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

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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
ratios
Chris Carbone1,*, Nathalie Pettorelli1
and Philip A. Stephens2
1
Institute of Zoology, Zoological Society of London, Regent’s Park,
London NW1 4RY, UK
2
School of Biological and Biomedical Sciences, University of Durham,
South Road, Durham DH1 3LE, UK
*Author for correspondence (chris.carbone@ioz.ac.uk).
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;
metabolism
1. INTRODUCTION
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.
2. MATERIAL AND METHODS
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].
3. RESULTS
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
3,195
¼140.9, p,
0.001, r
2
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 http://dx.doi.org/
10.1098/rsbl.2010.0996 or via http://rsbl.royalsocietypublishing.org.
Biol. Lett. (2011) 7, 312–315
doi:10.1098/rsbl.2010.0996
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
4. DISCUSSION
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
ave.
weight
(kg)
no.
populations
carnivore density, N(km
22
)
prey biomass,
P(kg km
22
) range
(min–max)
range
(min–max) slope intercept r
2
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
Canadian
lynx
Lynx canadensis 11.2 28 0.02–0.226 0.4954 0.0047 0.65 16.8–1386.0
European
badger
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
spotted
hyena
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
a
estimated parameters AIC DAIC wr
2
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
a
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)
on June 10, 2011rsbl.royalsocietypublishing.orgDownloaded from
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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0.1
0
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1.0
–1.0 –0.5 0 0.5 1.0 1.5 2.0 2.5 3.0
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density and log prey biomass density
lo
g
carnivore bod
y
mass (M, k
g
)
Figure 1. The slope (s) of the predator–prey population
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... Karanth et al. (2004b) reported a functional relationship between large predators' abundances and their prey under a wide range of ecological conditions. Prey density is one of the important factors determining the abundance of tigers (Karanth et al., 2004b) and leopards (Carbone, Pettorelli & Stephens, 2011). Similar studies have found multiple correlates associated with tiger and leopard densities. ...
... The undisturbed habitats are associated with high prey abundance (wild prey) and low anthropogenic influence. The densities of tigers and leopards have been reported to depend on prey biomass (Karanth et al., 2004b;Carbone & Gittleman, 2002;Khorozyan, Malkhasyan & Abramov, 2008;Carbone, Pettorelli & Stephens, 2011). Although tiger density was positively correlated with sal dominated habitats; however, contrary to our expectations, the tiger density was also positively associated with disturbed habitats. ...
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... As the currency of ecosystem function, energetic demand influences the behavioral decisions animals make, dictating, where and how often they feed [1][2][3][4]. Mammalian apex carnivores in particular experience intrinsically elevated energy demands associated with large body size [5], endothermy [6] and carnivory [7,8]. ...
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Background Environmental conditions can influence animal movements, determining when and how much animals move. Yet few studies have quantified how abiotic environmental factors (e.g., ambient temperature, snow depth, precipitation) may affect the activity patterns and metabolic demands of wide-ranging large predators. We demonstrate the utility of accelerometers in combination with more traditional GPS telemetry to measure energy expenditure, ranging patterns, and movement ecology of 5 gray wolves ( Canis lupus ), a wide-ranging social carnivore, from spring through autumn 2015 in interior Alaska, USA. Results Wolves exhibited substantial variability in home range size (range 500–8300 km ² ) that was not correlated with daily energy expenditure. Mean daily energy expenditure and travel distance were 22 MJ and 18 km day ⁻¹ , respectively. Wolves spent 20% and 17% more energy during the summer pup rearing and autumn recruitment seasons than the spring breeding season, respectively, regardless of pack reproductive status. Wolves were predominantly crepuscular but during the night spent 2.4 × more time engaged in high energy activities (such as running) during the pup rearing season than the breeding season. Conclusion Integrating accelerometry with GPS telemetry can reveal detailed insights into the activity and energetics of wide-ranging predators. Heavy precipitation, deep snow, and high ambient temperatures each reduced wolf mobility, suggesting that abiotic conditions can impact wolf movement decisions. Identifying such patterns is an important step toward evaluating the influence of environmental factors on the space use and energy allocation in carnivores with ecosystem-wide cascading effects, particularly under changing climatic conditions.
... The density of leopards has been found to be associated with prey abundance. A decrease in prey abundance is likely to result in a reduced density of large carnivore species (Carbone et al., 2011). ...
