Repository logo

Graduate Degree Program in Ecology

Permanent URI for this community

https://hdl.handle.net/10217/100395
These digital collections include theses, dissertations, faculty publications, photographs, and datasets from the Graduate Degree Program in Ecology.

Browse

Browsing Graduate Degree Program in Ecology by Author "Aldridge, Cameron L., committee member"

Now showing 1 - 3 of 3
  • Thumbnail Image
    ItemOpen Access
    Black bear fitness and interactions with humans in an anthropogenic context
    (Colorado State University. Libraries, 2022) Nelson, Shelley Laine, author; Aubry, Lise M., advisor; Aldridge, Cameron L., committee member; Baruch-Mordo, Sharon, committee member; Reynolds-Hogland, Melissa, committee member
    Multiple studies confirm that anthropogenic pressure has reshaped at least 75% of the global terrestrial biosphere, converting these areas to more anthropogenic biomes. These anthropogenic landscapes have played a key role in altering vertebrate life history strategies (e.g., shifts in breeding phenology, reduced home range, increased competition for resources, increased mortality from anthropogenic causes). Large carnivores are particularly at risk in anthropogenic landscapes because of their large home ranges, high dietary needs, and long generation times, which increases their likelihood of conflict with humans. In the northeastern U.S., populations of American black bears (Ursus americanus) have increased rapidly, more than any other black bear population in the country, with human-bear interactions (HBI) on the rise since the middle of the 20th century. One state in particular, New Jersey, currently sustains the highest coupled density of black bears and humans in the country. Previous research in New Jersey found anthropogenic environments supported higher cub production of female black bears than wildland conspecifics, but females also suffered higher mortality costs. Knowledge gaps remain of the specific ecological components contributing to changes in female black bear (sow) fitness and how these shifts may shape the dynamics of HBI. To bridge these knowledge gaps, I first used statewide, long-term HBI reported incidents (2001 – 2017) in New Jersey, and quantified relative risks and shifts in HBI over space (e.g., land cover types) and time (e.g., bear life cycle stages). I then used 35 years of sow den surveys (1984 – 2019) to examine the relative effects of anthropogenic change (e.g., garbage production, urban development), landscape composition and configuration, natural resource availability, harvest, and individual characteristics (e.g., prior conflict behavior) on sow reproductive components (e.g., body mass and litter size). I found HBI varied by bear life cycle stage and landcover type, and individual characteristics and the environmental context experienced by sows both played important roles in shaping sow fitness and reproduction. I found there were significantly lower odds of more severe HBI during denning. When bears emerge from dens in the spring, there were significantly higher odds of more nuisance HBI, and more specifically garbage complaints. During the breeding and summer activity period, there were significantly higher odds of both benign and more severe HBI occurring. During hyperphagia there were higher odds of more severe and nuisance HBI, when bears are foraging excessively to prepare for winter denning. Spatially, most conflicts occurred in anthropogenic-dominated areas, which also supported the highest odds of garbage complaints. Agricultural areas also supported the highest odds of more severe HBI. My results demonstrated sow body mass is tightly linked to agricultural and developed-low intensity land covers, likely due to the reliable food subsidies in those landscapes, but only apparent within certain sow home range extents. Yet, I found specific anthropogenic food subsides (e.g., trash and corn production) may not be as important to sows, rather increased anthropogenic stimuli (e.g., from cultivated crop and developed-low density land covers) is. I also found that a prior history of conflict with humans contributed to increased sow body mass. Litter size varied with respect to maternal condition, experience, and litter composition (e.g., same sex-female or male litters, mixed sex litters). Results failed to support the assumption of a trade-off between litter size and litter mass that is implicit in many life-history studies. Though, I found litter size and mass were more constrained in older sows compared to younger and middle-aged sows, with a similar relationship apparent in lighter sows versus medium weight and heavy sows. Results revealed sows could be investing more into sons in male-biased triplet litters, because their litter mass exceeded litter mass in other litter types (e.g., female-biased, same sex ratio). My results demonstrate sows may be circumventing trade-offs by continually acquiring more resources for larger litter size and mass, which is likely contributing to the high abundance and success of black bears in New Jersey. My results provide valuable insight in directing management focus towards specific life cycle events and land cover types, where anthropogenic change may simultaneously influence reproductive fitness and HBI, which often results in negative outcomes for black bears in New Jersey. Between 2001 and 2015, >$12 million has been allocated to bear management in New Jersey which at current conflict levels is not economically, environmentally, or socially sustainable long term. My results help guide management so that black bears can continue to thrive in the northeastern U.S., while minimizing human-bear conflicts and cost associated with them, and thus maximizing human-black bear coexistence in this human-dominated landscape.
