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The bigger they come, the harder they fall: Body size and prey abundance influence predator-prey ratios



Large carnivores are highly threatened, yet the processes underlying their population declines are still poorly understood and widely debated. We explored how body mass and prey abundance influence carnivore density using data on 199 populations obtained across multiple sites for 11 carnivore species. We found that relative decreases in prey abundance resulted in a five- to sixfold greater decrease in the largest carnivores compared with the smallest species. We discuss a number of possible causes for this inherent vulnerability, but also explore a possible mechanistic link between predator size, energetics and population processes. Our results have important implications for carnivore ecology and conservation, demonstrating that larger species are particularly vulnerable to anthropogenic threats to their environment, especially those which have an adverse affect on the abundance of their prey.
doi: 10.1098/rsbl.2010.0996
, 312-315 first published online 24 November 20107 2011 Biol. Lett.
Chris Carbone, Nathalie Pettorelli and Philip A. Stephens
prey ratiosabundance influence predator
The bigger they come, the harder they fall: body size and prey
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Population ecology
The bigger they come, the
harder they fall: body size
and prey abundance
influence predatorprey
Chris Carbone1,*, Nathalie Pettorelli1
and Philip A. Stephens2
Institute of Zoology, Zoological Society of London, Regent’s Park,
London NW1 4RY, UK
School of Biological and Biomedical Sciences, University of Durham,
South Road, Durham DH1 3LE, UK
*Author for correspondence (
Large carnivores are highly threatened, yet the
processes underlying their population declines
are still poorly understood and widely debated.
We explored how body mass and prey abundance
influence carnivore density using data on 199
populations obtained across multiple sites for
11 carnivore species. We found that relative
decreases in prey abundance resulted in a
five- to sixfold greater decrease in the largest
carnivores compared with the smallest species.
We discuss a number of possible causes for this
inherent vulnerability, but also explore a possible
mechanistic link between predator size, ener-
getics and population processes. Our results
have important implications for carnivore ecol-
ogy and conservation, demonstrating that larger
species are particularly vulnerable to anthropo-
genic threats to their environment, especially
those which have an adverse affect on the
abundance of their prey.
Keywords: carnivore ecology; predatorprey
relationships; abundance scaling; climate change;
It is well recognized that large carnivores are highly
threatened, owing to a combination of environmental
change, biological factors and human pressures [1,2].
However, the main processes underlying global
declines in large carnivores are still widely debated
[3]. Body mass and prey abundance are known to
influence average abundance across mammalian carni-
vores [4]. However, there is also evidence that larger
carnivore species are rarer than expected based on
typical abundance mass relationships [5,6]. Carni-
vores are extremely wide ranging, with day ranges
two- to threefold that of herbivores of the same size
[7] and, across species, exhibit steeper scaling in day
range and home range [810]. This increase in ran-
ging behaviour would influence individual energetic
rates and is consistent with the finding that energetics
may place evolutionary constraints on body size in
predators [11,12]. Ultimately, size and energetics
may be linked with the intrinsic factors identified in a
global analysis of the threat status of mammals [13].
The interplay between the environment, body size
and the intrinsic factors driving this vulnerability
remains poorly understood. Studies that identify
causes of changes in species abundance in relation to
size and ecology have the potential to greatly improve
our understanding of population processes.
In this study, we present an analysis of predator
prey ratios obtained across multiple sites for 11 species
of carnivores. We focus on a key environmental factor,
food availability (prey abundance), in order to explore
whether large carnivores show a greater population
response to changes in the relative abundance of
their food resources.
To compare carnivore abundance across species in relation to vari-
ation in prey biomass density (enabling a comparison across
different species of carnivores that feed on prey of different sizes
[4,14]), we explored how the logarithm (base 10) of carnivore den-
sity (logN) relates to log carnivore body mass (logM) and log prey
biomass density (logP) for 199 predator– prey population estimates
obtained from 11 species of carnivores (all with six or more
population estimates; table 1; see also the electronic supplementary
material). In our data analysis, we compared the explanatory
power of four different linear combinations of these predictors
using Akaike Information Criterion (AIC) [15,16]. We excluded
data on the population densities of two species, the African wild
dog (Lycaon pictus) and cheetah (Acinonyx jubatus), which are
known to be poorly related to prey availability, owing to competition
with other carnivores [1720]. Whether or not wild dogs and chee-
tahs are included, our conclusions remain unaffected and the fitted
models remain significant (electronic supplementary material,
table S2); here, however, we focus on the results with wild dogs
and cheetahs omitted.
