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- All Subjects: Plant sciences
- Creators: Breslin, Peter
Description
Die-off of screwbean mesquite (Prosopis pubescens), a species native to the American Southwest, has been documented regionally within the last decade. Historical causes for episodic mortality of the more widely distributed velvet mesquite (Prosopis velutina) and honey mesquite (Prosopis glandulosa) include water table declines and flood scour. Causes of the recent die-offs of P. pubescens have received little study. Numerous riparian restoration projects have been implemented regionally that include screwbean mesquite. Restoration propagules from foreign sources can introduce diseases, and low genetic diversity plantings may allow for disease irruptions. I asked: 1) Are die-offs associated with a particular age class, 2) Is die-off suggestive of a pathogen or related to specific environmental stressors, 3) Are mortality influences and outcomes the same between restoration and local populations, 4) Are particular land uses and management associated with die-off, and 5) Are populations rebounding or keeping pace with mortality?
I documented the screwbean mesquite population status at rivers and wetlands in Arizona with varying levels of restoration. I used logistic regression and Pearson correlation analysis to explore mortality response to site factors and disease related variables. I compared mortality response and disease severity between local and restoration populations.
Biotic damage surfaced as the most important factor in statistical analyses, suggesting that mortality was caused by a pathogen. Mortality was greatest for young size classes (3 to 14 cm), and biotic damage was higher for individuals at infrequently flooded areas. Strong differences were not found between local and restoration populations – however restoration populations were less stressed and had lower biotic damage. Novel urban and restored sites may provide refuge as site conditions at other locations deteriorate. A culmination of past water diversion, development and land use may be surfacing, rendering riparian species vulnerable to diseases and triggering such events as region-wide die-off.
I documented the screwbean mesquite population status at rivers and wetlands in Arizona with varying levels of restoration. I used logistic regression and Pearson correlation analysis to explore mortality response to site factors and disease related variables. I compared mortality response and disease severity between local and restoration populations.
Biotic damage surfaced as the most important factor in statistical analyses, suggesting that mortality was caused by a pathogen. Mortality was greatest for young size classes (3 to 14 cm), and biotic damage was higher for individuals at infrequently flooded areas. Strong differences were not found between local and restoration populations – however restoration populations were less stressed and had lower biotic damage. Novel urban and restored sites may provide refuge as site conditions at other locations deteriorate. A culmination of past water diversion, development and land use may be surfacing, rendering riparian species vulnerable to diseases and triggering such events as region-wide die-off.
ContributorsMadera, Robert (Author) / Stromberg, Juliet (Thesis advisor) / Stutz, Jean (Committee member) / McCue, Kimberlie (Committee member) / Arizona State University (Publisher)
Created2016
Description
In the face of the sixth mass extinction on Earth, with the flowering plant family Cactaceae assessed as the fifth most endangered plant or animal family by the International Union for the Conservation of Nature (IUCN), it is imperative that all available tools be used to understand the biodiversity, habitat suitability, climate change impacts and population viability of cacti. Within the Cactaceae, Mammillaria Haw and the closely related genus Cochemiea (K. Brandegee) Walton of Baja California, Mexico, are species-rich, with 46 regionally endemic taxa, 12 of which have been assessed as threatened or endangered by the IUCN. This study clarifies the evolutionary relationships in the Mammilloid clade, a complex and species-rich clade in tribe Cacteae, and generic circumscription of the genera Mammillaria Haw. and Cochemiea (K. Brandegee) Walton, estimates divergence times, diversification rates and ancestral ranges and explores habitat suitability and the risk of extinction of a representative species within these genera. The r species, Cochemiea halei (K. Brandegee) Walton, a narrowly distributed island endemic, is assessed using species distribution modeling (SDM) and population viability analysis (PVA). SDM in this study includes projections to two climate change scenarios over the next century, using four representative particle concentration pathways, and the PVA uses habitat-specific deterministic and stochastic models. The results of molecular phylogenetic analyses of the Mammilloid cladde restore the genus Mammillaria to monophyly via new combinations in the genus Cochemiea. The taxa in this study are shown to be of recent origin resulting from rapid diversification and radiation. Geological and climatic forces at multiple scales appear to be responsible for the high degree of biodiversity and endemism of these cacti. SDM shows that C. halei is likely to be stranded in its fragmented island habitat, has a facultative adaptation to ultramafic soils, and faces a 21%–53% contraction of its range on the islands under climate change scenarios. PVA suggests that C. halei is at increased risk of extinction in response to slight decreases in fecundity and persistence. In general, the perspectives in this dissertation fill several gaps in our prior knowledge of the evolution, biogeography, and conservation pressures of an important, species-rich group of cacti, occurring in a region of high biodiversity and endemism.
ContributorsBreslin, Peter (Author) / Wojciechowski, Martin F (Thesis advisor) / Albuquerque, Fabio (Committee member) / Fehlberg, Shannon (Committee member) / Majure, Lucas (Committee member) / Rebman, Jon (Committee member) / Arizona State University (Publisher)
Created2020