Browsing by Author "Nick M. Haddad, Committee Member"

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Habitat Ecology of the Carolina Madtom, Noturus furiosus, an Imperiled Endemic Stream Fish
(2008-12-09) Midway, Stephen Russell; D. Derek Aday, Committee Co-Chair; Thomas J. Kwak, Committee Co-Chair; Nick M. Haddad, Committee Member; Kevin Gross, Committee Member
The Carolina madtom Noturus furiosus is an imperiled stream catfish (Ictaluridae) endemic to the Tar and Neuse river basins in North Carolina. The species is listed as State Threatened, and whereas the Tar Basin population resembles its historical distribution, the Neuse Basin population has shown recent significant decline. Quantifying habitat use and availability is critical for effective management and subsequent survival of the species. This study combined field and laboratory research to investigate habitat use and suitability, as well as efficacy of an artificial cover unit. To assess habitat suitability, we investigated six reaches (three in each river basin) to (1) quantify Carolina madtom microhabitat use, availability, and suitability, (2) compare suitable microhabitat availability between the two basins, and (3) examine the effectiveness of an instream artificial cover unit. We also conducted laboratory experiments to examine madtomsâ€™ use of the same artificial cover unit relative to three natural cover types. Carolina madtom were located and their habitat use was quantified at four of six survey reaches; the species appeared to be absent at two reaches in the impacted Neuse Basin. Carolina madtom most frequently occupied shallow to moderate depths (0.5 m) of swift moving water over a sand substrate using cobble for cover. Univariate and principal components analyses both showed Carolina madtom use of instream habitat to be selective, or nonrandom. Interbasin comparisons suggested that most suitable microhabitats (particularly water depth and velocities) were more prevalent in the Neuse than in the Tar Basin, which is interesting considering that the Neuse population appears to be the more impacted of the two. Consequently, we suggest that other physical or biotic factors must be responsible for the decline in the Neuse Basin population. Our instream artificial cover units were occupied mainly by Carolina madtom (25% of the time), and rarely by a suite of other stream animals. Comparing areas with the artificial cover units (â€˜treated areasâ€™) to those without them (â€˜control areasâ€™), Carolina madtom abundance among all treated areas was statistically higher than the controls, demonstrating that madtoms will use suitable artificial cover when available. Microhabitat characteristics of occupied artificial cover units closely resembled those of natural microhabitat use. Results from the field component of the study provide habitat suitability criteria that can inform management and conservation of the Carolina madtom, and the artificial cover units present a cost-effective conservation and restoration option if increased management is deemed necessary. In the laboratory component of the study, Carolina madtom were placed in an experimental stream tank (44 cm x 88 cm in area and about 45 cm deep) and given 24 hours to make a selection among four cover options, three natural (one each of rock, leaf pack, and mussel shell) and the artificial cover unit. Among 30 experimental trials, Carolina madtom preferred the artificial cover unit, selecting it 63% of the time. Rock was selected 23% and leaf pack 13% of the time. Contrary to previous anecdotal observations, mussel shells were not selected during any trials. Results from the laboratory experiments, coupled with similar findings from instream work, indicate that artificial cover may be a viable option for species conservation and restoration. Given the State Threatened status and limited distribution, our results have implications for conservation and restoration of this native and endemic southeastern catfish. Successful management and conservation of declining Carolina madtom populations is dependent upon preserving Tar Basin habitat, identifying Neuse Basin impacts, and restoring Neuse Basin populations.
Implications of exotic species invasion for restoration of urban riparian forests
(2004-07-12) Vidra, Rebecca Lynn; Thomas R. Wentworth, Committee Member; George Hess, Committee Member; Jon M. Stucky, Committee Member; Nick M. Haddad, Committee Member; Theodore H. Shear, Committee Chair
Urban forests serve as remnant natural areas in otherwise degraded landscapes. Yet, these forests are commonly threatened by invasion of exotic plant species, which may compromise the structure and ecological functions of native communities. Restoration of these forests will inevitably require removal and continued control of exotic species invasions. I focused my research on urban riparian forests within Raleigh and Cary, North Carolina, USA. My goals are to understand the impacts of exotic species invasion on these forest communities, identify factors that make these sites susceptible to invasion, and make appropriate restoration recommendations. To address these goals, three major studies structured my research. First, I tested two major paradigms of current exotic species ecology using observational data from 23 urban riparian buffers. The competition paradigm was borne out by negative relationships between exotic and native species richness (r = -0.66, p = 0.0009). I also detected shifts in species composition away from native woody species in sites that have been invaded by exotic species. As suggested by the resource availability paradigm, certain environmental conditions do seem to favor exotic species in this study system. While light availability was not significantly correlated to invasion of exotic species, several measures of soil fertility were negatively correlated to native species and positively correlated to exotic species. Therefore, efforts to reduce fertilization from adjacent and upstream landscapes should be part of any restoration plan. My second approach involved conducting an experimental removal study at the North Carolina Museum of Art. I compared the species composition and native species recovery in three treatments: control, initially removing all vegetation and allowing regeneration, and initial removal with repeated removal of new exotic recruits. While the repeated removal treatment featured a different species composition than either of the other two treatments, this difference can be attributed to the lack of exotic species, not to the recovery of native species. These results indicate that repeated removal is necessary to prevent invasion in urban forests but that native supplemental plantings may be necessary to create a diverse community. My third approach involved evaluating the influence of landscape structure on patterns of exotic species invasion in urban riparian buffers. I found that invasion, measured as total percent cover of exotic species, is highest in the narrowest buffers. Buffers surrounded by more forest canopy cover are also more heavily invaded than those surrounded by less canopy cover. These findings suggest that processes outside the buffer, such as bird dispersal and vegetative spreading of ornamental plantings, may contribute to the invasion inside the buffer. Exotic species invasion does have implications for restoration of urban forests. Not only does invasion threaten native species richness, but native woody species appear to be most at risk for extirpation from these sites, with potential consequences for long-term forest succession. Because these forests are invaded by a suite of exotic plants, targeted efforts to remove those that are likely outcompeting native species is a good first step. Managing land use practices outside of the forests, while difficult, is necessary to reduce both the stress on the forest (e.g., fertilization) and invasion opportunities (e.g., bird dispersal, ornamental plantings). The results of this research will help managers identify sites at future risk for invasion and focus efforts on managing both the exotic species and site conditions to restore the health of these ecologically valuable forest communities.
