Redundancy among three herbivorous insects across an experimental current velocity gradient

Area of Science:

• Ecology
• Aquatic Ecology
• Stream Ecology

Background:

• Algal periphyton forms the base of many stream food webs.
• Herbivorous insects are key grazers that control periphyton biomass.
• Current velocity is a major environmental factor structuring stream communities.

Purpose of the Study:

• To determine how local current velocity affects the periphyton removal rates of different herbivorous insect species.
• To investigate if herbivore species "function" similarly or differently in cropping periphyton under varying current conditions.
• To assess the potential for species redundancy or complementarity in periphyton removal.

Main Methods:

• Streamside experiments using ceramic tiles with controlled periphyton growth.
• Exposure of tiles to three distinct current velocity regimes: slow, medium, and fast.
• Testing four grazer treatments: three mayfly and caddisfly species (Baetis, Drunella, Glossosoma) individually and combined.

Main Results:

• Periphyton removal varied among species and with current velocity.
• Glossosoma and Baetis showed increased removal in faster currents, while Drunella's removal was consistent.
• At fast currents, all species removed similar amounts of periphyton; at slower currents, differences emerged.

Conclusions:

• Herbivory rates are species-specific and context-dependent, influenced by local current velocity.
• Some herbivore species exhibit functional redundancy in periphyton removal across different current speeds.
• Current-driven species interactions likely contribute to the co-existence of herbivorous insects in heterogeneous stream environments.