can be observed in open marine systems where
marine mammal culling programs may be tested by measuring corre-
lations with shery yields (Bax, 1998;Morissette et al., 2012). Short-
comings of retrospective analyses and correlational studies render it
dicult to identify evidence supporting any positive eects accrued
from predator removal, particularly in the context of dierent problems
that arise where predator removal is being considered as a management
strategy.
Experimental approaches to predator removal have more power to
detect main eects on livestock depredation or species recovery.
Controlled experiments using reference sites may be necessary but be-
fore-after-control-impact (BACI) studies can be useful to relate demo-
graphic trends to predator removal; however, BACI cannot account for
changes to the environment that occur over time (e.g. Hervieux et al.,
2014). Marcström et al. (1988) monitored grouse (Bonasa bonasia,La-
gopus lagopus,Tetrao tetri) and capercaillie (Tetrao urogallus) popula-
tions across eight years, the rst four with fox (Vulpes vulpes) and
R.J. Lennox et al. Biological Conservation 224 (2018) 277–289
278
marten (Martes martes) removal followed by four years without killing.
Although removal improved nesting success and increased adult density
over time, the authors still cautioned that factors other than predator
removal could have stimulated the increases. Simulations can be useful,
such as Martin et al. (2010), in which the number of removed raccoons
(Procyon lotor) necessary to achieve oystercatcher productivity (Hae-
matopus palliatus) was simulated, suggesting that the specic number
targeted should depend on the density of raccoons. Ernest et al. (2002)
similarly used simulation to calculate the number of mountain lion
removals necessary to reduce extinction risk of bighorn sheep (Ovis
canadensis). Such frameworks are one solution for testing the ecacy of
predator removal programs prior to implementation.
Attributing predator removal to livestock depredation, species re-
covery, or direct conict with humans is complicated when the mea-
surement of outcomes is restricted to relatively short intervals after
predator removal. The period immediately following the action of
predator removal is the period most likely to indicate a reduction in
predator density and conict and an increase in prey density, but this
may decrease at longer post-treatment intervals (e.g. Engeman et al.,
2006;Magella and Brousseau, 2001;Sagør et al., 1997;van Eeden et al.,
2018). Short-term increases to nesting success or juvenile survival fail
to consider density-dependence that manifests in the longer-term and
cannot demonstrate success of predator removal when there is no de-
monstrated benet to the population in subsequent years. Several stu-
dies observed increased nesting success of ducks following predator
removal (Garrettson and Rohwer, 2001;Pearse and Ratti, 2004;Pieron
and Rohwer, 2010), but a longer-term study conducted by Pieron et al.
(2013) found that benets to nesting did not carry over to the breeding
population and therefore the latter studies provided no evidence to
support predator removal (see meta-analysis by Côté and Sutherland,
1997). Although removal must generally be sustained (e.g. seasonally
or annually) for benets to be realized, success must be demonstrable
and persistent over time (Bergstrom et al., 2014;van Eeden et al.,
2018). Moreover, the benets must outweigh the costs (Chessnes et al.,
1968). A lack of longer term monitoring to determine whether predator
removal was eective limits the power to interpret whether it was a
successful intervention (van Eeden et al., 2018).
3. Synthesis
Our searches identied 141 empirical studies in which predator
removal was studied by haphazardly culling predators with traps, guns,
or poisons (N= 87), selectively removing predators (N= 10), con-
trolled removal (i.e. a pre-specied number; N= 21), observing a
natural decrease (N= 1), or in a simulation (N= 10). Studies were
conducted on data from 1 to 78 years (mean ± SD = 9 ± 12 years).
Most studies (N= 104) were conducted to evaluate whether predator
removal could improve prey populations, followed by studies de-
termined to evaluate impacts on domestic animals (N= 28) and direct
interactions with humans (N= 8).
We evaluated a large number of these studies (N= 37) to have
equivocal results, for example owing to a lack of statistical analysis,
poor control to detect main eects, or because the study did not include
sucient information with which to make a determination about suc-
cess (Fig. 1). Frequently, this arose because predator removal resulted
in increased breeding success without evidence that this contributed to
subsequent increases in the population. Although the scope of a study
may have intentionally been focused on briefer time scales or questions,
for our purposes and based on our denition of success we could not
describe such results as indicative of success. Most studies we evaluated
we determined to have failed (N= 67) owing to direct evidence that
predator removal had either not succeeded in limiting the predator
population or had no statistical demonstration of success in reducing
livestock losses, increasing prey densities, or mitigating direct conict
with humans (Fig. 1). Studies that were successful (N= 36) demon-
strated that predators were agents of additive mortality and that their
removal resulted in subsequent increases in prey.
An important caveat of this bibliometric approach is that studies
that were deemed to be successful or failed may have been so because
of some idiosyncrasy in the sampling protocol that could not be ex-
pected to be consistent among studies. When measurements were made
(e.g. when prey abundance was measured) and when interventions
were undertaken (e.g. what season the predator was removed in) could
inuence the outcome and the determination of success or failure.
Successes or failures could also emerge consistently for similar taxa that
were overrepresented in the literature, a limitation of the vote-counting
approach that we used to present percentages.
The numbers presented in this bibliometric analysis are intended
only to represent relevant information and a summary of published
literature and are not intended to provide evidence for or against pre-
dator removal without further context. Below, we discuss factors as-
sociated with success and failure in predator removal with the objective
of introducing more context, nuance, and interpretation of the litera-
ture covered in our bibliometric review along with other research fo-
cused on the relationship between predators and their prey in an eort
to address the question of predator removal from a conservation per-
spective.
4. Factors contributing to success and failure
4.1. Resulting in success
A prevailing hypothesis is that predator removal can be im-
plemented to achieve wildlife management objectives. We predicted
that predator removal would be successful in some contexts, speci-
cally, when implemented as a solution for short-term conservation
challenges in which the return or replacement of the predator popula-
tion in the long-term is not necessarily relevant to success (see Table 1).
Fig. 1. Bibliometric summary of studies reviewed in this paper based on the
three motivations for predator removal and the outcome. Studies are sum-
marized in Table S1. Success was evaluated based on the denition in Table 2.
Shading indicates our evaluation of the study as representing a success, failure,
or equivocal outcome. Equivocality was ascribed for studies with inconclusive
study design to determine success based on our denition.
R.J. Lennox et al. Biological Conservation 224 (2018) 277–289
279
Table 1
In our literature review we identied outcomes of experiments that yielded success or failure given three motivations for removing predators and based on our denition of success (see Table 2). Here we review 11 of the
common outcomes of predator removal, two of which we considered to be successful and nine of which we considered to result in failure. Rows are populated with examples of the predator removed and references to
literature demonstrating the given outcome for dierent motivations. References without species are those that removed multiple predators or predators were generalized (e.g. in a simulation). Refer to Table S1 for a
comprehensive review of the appraised literature.
Outcome Evaluation Protection of domestic animals Preservation of prey Mitigating risks of direct
conict
Removal of problem predatorsknown to instigate conict reduces future
conict
Success Canis latrans:Blejwas et al., 2002,Till and
Knowlton, 1983
Canis lupus:Blejwas et al., 2002
Lynx lynx:Stahl et al., 2001
Arctocephalus pusillus:Makhado et al., 2009
Larus michahellis:Sanz-Aguilar et al., 2009
Measurable reduction in conict or improvement in prey demographics
while maintaining predators in the ecosystem
Success Canis lupus:Bradley et al., 2015
Lynx lynx:Herndal et al., 2005
Pogonias cromis:George et al., 2008
Arctocephalus pusillus:Weller et al., 2016
Fletcher et al., 2010
Canis latrans:Smith et al., 1986;Reynolds et al., 2010
Canis lupus:Bjorge and Gunson, 1985,Boertje et al., 1996,
Gasaway et al., 1983,Hayes et al., 2003,Hervieux et al., 2014,
Keech et al., 2011,Potvin et al., 1992
Conspecics immigrate, replace predators, and conict persists Failure Canis lupus (Wielgus and Peebles, 2014
[refuted by Poudyal et al., 2016],
Fernández-Gil et al., 2016
Caracal caracal Bailey and Conradie,
2013;Conradie and Piesse, 2013)
Puma concolor (Peebles et al., 2013), Canis
dingo (Allen, 2014, 2015)
Greentree et al., 2000
Removal was equally or less eective than non-lethal alternatives Failure McManus et al., 2015,Palmer et al., 2005
Predator population becomes imperilled by introgression with congeneric
species or suers depensation due to superadditive mortality
Failure Canis lupus:Chapron and Treves, 2016
Puma concolor:Cooley et al., 2009
Ursus arctos:Swenson et al., 1997
Unknown mechanisms of compensatory mortality reveal short-term
success (e.g. improved nesting or hatching rates) but no evidence of
increases in abundance or density in subsequent years
Failure Amundson et al., 2013,Ellis-Felege et al., 2012,Littleeld and
Cornely, 1997
Conspecics increase reproductive rate, predator population increases, and
conict persists
Failure Canis latrans:Knowlton, 1972
Density independent conict yields no benets of removing predators on
the incidence of conict
Failure Canis lupus:Eggemann, 2015
Epinephelus itajara:Frias-Torres, 2013
Larus cachinnans:Bosch, 1996
Puma concolor:Peebles et al.,
2013,Teichman et al., 2016
Ursus americanus:Obbard
et al., 2014
Ursus arctos:Artelle et al.,
2016
Ursus thibetanus;Huygens
et al., 2004
Wetherbee et al., 1994
Disappearance of a predator releases a mesopredator from competition,
which maintains depredation
Failure Canis dingo:Wallach et al., 2010
Canis lupus:Rutledge et al., 2012
Corvus brachyrhynchos:Clark et al., 1995
Lynx lynx:Palomares et al., 1995;Bodey et al., 2011,Prugh and
Arthur, 2015
Loss of predators deregulates pathogens within populations, resulting in
increased disease-related mortality of prey
Failure Packer et al., 2003
R.J. Lennox et al. Biological Conservation 224 (2018) 277–289
280
4.1.1. Protection of domestic animals
When predators encroach on property or property development
intersects with predator ranges, the presence of predators can become
problematic if they threaten production animals (e.g. farms, ranch land,
aquaculture facilities). Apex predators such as sharks, wolves (Canis
lupus), dingoes (Canis dingo), lions (Panthera leo), tigers (Panthera tigris),
cougars (Puma concolor), jaguars (Panthera onca), and leopards
(Panthera pardus), for example, can aect the livelihoods of pastoralists,
but so too can mesopredators (Davis et al., 2015) such as coyotes (Canis
latrans), jackals (Canis spp.), crows (Corvus corax) and red foxes (Vulpes
vulpes).
