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Data from: Divergent investment in direct versus indirect defense in Populus tremuloides across a latitudinal gradient

Soule, Abrianna1

Published Jul 28, 2026 on Dryad. https://doi.org/10.5061/dryad.t1g1jwtbc

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Abstract

Theory predicts that plant defense against herbivores should be greatest towards the equator due to the strong selective pressure of more populous and diverse herbivore communities, yet recent work suggests variation in plant defense is more complex, predicting divergent patterns of investment across defense types and underlying environmental drivers. To address gaps in previous research, we measure multiple defense types in the same system and consider both biotic and abiotic variables hypothesized to underlie latitudinal gradients. Using the tree species trembling aspen (Populus tremuloides), we combine field surveys of biotic interactions and defense traits with climate data and metabolomic analysis of plant chemistry across a continental-scale latitudinal gradient. While some metrics of defense investment were greater at lower latitudes, we found that the environmental variables underlying variation in defense traits differed across defense types, with direct defense decreasing along a precipitation gradient and indirect defense increasing with temperature and growing season length. Incorporating proxies for predation and herbivory pressure further suggested that variation in defensive traits is driven by an interplay between biotic and abiotic variables. Together, our findings reinforce that, even within a single species, different defense strategies can correlate with distinct environmental variables across latitude, consistent with complexity in the selective mechanisms shaping defense variation across space. These results illustrate the importance of considering the full scope of defense strategies and environmental pressures within a system when testing classic hypotheses of plant defense.