Most of the data used in this study were obtained from studies
specifically focused on predator– prey relationships for a single carni-
vore species. Inevitably, the methods used in these studies somewhat
varied. In some instances, data on prey density in one year were com-
pared with predator density estimated in the next; in other instances,
these data might be matched within the same year [4]. In addition,
given the practical difficulties of getting such information, we
found that most data were only available from different locations
and periods across the species’ ranges. Ideally, longitudinal data
(from the same populations across years) should be used; nonethe-
less, we believe that these data have the potential to provide
important insights into predator– prey relationships and a general
understanding of consumer–resource relationships [21].
The model including all predictors (logP, logMand the
interaction between them) explained 68 per cent of the
variability in log carnivore densities, enjoying substan-
tially more support than the next best alternative
(DAIC ¼11.24 between this and the next best
model; table 2). This relationship is best described
by a linear model of the form log N¼1.06 2
1.29 logMþ0.33 logPþ0.21 logMlogP(all pre-
dictors are significant with p,0.001 and the full
model is also significant with F
¼140.9, p,
0.001, r
¼0.68). The coefficients confirm that
carnivore densities are negatively affected by body
mass and positively affected by prey availability;
crucially, the significant interaction term shows that
the densities of the larger species of carnivores are dis-
proportionately lower in areas of low prey density.
Intriguingly, the slopes of the predator– prey responses
seem to increase linearly with log carnivore body
mass (figure 1).
Electronic supplementary material is available at
10.1098/rsbl.2010.0996 or via
Biol. Lett. (2011) 7, 312–315
Published online 24 November 2010
Received 23 October 2010
Accepted 3 November 2010 312 This journal is q2010 The Royal Society
on June 10, 2011rsbl.royalsocietypublishing.orgDownloaded from
Focusing on a common threat, that of declining food
resources [22], this study confronts the important
question of how mammalian carnivores of different
size might respond to differing environmental con-
ditions. Compared with the overall variation across
the dataset, the carnivore mass–prey biomass inter-
action term explains only 2 per cent of the variation;
nevertheless, slopes of the relationship between preda-
tors and prey vary substantially and carnivore mass
explains nearly 80 per cent of the variation in these
slopes (figure 1)—a result of great biological signifi-
cance. A given reduction in prey abundance, leads to
a five- to sixfold greater reduction in the larger
carnivores when compared with the smallest carnivores.
What mechanisms could drive this apparent vulner-
ability? One possibility is that, because large carnivores
consume large prey [12], which themselves may be vul-
nerable to threat processes [13], there may be an
interaction across populations between predator and
prey. However, our analysis of carnivore abundance
controls for prey abundance and so does not support
this argument unless more subtle processes, unrelated
to abundance, are taking place. Alternatively, previous
work has shown that energetic costs may limit body
size in larger carnivores [11]. It is possible that similar
physiological factors influence population processes
as well. Physiologists have long been interested in
metabolic costs under different levels of exercise
[23,24]. Such studies have shown that, at maximum
energy expenditure, large animals have relatively high
metabolic rates [2527]. Carnivores have larger
home ranges [2831] and hunt for longer [32,33]in
areas of low prey density or productivity. Building on
earlier physiological arguments, we might expect that
when large carnivores work harder to maintain their
energy budgets under conditions of low prey abun-
dance, this in turn may influence their population
density. If this is the case, predatory species with extre-
mely high hunting costs will be particularly susceptible
to changes in the environment that influence feeding
ecology, because any increase in the time spent hunting
greatly adds to overall energy expenditure [34]. In
energetically stressful situations, both survival and
reproduction are subject to reductions; this situation
could be exacerbated in large carnivores by life-history
attributes that already render them vulnerable to
extinction [35]. Future work on this topic, using
models of predatorprey dynamics to assess the
influence of size and habitat productivity, might be
particularly useful in providing specific testable
predictions [36,37].
Understanding the links between physiology, behav-
iour and population phenomena remains one of the
great challenges in ecology [38], and the current back-
drop of declining environmental conditions, climate
change and biodiversity loss makes that challenge par-
ticularly important [39]. Carnivores represent ideal
Table 1. Summary of carnivore density and prey biomass density used in this study, obtained from Carbone & Gittleman [4]
and additional sources (see the electronic supplementary material); see text for details.
