Forest-lake ecotones in a tropical forest: Terrestrial invertebrate inputs to lakes decrease with forest distance

1. Ecotones between tropical forests and lakes compose an ecosystem interconnection with a high abundance of terrestrial invertebrates, which represent an outstanding resource for the aquatic fauna. However, there is still little quantitative 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 selected 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 morphometry 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 ecosystem. Hence, if the distance from the forest increases due, for instance, to severe 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.

Automated summary

This study quantified the contribution of terrestrial invertebrates to tropical lakes by setting up pan traps in six lakes located in the Atlantic rainforest in south-eastern Brazil. The total abundance, biomass, and richness of insect orders were examined. The distance from the forest and the morphometric characteristics of each lake were measured to assess their influence on terrestrial invertebrate inputs.