<p> In Louisiana, human actions, such as levee construction for flood protection, have disrupted the connectivity between many rivers and their surrounding wetlands, leading to marsh degradation and land loss. River sediment diversions from the Mississippi River into adjacent wetlands are currently proposed as a large-scale wetland restoration technique. The reintroduction of sediment-rich waters into adjacent wetlands will also come with altered hydrology and nutrient loads. Despite hydrology and nutrient loading being central to many previous studies, many uncertainties remain regarding the marsh response to this type of large-scale environmental alteration. </p><p> To better understand the effect of river sediment diversion related increases in nutrient supply and altered hydrology on tidal freshwater marsh species specific responses and soil physico-chemical properties, we conducted a greenhouse experiment consisting of three common tidal freshwater and brackish marsh species (<i>Panicum hemitomon, Sagittaria lancifolia</i>, and <i> Spartina patens</i>). To mimic diversion specific conditions, we tested high and low nitrate loading rates (35 g N m² y^&ndash;1 and 0.25 g N m² y^&ndash;1, respectively) and two hydrologic regimes to compare diversion and non-diversion. Units were also set at two different soil surface elevations within each treatment, to simulate healthy and degraded marsh types. </p><p> Growth responses measured throughout the study differed between species, but were not influenced by the treatments. After 3 months, aboveground and belowground biomass was not impacted by the treatment for any of the species. Soil redox potential was influenced by changes in hydrology but recovered to pre-study conditions by harvest. This study provides an insight into how proposed river diversion conditions and subsequent recovery may influence the productivity of freshwater marshes. We also further highlight the need for a more complete understanding of how changes in flooding depth, duration, and nitrate load from proposed river sediment diversions will influence the productivity of marshes in receiving basins.</p><p>

<p> While it is clear that thermodynamics plays a nontrivial role in biological processes, exactly how this affects the macroscopic structuring of living systems is not fully understood. Thus, the objective of this dissertation was to investigate how thermodynamic variables such as exergy, entropy, and information are involved in biological processes such as cellular metabolism, ecological succession, and evolution. To this end, I have used a combination of mathematical modelling, <i>in silico</i> simulation, and both laboratory- and field-based experimentation. </p><p> To begin the dissertation, I review the basic tenets of biological thermodynamics and synthesize them with modern fluctuation theory, information theory, and finite time thermodynamics. In this review, I develop hypotheses concerning how entropy production rate changes across various time scales and exergy inputs. To begin testing these hypotheses I utilized a stochastic, agent-based, mathematical model of ecological evolution, The Tangled Nature Model. This model allows one to observe the dynamics of entropy production over time scales that would not be possible in real biological systems (i.e., 10⁶ generations). The results of the model&rsquo;s simulations demonstrate that the ecological communities generated by the model&rsquo;s dynamics have increasing entropies, and that this leads to emergent order, organization, and complexity over time. To continue to examine the role of thermodynamics in biological processes I investigated the bioenergetics of marine microbes associated with benthic substrates on coral reefs. By utilizing both mesocosm and <i> in situ</i> experiments I have shown that these microbes change their power output, oxygen uptake, and community structure depending upon their available exergy. </p><p> Overall, the data presented herein demonstrates that ecological structuring and evolutionary change are, at least in part, determined by underlying thermodynamic mechanisms. Recognizing how physical processes affect biological dynamics allows for a more holistic understanding of biology at all scales from biochemistry, to ecological succession, and even long-term evolutionary change.</p><p>

In the present study, I demonstrated the ability of the xylem-feeding leafhopper, Carneocephala floridana, to discriminate between differentially fertilized Spartina alterniflora, which possessed varying levels of foliar nitrogen content. The hopper was capable of detecting, and preferentially fed upon, minimally fertilized plants, which did not differ in percent of foliar nitrogen from unfertilized control plants. / Chemical analyses of the xylem sap and performance data from another host plant, Borrichia frutescens, confirmed that amino acid levels in highly fertilized plants become very unbalanced and are either unusable, or toxic, to C. floridana. Highly fertilized plants had elevated levels of NH$\sb4\sp+$, and a nitrogen content, that is probably well above those found in naturally occurring B. frutescens. These results suggested that a threshold detection mechanism may be operating. C. floridana's host plants show seasonal trends in their nitrogen content. While, the field patterns of C. floridana did not suggest that the hopper switches host plants based solely on interspecific nitrogen content; intraspecific nitrogen content did show several trends that were consistent host plant usage. My results suggest that the spatial and temporal distribution natural populations of C. floridana may be influenced by host plant nitrogen, but crude nitrogen is not a good predictor of interspecific host plant preference. / In addition, egg mortality and parasitism rates were also higher on the grasses compared to the herbaceous species. It appears that host plant water content may be largely responsible for plant mediated egg mortality. In addition, high parasitism rates on the two grass species may be related to the orientation of eggs, which are laid in parallel packets just below the surface of the epidermis. Conversely, eggs laid on the two herbaceous species appear to be less accessible to searching parasitoids. / My data suggest that Carneocephala floridana should utilize the two grasses only when the two herbaceous species are unavailable. In the salt marshes of Florida's northern Gulf coast, this occurs during the winter when the herbaceous species experience a substantial dieback. / Source: Dissertation Abstracts International, Volume: 52-08, Section: B, page: 4007. / Major Professor: Donald R. Strong. / Thesis (Ph.D.)--The Florida State University, 1991.