species scientific name
carnivore density, N(km
prey biomass,
P(kg km
) range
(min–max) slope intercept r
least weasel Mustela nivalis 0.14 7 0.52–80.0 0.1615 3.49 0.02 23.9–832.5
arctic fox Alopex lagopus 3.19 14 0.022–0.286 0.2385 0.0268 0.47 1.0 2810.9
Lynx canadensis 11.2 28 0.02–0.226 0.4954 0.0047 0.65 16.8–1386.0
Meles meles 13.0 9 0.79–8.4 0.3437 12.74 0.73 352.8 –71 400.0
coyote Canis latrans 13.0 19 0.023 0.444 0.508 0.0092 0.21 34.5 1485.0
wolf Canis lupus 46.0 20 0.005 0.042 0.6661 0.0003 0.49 89.0–810.5
leopard Panthera pardus 46.5 19 0.005–0.303 0.5079 0.0025 0.51 13.2–41 62.9
Crocuta crocuta 58.6 19 0.005–1.842 0.7733 0.0004 0.52 126.0– 17 262.6
lion Panthera leo 142.0 40 0.008 –0.52 0.5854 0.0011 0.66 35.0–14 198.4
tiger Panthera tigris 181.0 16 0.006–0.168 0.7352 0.0002 0.72 171.0–5828.6
polar bear Ursus maritimus 310.0 8 0.003 0.021 0.8806 00000.9 0.89 41.8– 337.0
Table 2. Models fitted to empirical data on carnivore densities.
fitted model
estimated parameters AIC DAIC wr
lm(logNlogM)3 2168.22 168.79 0 0.25
lm(logNlogP)3 2156.90 180.10 0 0.20
lm(logNlogMþlog P)4 2325.76 11.24 0 0.66
lm(logNlogMlog P)5 2337.00 0.00 1.00 0.68
Model specifications are compatible with R [16] and represent single predictor linear models in the first two cases, a two predictor linear
model in the third case and a model containing both predictors and their interaction in the final case.
Size, abundance and predatorprey ratios C. Carbone et al. 313
Biol. Lett. (2011)
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species for exploring such relationships because, not
only do we know a great deal about their behaviour
and diets [40], but we also have good information on
the abundance and distributions of many of their
prey [4]. We believe that further research exploring
the link between physiology, behaviour and carnivore
population dynamics represents a valuable opportunity
to establish clear relationships, from individual behav-
iour to population processes and macroecological
patterns. This research also has important implications
for the conservation of our largest carnivore species,
which seem especially vulnerable to conditions
influencing the abundance of their prey.
We thank Blaire Van Valkenburgh and Shai Meiri for their
helpful comments on earlier drafts of the manuscript.
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... One of the critical considerations in this study is the significant association of prey body size classes (large, medium and small) with fT3M measures. This was considered based on our available knowledge that large terrestrial predator distribution and abundance is significantly driven by higher biomass availability (Carbone et al., 2011), and they are known to prefer large-bodied prey due to higher energy gains (Carbone et al., 1999(Carbone et al., , 2007(Carbone et al., , 2011Carbone and Gittleman, 2002;Radloff and Du Toit, 2004). Work on leopard energet-ics has also reported increased energy expenditure between meals when meal size from previous kill is large (Wilmers et al., 2017). ...
... One of the critical considerations in this study is the significant association of prey body size classes (large, medium and small) with fT3M measures. This was considered based on our available knowledge that large terrestrial predator distribution and abundance is significantly driven by higher biomass availability (Carbone et al., 2011), and they are known to prefer large-bodied prey due to higher energy gains (Carbone et al., 1999(Carbone et al., , 2007(Carbone et al., , 2011Carbone and Gittleman, 2002;Radloff and Du Toit, 2004). Work on leopard energet-ics has also reported increased energy expenditure between meals when meal size from previous kill is large (Wilmers et al., 2017). ...
Full-text available
Apex predators have critical roles in maintaining the structure of ecosystem functioning by controlling intraguild subordinate populations. Such dominant-subordinate interactions involve agonistic interactions including direct or indirect impacts on the subordinates. As these indirect effects are often mediated through physiological processes, it is important to quantify such responses to better understand population parameters. We used a large carnivore intraguild system involving tiger (Panthera tigris) and leopard (Panthera pardus) to understand the dietary and physiological responses under a spatio-temporal gradient of tiger competition pressures in Rajaji Tiger Reserve (RTR) between 2015 and 2020. We conducted systematic faecal sampling in the winters of 2015 and 2020 from the park to assess diet and physiological measures. Analyses of leopard-confirmed faeces suggest a dietary-niche separation as a consequence of tiger competition. In 2020, we found an increased occurrence of large-bodied prey species without tiger competition in western-RTR. Physiological measures followed the dietary responses where leopards with large-sized prey in the diet showed higher fT3M and lower fGCM measures in western-RTR. In contrast, eastern-RTR leopards showed lower levels of fT3M and fGCM in 2020, possibly due to intense competition from tigers. Overall, these patterns strongly indicate a physiological cost of sympatry where competition with dominant tigers resulted in elevated nutritional stress. We recommend expansion of leopard monitoring and population estimation efforts to buffers, developing appropriate plans for human-leopard conflict mitigation and intensive efforts to understand leopard population dynamics patterns to ensure their persistence during the ongoing Anthropocene.
