Browsing by Subject "Snails"
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Item Effects of treefall gaps on a tropical land snail community(Texas Tech University, 1991-05) Alvarez, JavierLand snails were collected from quadrats positioned outside and inside treefall gaps in the Tabonuco Forest of Puerto Rico to determine the effects of treefall gaps on the species abundance, richness, evenness, diversity, and distribution of land snails during the dry and wet seasons. This study also determined the importance of atmospheric and litter temperature, relative humidity, litter and soil moisture, slope, and substrate type in determining the spatial distribution of the land snails. Only two species, H. tridens and £.. caracolla. respond to patches created by treefalls. In particular, the abundance of R. tridens was higher in gaps, whereas that of £.. caracolla was higher in the surrounding undisturbed forest. Such differences in habitat use by ti- tridens and £.. caracolla may be attributed to differences in diet and body water loss rates. However, patchiness does not have a pervasive influence at the community level. In general, treefall gaps have little effect on the richness, evenness, diversity, and distribution of land snails of the Tabonuco Forest.Item Habitat associations and abundance estimates of native and exotic freshwater snails in a West Texas Spring(2012-05) Bradstreet, Jeff; Rogowski, David L.; Taylor, Christopher M.; Salice, Christopher J.Isolated springs in West Texas are fragile systems often with high levels of endemism. The two biggest threats to these systems are habitat loss and invasion by nonnative species. San Solomon Springs, located in Balmorhea State Park, is a refuge for native and endangered aquatic species. Two native snail species, which are candidates for federal listing, the Phantom Cave Snail (Pyrgulopsis texana) and the Phantom Spring tryonia (Tryonia cheatumi), have a very limited distribution and rely on the springs at Balmorhea. Two exotic snails have established populations in San Solomon Springs, the red rim melania (Melanoides tuberculata) and the quilted melania (Tarebia granifera). Snails are important components of freshwater systems and understanding habitat usage is necessary for recognizing community patterns and improving conservation efforts of native species. We conducted a field study looking at habitat associations of the two native and two exotic snails at San Solomon Springs from May 2010 to May 2011. Our goals were to (1) measure habitat parameters, (2) measure snail density, and (3) determine the habitat associations among the four snail species. We also conducted a lab experiment to confirm our findings in the field study. We found that P. texana was associated with harder substrate, higher temperatures, and faster water velocity. M. tuberculata and T. granifera were both associated with deeper water and softer substrate. Habitat parameters did not account for much of the variation in T. cheatumi density. Data from this study will serve as a baseline for future studies.Item Patterns of abundance, species richness, habitat use and morphology in tropical terrestrial molluscs: effects of disturbance and elevation(Texas Tech University, 1997-08) Alvarez, JavierSpatial variation resulting from natural disturbances and elevational gradients is of particular importance to the distribution and abundance of organisms that are sessile or of low vagility. This study examined the influence of disturbance, in the form of canopy openness, and elevation on the terrestrial mollusc fauna of the Luquillo Experimental Forest (LEF) of Puerto Rico. Of 14 species of terrestrial molluscs collected in the LEF, only Polvdontes acutanqula and Platvsuccinea portoricensis responded to canopy openness. Moreover, significant responses to canopy openness did not diminish with increasing elevation. This limited response to canopy openness by particular species was reflected in the absence of significant differences in species richness between categories of canopy openness. Nonetheless, significant differences in abundance associated with elevation were detected in all but one species, Alcadia striata. Regardless of elevation, densities of all species of land molluscs, except for Gaeotis niqrolineata were higher in the wet than in the dry season. Mean species richness also increased significantly from the dry to the wet season, peaking at an elevation of 400 m in both seasons. The elevational pattern in species richness of land molluscs appears to be related to changes in temperature. Mean elevational range size increased with elevation. Land molluscs in the LEF, particulahy G. niqrolineata. exhibited a strong affinity for the palm, Prestoea montana. Seasonal and elevational differences in substrate associations of land molluscs also were detected. Finally, the relationship between body size and elevation differed among species of land molluscs. Of those with ranges spanning the entire elevational radient (200 m to 1000 m), most showed a positive relationship between body size and elevation.Item The impact of Hurricane Hugo on two common tree snails in the Luquillo Experimental Forest of Puerto Rico: a long-term study(Texas Tech University, 1995-08) Secrest, Michele F.The role of disturbance in structuring communities is widely recognized in ecology (Dayton, 1971; Pickett and White, 1985; Piatt and Strong, 1989; Sousa, 1984; Waide and Lugo, 1992; White, 1979). Disturbance may be narrowly or broadly defined, depending on the system of interest and focal organism. Moreover, the impact of a disturbance may range from altering habitat structure, resources, and microclimate, to disrupting biological interactions and lowering species densities (Browkaw, 1985; Denslow, 1985). Depending on the severity, intensity, frequency, and magnitude of a disturbance event, complete recovery from the event may take days or years (Waide and Lugo, 1992). Many processes require sufficient time to recover from such events. Thus, the spatial and temporal aspects of a disturbance event are crucial to understanding their long-term effects on organisms and communities. Long-term ecological research is essential when studying slow processes, rare events, processes with high annual variability, subtle processes, or complex phenomena (Franklin, 1989). All of these processes require more than one or two seasons to be detected or evaluated. Moreover, several years of data collection may be required to distinguish such processes from natural background variation within the system of interest Hurricanes are high intensity, infrequent events that necessitate long-term ecological studies. The immediate impact of hurricanes on organisms (Gannon and Willig, 1994; Waide, 1991a, b; Willig and Camilo, 1991) and the environment (Basnet et al., 1992; Boose et al, 1994; Lodge and McDowell, 1991; Lugo et al, 1983; Reilly, 1991; Wadsworth and Englerth, 1959; Walker, 1991; Zimmerman et al., 1994) have received considerable study; however, the ramifications of such an event extend well beyond the event and have yet to be addressed from a long-term perspective.