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Dryad

Aquatic top predator prefers terrestrial prey in an intermittent stream

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Nov 21, 2024 version files 56.69 MB
Dec 24, 2024 version files 56.69 MB

Abstract

Ecosystems are often trophically entangled, sharing subsidies of energy and nutrients across habitat boundaries (e.g., forest to stream, stream to forest). In freshwater habitats surrounded by riparian vegetation, aquatic consumers may benefit from pulsed inputs of terrestrial organic matter, such as leaf litter and drowning organisms. This is especially pronounced in intermittent streams where the boundary between terrestrial and aquatic habitats is seasonally blurred. Over the past 10 years, we observed an aquatic insect predator Abedus indentatus (Hemiptera: Belostomatidae) largely feeding on terrestrial organisms in intermittent streams at Pinnacles National Park, California. To expand on these observations, we developed a behavioral assay where predators were presented with a range of prey comprising 11 species of various sizes from both aquatic and terrestrial habitats. We found that predator behavior was non-random and often influenced by prey characteristics. In particular, we found that predators tended to prefer large, terrestrial prey. Additionally, we found a positive relationship between size and strike probability among aquatic prey; however, this relationship did not hold for terrestrial prey items, indicating that certain size breakpoints might overcome increased levels of prey defense. Our results indicate that A. indentatus might favor prey items with weaker defenses within aquatic environments. However, other factors (i.e., prey size) might mediate foraging behavior. Because aquatic macroinvertebrate predators in intermittent streams depend on the terrestrial-aquatic interface, local predator dynamics may not be fully understood without considering fluxes of prey crossing ecosystem boundaries.