An examination of index‐calibration experiments: counting tigers at macroecological scales

Methods in Ecology and Evolution, Journal Year: 2015, Volume and Issue: 6(9), P. 1055 - 1066

Published: Feb. 23, 2015

Summary An index‐calibration experiment involves rigorous estimation of animal abundance at a small scale to calibrate less rigorously derived index abundance. The efficacy such experiments has been matter much controversy. In this study, we develop theoretical models and test them with empirical data on large‐scale tigers Panthera tigris advance our understanding We propose two that describe the sampling processes involved in typical experiments. Using analytical derivations some simulations, evaluate relative roles these parameters (coefficient determination) statistic – common inferential tool used calibration make predictions about using estimates from occupancy surveys India. then compare tiger sign (IC‐Karanth IC‐Jhala). Our show increases when individual‐specific detection probability is high constant, variance‐to‐mean ratio increases, precision improves declines mean increases. All showed poor performance ( < 0·40). Inference IC‐Karanth was extremely ) comparable model P value = 0·0754). Anomalously 0·0001), inference IC‐Jhala exceedingly ). study shows direct yield inferences unless all process lie within limited range. Ignoring consequence effect during survey design could result expenditure huge resources little gain ecological inference. Analysis joint likelihood models, appropriate designs, may be more fruitful than clinging composite, ‐based models.

Language: Английский

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EDITOR'S CHOICE: Safeguarding Sumatran tigers: evaluating effectiveness of law enforcement patrols and local informant networks

Journal of Applied Ecology, Journal Year: 2015, Volume and Issue: 52(4), P. 851 - 860

Published: May 11, 2015

Summary The United Nations recently listed illegal wildlife trade as a serious crime because of the escalating demand for highly prized species, such tiger and rhinoceros, failure to effectively control trade. In turn, this places greater urgency on reducing supply by securing source populations these species. Yet, whether law enforcement strategies designed mitigate poaching are succeeding remains poorly understood, despite millions dollars invested annually in mainstay conservation strategy. Here, we assess performance one Asia's longest running programmes, from Kerinci Seblat National Park Sumatra, investigating forest ranger patrols reduced occurrence snare traps set its ungulate prey base; local informant reports influenced patrol success; resulting population trends target species changed response actions. A total 4433 were removed during 642 foot conducted 2000 2010. Controlling influence varying detection probabilities, well accessibility other possible determinants hunting, revealed that sites with frequency patrols, rather than combined distance walked, had lower years. Patrols basis ‘tip‐offs’ significantly more likely detect routine increasing detections over 40%. There no significant changes occupancy status base 2004 2011, suggesting it remained stable period. relatively good condition predator was further supported results an independent survey 2008–2009 which widespread occurrence. Synthesis applications . Our not only demonstrate effectiveness strategy protecting wildlife, but highlight benefits cultivating network reliable informants. study also represents critical step helping urgently needed assessments become common place fight save flagship

Language: Английский

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Population Status of a Cryptic Top Predator: An Island-Wide Assessment of Tigers in Sumatran Rainforests

PLoS ONE, Journal Year: 2011, Volume and Issue: 6(11), P. e25931 - e25931

Published: Nov. 2, 2011

Large carnivores living in tropical rainforests are under immense pressure from the rapid conversion of their habitat. In response, millions dollars spent on conserving these species. However, cost-effectiveness such investments is poorly understood and this largely because requisite population estimates difficult to achieve at appropriate spatial scales for secretive Here, we apply a robust detection/non-detection sampling technique produce first reliable metric (occupancy) critically endangered large carnivore; Sumatran tiger (Panthera tigris sumatrae). From 2007–2009, seven landscapes were surveyed through 13,511 km transects 394 grid cells (17×17 km). Tiger sign was detected 206 cells, producing naive estimate 0.52. after controlling an unequal detection probability (where p = 0.13±0.017; ±S.E.), estimated occupancy 0.72±0.048. Whilst Sumatra-wide survey results gives cause optimism, significant negative correlation between recent deforestation found. For example, Northern Riau landscape had average rate 9.8%/yr by far lowest (0.33±0.055). Our highlight key areas need protection have led one area (Leuser-Ulu Masen) being upgraded as ‘global priority’ wild conservation. Sumatra has highest global rates two largest identified study will become highly fragmented if respective proposed roads networks approved. Thus, it vital that Indonesian government tackles threats, e.g. improved land-use planning, succeed meeting its ambitious National Recovery Plan targets doubling number tigers 2022.

Language: Английский

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Management decision making for fisher populations informed by occupancy modeling

Journal of Wildlife Management, Journal Year: 2016, Volume and Issue: 80(5), P. 794 - 802

Published: April 27, 2016

Harvest data are often used by wildlife managers when setting harvest regulations for species because the regularly collected and do not require implementation of logistically financially challenging studies to obtain data. However, available an area had previously supported a season, alternative approaches required help inform management decision making. When distribution or density across large areas, occupancy modeling is useful approach, under certain conditions, can be as surrogate density. We collaborated with New York State Department Environmental Conservation (NYSDEC) conduct camera trapping study 70,096-km2 region southern in areas that were currently open fisher (Pekania [Martes] pennanti) those been closed approximately 65 years. detection–nondetection at 826 sites model function site-level landscape characteristics while accounting sampling variation. Fisher was influenced positively proportion conifer mixed-wood forest within 15-km2 grid cell negatively associated road agriculture. Model-averaged predictions indicated high probabilities (>0.90) densities low (<1 km/km2) coniferous mixed proportions (>0.50). Predicted ranged 0.41–0.67 units (WMUs) trapping, which could guide minimum threshold opening new seasons. There 5 WMUs but average predicted 0.52 (0.07 SE), above 0.41. These consideration NYSDEC conservative season. demonstrate use aid making harvest-related unavailable budgetary constraints allow capture–recapture directly estimate © 2016 The Wildlife Society.

Language: Английский

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Predicting bobcat abundance at a landscape scale and evaluating occupancy as a density index in central Wisconsin

Journal of Wildlife Management, Journal Year: 2015, Volume and Issue: 79(3), P. 469 - 480

Published: Feb. 25, 2015

The abundance of low-density species like carnivores is logistically difficult to directly estimate at a meaningful scale. Predictive distribution models are often used as surrogate for density estimation. But because can continue increase occupancy asymptotes 1, may have little value an index, and home range expansion in marginal habitat further confound the association. We sought bobcat population size landscape scale (14,286 km2) central Wisconsin, which provided opportunity relate predicted occurrence individual space use density. sampled bobcats using motion-sensitive trail cameras 9 arrays across Wisconsin. estimated site-specific occupancy, regressed these estimates linear or asymptotic functions determine strength shape their subsequently modeled both parameters relative covariates repeated regression process. A functional relationship between was most supported when detection were held constant (wi= 0.97, R2 = 0.72) detection, occurrence, function 0.99, 0.95). This suggests that presence-absence data alone be efficient reliable method inferring spatial patterns identifying types with greater potential northern parts its range. Bobcat positively associated surrounding woody cover wetland edge Our spatially explicit capture-recapture model 362 adult individuals (95% CI 272–490) study area. © 2015 Wildlife Society.

Language: Английский

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