Environmental Predictability, Variability, and Spermophilus columbianus Life History over an Elevational Gradient.
Ecology: Vol. 66, No. 6, pp. 1784–1794, by Richard M. Zammuto and John S. Millar. 1985.
Abstract. We quantitatively tested various aspects of the theory of r—
and K—selection for six populations of Columbian ground squirrels from
Alberta, Canada. Three measures of environmental predictability (maximum and
minimum temperatures, precipitation) and a presumed measure of food resource
levels supported the prediction that environments at lower elevations were less
predictable, and had greater, more variable food resource levels than environments
at higher elevations. Columbian ground squirrels in more predictable environments
(i.e., at higher elevations) had higher adult survival rates, later ages at
maturity, and possibly lower genetic variabilities than did squirrels in less
predictable environments (at lower elevations). Body mass was greater at lower
elevations than at higher elevations. Litter size showed no trend with respect
to elevation, but it tended to be most variable in unpredictable environments
at lower elevations. Although they were more predictable, the daily minimum
temperatures at higher elevations tended (P = .06) to show wider variation than
the minimum temperatures at lower elevations. Previous apparent problems with
r—K theory may be attributable in part to the assumption that predictability
and stability should covary. The major difference between the pattern emerging
from our study and that predicted by traditional theory is that predictability
of environments, and concomitantly the occurrence of K—strategists, was
found to increase with movement up an elevational gradient. Portions of r—K
theory may be found to be useful once all of its parameters are consistently
measured.
Right-click and save to download full paper (2200 KB PDF download)