TROPICAL FOREST FRAGMENTATION AND ISOLATION PROMOTE ASYNCHRONY AMONG POPULATIONS OF A FRUGIVOROUS RODENT

1. Spiny rat Proechimys semispinosus populations on eight small islands in Gatun Lake (central Panama) were censused monthly for 1 year by live-trapping to examine seasonal patterns of demography in a fragmented landscape. 2. The annual fluctuation in density, breeding activity, age structure, and sex ratio from all populations combined was similar to populations studied previously in central Panama. Densities were lowest at the beginning of the rainy season and peaked in the late rainy season. Breading occurred all year, but the number of births was greatest in April. The proportion of adults peaked in mid-dry f season and was lowest in mid-rainy season. 3. Each separate population also showed distinct fluctuations, but the timing of peaks and lows varied among populations. Density peaked during any month from April through December, and each population had a period of reproductive quiescence when no births occurred. The length of the breeding season varied from 4 to 11 months. Only the proportion of adults showed a high degree of synchrony among populations. 4. Asynchrony among isolated populations of this tropical rodent contrasts with temperature rodents, which generally show a high degree of synchrony among isolated populations. 4. Asynchrony among isolated populations of this tropical rodent contrasts with temperature rodents, which generally show a high degree of synchrony among isolated populations. 5. This tropical-temperature dichotomy may be caused by differential use of environmental cues such as photoperiod to initiate and terminate breeding, and by the high diversity and patchiness of tropical forests.