... Prey availability is an important determinant of carnivore density (Carbone et al. 2011;Khorozyan et al. 2008). The estimated density of wild prey species (ungulates) in EFD is 17.19 ± 3.04 per km 2 (WWF-India, 2017 unpublished data). ...
The study aims to assess the population status and density of the Leopard (Panthera pardus fusca) in the Erode Forest Division, Tamil Nadu. The Erode Forest division has numerous villages within its boundaries and is exposed to associated biotic pressures. In order to improve the management practices of the wildlife in the area and to enhance its conservation, it is relevant to assess its status. In 2018 and 2020, we estimated the population density of the leopard in the entire forest division using 2 km2 sample grids and the camera trapping method. In each grid, we deployed a pair of camera traps, the cumulative number of trap-nights being 22983 (10732 trap nights in 2018 and 12251 in 2020). We analysed the obtained data using spatially explicit capture-recapture models (SECR). The surveys yielded 198 images of the leopard in 2018 and 272 images in 2020, of which 48 and 44 leopard individuals were identified in the respective years based on the rosette pattern. The density estimates were 5.16 (SE = ±0.89) and 4.00 (SE ± 0.72) individuals/100 km2 in 2018 and 2020, respectively. We found that in some regions overlapping with the human-use area, leopard densities were high, indicating that the species successfully exploits areas near human habitation and highlighting its high potential for interaction with humans. This baseline estimate and insights will help prioritize management actions, strengthen large mammal conservation beyond the boundaries of protected areas (PA), and plan human-wildlife conflict mitigation measures to enable the persistence of large carnivores in multi-use forests.
... In our Mediterranean study area, the availability of large, substantial prey to wolves was remarkably high, including three species of wild ungulates for an overall density of c. 20-30 individuals/km 2 (see "Methods" section). The importance of preserving a rich and diverse prey community to enhance carnivore conservation has been largely emphasised, with prey depletion hampering carnivore persistence [12,30], promoting predator interest to use livestock as an alternative prey [44,60], and stimulating interspecific competition [35]. Access to a rich prey spectrum would make large carnivores not particularly interested to mesocarnivores as potential prey, as well as increasing their tolerance towards scavengers in proximity to carcasses. ...
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Background There is need of information on ecological interactions that keystone species such as apex predators establish in ecosystems recently recolonised. Interactions among carnivore species have the potential to influence community-level processes, with consequences for ecosystem dynamics. Although avoidance of apex predators by smaller carnivores has been reported, there is increasing evidence that the potential for competitive-to-facilitative interactions is context-dependent. In a protected area recently recolonised by the wolf Canis lupus and hosting abundant wild prey (3 ungulate species, 20–30 individuals/km2, together), we used 5-year food habit analyses and 3-year camera trapping to (i) investigate the role of mesocarnivores (4 species) in the wolf diet; (ii) test for temporal, spatial, and fine-scale spatiotemporal association between mesocarnivores and the wolf. Results Wolf diet was dominated by large herbivores (86% occurrences, N = 2201 scats), with mesocarnivores occurring in 2% scats. We collected 12,808 carnivore detections over > 19,000 camera trapping days. We found substantial (i.e., generally ≥ 0.75, 0–1 scale) temporal overlap between mesocarnivores—in particular red fox—and the wolf, with no support for negative temporal or spatial associations between mesocarnivore and wolf detection rates. All the species were nocturnal/crepuscular and results suggested a minor role of human activity in modifying interspecific spatiotemporal partitioning. Conclusions Results suggest that the local great availability of large prey to wolves limited negative interactions towards smaller carnivores, thus reducing the potential for spatiotemporal avoidance. Our study emphasises that avoidance patterns leading to substantial spatiotemporal partitioning are not ubiquitous in carnivore guilds.
... However, despite the minimum distance adopted of 1 km, the average distance between sampling sites was 2.8 ± 0.8 km and it is noteworthy that poaching could eventually negatively impact these species indirectly due to the extirpation of their main prey, which are the species directly impacted by poaching in the present study. This indirect impact of poaching can be predicted as large carnivores are especially vulnerable to low density and biomass of their preferred prey (Carbone et al. 2011) and prey depletion is one of their major threats worldwide (Wolf and Ripple 2016). Overexploitation of wildlife for meat is a widespread phenomenon, which may drive populations of many species toward extinction and may, in turn, to affect large carnivores (Milner-Gulland et al. 2003; Ghoddousi et al. 2017). ...
