Browsing by Author "Savidge, Julie A., committee member"

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Open Access
Breeding season habitat use of Conservation Reserve Program (CRP) land by lesser prairie-chickens in west central Kansas
(Colorado State University. Libraries, 2004) Fields, Tamara Leigh, author; White Gary, advisor; Leininger, Wayne, committee member; Savidge, Julie A., committee member
Lesser prairie-chicken (Tympanuchus pallidicinctus) populations have drastically declined throughout their range since the 1800's. In Kansas, counts of leks and individual birds indicate that populations have experienced significant declines since 1964. The primary cause of range-wide and statewide declines has been deterioration of suitable habitats. Recently, populations of lesser prairie-chickens have expanded northward and westward in Kansas. The range expansion has been attributed to an increase in CRP (Conservation Reserve Program) lands. This study assessed the importance of CRP and the interseeding of forbs in CRP to lesser prairie-chickens. Invertebrate sampling was conducted in June, July, and August 2001 to determine whether interseeding increased invertebrate biomass and diversity. Sweepnet samples were collected on five grassland CRP fields that were successfully interseeded with alfalfa and sweet clover in alternating strips on 50% of the field. Total invertebrate biomass and diversity were greater on interseeded CRP plots compared to grass CRP plots. There was no evidence of a treatment effect on orthoptera, lepidoptera larvae, hemiptera, hymenoptera, and coleoptera biomass. However, differences in orthoptera biomass between grass and interseeded plots suggest that the majority of the treatment effect on total biomass could be attributed to this order. Greater total invertebrate biomass and count diversity was attributed to the abundance of forbs found within interseeded fields. Seventy-one female lesser and greater prairie-chickens (Tymanuchus cupido) were equipped with transmitters during the 2002 and 2003 breeding seasons to monitor habitat selection and survival. Fields were classified into five habitat types: native rangelands, croplands, grassland CRP (GCRP), interseeded CRP (ICRP), and forb CRP (FCRP). Habitat selection of pre- and post-nesting hens (n = 68), nesting hens (n = 60), and hens with broods (n = 27) was determined by comparing use to habitat availability within the southwest quarter of Gove County. Hens used cropland less than expected and ICRP more than expected. Nesting hens used FCRP, rangeland, and cropland less than expected and GCRP and ICRP more than expected. Greater use of ICRP and GCRP fields was attributed to the abundance of invertebrates and cover provided by ICRP and GCRP, respectively. Lastly, hens with broods used cropland less than expected and demonstrated no habitat selection for any habitat types. The lack of selection by hens with broods is most likely a product of small sample sizes in my study. Lack of selection was also a product of high rangeland brood use and the high availability of this habitat type. Additionally, habitat type was not considered the most important determinant of a brood's location. Instead, broods were frequently located in heterogeneous fields characterized by grassy cover interspersed with an abundance of forbs. A number of nest and brood statistics were computed as an index of reproductive success. Nesting rate was 89. 7%, hatchability was 76.5%, renesting rate was 19.1 %, and mean clutch size was 11.2 eggs. Apparent brood success (~ 1 chick survived) to 14 days was 65.6%, and 53.8% of these broods survived to 60 days. Only 28% of tracked broods survived from hatch to 60 days post-hatch. In addition to complete brood loss, the number of chicks per brood declined from 9.6 (SE= 0.7) at hatch to 5.0 (SE= 3.7) 60 days post-hatch. Mean recruitment at 60 days post-hatch was 0.59 chicks per hen (SE = 0.10), overall chick survival for pre-fledge broods was 0.433 (SE= 0.03), overall chick survival for post-fledge broods was 0.372 (SE = 0.05), and overall chick survival over the entire period was 0.161 (SE= 0.02). Survival rate of hens, nests, and broods were estimated using Program MARK. The known fate data type was used to model weekly survival probabilities of hens as a function of eight time-specific and individual covariates. The same data type was used to evaluate the effects of 13 sources of variation on the daily nest survival probabilities. To model daily brood survival probabilities as a function of 14 sources of variation, the nest survival data type available in Program MARK was used. All candidate models within each survival analysis were ranked based on a small sample Akaike's Information Criteria {Al Cc)- In addition to evaluating the effects of different sources of variation, the best model within each analysis was used to estimate model-conditional survival estimates. The level of model selection uncertainty within the hen survival analysis indicates that none of the models approximated weekly hen survival probabilities well. However, the best model suggested a positive association between survival and weekly precipitation. The probability of a female prairie chicken surviving the breeding season was 0.62 (SE= 0.14) and 0.66 (SE= 0.12) in 2002 and 2003, respectively. Daily survival probabilities of nests were a function of a quadratic time trend, nest age, and temperature. Daily nest survival probabilities declined as the season progressed. Nest age and temperature were also negatively correlated with daily nest survival. The probability of a nest surviving from May 10 to June 1 was 0. 