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Terrestrial large carnivores have great ecological, economic and cultural importance, but are in global decline due to habitat loss, prey depletion, poaching, retributive killing and regulated hunting. While regulated carnivore hunting potentially reduces conflict with humans and livestock, increases social tolerance and provides revenue for conservation, it can also drive population declines. Some policies regulating carnivore hunting acknowledge and address negative effects on demography and population dynamics, but others do not. Using wolves as an example, we identify four aspects of hunting policy that do not align well with ecological theory and data, and suggest resolutions for these problems that have broad relevance to exploited carnivore populations.
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INSIGHTS |
PERSPECTIVES
18 DECEMBER 2015 • VOL 350 ISSUE 6267 1473SCIENCE sciencemag.org
PHOTO: © DESIG N PICS I NC/ALAMY STO CK PHOTO
dressing underlying issues. Alternatives, such
as creating a new position within OSTP, are
insufficient to navigate complex interagency
chains of command.
Last, to mature and learn, oversight in-
stitutions must approach governance as
a long-term strategic challenge in need of
management and research, as well as the in-
volvement of the general public. Investing in
interdisciplinary research centers is one way
to bring focus to critical risk governance top-
ics like leadership, organization, and learning
in a future of distributed biological knowl-
edge and technology. If we do not address the
foundational challenge of emergent technol-
ogies and biological risk properly, we should
expect reactive and poorly conceived restric-
tions on potentially beneficial research, as
well as many more normal “accidents” with
increasingly consequential risks to people
and the environment, as biotechnology pro-
liferates globally.
REFERENCES AND NOTES
1. White House, “Next steps to enhance biosafety and biosecu-
rity in the United States” [memo] (White House, Washington,
DC, 2015).
2. White House, “Enhancing biosafety and biosecurity in the
United States” [memo] (White House, Washington, DC,
2015).
3. A. Young , N. Penzen stad ler, US A To d a y , 28 May 2015; http://
bit.ly/SecretBiolabs.
4. Committee for Comprehensive Review of DoD Laboratory
Procedures, Processes, and Protocols Associated with
Inactivating Bacillus anthracis Spores, “Review Committee
report: Inadvertent live shipment of live Bacillus anthracis
spores by DoD” (DOD, Washington, DC, 2015); http://bit.ly/
ShipmentSafety.
5. GAO, Preliminary Observations on Federal Efforts
to Address Weaknesses Exposed by Recent Safety
Lapses (GAO, Washington, DC, 2015); www.gao.gov/
assets/680/671679.pdf.
6. F. Sharples et al., Potential Risks and Benefits of Gain-of-
Function Research: Summary of a Workshop (National
Academies Press, Washington, DC, 2015).
7. H. V. Fineberg, Science 347, 929 (2015).
8. K. A. Oye et al., Science 345, 626 (2014).
9. O. S. Akbar i et al., Science 349, 927 (2 015) .
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Institutional Oversight of Life Sciences Dual Use Research
of Concern (Government Printing Office, Washington, DC,
2014); www.phe.gov/s3/dualuse/Documents/durc-policy.
pdf.
1 1. M. Roge rs, Roll. Stone 187, 37 (1975).
12 . S. Wr igh t, Perspect. Biol. Med. 44, 235 (2001 ).
13. OSTP, DHHS, U.S. Government Gain-of-Function Deliberative
Process and Research Funding Pause on Selected Gain-of-
Function Research Involving Influenza, MERS, and SARS
Viruses (OSTP, DHHS, Washington, DC, 2014); www.phe.gov/
s3/dualuse/Documents/gain-of-function.pdf.
14. White House, “Doing diligence to assess the risks and ben-
efits of life sciences gain-of-function research” [blog] (White
House, Washington, DC, 2014); http://bit.ly/DiligentAssess.
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new-game-new-rules.
16 . D. A. Relm an, J. Infect. Dis. 209, 170 (2 014) .
17. K. W. Bern ard, Biosecur. Bioterror. 11, 157 (2013).
ACKNOWLEDGMENTS
The authors thank S. Falkow, D. Endy, A. Zegart, S. Sagan, K.
Bern ard, K. Oye , S. Weiss-Eva ns, C. Perro w, S. Hecke r, and L.
