Invasive woody shrubs are a problem when they displace native species and threaten habitats, especially those that harbor rare or endangered species. They not only compete with native plants, but also alter habitat and food that many organisms depend upon. Invasive plants undergo a release from their specialist predators in the nonnative range, providing them advantages over native species. Because modes and pathways of how invasive species spread are not fully understood, predicting spread and implementing restoration ecological controls remain inexact. Due to the lack of comparative studies on woody shrubs, especially invasive privets, we understand very little about conditions affecting their invasiveness. A study was conducted near Dallas, Texas to determine if privet has allelopathic properties that influences growth of native plants. Soil nutrients and other analyses were made and compared between field plots supporting privet, plots in which privet has been removed, and plots where privet has not been observed. In some field plots, natives were planted under the three previously mentioned conditions, and their survival and condition were monitored to evaluate effects of privet on their establishment and growth. It was found that Chinese privet did hinder seed germination in red mulberry, soapberry and beautyberry and root formation in beautyberry cuttings. The soil in the sites were found to be normal for bottomland forests that endured two flooding events within one year.

I examine three aspects forest vegetation of northern Florida: the Land Office Survey records of the abundance and distribution of woody species across northern Florida in the early nineteenth century; the abundance and distribution of woody species across a sharp elevation gradient in the hardwood slope forests along the Apalachicola River; and the population decline of Torreya taxifolia. / Land Office Survey data was tabulated for all available bearing trees north of Gainesville. This study includes 131,227 trees sampled at 49,896 section corners and mid-point lines. This data tabulation shows that northern Florida was dominated by pines prior to U.S. settlement. Over 77 percent of bearing trees were pines. Pineland oaks are the next most abundant species after pine. Wetlands trees, such as bay, gum, and cypress were dominant species in the absence of pine. The mixed hardwood species are a diverse group, including beech, magnolia, and dogwood, with no clear dominant among them. / The second portion of this research examines the spatial relationships among the species of the hardwood slope forests along the Apalachicola River. Species distributions were sampled using 80 belt transects in four ravine systems. Species turnover across elevation is high, but measures of species diversity and forest structure do not change with elevation. Distribution patterns of the major species indicate that assemblages in the adjacent elevation samples in the middle and upper slope positions are more similar to one another than are assemblages from the lower elevations. The assemblages do not, however, appear to form sub-communities with respect to elevation. / Finally, I examine hypotheses for the decline of Torreya taxifolia, a narrowly endemic conifer native to ravines along the Apalachicola River. Included in this analysis of the torreya decline is a demographic summary of 108 torreya on preserve land. Most individual torreya are multiple stemmed and less than 14 years old. Further, these individuals are most frequently grown at low elevations and under moderate to dense canopy shade. Among the many hypotheses proposed to explain the decline, I present evidence that fire suppression may have allowed fungal populations to soar, contributing to the onset of disease. / Source: Dissertation Abstracts International, Volume: 51-12, Section: B, page: 5692. / Major Professor: Joseph Travis. / Thesis (Ph.D.)--The Florida State University, 1990.

The plants and sediments of two shallow, sub-tropical lakes in north Florida (Lake Jackson and Lake Hall located in Leon County) were sampled, identified, and analyzed for PAH content at 16 different stations quarterly. Stations were chosen so that areas affected by stormwater and relatively pristine areas were surveyed. Sediments from areas that received stormwater runoff were found to have elevated PAH concentrations, while stations distant were characterized by lower PAH concentrations. / The PAH content of rooted vegetation was found to have a significant relationship with the concentrations of PAHs in the sediments upon which they grew. There was no relationship between the PAH concentrations in non-rooted plants and the sediments where they were found. Plant growth and PAH assimilation experiments were performed on sixty-six plants that included indigenous rosette monocots and vittate dicots which were planted in sediments spiked with varying concentrations of PAHs. These sediments were completely segregated from the water column which was verified by analysis. / It was conclusively shown that the sediment PAHs exerted a deleterious effect on the growth of the subject aquatic macrophytes, and that the PAHs from the sediment entered the plants through their root systems. These experiments showed that the roots of aquatic plants will reach a PAH concentration almost nine times higher than the PAH concentrations of their shoots. There was a difference in the types of PAHs which were accumulated by the plants: the most readily accumulated PAHs were the most water soluble. The evidence indicates that partitioning occurs from the aqueous phase. / There were species-specific differences in the degree of accumulation of sediment PAHs. Saturation phenomena for PAH bioconcentration were observed. A model was developed that incorporated equilibrium constants, constants for adsorption and desorption, and saturation levels of PAHs for aquatic plants. The field data, the microcosm experiments and the model all lead to the conclusion that aquatic macrophytes accumulate sediment PAHs acropetally and transport them to their shoots. / Source: Dissertation Abstracts International, Volume: 56-12, Section: B, page: 6491. / Major Professor: Robert J. Livingston. / Thesis (Ph.D.)--The Florida State University, 1995.

