SPACING PATTERNS WITHIN POPULATIONS OF A TROPICAL-FOREST-RODENT, PROECHIMYS-SEMISPINOSUS, ON 5 PANAMANIAN ISLANDS

Spacing patterns of adult Proechimys semispinosus (Central American sp iny rat) within five island populations in central Panama were determi ned by live-trapping over a one-year period. Home ranges were describe d by minimum convex polygons for each individual that had a sufficient number of captures to allow accurate description. Home-range size was calculated as the area of an individual's polygon. The total area of overlap of each individual's home range with every other consexual's h ome range was also calculated. Mean home-range size and overlap were c ompared among islands and between sexes with two-way analysis of varia nce and were related to mean density of adult males and females and is land size with linear regression analysis. Home-range size and overlap were also compared while controlling for density using analysis of co variance. Home-range size varied between the sexes but not among islan ds, with males generally having larger home ranges than females. Home- range size showed a negative relationship to density, and the differen ce in home-range size between the sexes prevailed even after controlli ng for density. Home-range overlap varied among islands but not betwee n the sexes. There was no linear relationship between overlap and dens ity, although individuals within two low-density populations had nearl y exclusive home ranges. The high degree of overlap among home ranges within some populations suggests that P. semispinosus do not maintain large exclusive territories. Such territories may be economically inde fensible because of the spatial and temporal distribution of resources (i.e. primarily falling fruit). Although theory predicts that spatial ly patchy and poorly renewable resources promote territoriality, resou rces in tropical forests of the study area may be randomly or too patc hily distributed or ephemeral to permit maintenance of territories tha t span a large portion of an animal's home range. More detailed study is necessary to reveal finer-scale patterns of territoriality (e.g. de fence of burrows or concentrations of fallen fruit).