Abiotic mosaics affect seasonal variation of plant resources and influence the performance and mortality of a leaf‐miner in Gambel's oak (Quercus gambelii, Nutt.)

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AbstractConceptual models of terrestrial trophic dynamics have emphasized the potential influence of various abiotic factors, though empirical studies have found generalities to be scarce. Progress may result through an increased use of experimental gradients in tandem with existing, natural gradients of abiotic factors that are more difficult to manipulate. Along an elevation/climatic gradient, a fertilization experiment was conducted to examine the impact of environmentally induced variation in foliar nitrogen on tri‐trophic interactions for Phyllonorycter sp., a leaf‐miner (Lepidoptera: Gracillariidae), in Rocky Mountain white oak, Quercus gambelii. Microclimate determined the relative effect of host‐plant and natural‐enemy effects for Phyllonorycter sp. Cooler, more humid microclimates resulted in a higher biomass payoff (total biomass/density). Further, increased seasonal variation in foliar nitrogen content at warmer, drier sites significantly increased parasitism rates. Fertilization treatments increased foliar nitrogen content and resulted in increased early‐instar mortality. Fertilization treatment also acted in a non‐linear fashion with microclimate to influence spatial patterns in parasitism rates. Overall, microclimate was found to affect characteristics of each trophic level, including host‐plant nitrogen dynamics, Phyllonorycter sp. performance, and parasitism rates. Additionally, nutrient availability altered patterns of parasitoid‐related mortality in Phyllonorycter sp. within microclimates. These results suggest that local topographic variation in combinations of abiotic factors, or abiotic mosaics, has important effects for spatial patterns of tri‐trophic interactions.