Habitat differences in mass-specific litter sizes of hispid cotton rats

Abstract

Litter size and body size of Sigmodon hispidus are known to covary positively both among and within some populations. In captivity, litter size varies with quality of diet. In the field, however, variation in maternal size can obscure nutritional effects on litter size. We reexamine litter sizes from sites in central Oklahoma varying in primary productivity due to application of herbicides and controlled burning. Mass-specific litter size of cotton rats showed no significant response to burning. In areas treated with tebuthiuron, litters were larger and population densities and primary productivity of monocots were higher than in areas receiving triclopyr. Slopes of the relationship between litter size, a component of fitness, and maternal mass did not differ significantly between habitats. Thus, percentage increase in litter size in the better habitat was greater for smaller breeding females. This implies that gains in fitness related to habitat productivity are size-specific in these populations.