Eden for helpful discussions. D.A.R. is a former member of
the NSABB. F.F. was a member of the President’s Council on
Bioethics.
10.1126/science.aad8849
CONSERVATION POLICY
Questionable policy for large
carnivore hunting
U.S. wolf-hunting policies do not align with ecological
theory or data
By Scott Creel,1,2* Matthew Becker,2
David Christianson,3 Egil Dröge,1 Neil
Hammerschlag,4 Matt W. Hayward,5 Ullas
Karanth,6 Andrew Loveridge,7 David W.
Macdonald,7 Wigganson Matandiko,1
Jassiel M’soka,1,8 Dennis Murray,9 Elias
Rosenblatt,1 Paul Schuette10
Terrestrial large carnivores are in rapid
global decline, with consequences for
ecosystem structure and function.
Among drivers of these declines, le-
gal hunting is unique because it is
intentional and thus relatively easily
controlled. Although regulated carnivore
hunting potentially reduces conflict and pro-
vides revenue for conservation, it can also
drive population declines (15).
Some policies regulating carni-
vore hunting address negative
effects on demography and population dy-
namics, but others do not. Here, we use wolf
harvesting in the western United States to
illustrate four aspects of policy that do not
align well with ecological theory and data,
and we suggest resolutions.
Policies regulating human effects on lions,
cougars, leopards, and tigers have responded
to research by moving to better evaluate and
mitigate demographic costs (1, 2, 5, 6). For e x-
ample, policies for lions (Panthera leo) include
temporary hunting closures to allow popula-
tion recovery (5) and reduced quotas with
sex- and age-limited harvesting (2). None-
theless, hunting policies for large carnivores
still often suffer from a lack of science-based
guidance. For example, policies for harvest of
wolves (Canis lupus) in the Northern Rocky
Mountains Distinct Population Segment
(NRM DPS) suggest that annual harvest of
up to 50% of the population has little or no
effect on dynamics. Wolves were reintro-
duced in the mid-1990s, and the NRM DPS
grew steadily until 2009 (see the chart, part
A). Legal hunting began immediately after
removal of the Endangered Species Act (ESA)
POLI CY
Where next? Survival
and reproduction of
wolves in the Northern
Rockies have declined.
Published by AAAS
INSIGHTS |
PERSPECTIVES
1474 18 DECEMBER 2015 • VOL 350 ISSUE 6267 sciencemag.org SCIENCE
GRAPHS: P. HUEY/SCIENCE
protections in 2008, occurred in 3 of the 5
years considered here (2009–10 and 2011–13),
and continues today. A recent review of cur-
rent policies by the U.S. Fish and Wildlife Ser-
vice (USFWS) concluded that harvesting “has
not increased any risk” to the NRM DPS (7).
Several patterns in the data used to draw
these conclusions call them into question
(see the chart). We analyze previously pub-
lished results and information directly re-
ported in USFWS species recovery reports
[see supplementary materials (SM)], which
have been used as the basis for delisting and
increasingly heavy harvest. The issues identi-
fied by this analysis are not unique to wolves,
and the recommendations that it yields are
relevant to other large carnivores.
SIZE, STRUCTURE, DYNAMICS. For
wolves (and most other large carnivores),
adult mortality rates are low in the absence
of human offtake (8), which leaves little scope
for hunting to substitute for other causes of
death (compensatory mortality) (8, 9). Hence,
adult mortality rates increase in an additive,
nearly one-to-one manner as human offtake
increases (see the chart, part B) (3, 8).
Increased adult mortality was correlated
with a decrease in wolf pack size since the
onset of legal hunting in Montana and Idaho,
where pack size declined by 29 to 33% be-
tween 2008 and 2013 (10). Beyond reducing
group size, harvesting mortality can also
disrupt social organization (3, 4), and both
40
100
400
1000
1995 2000 2005 2010
State
Year
Wolves counted
3 states
ID
MT
WY
State
3 states
ID
MT
WY
Population
ID
MT
GYA
Region
CID
NWMT
GYA
0.2
0.4
0.6
0.8
1.0
0.0 0.1 0.2 0.3 0 .4 0.5
Anthropogenic kill rate
Annual survival
0.5
1.0
1.5
2.0
0.0 0.1 0.2 0.3 0 .4 0.5
Anthropogenic kill rate
Population growth rate
0.1
0.2
0.3
0.4
2009 2010 2011 2012 2013
Year
Anthropogenic kill rate
A
B
C
D
Temporal trends in dynamics of wolves. In the
original NRM DPS, data were reported by state (ID,
Idaho; MT, Montano; WY, Wyoming; or all three states) or
regional boundaries (NWMT, Northwest Montana; GYA,
Greater Yellowstone Area; CID, Central Idaho), in USFWS
population recovery reports (18). See SM for details.
