Among‐Species Overlap in Rodent Body Size Distributions Predicts Species Richness Along a Temperature Gradient
This work is supported by National Science Foundation, grants 1550765 (awarded to PLZ, SR, AS, BB; supporting QDR and JMG) and 1550745 (awarded to BB), the Israel Science Foundation Grant 1356/15 (awarded to JB), Michigan State Univ. (PLZ and QDR), Bryn Mawr College (SR and JMG), and Academia Sinica (M‐NT).
Temperature is widely regarded as a major driver of species richness, but the mechanisms are debated. Niche theory suggests temperature may aﬀect richness by ﬁltering traits and species in colder habitats while promoting specialization in warmer ones. However, tests of this theory are rare because niche dimensions are challenging to quantify along broad thermal gradients. Here, we use individual-level trait data from a long-term monitoring network spanning a large geographic extent to test niche-based theory of community assembly in small mammals. We examined variation in body size among 23 communities of North American rodents sampled across the National Ecological Observatory Network (NEON), ranging from northern hardwood forests to subtropical deserts. We quantiﬁed body size similarity among species using a metric of overlap that accounts for individual variation, and ﬁt a structural equation model to disentangle the relationships between temperature, productivity, body size overlap, and species richness. We document a latitudinal gradient of declining similarity in body size among species towards the tropics and overall increase in the dimensions of community-wide trait space in warmer habitats. Neither environmental temperature nor net primary productivity directly aﬀect rodent species richness. Instead, temperature determines the community-wide niche space that species can occupy, which in turn alters richness. We suggest a latitudinal gradient of trait space expansion towards the tropics may be widespread and underlie gradients in species diversity.
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Read, Q.D., J.M. Grady, P.L. Zarnetske, S. Record, B. Baiser, J. Belmaker, M-N. Tuanmu, A. Strecker, L. Beaudrot, K. Thibault. 2018. Among-species overlap in rodent body size distributions predicts species richness along a temperature gradient. Ecography