Browsing by Subject "life history"
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Item Breeding biology and habitat associations of the Altamira Oriole and Northern Beardless-Tyrannulet in the Lower Rio Grande Valley, Texas(Texas A&M University, 2004-11-15) Werner, Scott MichaelI studied the breeding biology and nesting ecology of the Altamira Oriole (Icterus gularis) and Northern Beardless-Tyrannulet (Camptostoma imberbe), two songbirds inhabiting remnant tracts of Tamaulipan brushland of the Lower Rio Grande Valley, Texas during 2002-2003. I found 76 active oriole nests, 7 of which were reused for second broods, for a total of 83 nesting attempts. I estimated that nearly 20% of the oriole breeding population were subadult, or second-year orioles, which is extremely rare for this species. Oriole breeding pairs were found in high densities and may be at their highest level at the study sites since the 1970s. Fifty-nine percent of oriole nests fledged, and 37% failed. Six nests produced Bronzed Cowbird (Molothrus aeneus) fledglings. Vegetation analysis suggests that orioles prefer the tallest trees at the sites in which to place their nests. A greater number of fallen logs near the nest was also a predictor of nest sites, which suggests that orioles prefer scattered woodlands, but also that many of the forests probably continue to shift to a more open, thorn-scrub climax stage. I monitored 28 Northern Beardless-Tyrannulet nests, which were restricted to a smaller number of study tracts than Altamira Orioles. Historical records are lacking for Northern Beardless-Tyrannulets at these sites, but my surveys indicated that there were similar seasonal numbers of tyrannulets at some of the study sites as there were during 1996-1998. Forty-three percent of nests were successful and 57% failed. Higher abundances of epiphytic Spanish moss (Bromeliaceae: Tillandsia usneoides) and ball moss (Bromeliaceae: Tillandsia recurvata) were the most important predictors of nest sites. The continued existence of these two species in South Texas will depend upon the preservation of tall forests, and in the case of the tyrannulet, forests rich in Tillandsia epiphytes.Item Microplitis croceipes (Hymenoptera: Braconidae): A Life History Study and in vitro Rearing(2012-10-19) McLoud, Laura AnnMicroplitis croceipes (Hymenoptera: Braconidae) is an endoparasitoid and potential biological control agent of the tobacco budworm, Heliothis virescens (Lepidoptera: Noctuidae), an agricultural pest. The first objective of the following research was to amend current larval life history descriptions of M. croceipes. Larval head capsule width measurements were used to distinguish instar, and exuvium in abdominal cavities of post-egression hosts were indicative of a molt during parasitoid egression. Data revealed the larvae of M. croceipes pass through five instars, rather than three, as is indicated in the literature. The second objective was to investigate the suitability of potential artificial diets to be used in in vitro rearing of M. croceipes larvae. Three concentrations each of glucose, trehalose, and protein, as well as a combination diet (derived from initial diet trials) were tested. Growth, molting, and death were noted for each diet, and data indicated that diet had a significant effect for each performance measure (p = 0.0000, p < 0.0001, p < 0.0001, respectively). Data also indicated that trehalose and protein were more vital to larval parasitoid development (growth and molting) than was glucose, but no larvae were reared passed the second instar on an artificial diet. The final goals of the research were to evaluate the plausibility of rearing M. croceipes larvae to adulthood in vitro and to investigate post-egression host defensive behavior. Larvae were dissected from their hosts just prior to egression and placed in a cell culture plate in previously collected host hemolymph. Larvae were able to initiate pre-egression behavior in an in vitro environment, and a small percentage (6.67%) exhibited ecdysial splitting of the cuticle, however, no larvae were able to make the final molt in vitro. Post-egression hosts exhibited defensive behavior that may suggest they play a role in protecting pupating parasitoids. When the parasitoid exuvium was pulled from the egression wound in the host, hemolymph loss occurred and duration of the defensive behavior significantly decreased (p < 0.0001), indicating the exuvium acted to plug the egression wound, which prevented the host from bleeding to death and made it possible for the host to exhibit defensive behavior.Item Mycorrhizal Associations, Life History, and Habitat Characteristics of the Endangered Terrestrial Orchid Spiranthes parksii Correll and Sympatric Congener Spiranthes cernua: Implications for Conservation(2013-12-10) Ariza, Martha CSpiranthes parksii Correll is a federally listed endangered terrestrial orchid endemic of Texas. The species exhibit a very limited geographic distribution and most remaining populations are threatened by habitat loss and fragmentation. Development of in situ and ex situ conservation strategies is fundamental for the protection and re-introduction of the species in their natural habitat. In this dissertation the life history, symbiotic mycorrhizal fungal associations, and habitat characteristics of S. parksii and sympatric congener Spiranthes cernua were investigated by the use of in situ, and ex situ methods. The central research objective was to investigate the orchid-fungal relationship and its distribution in natural habitats and to provide critical information for conservation of the species. Population dynamics and reproductive phenology of both species were studied from 2007 to 2013. Demographic parameters, cost of reproduction, and response to environmental conditions were analyzed. Results indicate that probability of flowering is strongly influenced by vegetative size and environmental conditions in the year preceding a flowering event. Reproductive effort resulted in a decrease in plant size, reducing the probability of flowering subsequently. Environmental conditions explained ?70% of the annual variation in the proportion of flowering plants and inflorescence characteristics. Mycorrhizal fungi associations and belowground phenology of both species were studied for three growing seasons. Data suggest that both species form generalist mycorrhizal associations with fungi tentatively classified, as Epulorrhiza sp., and Ceratobasidium sp. Both orchids sustain mycorrhizal colonization throughout their life cycle. However, seasonal changes in mycorrhization reveled a distinctive annual cycle of infection and digestion of fungal hyphae. Seed viability, in situ germination, seedling development, and mycorrhization were examined in situ by using orchid seed baits. Results suggest that S. parksii seeds are short-lived and germination is constrained by rapid reduction in seed viability, prevailing environmental conditions, and distribution of compatible mycorrhizal fungi. Data indicates a small optimal window for recruitment restricted to the first spring after dispersal. Microhabitat characteristics of S. parksii were compared to microsites of sympatric S. cernua, historical S. parksii microsites and vacant microsites currently not supporting either orchid. Vegetation, edaphic, and environmental parameters were evaluated. The study found that microsites currently occupied by S. parksii differ significantly from other types in canopy cover, leaf litter, herbaceous cover, and soil pH. Furthermore, woody encroachment may significantly affect the availability of suitable microsites not only as a result of altered light environments, but also due to changes in community composition, microclimatic, and edaphic conditions.