Abstract
Animals and plants engineer their physical environment by building structures that create or modify habitat. Biotic effects on physical habitats can influence community composition, trophic dynamics, and ecosystem processes; however, the scales and mechanisms regulating the importance of biotic engineering effects are not well documented. We used a laboratory experiment with common and abundant silk net-spinning caddisflies (Trichoptera:Hydropsychidae) to investigate how biotic structures built in riverbeds influence fluid dynamics at micro spatial scales (1 cm) over 2 months. We made velocity measurements with acoustic doppler velocimetry around caddisfly silk structures to test how they influence flow velocity and whether these effects are maintained after the structure is abandoned. We found that caddisfly retreats reduced flow downstream by 85% and upstream by 17% compared to gravels without caddisfly retreats. We also found that experimentally abandoned caddisfly retreats could persist for at least 60 days, suggesting legacy effects of the structures. Although aquatic insects are rarely accounted for in hydrological models, our study suggests that small, but numerous caddisfly larvae could have substantial hydraulic effects. Future work could address variation in the magnitude and duration of biotic engineering among different silk-producing species, densities through space or time, and hydrologic regimes.
Highlights
Organisms that maintain, modify, or create habitat for themselves or other species can have substantial effects on environmental physical processes (Jones et al, 1994; Jones, 2012)
We show that a silk net retreat built by a common aquatic insect, the hydropsychid caddisfly, can reduce flow velocity by up to 85%
The findings from this experiment support those from fluid dynamics modelling showing that simulated, aggregated hydropsychid silk structures in the pore spaces of a gravel bed (0.2 m2) can reduce velocity at larger spatial scales by up to 70% when measuring the influence of multiple silk structures (Juras et al, 2018)
Summary
Modify, or create habitat for themselves or other species can have substantial effects on environmental physical processes (Jones et al, 1994; Jones, 2012). These effects derive from activity of animals and plants that range in body size, abundance, and behaviors and can result in a fundamental influence on landscape features (Cuddington et al, 2007). The relationships and feedbacks between river invertebrates and their physical environments are important to understanding the functionality of freshwater ecosystems
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