Browsing by Author "Nick Haddad, Committee Member"

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The Effects of Food Abundance, Foraging Rules and Cognitive Abilities on Local Animal Movements
(2006-11-22) Favreau, Jorie Marie; Richard Lancia, Committee Member; Nick Haddad, Committee Member; Roger A. Powell, Committee Chair; Michael Mitchell, Committee Member; Roland Kays, Committee Member; George R. Hess, Committee Member
Movement is nearly universal in the animal kingdom. Movements of animals influence not only themselves but also plant communities through processes such as seed dispersal, pollination, and herbivory. Understanding movement ecology is important for conserving biodiversity and predicting the spread of diseases and invasive species. Three factors influence nearly all movement. First, most animals move to find food. Thus, foraging dictates, in part, when and where to move. Second, animals must move by some rule even if the rule is "move at random." Third, animals' cognitive capabilities affect movement; even bees incorporate past experience into foraging. Although other factors such as competition and predation may affect movement, these three factors are the most basic to all movement. I simulated animal movement on landscapes with variable amounts of food per food patch, variable number of patches, and variable spatial distributions of food patches. From the results of my simulations, I formulated a series of hypotheses about the effects of food abundance on animal movement in nature. I also resolved the apparent paradox of real animals' movements sometimes correlating positively and sometimes negatively with food abundance. I simulated variable foraging rules belonging to 3 different classes of rules (when to move, where to move, and the scale at which to assess the landscape). Simulating foraging rules demonstrated that variations in richness and density tend to have the same effects on movements, regardless of foraging rules. Still, foraging rules affect the absolute distance and frequency of movements. In my third set of simulations, I simulated a range of spatial and temporal cognitive constraints and demonstrated that omniscience is not necessarily the optimal cognitive state from an energetic standpoint. I tested my hypotheses on the effects of food abundance with data from free ranging female black bears (Ursus americanus) in Pisgah Bear Sanctuary (North Carolina, USA) and female kinkajous (Potos flavus) in Parque National Soberanía (Panama), two species with low predation risk. Depending on the season, black bear movements can be explained, by food patch richness, density or both richness and density. Kinkajou move length but not number of moves can be explained by patch richness and density. Instead of kinkajous adjusting their number of moves when food density changed, kinkajous increased the amount of time they foraged. Moonlight was also a good predictor of number of moves. None of kinkajous' 3 dietary preferences best explained moves.
Impact of Plant Suitability, Biogeography, and Ecological Factors on Associations between the Specialist Herbivore Heliothis subflexa G. (Lepidoptera: Noctuidae) and the Species in its Host Genus, Physalis L. (Solanaceae), in West-Central Mexico
(2006-06-01) Bateman, Melanie Lynn; Fred Gould, Committee Chair; George Kennedy, Committee Member; Trudy Mackay, Committee Member; Nick Haddad, Committee Member
Caterpillars of the moth species Heliothis subflexa G. (Lepidoptera: Noctuidae) are known to feed exclusively on fruits of plants in the genus Physalis L. (Solanaceae). However, data were lacking on whether H. subflexa is constrained to feeding on a subset of the approximately 90 species in this plant genus. The purpose of this research has been to determine which Physalis species are utilized by H. subflexa and to assess the relative importance of plant nutritional suitability, biogeography, and ecological factors in shaping the realized host range of H. subflexa. This was accomplished through a combination of field observations of plants of 17 Physalis species occurring at 76 field sites in West-Central Mexico, a common garden study, and laboratory bioassays. Variation among Physalis species in their biogeography, life history, fruit traits, and concentrations of essential fatty acids were characterized to determine if these factors impact H. subflexa host use. The realized host range of this specialized herbivore proved to be constrained to thirteen of the seventeen Physalis species examined in this study. Heliothis subflexa varied with respect to the frequency and the intensity with which it infested these thirteen host species. Although H. subflexa's potential host range included species that it did not infest in the field, some of the potential hosts were suboptimal for larval development, and survivorship on these Physalis species did not differ from survivorship on fruits of a non-Physalis species, Nicandra physalodes, which is not infested by H. subflexa. Positive correlations found between patterns of host use in the field, the common garden, and the laboratory bioassays indicates that plant suitability to larvae and attractiveness to ovipositing females are important determinants of H. subflexa's realized host range. Heliothis subflexa associations with Physalis species are also influenced by biogeographical factors. Differences in host associations at low versus high elevations may be associated with contemporary population isolation and differentiation.