(A) Population counts since wolf reintroduction in the
mid-1990s, described by USFWS as minimum number
known alive. Red line denotes the onset of legal hunting.
Ordinate is log10 scale d. (B) Human offtake causes wolf
survival rates to decline in an additive manner, with
little evidence of compensation. Each point represents 1
year (8), and shading shows 95% confidence intervals.
The red line denotes completely additive mortality. (C)
Recent data (10) confirm the prior conclusion (3) that
anthropogenic mortality has an additive (rather than
compensatory) effect on annual population growth
rates ( λ), and that anthropogenic mortality above ~25%
typically yields a declining population with λ< 1. Each
point represents 1 year (1998–2014), and shading shows
95% confidence intervals. (D) Total anthropogenic
mortality has increased substantially since the onset
of hunting [denoted with red line as in (A)], doubling
within the original NRM DPS between 2010 and 2013,
coincident with a shift from steady population growth to
gradual decline. Total anthropogenic mortality combines
sport hunting with other direct human killing, primarily
in response to predation on livestock, and expresses it
as a proportion of the population count.
Published by AAAS
18 DECEMBER 2015 • VOL 350 ISSUE 6267 1475
effects can reduce juvenile survival and re-
cruitment (addition to the population, which
depends on litter size and juvenile survival).
Pup survival in 10 Idaho packs decreased
from 60% in years without hunting to 38%
in years with hunting (11). Direct trapping or
shooting of pups could explain only 27% of
this decrease, with the rest attributed to dis-
ruption of pack size and social organization
(11). Recruitment showed a similar decrease
in years with hunting, dropping from 3.2 to
1.6 pups recruited per pack (11).
Because the population growth rate (λ) is
equal to the sum of the adult survival rate
and per-capita recruitment, reduced local
population growth is inevitable when adult
survival and juvenile recruitment decline
(see the chart, part C). The mean annual sur-
vival of NRM wolves before legal hunting was
0.75 [95% confidence interval (CI) of 0.728 to
0.77 2] (12), so population decline would be
expected if recruitment fell below 0.25 re-
cruits per individual (13). The mean pack size
and recruits per pack reported for Idaho (10,
11) suggest that recruitment dropped below
this threshold by 2013, to 0.20 recruits per
individual. This would predict population
decline even if harvest mortality was com-
pletely compensatory. This prediction is cor-
roborated by a 25% decrease in the number
of wolves harvested in Idaho and Montana in
2013 (10, 14), despite extended hunting sea-
sons and liberalized hunting limits that have
increased the proportion of the population
killed (see the chart, part D), a pattern that
is commonly taken to indicate that harvest is
driving a decline.
BOUNDARIES, DETECTION, GOALS.
Several lessons can be learned by considering
discrepancies between our analysis and the
recent USFWS review concluding that policy
has not increased risk to these populations.
These lessons are broadly applicable to other
exploited carnivores.
Effects of a policy must be considered
within the area to which it applies. Carni-
vore distributions do not follow political
borders, but hunting policies do. The rela-
tively constant number of wolves within the
entire NRM DPS has been taken as evidence
that state-level policies do not increase risk
for NRM wolves. However, the DPS origi-
nally included only Montana, Idaho, and
Wyoming, and has expanded to include
wolves in Washington and Oregon. If one
evaluates a state’s policies by examining ef-
fects within its borders, it is reasonable to
conclude that risks have increased in some
cases. To illustrate, International Union for
Conservation of Nature Red List Criterion
C1 classifies a population segment as endan-
gered if it holds fewer than 2500 individuals
and has declined by ≥20% in <5 years. In
Idaho, delisting and subsequent legal har-
vest produced a 22.4% decline in population
counts from 2008 to 2013 (from 849 to 659)
(10). With no stated population target (other
than avoiding relisting under the ESA), cur-
rent policy does not adequately define a
shut-off for this decline.