Predator removal can acutely reduce conict when known predators
are dispatched, but removals must often be of sucient frequency or
magnitude that they actually aect the population size or structure of
the predator such that immigration does not compensate for removal
(Bjorge and Gunson, 1985;Herndal et al., 2005;Landa et al., 1999).
For example, Bradley et al. (2015) found that wolf removal was suc-
cessful at reducing livestock depredation if the entire pack was elimi-
nated. Wagner and Conover (1999) killed coyotes and found that pas-
tures with removal experienced slower rates of lamb depredation
following removal (but see Treves et al., 2016 Supplementary material).
In some cases, the success of predator removal is highly concentrated
and neighbouring areas will suer increased pressure; this may be a
success on a small spatial or temporal scale but in general it would not
achieve the desired outcomes (Santiago-Avila et al., 2018). Whether
predators are actively targeting livestock or are encountering them
opportunistically can aect success of the removal program. Odden
et al. (2013) suggested that increased sheep production and decreased
roe deer (Capreolus capreolus) density triggered a shift by lynx (Lynx
lynx) towards sheep depredation, a type III functional response (i.e.
preferentially targeting abundant species) that supports either lynx
removal or roe deer conservation/supplementation. Moreover, there
are dierent patterns of depredation for male and female animals.
Males are generally more frequent livestock predators than females
among solitary species, requiring selective removal to be successful
(Felids: Odden et al., 2002; polar bear Ursus maritimus:Stenhouse et al.,
1988).
Individuals within a population can dier in their propensity to
depredate livestock for many reasons. Selective removal of individuals
known to depredate livestock could be most eective in reducing future
problems than haphazard culling (e.g. Woodroe and Frank, 2005), the
challenge being to accurately identify the oending individuals (Stahl
et al., 2002;Swan et al., 2017). In our bibliometric review, we ascribed
success to 40% of selective removals (N= 10) and only 19% in which
predators were non-selectively removed by haphazard culling (N= 87)
or public hunts (N= 11). Blejwas et al. (2002) found that only selective
removal of coyotes following depredation events reduced subsequent
depredations and not pre-emptive or non-selective removal. Some
predators socially transmit knowledge that livestock are prey (e.g. to
ospring; Mondoland Hoogesteijn, 1986) and systematic removal of
known predators could instill wariness in predators by hunting for
fear(Cromsigt et al., 2013) or social transmission of risk (e.g. invasive
lionsh; Côté et al., 2014). In spite of a long history of predator per-
secution, we did not identify examples that support this, suggesting
more research is needed to address this question.
4.1.2. Preservation of prey species
When prey species or populations are declining in abundance, there
may be added pressure for managers to take remedial action (Lessard
et al., 2005;Reynolds and Tapper, 1996). This is particularly true of
economically important species that are hunted or shed or those that
are at risk of extinction. Most examples of success were from studies
aiming to preserve prey, although not on a relative basis as only 26%
were deemed to be successful.
Many of the most important terrestrial game species are herbivores
whose populations may be moderated by depredation. Removing pre-
dators can release prey species from predation and, so long as mortality
from those predators is additive and not compensatory, the prey species
could increase in following years and re-establish a higher abundance.
The most successful examples of preserving prey by removing predators
emerge from studies of predator removal in northern ecosystems with
fewer trophic linkages and more direct inuences of predators. Jarnemo
and Liberg (2005) correlated roe deer (Capreolus capreolus) population
growth to a disease outbreak that reduced red fox density and released
the deer from predation. Moose and caribou (Rangifer tarandus caribou)
survival has also improved following removal of wolves as demon-
strated by several studies observing increases in prey abundance
(Boertje et al., 1996;Hayes et al., 2003;Gasaway et al., 1983;Keech
et al., 2011).
Prey species suering from depensation may specically benet
from predator release (e.g. Liermann and Hilborn, 2001;Stephens and
Sutherland, 1999). For example, cormorant (Phalacrocorax auritus)
culling preceded yellow perch (Perca avescens) abundance increases in
Lake Huron, suggesting that removing the predators assisted in rebound
of its prey. Although human intervention is generally the mechanism
for small population size of prey species, the added pressure of preda-
tion can still be linked to depensation (Gascoigne and Lipcius, 2004;
Kramer and Drake, 2010;Liermann and Hilborn, 2001). Juveniles of
Table 2
Proposed maxims of predator removal summarizing important ndings about successful applications of predator removal for management.
1 Predator removal is an interdisciplinary topic necessitating consideration of ecological, economic, sociological, political, and other dimensions.
2 Failure to consider ecological issues when initiating predator removal can harm the ecosystem.
3 From an ecological perspective, successful predator removal would reduce predator population to a size (or demographic state) that would not negatively impact the
persistence of that population or its competitive status relative to mesopredators, but still provide demonstrable benets to the prey species following predator removal.
4 The functional response of the predator is essential to consider because it inuences the rate of depredation of prey species.
5 Targeted removal of problem individuals may be an eective application of predator removal (Swan et al., 2017), as opposed to indiscriminate or retaliatory killing, but it is
logistically dicult to condently identify culprit predators (Stahl et al., 2002).
6 Killing predators seems to generally result in an increase of local depredation of livestock resulting from demographic compensation via increased birth rates of predators
(Knowlton, 1972), immigration (Sagør et al., 1997), or release of mesopredators/invasive species (Wallach et al., 2015).
7 Among humans, there are broad demographic dierences in attitudes towards predators, with support for predator removal generally from older and more rural individuals
(Andersone and Ozolinš, 2004;Lüchtrath and Schraml, 2015).
8 Justiable objectives for removal, especially the number to be removed, are necessary in planning predator removal rather than haphazard killing. Understanding the
demographics and population dynamics of the predator is therefore essential. Adaptive management approaches can be applied to attempt sustainable removal that does not
imperil the predator population (e.g. Martin et al., 2010).
9 Whether predator removal is actually eective at reducing conicts or satisfying human attitudes towards predators is essential to its overall success as a management
practice but the evidence for it is either equivocal or decient.
10 There are increasing examples of non-lethal alternatives to predator removal, although many require scientic validation (Ogada et al., 2003;Okemwa, 2015).
11 Evidence that conicts are mechanistically linked to depredation is important before beginning predator removal, along with evidence that predator removal will resolve the
conict, which can be tested via simulation (e.g. Morissette et al., 2012).
12 Coexistence with predators is possible and the most sensible way forward, but interdisciplinary research is necessary to continue to rene understanding of the human
dimensions of predator removal (Carter and Linnell, 2016; Johnson and Wallach, In Press; Woodroe et al., 2005).
