Browsing by Subject "Ecology, Evolution, and Behavior"

Now showing 1 - 5 of 5
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    The effects and importance of natural enemies on immature monarch (Danaus plexippus) populations.
    (2010-08) De Anda, Alma Patricia
    Abstract summary not available
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    From Soil to Squirrel: The Legacy of Lead Pollution & Its Effects on Urban Wildlife Behavior
    (2024-04-18) Schulz, Rachel K; Devitz, Amy-Charlotte; Snell-Rood, Emilie C
    Urbanization increasingly threatens wildlife through the introduction of novel threats and pollution. Animals can use behavior to adapt to urban environments and urban pollutants drive changes in behavior, leading to populations of urban wildlife with some behaviors that are distinct from rural populations. Lead (Pb) pollution is ubiquitous in urban areas, but there can be significant local variation in soil lead levels. In this study, I examined the relationship between soil lead, hair lead, docility, and aggressive and social behavior in eastern gray squirrels (Sciurus carolinensis) and eastern chipmunks (Tamias striatus) in Minneapolis and Saint Paul, Minnesota. Docility was measured through a struggle test and aggressive and social responses were measured in a mirror image stimulation trial. Soil lead and hair lead were significantly positively correlated in gray squirrels and chipmunks, and there was no difference in hair lead based on species or sex. Chipmunks had significantly longer struggle times than gray squirrels, but struggle time did not vary based on hair lead or sex. Only six of 235 animals displayed aggression in the mirror image stimulation trial, and frequency of contacting the mirror in a nonaggressive way was not correlated with hair lead, species, or sex. These results provide correlational evidence of lead transfer from soils to gray squirrels and chipmunks, though the magnitude of lead accumulation does not seem to depend on the distinct life histories of these two species. At the levels currently present in these urban environments, lead does not affect aggressive or social behavior in gray squirrels or chipmunks. Future studies should examine aggression through direct observation rather than a mirror image stimulation trial to better quantify aggression in these species that have low territorial aggression.
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    Multiple scale spatial dynamics of the moose-forest-soil ecoystem of Isle Royale National Park, MI, USA
    (2008-11) De Jager, Nathan R.
    Moose (Alces alces) make foraging decisions at scales that range from plant stems (centimeters) to home ranges (kilometers). These decisions determine the spatial distribution of forage consumption and the consequent impacts on plant communities and nutrient cycles. From the fine scale changes in the size and density of plant stems to the distribution of plant patches and community assemblages across landscapes, the effects of moose browsing at one spatial scale may amplify spatial heterogeneity at scales that are orders of magnitude larger than the scales at which the interactions originally took place. In this thesis, I focused on how gradients of moose browsing in two valleys at Isle Royale National Park, MI, USA influenced plant fractal geometry and how such changes to plant geometry feedback to moose foraging across larger previously browsed landscapes. I also examined changes in larger scale patterns of forage availability, plant community composition, and soil fertility in response to recent declines in island-wide moose population density. Increasing moose browsing influenced the geometry of deciduous and conifer species differently. The fractal dimension of bite density, bite mass, and forage biomass of aspen saplings all responded quadratically to increasing moose browsing and were greatest at intermediate browsing rates. In contrast, fractal dimension of bite density, bite mass, and forage biomass of balsam fir all declined steadily with increasing moose browsing. These different responses of plant canopies to increased browsing as well as seasonal changes in bite mass altered the distribution of foraging mechanisms across larger previously browsed landscapes. At the larger scale, recent (2005-2007) landscape patterns of available and consumed browse became decoupled from each other and distributions of available forage, plant species composition, and soil fertility were qualitatively different from patterns documented in the early 1990's. These changes are coincident with and likely driven by recent declines in the island-wide moose population of Isle Royale. Collectively, these two studies suggest that large scale landscape patterns of browse availability, species composition, and soil fertility may emerge from finer scale impacts of browsing on plant geometry and the feedbacks to larger scale foraging decisions that moose make in addition to population density. The long-term dynamics of landscape patterns in boreal forests are therefore dependant on both fine scale foraging decisions and large scale population dynamics.
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    Transmission of Barley/Cereal yellow dwarf viruses by aphid vectors
    (2013) Kempnich, Michael;
    Barley and Cereal yellow dwarf viruses (B/CYDVs) negatively impact the fitness of host plants and have a destabilizing effect on established ecosystems. Plant and B/CYDV pathogen interaction dynamics can be significantly altered by increasing worldwide nitrogen and phosphorous input. Viruses rely on interactions between host plants, insect vectors and environmental factors in order to spread. Relationships between virus transmission and both the level of and ratio between host nitrogen and phosphorous resources are difficult to establish, especially in natural systems, and remain poorly understood. In order to assess the relationships between host resources and vectored-disease spread in controlled conditions, we developed a method of inoculation of healthy plants using aphid vectors that previously fed on virus infected fresh plant leaves. While we originally tested an inoculation method in which aphids fed on a homogeneous virus inoculum obtained by grinding and clarifying infected plant tissues, this resulted in low aphid survival and low virus transmission rate in our lab conditions. We will use the inoculation technique developed in this study to test the effects of host nutrient levels and ratios on virus transmission rate. The results obtained under laboratory conditions will allow us to make predictions on the broad connections between human nutrient loading and rates of viral infection.
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    The urban-rural environment: effects of impervious surface land cover on lake ecosystems
    (2010-11) Haustein, Mitchell Donald
    The rate of urbanization of land has increased dramatically over the past decades and is expected to continue increasing as global populations continue to rise. Modifications of land associated with urbanization undoubtedly affect the adjacent and surrounding ecosystems, and urban ecosystem science has become an increasingly popular area of research to assess and quantify the ramifications of such drastic changes. The prevalence of impervious surfaces, one of the most defining characteristics of urban areas, has fundamentally altered the hydrology of urban ecosystems through decreased infiltration of surface water and rerouted hydrological flow paths. As a result, aquatic ecosystems positioned within urbanized areas have been significantly influenced by increases in stormwater runoff associated with efficient drainage networks. The altered hydrology within these urban systems has been shown to consistently negatively impact overall stream health. In contrast, urban lakes have been much less studied, yet have clearly been impacted by urbanization. Shallow lakes within the Twin Cities Metropolitan Area, Minnesota were assessed in 2007 for phytoplankton nutrient limitation and in 2007-2009 for nutrient biogeochemistry. Phytoplankton exhibited either multiple or co-nutrient limitation by nitrogen, phosphorus, and silica in 12 of the 17 lakes sampled in 2007. Strong negative relationships were observed across a gradient of impervious surface percentage within surrounding lake buffers for both TDN and DOC in 2007 and 2008. However, this gradient of imperviousness ranged from an agriculturally dominated landscape to a highly urbanized landscape. Therefore, lakes assessed in 2009 included reference sites dominated by forested land cover; these displayed similar concentrations iii of TDN and DOC as urban lakes. Chemical characterization of the DOC across these lakes nevertheless suggests DOC within urban lakes is dominated by autochthonous sources, while DOC in forested and agricultural lakes is dominated by allochthonous sources. These results suggest that urbanization, characterized by impervious surface land cover, and agricultural land use affect nutrient biogeochemistry and DOC character within lakes.