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Spacing patterns of individuals within an island population of the Central American spiny rat Proechimys semispinosus were studied by radio-tracking eight adults for 2 months during the rainy season and eight adults for 1 month during the dry season in central Panama. All trees ≥10 cm diameter at breast height on the island were mapped, tagged, identified to species, and inventoried monthly to determine fruit production. Diurnal telemetry was conducted to locate daytime resting burrows. Burrow habitat was quantified by measuring nine variables at each burrow site. Individuals had larger home ranges and greater home-range overlap during the rainy season, and males had marginally larger home ranges than females. No evidence was found of attraction, avoidance or exclusive use of space by adult spiny rats. Thirty-six located burrows had nine instances of co-occupancy. Burrows were located close to water and had little herbaceous cover. The presence of broadly overlapping home ranges, larger home ranges of males vs females, greater numbers of burrows of females in home ranges of males vs those of females, and larger home ranges of sexually active males suggest that P. semispinosus had a promiscuous mating system within this population.

Spacing patterns of adult Proechimys semispinosus (Central American spiny rat) within five island populations in central Panama were determined by live-trapping over a one-year period. Home ranges were described 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 home range was also calculated. Mean home-range size and overlap were compared among islands and between sexes with two-way analysis of variance and were related to mean density of adult males and females and island size with linear regression analysis. Home-range size and overlap were also compared while controlling for density using analysis of covariance. Home-range size varied between the sexes but not among islands, with males generally having larger home ranges than females. Home-range size showed a negative relationship to density, and the difference in home-range size between the sexes prevailed even after controlling for density. Home-range overlap varied among islands but not between the sexes. There was no linear relationship between overlap and density, although individuals within two low-density populations had nearly 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 indefensible because of the spatial and temporal distribution of resources (i.e. primarily falling fruit). Although theory predicts that spatially patchy and poorly renewable resources promote territoriality, resources in tropical forests of the study area may be randomly or too patchily distributed or ephemeral to permit maintenance of territories that span a large portion of an animal's home range. More detailed study is necessary to reveal finer-scale patterns of territoriality (e.g. defence of burrows or concentrations of fallen fruit).