Browsing by Author "Kenneth Pollock, Committee Member"

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Coevolution Between Grasshopper mice (Onychomys spp.) and Bark and Striped Scorpions (Centruroides spp.)
(2004-11-29) Rowe, Ashlee Hedgecock; James Gilliam, Committee Member; John Godwin, Committee Member; Kenneth Pollock, Committee Member; Harold Heatwole, Committee Chair
Asymmetrical selection has been proposed as the strongest argument for rejecting hypotheses of coevolutionary arms races between predators and prey. In many cases there is evidence of increased investment by the prey in response to the predator, but no evidence of increased investment by the predator in response to the prey, thus producing asymmetry in selection. However, selection against a predator may be increased when the interaction is with a "dangerous" prey. Predators are most likely to respond evolutionarily to potentially lethal prey. This study employs grasshopper mice (Onychomys spp.) and bark and striped scorpions (Centruroides spp.) as a model to test the hypothesis that interspecific interaction between a predator and a potentially lethal prey will result in behavioral and physiological adaptations that reciprocally mediate their interaction (i.e., coevolution). Bark scorpions (Centruroides exilicauda) and striped scorpions (Centruroides vittatus) produce a potent venom containing neurotoxins that selectively bind to the ion-channels of vertebrates. Vertebrate-specific neurotoxins may produce lethal effects in mammals, especially small mammals. Southern grasshopper mice (Onychomys torridus) and Mearns' grasshopper mice (O. arenicola) are known to be voracious predators on scorpions. Southern grasshopper mice are broadly sympatric with bark scorpions in the Sonoran Desert, and Mearns' grasshopper mice are broadly sympatric with striped scorpions in the Chihuahuan Desert. The third species in this genus, the northern grasshopper mouse (O. leucogaster) is broadly allopatric with Centruroides spp. In a preliminary study, both southern and Mearns' grasshopper mice demonstrated resistance to bark and striped scorpion neurotoxins. The evolution of toxic venom and resistance to that venom strongly suggests a coevolutionary relationship between Onychomys spp. and Centruroides spp. To test this hypothesis, I evaluated the predator-prey relationship between grasshopper mice and their toxic scorpion prey during staged feeding trials. Additionally, I compared the geographic patterns of venom resistance in all three species of grasshopper mice with geographic patterns of venom toxicity in bark and striped scorpions. Results from the feeding study demonstrated that grasshopper mice do not distinguish between toxic and non-toxic species of scorpions; mice attacked, incapacitated, and consumed bark and striped scorpions without hesitation and as effectively as they attacked crickets and non-toxic scorpions in the genus Vaejovis. The feeding experiments indicate that grasshopper mice have the ability to prey on bark and striped scorpions in habitats where they co-occur. Venom resistance analyses demonstrated that all three species of grasshopper mice have evolved some resistance to the vertebrate-specific neurotoxins produced by Centruroides spp. The assays show that patterns of venom toxicity in Centruroides and venom resistance in Onychomys co-vary geographically, both within and among species; i.e., populations of Onychomys interacting with the most toxic populations of Centruroides were extremely resistant; populations of Onychomys interacting with only moderately toxic populations of Centruroides were only moderately resistant; and populations of Onychomys not sympatric with Centruroides were only weakly resistant. Such systematic covariation between venom toxicity in the scorpions and venom resistance in the mice is consistent with a coevolutionary, arms race hypothesis.