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281
species at risk such as marine turtles (Gascoigne and Lipcius, 2004) and
salmon (Oncorhynchus sp.; Wood, 1987) that rely on safety in numbers
to saturate predators during migration can undergo rapid declines from
depredation (Hervieux et al., 2014;Liermann and Hilborn, 2001) and
predator removal may facilitate increased juvenile survival and re-
cruitment to such populations (Engeman et al., 2006;Pichegru, 2013;
Hervieux et al., 2014;Makhado et al., 2009). However, it is not uni-
versally eective and alternate actions may have higher success than
predator removal (Ratnaswamy et al., 1997). Improving juvenile sur-
vival may be a relevant management outcome for some species, but it
does not necessarily improve population growth rate or abundance
when there is density dependent or otherwise compensatory mortality
and therefore studies that only observed increased egg hatching or ju-
venile densities were evaluated as equivocal without longer-term in-
vestigation (see Pieron et al., 2013). Considering generalist predators
that consume fewer prey at smaller prey densities (type III functional
response characterized by a logistic-type relationship between prey
density and prey consumption, in which depredation is low until prey
achieve a relatively high density and predators begin targeting that
species), predator removal will not likely have a considerable eect
because they would more likely switch to alternative prey instead of
expending energy pursuing the rarer prey species (Murdoch, 1969; e.g.
Middlemas et al., 2006). Specialization may also occur within species,
in which cases the selective removal of specialized individuals can be an
eective application of predator removal to release prey from depre-
dation pressure (Sanz-Aguilar et al., 2009). Although predator removal
may be eective when problems arise because of specialization, re-
moval is not necessarily the most eective management option; alter-
natives such as exclosures may be more eective for reducing depre-
dation and recovery of species at risk and should be tested (Rimmer and
Deblinger, 1990;Reynolds and Tapper, 1996;Smith et al., 2011;
Stringham and Robinson, 2015). However, the logistics of fencing o
entire areas (e.g. breeding sites) to exclude predators are questionable
and the long-term consequences can also be destructive (Hayward and
Kerley, 2009).
4.1.3. Mitigating risks of direct human-wildlife conict
Direct human-wildlife conict has stimulated eorts to kill pre-
dators after attacks or a pre-emptive strike against future conict
(Gallagher, 2016). Few examples in the literature were identied that
studied predator removal for relieving direct conict between humans
and predators (N=8), with no examples of success. Fukuda et al.
(2014) was determined to provide equivocal evidence for predator re-
moval because it lacked proper control. However, they provide a salient
example for future research in which predators that attack humans may
learn to target them, in which case removing individual animals that
have attacked humans could reduce future conict (e.g. saltwater cro-
codiles Crocodylus porosus). There is a threat of animals habituating to
humans, which may lead to more direct conict in subsequent years
and require removal of problem individuals (Linnell and Alleau, 2016).
Predators infected with rabies or other diseases that increase conict
may also require lethal control (Linnell and Alleau, 2016). However,
there is limited evidence that targeted killing of animals that have a
history of interacting with humans reduces future conicts, probably
because such events are rare to observe, precluding experimentation or
analysis (Swan et al., 2017).
4.2. Resulting in failure
The prevailing alternate hypothesis that we tested in conducting this
literature review was that predator removal is not an eective tool for
conservation or management of ecosystems. We reviewed the literature
to identify research that described experiences or experiments with
predator removal that have yielded perverse impacts on the ecosystem,
or failure to achieve the desired objectives, which were dierent de-
pending on the motivation for predator removal. Thus, we have divided
this section into the familiar subheadings based on those motivations
(see Table 1).
4.2.1. Protection of domestic animals
Protecting domestic animals by removing predators should reduce
the rate of depredation on those domestic animals (Eklund et al., 2017).
However, predator removal eorts fail when depredation rates do not
respond to culling because the predator population compensates or is
replaced by another predator. When there are multiple predatory spe-
cies, Kissui (2008) found that pastoralists had diculty identifying
which species was responsible for livestock depredation and that higher
visibility of lions during daytime caused them to be incorrectly accused.
Targeted killing of leopards and caracals (Caracal caracal;Bailey and
Conradie, 2013;Conradie and Piesse, 2013), cougars (Peebles et al.,
2013), dingoes (Allen, 2014, 2015), and wolves (Wielgus and Peebles,
2014 [refuted by Poudyal et al., 2016]; Fernández-Gil et al., 2016)
designed to reduce livestock depredation actually increased depreda-
tion in subsequent years (but see Bradley et al., 2015). Removal of
adults may have triggered compensation via rapid replacement by im-
migrants in open systems (e.g. Baker and Harris, 2006;Bjorge and
Gunson, 1985;Lieury et al., 2015;Sagør et al., 1997), enhanced local
juvenile survival (Kemp, 1976;Peebles et al., 2013), or increased re-
productive rates (Knowlton, 1972;Pitt et al., 2001). These demographic
responses maintain or increase the number of local predators, stabilize
the probability of further conict, and represent distinct failures (Boyce
et al., 1999;Sacks et al., 1999). Demographic responses of predators to
culling may therefore render predator removal largely ineective unless
removal is so extensive that it alters predator demography on a broad
scale, perhaps to impose an alternative stable state (Greentree et al.,
2000;Herndal et al., 2005). Removal can imperil the predators by
accelerating their population declines if mortality is additive (or even
super-additive; Creel and Rotella, 2010), for example when it instigates
increased poaching (Chapron and Treves, 2016) or infanticidal beha-
viour (e.g. cougar: Cooley et al., 2009; grizzly bear Ursus arctos:
Swenson et al., 1997; lion: Packer et al., 2009). Removal can also isolate
remaining individuals, resulting in increased dependence on livestock
in the absence of a group that would otherwise target wild prey (Bjorge
and Gunson, 1985) or result in hybridization and degradation of genetic
integrity (Rutledge et al., 2012). Short of predator eradication, removal
generally does not protect domestic animals in the long-term.
Extensive removal of predators or eradication of top predators can
also release subordinate species from competition (i.e. mesopredator
release; Crooks and Soulé, 1999). Mesopredators can be of equal or
greater possible or perceived threat to livestock and may be invasive
species that become dicult to remove (Gross, 2008;Wallach et al.,
2010), with cascading changes at other trophic levels (Hebblewhite
et al., 2005;McPeek, 1998;McClanahan and Muthiga, 1988;Ritchie
and Johnson, 2009). Mesopredator release can undermine predator
removal and sustain depredation of domestic animals. In some cases,
multiple mesopredators replace one extirpated top predator, compli-
cating further control eorts.
4.2.2. Preservation of prey species
Removing predators theoretically reduces the extent to which prey
species are removed from a population (e.g. Weller et al., 2016) given
an assumption that predation contributes to additive and not compen-
satory mortality of the prey species, and therefore removal of the pre-
dators will directly contribute to an increase in prey (e.g. Flaaten,
1988). Evidently, this presupposes negligible eects of bottom-up
processes (see Grange and Duncan, 2006;Elmhagen and Rushton,
2007), that the prey would not be limited by density-dependent re-
source limitation, and that prey is limited by a specic predator (Frias-
Torres, 2013;Parker, 1984). However, most acknowledge both forms of
regulation are simultaneously important in ecosystems and the relative
importance of top down vs. bottom up control can shift in relation to
productivity (Oksanen et al., 1981). Despite repeated eorts to connect
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282
predation to declines of economically important shes, evidence for
such a relationship is tenuous (Anon., 1986;Trzcinski et al., 2006).
Eggemann (2015) also suggested that wolf depredation of moose (Alces
alces) is density independent, meaning that reduced pack size could not
succeed to increase moose escapement availability to hunters (also
Kauhala et al., 2000). Similarly, Serrouya et al. (2017) showed that
removing moose was eective for recovery of caribou in British Co-
lumbia because of apparent competition between wolves and caribou;
although moose removal was not compared to wolf removal, this shows
how predators can be incorrectly persecuted if alternative solutions to
maintaining prey densities are not explored. Using Ecopath with Ecosim
for mass balanced simulation based on foraging arena theory,
Morissette et al. (2012) tested whether marine mammal removal would
increase shery yield and suggested that it would more likely lead to
reductions than increases because of limited actual competition be-
tween sheries and whales (see also Gerber et al., 2009). Yodzis (1998)
also predicted a decline of sheries yields during cape fur seal (Arcto-
cephalus pusillus) culling programs that were proposed to increase
yields. Lessard et al. (2005) simulated seal removal and predicted an
increase in Pacic salmon smolt survival but suggested that it might
increase predatory sh populations, which would replace the seals in
depredating the smolts; generalist predators such as seals often regulate
multiple populations within a community and removing these predators
can lead to disequilibrium in the ecosystem.