Climate change and the accompanying increase in global surface temperatures pose a major threat to freshwater ecosystems, especially at high latitudes where warming is predicted to be particularly rapid. To date many aspects of how rising temperatures can impact fresh waters remain unknown. Information about temperature effects on the level of communities, food webs, ecosystems is especially scarce. The few studies focusing on higher levels of organisation have used either laboratory microcosm experiments, which can lack realism or space-for-time substitution across large ranges of latitude, which can be confounded by bio-geographical effects. This study aimed to overcome these shortcomings by using a “natural experiment” in a set of 16 geothermally heated streams in the Hengill area, South-West Iceland, with water temperatures ranging from 4ºC to 49ºC (mean temperature). Data were analysed for two seasons, August 2008 and April 2009. The principal goal of this study was to assess the effects of temperature on the structure and functioning of food webs. Additionally the persistence of the community structures along the temperature gradient was examined through time (comparison of previously collected data in August 2004 and August 2008). Abundances of cold-stenotherm species decreased whereas those of eurythermal species increased with increasing temperatures leading to knock-on effects on abundances of other species. Species community overlap between streams declined as temperature difference between streams increased. The persistence of species composition through time was weakened at the extremes of the temperature gradient. Food webs showed a clear size structuring in analyses of trivariate food webs, abundance and biomass size spectra. Analysis of connectance, complexity, mean link length, mean 2-span, mean community span and slopes and intercepts of linear regressions fitted to the trivariate foods or size spectra revealed the impact of temperature change on freshwater ecosystems.

Climate change can have potentially catastrophic effects upon biodiversity and food web structure and according to the fourth IPCC report, ambient temperatures will rise by between 3.0-5.0 °C over the next century, with already an average increase in global surface temperature of ~0.74°C in the past 100 years. This has known implications in ecology from individuals to ecosystems. The microbial loop consists of small organisms ranging in body size from bacteria (1-15 μm), single-celled eukaryotes (10-1000 μm) and multicellular organisms (250 – 1000 μm) that assimilate dissolved organic carbon into the “classical food web”. ! The principal goal of this thesis was to assess how rising global temperatures might impact the natural microbial assemblages in 20 mesocosms under 2 treatments – 10 warmed (in line with IPCC predictions) and 10 ambient. The abundance and body mass of 4 major microbial loop taxa (desmids, flagellates, heterotrophic protists and meiofauna) were quantified at monthly intervals over a 2-year period. Secondly, in a microcosm experiment, the population dynamics of three pure cultures of ciliates were monitored across a temperature gradient; the rate of population decline under starvation and changes in body size were quantified.! Results showed that (1) rising global temperatures alters the size spectrum in the autotrophic protists, (2) temperature interacts with temporal and spatial gradients, resulting in changes in phenology (3) these changes in phenology are observable at both the community level and the population level within the microbial assemblage of the mesocosms and (4) extinction rates and body mass reduction in experimental microcosms were faster at warmer temperatures and partially support predictions of the metabolic theory of ecology.! The implications of these findings are discussed in terms of (1) continued research into the role that small organisms play in community and ecosystem ecologyand (2) the use of these small organisms in experiments as models to inform ecological theory by scaling up from microcosms and finally, (3) I discuss future directions in freshwater microbial ecology, focusing on the increased use of molecular techniques.

