Entomology
Permanent URI for this communityhttp://hdl.handle.net/1903/11813
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Item Insectivorous birds reduce herbivory but do not increasemangrove growth across productivity zones(Wiley, 2022-05-24) Forde, Alexander J.; Feller, Ilka C.; Parker, John D.; Gruner, Daniel S.Top-down effects of predators and bottom-up effects of resources are important drivers of community structure and function in a wide array of ecosystems. Fertilization experiments impose variation in resource availability that can mediate the strength of predator impacts, but the prevalence of such interactions across natural productivity gradients is less clear. We studied the joint impacts of top-down and bottom-up factors in a tropical mangrove forest system, leveraging fine-grained patchiness in resource availability and primary productivity on coastal cays of Belize. We excluded birds from canopies of red mangrove (Rhizophoraceae: Rhizophora mangle) for 13 months in zones of phosphorus-limited, stunted dwarf mangroves, and in adjacent zones of vigorous mangroves that receive detrital subsidies. Birds decreased total arthropod densities by 62%, herbivore densities more than fivefold, and reduced rates of leaf and bud herbivory by 45% and 52%, respectively. Despite similar arthropod densities across both zones of productivity, leaf and bud damage were 2.0 and 4.3 times greater in productive stands. Detrital subsidies strongly impacted a suite of plant traits in productive stands, potentially making leaves more nutritious and vulnerable to damage. Despite consistently strong impacts on herbivory, we did not detect top-down forcing that impacted mangrove growth, which was similar with and without birds. Our results indicated that both top-down and bottom-up forces drive arthropod community dynamics, but attenuation at the plant-herbivore interface weakens top-down control by avian insectivores.Item Foraging connections: Patterns of prey use linked to invasive predator diel movement(PLoS, 2018-08-15) Johnston, Cora A.; Rankin, Erin E. Wilson; Gruner, Daniel S.Invasive predators can profoundly impact native communities, especially in insular ecosystems where functionally equivalent predators were evolutionarily absent. Beyond direct consumption, predators can affect communities indirectly by creating or altering food web linkages among existing species. Where invasive predators consume prey from multiple distinct resource channels, novel links may couple the dynamics of disjunct modules and create indirect interactions between them. Our study focuses on invasive populations of Eleutherodactylus coqui (Anura: Leptodactylidae) on Hawaii Island. Coqui actively forage in the understory and lower canopy at night but return to the forest floor and belowground retreats by day. Recent dietary studies using gut contents and naturally occurring stable isotopes indicate higher than expected consumption of litter arthropods, which in these Hawaiian forests are primarily non-native species. We used laboratory studies to observe diurnal and nocturnal foraging behavior, and experimental field additions of C4 vegetation as a litter tracer to distinguish epigaeic sources from food web pools in the C3 canopy. Lab trials revealed that prey consumption during diurnal foraging was half that consumed during nocturnal foraging. Analysis of δ13C isotopes showed incorporation of C4 carbon into litter arthropods within one month, and Bayesian mixing models estimated that 15±25% of the carbon in coqui tissue was derived from litter sources. These results support recent findings that E. coqui are not quiescent diurnally but instead actively forage. Such activity by a mobile invasive predator may introduce a novel linkage that integrates detrital and foliar resource pools, potentially distributing influences of invasive litter arthropods through the broader system to amplify impacts on native species.