The trophic position of the predator contributes to its functional
response to changes in prey, an important factor when considering re-
moval (Bowen and Lidgard, 2013). Removing a mesopredator will most
likely yield compensatory depredation by other mesopredators (Clark
et al., 1995). Elimination of a top predator could release herbivores
from control, resulting in extensive damage to landscapes and changes
to habitat suitability that cause shifts in the community (Bertness et al.,
2014;Ripple and Beschta, 2006). Hunters can compensate for predation
mortality but will generally remove highly t phenotypes (Allendorf
and Hard, 2009) whereas predators target weak or diseased prey
(Genovart et al., 2010;Krumm et al., 2010;Quinn and Cresswell,
2004); loss of predators can then proliferate disease within prey po-
pulations (Packer et al., 2003) and can spill over to infect domestic
animals (Cross et al., 2007). Even when removal is successful in the
short-term, compensatory processes may regulate predator populations
such that removal is ineective in the long-term (e.g. Donehower et al.,
2007). Long-term studies or simulation models are necessary to detect
eects of predator removal on prey (see Costa et al., 2017).
4.2.3. Mitigating risks of direct human-wildlife conict
Predatory animals are often perceived as threats to human safety in
spite of infrequent interactions and small odds of actual conict relative
to many other habitual activities such as driving cars (Slovic, 1987).
According to the social amplication of risk framework, empirically
rare events contribute disproportionally to concern among the public
and lead to economically, socially, or ecologically illogical responses
(e.g. fear of ying; Kasperson et al., 1988). This framework could be
applicable to human-wildlife conict if the perceived risk of direct at-
tack on humans is higher than the actual risk. Sharks are often victi-
mized by social amplication of risk, which has resulted in publicized
and prominent state-sponsored programs that aim to cull sharks near
beaches (e.g. Wetherbee et al., 1994;Gallagher, 2016). The major
failure of shark culling programs, however, has been exemplied by a
lack of evidence that it actually decreases attacks (Wetherbee et al.,
1994), arising in part because many large predatory shark species are
migratory and therefore there is a low probability that locally-based
actions will be eective once they cease and sharks from surrounding
and more distant areas move into these managed areas continually
(Holland et al., 1999). Gray and Gray (2017) found limited support
among patrons for lethal control of sharks. Correspondingly, we found
no research asking whether culling programs actually aected the
perception of risk by patrons; safety is dicult to guarantee, and a
perception of safety may encourage reckless behaviour (e.g. ignoring
key risk factors associated with shark attack) that increases the like-
lihood of negative encounters with sharks (e.g. swimming oshore).
The legacies of such eorts could instead just be negative public per-
ception of the animals, increased fear, and impoverished conservation
status of the targeted species. Perversely, Teichman et al. (2016) found
that human-cougar conict was higher in areas of cougar trophy
hunting yet Gilbert et al. (2017) suggested that economic value of
cougar populations exceeds the costs because they control deer popu-
lations that cause costly collisions with vehicles. Skonhoft (2006) dis-
cussed this in terms of Scandinavian wolves, suggesting there is an
equilibrium possible between the economic losses of lucrative moose
depredated by wolves (Alces alces) and gains in terms of reduced ve-
hicle-moose collisions and damage to foliage caused by moose browsing
in the winter, emphasizing the value of maintaining predators and the
costs of predator removal.
There was no direct evidence that removing predators changes
outcomes for human-wildlife conict. Obbard et al. (2014) found no
inuence of black bear removal on future conict with humans and
Artelle et al. (2016) perversely observed that removal of grizzly bears
was followed by no dierence in future conicts rather than a reduc-
tion. Although data in Artelle et al. (2016) do not suggest causality, it
does indicate that removal was not successful at mitigating conicts.
Treves et al. (2010) further suggested that the number of black bears
(Ursus americanus) killed by hunters did not reduce, and was actually
correlated with increases in, reports of conict in subsequent years
(although it is relevant to note that complaints were not necessarily
related to predatory activity of bears, but also property damage). Ap-
parently, overlap between humans and black bears increases during
poor years when urban resources aggregate the animals, meaning that
removal of predators in these years has disproportionately high impact
on the population (Baruch-Mordo et al., 2014).
5. Discussion
We evaluated the two opposing hypotheses considering the (a)
success or (b) failure of predator removal as in the conservation and
management of ecosystems. We selected a qualitative approach to
testing these hypotheses by searching for published evidence of success
and failure. We identied examples of success but ultimately found
much more consistent evidence for failure (Table 1). Evidence that
removing predators achieved conservation-sound outcomes was con-
text-specic (see Section 4.1). Removing predators presumes that eco-
system-level responses are predictable (Ramsey and Norbury, 2009),
yet theoretical and empirical evidence often suggests the contrary (Bax,
1998;Ruscoe et al., 2011;Yodzis, 2000). An exception may exist in
ecosystems where predators and prey are very closely linked (e.g.
northern terrestrial ecosystems) or the prey are suering from de-
pensatory population declines associated with depredation by predators
with a type II functional response. Although predators can inuence
ecosystems (Holt et al., 2008;Nelson et al., 2004), other factors can
make the ultimate response of an ecosystem unpredictable, even with
rigorous scientic evaluation. The full range of complexity at the eco-
system scale is poorly understood, especially as it pertains to processes
such as parasites in ecosystem dynamics (Roche et al., 2012). This was
observed consistently in study designs, which were often either short in
duration or lacking in control, rendering it dicult to avoid type I
error.
Many governments are responsible for establishing and maintaining
protected areas, zoning property (for agriculture or developing buers),
and formulating wildlife management regulations (Rands et al., 2010;
Treves et al., 2017). Strong policy based on available evidence can
contribute to eective conservation of predators in many ways, in-
cluding the establishment of suitable regulations and protected areas
(Linnell et al., 2001). However, predators are important components of
the landscape not just in designated areas but also in areas of human
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283
use (Dorresteijn et al., 2015;Gilbert et al., 2017;Kuijper et al., 2016;
López-Bao et al., 2017). When conicts arise, retaliatory killing by local
stakeholders may be understandable but can undermine conservation
eorts for both predators and the broader ecosystem. It is important to
accurately document the movements and actions of depredating species
and maintain records of conicts to determine the appropriate course of
action and to advance the science of predator conict to develop re-
solutions. In its present form, our ndings suggest that success in pre-
dator removal is highly contextual and should not be assumed by
management without rigorous testing.
5.1. Alternative actions for managing human-predator conict
Human-predator conict challenges managers because depredation
can be damaging to some livelihoods and traumatic for individuals (e.g.
pastoralists, aquaculturists, shers; Butler, 2000;Graham et al., 2005;
Mishra, 1997;Patterson et al., 2004). Attitudes of retaliation (Holmern
et al., 2007;Kissui, 2008;Thorn et al., 2012) are understandable, even
though conicts tend to be isolated incidents (Cozza et al., 1996;
Chavez and Gese, 2005). Economic losses to depredation are, however,
generally less than those attributable to other sources of mortality such
as disease (Breck and Meier, 2004;Frank, 1998;Mazzolli et al., 2002;
Mizutani, 1999;Kissui, 2008;Rasmussen, 1999). Livestock often com-
prises smaller components of the diet of predators than assumed by
some pastoralists (Allen, 2015;Boast et al., 2016;Davis et al., 2015).
Kaltenborn and Brainerd (2016) suggested that restoration of predators
to large population sizes and then opening recreational hunting seasons
could be a more eective alternative to balance socioeconomic objec-
tives. However, sustainable harvest limits are incalculable without de-
mographic data (Packer et al., 2009;Treves, 2009). Moreover, human
harvests tend not to be non-selective for problem predators (Sunde
et al., 1998) or can undermine conservation (Creel and Rotella, 2010).
Where livestock comprise a more important food source for predators,
conservation or restoration of native prey sources could mitigate losses
(Meriggi and Lovari, 1996;Odden et al., 2013). Husbandry practices
can alternatively reduce conict with wildlife without ecological issues
or social controversy (e.g. Jackson and Wangchuk, 2004;Johnson and
Wallach, 2016). Fencing is already used by pastoralists (Hayward and
Kerley, 2009) with variable success (Eklund et al., 2017). Birthing of
calves during a short period may facilitate predator satiation, reducing
depredation on farms (Palmeira et al., 2008). Calves can also be kept
centralized and away from edges (Palmeira et al., 2008). Deterrent
devices (e.g. adry) also hold promise for reducing depredation (Ogada
et al., 2003;Okemwa, 2015), evidenced by a 9397% reduction in
depredation of aquaculture sites using a non-lethal deterrent by seals
(Götz and Janik, 2016). In scientic study, predator removal should be
tested against realistic alternatives because in some cases deterrents are
just as eective (Harper et al., 2008;Ratnaswamy et al., 1997) and may
be more economical (McManus et al., 2015). When conicts do arise,
the costs can be oset with subsidies (Bulte and Rondeau, 2005;
Dickman et al., 2011;Mishra et al., 2003). Challengingly, some gov-
ernments do not have the resources to support conservation initiatives
or compensate farmers for losses and in others, the systems are not
developed to properly address the problems (Chen et al., 2015). In
developing countries, this leads to continued persecution of predators,
maybe out of bare necessity to maintain herds in some cases (Dar et al.,
2009), but improved education and validation of eective alternatives
hold promise for resolving conict.
