Theses and Dissertations
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- All Subjects: Ecology
- Creators: Dean, W.P. Carey School of Business
- Creators: Saul, Steven E
This study examined crayfish diet within varying hydrologic environment in lotic systems using stable isotope analysis of crayfish and basal resources to add depth to previous findings. Crayfish are numerous and are omnivorous, opportunistic feeders, feeding on invertebrates, vegetation and detritus. Arizona streams stand apart from the Eastern and Northwestern aquatic ecosystems of the United States because Arizona has no native crayfish species. Two species have been introduced and become widely established in Arizona (Orconectes virilis and Procambarus clarkii), with concern for further introduction of crayfish species and more information on how these two species impact the native species in the streams is needed. Previous studies have focused on crayfish abundance with hydrologic variation and crayfish diets within a lentic system, but few have focused on how the diet of consumers varies with hydrologic variability. Crayfish are hardy and have a dramatically increasing population within Arizona and therefore inhabit systems with a wide range of hydrologic variability which may contribute to spatial variability. The results show that crayfish diets do show a significant level of seasonal variation in some study locations, in both C source and trophic level. Hydrologic variation was also shown to impact crayfish diet at several study sites, with increasing magnitude of event (both floods and droughts) correlating with a change toward more aquatic C sources and lower trophic position in several of the study sites. In some locations, the correlation was not as strong with variation and diet change and showed less change in C source and rather showed an increase in trophic position.
I compiled a geodatabase of climate, bioclimatic (interactions between precipitation and temperature), vegetation, soil, and topographical variables that are known to influence both richness and abundance and used 15 years of bird point count survey data from urban and non-urban sites established by Central Arizona–Phoenix Long-Term Ecological Research project to test that relationship. I built generalized linear models (GLM) to elucidate the influence of each environmental variable on richness and abundance values taken from 47 sites. I used principal component analysis (PCA) to reduce 43 environmental variables to 9 synthetic factors influenced by measures of vegetation, climate, topography, and energy. I also used the PCA to identify uncorrelated raw variables and modeled bird richness and abundance with these uncorrelated environmental variables (EV) with GLM.
I found that bird richness and abundance were significantly different between seasons, but that richness and winter abundance were not significantly different across years. Bird richness was most influenced by soil characteristics and vegetation while abundance was most influenced by vegetation and climate. Models using EV as independent variables consistently outperformed those models using synthetically produced components from PCA. The results suggest that richness and abundance are both driven by climate and aspects of vegetation that may also be influenced by climate such as total annual precipitation and average temperature of the warmest quarter. Annual oscillations of bird richness and abundance throughout the urban Phoenix area seem to be strongly associated with climate and vegetation.
My objective was to relate capture rates of a fossorial anuran and lizard abundance to aspects of native, invaded, and shrub-encroached riparian habitats in order to forecast the potential winners and losers of riparian habitat xerification and invasion.
I measured habitat and monitored herpetofauna at 18 sites near the confluence of the San Pedro River and Gila River in Pinal County, Arizona in 2016 and 2017. Sites were divided into three categories based on dominant tree genus; Populus-Salix, Prosopis, and Tamarix, which represented native riparia, xeric riparia, and invaded riparia, respectively.
Habitat measurements indicated that sites varied significantly in structure, and that dominant tree species was a useful descriptor of habitat physiognomy. Results from herpetofauna trapping demonstrated that Scaphiopus couchii, a fossorial anuran, occupy Prosopis sites at a much higher rate than at Tamarix sites, which were almost completely avoided. S. couchii was also found to be closely tied to xero-riparian habitat components present at Prosopis sites and soil analyses indicate that aspects of soil moisture and texture play an important role in the partitioning of this species across altered riparian habitats. Lizard abundance was found to be significantly lower in Tamarix habitat, with the majority of captures attributed to the generalist whiptail Aspidoscelis tigris. Additionally, more than half of lizard species that were analyzed displayed a negative association to Tamarix habitat. Of the three habitat types considered, Populus-Salix supported the greatest abundance of lizards.
Based on this study, the deleterious effects of xerfication on a riparian herpetofauna community may be lesser than those of Tamarix invasion. These two forms of riparian habitat shift often co-occur, with the ultimate cause being changes in hydrologic regime. This may imply that a bottom-up approach, wherein historic hydrology is restored to restore or maintain native habitats, to riverine management is appropriate for riparian herpetofauna conservation.