Vertebrate Community Responses to Livestock Grazing in an Ancient Mediterranean Rangeland System:Rethinking the Role of Grazing in Biodiversity Conservation

Grazing;Mediterranean;Livestock;Biodiversity;Natural Resources and Environment

Victor, ErinButt, Bilal ;

University of Michigan

关键词: Grazing;    Mediterranean;    Livestock;    Biodiversity;    Natural Resources and Environment;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/109689/Erin_Victor%28O%27Brien%29_Thesis_December_2014.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Despite claims that livestock grazing may be a useful conservation tool for promotingbiodiversity, the effect of livestock grazing on vertebrate populations remains controversial andpoorly understood. This is particularly the case for Mediterranean ecosystems that have beengrazed by livestock for thousands of years. The aim of my thesis is to understand: (1) the natureof the relationship between livestock grazing and vertebrate abundance and species richness and;(2) the mechanisms that drive this relationship.Methods. I sampled small mammal, reptile, and passerine bird species across a range oflivestock grazing intensities in a mediterranean pastoral system in the Aegean Sea (Greece).This study was conducted in a mediterranean summer-deciduous scrubland habitat withlimestone substrate and shallow soils, which is widespread throughout the region. UsingGeneralized Linear Modeling (GLM), I determined the nature of the relationship betweenlivestock grazing and vertebrate abundance and richness metrics. An information-theoreticapproach was used to elucidate which habitat characteristics mediated by livestock grazing bestpredicted vertebrate responses.Results. I found that terrestrial (small mammal and reptile) vertebrate responses to changinglivestock stocking rate were different from those of passerine birds. Terrestrial speciesabundance decreased exponentially with increasing livestock stocking rate; however speciesrichness exhibited a unimodal relationship with stocking rate, peaking at intermediate stockingrates. The response of terrestrial assemblages was best predicted by invertebrate foodavailability. Passerine bird species richness and abundance showed no relationship with levels ofgrazing, however avian population abundance and species richness were significantly correlatedwith vegetation structural heterogeneity.Conclusions. My findings indicate that there is no ideal grazing level that optimizes vertebrateabundance and richness across different vertebrate groups. However light to intermediate grazingdisturbance can be important in promoting terrestrial species richness, thus indicating thatagricultural policy encouraging a mosaic of grazing intensities at the regional level could supportdiverse vertebrate assemblages.