Measuring Conservation Success: An Investigation of Land Trusts in North Carolina
(2010-04-02) Alexander, Louise Boatwright; Peter White, Committee Member; Nick Haddad, Committee Member; George Hess, Committee Chair
Local land trusts in North Carolina protect land to conserve natural resources and biodiversity, and to provide public benefits, such as clean air and water. However the success of their efforts is commonly reported in terms of the amount of land protected or money raised in support of conservation rather than in measures that describe whether or not conservations goals have been achieved. In order to determine if the conservation lands protected by local land trusts are meeting the goals they were intended to serve, I reviewed published research, literature and methodologies to identify common practices used to measure conservation success. Findings indicate three fundamental processes that allow organizations to evaluate the effectiveness of their interventions which are; 1) conducting status assessments that include articulating specific goals and describing the project context; 2) identifying threats to conservation targets; and 3) identifying, developing, and monitoring specific indicators whose status is a measurable reflection of the conservation targets and interventions. I also surveyed 24 land trusts in North Carolina to determine why they protect lands, what activities they perform that would allow them to evaluate the conservation impact of their work, and how success is reported to the public. From the survey, I conclude that land trusts in North Carolina are unable to determine if the lands they have protected are meeting their conservation goals because they are not consistently setting measurable goals, indentifying specific conservation targets, or monitoring indicators that would reflect conservation impact, processes identified in the literature review as necessary to evaluate conservation projects. I identify the Open Standards for the Practice of Conservation framework as an applicable tool for local land trusts to use to focus their conservation efforts and develop measurable goals and report their conservation success.
Nesting Ecology and Conservation of Least Terns in St. Croix, USVI
(2007-05-30) Lombard, Claudia Danielle; Theodore R. Simons, Committee Co-Chair; Kenneth H. Pollock, Committee Member; Nick Haddad, Committee Member; Jaime A. Collazo, Committee Co-Chair
Little is known about the Least Tern (Sterna antillarum antillarum) in the Caribbean, including the U.S. Virgin Islands. Concerns about predation rates and human disturbance on St. Croix prompted a study of their nesting ecology and a population viability analysis to determine their status and help formulate conservation strategies. From 2003 to 2006 I monitored 56 colonies (4,640 nests) built on salt ponds, sandy beaches, offshore cays, and an industrial park. Daily nest survival rates averaged 0.92 ± 0.04. Rainfall significantly and negatively influenced daily survival rates. The impact was most severe when precipitation events exceeded 190 mm. In densely human populated areas, mammalian predation was more pervasive. Five colonies were protected from predation (exclosure) and flooding (elevated platform) to determine the gains in nest survival. These colonies yielded a daily nest survival of 0.957 ± 0.02, or a gain of ˜100% in nest survival (0.24 to 0.50). Chick survival rates were 0.30 ± 0.11 (n = 44). Estimated breeding productivity was 0.08 (i.e., female fledglings⁄female). Breeding productivity needs to be at least 0.33 to attain a   1. This threshold assumed daily nest survival rates of at least 0.957, chick survival rates  0.5, and medium survival rates (i.e., 0.56 for S1, 0.81 for S2 and S3 and 0.92 for S4). A viability analysis predicted persistence of the St. Croix population only under the most optimistic age-specific survival rates or when immigration from other populations was allowed. Increasing reproductive output by implementing nest protection measures was not an effective tool to reduce extinction risks. Implementing a 25% management effort improved time to quasi-extinction by only 8.4 months when compared to a scenario with no management. Applying management to all nests (100%) increased the time to quasi-extinction by only 6 years. The Least Tern population nesting on St. Croix is the largest known in the Caribbean. The annual number of nests ranged from 919 