When prey species decline, hunters may support and lobby for
predator removal (Franzmann, 1993) and conservation movements
may support protection of species at risk by controlling their predators.
Species persistence is considered a priority of conservation science and
is often nested within the laws of regional and national management
plans. Predator removal may appear to be a logical solution for main-
taining adult populations and increasing juvenile survival during spe-
cies declines; however, our results clearly show that studies are needed
to demonstrate this (Oro and Martínez-Abraín, 2007). Deterrents or
barriers can reduce predator access to endangered species and may be
more eective and economical in many scenarios (Shivik, 2006;Smith
et al., 2011;Yurk and Trites, 2000). Emerging solutions that use sensory
modalities to mitigate predation can also yield promising results, for
example, Neves et al. (2006) tested taste aversion methods of reducing
nest predation of endangered roseate tern (Sterna dougallii). Guardian
animals have also shown promise for livestock (Meadows and
Knowlton, 2000;Smith et al., 2000;van Bommel and Johnson, 2012)
and species at risk (King et al., 2015).
The willingness to pay for hunting/shing for large predators may
be high, species of recreational importance tend to have higher ac-
ceptability and be better conserved, and illegal hunting can undermine
ecological, economic, and sociological objectives of wildlife manage-
ment. Therefore, managed hunts or sheries targeting predators have
been proposed as a solution to reduce poaching, maintain stable pre-
dator populations, fund conservation initiatives, and increase accept-
ability of some predators (Creel et al., 2016;Gallagher et al., 2016;
Kaltenborn and Brainerd, 2016;Lindsey et al., 2007). Sportspeople and
guides can keep watch for illegal activity, particularly in remote areas
and activity can also reduce predator activity (Harper et al., 2008). The
result of such managed hunts would, however, probably result in
random, rather than targeted, removal that would not likely have any
eect on the rate of predator conict (Packer et al., 2009;Treves, 2009)
unless it can be condently applied to maintain a smaller predator
population without resulting in depensation.
5.2. Social and economic costs of failure
Killing by people is the largest threat to the conservation of many
predators (Kissui, 2008;Ripple et al., 2016;Woodroe and Ginsberg,
1998). In spite of the problems with implementing predator removal for
management, human-wildlife conict persists (Treves and Karanth,
2003) and predator persecution and removal will likely continue, par-
ticularly when there is direct conict between a human and a predator.
Research on human attitudes towards predators is plentiful, relating
demographics to perception of predators (e.g. nationality, gender, age;
Andersone and Ozolinš, 2004;Lüchtrath and Schraml, 2015). Attitudes
towards predators depend greatly on exposure and experience as well
as cultural values towards wildlife, for example, rural people tended to
favour control more than urban dwellers (Andersone and Ozolinš,
2004).
It should be possible to quantify the carrying capacities and de-
mographics of predators to maintain a smaller population of predators
to limit conicts, although in general we found that this is likely only
possible via continued intervention (e.g. Landa et al., 1999). Careful
calculation and monitoring would be essential for this because of un-
anticipated changes in demography arising from human-induced mor-
tality and the potential for additive or super-additive (rather than
compensatory) mortality following intervention that imperils the pre-
dators (Creel and Rotella, 2010). Indeed, Bradley et al. (2015) found
that partial wolf pack removal was eective for mitigating livestock
depredation while maintaining wolves in the northern Rocky Moun-
tains; however, more rigorous methods can be implemented to calculate
removal targets. The justication for predator removal targets and how
they are dened is often weak and idiosyncratic. Strategies can include
controlled removal with a stated goal (e.g. 50% reduction), haphazard
culling (e.g. opportunistic removal), or selective removal (e.g. removing
problem individuals), with variation in the expected outcomes. In
Western Australia, the social licence and evidence for culling has re-
cently been questioned (Legge et al., 2017). Simulation to determine
the optimal number of predators to be removed to achieve conservation
objectives can assist with validating predator removal prior to im-
plementation (Ernest et al., 2002;Martin et al., 2010).
Modern management of predator conicts must include stake-
holders (Breitenmoser, 1998) and consider predators in an ecosystem
R.J. Lennox et al. Biological Conservation 224 (2018) 277–289
284
context rather than as individual species in conict with humans. There
is limited evidence that retaliation against a species or pre-emptive
culling decreases conicts or generates a sense of security in landscapes
where predators exist. This points to a failure to consider the broader-
scale processes that regulate predator populations and ecosystems
(Berlow, 1999) as well as a lack of understanding of the human di-
mension of attitudes towards wildlife that promote negative percep-
tions. Moreover, it ignores the positive impacts of predators and intact
ecosystems by regulating herbivores, mesopredators, and disease. Pre-
dator removal can also disconnect public perceptions of nature by ac-
climating people to manipulated and arguably depauperate ecosystems
(Wallach et al., 2015), an outcome that can shift baselines and reduce
support for conservation initiatives (Chapron and Treves, 2016). This
problem is exemplied in coyote control, where Berger (2006) calcu-
lated a long-term expenditure of over a billion dollars for coyote re-
moval programs in the United States that were intended to improve the
sheep farming industry and wool production had no measurable ben-
ets across 78 years of data.
5.3. Study context and future research directions
Evaluating the contribution of predators and the success of predator
removal to conservation eorts has been attempted elsewhere in the
ecological literature. Meta-analysis is well suited to this problem be-
cause it reduces type II error (compared to vote-counting approaches)
and weights studies by their sample size; however, it can be overly
inuenced by few studies with large sample sizes. Whereas meta-ana-
lysis is suited to analyzing studies with similar intervention, endpoint,
and subjects (Eysenck, 1994; see Smith et al., 2010, 2011 for eective
examples of this), it is constraining for broad topics such as predator
removal (Haddaway et al., 2015), which is conducted for many dif-
ferent reasons on a variety of taxa, making it dicult to generate re-
liable numerical assessments that could be considered relevant across
socioecological contexts. Instead, we opted for a qualitative review with
bibliometric analyses to reveal successes and failures with appropriate
consideration to context. There are lessons to be gained from viewing
many dierent, often disparate predator removal attempts through a
common lens and identifying how varying inputs (e.g. motivations,
taxa) contribute to outcomes to address future problems that arise.
Provided that future studies on this topic address some of the de-
ciencies in experimental design noted here, there is potential to im-
prove the quality of the evidence base such that meta-analysis within
the context of a systematic review should be possible and will help to
ensure evidence-based environmental management in the future
(Sutherland et al., 2004).
6. Conclusion
Human-wildlife conict will persist with direct impacts on ecosys-
tems globally. Desire to manage predator populations will therefore
continue in spite of growing conservation concern for many predators
(and in some cases, recovery of their populations; Curtis et al., 2014).
Our review suggests that the success of predator removal depends
on the motivation and design of the eort because of the variability in
success identied across studies. More research is needed to determine
whether predator removal reduces direct conict with humans or
human fear. However, there was some circumstantial support that re-
moving predators facilitated prey recovery and some evidence that it
assisted with protection of domestic animals. Nonetheless, a main ta-
keaway from this review is the inconsistencies and idiosyncrasies of
outcomes. Predator control should be pre-empted by research to justify
the action and set removal targets, with anticipated outcomes stated
and follow-ups planned to evaluate the action. Alternative actions may
be equally or more eective and should be studied in parallel when
possible. Some studies are not designed to detect main eects of pre-
dator removal and are instead retrospective and correlative because
predator removal may not always be motivated by conservation (Treves
et al., 2016). How the decision to remove predators is arrived at typi-
cally remains unclear. Although much can be learned from experi-
mental approaches (e.g. Lieury et al., 2015), they can be costly, ethi-
cally controversial, and require the removal of predators for didactic
purposes. Simulation approaches or predictive modelling have the po-
tential to become increasingly useful tools prior to implementing re-
moval in order to project whether the predator removal is likely to
achieve the desired outcomes (e.g. Martin et al., 2010;Morissette et al.,
2012;Yodzis, 1998). However, such eorts need to consider and ac-
count for many potentially confounding external variables such as food
availability and competition in order to conclude whether predator
removal is likely to be successful as well as the potential for immigra-
tion compared to compensation (Creel et al., 2015).
6.1. Promoting coexistence
Coexistence with predators is the desired way forward for many
(Bergstrom, 2017;Carter and Linnell, 2016;Johnson and Wallach,
2016;Woodroe et al., 2005), and there are increasing examples that
predators can persist even among dense human populations (Chapron
et al., 2014;Elliot et al., 2016;Gilbert et al., 2017). Indeed, predators
play important ecological roles in rural areas and even in urban regions
(Gilbert et al., 2017). We propose that paradigms positing predator
persecution as a positive management intervention require reassess-
ment (see also Graham et al., 2005). However, interdisciplinary ap-
proaches that consider socio-ecological perspectives (e.g.; Bisi et al.,
2007; Elliot et al., In Press; Hill, 2015;Kaltenborn et al., 2006) will be
integral for determining how human perceptions, values, and attitudes
towards predators are shaped, and how they can be accounted for to
meet the needs of humans and predators and minimise conict in an
increasingly crowded landscape.
