Forest–lake ecotones in a tropical forest : terrestrial invertebrate inputs to lakes decrease with forest distance.

Abstract

1. Ecotones between tropical forests and lakes compose an ecosystem intercon- nection with a high abundance of terrestrial invertebrates, which represent an

outstanding resource for the aquatic fauna. However, there is still little quantita- tive information on tropical forest contribution in terms of invertebrate inputs

into lacustrine systems and the factors controlling this flux.

2. To quantify the terrestrial invertebrate contribution into tropical lakes, we se- lected six lakes located in the Atlantic rainforest, south-eastern Brazil, and used

pan traps placed in the lakeshore. We focused on total abundance, biomass, and

richness of insect orders. To assess the influence of forest and lake morphom- etry on terrestrial invertebrate inputs into lakes, we measured the forest–lake

distance and considered the morphometric characteristics of each lake. 3. Distance from forest negatively affected the invertebrate biomass reaching the lakes. The dissimilarity across different ecotones also increased with distance from the forest. Perimeter-to-area ratio negatively affected the invertebrate abundance, suggesting that more dendritic lakes receive more invertebrates from the forest. 4. We estimated that annually, on average 21 tons of terrestrial invertebrates fall

into the studied lakes, representing a massive food resource for the aquatic eco- system. Hence, if the distance from the forest increases due, for instance, to se- vere drought or deforestation, it will create an herbaceous environment unable to provide such a quantity of insects to the water ecosystems, compromising aquatic and terrestrial trophic webs dynamics.