Graminoid responses to grazing by large herbivores: adaptations, exaptations, and interacting processes

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...

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Bibliographic Details
Published in:Annals of the Missouri Botanical Garden 1985, Vol.72 (4), p.852-863
Main Author: Coughenour, M.B
Format: Article
Language:English
Subjects:
ADAPTACION FISIOLOGICA
ADAPTATION
Animal and plant ecology
Animal, plant and microbial ecology
Autoecology
Biological and medical sciences
Defoliation
EVOLUCION
EVOLUTION
Fundamental and applied biological sciences. Psychology
GRAMINEAE
Grasses
GRASSLANDS
GRAZING
HERBAGE
HERBIVORE
HERBIVORES
HERBIVOROS
Meristems
PASTOREO
PATURAGE
Phenotypic traits
Photosynthesis
Plant growth
Plants
Plants and fungi
PRADERAS
SEMIARID ZONES
ZONA SEMIARIDA
ZONE SEMI-ARIDE
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Summary: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.
ISSN:0026-6493
2162-4372
DOI:10.2307/2399227