Discontinuities in fish assemblages and efficacy of thermal restoration in Toxaway River, NC
(2003-07-29) Robinson, Jason Lesley; Peter Rand, Committee Chair; Tom Kwak, Committee Co-Chair; Kenneth Pollock, Committee Member
Biogeographical studies in the Toxaway and Horsepasture Rivers, (Transylvania County, NC) were initiated along with the creation of a state park in the area. This region is noted for extreme topographic relief, high annual rainfall totals and many rare and endemic plants and animals. The study area encompasses a portion of the Blue Ridge Escarpment and the associated Brevard Fault Zone. These geologic features are important factors in determining the distribution of stream habitats and organisms. I hypothesize that major waterfalls and cascade complexes have acted to discourage invasion and colonization by fishes from downstream. This hypothesis is supported by longitudinal fish assemblage patterns in study streams. Fish species richness in Toxaway River increased from 4 to 23 between Lake Toxaway and Lake Jocassee, a distance of 10 river kilometers. No species replacement was observed in the study area, but additions of up to 7 species were observed in assemblages below specific waterfalls. A second component of the research examines the efficacy of a rapid bioassessment procedure in detecting thermal and biological changes associated with a reservoir mitigation project in an upstream site on Toxaway River. The mitigation project began in the winter of 2000 with the installation of a hypolimnetic siphon to augment the overflow release with cooler water during summer months. I record a greater summer temperature difference on Toxaway River below Lake Toxaway (comparison of pre- vs. post-manipulation), relative to control sites. The cooling effect of the mitigation decreases in magnitude with increasing distance from the dam. I offer a critique of the mitigation effort based on a mismatch between the longitudinal extent of thermal restoration and the distribution of target organisms that were expected to benefit from the manipulation.. Secondly, I highlight some of the important limitations in drawing inferences from data collected using a rapid bioassessment approach. I conclude with suggestions on how to improve future research efforts in this area. I emphasize the importance of implementing process-oriented field work that could provide insights into mechanisms responsible for biological changes downstream from reservoir ecosystems.
Effects of Stocked Trout on Native Nongame Riverine Fishes.
(2010-05-20) Weaver, Daniel; Thomas Kwak, Committee Chair; Kenneth Pollock, Committee Member; Robert Dunn, Committee Member
Fish Populations Associated with Habitat-Modified Piers and Natural Woody Debris in Piedmont Carolina Reservoirs
(2002-06-20) Barwick, Robert Dempsey; Kenneth Pollock, Committee Member; Thomas Kwak, Committee Co-Chair; Richard Noble, Committee Co-Chair
A primary concern associated with reservoir residential development is the loss of littoral habitat complexity. One potential approach to compensate for this loss is to deploy artificial habitat modules under existing piers, but the benefit of this practice on developed reservoirs has not been demonstrated. To determine the effect of pier habitat modifications, 77 piers located on 47, 100-m transects on two Piedmont Carolina reservoirs were selected for modification using plastic "fish hab" modules augmented with brush (brushed habs), hab modules alone (habs), or as reference piers without modification. Fish were sampled from all piers and transects in April, July, and October 2001 using a boat-mounted electrofisher. Generally, catch rates were higher at brushed hab piers and piers with habs than at reference piers during all seasons. Similarly, fish abundance was generally higher on transects containing natural woody debris, brushed habs, or habs than that on reference developed transects during spring and summer with exceptions during fall. On these reservoirs, fish abundance associated with developed shorelines appears to be related to the structural complexity of available habitat, regardless of structure composition. Supplementing piers with habitat structures appears to serve as an effective management technique to enhance littoral habitat complexity in residentially developed reservoirs.
