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Accueil du site → Doctorat → États-Unis → 1984 → Demographic sensitivity of two perennial desert grasses (Bouteloua eriopoda Torr. and Sporobolus flexuosus Thurb.) with inferences toward ecological dominance and subdominance

New Mexico State University (1984)

Demographic sensitivity of two perennial desert grasses (Bouteloua eriopoda Torr. and Sporobolus flexuosus Thurb.) with inferences toward ecological dominance and subdominance

Gross, Bryan D.,

Titre : Demographic sensitivity of two perennial desert grasses (Bouteloua eriopoda Torr. and Sporobolus flexuosus Thurb.) with inferences toward ecological dominance and subdominance

Auteur : Gross, Bryan D.,

Université de soutenance : New Mexico State University

Grade : Doctor of Philosophy (PhD) 1984

Résumé
The objective of this study was to determine if differences in ecological role of two perennial grasses, in a southern New Mexico desert grassland, could be explained by species demography. It was hypothesized that demographic insensitivity to the environment favors dominance, while sensitivity results in subdominance. Analysis of black grama (Bouteloua eriopoda Torr.) and mesa dropseed (Sporobolus flexuosus Thurb.) was conducted on a cohort basis for 42 years of data. Species demography was analyzed on a life table basis and by regression analysis, with intraspecific density and various environmental components used as causal variables. Results indicated few differences in mean demography of the species, although black grama was characterized by a more constant age-specific mortality risk and mesa dropseed by high reproduction. The demographic feature unique to the species was variability of survival and reproduction. Mesa dropseed was characterized by greater variability of both fitness parameters. Environmental dependence results showed that each species was characterized not by overall unique sensitivity, but instead by age-dependent patterns. Sensitivity to short-term environmental events was greatest for first- and second-year age-states, and was more pronounced in mesa dropseed than in black grama. Older plants of each species were sensitive to longer-term environmental events. The sensitivity of adults of each species was similar. Survival sensitivity to intraspecific density was also age-dependent. Highest density sensitivity occurred in mature and firstyear plants of both species, while lowest sensitivity to density occurred in secondyear plants. Black grama was more sensitive to density than was mesa dropseed. This was also true for reproduction. Results did not firmly support the initial hypotheses. Each species did not demonstrate overall uniqueness of demography since this was strongly age-dependent. Species demographic behavior, and perhaps relative ecological roles, are strongly dependent upon variability of population age structure.

Sujets : Grasses. Desert plants. Black grama grass. Mesa dropseed grass.

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Page publiée le 28 janvier 2018, mise à jour le 11 novembre 2018