Anthropogenically-driven climate warming is a hypothesized driver of
animal body size reductions. Less understood are effects of other
human-caused disturbances on body size, such as urbanization. We
compiled 140,499 body size records of over 100 North American mammals to
test how climate and urbanization, and their interactions with species
traits, impact body size. We tested three hypotheses of body size change
across urbanization gradients; urban heat island effects, fragmentation,
and resource availability. Our results unexpectedly demonstrate
urbanization is more tightly linked with body size changes than
temperature, most often leading to larger individuals, thus supporting
the resource availability hypothesis. In addition, life history traits,
such as thermal buffering, activity time, and average body size play
critical roles in mediating the effects of both climate and urbanization
on intraspecific body size trends. This work highlights the value of
using digitized, natural history data to track how human disturbance
drives morphological change.
Mammalian body size is determined by interactions between climate, urbanization, and ecological traits