Evaluation of effects on populations must
consider sampling design and effort to con-
trol for effects on detection. First, when sam-
pling effort and population counts change
in parallel, there is reason to believe that
trends in the counts might not describe true
dynamics. For example, while the Idaho pop-
ulation count decreased 22.4% from 2008 to
2013, the Montana count increased compa-
rably (see the chart, part A) (10), a surprising
result given reported decreases in survival
(8) and reproduction (11). During this period,
Montana added additional staff and volun-
teers to monitor the wolf population and
initiated a program to gather sightings from
the public (eventually with >80,000 reports
annually) (10). Second, the USFWS evalua-
tion of wolf population trends (7) incorrectly
asserts that these counts represent “the ab-
solute minimum number of wolves alive.” In
Idaho, which holds the largest segment of
the NRM DPS, tabulated counts are adjusted
by substituting mean pack size for smaller
pack counts that might have been incom-
plete (74% of packs in 2013) and then multi-
plying the adjusted count by 1.125 to account
for unseen wolves suspected to be living out-
side of packs (10). Consequently, the Idaho
estimate is ~1.75 times the number of indi-
viduals known to be alive, and the biggest
increase in the minimum estimated NRM
DPS occurred in 2006 with the adoption of
this method. Recent studies of lions and ti-
gers illustrate the importance of population
monitoring that accounts for sampling effort
and detection (5, 6).
Policy cannot ignore the distinction be-
tween local compensation and immigration
from an external source population. The
suggestion that wolves “can apparently with-
stand human-caused mortality of 28 to 50%
without declining’’ (15) derives from studies
[e.g., (16, 17)] in which an external source
population was available to provide immi-
grants to offset local losses (13). For lions,
harvest mortality outside of national parks
affects population dynamics within adjacent
parks (4, 5). A clear focus on the distinction
between true compensation and source-sink
dynamics would improve policy.
Clearly defined, quantitative policy goals
are needed for science-based evaluation. Such
goals require consideration of population via-
bility and sustainable offtake based on robust
science by using all available data. Policies for
hunting of wolves in the NRM do not specify
maximum harvest or targets for population
size or growth (other than avoiding decline
sufficient to trigger relisting under the ESA).
Well-regulated hunting of large carnivores
can yield costs and benefits for conservation
but requires attention to both.
REFERENCES AND NOTES
1. H . S. Coole y et al., Ecology 90, 2913 (2009).
2. K. Whitman et al., Nature 428, 175 (2004).
3. S . Creel, J. J. Rot ella, P LOS ON E 5, e12918 (2010).
4. A. J. Loveridge et al., Biol. Conserv. 134, 548 (2007).
5. E. Rosenblatt et al., Biol. Conserv. 180, 176 (2014).
6. K. U. Karanth et al., Anim. Conserv. 6, 141 (2003).
7. M. D. Jiminez, U.S. Fish and Wildlife Service Review of the
2013 Wolf Population in the NRM DPS (USFWS, Helena, MT,
2014) .
8. D. L. M urray et al. , Biol. Conserv. 143, 2514 (2010).
9. A. M. Sparkman et al., PLOS ON E 6, e20868 (2011).
10. USFWS et al., Northern Rocky Mountain Wolf Recovery
Program 2013 Interagency Final Report (USFWS Ecological
Services, Helena, MT, 2014).
11 . D. E. Ausband et al., Anim. Conserv. 18, 415 (2015).
12. D. W. Smith et al., J. Wildl. Manage. 74, 620 (2010).
13. The relation between λ and anthropogenic mortality has
been debated (3, 17). Recruitment is collinear with anthro-
pogenic mortality (3, 11) and is a direct, additive component
of λ. Thus, its inclusion as a predictor of λ is not statistically
valid and would produce biased estimates of the relation
between λ and human offtake. Analyses with this problem
[e.g., ( 17)] have been used to suggest that annual harvest
rates of 50% or more are sustainable for wolves.
14. Oregon and Washington do not yet allow hunting.
Wyoming’s wolf management plan was challenged in
court, and the state’s regulations for wolf hunting were
only implemented briefly in 2008 and then again in 2012.
