Browsing by Subject "invertebrates"
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Item Aquatic macrophyte and animal communities in a recently restored brackish marsh: possible influences of restoration design and the invasive plant species Myriophyllum spicatum(2012-07-16) Bell, Michael ThomasThe numerous benefits that wetlands provide make them essential to ecosystem services and ecological functions. Historically, wetland losses have been caused by natural and anthropogenic changes. In Texas, nearly 50% of coastal wetland habitat has been lost since the 1930s and losses in the Lower Neches watershed have been some of the most extensive. Restoration is a way to mitigate these losses and can be accomplished in many ways. Each restoration design creates different aquatic habitats that can influence both submerged aquatic vegetation (SAV) and faunal communities. The restoration of the Lower Neches Wildlife Management Area (LNWMA) has created the conditions for the growth of the invasive submerged macrophyte, Myriophyllum spicatum (Eurasian watermilfoil) which may be competing with the native aquatic grass, Ruppia maritima (widgeongrass) for essential nutrients. In this study, an attempt was made to link restoration design with both SAV and aquatic fauna community structures by using a throw trap to characterize assemblages observed in three different types of restored marshes. We also performed two controlled mesocosm experiments in 0.5 gal aquariums to determine growth inhibition by M. spicatum on R. maritima. Analyses using Kruskal-Wallis non-parametric test determined that temporal variations in fauna and SAV community composition was greater than any restoration effect. Discriminant Function Analyses (DFAs) determined two to three key faunal species that best predicted association among restoration designs, but linear regressions could not determine any consistent relationship between individual species density and biomass of the dominant SAV species, M. spicatum. For the mesocosm experiments, M. spicatum inhibited the biomass production and branch count of R. maritima when the two species are grown together (ANOVA, p = 0.004 and 0.003, respectively). Changes in SAV assemblages due to competition and habitat characteristics could play a major role in determining faunal community. In order to minimize the temporal effect observed and better determine any habitat pattern that may be present, a much longer study is necessary.Item Associations of watershed and instream environmental factors with aquatic macrofauna in tributaries of the Pedernales River, Texas(Texas A&M University, 2005-08-29) Birnbaum, Jenny SueIntermittent headwater streams serve important functions in semi-arid rangelands, both for humans and wildlife. However, few studies have assessed species-environment relationships for fish and benthic macroinvertebrate assemblages in these systems. Additionally, no published studies could be found that addressed the influence of juniper coverage in watersheds on assemblage structure of these taxa. Increased juniper coverage in recent decades is believed to be associated with decreased water yields in central Texas streams. During summer 2003 and spring 2004, I examined potential effects of juniper cover on aquatic ecology. Fishes, benthic macroinvertebrates, and the physicochemical habitat were investigated in spring-fed headwater tributaries of the Pedernales River. My objectives were to: 1) describe the typical fish and benthic macroinvertebrate assemblages in headwater creeks of the Pedernales River basin; 2) compare seasonal variability of fish and benthic macroinvertebrate assemblages; 3) identify species-environment relationships in this river basin; and 4) evaluate the influence of juniper coverage in the watershed, relative tolocal and landscape-level environmental factors, on the structure of fish and benthic macroinvertebrate assemblages. A total of 4,181 individual fish were collected in summer 2003 samples, 551 fish were collected in spring 2004, 59,555 macroinvertebrates were captured in summer 2003 samples, and 51,500 macroinvertebrates were collected in spring 2004. Assemblages were typical for the area and habitat conditions. Faunal richness was lower in spring than in summer, possibly due to a combination of sampling after a relatively dry period in the spring, and lack of winter refugia in the form of deep pools. Fish assemblages may structure based principally on abiotic factors in spring, the harsher season (less available water), whereas predation pressure may influence structure in summer. Another important environmental gradient for both fish and invertebrate assemblages contrasts pool and run mesohabitats. In general, juniper cover was weakly associated with fish and invertebrate assemblages, although it tended to be associated with relatively high quality habitat for sensitive taxa (flowing runs with coarse substrate; deep, connected pools). In these intermittent streams, local-scale environmental factors probably are the dominant influences on fish and benthic macroinvertebrate assemblages. Implications for future studies are discussed.Item Influences of vegetation characteristics and invertebrate abundance of Rio Grande wild turkey populations, Edwards Plateau, Texas(Texas A&M University, 2005-02-17) Randel, Charles JackSince 1970, Rio Grande wild turkey (Meleagris gallapavo intermedia) numbers in the southern region of the Edwards Plateau of Texas have been declining. Nest-site characteristics and invertebrate abundance were hypothesized as limiting wild turkey numbers in declining regions. Wild turkeys were trapped and fitted with mortality-sensitive radio transmitters on 4 study areas; 2 within a region of stable (northern Edwards Plateau) populations, and 2 within a region of declining populations. Monitoring occurred from February 2001 to August 2003. Nest-site locations were determined via homing during the breeding season. Following nesting attempts/completions, nest fate, vegetation height, visual obstruction, litter depth, percent cover, and cover scores of forbs, grass, litter, and bare ground at each nest site and surrounding area were sampled. This was done to determine if wild turkey hens selected nest sites with vegetative characteristics differing from surrounding habitat. Brood survival was calculated as >1 poult surviving to 2-weeks. Broods were followed for 6-weeks post-hatch or to brood failure. Invertebrates were collected, via sweep-net and D-vac, at each visually confirmed brood location and a paired random site to determine if wild turkey hens selected brood habitat based on invertebrate abundance. Analyses were performed to determine if invertebrate abundance differed between study regions. Turkey hens selected nest sites with greater visual obstruction and more litter depth on both regions of stable and declining turkey abundance. No vegetative differences were detected between stable and declining region nest sites. Frequency of Orthoptera was 3?5 times greater at nest sites on stable regions than declining regions in all 3 years. Orthoptera is a noted food source for young galliformes and comprised the majority of dry mass in invertebrate samples, nest sites and brood locations, on both the stable and declining regions. No differences in total invertebrate dry mass were detected between regional brood locations. Nest-site vegetative characteristics did not alter nest success between regions. The 2 overall objectives of this study were to determine if nest-site vegetation characteristics and invertebrate abundance affected wild turkey numbers in the Edwards Plateau. Regional differences in vegetative characteristics were not detected, thus not likely to be causing differences in turkey numbers between regions. Nest-site invertebrates were found to be 3?5 times greater at stable region nest sites, possibly giving wild turkey poults from stable regions greater initial chances of survival.