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Assessing the performance of index calibration survey methods to monitor populations of wide-ranging low-density carnivores

Droge, Egil and Creel, Scott and Becker, Matthew S. and Loveridge, Andrew J. and Sousa, Lara L. and Macdonald, David W. (2020). Assessing the performance of index calibration survey methods to monitor populations of wide-ranging low-density carnivores. Ecology and Evolution. 10 , 3276-3292
[Journal article]

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Abstract

Apex carnivores are wide-ranging, low-density, hard to detect, and declining throughout most of their range, making population monitoring both critical and challenging. Rapid and inexpensive index calibration survey (ICS) methods have been developed to monitor large African carnivores. ICS methods assume constant detection probability and a predictable relationship between the index and the actual population of interest. The precision and utility of the resulting estimates from ICS methods have been questioned. We assessed the performance of one ICS method for large carnivores-track counts-with data from two long-term studies of African lion populations. We conducted Monte Carlo simulation of intersections between transects (road segments) and lion movement paths (from GPS collar data) at varying survey intensities. Then, using the track count method we estimated population size and its confidence limits. We found that estimates either overstate precision or are too imprecise to be meaningful. Overstated precision stemmed from discarding the variance from population estimates when developing the method and from treating the conversion from tracks counts to population density as a back-transformation, rather than applying the equation for the variance of a linear function. To effectively assess the status of species, the IUCN has set guidelines, and these should be integrated in survey designs. We propose reporting the half relative confidence interval width (HRCIW) as an easily calculable and interpretable measure of precision. We show that track counts do not adhere to IUCN criteria, and we argue that ICS methods for wide-ranging low-density species are unlikely to meet those criteria. Established, intensive methods lead to precise estimates, but some new approaches, like short, intensive, (spatial) capture-mark-recapture (CMR/SECR) studies, aided by camera trapping and/or genetic identification of individuals, hold promise. A handbook of best practices in monitoring populations of apex carnivores is strongly recommended.

Authors/Creators:Droge, Egil and Creel, Scott and Becker, Matthew S. and Loveridge, Andrew J. and Sousa, Lara L. and Macdonald, David W.
Title:Assessing the performance of index calibration survey methods to monitor populations of wide-ranging low-density carnivores
Series Name/Journal:Ecology and Evolution
Year of publishing :2020
Volume:10
Page range:3276-3292
Number of Pages:17
Publisher:WILEY
ISSN:2045-7758
Language:English
Publication Type:Journal article
Article category:Scientific peer reviewed
Version:Published version
Copyright:Creative Commons: Attribution 4.0
Full Text Status:Public
Subjects:(A) Swedish standard research categories 2011 > 1 Natural sciences > 106 Biological Sciences (Medical to be 3 and Agricultural to be 4) > Ecology
Keywords:carnivores, IUCN criteria, lion, Panthera leo, population monitoring, spoor counts, statistical power, track counts
URN:NBN:urn:nbn:se:slu:epsilon-p-109705
Permanent URL:
http://urn.kb.se/resolve?urn=urn:nbn:se:slu:epsilon-p-109705
Additional ID:
Type of IDID
DOI10.1002/ece3.6065
Web of Science (WoS)000518651000001
ID Code:21217
Faculty:S - Faculty of Forest Sciences
Department:(S) > Dept. of Wildlife, Fish and Environmental Studies
Deposited By: SLUpub Connector
Deposited On:14 Jan 2021 11:03
Metadata Last Modified:15 Jan 2021 19:20

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