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.biocon.2018.05.003.
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... Predator removal may be championed as a mode of releasing more prey for humans to harvest, despite the reality that the approach rarely works (Lennox et al., 2018). Increasing hunting effort or modifying hunting to reduce vehicular collisions or disease spreading from animals to humans is unlikely to compensate for predators that are lost, at least not efficiently. ...
... We have endeavoured to provide a perspective of the myriad ways in which the behaviour and influence of humans differs from other apex predators (Box 1). Despite a large and growing literature on vulnerability to harvest (Lennox et al., 2017), landscape effects (Ciuti et al., 2012), harvest-induced evolution (Allendorf & Hard, 2009), disease ecology (Ostfeld & Holt, 2004), predator removal (Lennox et al., 2018) and ecosystem services of predators , no research has yet provided this comprehensive comparison between predators and humans (Table 1; Figure 1). ...
... Conflict arises, however, from belief that the resources required by predators to carry out these effects are in excess of the value they provide; yet, the bulk of empirical evidence is mounting in opposition of that perspective. Very limited evidence, for example, supports the idea that removing predators will likely improve prey yields in the long term (Lennox et al., 2018). Indeed, simulations have shown that removal of marine mammals would most likely decrease fishing yields (Gerber et al., 2009). ...
Article
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In nearly every ecosystem, human predators (hunters and fishers) exploit animals at extraordinarily high rates, as well as target different age classes and phenotypes, compared to other apex predators. Demographically decoupled from prey populations and technologically advanced, humans now impose widespread and significant ecological and evolutionary change. In this paper, we investigate whether there is evidence that humans provide complementary services and whether ecosystem services of predators can be maintained by humans where wild predators are lost. Our objective is to contribute to two key ecological themes: the compatibility of human harvesting within ecosystems and management approaches in consideration of the intentional or unintentional loss of predators. We reviewed evidence for five key effects of predators: natural selection of prey, disease dynamics, landscape effects, carbon cycling and human well‐being. Without carefully designed management strategies, such changes can impose harm to ecosystems and their constituents, including humankind. Ultimately, we applied this information to consider management paradigms in which humans could better support the role of, and potentially behave more like, apex predators and discuss the challenges to such coexistence. Read the free Plain Language Summary for this article on the Journal blog. Read the free Plain Language Summary for this article on the Journal blog.
... Where prey depletion occurs, large carnivores might forage closer to habitations or predate on domestic animals more often, which can lead to even more constraints in the use of space (i.e., abandonment of grazing or recreational area) (Thirgood et al., 2005;Moss et al., 2016). Such proximity is susceptible to induce defensive behavior (e.g., for protecting cubs) (Coltrane and Sinnott, 2015;Herrero et al., 2005;Kojola and Heikkinen, 2012;Pătrașcu et al., 2015;Quenette et al., 2011;Rauer, 1999), and the resulting situations can lead to the injury or death of the carnivores involved (Khorozyan and Waltert, 2020;Lennox et al., 2018;Treves et al., 2009). Their conservation is therefore all the more complex, although it remains important both at the species level and in terms of their structuring role in ecosystems (Ripple et al., 2014). ...
... Otherwise, inefficient intervention might become a financial burden or create social mistrust, ultimately hindering carnivore conservation (Dickman, 2010). Previous studies and reviews have identified great heterogeneity in the available information and scientific standards used for quantitative comparison (Khorozyan and Waltert, 2019;Lennox et al., 2018;Treves et al., 2019). To overcome this hindrance to solid proof-based evaluations, the authors of said reviews usually only considered case studies reporting experiments with high scientific standards (preferably "gold" or BACI). ...
... This approach enables the comparison of studies with different standards, thus extending the usable panel to be considered. For the purpose of consistency and consensus, and in line with other studies Waltert, 2019, 2020;Lennox et al., 2018;Moreira-Arce et al., 2018), we focused on three of the most used and documented interventions (i.e., lethal interventions, nonlethal interventions, and translocations), related to human-large carnivore conflicts at the global scale. ...
Article
Human-wildlife conflicts are associated with a threat to large carnivores, as well as with economic and social costs, thus challenging conservation management around the world. In this study, we explored the effectiveness of common management interventions used worldwide for the purpose of conflict reduction using an evidence-based framework combining expert assessment of intervention effectiveness, impact and uncertainty of assessment. We first conducted a literature review of human-large carnivore conflicts across the world. Based on this review, we identified three main types of management interventions (non-lethal, translocations, and lethal management) and we assessed their effectiveness. Our review indicates that, although the characteristics of conflicts with large carnivores are heavily influenced by the local context and the species, the main issues are depredation on livestock, space-sharing, and attacks on humans. Non-lethal interventions are more likely to reduce conflict, whereas translocations and lethal interventions are mostly ineffective and/or harmful to carnivore populations, without fostering successful long-term coexistence. The literature on conflict management is often imprecise and lacks consistency between studies or situations, which generally makes comparisons difficult. Our protocol allows for the reliable comparison of experiments characterized by heterogeneous standards, response variables, protocols, and quality of evidence. Nevertheless, we encourage the use of systematic protocols with common good standards in order to provide more reliable empirical evidence. This would clarify the relative effectiveness of conflict management strategies and contribute to the global reduction in the occurrence of human-large carnivore conflicts across the world.
... Where prey depletion occurs, large carnivores might forage closer to habitations or predate on domestic animals more often, which can lead to even more constraints in the use of space (i.e., abandonment of grazing or recreational area) (Thirgood et al., 2005;Moss et al., 2016). Such proximity is susceptible to induce defensive behavior (e.g., for protecting cubs) (Coltrane and Sinnott, 2015;Herrero et al., 2005;Kojola and Heikkinen, 2012;Pătrașcu et al., 2015;Quenette et al., 2011;Rauer, 1999), and the resulting situations can lead to the injury or death of the carnivores involved (Khorozyan and Waltert, 2020;Lennox et al., 2018;Treves et al., 2009). Their conservation is therefore all the more complex, although it remains important both at the species level and in terms of their structuring role in ecosystems (Ripple et al., 2014). ...
... Otherwise, inefficient intervention might become a financial burden or create social mistrust, ultimately hindering carnivore conservation (Dickman, 2010). Previous studies and reviews have identified great heterogeneity in the available information and scientific standards used for quantitative comparison (Khorozyan and Waltert, 2019;Lennox et al., 2018;Treves et al., 2019). To overcome this hindrance to solid proof-based evaluations, the authors of said reviews usually only considered case studies reporting experiments with high scientific standards (preferably "gold" or BACI). ...
... This approach enables the comparison of studies with different standards, thus extending the usable panel to be considered. For the purpose of consistency and consensus, and in line with other studies Waltert, 2019, 2020;Lennox et al., 2018;Moreira-Arce et al., 2018), we focused on three of the most used and documented interventions (i.e., lethal interventions, nonlethal interventions, and translocations), related to human-large carnivore conflicts at the global scale. ...
... Where prey depletion occurs, large carnivores might forage closer to habitations or predate on domestic animals more often, which can lead to even more constraints in the use of space (i.e., abandonment of grazing or recreational area) (Thirgood et al., 2005;Moss et al., 2016). Such proximity is susceptible to induce defensive behavior (e.g., for protecting cubs) (Coltrane and Sinnott, 2015;Herrero et al., 2005;Kojola and Heikkinen, 2012;Pătrașcu et al., 2015;Quenette et al., 2011;Rauer, 1999), and the resulting situations can lead to the injury or death of the carnivores involved (Khorozyan and Waltert, 2020;Lennox et al., 2018;Treves et al., 2009). Their conservation is therefore all the more complex, although it remains important both at the species level and in terms of their structuring role in ecosystems (Ripple et al., 2014). ...
... Otherwise, inefficient intervention might become a financial burden or create social mistrust, ultimately hindering carnivore conservation (Dickman, 2010). Previous studies and reviews have identified great heterogeneity in the available information and scientific standards used for quantitative comparison (Khorozyan and Waltert, 2019;Lennox et al., 2018;Treves et al., 2019). To overcome this hindrance to solid proof-based evaluations, the authors of said reviews usually only considered case studies reporting experiments with high scientific standards (preferably "gold" or BACI). ...
... This approach enables the comparison of studies with different standards, thus extending the usable panel to be considered. For the purpose of consistency and consensus, and in line with other studies Waltert, 2019, 2020;Lennox et al., 2018;Moreira-Arce et al., 2018), we focused on three of the most used and documented interventions (i.e., lethal interventions, nonlethal interventions, and translocations), related to human-large carnivore conflicts at the global scale. ...
