Similarity of mammalian body size across the taxonomic hierarchy and across space and time.
Although it is commonly assumed that closely related animals are similar in body size, the degree of similarity has not been examined across the taxonomic hierarchy. Moreover, little is known about the variation or consistency of body size patterns across geographic space or evolutionary time. Here, we draw from a data set of terrestrial, nonvolant mammals to quantify and compare patterns across the body size spectrum, the taxonomic hierarchy, continental space, and evolutionary time. We employ a variety of statistical techniques including "sib-sib" regression, phylogenetic autocorrelation, and nested ANOVA. We find an extremely high resemblance (heritability) of size among congeneric species for mammals over approximately 18 g; the result is consistent across the size spectrum. However, there is no significant relationship among the body sizes of congeneric species for mammals under approximately 18 g. We suspect that life-history and ecological parameters are so tightly constrained by allometry at diminutive size that animals can only adapt to novel ecological conditions by modifying body size. The overall distributions of size for each continental fauna and for the most diverse orders are quantitatively similar for North America, South America, and Africa, despite virtually no overlap in species composition. Differences in ordinal composition appear to account for quantitative differences between continents. For most mammalian orders, body size is highly conserved, although there is extensive overlap at all levels of the taxonomic hierarchy. The body size distribution for terrestrial mammals apparently was established early in the Tertiary, and it has remained remarkably constant over the past 50 Ma and across the major continents. Lineages have diversified in size to exploit environmental opportunities but only within limits set by allometric, ecological, and evolutionary constraints.
Smith
Felisa A
FA
National Center for Ecological Analysis and Synthesis, Working Group on Body Size in Ecology and Paleoecology, Santa Barbara, California 93101-5504, USA. fasmith@unm.edu
Brown
James H
JH
Haskell
John P
JP
Lyons
S Kathleen
SK
Alroy
John
J
Charnov
Eric L
EL
Dayan
Tamar
T
Enquist
Brian J
BJ
Ernest
S K Morgan
SK
Hadly
Elizabeth A
EA
Jones
Kate E
KE
Kaufman
Dawn M
DM
Marquet
Pablo A
PA
Maurer
Brian A
BA
Niklas
Karl J
KJ
Porter
Warren P
WP
Tiffney
Bruce
B
Willig
Michael R
MR
D000818:Animals; D005075:Biological Evolution; D049628:Body Size; D002965:Classification; D005843:Geography; D008322:Mammals / Q000033:anatomy & histology* / Q000145:classification*; D012044:Regression Analysis