Conference Paper
It is suggested climate change contributes considerably to global biodiversity loss. Southeast Asia, one of the world’s richest biodiversity hotspots, is predicted to lose most of its species by 2100. Hence, it is important to identify the key impact of environmental changes in order to develop more appropriate and effective conservation plans to mitigate species extinction risks. In this thesis, Species Distribution Modelling (SDM) techniques were used to predict potential species distributions in relation to 6 climatic variables. The effects of climate changes on large mammal distributions were examined across three time intervals: past (the last interglacial ~120,000 – 140,000 years before present), present (AD 1945 - present) and future (2050); while rates of species range shifts between the time intervals were also determined. It is found that large mammals are particularly vulnerable to climate change. The species will have to move 33 – 105 times faster than they once did in the past in order to search out suitable habitat. There is also evidence of niche conservatism and niche shift among the taxa. However, species niche shifts likely result from anthropogenic factors. Limited availability of species occurrence data in many parts of the world leads to an increased use of species range maps in research on species responses to changing environments. Predictions based on SDMs suggest that relying on a single data source may skew the species’ realistic threatened status and misguide conservation planning. The Zonation software was employed to evaluate the effectiveness of protected areas (PAs) in Thailand under future warming climate and identify high priority areas. Currently, nearly 60% of high priority areas fall within the PAs. In the future, the conservation values of the PAs are expected to remain relatively unchanged. However, it is suggested that enhancing PAs connectivity in the northern part of the country may yield a high return on conservation investment. A deliberate and consistent conservation effort will also be needed to maintain the effectiveness of the existing PAs.
... Stephens, 2011) and time periods (Jablonski et al., 1996; Yom-Tov, 2001; Van Buskirk et al., 2010). While evaluation of body size may be relatively easy for captive individuals it is more difficult for free-ranging animals. ...
Thesis
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Determining populations of leopards (Panthera pardus) is important for both their conservation and also that of their prey. Camera-trapping has emerged as a powerful and non-invasive tool for studying carnivores in their natural habitats especially for species that are elusive or occur at low densities such as leopards. This thesis presents the Baited-Camera Trapping (BCT) method of censusing leopards, a Zimbabwean conceived design modification of the conventional unbaited setup. This method has been documented to improve capture rates and provide robust and novel data for leopard surveys in savanna environments. This study used single cameras coupled with bait to survey a population of leopards at Malilangwe Wildlife Reserve (MWR), a privately owned medium-sized property in south-eastern Zimbabwe. The objectives of the study were to: (1) conduct a cost-benefit analysis to determine the optimal density and exposure length of baits for censusing leopards at MWR, (2) develop a technique for estimating body dimensions of leopards from camera trap photographs, (3) determine the influence of competing carnivores on the feeding habits of leopards in a savanna ecosystem, and (4) to review the application of the BCT method in comparison with conventional camera trapping. Data were collected from July 2017 to January 2018 and the CAPTURE software was used for population size analysis and the Statistical Package for Social Scientists were used for cost-benefit analyses. Generalized Linear Mixed Effects Modelling, performed using the R statistical software, was used to compare actual and photograph based body measurement data as well as to analyze the influence of competing predators on feeding duration and resting distances of leopards at bait stations. This study estimated the leopard population at MWR at 61 (61-67) individuals and concludes that using BCT stations at a density of 0.24 cameras km-2 km for 9 days is the optimal and cost-effective sampling effort required to provide reliable population statics in semi-arid savannas. The study established that the type of body measurement and the posture of a leopard in a photograph had a significant influence on the accuracy of image-based measurements. Body length measurements taken from the level back-straight forelimb-parallel tail posture were the most accurate [mean error = 2.0 cm (1.5-2.7 cm)] while head-to-tail and tail length measurements and variations from the level back-straight forelimb-parallel tail posture did not provide sufficient accuracy. The findings also showed that the presence of male leopards at feeding locations was associated with shorter feeding durations while lion presence caused feeding leopards to wait longer from bait sites. The thesis provides the first published record of the BCT method outlining a step-by-step procedure for replication by other researchers and a comparative review of the method with traditional survey approaches. The findings in this thesis underscore the ability of BCT method to investigate multiple leopard population ecology questions which enhances its cost-benefit ratio. Furthermore, the method provides new information which can broaden the scope of research and inform management and policy direction. It is recommended that (i) researchers and managers incorporate cost-benefit analysis in their work as this is essential for informing effective application of effort and resources, (ii) researchers take advantage of the BCT method to collect behaviour and morphological data for species that are less understood such as leopards to maximize on the capital investment, (iii) managed wildlife areas that contain leopards consider the uptake of the BCT techniques as a wide encompassing population monitoring option, and (iv) regulatory authorities that supervise hunting operations such as the Zimbabwe Parks and Wildlife Management Authority adopt the BCT technique to enhance their information management portfolios and quota setting for sustainable harvest practises.
