Matching Items (3)
Description
Human-induced rapid environmental change (HIREC) influences nearly all of Earth's ecosystems through processes such as urbanization. Previous studies have found that urbanization influences biodiversity patterns, often yielding an increase in the abundance of a few urban-adapted taxa at the expense of native species diversity. The western black widow spider, Latrodectus hesperus, is a medically-important pest species that often forms dense urban subpopulations (i.e., infestations) relative to the low-density subpopulations found throughout undisturbed, desert habitat. Here, I employ field and laboratory studies to examine the population ecology and stoichiometry of this urban pest to increase our understanding of the mechanisms underlying its success. The population ecology of ten black widow subpopulations spread across metropolitan Phoenix, AZ was examined during the peak breeding season (June-August). This study revealed that arthropod prey abundance, female mass and population density of females showed significant spatial variation across the ten subpopulations. Additionally, prey abundance and foraging success, measured as the number of carcasses found in webs, were a strong determinant of female mass and population density within each subpopulation. To test the mechanisms that drive black widow infestations, I used ecological stoichiometry to examine the nutrient (nitrogen and phosphorus) composition of spiders and arthropod prey from urban habitat, desert habitat and a laboratory diet regime. These studies revealed that (1) spiders are more nutrient rich than cricket prey in the field, (2) spider subpopulations exhibit significant spatial variation in their nitrogen composition, (3) nutrient composition of urban spider subpopulations does not differ significantly from Sonoran desert subpopulations, (4) laboratory-reared spiders fed a diet of only laboratory-reared crickets are more nitrogen and phosphorus limited than field-captured spiders, and (5) cannibalism by laboratory-reared spiders alleviated phosphorus limitation, but not nitrogen limitation, when compared to field-captured spiders. This work highlights the need to examine the population ecology of species relationships, such as predator-prey dynamics, to fully understand the fecundity and population growth of urban pest species. Moreover, the integration of population ecology and stoichiometry illustrates the need to address mechanisms like nutrient limitation that may explain why urban pest populations thrive and native species diversity suffers following HIREC.
ContributorsTrubl, Patricia (Author) / Johnson, James C. (Thesis advisor) / Rutowski, Ronald (Thesis advisor) / McGraw, Kevin (Committee member) / Arizona State University (Publisher)
Created2012
Description
There has been important progress in understanding ecological dynamics through the development of the theory of ecological stoichiometry. This fast growing theory provides new constraints and mechanisms that can be formulated into mathematical models. Stoichiometric models incorporate the effects of both food quantity and food quality into a single framework that produce rich dynamics. While the effects of nutrient deficiency on consumer growth are well understood, recent discoveries in ecological stoichiometry suggest that consumer dynamics are not only affected by insufficient food nutrient content (low phosphorus (P): carbon (C) ratio) but also by excess food nutrient content (high P:C). This phenomenon, known as the stoichiometric knife edge, in which animal growth is reduced not only by food with low P content but also by food with high P content, needs to be incorporated into mathematical models. Here we present Lotka-Volterra type models to investigate the growth response of Daphnia to algae of varying P:C ratios. Using a nonsmooth system of two ordinary differential equations (ODEs), we formulate the first model to incorporate the phenomenon of the stoichiometric knife edge. We then extend this stoichiometric model by mechanistically deriving and tracking free P in the environment. This resulting full knife edge model is a nonsmooth system of three ODEs. Bifurcation analysis and numerical simulations of the full model, that explicitly tracks phosphorus, leads to quantitatively different predictions than previous models that neglect to track free nutrients. The full model shows that the grazer population is sensitive to excess nutrient concentrations as a dynamical free nutrient pool induces extreme grazer population density changes. These modeling efforts provide insight on the effects of excess nutrient content on grazer dynamics and deepen our understanding of the effects of stoichiometry on the mechanisms governing population dynamics and the interactions between trophic levels.
ContributorsPeace, Angela (Author) / Kuang, Yang (Thesis advisor) / Elser, James J (Committee member) / Baer, Steven (Committee member) / Tang, Wenbo (Committee member) / Kang, Yun (Committee member) / Arizona State University (Publisher)
Created2014
Description
Primary production in aquatic ecosystems is often limited by the availability of nitrogen (N) and/or phosphorus (P). Animals can substantially alter the relative availability of these nutrients by storing and recycling them in differential ratios. Variation in these stoichiometric traits, i.e., the elemental phenotype, within a species can link organismal evolution to ecosystem function. I examined the drivers of intraspecific variation in the elemental phenotype of aquatic consumers to test for the generality of these effects. Over a thermal gradient in Panamá, I found that average specific growth grate and body P content of the mayfly Thraulodes increased with environmental temperature, but that these patterns were due to site-specific differences rather than the direct effects of warmer temperature. In a meta-analysis of published studies, I found that in fishes intraspecific variation in dietary N:P ratio had a significant effect on excretion N:P ratio, but only when accounting for consumption. I tested for the effects of variation in consumption on excretion N:P ratio among populations of the fish Gambusia marshi in the Cuatro Ciénegas basin in Coahuila, Mexico. G. marshi inhabits warm groundwater-fed springs where it often co-occurs with predatory fishes and cool runoff-dominated wetlands which lack predators. Using stoichiometric models, I generated predictions for how variation in environmental temperature and predation pressure would affect the N:P ratio recycled by fishes. Adult female G. marshi excretion N:P ratio was higher in runoff-dominated sites, which was consistent with predators driving increased consumption rates by G. marshi. This result was supported by a diet ration manipulation experiment in which G. marshi raised on an ad libitum diet excreted N:P at a lower ratio than fish raised on a restricted diet ration. To further support the impacts of predation on phenotypic diversification in G. marshi, I examined how body morphology varied among habitats and among closely related species. Both among and within species, predation had stronger effects on morphology than the physical environment. Overall, these results suggest that predation, not temperature, has strong effects on these phenotypic traits of aquatic consumers which can alter their role in ecosystem nutrient cycling through variation in consumption rates.
ContributorsMoody, Eric Kellan (Author) / Elser, James J (Thesis advisor) / Sabo, John L (Thesis advisor) / Angilletta, Michael J (Committee member) / Capps, Krista A (Committee member) / Collins, James P. (Committee member) / Arizona State University (Publisher)
Created2017