70. Daily brood survival probabilities were a function of a quadratic time trend, brood age, hen age, forb composition and precipitation events. Daily brood survival declined as the season progressed. Brood age and forb composition were positively associated with daily survival, whereas precipitation was negatively correlated with daily survival. Broods tended by adult hens had higher daily survival probabilities than broods of juvenile hens. The probability of a brood surviving from June 1 to July 30 (hatch to 60 days post-hatch) was 0.52 and 0.06 for a brood reared by an adult and juvenile, respectively. The habitat selection analyses indicate that ICRP and GCRP may be beneficial to prairie chickens during the breeding season. Although there was no evidence that hen, nest, and brood survival were a function of habitat, the long-term benefit of CRP was evident. From field observations it was apparent that CRP may be allowing these birds to persist in dry years. In contrast, rangeland may be adequate when drought and the compounding effects of grazing do not decrease cover and food sources.
Open Access
Ecology and plant defense of two invasive plants, Hyoscyamus niger and Verbascum thapsus
(Colorado State University. Libraries, 2016) Fettig, Christa E., author; Hufbauer, Ruth A., advisor; McKay, John K., committee member; Norton, Andrew P., committee member; Savidge, Julie A., committee member
Understanding the factors that drive non-native plant populations to succeed in a new range and the ecological and biological differences that set introduced populations apart from their native counterparts can provide insight into ecological and evolutionary processes, as well as information crucial to management. In this dissertation, I present research on two different plant species that have been introduced to North America, both of which can now be found across the United States and throughout Canada. Chapters 1 and 2 focus on Hyoscyamus niger (black henbane, Solanaceae), a poisonous and state-listed noxious weed. In chapter one I experimentally evaluate whether introduced populations in the western United States are annual or biennial. Both of these life cycles are found in the native range, and have a clear genetic basis. I experimentally manipulated vernalization (a cold treatment for 19 weeks), and find that plants in the introduced range are biennial. Vernalization is critical for bolting and flowering to occur within a growing season. Interestingly, given enough time in a greenhouse setting, 26 percent of plants that were not vernalized were able to flower. This is unlikely to happen in nature, however, as warmer regions without a cold period to naturally vernalize plants are typically lacking sufficient resources (e.g. adequate water or space) for this species. Chapter two aims to understand basic biological and ecological characteristics of black henbane in the introduced range, which lays the groundwork for additional ecological and evolutionary research on this species and will also help direct appropriate management practices. In a greenhouse experiment, I test the effects of selfing and outcrossing. In field populations, I measure reproductive output, the size of seed banks of introduced populations, the viability of seed collected over four years, patterns of mortality, and fluctuation in the size of 15 populations. Black henbane is self-compatible, and capable of producing copious seed, and generating large seed banks in naturalized populations. Seeds remain viable for multiple years which may contribute to the dynamic fluctuations of field population sizes that were observed over four years. Populations are generally ephemeral, with high mortality at the rosette stage. Chapter 3 is focused on resistance and tolerance to herbivory, and how they might vary between ranges as well as within individual plants as predicted by optimal defense theory. Optimal defense predicts that defenses are allocated to different tissues based on their value to the plant. I use Verbascum thapsus (common mullein, Scrophulariaceae) to evaluate resistance to both a specialist and a generalist herbivore among plants from the native and introduced range and among leaves of different ages. I also measure tolerance to defoliation by simulating three levels of herbivory and evaluating the regrowth of above and below ground biomass. Both native and introduced mullein plants are highly defended against specialist and generalist herbivores, with high levels of both resistance and tolerance. In accordance with optimal defense theory, young leaves are more highly defended than older leaves.
