A recent study of tigers in Chitwan, Nepal (1) stirred controversy by challenging the “source-sink” approach that underlies current global tiger conservation strategies (2). The observed lack of difference in tiger density estimates inside the protected area compared with a multiple-use area outside is offered as evidence. Based on this result, the study questions the relevance of strictly protected tiger reserves involving regulation of extractive uses and relocation of human settlements. The study offers an alternate vision of sustainable, syntopic “coexistence” of tigers and humans as a solution to increasing human resource demands on tiger habitats

Goodrich, John

Gopalaswamy, Arjun M.

Karanth, Krithi K.

Robinson, John G.

Seidensticker, John

Ullas Karanth, K.

English

Publications of the IAS Fellows

LETTER
Sinks as saviors: Why flawed
inference cannot assist tiger recovery
A recent study of tigers in Chitwan, Nepal (1) stirred controversy
by challenging the “source-sink” approach that underlies current
global tiger conservation strategies (2). The observed lack of
difference in tiger density estimates inside the protected area
compared with a multiple-use area outside is offered as evidence.
Based on this result, the study questions the relevance of strictly
protected tiger reserves involving regulation of extractive uses
and relocation of human settlements. The study offers an alter-
nate vision of sustainable, syntopic “coexistence” of tigers and
humans as a solution to increasing human resource demands on
tiger habitats.
Long-term substantive studies contradict this alternative view.
Tiger densities in better-protected reserves are three- to five-
times higher than in areas with poorer protection and extractive
human uses (2, 3). At other ecologically comparable sites, such
as Kaziranga and Corbett (2), which curtail human uses, tiger
densities are five-times higher (17–19 tigers per 100 km2). Even
in Chitwan, tiger densities were much higher historically, under
stricter regulation of extractive uses (4).
Curiously, all evidence reported in this study itself strength-
ens the prevalent “source-sink” view. Naive tiger densities
(the number of individual tigers divided by the area of the
camera trap array) were 1.33- to 3-times higher inside the
protected reserve. Additionally, between 2010 and 2011
the number of individual tigers photo-trapped within the re-
serve increased from 12 to 18, but it decreased from 6 to 4
outside. At a “fine scale” of measurement (combined trapping
area ∼80 km2), this difference in tiger density is obvious.
Furthermore, results from the small cell (1 km2) occupancy
analysis indicate that tiger densities are higher inside the re-
serve because detection probability is monotonically related to
density at such cell sizes. Astonishingly, despite all contrary
evidence, the authors conclude that estimated densities do not
differ solely based on statistical insignificance. This anomaly
likely arises because the spatially explicit capture-recapture
models used are confronted with sparse data (only four to six
tigers were photo-captured outside) in very small areas (50 km2
inside, 30 km2 outside), generating unreliable estimates of tiger
densities (5).
Based on inference likely rooted in survey design flaws (5), the
authors boldly attack a “prevailing belief” that tigers cannot
spatially overlap with humans at fine spatial scales. Past studies
show that tigers do coexist at “fine scales” in human-dominated
landscapes, but with unacceptable levels of conflict, including
predation on humans, as in Chitwan (4). Furthermore, although
prescribing a radical reversal of current “source-sink” strategy
focusing on protected areas, the authors’ two-season study ig-
nores multisite, long-term studies of tiger population dynamics
that do support this approach (2–4).
Global spatial analyses show >70% of wild tigers now live and
reproduce in 6% of source habitats in protected reserves, and
their survival in surrounding landscape sinks depends on re-
plenishment from sources (2–4). The sober reality is that the
species has been extirpated from 93% of its former range be-
cause of conflict-ridden coexistence with humans. Hence, the
authors’ prescription of tiger population sinks over sources as
a future recovery strategy is doomed to failure.
K. Ullas Karantha,b,1, Arjun M. Gopalaswamyb,c, Krithi K.
Karanthb,d, John Goodriche, John Seidenstickerf, and John G.
Robinsona
aGlobal Conservation Program, Wildlife Conservation Society, Bronx,
NY 10460; bCentre for Wildlife Studies, Bangalore, 560042, India;
cWildlife Conservation Research Unit, Department of Zoology, Uni-
versity of Oxford, Oxford OX1 3PS, United Kingdom; dNicholas
School of Environment, Duke University, Durham, NC 27708; eTiger
Program, Panthera, New York, NY 10018; and fSmithsonian Con-
servation Biology Institute, Washington, DC 20013
1. Carter NH, Shrestha BK, Karki JB, Pradhan NMB, Liu J (2012) Coexistence between
wildlife and humans at fine spatial scales. Proc Natl Acad Sci USA 109(38):15360–15365.
2. Walston JS, et al. (2010) Bringing the tiger back from the brink—The six percent
solution. PLoS Biol 8(9):e1000485.
3. Karanth KU, et al. (2011) Monitoring carnivore populations at the landscape scale:
Occupancy modelling of tigers from sign surveys. J Appl Ecol 48(4):1048–1056.
4. Barber-Myer SM, et al. (2012) Influence of prey depletion and human disturbance on
tiger occupancy in Nepal. J Zool, 10.1111/j.1469-7998.2012.00956.x.
5. Sollman R, Gardner B, Lenot JL (2012) How does spatial study design influence density
estimates from spatial capture-recapture models? PLoS ONE 7(4):e34575.
Author contributions: K.U.K., A.M.G., and K.K.K. designed research; K.U.K., A.M.G., K.K.K.,
J.G., J.S., and J.G.R. performed research; A.M.G. contributed new reagents/analytic tools;
K.U.K. and A.M.G. analyzed data; and K.U.K., A.M.G., K.K.K., J.G., J.S., and J.G.R. wrote
the paper.
The authors declare no conflict of interest.
1To whom correspondence should be addressed. E-mail: ukaranth@gmail.com.
E110 | PNAS | January 8, 2013 | vol. 110 | no. 2 www.pnas.org/cgi/doi/10.1073/pnas.1216623110


Sinks as saviors: why flawed inference cannot assist tiger recovery

Indian Academy of Sciences

http://repository.ias.ac.in/111701/1/PNAS-2013-Karanth-E110.pdf

Sinks as saviors: why flawed inference cannot assist tiger recovery

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