The goal of this dissertation was to investigate some of the factors that determine species diversity across trophic levels at both broad and local scales. The taxa used to address these questions were grass and forb dwelling arthropods, mainly insects, found at experimental sites. The overriding question guiding this research is; what are the processes that determine arthropod diversity at local and regional scales? At local scales, I investigated trophic level diversity using correlational studies, measuring the natural variation in two grassland ecosystems. Results from this study support hypotheses from other empirical studies demonstrating that changes in diversity of a single trophic level can cascade to effect diversity at other, nonadjacent trophic levels. These studies were supplemented with a long-term manipulative experiment using the same ecosystems, in which I manipulated plant resources and higher trophic levels. After three years, and one year after the last experimental manipulations were applied, the plant resources manipulation (addition of fertilizers) tripled the average number of herbivore individuals and decreased herbivore diversity. Also at the local scale of diversity interactions, I conducted additional experiments measuring trophic level diversity, using the forage crop alfalfa (Medicago sativa ) and the associated arthropods as a model system. In this study I again manipulated plant resources and higher trophic levels and found significant positive associations between plant resources, plant defense, and herbivore diversity. Additionally, predator diversity and abundance were consistently associated with higher levels of herbivore diversity. This corroborates previous studies in these agricultural ecosystems demonstrating complex indirect trophic level interactions To examine larger scale patterns of diversity, I investigated regional and latitudinal gradients in arthropod abundance and diversity. Regionally, I conducted a study using alfalfa agroecosystems again and investigated the effects of climatic variation on the diversity of arthropod trophic groups across a large geographical area, from Colorado to Southern Arizona. I found that parasitoids were most susceptible to variations in climate, while herbivores and other enemies were more resilient to local climate, also in agreement with other studies demonstrating the differential susceptibility of natural enemies to climatic variation Finally, I investigated arthropod diversity along a latitudinal gradient from northern Colorado (N 40°30') to Ecuador (S 0°42'), using identical methods along the gradient and controlling some aspects of the type of community sampled (open fields versus forest edges). Arthropod species richness increased from the temperate latitudes to tropical regions, this however was not reflected in arthropod family richness or abundance. In addition, I found that controlling for community type across latitudinal gradients explained little of the variation in arthropod diversity. These results suggest that abiotic diversity-promoting mechanisms have a stronger influence on arthropod diversity than do biotic differences between community types. Results from the combined research that comprised my dissertation are the most thorough demonstration of 'diversity cascades' (indirect effects of biotic interactions on biodiversity) demonstrated to date. This is relevant to understanding a major global challenge: loss of biodiversity. Similarly, the consistent effect of plant resources on plant and animal abundance and diversity is relevant to the ubiquitous anthropogenic input of elements such as nitrogen and phosphorus. The results here are consistent with the hypothesis that as overall diversity increases, natural enemies have stronger effects on biotic communities, while less diverse communities are dominated by the effects of plant resource. (Abstract shortened by UMI.) / acase@tulane.edu

A thirteen month field study of the indigenous oyster populations in Lake Borgne, Louisiana was conducted to determine the suitability and potential of Lake Borgne as an area of commercial oyster production. Oyster cages were placed at four stations across the lake and were monitored on site each month. These cages were designed such that spat set, growth, nonpredator and predator mortality were all determined from each cage. Growth in length, width, depth and mortality were compared among seed, sub-market and market size oysters. Additionally, standard oyster dredge samples were taken at each site to compare traditional dredge data regarding spat set, growth and mortality with more reliable cage data. To characterize each sampling station and correlate oyster productivity with specific environmental conditions, the following physicochemical parameters were monitored monthly at each station: salinity; conductivity; temperature; pH; dissolved oxygen; biological oxygen demand; turbidity; precipitation The comparison among the three dimensions of oyster growth revealed that length is most reflective of an oyster's environment and can be best used when evaluating a habitat's suitability for oyster growth. In Lake Borgne, growth was slightly greater at stations 2 and 3, but was surprisingly similar among the stations and sizes, approximately 19 mm/year. When coupled with spat measurements pointing to a first year growth of approximately 42 mm/year, this indicates that market size oysters are attainable in 2-$2{1\over2}$ years, with best growth in the early to mid-summer. Mortality was highest at station four. However, indications are that this is largely due to lack of bed maintenance. Throughout the lake, the annual mortality rate was 34% and primarily the result of predatory crabs and fish in the late summer and early fall, as well as low salinities and temperatures in the winter. Spat set was most successful at station two in the early summer and early fall, with an annual rate of 164%. Yet this is attributable, to a large extent, to the higher population density in this area. It is very probable that increased planting of oysters in other areas could result in a lake-wide set close to that at station two. The only criterion in the cage study that was accurately reflected in the dredge study was spat set / acase@tulane.edu

Forest fragmentation causes diverse changes to natural communities. Changes in spider communities' species diversity provide tools to understand the effects of area and isolation in a fragmented landscape. Bottomland Hardwood forest provides an excellent opportunity to study fragmentation because it has undergone profound loss and subdivision The present study was carried out in 11 fragments of three size classes, the small ranging from 2.7 to 91 ha, medium from 1,042 to 5,294 ha, and large from 32,348 to more than 460,000 ha. The forest remnants were located inside and around New Orleans, Louisiana. A rapid assessment methodology was used to measure the biological diversity of spiders in the fragments. A total of 3,538 adult female spiders in 127 morphospecies were collected in 274 sampling units. The expected number of species for Bottomland Harwood forest was calculated between 161 and 210 species using EstimateS software. Evaluation of the effects of Bottomland Forest fragmentation on the spider community demonstrated significant negative consequences of area reduction on spider species diversity. Not only did species richness decrease, but also species composition changed with decreased fragment size. Species composition was influenced by both population extirpations in small fragments and by the presence of spider species adapted to open areas moving inside a small forest remnant. Spider species composition inside small sized fragments differed from the species observed both in medium and large sized fragments Functional (guild) community relationships were also distorted by fragmentation. The dominance of some species of spiders was more pronounced in small and medium sized fragments. For example, large-bodied, orb-weaving spiders tended to decrease from, and small theridiids increased proportionately in the small fragments. Size of prey was also affected significantly for hymenopterans, dipterans, and homopterans, suggesting more complex effects of forest fragmentation. Another observation from the present study was the strong effect of the surrounding matrix on the diversity of species, exemplified by the unusually high diversity of a fragment surrounded by agricultural activities in comparison to others engulfed by urban development This study supported the advantages of using rapid assessment techniques in the evaluation of biological diversity and for the first time this technique was used in fragmented habitats. The use of non-parametric analysis to predict species richness provided consistent results for medium and large sized fragments and more variable results in the small ones as a consequence of the elevated proportion of singletons observed there / acase@tulane.edu