... We suggest that the energetic costs of avoiding risk from humans may itself lead to reduced long-term space use for many wildlife species living in human-dominated landscapes, potentially contributing to the global trend of diminished movements near people. Our findings demonstrate that behavioral changes induced by the fear of humans can substantially impact an animal's energy budget, in this case, exacerbating the already high energetic demands of a large carnivore (11,24,40). Managing risk from people may therefore come at the cost of reductions in a range of other crucial behaviors, including long-range movements and territorial defense. ...
Article
Energetic demands and fear of predators are considered primary factors shaping animal behavior, and both are likely drivers of movement decisions that ultimately determine the spatial ecology of wildlife. Yet energetic constraints on movement imposed by the physical landscape have only been considered separately from those imposed by risk avoidance, limiting our understanding of how short-term movement decisions scale up to affect long-term space use. Here, we integrate the costs of both physical terrain and predation risk into a common currency, energy, and then quantify their effects on the short-term movement and long-term spatial ecology of a large carnivore living in a human-dominated landscape. Using high-resolution GPS and accelerometer data from collared pumas ( Puma concolor ), we calculated the short-term (i.e., 5-min) energetic costs of navigating both rugged physical terrain and a landscape of risk from humans (major sources of both mortality and fear for our study population). Both the physical and risk landscapes affected puma short-term movement costs, with risk having a relatively greater impact by inducing high-energy but low-efficiency movement behavior. The cumulative effects of short-term movement costs led to reductions of 29% to 68% in daily travel distances and total home range area. For male pumas, long-term patterns of space use were predominantly driven by the energetic costs of human-induced risk. This work demonstrates that, along with physical terrain, predation risk plays a primary role in shaping an animal’s “energy landscape” and suggests that fear of humans may be a major factor affecting wildlife movements worldwide.
... Assessing temporal overlap in activity patterns of carnivores and their preys may provide valuable insights into behavioural mitigations of competition (Saisamorn et al. 2019;Mori et al. 2020a). In detail, interactions among mammalian carnivores and their prey species may be extremely difficult to be determined, due to their cryptic nature and low abundance (Carbone et al. 2011;Ripple et al. 2014). Yet, understanding how carnivores interact with their prey is pivotal for their conservation, as it can provide information on species niche preferences (Ripple et al. 2014). ...
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Assessing carnivores and prey temporal activity patterns as well as their overlap provides valuable insights into behavioural mitigations of competition. Moon phases may also play an important role in shaping wild mammals’ activity rhythms with prey showing peaks of activity in darkest nights. Camera trapping has enriched the possibility to conduct systematic studies of activity patterns and temporal niche overlap on mammalian guilds. In this study, we used camera traps to investigate intra-guild interactions and temporal partitioning among three meso-carnivores and their common prey in two Mongolian areas characterized, respectively, by a grassland and a forest–alpine meadow. We detected a moderate–high interspecific overlap in red foxes, pikas and tolai hares. We found a moderate overlap of temporal activity patterns among nocturnal carnivores as well as among nocturnal prey species. Interestingly, we observed a moderate overlap between hares and meso-carnivores. Amongst nocturnal species, the red fox and the stoat had a peak in activity in the brightest nights, the stone marten and the Mongolian silver vole preferred to range in dark nights, whereas activity of the tolai hare was not dependent on moon phases. Our work provides some first insights of temporal pattern interactions within a small- and meso-mammal assemblage in Central Asia. Our results indicate that meso-carnivores and their potential prey can co-occur in Central Mongolia by means of temporal partitioning.
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The spotted hyena (Crocuta crocuta Erxleben) and the lion (Panthera leo Linnaeus) are two of the most abundant and charismatic large mammalian carnivores in Africa and yet both are experiencing declining populations and significant pressures from environmental change. However, with few exceptions, most studies have focused on influences upon spotted hyena and lion populations within individual sites, rather than synthesizing data from multiple locations. This has impeded the identification of over-arching trends behind the changing biomass of these large predators. Using partial least squares regression models, influences upon population biomass were therefore investigated, focusing upon prey biomass, temperature, precipitation, and vegetation cover. Additionally, as both species are in competition with one other for food, the influence of competition and evidence of environmental partitioning were assessed. Our results indicate that spotted hyena biomass is more strongly influenced by environmental conditions than lion, with larger hyena populations in areas with warmer winters, cooler summers, less drought, and more semi-open vegetation cover. Competition was found to have a negligible influence upon spotted hyena and lion populations, and environmental partitioning is suggested, with spotted hyena population biomass greater in areas with more semi-open vegetation cover. Moreover, spotted hyena is most heavily influenced by the availability of medium-sized prey biomass, whereas lion is influenced more by large size prey biomass. Given the influences identified upon spotted hyena populations in particular, the results of this study could be used to highlight populations potentially at greatest risk of decline, such as in areas with warming summers and increasingly arid conditions.
