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Plant–herbivore interactions account for much of the biodiversity observed in an ecosystem. Plants may alter defense expression dependent on the specific herbivore present. Many studies focus on the optimization of these defenses against a single herbivore, but in an ecological context, there may be a myriad of herbivores at any given time. We designed a study to examine defenses employed by swamp white oak (Quercus bicolor) against insects and large mammals. We established six deer exclosures with trees located inside and outside each exclosure. Outside the exclosures, physical constraints only allow deer to feed up to a browseline on trees, whereas insects can potentially access all portions of the tree. Trees inside exclosures were only accessible to insect herbivores. Furthermore, insecticides were applied to half of the exclosures to create insect‐free (i.e., insecticide applied), deer‐free (i.e., inside exclosures), deer‐only (i.e., outside exclosures with insecticide), and herbivore‐free (i.e., inside exclosures with insecticide) environments. This design allowed us to analyze simultaneous defensive responses of individual trees to mammal and insect herbivores. We predicted that because insects represent a continuous threat, plants should invest in fixed concentrations of defenses (e.g., polyphenols, tannins, and condensed tannins), even when deer are absent. When deer are present, plants should increase investment in defenses in tissues that deer have access to. We found that plant defense strategies varied spatially on individual trees. When only insects were present, nutritional constituents (e.g., nitrogen and non‐structural carbohydrates) did not change but antinutritional constituents increased. Contrastingly, when deer were present, both nutritional and antinutritional constituents decreased. We found a decrease in insect functional group diversity when deer were present. Our findings suggest that plants may partition defense strategies depending on the most prominent herbivore pressure. However, changes in insect functional group diversity may result from either changes in plant defense strategy or intraspecific competition among multiple herbivores. Future studies should investigate patterns of chemical heterogeneity displayed by plants in response to diverse herbivore pressures. [ABSTRACT FROM AUTHOR]

Deer support high tick intensities, perpetuating tick populations, but they do not support tick-borne pathogen transmission, so are dilution hosts. We test the hypothesis that absence of deer (loss of a dilution host) will result in either an increase or a reduction in tick density, and that the outcome is scale dependent. We use a complementary methodological approach starting with meta-analysis, followed up by a field experiment. Meta-analysis indicated that larger deer exclosures reduce questing (host-seeking) tick density, but as the exclosure becomes smaller (<2.5 ha) the questing tick density is increased (amplified). To determine the consequences for tick-borne pathogen transmission we carried out a field experiment, comparing the intensity of ticks that fed on hosts competent for tick-borne pathogen transmission (rodents) in two small (<1 ha) deer exclosures and their replicated controls. Intensity of larval ticks on rodents was not significantly different between treatments, but nymph intensity, the tick stage responsible for tick-borne encephalitis (TBE) transmission, was higher in deer exclosures. TBE seropositive rodents were found in a deer exclosure but not in the controls. We propose that localized absence of deer (loss of a dilution host) increases tick feeding on rodents, leading to the potential for tick-borne disease hotspots. [ABSTRACT FROM AUTHOR]