Food Web Interactions of Larval Yellow Perch, Perca flavescens, in Lake Michigan: Implications for Recruitment
(2005-01-16) Fulford, Richard Stewart; James Rice, Committee Chair; Kenneth Pollock, Committee Member; Peter Rand, Committee Member; James Gilliam, Committee Member
Variability in annual recruitment for many fishes is correlated with survival during the larval phase. Yellow perch in Lake Michigan have experienced sustained recruitment failure since 1990 and this has been blamed on low larval survival. Direct examination of factors important to larval yellow perch survival in Lake Michigan is complicated by the large size of the lake (52,000 km2) and the short length of the pelagic larval period (30-40 days). Individual-based modeling is a valuable indirect method for assessing the importance of multiple factors to larval survival. I used an individual-based modeling approach combined with field data collection to test four hypotheses regarding factors limiting survival of larval yellow perch in Lake Michigan. I tested whether larval survival is limited by prey community composition, size-selective predation, advection of larvae into offshore habitat or an interaction of these factors. I sampled larval and zooplankton abundance in Lake Michigan along a transect from 1 – 32 km from shore in 2000 and 2001. I conducted laboratory experiments to quantify larval vulnerability to predation by three typical predators as a function of both predator and prey size. I also conducted laboratory experiments to quantify larval selectivity for different zooplankton prey as a function of larval size and prey community composition. I used the results of these experiments to develop an individual-based model specifically to describe growth and survival of larval yellow perch. Field data suggest that larval yellow perch are being transported from the nearshore to the offshore zone of Lake Michigan, but the timing of this transport varies between years. Model simulations in which the offshore prey community and the timing of larval advection were both varied suggested that larval survival will be highest in years when advection occurs within two weeks of peak hatch, allowing larvae to exploit offshore prey resources early during ontogeny. The model predicts that larvae will make foraging decisions based on prey availability as well as innate preference and they will change their diet if they are exposed to different prey communities. Model simulations also demonstrated that predation currently may not be an important factor for survival of larval yellow perch in Lake Michigan. This result is because alewife is the only fish abundant in Lake Michigan known to eat larval yellow perch. Experimental results suggest that alewife feeding rate on larval yellow perch is a positive function of larval density; yellow perch densities are currently too low to induce significant predation by alewife. Predation appears to be more important in smaller systems where larval densities are higher and larvae are exposed to other predator species. Larval survival in Lake Michigan appears to be primarily limited by an interaction of prey community composition and the timing during the larval period of offshore advection. Both factors vary between years and a good year-class is predicted when the offshore prey community is rich in cyclopoid copepods and larvae are advected offshore early. Early access to cyclopoid copepods results in an earlier transition from feeding on rotifers to feeding on copepods, which is predicted to increase larval growth and decrease mortality. These results suggest that survival of larval yellow perch in Lake Michigan is affected more by density-independent factors such as physical transport and prey community composition; Lake Michigan more closely resembles a marine environment than a typical lake with respect to larval recruitment processes. The unique aspects of larval yellow perch dynamics in Lake Michigan must be considered when applying lessons learned from analysis of larval yellow perch in other lakes to understanding survival of larval yellow perch in a large meso-oceanic system like Lake Michigan.
Occupancy Modeling and Strategic Habitat Conservation for Avian Species in the Southeastern Coastal Plain of the United States.
(2010-04-15) Iglecia, Monica; Jaime Collazo, Committee Chair; Kenneth Pollock, Committee Member; Nicholas Haddad, Committee Member; Alexa McKerrow, Committee Member
Protecting Biodiversity through Monitoring of Management Indicator Species: Questioning Designations of Ursus Americanus (black bear) and Plethodon jordani (Jordan's salamander)
(2003-11-17) Sevin, Jennifer Ann; Harold Heatwole, Committee Member; Alvin Braswell, Committee Member; Kenneth Pollock, Committee Member; Roger Powell, Committee Chair
