Global drivers of population density in terrestrial vertebrates

Abstract

Aim: Although the effects of life history traits on population density have been investigated widely, how spatial environmental variation influences population density for a large range of organisms and at a broad spatial scale is poorly known. Filling this knowledge gap is crucial for global species management and conservation planning and to understand the potential impact of environmental changes on multiple species. Location: Global.Time period: Present.Major taxa studied: Terrestrial amphibians, reptiles, birds and mammals.Methods: We collected population density estimates for a range of terrestrial vertebrates, including 364 estimates for amphibians, 850 for reptiles, 5,667 for birds and 7,651 for mammals. We contrasted the importance of life history traits and environmental predictors using mixed models and tested different hypotheses to explain the variation in population density for the four groups.We assessed the predictive accuracy of models through cross-validation and mapped the partial response of vertebrate population density to environmental variables globally.Results: Amphibians were more abundant in wet areas with high productivity levels, whereas reptiles showed relatively higher densities in arid areas with low productivity and stable temperatures.The density of birds and mammals was typically high in temperate wet areas with intermediate levels of productivity. The models showed good predictive abilities, with pseudo-R 2 ranging between 0.68 (birds) and 0.83 (reptiles).Main conclusions: Traits determine most of the variation in population density across species, whereas environmental conditions explain the intraspecific variation across populations. Species traits, resource availability and climatic stability have a different influence on the population density of the four groups. These models can be used to predict the average species population density over large areas and be used to explore macroecological patterns and inform conservation analyses.abundance, amphibians, birds, mammals, population density, reptiles | I NTR OD U CTI ONPopulation density is one of the key demographic parameters determining the dynamics of populations. Clearly, it also represents a crucial information for conservation planning as it is a direct proxy for extinction risk (Brown, Mehlman, & Stevens, 1995;Currie & Fritz, 1993;Sanderson, 2006). In a macroecological context, research has mostly focused on the biological predictors of average population density per 968 |

Applying habitat and population‐density models to land‐cover time series to inform IUCN Red List assessments

“…; Santini et al. ). Our predictions were fairly consistent with published IUCN Red List assessments, suggesting that the procedure is reliable for preliminary species assessments.…”

“…We therefore tested multiple criteria, with small defined as fragments <100 km 2 ; fragments supporting <100, <500, <1000, or <5000 individuals according to our population density models (Santini et al. ); or fragments supporting less than a viable population size according to Hilbers et al. () based on viability targets with 5 assumed proportions of the maximum population growth rate (0.2, 0.4, 0.6, 0.8, or 1).…”

Addressing common pitfalls does not provide more support to geographical and ecological abundant‐centre hypotheses

“…Third, the decline in population abundance might not be linear from the centre to the edge (or from high to low suitability), but could rather show no relationship and present a sharp decline at the very edge (Pironon et al 2017). This does not imply a lack of influence of climate and energy availability on large scale patterns of population density (Currie and Fritz 1993, Pettorelli et al 2009, Santini et al 2018b), but it rather suggests that the current geographic range of species is a poor reflection of their Grinellian niche (Soberon 2007), and suitable conditions for high population abundance can be at the margin of the current geographic range or the estimated environmental space from observed occurrences. Fourth, populations fluctuate in time because of demographic and environmental stochasticity.…”

“…We definitely need more research to better understand the drivers of the intra-specific variation of population density within species range, and the relative importance of factors acting at different spatial scales (Santini et al 2018b). Our research cannot provide a definitive conclusion about the validity of the abundant-centre hypothesis, as -although to a lesser extent than previous papers -it is affected by some limitations.…”

Testing the role of ecological selection on colour pattern variation in the butterfly Parnassius clodius

“…Variation in predator communities probably has a strong affect in geographic variation of warning coloration, as has been shown for many other organisms (Briolat et al, ). Bird abundance is typically greater in wet temperate habitats in western North America (Cady, O'Connell, Loss, Jaffe, & Davis, ; Santini et al, ), so may be cross‐correlated with temperature seasonality and solar radiation. More detailed research into the effects of predation and predator communities will be necessary in order to enhance our understanding of selection on aposematism within this species.…”