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.
Displaying 1 - 2 of 2
Filtering by
- All Subjects: Ecology
Description
Niche variation among sexes and life stages within a population has been documented in many species, yet few studies have investigated niche variation within demographic groups or across ecological contexts. We examined the extent to which pregnant California sea lions (Zalophus californianus) at each of three breeding colonies target alternative prey resources and habitats. The three colonies are distributed across distinct regions of the Gulf of California, Mexico and have divergent population dynamics. We compared the nature of niche variation among colonies and investigated the fitness consequences of different foraging strategies within each colony. We analyzed the δ13C and δ15N values from fur collected from 206 suckling pups to characterize relative maternal foraging locations (δ13C) and trophic levels (δ15N) during the metabolically demanding late stages of gestation and lactation that occur simultaneously in California sea lions. The δ13C and δ15N values were regressed against pup body condition index values to compare the relative individual-level fitness benefits of different maternal foraging strategies. We found that the nature and extent of niche variation differed among colonies. Niche variation was most pronounced at the two largest colonies that appear to experience the highest levels of intraspecific competition and the variation was consistent with habitat features. One colony (Granito) displayed two distinct foraging groups with indistinguishable median pup body condition values, whereas the second (San Jorge) exhibited continuous niche variation and pup body condition varied in relation to maternal foraging location and trophic level, suggesting disparities among alternative foraging strategies. For the smallest colony (Los Islotes), females occupy similar niches with a few outliers. Body condition values of pups at this colony were most variable, but did not vary with maternal foraging strategy. Our results provide evidence for intrapopulation niche variation among demographically similar individuals during a period of high metabolic stress and reproductive importance. This work suggests possible fitness benefits conferred by alternative foraging strategies, and calls into question the common assumption that members of a population are ecologically equivalent. Future research aimed at understanding animal foraging strategies should consider the nature and extent of niche variation in the context of local ecological conditions.
ContributorsCrawford, Tara Gancos (Author) / Gerber, Leah R. (Thesis advisor) / Ogle, Kiona (Committee member) / Kurle, Carolyn M (Committee member) / Arizona State University (Publisher)
Created2013
Description
Climate change is making the arid southwestern U.S. (“Southwest”) warmer and drier. Decreases in water availability coupled with increases in episodic heat waves can pose extraordinary challenges for native riparian tree species to persist in their current ranges. However, the morpho-physiological mechanisms that these species deploy to cope with extreme temperature events are not well understood. Specifically, how do these species maintain leaf temperatures within a safe operational threshold in the extreme conditions found across the region? Morpho-physiological mechanisms influencing intraspecific local adaptation to thermal stress were assessed in Populus fremontii using two experimental common gardens. In a common garden located near the mid-point of this species’ thermal distribution, I studied coordinated traits that reflect selection for leaf thermal regulation through the measurement of 28 traits encompassing four different trait spectra: phenology, whole-tree architecture, and the leaf and wood economic spectrum. Also, I assessed how these syndromes resulted in more acquisitive and riskier water-use strategies that explained how warm-adapted populations exhibited lower leaves temperatures than cool-adapted populations. Then, I investigated if different water-use strategies are detectable at inter-annual temporal scales by comparing tree-ring growth, carbon, and oxygen isotopic measurements of cool- versus warm-adapted populations in a common garden located at the extreme hottest edge of P. fremontii’s thermal distribution. I found that P. fremontii’s adaptation to the extreme temperatures is explained by a highly intraspecific specialized trait coordination across multiple trait scales. Furthermore, I found that warmer-adapted populations displayed 39% smaller leaves, 38% higher midday stomatal conductance, reflecting 3.8 °C cooler mean leaf temperature than cool-adapted populations, but with the tradeoff of having 14% lower minimum leaf water potentials. In addition, warm-adapted genotypes at the hot edge of P. fremontii’s distribution had 20% higher radial growth rates, although no differences were detected in either carbon or oxygen isotope ratios indicating that differences in growth may not have reflected seasonal differences in photosynthetic gas exchange. These studies describe the potential effect that extreme climate might have on P. fremontii’s survival, its intraspecific responses to those events, and which traits will be advantageous to cope with those extreme environmental conditions.
ContributorsBlasini, Davis E (Author) / Hultine, Kevin R (Thesis advisor) / Day, Thomas A (Thesis advisor) / Ogle, Kiona (Committee member) / Throop, Heather (Committee member) / Gaxiola, Roberto (Committee member) / Arizona State University (Publisher)
Created2022