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Hunting in tropical forests provides nutrition and financial income for local communities and is deeply rooted in social and cultural traditions. On the other hand, this activity, by locally reducing or extirpating populations of game species, may be responsible for the degradation and loss of key forest maintenance services. In Brazil, hunting is illegal (hereafter referred to as poaching). We evaluated, by accounting for imperfect detectability, the effects caused by poaching on mammals in the Vale Natural Reserve. We collected data over 5-years (between 2013 to 2018) using line-transect and camera-trapping to evaluate poaching effects on the density, biomass, richness, and site occupancy of mammalian species. Our complete data set included a total survey effort of 32,175 camera days across five camera trap surveys (825 working days), with a total of 25,254 records of 27 non-volant mammals. We found a negative effect of poaching index on overall-species richness based on our multi-species occupancy model. The greatest reduction in biomass occurred for ungulates and armadillos. Our results suggest that poaching can have large consequences for biodiversity in one of Brazil's largest Atlantic Forest remnants. Ours is the first study in the Atlantic Forest estimating the medium-term poaching impact on mammalian populations, demonstrating a potentially negative effect on density, biomass, and occupancy of species which are of importance for local ecosystem functioning. We demonstrate the need to start monitoring other populations of vertebrates that are a target to poaching, not only in the Atlantic Forest but in other Neotropical ecosystems.
... While the species that associate with these foundational shrub species may directly benefit, the probability of more complex trophic interactions increases due to the variation in community composition (Van der Putten et al. 2004). Numerous indirect feedbacks may also result from this positive association including varying foraging herbivores (Kotler et al. 1991) as well as the association of predator species (Carbone et al. 2011). Predator species, such as Crotalus oreganus (northern Pacific rattlesnake), consume smaller vertebrates (Holding et al. 2018) which use shrub species as a refuge from predators, thus impacting community composition and association. ...
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Facilitative interactions between shrub and animal species influence the structure and composition of communities. The benefits associated with woody shrub species can critically influence local animal populations, in particular. Here, we tested the relative importance of the density of shrub species on the local abundance of animal populations using a meta‐analysis. Full‐text review for shrub density, animal abundance or density and sampling effort, resulted in a total of 113 independent observations that reported both shrub density and animal abundance. A meta‐regression of shrub density on animal density with feeding functional group of the animal species as a moderator was used to test the predictive capacity of this simple vegetation measure on animal populations. Shrub density positively predicted animal abundance in these studies – particularly in deserts and grasslands. Shrub and woody plant density can thus be used as a potential rapid proxy for habitat in predicting local animal abundances. This method can support restoration and conservation of resident animal species in impacted ecosystems structured by woody shrubs globally.
... (1) Trophic cascades in animal communities While some large carnivore species are directly persecuted for trade (Dinerstein et al., 2007), their higher energetic requirements also make them particularly susceptible to the depletion of prey via exploitation for trade. A study of 199 populations across 11 carnivore species revealed that cyclical decreases in prey abundance caused a fiveto sixfold greater decline in the largest versus the smallest carnivore species (Carbone, Pettorelli & Stephens, 2011). Thus, where wildlife trade causes severe reductions in the prey base, predators are also likely to decline. ...
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Wildlife trade is a key driver of extinction risk, affecting at least 24% of terrestrial vertebrates. The persistent removal of species can have profound impacts on species extinction risk and selection within populations. We draw together the first review of characteristics known to drive species use – identifying species with larger body sizes, greater abundance, increased rarity or certain morphological traits valued by consumers as being particularly prevalent in trade. We then review the ecological implications of this trade‐driven selection, revealing direct effects of trade on natural selection and populations for traded species, which includes selection against desirable traits. Additionally, there exists a positive feedback loop between rarity and trade and depleted populations tend to have easy human access points, which can result in species being harvested to extinction and has the potential to alter source–sink dynamics. Wider cascading ecosystem repercussions from trade‐induced declines include altered seed dispersal networks, trophic cascades, long‐term compositional changes in plant communities, altered forest carbon stocks, and the introduction of harmful invasive species. Because it occurs across multiple scales with diverse drivers, wildlife trade requires multi‐faceted conservation actions to maintain biodiversity and ecological function, including regulatory and enforcement approaches, bottom‐up and community‐based interventions, captive breeding or wildlife farming, and conservation translocations and trophic rewilding. We highlight three emergent research themes at the intersection of trade and community ecology: (1) functional impacts of trade; (2) altered provisioning of ecosystem services; and (3) prevalence of trade‐dispersed diseases. Outside of the primary objective that exploitation is sustainable for traded species, we must urgently incorporate consideration of the broader consequences for other species and ecosystem processes when quantifying sustainability.
... The probability of exposure is as much a function of abundance as of time. Prey abundance is an important determinant of interaction strength (Carbone et al., 2011;Wellenreuther & Connell, 2002), since predator experience of novel prey will likely increase with prey density (Saul & Jeschke, 2015). Yet, invader abundance has rarely been considered when assessing how novel predatorprey interactions evolve (but see: Nelson et al., 2011). ...
