. Bulletin. Science; Natural history; Natural history. IV 7 2 POPULATION DENSITY 01 nil HISPID COTTO R U Mares (1972). Determination of population den- sities was based on numbers of individual cotton rats caught (.luring each trapping period. I he paucity of previously uncaptured rats obtained at the close of each trapping period indicated thai most rats on the grid had been accounted for (see Davenport, 1964; of. Van Vleck, 1968). Ecologi- cal density (number per preferred habitat—Odum, 1971 ) was estimated by assuming that the popula- tion was distributed throughout the different habi- tats
. Bulletin. Science; Natural history; Natural history. IV 7 2 POPULATION DENSITY 01 nil HISPID COTTO R U Mares (1972). Determination of population den- sities was based on numbers of individual cotton rats caught (.luring each trapping period. I he paucity of previously uncaptured rats obtained at the close of each trapping period indicated thai most rats on the grid had been accounted for (see Davenport, 1964; of. Van Vleck, 1968). Ecologi- cal density (number per preferred habitat—Odum, 1971 ) was estimated by assuming that the popula- tion was distributed throughout the different habi- tats in the proportions shown by trap success (see Fleharty and Mares, 1972). From October of 1967 through February of 1969, weights of rats were recorded at the time of capture and the "cap- ture calendar" method (Andrzcjcwski, 1963, 1967) was used to determine age structure of the popu- lation. Meteorological data were obtained from the Fort Hays Agricultural Experiment Station, which is located about two miles from the study area. RESULTS. S A 1965 W S SAWSSAWS 1966 1967 SEASONS Figure I. line graph showing number of caught on grid in spring, summer, autumn, of 1965-1968. SAW 1968 cotton rals and winter If data pertaining to the last year of study are dis- regarded, crude density (number per entire study area) ranged from a low of per hectare (one rat on grid) in May of 1965 to a high of per hectare (115 rats on grid) in October of 1967. Greatest densities occurred in autumn of each year, whereas least densities occurred in the springs of 1965, 1966, and 1968, and in summer of 1967 (Fig. 1). Males were significantly more numer- ous than females (P < .05); a total of 516 males (57 percent) and 390 females (43 percent) were captured. Ecological densities were greatest in low-lying plant communities dominated by Andropogon gerardi (Fleharty and Mares, 1972). Monthly estimates of density in a draw, where the vegeta- tion consisted principally of A. gerardi, K
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