Mammalian Nest Predators Respond to Greenway Width, Habitat Structure, and Landscape Context
(2003-08-31) Novotny, Kristen Elise; Nick M. Haddad, Committee Member; George R. Hess, Committee Chair; Christopher E. Moorman, Committee Member
Birds of conservation concern breed in suburban greenways, yet abundant populations of mammals that depredate bird nests may compromise nest success. We evaluated how three factors influenced total mammalian nest predator abundance and individual species abundance in greenways of Raleigh and Cary, North Carolina, USA: 1) the width of the forested corridor containing the greenway, 2) the type of land-use adjacent to the forested corridor, and 3) the habitat structure within the greenway. Forest corridor width and adjacent land-use were measured for 34 greenway segments using aerial photographs. Several measures of habitat structure within the greenway were collected in the field during September 2002, including trail width and surface type, stream width, and percentage of mature forest. We measured the relative abundance of mammalian nest predators with scent-station transects, operated for five nights during the 2002 breeding season. Mammalian nest predators were significantly more abundant in greenways within narrower forested corridors. Mammalian nest predator abundance was lowest in greenways with forested corridors wider than 200 meters, and continued to decline as forest corridor width increased. Most of the species we identified are known to inhabit edge habitat, which was present throughout greenways within narrow forested corridors. We found no relationship between categorical measures of land-use context (low-density residential, high-density residential, office/institutional) and mammalian nest predator abundance. Specific landscape features adjacent to the greenway, however, did affect mammalian nest predator abundance. Greenways adjacent to landscapes with fewer buildings had a higher abundance of total mammalian nest predators, and the abundance of individual species varied with the amount of canopy, lawn, and pavement in the adjacent landscape. The habitat structure of the greenway was correlated with the mammalian nest predator community, yet no habitat structure variables were significant in all species models. Segments with wider trails had a higher abundance of mammalian nest predators, as did sampling areas located closer to trails and with more mature forest. Raccoon abundance was higher in segments with wider trails, and lower in segments near parking lots or roads, playing fields, and backyards. Opossum abundance was higher in segments near water and trails. Gray squirrel abundance was higher in segments near backyards. Domestic cat abundance was higher in segments with more mature forest, near parking lots or roads, and lower further from streams. To reduce the risk of avian nest predation by mammals, greenways should be designed with wider forest corridors and narrower trails, particularly natural dirt footpaths instead of paved or cleared trails. Additional features of greenways are likely to increase the abundance of particular species. Greenway forest corridors with more paved areas in the adjacent landscape are likely to have higher abundances of rats and mice, and domestic cats if the paved area borders the greenway. Increasing lawn in the adjacent landscape is likely to increase opossum abundance in greenways. Greenways that border backyards are likely to have a higher abundance of gray squirrels. Increasing canopy cover in the adjacent landscape will positively influence raccoon abundance, as will increasing mature forest within the greenway habitat for total mammalian nest predators and domestic cats. Many of these vegetative characteristics also create habitat for birds of conservation concern. Management of these features must balance reduction of predator communities with promotion of desired bird communities.
Towards a Movement Ecology: Modeling the Behavioral Response of Invasive Snails to Resources and Competition.
(2008-03-03) Snider, Sunny Brooke; Nick M. Haddad, Committee Member; James F. Gilliam, Committee Chair; Jay F. Levine, Committee Member; Kevin Gross, Committee Member
The movement of individuals is one of the fundamental components of contemporary ecological problems such as metapopulation theory, epidemic models, competitive coexistence, and invasion dynamics. Advection-diffusion models, sometimes with a reaction term, have been usefully applied to such problems. For this dissertation, I broadened this approach by seeking to understand the effects of certain biotic and abiotic factors on movement ecology, and asking how to incorporate flexible behavioral responses into classical advection-diffusion models. I asked how resources, competitive environment, and habitat structure, interacting with body size or not, affect the movement behaviors of two coexisting invasive snails (Melanoides tuberculata and Tarebia granifera), and whether including the behavioral response to these factors improves advection-diffusion models of movement. I also made natural history observations regarding the snail system to provide a biological context for my empirical work. To address these questions, I conducted replicated experiments and observational studies, extended advection-diffusion models, and arbitrated among candidate models using AIC (Akaike's Information Criterion) model selection. Specific studies included (1) behavioral response to phenotypic and resource heterogeneities, and their interaction, (2) behavioral response to intraspecific and interspecific competition, and (3) behavioral response to spatially uniform versus spatially heterogeneous environments. In summary, this dissertation provides insights into modeling movement behaviors, using two coexisting invasive snails as the model system. I advocate for a behaviorally informed modeling framework that integrates sentient responses of individuals in terms of movement, improving our ability to accurately model ecological processes that depend on movement ecology.