Thus, data are not yet available to assess the conse-
quences of the policy that Wyoming has proposed, which
would allow unlimited year-round hunting in most of the
state, as with coyotes.
15. Idaho Wolf Conservation and Management Plan
(Idaho Department of Fish and Game, Boise, ID,
2015); www.fishandgame.idaho.gov/public/wildlife/
wolves/?getPage=161.
16. L. G. Adams et al., Wildl. Monogr. 170, 1 (2008).
17. J. A. Gude et al., J. Wildl. Manage. 76, 108 (2012).
18. Endangered Species, Western Gray Wolf (USFWS, 2015);
www.fws.gov/mountain-prairie/es/grayWolf.php.
SUPPLEMENTARY MATERIALS
www.sciencemag.org/content/350/6267/1473/suppl/DC1
10.1126/science.aac4768
“policies for harvest of
wolves in the Northern Rocky
Mountains…suggest that
annual harvest of up to 50%
of the population has little
or no effect….
1Montana State University, Bozeman, MT 59717, USA. 2Zambian
Carnivore Programme, Mfuwe, Zambia. 3University of
Arizona, Tucson, AZ 85721, USA. 4University of Miami, Miami,
FL 33149, USA. 5Bangor University, Bangor, LL57 2UW, UK.
6Wildlife Conservation Society, Bangalore, Karnataka 560
070, Ind ia. 7WildCRU, Oxford University, Recanati-Kaplan
Centre, Oxfordshire OX13 5QL, UK. 8Zambia Wildlife Authority,
Chilanga, Zambia. 9Trent University, Peterborough, Ontario
K9J 7B8, Canada. 10State University of New York College of
Environmental Science and Forestry, Syracuse, NY 13210, USA.
*Corresponding author. E-mail: screel@montana.edu
SCIENCE sciencemag.org
Published by AAAS
... Although the prior literature would seem to guide decisionmakers in Wisconsin to choose a Fall 2021 wolfs-hunt quota that would not change the population, the wide variation in estimates above and the novelty of a second wolf-hunt in a single year produces new and greater uncertainties than the literature addresses. Also, in a series of papers on wolf science and policy in Wisconsin, we have shown how omissions of a history of methodological changes in censuses, censoring the information available in the disappearances of marked wolves, and a lack of alternative management scenarios altogether could both distort wolf policy and mire the science in uncertainties due to methods [23,33,[37][38][39][40][41][42][43][44][45][46]. ...
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ABSTRACT  Our understanding of wolf (Canis lupus) population dynamics in North America comes largely from studies of protected areas, at-risk populations, and wolf control programs, although most North American wolves experience moderate levels of regulated harvest. During 1986–1992, we investigated the population dynamics and harvests of wolves in the newly created Gates of the Arctic National Park and Preserve in northern Alaska, USA, where wolves were harvested by local residents. Our objectives were to determine wolf abundance, estimate important vital rates (i.e., productivity, survival, emigration), and characterize wolf harvests. We monitored 50 radiocollared wolves in 25 packs over 4 years (Apr 1987–Apr 1991) to assess patterns of dispersal, emigration, survival and mortality causes in the wolf population. We determined pack sizes, home ranges, and pups per pack in autumn (1 Oct) for instrumented wolf packs, and calculated wolf densities in autumn and spring (15 Apr) based on the number of wolves in instrumented packs and the aggregate area those packs inhabited. We also gathered information from local hunters and trappers on the timing, location, methods, and sex-age composition of wolf harvests during 6 winter harvest seasons (Aug 1987–Apr 1992).Wolf densities averaged 6.6 wolves per 1,000 km2 and 4.5 wolves per 1,000 km2 in autumn and spring, respectively, and spring densities increased by 5% per year during our study. On average, pups constituted 50% of the resident wolf population each autumn. An estimated 12% of the population was harvested annually. Natural mortality, primarily intraspecific strife, equaled 11% per year. Young wolves emigrated from the study area at high annual rates (47% and 27% for yearlings and 2-yr-olds, respectively), and we estimated the emigration rate for the population at ≥19% annually. Yearlings and 2-year-olds were lost from the population at rates of 60% per year and 45% per year, respectively, primarily as a result of emigration; mortality was the principal cause of the 26% annual loss of wolves ≥3 years old.On average, 47 wolves were harvested each winter from our study population, or twice the harvest we estimated from survival analyses of radiocollared wolves (23 wolves/yr). We suggest that the additional harvested wolves were transients, including local dispersers and migrants from outside the study area. Trapping harvest was