Open Access
Home range, site fidelity, reproductive ecology, and den site characteristics of the San Clemente Island fox
(Colorado State University. Libraries, 2012) Resnik, Jessica Ruth, author; Andelt, William F., advisor; Savidge, Julie A., committee member; Stanley, Thomas R., committee member; Theobald, David M., committee member
Since 2004, the endangered status of 4 island fox (Urocyon littoralis) subspecies has prompted increased efforts to understand and manage island foxes on all 6 islands where they occur. High rates of vehicle-related mortalities and potential for exposure to pathogens are of particular concern on San Clemente Island, California. Basic spatial ecology of the San Clemente Island fox (U. l. clementae) is needed for effective management but is currently inferred from home range studies on other island fox populations. Additionally, little is known about reproduction and denning of this subspecies, and island foxes in general. To better inform management strategies, I studied the spatial and reproductive ecology of this subspecies. During 2006-2007, I collected telemetry locations throughout the diel period for a random sample of foxes (n = 29), a sample with home ranges that included roads (n = 18) and a sample with home ranges that excluded roads (n = 19). I also monitored the movements of females in the random sample during 2007 to determine the proportion producing litters, number of kits in weaned litters, chronology of reproduction, and den site characteristics. I found that San Clemente Island foxes had home ranges (mean = 0.75 km2, SE = 0.9) and core areas (mean = 0.19 km2, SE = 0.03) 36-116% larger than reported in published studies for other island fox subspecies. Home ranges were largest during the pup-independence season (mean = 0.76 km2, SE = 0.07), but did not vary between pup-dependence (mean = 0.68 km2, SE = 0.11) and breeding (mean = 0.66 km2, SE = 0.10) seasons. Core area sizes were similar among all seasons. Annual home ranges and core areas for foxes living near roads were 77% and 82% larger compared to non-road foxes. Seasonal home ranges were larger for road foxes than for non-road foxes during the pup-independence and breeding seasons, but were similar in size during the pup-dependence season. Site fidelity between seasons ranged from 18-50%, was greater for home ranges of males than females, and was not different between genders for core areas. I did not detect dispersal during the home range study. Only 3 or 4 of 23 females produced a total of 6 pups. Of 13 females recaptured and examined for reproductive status, most had lactated in previous years (n = 7), or had some evidence of lactating but not weaning pups (n = 4); two females had never lactated. Breeding and parturition occurred two months earlier than reported for other island fox subspecies in wild-born or captive breeding populations since the 1970s. Females used two or three dens in succession and dens were almost exclusively found in rock crevices. Five of 23 foxes had home ranges that included supplemental food sources and human habitation, including all four females observed with pups, suggesting this could be a factor in reproductive success. I recommend caution when generalizing findings from other island fox subspecies and suggest managers establish subspecies-specific information to better inform conservation strategies on the different islands.
Open Access
Reproductive ecology of the island scrub-jay (Aphelocoma insularis)
(Colorado State University. Libraries, 2010) Caldwell, Luke, author; Angeloni, Lisa M., advisor; Sillett, T. Scott, committee member; Savidge, Julie A., committee member
The small population size and limited range of the Island Scrub-Jay make it a species of conservation concern, yet its reproductive ecology is poorly known. From 2008 - 2010 I investigated factors influencing nest success, quantified annual fecundity per pair, and documented breeding behavior. Nest predation was the major factor influencing nest success, accounting for 92 percent of documented nest failures. Nests that were initiated earlier in the breeding season, nests that were higher and more concealed, and nests of breeding pairs that had smaller home ranges had higher daily nest survival. Despite a low estimated daily nest survival rate of 0.945 ± 0.004 SE, the high frequency of renesting allowed pairs to maintain a mean fecundity of 1.13 ± 0.15 SE. Island Scrub-Jays may benefit from an increase in breeding habitat and lower nest predation from the ongoing regeneration of woody vegetation and understory structure following the removal of exotic herbivores on Santa Cruz Island.