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Apex predators are threatened globally, and their local extinctions are often driven by failures in sustaining prey acquisition under contexts of severe prey scarcity. The harpy eagle Harpia harpyja is Earth's largest eagle and the apex aerial predator of Amazonian forests, but no previous study has examined the impact of forest loss on their feeding ecology. We monitored 16 active harpy eagle nests embedded within landscapes that had experienced 0 to 85% of forest loss, and identified 306 captured prey items. Harpy eagles could not switch to open-habitat prey in deforested habitats, and retained a diet based on canopy vertebrates even in deforested landscapes. Feeding rates decreased with forest loss, with three fledged individuals dying of starvation in landscapes that succumbed to 50-70% deforestation. Because landscapes deforested by > 70% supported no nests, and eaglets could not be provisioned to independence within landscapes > 50% forest loss, we established a 50% forest cover threshold for the reproductive viability of harpy eagle pairs. Our scaling-up estimate indicates that 35% of the entire 428,800-km 2 Amazonian 'Arc of Deforestation' study region cannot support breeding harpy eagle populations. Our results suggest that restoring harpy eagle population viability within highly fragmented forest landscapes critically depends on decisive forest conservation action.
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Felidae species show a great diversity in their diet, foraging and hunting strategies, from small to large prey. Whether they belong to solitary or group hunters, the behavior of cats to subdue resisting small or large prey presents crucial differences. It is assumed that pack hunting reduces the per capita risk of each individual. We hypothesize that the sacroiliac articulation plays a key role in stabilizing the predator while subduing and killing prey. Using CT-scan from 59 felid coxal bones, we calculated the angle between both iliac articular surfaces. Correlation of this inter-iliac angle with body size was calculated and ecological stressors were evaluated on inter-iliac angle. Body size significantly influences inter-iliac angle with small cats having a wider angle than big cats. Arboreal species have a significantly larger angle compared to cursorial felids with the smallest value, and to scansorial and terrestrial species with intermediate angles. Felids hunting large prey have a smaller angle than felids hunting small and mixed prey. Within the Panthera lineage, pack hunters (lions) have a larger angle than all other species using solitary hunting strategy. According to the inter-iliac angle, two main groups of felids are determined: (i) predators with an angle of around 40° include small cats (i.e., Felis silvestris, Leopardus wiedii, Leptailurus serval, Lynx Canadensis, L. rufus ; median = 43.45°), the only pack-hunting species (i.e., Panthera leo ; median = 37.90°), and arboreal cats (i.e., L. wiedii, Neofelis nebulosa ; median = 49.05°), (ii) predators with an angle of around 30° include solitary-hunting big cats (i.e., Acinonyx jubatus, P. onca, P. pardus, P. tigris, P. uncia ; median = 31.80°). We suggest different pressures of selection to interpret these results. The tightening of the iliac wings around the sacrum probably enhances big cats’ ability for high speed and large prey control. In contrast, pack hunting in lions reduced the selective pressure for large prey.
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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.
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Data on lion home range size, pride size, density, group size, cub survival, litter size and adult sex ratio were extracted from studies carried out in 10 habitats. The data were compared with five measures of food supply: mean prey biomass, prey biomass during the season of greatest abundance, prey biomass during the season of least abundance, biomass of middle-sized prey species (i.e. those with mean adult live-weights between 50 and 250 kg), and the mean size of carcasses fed on by lions. The results indicated that range size is inversely correlated with the abundance of prey during the period of least abundance, but not with overall prey abundance. Range size showed no consistent variation with pride size or with minimum metabolic requirements. Pride size (measured in terms of average number of animals per pride and average number of adult females) and cub survival strongly correlated with lean season food abundance. No relationship was found between group size or litter size and any of the measures of food supply Adult sex ratio did not vary consistently with food supply or lion density, although the data did suggest that prides inhabiting small, circumscribed reserves may experience less inter-male competition and this, in turn, may affect the adult sex ratio.
Article
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.
Article
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.
Article
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