Interactions between freshwater snails and tadpoles: competition and facilitation

Area of Science:

• Ecology
• Aquatic ecosystems
• Interspecies interactions

Background:

• Ponds of intermediate size often support high densities of freshwater snails and anuran tadpoles.
• Both snails and tadpoles consume periphytic algae, suggesting potential for strong competitive interactions.
• Previous research indicates potential for competition between these distantly related taxa in pond environments.

Purpose of the Study:

• To investigate the competitive interactions between two snail species (Lymnaea stagnalis, L. peregra) and tadpoles (Rana temporaria).
• To assess the impact of these interactions on snail growth, egg production, and tadpole metamorphosis.
• To monitor effects on the shared food resource, periphyton.

Main Methods:

• Field experiment manipulating densities of Lymnaea snails and Rana temporaria tadpoles.
• Measurement of snail growth, egg production, and tadpole metamorphosis (size, time).
• Monitoring of periphyton biomass using artificial substrates.

Main Results:

• Periphyton biomass was significantly reduced by the presence of snails and/or tadpoles.
• Snail growth and egg production were unaffected by coexistence, except for reduced egg production in L. stagnalis at high tadpole densities.
• Tadpole growth and metamorphosis were negatively impacted by increasing tadpole density, but positively influenced by snail presence, suggesting an indirect mutualistic relationship.

Conclusions:

• Snails and tadpoles exhibit complex interactions, with tadpoles negatively impacting snails via resource competition.
• Snails facilitate tadpole growth indirectly by consuming less preferred algae (Cladophora sp.), enhancing microalgal availability for tadpoles.
• This indirect mutualism highlights intricate food web dynamics and resource partitioning in freshwater pond ecosystems.