Loss of biological diversity is occurring on a global scale, with the southern Appalachians being no exception. As a result of legislation requiring all national forests to maintain viable plant and animal populations, the Forest Service incorporated use of Management Indicator Species (MIS). For an organism to be a good MIS, it must be easy to monitor, be associated with the community type or habitat it supposedly indicates, respond measurably to changes in habitat caused by management activities, and represent other species response to management activities. This study questions the designations of Ursus americanus and Plethodon jordani as MIS in Pisgah National Forest and investigates methods and indexes used in monitoring salamanders. I found a high year-to-year repeatability in sampling of salamander abundances. Single sampling efforts at sites where highly correlated with the average of two or more sampling efforts at the same sites, indicating single searches are efficient in detecting abundances of salamanders at sites. In comparing two area-constrained search methods for salamanders, I found the two methods to produce different densities, Simpson diversity indexes, and species equitability, along with different abundances of most salamander species. Search methods are therefore not equivalent in detection of salamanders. Searching at night was a more efficient sampling method for P. jordani than searches of natural cover during the day. I found P. jordani, which is designated as a MIS for woody debris special habitats, to be minimally associated with woody debris as a cover object during the day. Juvenile and small adult P. jordani preferred to use woody debris than rocks as a cover object during dry conditions. P. jordani were found to use all substrate types at night and preferred woody debris to understory, soil, and rocks. P. jordani did not use woody debris more than leaf litter or tree trunk substrates at night and their use of substrates did not differ from those of Desmognathus ocoee. Black bears and salamanders prefer similar mature forest habitats, but whether black bears serve as a good MIS for mature forest salamanders is unclear. HSIs did not show many correlations with salamanders. Reduction of the black bear habitat suitability index model showed few habitat factors important for black bears were important for salamanders. Investigating the use of an animal existing on one scale to indicate for an animal on another scale merits further study.
Raccoon Ecology and Management on Cape Lookout National Seashore, North Carolina.
(2010-04-27) Waldstein, Arielle; Theodore Simons, Committee Chair; Kenneth Pollock, Committee Member; Michael Stoskopf, Committee Member; Allan O'Connell Jr, Committee Member
Spatiotemporal Variation in Broodstock Reserve Fecundity at Multiple Scales
(2009-05-15) Mroch, Raymond Millard III; David B. Eggleston, Committee Chair; Daniel Kamykowski, Committee Member; Kenneth Pollock, Committee Member
A major expectation of marine no-take reserves is that organisms within a reserve, over time, will export eggs and larvae to help sustain populations within and outside of reserves. Because fecundity and reproductive output can vary in space and time, the success of broodstock reserves depends on selecting the habitat or location that maximizes reproductive output to the target population. The goals of this study were to quantify spatial and temporal variation in (1) per capita fecundity (# eggs/individual) of female eastern oysters (Crassostrea virginica) within a network of marine broodstock reserves in Pamlico Sound, North Carolina; (2) fecundity per square meter (eggs/m2); (3) reserve fecundity (# eggs/reserve); and (4) the effects of endogenous and exogenous factors on spatiotemporal variation in per capita fecundity. A total of 1768 oysters were collected by scuba divers from six broodstock reserves over five sampling periods during 2006-2008 and processed in the laboratory for fecundity. Per capita fecundity ranged from 0 to 340,500 eggs, and mean per capita fecundity increased exponentially with oyster size (LVL mm) peaking in May of all years. In general, there were distinct spatial differences in fecundity depending upon the response variable, with per capita fecundity highest at more inshore reserves of moderate salinity, and fecundity m2 and reserve fecundity highest at more seaward reserves with relatively high salinity. Ranking of broodstock reserves for management purposes will likely depend upon the specific management goal. For example, if the goal is to expand broodstock reserves at locations that maximize reproductive potential per square meter of habitat created or improved, then reserves such as Ocracoke and Hatteras, that combine the joint effects of relatively high oyster density, size and per capita fecundity, would be ranked highest for expansion. If the management goal is to rank conservation of current broodstock sanctuaries, then relatively high salinity reserves such as Hatteras, that combine the joint effects of relatively high m2 fecundity and large substrate surface area, provide the greatest reproductive potential in terms of reserve fecundity. Lastly, if the management goal is to augment oyster densities via stocking with oyster spat at sites with high reproductive potential at the individual level, then more inland reserves such as Bluff Point and West Bay would be ranked highest. These results highlight the need to consider time and space when measuring reproductive potential of marine reserves, as well as the need to consider a comprehensive suite of response variables that best inform managers.