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As invasive species spread, the ability of local communities to resist invasion depends on the strength of biotic interactions. Evolutionarily unused to the invader, native predators or herbivores may be initially wary of consuming newcomers, allowing them to proliferate. However, these relationships may be highly dynamic, and novel consumer–resource interactions could form as familiarity grows. Here, we explore the development of effective biotic resistance towards a highly invasive alga using multiple space‐for‐time approaches. We show that the principal native Mediterranean herbivore learns to consume the invader within less than a decade. At recently invaded sites, the herbivore actively avoided the alga, shifting to distinct preference and high consumptions at older sites. This rapid strengthening of the interaction contributed to the eventual collapse of the alga after an initial dominance. Therefore, our results stress the importance of conserving key native populations to allow communities to develop effective resistance mechanisms against invaders.
... One of the main causes of global biodiversity decline is habitat loss due to agricultural expansion (Foley et al. 2005). This constitutes a severe threat for large carnivores as they occur at a low number, have slow population growth rates, and require sufficient prey and large areas (Carbone et al. 2011), all of which make them particularly vulnerable to extinction (Boron et al. 2016). Their prey requirements also make them prone to conflict with humans and retaliatory killing, further increasing their vulnerability (Inskip and Zimmermann 2009). ...
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The influence of bottom-up food resources and top-down mortality risk underlies the demographic trajectory of wildlife populations. For species of conservation concern, understanding the factors driving population dynamics is crucial to effective management and, ultimately, conservation. In southeastern British Columbia, Canada, populations of the mostly omnivorous grizzly bear (Ursus arctos) are fragmented into a mosaic of small isolated or larger partially connected sub-populations. They obtain most of their energy from vegetative resources that are also influenced by human activities. Roads and associated motorized human access shape availability of food resources but also displace bears and facilitate human-caused mortality. Effective grizzly bear management requires an understanding of the relationship between habitat quality and mortality risk. We integrated analyses of bottom-up and top-down demographic parameters to understand and inform a comprehensive and efficient management paradigm across the region. Black huckle-berry (Vaccinium membranaceum) is the key high-energy food for grizzly bears in much of southeastern British Columbia. Little is known about where and why huckleberries grow into patches that are useful for grizzly bears (i.e., densely clustered fruiting shrubs that provide efficient access to high energy food) and how Wildlife Monographs. 2023;e1078. |
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The restoration of ecosystems through trophic rewilding has become increasingly common worldwide, but the effects on predator–prey and ecosystem dynamics remain poorly understood. For example, predation pressure may impose spatiotemporal behavioural adjustments in prey individuals, affecting herbivory and predation success, and therefore potentially impinging on the long-term success of trophic rewilding through apex predator reintroduction. Predation risk might have detrimental effects on prey through displacement from water or other vital resources. We investigated how five species of African ungulates responded behaviourally to changes in predation risk, following cheetah releases in the system. We grouped ungulates by body size to represent preferred prey weight ranges of the cheetah and examined changes in visitation rates, duration of stay, and activity patterns at waterholes with and without cheetah presence. During cheetah presence, visitation rates of ungulates were low for medium-sized species but high for large-sized species, suggesting that the species within the cheetah’s preferred prey weight range adjusted behaviourally to minimize waterhole visits. Visits to waterholes were longer for small- and large-sized ungulates with cheetah presence, possibly indicating increased vigilance, or a strategy to maximize water intake per visit while minimizing visits. We did not detect significant differences in circadian or seasonal activity in waterhole visits, which may be attributable to the need of ungulates to access water year-round in our semi-arid study system and where migration was impeded due to physical barriers (fencing). We recommend further research into the long-term behavioural consequences of trophic rewilding on prey populations and trophic cascades to assist the success of recovery programs and to minimize potential detrimental effects at target sites.
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Understanding why some species are at high risk of extinction, while others remain relatively safe, is central to the development of a predictive conservation science. Recent studies have shown that a species' extinction risk may be determined by two types of factors: intrinsic biological traits and exposure to external anthropogenic threats. However, little is known about the relative and interacting effects of intrinsic and external variables on extinction risk. Using phylogenetic comparative methods, we show that extinction risk in the mammal order Carnivora is predicted more strongly by biology than exposure to high-density human populations. However, biology interacts with human population density to determine extinction risk: biological traits explain 80% of variation in risk for carnivore species with high levels of exposure to human populations, compared to 45% for carnivores generally. The results suggest that biology will become a more critical determinant of risk as human populations expand. We demonstrate how a model predicting extinction risk from biology can be combined with projected human population density to identify species likely to move most rapidly towards extinction by the year 2030. African viverrid species are particularly likely to become threatened, even though most are currently considered relatively safe. We suggest that a preemptive approach to species conservation is needed to identify and protect species that may not be threatened at present but may become so in the near future.
