Theses and Dissertations
This collection includes both ASU Theses and Dissertations, submitted by graduate students, and the Barrett, Honors College theses submitted by undergraduate students.
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- All Subjects: Ecology
- Creators: Gerber, Leah
Description
Aboveground net primary production (ANPP) and belowground net primary production (BNPP) may not be influenced equally by the same factors in arid grasslands. Precipitation is known to affect ANPP and BNPP, while soil fauna such as nematodes affect the BNPP through herbivory and predation. This study on black grama grass (Bouteloua eriopoda) in the Chihuahuan Desert investigates the effects of precipitation and nematode presence or absence on net primary production (NPP) as well as the partitioning between the aboveground and belowground components, in this case, the fraction of total net primary production occurring belowground (fBNPP). I used a factorial experiment to investigate the effects of both precipitation and nematode presence on the components of NPP. I used rainout shelters and an irrigation system to alter precipitation totals, while I used defaunated and re-inoculated soil for the nematode treatments. Precipitation treatment and seasonal soil moisture had no effect on the BNPP and a nonsignificant positive effect on the ANPP. The fBNPP decreased with increasing precipitation and seasonal soil moisture, though without a significant effect. No predator nematodes were found in any of the microcosms at the end of the experiment, though other functional groups of nematodes, including herbivores, were found in the microcosms. Total nematode numbers did not vary significantly between nematode treatments, indicating that the inoculation process did not last for the whole experiment or that nematodes had little plant material to eat and resulted in low population density. Nematode presence did not affect the BNPP, ANPP, or the fBNPP. There were no significant interactions between precipitation and nematode treatment. The results are inconclusive, possibly as a result of ecosystem trends during an unusually high precipitation year, as well as the very low NPP values in the experiment that correlated with low nematode community numbers.
ContributorsWiedenfeld, Amy (Author) / Sala, Osvaldo (Thesis advisor) / Gerber, Leah (Committee member) / Hall, Sharon (Committee member) / Arizona State University (Publisher)
Created2018
Description
Limited funding hinders endangered species recovery. Thus, decision makers need to strategically allocate resources to save the most species. Decision science provides guidance on efficient prioritization of conservation actions. However, endangered species recovery cost estimates are incomplete, so decision makers need to understand the implications of different cost estimation approaches. To test how different ways of estimating the expected costs of recovery action influence suggested recovery priorities, I used three different cost estimation scenarios for prioritizing recovery effort for 29 endangered species in Arizona. My scenarios explored “remaining” costs, calculated by subtracting historical spending from recovery plan cost estimates, “average” costs which substituted the average cost for actions in recovery plans, and “micro” and “macro” overlaps accounting for efficiency of costs due to implementing shared recovery actions for species with overlapping ranges. These different methods of estimating costs resulted in different numbers of recovery plans funded. At a representative budget, the macro overlap scenario recommended funding for 97% of plans as compared to 93% of plans under the baseline cost scenario. In contrast, the micro overlap (59%), the average (28%), and remaining (24%) cost estimation approaches all resulted in less plans recommended for funding than the baseline. There were also differences in how individual plans were ranked across the scenarios and variation in species chosen for funding. The order of recovery plans was similar between the baseline and the remaining scenario (WS = 0.833), and the baseline and the average scenario (WS=0.811). The similarity metric is based on the identity of species ranked equally. In contrast, there was less similarity in plan ranking between the baseline, the macro (WS=0.777), and micro (WS=0.442) overlap scenarios. A group of 4 plans remained within the top priority ranks, 5 plans were ranked as high priority for all scenarios except the remaining cost scenario, and 5 plans were consistently ranked as low priority. My results show how cost estimation approaches influence species priority rankings and can be used to help decision makers determine implications when they are exploring options for prioritization.
ContributorsSansonetti, Alice Maria (Author) / Gerber, Leah (Thesis advisor) / Iacona, Gwen (Thesis advisor) / Maas, Amy (Committee member) / Arizona State University (Publisher)
Created2023