well-distributed throughout the trapping season (Nov-Apr), whereas shooting harvest occurred mainly in February and March. Of 35 individuals who harvested wolves in the area, 6 accounted for 66% of the harvest.We analyzed information from North American wolf populations and determined that annual rates of increase have an inverse, curvilinear relationship with human-caused mortality (r2 = 0.68, P < 0.001) such that population trends were not correlated with annual human take ≤29% (P = 0.614). We provide evidence that wolf populations compensate for human exploitation ≤29% primarily via adjustments in dispersal components (i.e., local dispersal, emigration, and immigration), whereas responses in productivity or natural mortality have little or no role in offsetting harvests. Given the limited effects of moderate levels of human take on wolf population trends and biases in assessing wolf populations and harvests resulting from the existence of transient wolves, the risks of reducing wolf populations inadvertently through regulated harvest are quite low.RESEMEN  Nuestra comprensión de la dinámica poblacional del lobo (Canis lupus) en Norteamérica procede sobre todo de estudios en áreas protegidas, de poblaciones amenazadas y de programas de control de lobos, aunque la mayoría de los lobos norteamericanos experimentan niveles moderados de explotación regulada. Durante 1986–1992, hemos investigado la dinámica poblacional y el aprovechamiento del lobo en el recientemente creado Parque Nacional y Reserva Gates of the Arctic, en el norte de Alaska, donde los lobos fueron explotados por los residentes locales. Nuestros objetivos han sido determinar la abundancia de lobos, estimar los parámetros vitales más importantes (productividad, supervivencia, emigración) y caracterizar la explotación de los lobos. Hemos seguido 50 lobos radiomarcados en 25 manadas durante 4 años (abril de 1987–abril de 1991) para conocer los patrones de dispersión, la emigración, la supervivencia y las causas de mortalidad de la población. Hemos determinado los tamaños de manada, las áreas de campeo y los cachorros/manada en otoño (1 de octubre) en las manadas con lobos marcados, y hemos calculado la densidad de lobos en otoño y primavera (15 de abril) considerando el número de lobos en las manadas controladas y la superficie total ocupada por dichas manadas. También hemos recogido información de cazadores y tramperos locales sobre la estacionalidad, localización, métodos y composición de sexo y edad de los lobos muertos en 6 periodos invernales de aprovechamiento (agosto de 1987–abril de 1992).La densidad media fue de 6,6 lobos/1.000 km2 y 4,5 /1,000 km2 en otoño y primavera, respectivamente, y las densidades en primavera aumentaron un 5% anual durante el estudio. De media, los cachorros constituyeron el 50% de la población residente cada otoño. Hemos estimado que cada año se extrajo el 12% de la población. La mortalidad natural, fundamentalmente por luchas intraespecíficas, alcanzó el 11% anual. Los ejemplares jóvenes del área de estudio presentaron elevadas tasas anuales de emigración (el 47% y el 27% para lobos de 1 a 2 años y de 2 a 3 años, respectivamente), y la tasa de emigración anual estimada para la población ha sido ≥19%. El 60% y el 45% de los lobos de 1 a 2 y de 2 a 3 años respectivamente desaparecieron cada año de la población, sobre todo a causa de la emigración; la mortalidad fue la principal causa de la pérdida del 26% anual de los lobos ≥3 años.De media, se extrajeron 47 lobos cada invierno en los programas de aprovechamiento en el área de estudio, es decir, el doble de la cifra que hemos estimado analizando la supervivencia de los lobos radiomarcados (23 lobos/año). Sugerimos que los restantes lobos extraídos eran transeúntes, incluyendo dispersants locales y migrantes de fuera del área de estudio. La extracción por trampeo estuvo bien distribuida a lo largo de la estación de trampeo (noviembre-abril), mientras que la extracción con armas de fuego se produjo sobre todo en febrero y marzo. De los 35 individuos que extrajeron lobos en la zona, 6 acapararon el 66% de las capturas.Tras analizar la información de las poblaciones norteamericanas de lobos, hemos determinado que las tasas anuales de aumento muestran una relación inversa y curvilinear con la mortalidad causada por el hombre (r2 = 0,68, P < 0,001), de tal forma que las tendencias de las poblaciones no estaban correlacionadas con la mortalidad humana cuando ésta fue ≤29% anual (P = 0,614). Aportamos pruebas de que, cuando las tasas anuales de explotación por el hombre son ≤29%, las poblaciones de lobos las compensan fundamentalmente ajustando los componentes de la dispersión (es decir, la