Intraspecific shifts of xerophytic grasses along the leaf economic spectrum in response to long-term vertebrate herbivory

Abstract

The leaf economic spectrum (LES) assumes the existence of a multidimensional space with a main variation axis (from ‘conservativeness’ to ‘acquisitiveness’) along which all vascular plants are distributed. There is debate as to whether sustained herbivory selects for increasing acquisitiveness or conservativeness. We studied whether long-term ungulate herbivory promotes shifts along the LES of populations of the same species. Our study system was the semi-arid Chaco forest-shrubland of Central Argentina, where we identified, for each of six native grasses, close populations subjected to long-term ungulate herbivory or free from it. In each population, we measured LES-relevant foliar traits: leaf area, specific leaf area, leaf toughness and leaf dry matter content. We found intraspecific pattern of LFT correlation to be qualitatively consistent with the LES. Herbivory led to a more acquisitive leaf syndrome in all species. In some cases, we also observed a change in slope, that is, a change in the arrangement of traits in multivariate space. This suggests that long-term herbivory could be changing not only the position of populations on the LES but also the patterns of resource allocation, involving e.g. differences in photosynthetic rates as a function of differential resource allocation and metabolic activity.