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Most recent population viability analyses, especially those of long-lived species, rely on only a few years of data or data from a closely related species, combined with educated guesswork, to estimate model parameters and the variability surrounding those measures. This makes their conclusions or predictions difficult to evaluate. In out study, we used 20 years of demographic data on Serengeti cheetahs (Acinonyx jubatus) to conduct a population viability analysis First we constructed a model of the deterministic growth rate and found that the cheetah population is nearly self-replacing (lambda = 0.997). Our model showed that population growth was most strongly influenced by adult survival, followed by juvenile survival, which is typical of long-lived, iteroparous species. We then examined extinction risk and long-term projections of cheetah population size with our stochastic mode, Popgen, We compared the projections with over 20 years of field data and found that demographic stochasticity trials produced a stable population size, whereas environmental stochasticity trials were slightly more pessimistic. Extinction risk was highly sensitive to both adult survival and juvenile survival (from 0-1 years). Decreasing the variance in survival rates also decreased extinction risk. Because lions are the major predator on cheetah cubs, we used our demographic records to simulate the effect of different lion numbers on juvenile survival. High lion abundance and average lion abundance resulted in extinction of nearly all cheetah populations by 50 years, whereas with low lion abundance most cheetah populations remained extant. Conservation of cheetahs may not rely solely on their protection inside national parks, but may also rely on their protection in natural areas outside national parks where other large predators are absent.
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The African wild dog Lycaon pictus is critically endangered, with only about 5,000 animals remaining in the wild(1). Across a range of habitats, there is a negative relationship between the densities of wild dogs and of the spotted hyaena Crocuta crocuta(2). It has been suggested that this is because hyaenas act as 'kleptoparasites' and steal food from dogs. We have now measured the daily energy expenditure of free-ranging dogs to model the impact of kleptoparasitism on energy balance, The daily energy expenditures of six dogs, measured by the doubly labelled water technique, averaged 15.3 megajoules per day. We estimated that the instantaneous cost of hunting was twenty-five times basal metabolic rate. As hunting is energetically costly, a small loss of food to kleptoparasites has a large impact on the amount of time that dogs must hunt to achieve energy balance. They normally hunt for around 3.5 hours per day but need to increase this to 12 hours if they lose 25% of their food. This would increase th
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We measured daily movements and use of home ranges for 14 radio-collared pine martens (Martes martes) in Bialowieza National Park (eastern Poland) in 1991-1996. Data were collected during 70 continuous sessions of 24-h radio-tracking with locations taken at 15-min intervals. Daily movement distance (DMD, sum of straight-line distances between consecutive locations) averaged 5.1 km(.)d(-1) (min-max: 0.4-12.6) in females and 5.8 km(.)d(-1) (min-max: 0.7-12.7) in males. The mean speed of martens was 0.6 km(.)h(-1) (min-max: 0.2-1.4). Daily ranges (DR) used by martens averaged 49 ha. (min-max: 1-149) in females and 54 ha (min-max: 1-182) in males and constituted 0.3% to 88% (mean 26% and 29%, respectively) of annual home ranges held by martens. Indices of penetration of daily ranges (IPDR, in metres of route per hectare of DR) showed whether the daily routes of martens were densely packed and concentrated or loosely distributed. IPDR averaged 220 m(.)ha(-1) in females and 139 m(.)ha(-1) in males. Ambient temperature, abundance of forest rodents (martens' main prey resource), sex, and reproductive activity of an animal were crucial factors shaping the variation in all parameters. DMD, DR, and speed were positively correlated with ambient temperature (from -17 degreesC to 26 degreesC). With increasing temperature, martens moved faster, covered longer distances, and used larger daily ranges. Mobility and home range use were affected by breeding activity. In spring, females rearing cubs had longer DMD and moved faster than non-breeding females. In summer, males covered larger daily ranges during the mating period than outside it. We reviewed the available data on pine martens' wintertime DMD in Europe. In locations ranging from 41degrees to 69degrees N, the average and maximum recorded DMD of martens increased from south to north. We propose that pine martens have to cover longer routes to fulfil their food requirements in the conditions of declining ecosystem productivity and shrinking prey resources found along the south-north gradient.