Agrostis species have been known to rapidly evolve ecotypes in response to geographically localized variations in soil chemistry. Two Agrostis taxa occur in the geothermal habitats of Yellowstone National Park: Agrostis rossiae is endemic to Yellowstone, and Agrostis scabra occurs both in the thermal areas and in a variety of non-thermal habitats. I noticed that every thermal population of Agrostis is surrounded by a non-thermal population of A. scabra that is reproductively isolated from the thermal area by its later flowering time. This suggested that ecotype evolution had happened twice, producing thermal A. scabra and A. rossiae in separate events. I used randomly amplified polymorphic DNA (RAPD) markers to resolve the historical relationships among the Yellowstone thermal populations, the non-thermal A. scabra populations, seven other non-thermal Agrostis species that occur in Wyoming, and thermal Agrostis populations in California and Kamchatka. Contrary to my original hypothesis, I found that none of the populations of the thermal taxa are ecotypes of non-thermal Agrostis scabra, but instead constitute a single, previously unrecognized endemic taxon that currently has four names. A UPGMA phenogram showed that while the thermal populations form geographically distinct subclusters, populations of the two morphologically distinct thermal taxa (A. rossiae and thermal A. scabra) do not cluster independently. Even though currently confused with the thermal populations, non-thermal A. scabra does not appear to be closely related. I used a series of field and laboratory experiments, as well as extensive field monitoring, to show that there are no important ecological differences between A. rossiae and thermal A. scabra. The ecological factor primarily responsible for the geographic separation of the thermal and non-thermal populations is the seasonal fluctuation of soil temperature relative to the life cycle of the plants. Lethal summer soil temperatures in the thermal areas are selecting for precocious flowering and an annual habit, which excludes the more slowly maturing non-thermal plants. The thermal plants, in contrast, do not grow in the non-thermal matrix in prevailing cool field temperatures, but do grow in these habitats under artificially elevated temperatures. The thermal taxa may have reduced competitive ability at cooler temperatures / acase@tulane.edu

A freshwater clam, Nephronaias tempisquensis, was studied in its seasonal tropical environment. This particular research was conducted because many studies of unionids from temperate waters have been conducted, but little is known of unionids from tropical waters. In mussels from temperate regions, initiation of reproductive activity, the age of sexual maturity, and seasonal activities vary among species. Nephronaias tempisquensis is an endemic clam of the tropical Tempisque River drainage basin. Its reproductive activities, population fluctuations and some of the possible environmental factors affecting its distribution are analyzed Sample collection was conducted over a period of 26 months, in three phases. The first phase of the study was begun in 1976 with monthly collections of mussels in different parts of the Rio Tempisque; individual size and distribution of the population were studied The second phase of the sampling was conducted during a period of 18 months (1979-1981); clams were collected at random from Rio Tempisque, Rio Canas, and occasionally from Rio Tempisquito and Rio Salto. Analysis in vivo of the clams and host-glochidia relationships were recorded The third phase of the study was conducted in the hope of finding the clams' natural feeding habits. Clams from Rio Tempisque, Rio Tempisquito and Rio Canas were collected and examined In all phases, external factors that probably strongly influenced the clams under study were also considered: pH, nature of the substratum, water and air temperatures, light periods and predators Among the environmental parameters that were considered for this study, rainfall is the most important factor that affects the populations of Nephronaias tempisquensis Reproductive activity is related to the most favorable environmental conditions, the beginning of the summer, and during the 'little summer'. However, reproductive activity in Nephronaias tempisquensis is continuous, but increases twice a year; from November through December and January, and from June through August Sexual dimorphism of the shells of N. tempisquensis is present, though very difficult to determine without histological studies. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI / acase@tulane.edu