The role of local versus biogeographical processes in influencing diversity and body‐size variation in mammal assemblages

Abstract

Our objective was to estimate and analyze the body‐size distribution parameters of terrestrial mammal assemblages at different spatial scales, and to determine whether these parameters are controlled by local ecological processes or by larger‐scale ones. Based on 93 local assemblages, plus the complete mammal assemblage from three continents (Africa, North, and South America), we estimated three key distribution parameters (diversity/size slope, skewness, and modal size) and compared the values to those expected if size distributions are mainly controlled by local interactions. Mammal diversity decreased much faster as body size increased than predicted by fractal niche theory, both at continental and at local scales, with continental distributions showing steeper slopes than the localities within them. South America showed a steeper slope (after controlling for species diversity), compared to Africa and North America, at local and continental scales. We also found that skewness and modal body size can show strikingly different correlations with predictor variables, such as species richness and median size, depending on the use of untransformed versus log‐transformed data, due to changes in the distribution density generated by log‐transformation. The main differences in slope, skewness, and modal size between local and continental scales appear to arise from the same biogeographical process, where small‐sized species increase in diversity much faster (due to higher spatial turnover rates) than large‐sized species. This process, which can operate even in the absence of competitive saturation at local scales, generates continental assemblages with steeper slopes, smaller modal sizes, and higher right skewness (toward small‐sized species) compared to local communities. In addition, historical factors can also affect the size distribution slopes, which are significantly steeper, in South American mammal assemblages (probably due to stronger megafauna extinction events in South America) than those in North America and Africa.

Elevation patterns and critical environmental drivers of the taxonomic, functional, and phylogenetic diversity of small mammals in a karst mountain area

“…They play key roles in trophic and food web dynamics, including important ecological roles in mountain ecosystems such as arthropod predators (Carvalho, Fernandez, & Nessimian, 2005), seed predators and dispersers (Martin‐Regalado, Briones‐Salas, Lavariega, & Moreno, 2019), as ecosystem engineers in soil aeration and nutrient mixing through their burrowing (Zhang, Zhang, & Liu, 2003), and as a resource for organisms in higher trophic levels (Wright, Gompper, & DeLeon, 1994). These taxa are particularly suitable for examining elevation patterns because they are commonly found along mountain slopes, have higher speciation rates and higher species turnover between habitats compared with larger mammals (Lopez et al., 2016). Indeed, a rodent species was recently discovered to be the world's highest dwelling mammal (Storz et al., 2020).…”

Systematic deviations from linear size spectra of lake fish communities are correlated with predator–prey interactions and lake‐use intensity

“…Body size is a fundamental attribute of organisms as many physiological rates, such as respiration, reproduction and growth, are size-dependent (Brown et al 2004). Furthermore, body size plays a key role in determining ecosystem-level attributes, including population density (Cyr et al 1997, Brown et al 2004, species diversity (Lopez et al 2016, Brucet et al 2017, and the intensity of predator-prey interactions (Woodward andWarren 2007, Hatton et al 2015).…”

Climate change should drive mammal defaunation in tropical dry forests

“…The predominance of highly‐vagile large‐sized species across lowland assemblages and the faster turnover of small‐sized species in highlands help to explain the increase in mammal beta‐diversity along elevational gradients in the Caatinga (Lopez et al, 2016; Melo et al, 2009). While small‐sized mammals certainly occur across Caatinga lowlands, the future homogenization is expected to be primarily driven by the loss of suitable habitats for typically small‐sized mammals—adults weighting ≤1 kg, sensu Chiarello (2000)—which constitute 54% of species in the region (Figure 1).…”