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La dimension du domaine vital des carnivores varie énormément entre les populations d'une même espèce. Une des raisons souvent mentionnées pour expliquer ce phénomène est la variation de la densité de population des proies et de la productivité environnementale. L'obtention de données fiables sur la densité des proies demande beaucoup de temps et d'effort. Par conséquent, une méthode permettant aux scientifiques et aux gestionnaires d'extrapoler les dimensions des domaines vitaux peu importe où l'on se trouve serait un outil précieux. Or, le potentiel des différents indices de télédétection donnant des renseignements sur la productivité environnementale n'a pas encore été évalué à sa juste valeur. Dans cette étude, nous avons vérifié l'utilité d'un indice de télédétection déjà disponible, la fraction de radiation photosynthétiquement active (FRPA) qui est absorbée par les couverts de végétation, pour expliquer la variation de la taille du domaine vital entre les populations de douze espèces de carnivores. Dans les modèles de régression multiple, nous avons trouvé que l'indice de la FRPA ajoute un pouvoir prédictif aux modèles pour huit des douze espèces à l'étude. Le pouvoir explicatif varie de 16 à 71% selon les espèces. Nous suggérons que l'utilisation d'indices de télédétection, comme la FRPA, pourrait être un outil puissant pour prédire les dimensions de domaines vitaux des carnivores. Il est toutefois nécessaire de continuer à développer cette méthodologie de façon à la rendre plus performante. Nomenclature: MacDonald, 2001.
Rapid faunal assessments can use different methods depending on environmental conditions and costs. To compare the efficiency of three methods in detecting species richness and abundance, we tested them in the grasslands of Emas National Park, central Brazil. Track census was the most effective method for detecting richness, followed by camera-trapping and direct faunal counts. Track census reached an asymptote for number of species after only 12 days, but all methods converged on similar estimates of species richness after around 30 days. There was no significant spatial correlation for species richness or total abundance, between camera trap and tracks, across the 29 samples distributed in the park. However, for some species, abundance showed significant spatial correlation between methods. Also, these rates were significantly correlated across species and the spatial correlation between methods was significantly associated with log-transformed body mass across species. We conclude that, despite the high initial costs for camera-trapping, this method is the most appropriate for mammal inventory in all environmental conditions, allowing a rapid assessment of wildlife conservation status.
African wild dogs (Lycaon pictus) are endangered largely because their population-density is low under all conditions. Interspecific competition with larger carnivores may be a factor limiting wild dog density. The density of wild dogs on a 2600-km² area of the Selous Game Reserve (Tanzania) was 0.04 adults/km². Spotted hyaena (Crocuta crocuta) density for the same area was estimated by audio playbacks as 0.32 hyaenas/km². Lion (Panthera leo) density, determined from the ratio of hyaenas to lions, was 0.11 lions/km². Across six ecosystems including Selous, there were strong negative correlations between wild dog and hyaena densities (r = −0.92; p = 0.01) and between wild dog and lion densities (r = −0.91; p = 0.03). Hyaenas out-numbered wild dogs by ratios ranging from 8:1 to 122:1. Ratios of lions to wild dogs ranged from 3:1 to 21:1. The diets of hyaenas and wild dogs overlap extensively; those of wild dogs and lions show less overlap. Where hyaenas are common and visibility is good, interference competition from hyaenas at wild dog kills is common and reduces wild dogs’ feeding time. Where hyaena density is lower and visibility is poor, interference competition at wild dog kills is rare. Wild dogs are commonly killed by lions and occasionally by hyaenas. These data suggest that competition with spotted hyaenas may limit or exclude wild dogs when hyaena density is high. Competition with lions appears less intense, but direct predation by lions on wild dogs is important. Competition and predation by larger carnivores may be of broad importance to the conservation of wild dogs and other medium-sized carnivores.
The positive correlation between total large herbivore biomass and rainfall in arid/eutrophic savannas also applies for 19 out of 23 individual herbivore species. Herbivores are divided into arid and moist savanna species, on the basis of the rainfall at which their peak population densities occur on soils of low nutrient status (<820 and = or >1000 mm, respectively). These groups reflect the division between arid/eutrophic and moist/dystrophic savannas. Arid savanna herbivores, which dominate total herbivore biomass, include grazers, mixed feeders and browsers and are less selective feeders. Their biomass tends to decline at higher levels of rainfall on low nutrient status soils and only the larger species are widespread in moist/dystrophic savannas where mean annual rainfall >1000 mm. Moist savanna species are mainly highly selective grazers and occur widely in moist/dystrophic savannas. Their biomasses are usually low and show a positive correlation with rainfall on soils of low nutrient status. Large carnivore biomass is positively correlated with rainfall in arid/eutrophic savannas, reflecting a positive relationship to prey biomass. The biomass of individual carnivore species is most closely correlated with the biomass of the preferred size class of prey. Natural populations of large savanna mammals tend to be close to the limits set by their food resources. -from Author