To determine whether cotton rats (Sigmodon hispidus) establish home ranges, and whether home—range size and shape vary temporally, we measured site fidelity at daily and multiday intervals. The concept of site fidelity can be used to provide a quantitative measure of the existence of a home range. Mean squared distance from the center of activity (MSD) and a linearity index (LI) were used to measure site fidelity of the hispid cotton rat. Significant differences for these metrics between actual and simulated, random movement showed that home ranges existed for both daily and multiday periods. Home—range characteristics varied with temporal scale. Daily home ranges were more concentrated (lower MSD), linear (higher LI), and elongate (higher eccentricity, ECC) than multiday home ranges. The effects of sex, age, and season on MSD, LI, and ECC differed for daily and multiday home ranges. The area of daily home range was not different between sexes or ages, or among seasons, but multiday home ranges was larger for males, for adults, and in winter and summer. Knowing that home ranges exist is a necessary prerequisite for ecology or behavioral interpretation of space—use patterns before comparisons of home—range characteristics are made, however, the temporal scale of measurement must be considered, because scale alone can yield differences in size and shape.

No abstract

The Chinese tallow tree, Sapium sebiferum, was introduced to the Texas Gulf Coast in the early 1900's and has spread into coastal prairie habitats. Since coastal prairie contains few deciduous trees, we studied leaf fall dynamics, rate of decomposition, and the quantity and rate of nutrient input from decomposing tallow leaves. Among-year leaf fall averaged 382.6 g·m·yr, similar to other south temperat deciduous forests and about as predicted by Meentemeyer et al.'s (1982) AE-lignin model. Decay of tallow leaves (k=-4.33) was much more rapid than native black willow (k=-0.35) and than other temperate deciduous trees (k=-0.77). The ratio of lignin to initial nitrogen concentration, highly correlated with rate of decomposition for hardwood trees, was low for Chinese tallow and may contribute to rapid leaf decay. Taking AE and lignin content into account, Meentemeyer's (1984) model predicted k=-1.39 for Chinese tallow and k=-0.88 for black willow. Decay of tallow was much faster but decay of willow was slower than predicted, suggesting that decay on the coastal prairie may be controlled by factors other than lignin content and climate. N, P, and K characteristically accumulate as leaves decay. However, these elements did not accumulate as tallow leaves decayed, possibly because high densities of Armadillidium vulgare, a detritivore, reduced immobilization of elements by microbes. This would result in increased turnover of these elements. Accumulation of Al, Fe, Zn, and S in decaying tallow litter may be related to flood-drain cycles on coastel prairie clay soils. Ca, N, K, Mg, and S were added to forest soil in greatest amounts from decaying tallow leaves. Concentrations of P, K, NO-N, Zn, Mn, and Fe were significantly higher and Mg and Na were significantly lower in forest than in prairie soil, raising the possibility that Chinese tallow trees altered the distribution of nutrients in the soil profile. We conclude that the Chinese tallow tree may enhance productivity in ecosystems to which it has been introduced by addition of nutrients from rapid decay of leaves.

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Ecological interpretation of space use patterns often suffers from two methodological problems: inadequate number of captures per individual and pooling of data over time intervals. Insufficient sample size biases the computation of spatial areas, while pooling data over time intervals may mask shifts in space use due to changes in resource abundance. Radiotelemetry was used to alleviate these problems in an analysis of space use by the hispid cotton rat (Sigmodon hispidus). Home range area was greater for males than females, was largest during summer and winter months, was positively correlated with body hass, and was negatively correlated with population dencity. Exclusivity of home range revealed a high degree of ntolerance (41% exclusivity) and was positively correlated with body mass for males. In addition, like-sex categories (male-male, female-female) were more exclusive than unlike sex categories (male-female).Habitat composition of home ranges of females was significantly different from that of males and from that available. This result suggested home ranges of females were responsive to habitat composition (and quality), while males may respond more to female occurrence than resource availability.Space-use patterns of the hispid cotton rat indicated a solitary existence with greater tolerance of individuals of the opposite sex. Home range size decreased as population size increased, whereas home range overlaps were not affected by population density. These results reinforced the view of a dominance hierarchy in this species and suggested the existence of a polygynous mating system.