BODY SIZE AND LOCAL COMMUNITY STRUCTURE OF MAMMALS ACROSS TIME AND SPACE.
Lyons, S. Kathleen*,1, Lyons, , 1 National Center for Ecological Analysis and Synthesis, Santa Barbara, CA
ABSTRACT- The body size distributions of Recent North American mammals differ with spatial scale; continental faunas are right-skewed and highly modal, whereas local faunas are essentially uniform. Modal-sized species turnover more rapidly across space, while larger and smaller species occur repeatedly in different local faunas. However, Recent South American mammals in tropical communities show more peaked body size distributions. Moreover, the uni-modal continental scale body size distributions are unique to the present with bimodal distributions being the norm throughout the Cenozoic of North America. I collected body size and species composition data for 328 fossil communities in North America across the last 40 kya and 326 Recent communities across the globe. Assemblages were compared to uniform distributions and a random draw from continental distributions. A majority (>65%) of fossil assemblages were not significantly different from a uniform distribution and most (>75%) were significantly different from a random draw from a continental distribution. In addition, a majority (>50%) of Recent assemblages were not significantly different from a uniform distribution and most (>60%) were significantly different from a random draw from a continental distribution. Second, the mean, median, skew and kurtosis for each local assemblage were calculated and examined for patterns with respect to age, elevation, and geographic position. North American fossil assemblages were similar to Recent assemblages in their body size distributions regardless of age. However, Recent assemblages across the globe showed a significant relationship with latitude. Tropical communities were more variable in the shapes of their body size distributions rather than simply being more peaked as suggested by studies of Recent South American tropical assemblages. Temperate communities had kurtosis values within a narrow range indicating that they tend to be uniform. This pattern was repeated on each continent regardless of whether the continental distribution was unimodal (NA & SA) or bimodal (AF & EA). The similarity between the body size distributions of Late Quaternary assemblages and Recent assemblages implies that body size plays a key role in local community structure. However, the role of body size is latitude dependent.
Key words: body size distributions, mammals, latitude, Quaternary
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