Comparison of density estimation methods for mammal populations with camera traps in the Kaa‐Iya del Gran Chaco landscape

Abstract

Sampling animal populations with camera traps has become increasingly popular over the past two decades, particularly for species that are cryptic, elusive, exist at low densities or range over large areas. The results have been widely used to estimate population size and density. We analyzed data from 13 camera trap surveys conducted at five sites across the Kaa-Iya landscape, Bolivian Chaco, for jaguar, puma, ocelot and lowland tapir. We compared two spatially explicit capture-recapture (SCR) software packages: secr, a likelihood-based approach, and SPACECAP, a Bayesian approach, both of which are implemented within the R environment and can be used to estimate animal density from photographic records of individual animals that simultaneously employ spatial information about the capture location relative to the sample location. As a non-spatial analysis, we used the program CAPTURE 2 to estimate abundance from the capturerecapture records of individuals identified through camera trap photos combined with an ad hoc estimation of the effective survey area to estimate density. SCR methods estimated jaguar population densities from 0.31 to 1.82 individuals per 100 km 2 across the Kaa-Iya sites; puma from 0.36 to 7.99; ocelot from 1.67 to 51.7; and tapir from 7.38 to 42.9. Density estimates using either secr or SPACECAP were generally lower than the estimates generated using the non-spatial method for all surveys and species; and density estimates using SPACECAP were generally lower than that using secr. We recommend using either secr or SPACECAP because the spatially explicit methods are not biased by an informal estimation of an effective survey area. Although SPACECAP and secr are less sensitive than non-spatial methods to the size of the grid used for sampling, we recommend grid sizes several times larger than the average home range (known or estimated) of the target species.

The importance of farmland for the conservation of the brown hyaena Parahyaena brunnea

“…However, costs are coming down and the development of spatiallyexplicit capture-recapture analysis promises more accurate and reliable density estimates. These methods are now being recommended as the standard for camera-trap surveys Noss et al, 2012) as they are more realistic than traditional capturerecapture methods, especially for wide-ranging species such as the brown hyaena that live at low density. With respect to the brown hyaena, however, there are potential problems with the assumptions of the spatially-explicit capture-recapture model.…”

“…The data augmentation value was set at 220 for the first survey and 200 for the second and third surveys. Convergence was checked by visual examination of the chains and, following Noss et al (2012), by using the Geweke statistic in the R package boa (Smith, 2007).…”

Estimación poblacional y conservación de felinos (Carnivora: Felidae) en el norte de Quintana Roo, México

“…En SPACECAP se especificó el modelo nulo con una función de detección media normal y un proceso binomial de presencias. En todos los análisis se utilizaron las especificaciones propuestas por Noss et al (2012) ya que no se contaba con suficientes datos para incluir covariantes y además se querían comparar los resultados utilizando los mismos modelos.…”

“…Se utilizaron los tres modelos para que los resultados pudieran ser comparados con trabajos realizados con anterioridad (en el caso de MMDM y ½ MMDM) en otras áreas de estudio Noss, Kelly, Camblos, & Ruiz, 2004;Di bitetti, Paviolo, & De Angelo, 2006;Chávez et al, 2007;Dillon & Kelly, 2008;Kelly et al, 2008), y SERC (SPACECAP) como un modelo más robusto y menos sesgado (Noss et al, 2012;Tobler, Carrillo-Percastegui, Zúñiga, & Powell, 2013).…”

“…Ya sea a través de medidas indirectas como la abundancia relativa (e.g., el número de rastros por unidad de esfuerzo) (Yasuda, 2004;Monroy-Vilchis, Zarco-González, Rodríguez-Soto, Soria-Díaz, & Urios, 2011), o estimaciones de densidad, calculada por medio de técnicas de captura-recaptura (CR) que son muy utilizadas y analizadas con el programa CAPTURE (Otis, Bumham, White, & Anderson, 1978;Rexstad & Burnham, 1991), para datos provenientes del trampeo fotográfico (Karanth & Nichols, 1998). Este método ha sido el más empleado para el estudio de felinos silvestres (Karanth & Nichols, 1998;Kelly, 2003;Maffei, Cuellar, & Noss, 2004;Silver et al, 2004;Chávez et al, 2007;Salom, Carrillo, Sáenz, & Mora, 2007;Dillon & Kelly, 2008;Noss et al, 2012).…”