Ciclagem de nutrientes em paisagens fragmentadas: a importância da qualidade da matriz

Abstract

The deforestation threatens ponds ecosystems and promotes the alteration of these ecosystems and hinders the access of organisms that use these ecosystems as breeding areas, for instance: anurans. The local extinction of species leads to the alteration of ecosystem processes, such as nutrient cycling. Scattered trees are important landscape structures in deforested matrices, increasing connectivity and biodiversity. The present study aims to combine concepts of landscape ecology, community ecology, and ecosystem ecology to understand the effect of scattered trees on ponds ecosystem in pasture areas. We aim to assess the effect of scattered trees on the biotic and abiotic characteristics of ponds, understand the effect of scattered trees on the composition of anuran tadpole communities, and understand how scattered trees affect ecosystem processes, such as tadpoles-driven nutrient cycling. We used an experimental system of artificial ponds, located in a pasture matrix, divided into three treatments: ponds at the forest edge, ponds under scattered tree canopy, and ponds in open pasture. In each ponds, we measured: temperature, oxygen, turbidity, conductivity, nutrient concentration, phytoplankton chlorophyll, allochthonous organic matter, tadpole species abundance and composition, and tadpole ammonia and phosphate excretion rates. Scattered-tree ponds had higher nutrient concentrations, phytoplankton chlorophyll, and allochthonous organic matter, while pasture ponds had higher oxygen and turbidity concentrations. There was no effect of scattered trees on tadpole community composition and abundance, nor did we observe effects of biotic and abiotic variables. Scattered-tree ponds had lower species richness and diversity than pasture and edge ponds. We found that species richness and diversity had a significant effect on tadpole community nutrient cycling. We did not observe any effect of treatments or biotic and abiotic variables on community nutrient cycling. Scattered trees are important landscape elements and elevates the heterogeneity in pasture areas, however this did not impact tadpoles role as nutrient recycler.