Herbivory effects on Ephedra spp. in the Chihuahuan Desert

Authors: WHITFORD, WALTER - Retired Non ARS Employee; STEINBERGER, YOSEF - Bar-Ilan University

Submitted to: Open Journal of Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2020
Publication Date: 2/17/2020
Citation: Whitford, W.G., Steinberger, Y. 2020. Herbivory effects on Ephedra spp. in the Chihuahuan Desert. Open Journal of Ecology. 10:37-44. https://doi.org/10.4236/oje.2020.102003.
DOI: https://doi.org/10.4236/oje.2020.102003

Interpretive Summary: The genus Ephedra (Grymnospermae; Gnetales, Ephedraceae) is composed of approximately 50 species in arid and semiarid ecosystems worldwide. Two species (Ephedra trifurca and E. torreyana), which are common in the northern Chihuahuan Desert of the USA, produce dry winged cone bracts and the seeds are wind dispersed. Other Ephedra species that occur in North America are animal dispersed. E. antisyphilitica with succulent, brightly colored cone bracts are dispersed by frugivorous birds and those with small, dry cone bracts and large seeds are dispersed by granivorous rodents (e.g., E. viridis and E. californica). The Ephedra species in the northern Chihuahuan Desert developed from two pairs of sister species distributed in southwestern North America: E. californica-E. trifurca and E. torreyana -E. viridis and probably occurred in the Late Miocene to Pliocene. They concluded that genetic and climatic changes documented for these regions related to the expansion of arid lands, contributed to the diversification in North American Ephedra, rather than adaptations to new climatic conditions.

Technical Abstract: Two species of Ephedra : E. trifurca and E. torreyana inhabit shrub and grassland habitats in the northern Chihuahuan Desert. E. torreyana is limited to black grama grasslands where grasses are taller than the shrub. E. torreyana is heavily browsed by vertebrates and E. trifurca is browsed during some years. We established an experiment with cylindrical exclosures that xcluded rabbits and rodents, rabbits but accessible to rodents, for comparison with E. torreyana plants available to all herbivores. Plants accessible to all vertebrate herbivores were significantly smaller with shorter stem lengths than plants in exclosures. We concluded that E. torreyana in black grama grassland are largely hidden from vertebrate herbivores and that intense herbivory reflects the degraded state of the study site which makes the E. torreyana evergreen shrubs apparent to vertebrates.