Аннотация:The problem of ascribing adaptive significance to traits that enable graminoids to tolerate or evade ungulate herbivory is examined.Some of these traits may have originally evolved in response to nongrazing selection pressures, thus constituting grazing exaptations rather than true adaptations.The fossil record indicates that semiarid habitats, extensive grasslands, and grazers appeared, interacted, and evolved together.However, several traits that are advantageous in semiarid habitats have beneficial effects for grazed plants.Other traits, such as developmental plasticity, enhance competitive ability in certain environments, but also increase grazing tolerance or resistance.Experiments and simulation modeling showed that defoliation responses are embedded in a network of interacting processes, including photosynthesis, transpiration, nutrient uptake, and resource allocation.Responses and adaptations to defoliation must be interpreted in this context.Although traits may have arisen due to non-herbivorous selection pressures, they may subsequently have been selected, combined, or amplified through grass-grazer coevolution to form species, polymorphic populations, phenotypically plastic individuals, or communities of species that evade, resist, or tolerate herbivory.
