A Macrophysiological Analysis of Energetic Constraints on Geographic Range Size in Mammals

Abstract

Physiological processes are essential for understanding the distribution and abundance of organisms, and recently, with widespread attention to climate change, physiology has been ushered back to the forefront of ecological thinking. We present a macrophysiological analysis of the energetics of geographic range size using combined data on body size, basal metabolic rate (BMR), phylogeny and range properties for 574 species of mammals. We propose three mechanisms by which interspecific variation in BMR should relate positively to geographic range size: (i) Thermal Plasticity Hypothesis, (ii) Activity Levels/Dispersal Hypothesis, and (iii) Energy Constraint Hypothesis. Although each mechanism predicts a positive correlation between BMR and range size, they can be further distinguished based on the shape of the relationship they predict. We found evidence for the predicted positive relationship in two dimensions of energetics: (i) the absolute, mass-dependent dimension (BMR) and (ii) the relative, mass-independent dimension (MIBMR). The shapes of both relationships were similar and most consistent with that expected from the Energy Constraint Hypothesis, which was proposed previously to explain the classic macroecological relationship between range size and body size in mammals and birds. The fact that this pattern holds in the MIBMR dimension indicates that species with supra-allometric metabolic rates require among the largest ranges, above and beyond the increasing energy demands that accrue as an allometric consequence of large body size. The relationship is most evident at high latitudes north of the Tropics, where large ranges and elevated MIBMR are most common. Our results suggest that species that are most vulnerable to extinction from range size reductions are both large-bodied and have elevated MIBMR, but also, that smaller species with elevated MIBMR are at heightened risk. We also provide insights into the global latitudinal trends in range size and MIBMR and more general issues of phylogenetic and geographic scale.

Overcoming phylogenetic and geographic uncertainties to test for correlates of range size evolution in gymnophthalmid lizards

“…The relationships between range size and body size conforms to the above‐diagonal triangular shape found by Brown and Maurer (; see Introduction), and subsequent studies in endothermic species groups (Brown and Maurer , Gaston and Blackburn , Agosta et al ). While smaller species may have big or small ranges, bigger species generally only show relatively big ranges.…”

“…Understanding the factors that constrain species range size is a central task for evolutionary biogeographical theory (Brown et al , Gaston and Blackburn , Jablonski , Gaston and Fuller , Agosta et al ). This endeavor has important conservation planning implications since species with small ranges can increase both regional diversity levels (Scott et al , Arita and Rodríguez ) and species extinction risk (Gaston and Blackburn , Jablonski, ).…”

“…Conversely, scatters distributed below the graph diagonal (Fig. B) may suggest morphologically induced dispersal costs (Gaston and Blackburn , Agosta et al ). Exemplifying this case, Lee et al () found that while typical lizards showed both big and small ranges, limbless ones showed only smaller ranges.…”

Mass‐independent maximal metabolic rate predicts geographic range size of placental mammals

“…Unsurprisingly, mammals that were endangered tended to have smaller range sizes than species that were not threatened. In addition, it has recently been proposed that both small and large mammals with high, mass‐independent, basal metabolic rates may be at greater risk for extinction (Agosta, Bernardo, Ceballos, & Steele, ). Our analyses suggest yet another possibility, if high mass‐independent MMR leads to larger range size, and if larger range sizes reduce extinction risk, then high mass‐independent MMR might be associated with a lower extinction risk.…”

“…Mass‐independent BMR (i.e. residual BMR from regression on mass) was correlated ( r 2 = .02, p < .001) with geographic range size for a large ( n = 574 species) sample of mammals (Agosta et al., ). For rodents only, the correlation ( r 2 = .05, p < .001) was a bit higher.…”