dispersión local, la emigración y la inmigración), mientras que las respuestas en productividad o mortalidad natural tienen un papel escaso o nulo al compensar las extracciones. Considerando que unos niveles moderados de extracción por el hombre tienen un impacto limitado sobre la tendencia de las poblaciones de lobos y que existen sesgos en la estima de las poblaciones y en la extracción causados por la existencia de lobos transeúntes, los riesgos de reducir las poblaciones de forma inadvertida con un aprovechamiento regulado son bastante bajos.RÉSUMÉ  Notre compréhension de la dynamique des populations de loups (Canis lupus) d'Amérique du Nord provient grandement d'aires protégées, de populations menacées ou de programmes de contrǒle bien que la plupart des loups du continent subissent des niveaux d'exploitation modérés. Entre 1986 et 1992, nous avons étudié la dynamique des populations et la récolte de loups dans le nouveau parc national et la réserve Gates of the Arctic, au nord de l'Alaska, où les résidents locaux récoltaient des loups. Nos objectifs étaient de déterminer l'abondance des loups, d'estimer des taux d'évènements naturels importants (c-à-d. la productivité, la survie, l'émigration), et de caractériser la récolte de loups. À l'aide de colliers émetteurs, nous avons suivi, pendant 4 ans (avril 1987 à avril 1991), 50 loups appartenant à 25 meutes afin d'évaluer leurs patrons de dispersion, l'émigration, la survie et les causes de mortalité au sein de la population. Nous avons déterminé la taille des meutes, les domaines vitaux, et le nombre de louveteaux par meute en automne (1er octobre) pour les meutes comptant des loups marqués, et nous avons calculé les densités de loups en automne et au printemps (15 avril) d'après le nombre de loups par meute suivie et l'aire que ces meutes habitaient. Nous avons également recueilli des informations auprès des chasseurs et trappeurs locaux sur la chronologie, le lieu, les méthodes et la composition (sexe/ǎge) de la récolte de loups durant 6 saisons hivernales (aoǔt 1987 à avril 1992).Les densités moyennes de loups atteignaient 6,6 loups/1 000 km et 4,5 loups/1000 km2 en automne et au printemps, respectivement, et les densités printanières augmentèrent de 5% par année durant notre étude. En moyenne, les louveteaux représentaient 50% de la population résidente, chaque automne. Nous avons estimé la récolte annuelle moyenne à 12% de la population. La mortalité naturelle, principalement des conflits intraspécifiques, atteignait 11% par année. Les jeunes loups émigrèrent de l'aire d'étude à des taux élevés (47% et 27% pour les loups d'un an et de deux ans, respectivement) et nous avons estimé le taux d'émigration annuel pour l'ensemble de la population à ≥19%. Les loups d'un an et de deux ans disparaissaient de la population à des taux annuels de 60% et 45%, respectivement, principalement à cause de l'émigration; la mort était la principale cause de disparition des loups de 3 ans et plus qui quittaient la population chaque année (26%).En moyenne, 47 loups furent récoltés chaque hiver dans la population étudiée, soit 2 fois la récolte estimée par les analyses de survie des loups marqués (23 loups par an). Nous proposons que le surplus de loups récoltés provenait d'animaux de passage, incluant les loups locaux en dispersion et d'autres provenant de l'extérieur de l'aire d'étude. La récolte par piégeage s'étendait uniformément durant toute la saison (novembre à avril) alors que la récolte par la chasse se concentrait surtout en février et mars. Six des 35 personnes récoltant des loups dans l'aire d'étude étaient responsables à elles seules de 66% des prises.Nous avons analysé des données provenant de diverses populations de loups d'Amérique du Nord et trouvé que les taux d'accroissement possédaient une relation inverse et curvilinéaire avec les causes de mortalité induites par les humains (r2 = 0,68, P < 0,001) de telle sorte que les tendances démographiques n'étaient pas corrélées aux récoltes humaines (P = 0,614). Nous fournissons des évidences à l'effet que les populations de loups compensent pour l'exploitation humaine ≤29% principalement par l'entremise d'ajustements dans les facteurs de dispersion (c.-à-d. dispersion locale, émigration, immigration), alors que la productivité et la mortalité naturelle compensent peu ou pas du tout pour les récoltes. Étant donné les effets limités d'une récolte humaine modérée sur les tendances démographiques des populations de loups et les biais d'estimation des effectifs et des récoltes à cause de l'existence de loups de passage, les risques de reduction accidentelle de populations de loups résultant d'une récolte réglementée sont très faibles.
