Cooperative Fish and Wildlife Research Units Program: Massachusetts
Education, Research and Technical Assistance for Managing Our Natural Resources

Social behaviors often are context-dependent; behaviors at high density may change or disappear at lower population densities. We analyzed spatial dispersion patterns and habitat associations at high and low population densities of male Espadarana (Centrolene) prosoblepon that declined following the invasion of a pathogenic fungus, Batrachochytrium dendrobatidis (Bd). We mapped the spatial location of male frogs on four permanent 200-m stream transects over 4 pre- and 7 postdecline yr. We calculated distances between nearest neighbors and between hot spots—defined as areas of high male density—and compared habitat associations of frogs at high and low densities. Average predecline density across transects was 0.034 ± 0.02 males m⁻¹ (mean ± SE) and dropped to 0.019 ± 0.02 males m⁻¹ postdecline. Nearest neighbor and between cluster distances did not change significantly between pre- and post-decline yrs. Nine of 21 hot spots persisted in the same location across 12 yrs, whereas 8 hot spots disappeared and 4 new hot spots appeared postdecline. We determined male abundance was correlated with the amount of leafy vegetation and stream width at high density, but we found no associations at low densities. Overall, spatial dispersion patterns were highly conserved for over a decade, despite a new cohort of individuals, a decline in abundance, and changes in physical structure associated with natural forest dynamics. Our results suggest spatial dispersion is density independent and that male hot spots are influenced by both physical habitat and social interactions.