Influence of temperature, landscape, and fine-scale forage availability on ungulate morphometrics

Abiotic and biotic variables strongly influence morphological variation in
wildlife, but there is disagreement on the relative importance of various
factors. Primary competing hypotheses regarding drivers of interpopulation
animal morphology include those related to heat regulation and those
related to forage availability. Despite data to support both hypotheses in
various systems, few have considered fine-scale forage availability data
across a large geographic area. White-tailed deer (Odocoileus virginianus)
body and antler size vary widely across their geographic distribution,
with larger deer often associated with landscapes providing large amounts
of high-quality forage. However, there is limited information on the
influence of temperature, landscape, and site-specific forage availability
on deer morphology across a wide geographic area. We collected body mass,
antler size, and site-specific growing-season forage availability from 35
locations across 21 eastern U.S. states. Average female body mass
increased by 1.4 kg for every 1˚C decrease in average annual temperature
and increased by 1.6 kg for every 10% increase in landscape crop coverage.
Mature male antler size also correlated with temperature and crop
coverage, with antler size increasing 4.9 cm for every 1˚C decrease in
average annual temperature and increasing 7.1 cm for every 10% increase in
landscape crop coverage. After controlling for landscape effects, adult
female mass was correlated with site-specific nutritional carrying
capacity based on a 0.3% phosphorus constraint (P NCC), with average
female body mass increasing 0.15 kg for every 1 deer day/ha increase in P
NCC. Male antler size was marginally correlated with P NCC as well, with
antler size increasing 0.7 cm for every 1 deer day/ha increase in P NCC.
Our results support the Resource Rule at the local scale, but temperature
and landscape factors contribute to interpopulation variation in
morphology across broad spatial scales.