Camera‐trapping provides insights into adult sex ratio variability in felids

Abstract

Adult sex ratio (ASR) plays a pivotal role in many ecological processes, such as population dynamics in time and space, extinction risk and reproductive success, but few patterns in the variability in ASR have been found across species. Due to the socio‐spatial structure and polygynous mating system found in felids, ASR is expected to be female‐biased in felids in a finite area; however, ASR is also commonly found to be either balanced or male‐biased in this taxonomic group. Therefore, investigating ecological correlates of the pattern of ASR variability in felids is of prime importance both for a better understanding of evolutionary ecology and for a more evidence‐based conservation of these threatened taxa. The aim of this review was to investigate whether the expected female‐biased ASR occurs in felids, and whether ASR is influenced by the size of the study area, the species’ body mass and the population density, taking into account the species‐specific home‐range requirements. We reviewed the camera‐trapping literature on felids to build a large global multi‐species data set on ASR variation. We used general linear mixed models to investigate ecological correlates of ASR. In small study areas, the ASR was balanced for all species, but in large areas the ASR was female‐biased for large and medium cats and male‐biased for small cats; sampling designs that are unsuitable for small cats (due to ‘gaps’ within the trapping grid) might explain this latter finding. Moreover, in large study areas, an increase in cat density was associated with more females, whereas in small areas the reverse was true. Our study provides a scientifically sound background for management and conservation actions of these flagship‐threatened taxa of carnivores, by indicating the importance of the study area on ASR in felids. Large areas can promote the recovery of large and medium cats, as more females can be hosted.

Spatial variance-mass allometry of population density in felids from camera-trapping studies worldwide

“…Our efforts for maintaining the dataset, analyzing it and disseminating our findings 46,47 have contributed to increase the scientific knowledge for this highly distinctive and charismatic taxon. Moreover, in this study we have found strong support for the VMA law for a whole taxon of carnivore species for the first time and evidently this result calls for other assessments of the VMA at the interspecific level in other taxonomic groups, both on the spatial and temporal variance in population density, before confirming its universality on ecological systems and discussing its implications more in depth.…”

“…Different arguments could indeed be formulated to explain this flattening of the VMA encompassing both a lower than expected variability in small species and larger variability than expected in large species. In a more optimistic scenario, our dataset may not be representative enough of the actual variability found in population densities of small cats; a scenario which we consider realistic given the strong bias in research efforts towards large cats 46 , 47 . In the worst case scenario, we cannot exclude that population densities of small cat populations are truly depressed, hence they are not able to attain their highest predicted population densities, thereby lowering the density variation in small species and ultimately flattening the VMA.…”

“…On the contrary, the development of SECR models overrides the need of estimating the area A because these models inherently estimate D by modelling the location of the home-ranges of the animals (detected and not detected) based on the spatial information provided by the captures themselves 45,75 . We further classified each entry as random vs. target records 46,47 by carefully inspecting the methods section to assess if a species-specific sampling was used for a given species. For entries reporting data for more than one species, year and period (e.g.…”

“…We searched the literature for camera survey-based estimates of population density for felids during 11 January 2012 until 14 December 2019 using the most common, freely accessible and widely used scientific bibliography database: Scirus, Web of Science, BioOne and Google scholar 46 , 47 . We used the term “camera-trapping” along with both common and scientific names for the 40 species of felids 60 .…”

“…Clearly, density estimates must be robust, standardized and independent from each other. Camera trap monitoring 45 has been used extensively to estimate population density or other population parameters of many species of Felidae 46,47 . Many cat species are naturally individually marked as their fur-coats feature stripes, rosettes and spots.…”