Effects Of A Climatic Gradient On Columbian Ground Squirrel (spermophilus Columbianus) Life History (tables, R-k Theory, Environmental Predictability)

Richard Michael Zammuto


Relationships among Columbian ground squirrel life history traits and environmental parameters were determined in order to test r-K theory over an elevational gradient in the Rocky Mountains of southwestern Alberta. The hypotheses tested were: (1) Columbian ground squirrels at lower elevations have smaller body sizes, earlier ages at maturity, lower adult survival rates, and larger litter sizes than squirrels at higher elevations, and (2) environments at lower elevations are less stable/more variable and less predictable than environments at higher elevations.;Over 500 ground squirrels were collected from 6 populations at different elevations (1300-2200m). Body weight, head-body length, reproductive condition, and litter size were determined. Ages were determined by examination of annual adhesion lines in the lower jawbone. Six life tables were constructed.;Variability and predictability of 3 meteorological variables were studied with respect to elevation. Other environmental factors were studied at the location of each population.;Body size (weight, length) was greater at lower elevations than at higher elevations. On average, squirrels matured later and lived longer at higher elevations than at lower elevations. Litter size did not vary (P > 0.05) with elevation.;Variabilities and predictabilities of maximum temperatures and precipitation did not vary (P > 0.05) with elevation. Minimum temperatures at higher elevations tended to be more predictable, but more variable (P = 0.06), than minimum temperatures at lower elevations. Standardized pooled predictabilities and variabilities of the 3 meteorological variables indicated that environments at higher elevations were more predictable than environments at lower elevations whereas variabilities of environments did not vary (P > 0.05) with elevation. Growing seasons were shorter, primary productivity (as indicated by tree-ring width) was lower, and winter soil temperatures below 50 cm were warmer at higher elevations than at lower elevations.;A variable environment may not necessarily be an unpredictable environment. Populations at higher elevations seemed to be limited by the summer environment while lower elevation populations seemed to be limited by the winter environment.;Contingent upon several assumptions, the original theory of r and K-selection was falsified by this empirical research. However, a number of the original predictions of the theory would have been supported if the locations of the predictable/unpredictable environments and r/K-strategists were reversed with respect to elevation.