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Indirect effects of largemouth bass dietary cues on macrophytes, mediated by crayfish behavior.
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In the landscape of fear, prey continually adjust their behavior to avoid potentially deadly encounters with predators (Laundre et al., 2010). These responses incur costs for prey that constitute the non-consumptive effects of the predator (Brown et al., 1999). Prey often avoid patches where predatory stimuli have been detected (Sih, 1980). Animals under threat may reduce their activity to decrease the chance of encountering the predator (Stein & Magnuson, 1976). Prey may also change mating behaviors because searching for mates usually requires activity which increases exposure to predators (Ryan, 1985). Grazing animals may forage differently because time spent foraging is time that is not spent vigilant to threats (Fortin et al., 2004). Alterations in prey behavior change the way that species interact within the community which can have significant impacts on diversity. Prey that change their foraging behavior in response to predatory stimuli can increase or decrease the abundance of the species they consume as food. This phenomenon is an example of a trait-mediated indirect effect (TMIE) (Abrams, 1995). Classic examples of TMIEs involve animals relocating to forage away from predatory threats, thereby reducing localized herbivory. The wolves in Yellowstone National Park release young aspens and willows from grazing pressure by driving elk away from lowland valleys to feed at higher elevations (Ripple & Beschta, 2006, 2007). Pools in stream ecosystems that hold predatory fishes have greater abundance of filamentous algae cover because herbivorous fishes will not feed near the predators (Power & Matthews 1983). Other animals change their dietary preferences when threatened. Grasshoppers feeding in prairies will consume herbaceous plants to avoid the grasses where spiders are hunting (Schmitz, 1998). When their predators are present, dark-eyed juncos will select seeds that can be swallowed with the head upright over seeds that need to be opened against the ground (Lima, 1988). Predator odor cues are especially important stimuli in aquatic environments because visibility is often limited due to turbidity or light penetration (Wisenden, 2000). Odor cues can be dispersed over long distances from their source (Atema, 2012), persist for considerable time in the environment (Turner & Montgomery, 2003), and contain highly specific information about the source predator (Ferrari et al., 2010). The specificity of chemoreception allows prey to distinguish threats from non-threats (Gherardi et al. 2011), identify different types of predators (Turner et al., 1999), and even discern details about the predator’s diet (Chivers & Smith, 1998). The dietary components of predator odor are known to modulate the strength of prey responses. Prey animals typically respond most strongly to the odors of predators that have consumed congeneric or conspecific prey. Turner (2008) found that two species of snails increased refuge use in the presence of odors from a sunfish that had consumed conspecific snails. Tadpoles reduce their movement more in the presence of odors from predatory fish and damselfly larvae that have recently consumed tadpoles, than they do for either predator on a general diet (Chivers & Mirza, 2001). However, changes in foraging behavior and dietary preferences of prey due to predator diet cues are not well studied in aquatic invertebrates. In freshwater streams, crayfish function as keystone species primarily because of their omnivorous diet (Momot, 1995). They also act as ecosystem engineers by digging burrows and modifying the structure of vegetated aquatic habitats (Creed & Reed, 2004). Adult crayfish feed heavily on macrophyte vegetation (Hogger 1988) and their herbivory can have significant impacts on aquatic macrophyte communities (Lodge et al., 1994). Crayfish are known to be selective in which macrophytes they consume (Chambers et al., 1991), and my previous work has shown that their macrophyte preferences change when predatory threats are present (Wood et al., 2018; in prep.). Recent research in the Laboratory for Sensory Ecology has demonstrated that rusty crayfish (Orconectes rusticus) significantly alter their behavior in response to largemouth bass (Micropterus salmoides) fed different diets (Beattie & Moore, 2018; in review). These results showed that rusty crayfish spent significantly more time in shelters in the presence of odors from bass that had consumed rusty crayfish, while bass fed a congeneric crayfish diet (Orconectes virilis) did not elicit the same response, suggesting that rusty crayfish can recognize differences in predator odor cues caused by diet (Beattie & Moore, 2018; in review). Therefore, I aim to investigate the foraging behavior and dietary preferences of rusty crayfish under the influence of odor cues from largemouth bass fed conspecific and congeneric crayfish diets. I will examine the impacts of altered crayfish foraging on macrophyte abundance, and the resulting indirect effect of the predator on the macrophyte community. Knowledge of changes in crayfish feeding patterns will allow us to better understand the importance of predator dietary cues in determining the behavior of prey, and their subsequent impacts on community dynamics and habitat.
UMBS Graduate Student Research Fellowship
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