Abstract
Global landscapes are changing due to human activities with consequences for both biodiversity and ecosystems. For single species, terrestrial mammal population densities have shown mixed responses to human pressure, with both increasing and decreasing densities reported in the literature. How the impacts of human activities on mammal populations translates into altered global density patterns remains unclear. Here we aim to disentangle the effect of human impacts on large‐scale patterns of mammal population densities using a global dataset of 6729 population density estimates for 468 mammal species (representing 59% and 44% of mammalian orders and families). We fitted a mixed effect model to explain the variation in density based on a 1‐degree resolution as a function of the human footprint index (HFI), a global proxy of direct and indirect human disturbances, while accounting for body mass, trophic level and primary productivity (normalized vegetation index; NDVI). We found a significant positive relationship between population density and HFI, where population densities were higher in areas with a higher HFI (e.g. agricultural or suburban areas – no populations were located in very high HFI urban areas) compared to areas with a low HFI (e.g. wilderness areas). We also tested the effect of the individual components of the HFI and still found a consistent positive effect. The relationships remained positive even across populations of the same species, although variability among species was high. Our results indicate shifts in mammal population densities in human modified landscapes, which is due to the combined effect of species filtering, increased resources and a possible reduction in competition and predation. Our study provides further evidence that macroecological patterns are being altered by human activities, where some species will benefit from these activities, while others will be negatively impacted or even extirpated.
Highlights
Population density of terrestrial mammals span from < 0.0001 to > 25 000 individuals km−2, and can vary over several orders of magnitude across conspecific populations (Santini et al 2018a, Stephens et al 2019) Understanding the drivers of this variation is a key objective of macroecology (Brown and Maurer 1989, Stephens et al 2019)
We found a significant positive relationship between terrestrial mammal population density and the Human footprint index (HFI) (Fig. 2)
We did not detect any significant effects of primary productivity (NDVI; p = 0.938) or the interaction between HFI and diet for carnivores (HFI:Diet (Carnivore); p = 0.543), but there was a significant interaction between HFI and diet for omnivores (HFI:Diet (Omnivore); p ≤ 0.001)
Summary
Population density of terrestrial mammals span from < 0.0001 to > 25 000 individuals km−2, and can vary over several orders of magnitude across conspecific populations (Santini et al 2018a, Stephens et al 2019) Understanding the drivers of this variation is a key objective of macroecology (Brown and Maurer 1989, Stephens et al 2019). There is a negative relationship between body mass and population density (i.e. larger species tend to have lower population densities) and this is a reflection of the variation in space use patterns and the relative energy use of species across the body size spectrum (Damuth 1981, 2007, Fa and Purvis 1997). Expected overall relationship Rationale Reference Human footprint − index (HFI). Population densities tend to be higher in temperate areas with intermediate Predictor
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