... Predators play a critical role within the ecological community, and their conservation and management are essential components of maintaining ecosystem health and biodiversity (Schmitz 2007, Schmitz et al. 2010. Despite their well-established role in shaping both ecosystem properties and function (Soulé et al. 1988), the wildlife management of reducing populations of predatory species (predator control), continues to be a widespread strategy for conserving threatened prey species throughout the world (Boertje et al. 1996, Hayes et al. 2003, Hervieux et al. 2014, Lennox et al. 2018. While many studies have explored distributional changes and numerical release of mid-sized (meso-) carnivore and prey populations following predator control (Polis et al. 1989, Palomares and Caro 1999, Ritchie and Johnson 2009) -often the outcome of behaviour changes -there is less research directly addressing behavioural changes among heterospecifics. ...
... Despite the potential for cascading impacts throughout the rest of the community, predator control remains a common strategy to mitigate livestock loss, and one of the most common strategies towards the conservation of threatened prey species (Boertje et al. 1996, Hayes et al. 2003, Hervieux et al. 2014, Lennox et al. 2018). In the northwestern Nearctic, wolf Canis lupus populations are reduced to conserve woodland caribou Rangifer tarandus caribou. ...
Article
Predator control remains one of the most common strategies for the conservation of threatened prey species. Despite significant and ongoing efforts to reduce predator populations, little is known about the impacts on the behaviour and interactions of target and non‐target species following numerical and potentially behavioural suppression of predators. We used camera‐trap data collected before and after an intensive wolf control program in northeastern Alberta's boreal forest to evaluate changes in activity patterns and overlap in wolves, competitors and prey. We hypothesized wolves would shift their activity toward increased nocturnality to avoid diurnal control efforts, and thereby cause a behavioural cascade where other species shift activity to maintain temporal segregation from wolves. Wolves shifted activity into the nighttime following predator control, reducing temporal overlap with the other, mostly diurnal, members of the community. Decreases in activity overlap between wolves and other species indicates reduced potential for wolf interactions with ungulate prey and large competitor species. Predator control may therefore not only release species from top to down regulation and competition following numerical suppression of top predators, but also through de‐coupling of temporal overlap, with potential effects on species interactions. Understanding the indirect impacts of conservation strategies such as predator control on both target and non‐target species provides insight into potential disruptions to top–down regulation and the associated species interactions that shape community structure.
... For large carnivores, there are a number of reasons for human-caused mortality, including wildlife-vehicle collisions or poaching (Ripple et al. 2014). However, retaliatory killing in response to conflict with humans is an increasingly important mortality factor in human-dominated landscapes (Treves and Karanth 2003;Lennox et al. 2018). This conflict usually occurs in the form of livestock depredation (Chapron et al. 2014;van Eeden et al. 2018), which in turn may result in the persecution and killing of carnivores, and ultimately elevate extinction risk (Michalski et al. 2006;Jędrzejewski et al. 2017). ...
... A first major insight from our work was that ignoring human-leopard conflict in connectivity assessments may lead to a substantial overestimation Fig. 4 Location of habitat patches, safe, severed, and high-risk corridors between Golestan National Park (GNP) and Jahan Nama Protected Area (JNPA), Iran of the extent of the corridor and the functional connectivity among habitat patches. Many leopard dispersal bottlenecks in the eastern Alborz Mountains were located in areas with high conflict risk (i.e., highrisk corridors), where the persecution of leopard is likely (Kiabi et al. 2002;Lennox et al. 2018), and local extinction risk is high (Jędrzejewski et al. 2017). These landscapes may act as 'ecological traps' when animals are funneled through them (Little et al. 2002;Kramer-Schadt et al. 2011;Northrup et al. 2012) and consequently, put dispersing individuals at risk of conflict. ...
Article
Full-text available
Objectives We identified safe dispersal corridors and conflict-prone movement bottlenecks for Persian leopard (Panthera pardus saxicolor) between protected areas in the Alborz Mountains, Iran, by mapping habitat, landscape permeability, and conflict risk. We then identified priority areas for conservation interventions according to the intensities of different threats. Methods We mapped land cover using Landsat satellite images, gathered data on leopard and prey distributions and livestock depredation events via interview surveys in 69 cells of 6 × 6 km each. We then used occupancy modeling to identify habitat patches, used circuit theory modeling to analyze landscape permeability, and assessed human-leopard conflict risk using generalized linear models. Results Leopard habitat use increased with prey availability and decreased with elevation. Prey distribution, in turn, was mostly negatively influenced by agricultural lands and distance from protected areas. Conflict risk (i.e., probability of leopard depredation on livestock) was high in landscapes where agriculture was widespread and historical forest loss high. Not accounting for conflicts overestimated connectivity among habitat patches substantially. Conclusions Human-carnivore conflicts are an important constraint to connectivity and should be considered in corridor assessments. Our study shows how habitat analysis, connectivity assessment, and conflict risk mapping can be combined to guide conservation planning for identifying habitat networks and safe corridors for carnivores in human-dominated landscapes.
... As outlined by McKinney (2006), some species exhibit high sensitivity to urbanization and disappear from such environments ('urban avoiders'), others may thrive as urban commensals and can even become dependent on urban resources ('urban exploiters'), while some species may show some use of urban habitats but still largely rely on natural resources ('urban adapters'). How urbanization impacts the behavior of carnivores has emerged as a key research focus in the urban ecology literature, in part due to their relatively high vulnerability to exploitation and habitat fragmentation (Stark et al. 2020) as well as increases in the number of 'nuisance' carnivores using urban areas that result in human−wildlife conflict (Bateman & Fleming 2012, Lennox et al. 2018. Although some carnivores (e.g. ...
... Such efforts lean heavily on deterrents aimed at preventing depredation, frequently positioned as "nonlethal alternatives" to the lethal control of "problem individuals." While these tools and techniques are often described as "straightforward" (Western Wildlife Outreach, 2014), questions remain around their effectiveness and associated costs (on the efficacy and ethics of lethal vs. nonlethal wildlife management, see DeCesare et al., 2018;Lennox et al., 2018;Moreira-Arce et al., 2018;Treves et al., 2019;Gamborg et al., 2020;Boronyak et al., 2021). ...
Chapter
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) Understanding Human–Canid Conflict and Coexistence: Socioeconomic Correlates Underlying Local Attitude and Support Toward the Endangered Dhole (Cuon alpinus) in Bhutan.
... Although there is agreement that predation vanishes when no predators exist, the quantitative relationships between predatory threats to people or property and key environmental variables, such as domestic and wild species ecologies, remain murky. Reviews examining predator removal show that removal efforts are rarely successful, even when efforts are directed at a speci c individual predator blamed for property damages [15][16][17][18][19][20] . e.g., cougars in Washington state, USA 21 , wolves in Michigan, USA 22 and in Spain 23 , and dingoes in Australia 24 . ...
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Given the ecological importance of top predators, societies are turning to non-lethal methods for coexistence. Coexistence is challenging when livestock are released within wild predator habitats, even when people supervise or use lethal methods. We report a randomized, controlled design to evaluate low-stress livestock handling (L-SLH), a form of range riding, to deter grizzly (brown) bears, gray wolves, cougars, black bears, and coyotes in Southwestern Alberta. The treatment condition was supervision by two newly hired and trained range riders and an L-SLH practicing range rider. This treatment was compared against a baseline pseudo-control condition of the single experienced range rider working alone. Cattle experienced zero injuries or deaths in either condition. We infer that inexperienced range riders trained and supervised by an experienced rider did not raise or lower the risk to cattle. Also, predators did not shift to the cattle herds protected by fewer range riders. Pending experimental evaluation of other designs, we recommend use of L-SLH.
Article
Predation as an important trophic interaction of ecological communities controls the large-scale patterns of species distribution, population abundance and community structure. Numerous studies address that predation can mediate diversity and regulate the ecological community and food web stability through changes in the behavior, morphology, development, and abundance of prey. Since predation has large effects on persistence and diversity, the local loss or removal of predation in a community can trigger a cascade of extinctions. In ecological theory, the effect of predation removal has been well studied in foodwebs, but it remains unclear in the case of a spatially distributed community connected by dispersal. In this study, the interaction between local and spatial processes is taken into account, we present how a predation turnoff in selective patches affects the synchronized oscillatory dynamics of a metacommunity. Using a simple predator–prey metacommunity with a diffusive dispersal, we show the impact of predation on synchronized, asynchronized and source–sink dynamics. Our results reveal that predation turnoff in very few patches stabilizes the metacommunity by damping the perfectly synchronized oscillatory state into multicluster equilibrium (i.e., steady) states. In a source–sink behavior, predation turnoff in a source patch reduces the number of sink patches and changes the clusters. In general, predation turnoff in low number of patches shows non-zero equilibrium states in both prey and predator populations, whereas predation turnoff in a larger number of patches can lead to the complete extinction of predators. Moreover, prey density from the patches where predation is absent goes to a saturating state near the carrying capacity. Thus, this study stresses that predation turnoff in selective patches acts as a stabilizing mechanism to promote the metacommunity persistence.
