Browsing by Author "Franklin, Alan B., advisor"
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Item Open Access Haemosporidian parasites of barred owls (Strix varia) and northern spotted owls (S. occidentalis caurina): investigating the effects of an invasive species on parasite transmission and community dynamics(Colorado State University. Libraries, 2013) Lewicki, Krista E., author; Huyvaert, Kathryn P., advisor; Franklin, Alan B., advisor; Piaggio, Antoinette J., committee member; Pejchar Goldstein, Liba, committee member; Foy, Brian D., committee memberAlthough the barred owl (Strix varia) was historically limited to eastern sections of North America, its range has steadily expanded westward over the past century. Currently the barred owl's range entirely overlaps the range of the federally threatened northern spotted owl (Strix occidentalis caurina) in the Pacific Northwest. Invasive species have been known to drastically impact a region's native species by altering the parasite communities among those species, yet little is known about the parasites of barred and northern spotted owls in particular. The purpose of this study was to determine if and to what extent avian blood parasite assemblages of barred and northern spotted owls have changed as a result of the range expansion by barred owls. Blood samples were collected from sympatric northern spotted and barred owls in northwestern California, as well as from barred owls from seven regions across the barred owl's historic range. I screened samples for blood parasites belonging to the genera Haemoproteus, Plasmodium, and Leucocytozoon, and I analyzed bird infection status and intensity using a combination of PCR and microscopy techniques. Additionally, a section of mitochondrial DNA was sequenced from all samples in which I detected Haemoproteus or Plasmodium parasites, and I used these sequence data to calculate parasite haplotype richness, haplotype diversity, and similarity of Haemoproteus and Plasmodium assemblages. Using these five metrics I evaluated predictions of four hypotheses describing how biological invasions might affect parasite assemblages of invasive and native hosts: the Enemy Release (i.e., hosts benefit from a loss of parasites in their invasive range), Enemy of My Enemy (i.e., invasive hosts introduce parasites to naïve native hosts), Parasite Spillback (i.e., invasive hosts act as a new reservoir to native parasites), and Increased Susceptibility (i.e., native hosts introduce parasites to naïve invasive hosts) Hypotheses. Analyses of Leucocytozoon spp. indicated that the population from which the samples were collected (i.e., eastern barred or western barred) was not important in determining a barred owl's infection status, which offered little support for the Enemy Release Hypothesis (ERH) in the context of Leucocytozoon parasites. However, population was an important explanatory variable in determining a barred owl's infection status, parasite richness, and parasite diversity in analyses of Haemoproteus haplotypes, offering strong support for the ERH in the context of this genus of parasite. These findings suggest that barred owls may be released from the costs associated with some, but not all, parasite infections in the Pacific Northwest. Additional analyses of Haemoproteus haplotypes allowed me to detect a phylogeographic pattern in which one haplotype was common in both barred and northern spotted owls throughout North America, three haplotypes appeared to be isolated to the barred owl's historic range, while a fifth haplotype was notably divergent from all of the other detected haplotypes and seemingly isolated to California owls. Furthermore, probability of infection analyses indicated that host population (i.e., western barred or northern spotted) was an important explanatory variable in determining parasite diversity and a bird's infection status. These findings offer some support for the Parasite Spillback Hypothesis, suggesting that barred owls may be contributing to higher parasite prevalence among northern spotted owls by serving as an added reservoir host to northern spotted owl populations. Plasmodium spp. infections were rare among both barred and northern spotted owls, and I found no evidence that the barred owl range expansion has yet impacted the occurrence of Plasmodium spp. within northern spotted owls. Overall, this study demonstrates the complexity of host-parasite relationships and suggests that differences in parasite ecology across genera play an important role in determining whether or not parasites will persevere and be transmitted across invasive and native host populations. In addition, this study has identified a number of blood parasite haplotypes infecting barred and northern spotted owls, yet many questions still remain regarding the true cost of these parasite infections among barred and northern spotted owls and the implications of these infections for northern spotted owl conservation and management.Item Open Access Occupancy dynamics of barred owls on a spotted owl landscape(Colorado State University. Libraries, 2024) McGee, Kaitlin R., author; Doherty, Paul, Jr., advisor; Franklin, Alan B., advisor; Bailey, Larissa, committee member; Hart, Sarah, committee memberInvasive barred owls (Strix varia) pose a significant threat to native northern spotted owls (Strix occidentalis caurina) in western North America. Barred owls compete with northern spotted owls for resources and habitat, leading to displacement and subsequent declines in northern spotted owl populations. This impact highlights the need for conservation efforts to mitigate the negative consequences of barred owl presence in spotted owl habitats. In my thesis, I explored barred owl habitat use in northern California using data on both lethal removals of barred owls and barred owl occupancy of non-removal areas from long-term studies. These studies provided a unique opportunity to study associations of barred owl land use both during initial colonization and over time. Barred owl land use was influenced by landscape factors such as topographic water accumulation, forest age, tree composition, and canopy cover as well as interspecific effects of northern spotted owls. I used these results to predict variation in barred owl use of landscapes, which can then focus barred owl management efforts in California.Item Open Access Out with the old and in with the new? Investigating competition between Barred Owls (Strix varia) and Northern Spotted Owls (Strix occidentalis caurina) in northwestern California with a playback experiment(Colorado State University. Libraries, 2010) Van Lanen, Nicholas J., author; Franklin, Alan B., advisor; Noon, Barry R., committee member; Reiser, Raoul Frederick, II, committee member; Huyvaert, Kathryn P., committee memberThe Northern Spotted Owl (Strix occidentalis caurina) is a controversial species in the Pacific Northwest that is listed as threatened under the Endangered Species Act. The Barred Owl (Strix varia), a species historically restricted to eastern North America, has recently expanded its range to completely overlap that of the Northern Spotted Owl. Recent evidence suggests that Barred Owls may displace Northern Spotted Owls from their territories. The focus of my study was to determine whether Barred Owls have the potential to competitively exclude Northern Spotted Owls from their territories. I used a playback experiment to observe and quantify aggressive vocal and physical behavior of Barred and Northern Spotted Owls during territorial defense. Trials consisted of displaying a Northern Spotted or Barred Owl taxidermy mount, and broadcasting recorded vocalizations of the corresponding species, in both Barred and Northern Spotted Owl territories. The frequency and intensity of residents' responses to playbacks were digitally recorded as was the acceleration experienced by the mount's head during physical attacks by the residents. When agonistic interspecific interactions occurred in this study I found that Barred Owls responded with higher levels of vocal and physical aggression than Northern Spotted Owls. However, the frequency of interspecific interactions was lower compared to intraspecific interactions among Northern Spotted Owls alone. This study suggests that Barred Owls are likely to assume the dominant role during interspecific interactions with Northern Spotted Owls and indicates that competitive exclusion is a plausible mechanism by which Barred Owls could contribute to the observed population declines of Northern Spotted Owls in areas of co-occurrence.