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Conservation practices are supposed to get refined by advancing scientific knowledge. We study this phenomenon in the context of monitoring tiger populations in India, by evaluating the ‘pugmark census method’ employed by wildlife managers for three decades. We use an analytical framework of modern animal population sampling to test the efficacy of the pugmark censuses using scientific data on tigers and our field observations. We identify three critical goals for monitoring tiger populations, in order of increasing sophistication: (1) distribution mapping, (2) tracking relative abundance, (3) estimation of absolute abundance. We demonstrate that the present census-based paradigm does not work because it ignores the first two simpler goals, and targets, but fails to achieve, the most difficult third goal. We point out the utility and ready availability of alternative monitoring paradigms that deal with the central problems of spatial sampling and observability. We propose an alternative sampling-based approach that can be tailored to meet practical needs of tiger monitoring at different levels of refinement.
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There is substantial interest in how mortality rates affect animal populations, but mechanisms explaining when and under what circumstances particular causes of death incur demographic responses are far from clear. In theory, small or expanding populations should experience additive mortality from anthropogenic causes of death, but whether such effects are homogenous across a population or expressed only in certain high-risk individuals is open for debate. We used competing risks models to analyze mortality patterns among radio-collared wolves (Canis lupus, n = 711) from three populations in northwestern United States (1982–2004), and evaluated the degree to which anthropogenic mortality was additive vs. compensatory to natural demographic processes. Almost 80% (n = 320) of wolves dying of known fates were killed by anthropogenic causes (legal control, illegal killing, harvest in Canada, vehicle collision), and additive effects of anthropogenic mortality were most pronounced in northwestern Montana where wolf exposure to humans and livestock was high compared to either the Greater Yellowstone Area or central Idaho, where anthropogenic risk was lower. In contrast, risk from natural hazards was lower in northwestern Montana than in the other areas, implying some degree of compensatory mortality from anthropogenic risk. Animals recruited to the study following human–wolf conflict had markedly higher anthropogenic risk than those recruited for standard monitoring purposes, and juvenile wolves as well as dispersers, succumbed to higher anthropogenic risk. Multivariate models revealed that increasing wolf population density promoted higher anthropogenic risk and reduced natural risk, indicating that partially-compensatory effects of anthropogenic mortality actually became increasingly additive with population density. The observed compensatory mortality and hazard heterogeneity in our study implies that demographic responses to mortality risk may be complex and more subtle than previously thought; the density-dependent effect of anthropogenic mortality portends a stabilizing influence of humans on recovering wolf populations. We conclude that future assessment of the role of anthropogenic mortality should include individual-based hazard estimation as a complement to traditional population-level approaches.
Article
Between 1999 and 2004 we undertook an ecological study of African lions (Panthera leo) in Hwange National Park, western Zimbabwe to measure the impact of sport-hunting beyond the park on the lion population within the park, using radio-telemetry and direct observation. 34 of 62 tagged lions died during the study (of which 24 were shot by sport hunters: 13 adult males, 5 adult females, 6 sub-adult males). Sport hunters in the safari areas surrounding the park killed 72% of tagged adult males from the study area. Over 30% of all males shot were sub-adult (<4 years). Hunting off-take of male lions doubled during 2001–2003 compared to levels in the three preceding years, which caused a decline in numbers of adult males in the population (from an adult sex ratio of 1:3 to 1:6 in favour of adult females). Home ranges made vacant by removal of adult males were filled by immigration of males from the park core. Infanticide was observed when new males entered prides. The proportion of male cubs increased between 1999 and 2004, which may have occurred to compensate for high adult male mortality.