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Large carnivores, such as gray wolves, Canis lupus, are difficult to protect in mixed-use landscapes because some people perceive them as dangerous and because they sometimes threaten human property and safety. Governments may respond by killing carnivores in an effort to prevent repeated conflicts or threats, although the functional effectiveness of lethal methods has long been questioned. We evaluated two methods of government intervention following independent events of verified wolf predation on domestic animals (depredation) in the Upper Peninsula of Michigan, USA between 1998–2014, at three spatial scales. We evaluated two intervention methods using log-rank tests and conditional Cox recurrent event, gap time models based on retrospective analyses of the following quasi-experimental treatments: (1) selective killing of wolves by trapping near sites of verified depredation, and (2) advice to owners and haphazard use of non-lethal methods without wolf-killing. The government did not randomly assign treatments and used a pseudo-control (no removal of wolves was not a true control), but the federal permission to intervene lethally was granted and rescinded independent of events on the ground. Hazard ratios suggest lethal intervention was associated with an insignificant 27% lower risk of recurrence of events at trapping sites, but offset by an insignificant 22% increase in risk of recurrence at sites up to 5.42 km distant in the same year, compared to the non-lethal treatment. Our results do not support the hypothesis that Michigan’s use of lethal intervention after wolf depredations was effective for reducing the future risk of recurrence in the vicinities of trapping sites. Examining only the sites of intervention is incomplete because neighbors near trapping sites may suffer the recurrence of depredations. We propose two new hypotheses for perceived effectiveness of lethal methods: (a) killing predators may be perceived as effective because of the benefits to a small minority of farmers, and (b) if neighbors experience side-effects of lethal intervention such as displaced depredations, they may perceive the problem growing and then demand more lethal intervention rather than detecting problems spreading from the first trapping site. Ethical wildlife management guided by the “best scientific and commercial data available” would suggest suspending the standard method of trapping wolves in favor of non-lethal methods (livestock guarding dogs or fladry) that have been proven effective in preventing livestock losses in Michigan and elsewhere.
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The expansion of moose into southern British Columbia caused the decline and extirpation of woodland caribou due to their shared predators, a process commonly referred to as apparent competition. Using an adaptive management experiment, we tested the hypothesis that reducing moose to historic levels would reduce apparent competition and therefor recover caribou populations. Nested within this broad hypothesis were three specific hypotheses: (1) sport hunting could be used to substantially reduce moose numbers to an ecological target; (2) wolves in this ecosystem were primarily limited by moose abundance; and (3) caribou were limited by wolf predation. These hypotheses were evaluated with a before-after control-impact (BACI) design that included response metrics such as population trends and vital rates of caribou, moose, and wolves. Three caribou subpopulations were subject to the moose reduction treatment and two were in a reference area where moose were not reduced. When the moose harvest was increased, the moose population declined substantially in the treatment area (by 70%) but not the reference area, suggesting that the policy had the desired effect and was not caused by a broader climatic process. Wolf numbers subsequently declined in the treatment area, with wolf dispersal rates 2.5× greater, meaning that dispersal was the likely mechanism behind the wolf numerical response, though reduced recruitment and starvation was also documented in the treatment area. Caribou adult survival increased from 0.78 to 0.88 in the treatment area, but declined in the reference. Caribou recruitment was unaffected by the treatment. The largest caribou subpopulation stabilized in the treatment area, but declined in the reference area. The observed population stability is comparable to other studies that used intensive wolf control, but is insufficient to achieve recovery, suggesting that multiple limiting factors and corresponding management tools must be addressed simultaneously to achieve population growth.
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Although participatory planning for conservation has gained prominence over the past few decades, whether this process is successful in protecting biodiversity is still controversial. Moreover, the initial, constitutive decisions about whom to include in the process may undermine the sometimes-implicit goal that non-participants will find the outcomes legitimate and equitable. Different pitfalls relate to the proper representation of all public interests, such as tyranny of the minority or conflicts of interest. We focus on the effective integration of the broad public interest into decisions on use and preservation of the environment, including biodiversity, and we argue why the broad public interest should be considered a prerequisite to processes that are democratic, legitimate and equitable. When narrower interests become entrenched, conservation conflicts can become chronic as opponents take irreconcilable positions and polarize debate. Participatory decision-making processes could be improved by codifying the democratic principles of intergenerational equity and the public trust doctrine. We make recommendations on how to integrate the broad public interest in conservation decisions.
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Over the last century, changing public attitudes about the value of wildlife have triggered substantial changes in species management that have both benefited and hindered conservation efforts. Understanding and integrating contemporary public values is therefore critical for effective conservation outcomes. Using historic and contemporary examples, we highlight how public attitudes—expressed through the media and cam-paigns—are shaping the management of introduced and native species, as values shift towards animal welfare and mutualism. We focus on the issue of deliberate human-caused killing of wildlife, because protests against such management have disrupted traditional political and management structures that favoured eradication of wildlife across many jurisdictions and ecological contexts. In doing so, we show that it is essential to work with multiple stakeholder interest groups to ensure that wildlife management is informed by science, while also supported by public values. Achieving this hinges on appropriate science communication to build a better-informed public because management decisions are becoming increasingly democratised.
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As a result of ecological and social drivers, the management of problems caused by wildlife is becoming more selective, often targeting specific animals. Narrowing the sights of management relies upon the ecology of certain 'problem individuals' and their disproportionate contribution to impacts upon human interests. We assess the ecological evidence for problem individuals and confirm that some individuals or classes can be both disproportionately responsible and more likely to reoffend. The benefits of management can sometimes be short-lived, and selective management can affect tolerance of wildlife for better or worse, but, when effectively targeted, selective management can bring benefits by mitigating impact and conflict, often in a more socially acceptable way.
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Top predators can suppress mesopredators by killing them, competing for resources and instilling fear, but it is unclear how suppression of mesopredators varies with the distribution and abundance of top predators at large spatial scales and among different ecological contexts. We suggest that suppression of mesopredators will be strongest where top predators occur at high densities over large areas. These conditions are more likely to occur in the core than on the margins of top predator ranges. We propose the Enemy Constraint Hypothesis, which predicts weakened top-down effects on mesopredators towards the edge of top predators’ ranges. Using bounty data from North America, Europe and Australia we show that the effects of top predators on mesopredators increase from the margin towards the core of their ranges, as predicted. Continuing global contraction of top predator ranges could promote further release of mesopredator populations, altering ecosystem structure and contributing to biodiversity loss.
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Large carnivores are persecuted globally because they threaten human industries and livelihoods. How this conflict is managed has consequences for the conservation of large carnivores and biodiversity more broadly. Mitigating human-predator conflict should be evidence-based and accommodate people’s values while also protecting carnivores. Despite much research into human-large carnivore coexistence strategies, there have been limited attempts to document the success of conflict mitigation strategies on a global scale. We present a meta-analysis of global research on conflict mitigation between large carnivores and humans, focusing on conflicts that arise from the threat that large carnivores pose to livestock industries. Overall, research effort and focus varied between continents, aligning with the different histories and cultures that shaped livestock production and attitudes towards carnivores. Of the studies that met our criteria, livestock guardian animals were most effective at reducing livestock losses, followed by lethal control, although the latter exhibited the widest variation in success and the two were not significantly different. Financial incentives have promoted tolerance in some settings, reducing retaliatory killings. In future, coexistence strategies should be location-specific, incorporating cultural values and environmental conditions, and designed such that return on financial investment can be evaluated. Improved monitoring of mitigation measures is urgently required to promote effective evidence-based policy.
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The aim of this study is twofold: to provide a theoreti­ cal and an applied analysis of multispecies fisheries. The theoretical part will include concepts and analysis which, hopefully, will be of interest not only to economists, but also to biologists and ecologists. The application of the theoreti­ cal model and analysis to the Barents Sea fisheries gives empiri­ cal content to the analysis, which is important for the advance­ ment of fisheries management science. It is also my firm belief that this kind of work in the end will be beneficial to the people trying to make a living from harvesting marine resources. For thousands of years man has been whaling, sealing and fishing in these cold and harsh surroundings. The relative importance of the different species in the ecosystem has changed throughout history. In the seventeenth century the abundant, slow-swimming Greenland right whale and the Biscayan right whale in the Barents Sea area were so valuable, especially to English and Dutch whalers, that the intensive exploitation of these common property resources probably were the main reason for the extinction of these two stocks. The two species are, however, still present in other parts of the North Atlantic Ocean. Except for these two stocks of whales there is no knowledge of other stocks of sea mammals or fish in this area being extinct in historical time.