to 1341. Three explanations can be advanced to reconcile the observed level of breeding activity and outcomes generated by model scenarios. One is that the species is indeed facing a precarious outlook. Least Terns are long-lived species and time lags may mask the population's downward trend in persistence. A second is that observed levels of reproductive activity might be maintained by immigration from source populations elsewhere in the Caribbean. Both of these possibilities are consistent with a population acting as a sink. The third explanation is that the status of the species is not as precarious because age specific survival rates are higher than assumed in my "base" model (i.e., medium survival rates). This possibility is plausible because many survival estimates for Least Terns were based on return rates, which are biased-low. Conservation efforts in St. Croix should be aimed at protecting existing and historical Least Tern breeding habitat, particularly the most isolated sites, and at minimizing egg and chick mortality. Improved reproductive rates alone, however, will not prevent a trajectory of decreasing persistence. My work underscored the importance of immigration and age-specific survival rates in maintaining a viable population. Estimates for these parameters are not available in the Caribbean. Reducing parameter uncertainty is necessary to set local management targets and formulate an integrated, multi-scale conservation strategy. Initially, efforts should focus on colonies closest to St. Croix to generate estimates of age-specific survival and movement rates. A focal geographic area facilitates addressing important study design considerations (e.g., sample size, sampling frequency) necessary for precise estimates. Subsequently, similar efforts could be extended to other focal areas. Molecular genetic approaches could help discern patterns of population connectivity and areas of conservation importance.
The Synchrony of Herbivore Presence, Induced Plant Volatiles, and Parasitoid Response
(2007-07-18) Puente, Molly Elizabeth; Coby Schal, Committee Member; Fred Gould, Committee Co-Chair; George Kennedy, Committee Co-Chair; Nicole Darnall, Committee Member; Nick Haddad, Committee Member
Parasitoids find chemical volatiles produced by herbivore-damaged plants attractive. It has been suggested that by manipulating these volatiles in crop plants, biological control can be enhanced in agricultural systems. Before this technology is implemented, it is important to understand the dynamics of the system. I used two different modeling approaches to address this phenomenon. In the first model, I combined a modified predator-prey functional response equation with an age-structured herbivore population model. In the second model I took a spatially-explicit stochastic simulation approach and examined the Brassica oleraceae, Pieris rapae, and Cotesia rubecula system in more detail. I looked at the effects of plant induction delay, plant relaxation delay, herbivore density, and parasitoid host-age preference. In both models, parasitoids gained the most from signals when all herbivore instars were viable hosts, herbivore density was low, and relaxation delays were short. In the stochastic simulation model, shorter induction delays could lead to considerable gains for the parasitoids. Together, the models indicate that there are some conditions that favor parasitoids following herbivore-induced plant volatiles. By creating plants that produce signals in the right time frame, it may be possible to optimize biological control. However, it is also apparent from my models that herbivore-induced volatiles are ineffective during herbivore outbreaks because parasitoids are limited by factors other the time it takes to find hosts, which is the primary way herbivore-induced plant volatiles aid foraging parasitoids. Improving biological control is one of the practices growers can adopt as part of Integrated Pest Management (IPM), and in the final section of this dissertation I discussed a survey exploring how growers adopt IPM. I found that practices consistent with IPM were adopted in a piecemeal fashion by cotton growers in Eastern North Carolina. My analysis indicated that growers did not see all these practices as part of a single management decision, but rather as parts of independent decisions dealing with weed management, insect management, crop management, and ecosystem management.