Herbivory, intraspecific trait variability and back to herbivory

Ungulate herbivory is a key driver of leaf trait syndromes and defense strategies at the ecological and macroevolutionary levels. Herbivory should also cause short-term evolution within plant populations, but few studies have experimentally tested this prediction. We set out to experimentally assess the plastic and heritable effects of contemporary history of ungulate herbivory on 1) leaf trait syndromes at the intraspecific level, and on the defense traits, 2) leaf size and 3) size of spines. We measured leaf traits (specific leaf area, leaf dry matter content, leaf nitrogen concentration and leaf mechanical resistance) in populations of six grass and four woody legume species that had grown under contrasting pressures of domestic ungulate herbivory for at least 40 years. We then performed a common garden experiment, measuring the same traits. Next, we performed cutting experiments on the plants grown in the common garden to measure leaf trait plasticity. In the woody species, we also measured the length of spines and the leaf size (average area per leaf), in the field and in the common garden experiment. We found that in grasses field herbivory over decades produced a displacement toward more acquisitive leaf trait syndromes. Most of these changes appeared largely due to plasticity. In woody legume species, in contrast, herbivory produced a displacement towards more conservative leaves, longer spines and smaller leaves, with the trait differences between histories of herbivory being mostly hereditary. These results point out that vertebrate herbivory can lead to evolutionary processes at contemporary time scales even in long-lived perennial plant species, but the direction of such change depends on the life form of the species. These divergent effects could depend on the predominant anti-herbivore strategies in the different life forms (tolerance versus resistance).

Automated summary

This study aimed to assess the plastic and heritable effects of ungulate herbivory on leaf trait syndromes and defense strategies in plants. The results showed that herbivory caused changes in leaf trait syndromes, with grass species showing more acquisitive traits and woody legume species showing more conservative traits. These findings suggest that vertebrate herbivory can lead to contemporary evolutionary processes, but the direction of change depends on the species' life form and anti-herbivore strategies.