  • Thumbnail Image
    ItemOpen Access
    Evaluation of population monitoring strategies for greater sage-grouse (Centrocercus urophasianus) in northwestern Colorado
    (Colorado State University. Libraries, 2017) Shyvers, Jessica E., author; Noon, Barry R., advisor; Walker, Brett L., advisor; Aldridge, Cameron L., committee member; Crooks, Kevin R., committee member
    Population monitoring programs are essential for the proper management of wildlife species but, despite recent advances in methodologies, generating accurate and defensible estimates of population size and trend remains a key challenge for wildlife biologists and managers and effective monitoring programs generally require considerable resources, effort and funding. For this reason, managers often turn to the use of population indices to monitor species. The greater sage-grouse (Centrocercus urophasianus) is a species of conservation concern throughout its range in western North America. Since the 1950s, high counts of males at leks have been used as an index for monitoring populations and are often assumed to represent overall population trend. However, the relationship between the lek-count index and true population size is unclear, resulting from a reliance on numerous untested assumptions, and the reliability of these counts for monitoring population trend has been questioned. In addition, lek-count data do not provide information about the female population, a crucial component for assessing a population's growth potential. There is a need for development and evaluation of alternative methods to obtain reliable estimates of population trend and test assumptions underlying the lek-count index. We tested two novel methods for monitoring a small greater sage-grouse population in Northwest Colorado. We found that a large and variable proportion of the lekking male population was missing from lek-count data each year when not all leks were known and counted, the lek-count index poorly represented true annual male abundance in small populations, and the possibility of large annual variation in male-to-female sex ratio should be considered when extrapolating female abundance from male count data. Our results suggest that, while lek-count data may be useful for detecting large changes in the abundance of lekking males over time, observations of trend based on annual lek-count index data may misrepresent true population trend in relatively small populations.
  • Thumbnail Image
    ItemOpen Access
    Influence of habitat complexity on diversity and community structure of arboreal spiders in grassland-shrub systems
    (Colorado State University. Libraries, 2023) Knutson, Eric M., author; Charkowski, Amy, advisor; Aldridge, Cameron L., committee member; Trivedi, Pankaj, committee member; Hufbauer, Ruth, committee member
    Revealing the ecological drivers of species distribution is one of the central issues in ecology. The ecological niche concept recognizes that distribution of species is influenced by abiotic (e.g., temperature, landscape characteristics, and nutrients) and biotic (e.g., food availability) factors through both direct and indirect mechanisms. Many of these niche factors can influence the spatial position of plants in a landscape. Plant communities often determine the physical structure of the environment (microclimate, plant architecture) and therefore, have a considerable influence on the distribution of animal species, such as arthropods, and on local community structure. For instance, vegetation structure provides spatial complexity by creating microenvironments that may enable more interactions with other species that live on plants or allow resource partitioning. In grasslands, much of the arboreal habitat is in the form of shrubs, but the role and importance of shrubs in distribution and diversity of arthropods in grasslands is unknown. Spiders are a useful indicator for examining the role of shrubs in arthropod ecology because they are genetically and behaviorally diverse predators and prey that can be captured and counted with a single method. Spiders are a key component of invertebrate communities of grasslands and arboreal spiders of grasslands provide a unique ecological system to study habitat association and community assemblage. However, most spider studies in prairie ecosystems have focused on ground dwelling taxa or those associated with agroecosystems. Only limited data exist for shrub-dwelling species and few studies have compared arboreal spider occupancy across different grassland shrub species. I endeavored to understand this system in more detail by investigating how arboreal spider community structure responds to native shrub species, plant community composition and landscape complexity. Since landscape complexity can be evaluated at multiple scales, landscape characteristics can be significant predictors of presence and abundance for a variety of taxa. I collected and identified 3,053 specimens to family, genus or species level and found that presence of certain shrub species predicted spider species occurrence and suggested diversity community structure patterns. I found that habitat association to combinations on shrub species indicated habitat specific niche partitioning of arboreal spiders in two Colorado grassland systems. Because shrub species occurrence is largely dependent on elevation and moisture gradients, spider occupancy may also be tied to similar gradients correlated with these landscape factors. Changes in the topography of the sampling area affected the local plant communities of shrubs across a recognized elevational gradient, which correlated to habitat zones for arboreal spiders in the local area.