The ecology of Attwater's pocket gopher, Geomys Attwateri : food habits, impact on resources, and the role of resources in demographic and life-history variation



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A combined kill-trapping and live-trapping study was conducted to elucidate the extent and nature of intraspecific demographic and life-history variation in Attwater's pocket gopher (Geomys attwateri) and to relate the observed variation to abundance and dispersion of resources (food) along a resource gradient. Dietary habits and preferences were also examined with respect to resource variation. In order to achieve the objective, preliminary information on the feeding habits of Attwater's pocket gopher and the impact of this fossorial rodent on its resources was required. The diet of Attwater's pocket gopher varied seasonally and generally reflected resource availability. Few species specific preferences were found, although perennial dicots were preferred. Preference for perennial dicots and avoidance of annual resources varied with resource availability. Perennial monocots were the most abundant resource in the diet. Utilization of perennial monocots by G. attwateri significantly reduced below-ground biomass of this resource category, whereas, burrowing and mound-building activities increased above-ground biomass of the preferred resource category, perennial dicots. Generally, plant species composition was not influenced by G. attwateri, but cover and frequency of most plant species increased in the absence of pocket gophers. Significant intraspecific variation was found for density, percentage of young disappearing/month, reproductive phenology, movement, and body mass. Sex ratio, age structure, growth rate, litter size, percentage of adults disappearing/month, and expectation of further life did not vary along the resource gradient. Plant resources directly affected population density (carrying capacity) of Attwater's pocket gopher. Low carrying capacity resulted from random dispersion of preferred resources, high abundance of annual resources, and probably low foraging efficiency. Low carrying capacity resulted in poor survival of young, hence, low density. The mechanism of density regulation was intraspecific aggression.



Pocket gophers--Ecology