Functional effects of deforestation on stream ecosystems in Madagascar based on growth and production of mayflies (Ephemeroptera)

The effects of deforestation on species richness and abundance of tropical freshwater organisms are increasingly well documented, but corresponding effects on functional properties of ecosystems, such as productivity and growth, are largely unknown. Here we investigated the biomass production and growth of eight species of mayflies (Ephemeroptera) in streams of eastern Madagascar. We compared three study sites in primary tropical forest with three in degraded open canopy area (savoka). All species were asynchronous and aseasonal. Seven species were multivoltine (3-4 generations per year) and one was semi-voltine. Biomass production of the most abundant species was 4-5 times greater in savoka than in forest, and standing biomass: productivity (P/B) was always higher in savoka. This production shift was mainly caused by the two Xyrodromeus species, both of which feed on periphytic algae that are more abundant in an open canopy. Surprisingly, Xyrodromeus females emerged more rapidly and were larger in size in savoka than in forest. Our results clearly indicate that deforestation in tropical Madagascar leads not only to a shift in mayfly community composition, but perhaps more importantly to functional changes in the ecosystem, namely standing biomass, annual production, and female size at maturity.