Invertebrate herbivory during the regeneration phase: experiments with a freshwater angiosperm

Abstract

Summary Invertebrate grazing during the regeneration phase is well known to exert a strong structuring effect in terrestrial plant communities. However, very few studies have investigated the effect of invertebrate herbivores on regenerating freshwater angiosperms, despite the obvious benefits for the development of general theories in plant community ecology. Our study investigated the parameters that determine the sensitivity of the freshwater macrophyte Potamogeton pectinatus L. to herbivory by the pond snail Lymnaea stagnalis (L.). P. pectinatus was raised from winter‐collected tubers in aquatic microcosms and submitted to grazing by snails at various densities and starvation levels. Newly sprouted P. pectinatus was much more sensitive to snail grazing than mature plants: survival of newly sprouted plants decreased as snail density increased, whereas the survival rate of mature plants was unaffected by snail density. Moreover, the sensitivity of newly sprouted P. pectinatus to herbivory decreased as its initial tuber mass increased. The damage to newly sprouted P. pectinatus by herbivory increased with snail starvation. However, the presence of an alternative, highly palatable, food (i.e. benthic algae) deflected feeding on P. pectinatus, even by extremely hungry snails. These results demonstrate the potential structuring role exerted by gastropods during the regeneration of freshwater macrophytes, supporting results from terrestrial systems. They also suggest that regenerating plants may avoid invertebrate herbivory by modulating their intrinsic characteristics (e.g. increasing propagule size) or by emerging under favourable environmental conditions (e.g. low invertebrate density, presence of alternative food). Herbivory during the regeneration phase is therefore pivotal to our understanding of plant dynamics in aquatic as well as terrestrial ecosystems, and should be integrated into explicative models of vegetation patterns across various environments.