Litter Invertebrate Communities along an Elevational Gradients

Relationships between litter invertebrate communities, climate, and forest net primary productivity (NPP) were investigated in two microhabitats along an elevational gradient in the Luquillo Experimental Forest. In forest floor litter communities, using palm litter as a control for forest type, although overall NPP declined with increasing elevation and rainfall, animal abundance, biomass and species richness were remarkably similar along the gradient. In non-palm litter, all community parameters declined with increasing elevation, along with NPP and litter nutrient concentra-tions. Nutrient concentrations were higher in palm than non-palm litter, and did not decline significantly along the gradient, and palm litter provided a more stable physical environment than other litter types. Thus, adaptations of invertebrates to the secondary factors of resource base and habitat (i.e. forest type), as seen in palm litter, may be more important in determining community structure than the primary effects of changing climate along the gradient. In structurally more complex bromeliad microcosms, which contain both litter and aquatic detritivore communities, abundance and species richness were independent of each other. Animal abundance declined, along with NPP, with increasing elevation, but species richness and animal biomass peaked at mid-elevation, confirming the monotonic pattern reported in other tropical elevation studies. The mid-elevation palo colorado forest is more architecturally complex, and richer in epiphytes and ground species than the other forests, and its intermediate climatic conditions may be more favourable to invertebrate survival than other forests. Bromeliad community parameters reflect forest characteristics specifically, rather than NPP and climate. The aquatic component of the bromeliad fauna was habitat-specific