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York University (1996)

The impacts of livestock grazing on sonoran desert scrub vegetation, insect and insectivorous bat communities

Hovorka, Mark D

Titre : The impacts of livestock grazing on sonoran desert scrub vegetation, insect and insectivorous bat communities

Auteur : Hovorka, Mark D

Grade : Master of Science (MS) 1996

Université de soutenance : York University

Résumé
I examined the impacts of livestock grazing history on Sonoran desertscrub vegetation, insect, and insectivorous bat communities in the vicinity of Tucson, Arizona. I compared communities between two pairs of ungrazed and currently grazed sites in the pediments and bajadas of the Rincon Mountains (ungrazed for 33 years), and the Tucson (ungrazed for 67 years) and Silver Bell Mountains. I sampled woody and succulent perennial species, used blacklight traps to sample insectivorous bats. Grazing had a significant impact on the plant community composition of the Rincon Mountain sites, but not the Tucson and Silver Bell Mountain sites. Palatable species and unpalatable or invasive ones were present in all sites, consistent with their history of grazing. Although not all differences were significant, in general palatable species abundance, species richness, species diversity, percentage cover, and Carnegiea gigantea density were greater in ungrazed sites, and unpalatable or invasive species were also more abundant in ungrazed than grazed sites. Grazing may reduce both seedling survival and the availability of suitable micro-habitats for germination in Sonoran desertscrub. Grazing history did not significantly influence the abundance of insect orders or bats at either pair of sites. Insect abundance was largely determined by ambient environmental conditions. Bats consumed small Lepidoptera, Coleoptera, Hymenoptera, and Hemiptera, the most abundant insect orders captured at blacklights, and the abundance of bat species was strongly and significantly associated with insect order abundance of bat species was strongly and significantly associated with insect order abundance at some sites. Eptesicus fuscus and Pipistrellus hesperus were more abundant along xeroriparian washes than adjacent upland habitats. The associations between highly variable bat activity and insect abundance and habitat use by bats indicate that bats are foraging opportunistically and may be adaptable to some forms of habitat disturbance.

Mots-clés : Grazing - Environmental aspects - Arizona. ; Desert ecology - Arizona.

Présentation (Amicus)

Page publiée le 27 mai 2011, mise à jour le 9 février 2018