<p> Wetlands exhibit high primary productivity and play a significant role in the global carbon cycle. Brackish and salt marshes co-occur in Southern California; yet, restoration designs often eliminate remnant brackish marshes, along with their ecosystem functions, without evaluation. Vegetation, soil organic matter, and carbon flux were compared between brackish and salt marsh habitats in the Huntington Beach Wetlands. Newland Brackish Marsh had more carbon aboveground in denser and taller vegetation than the other two marshes. Brookhurst Salt Marsh sediments had more organic matter than the other two marshes. CH₄ emissions were negligible at all sites, and there were no differences in CO₂ flux or aerobic and anaerobic microbial respiration among sites. Although these components of the carbon cycle were similar among sites in this project, such quantitative functional evaluations should be part of the restoration planning process.</p>

Debate over global declines of amphibian populations has focused researchers' attention on the lack of basic life-history information about and appropriate monitoring methods for amphibian species. We studied barking frogs ( Eleutherodactylus augusti) in a canyon in the Huachuca Mountains of southern Arizona. Annual (capture) surveys and radio-tracking revealed that most barking frogs in this canyon are strongly associated with limestone. Adults rarely moved between limestone outcrops and numbers of frogs on each outcrop were small. Subpopulations consisting of frogs on sets of neighboring outcrops probably function as a metapopulation. We evaluated four methods for monitoring population size of this species: mark-recapture, distance sampling, visual encounter surveys, and call counts. We found none of these to be able to detect changes in population size powerfully enough to alert managers to declines as they occur. We suggest resource managers focus monitoring efforts on distribution rather than population size.

Planners expect infrastructure development underway in Baja California to launch a wave of tourism. Managers will need information concerning the natural environment. This study focuses on the floral richness of the islands of Bahia de los Angeles, Baja California, Mexico. Results include island plant species inventories; a phytogeographic analysis evaluating the effects of island characteristics on plant species richness; a current human impact analysis, on floral richness; an evaluation of threats to floral richness and environmental health, including a non-native plant analysis; and management recommendations for preventing depletion of the native plant species richness on these islands from increased visitation. Floral richness ranges from 2 to 74 species per island. The best predictors of floral richness are the island area and the seabird presence or breeding. I recommend a combination of careful monitoring, dissemination of educational materials, and increased enforcement of current restrictions on island use to minimize human impacts.

Two aspects of ecosystem health in the Colorado River delta were investigated as part of the present dissertation. The following is a summary of the most important findings: Contaminants of natural origin (e.g. selenium) and anthropogenic activities (e.g. pesticides) represent a potential threat for humans and wildlife in the Colorado River delta. Fourteen locations were sampled for bottom material and biota from March 1998 to April 2000. Concentrations of selenium in bottom material ranged from 0.6-5.0 μg/g. Concentrations of selenium in biota ranged from 0.5-18.3 μg/g, 23% of these samples exceeded the toxic threshold where reproductive impairment in birds from dietary exposure is reported. Concentrations of DDE exceeded the lower critical dietary level for sensitive species in 30% of biota samples. No clear relationship could be found between the concentration of Se in bottom material and the concentration of Se in fish. Nevertheless, smaller Se concentrations in biota were found at sites that had an outflow and exposure or physical disturbance of the bottom material was uncommon. Greater concentrations of Se in biota were found at sites with strongly reducing conditions, no output, and subsequent periods of drying and flooding or dredging activities, and at sites that received water directly from the Colorado River. The southwestern willow flycatcher (Empidonax traillii extimus ) is an endangered neotropical migrant with only 300-500 breeding pairs. The objective of the second study was to determine the presence/absence of this bird in the Colorado River delta. Surveys were conducted from June to July, 1999 and from May to June, 2000 using an audio tape of this subspecies' songs to elicit responses. We detected a total of 50 willow flycatchers in the Colorado River delta in the months of May to June. None were detected in July, thus, the birds were most likely migrants. Restoration of the intensively used stopover sites of the Colorado River delta appears to be essential for the overall recovery of this subspecies. Additionally, we propose a possible willow flycatcher summer migratory route throughout the series of coastal estuaries found adjacent to the coast of Sonora.

Red brome [Bromus madritensis subsp. rubens (L.) Husn.] arrived in western North America before 1880 and has since invaded even relatively undisturbed areas. Populations of this annual grass, native to the Mediterranean Basin, fluctuate widely in response to variations in winter precipitation and can produce large amounts of persistent fine fuels. The biogeography portion of this research describes the arrival, spread, and current extent of red brome in western North America and estimates the potential climatic range of this grass in the USA. The ecology portion of this research investigates interactions between native Sonoran Desert winter annuals and four densities of red brome, from the equivalent of 300 to 1200 plants m⁻², at low (3) and high (540 μg NO₃ - g soil⁻¹) levels of soil nitrogen (N), to evaluate the relative intensity of interactions at low and high fertility. This study found no evidence of red brome occurrence in North America prior to 1879. This grass may have arrived with immigrants or agricultural products after the start of the California Gold Rush in 1848, perhaps in crop seed or in the fleece of sheep. Red brome appears best adapted to areas with minimum January temperatures between -5.4 and 3.9°C and total winter precipitation between 9.0 and 76.4 cm. However, the myriad factors mediating interactions among red brome, other species, and local environments in these areas will determine if this grass becomes established in any of these regions. This study found no evidence of reduced richness or diversity of Sonoran Desert annuals occurring with red brome. Red brome did not exclude species from this study, as neither emergence nor survival of native species were affected by this grass. However, red brome significantly interfered with growth of native species. Declines in total biomass of each of 11 analyzed species growing with red brome averaged 58.4% of biomass produced when this grass was not present. The intensity of interactions between red brome and Sonoran Desert annuals rarely varied with soil fertility and differences in growth of red brome and of native annuals between low and high N were similar.

Choosing where offspring will develop is especially important for insects whose larval stages are restricted to a particular host resource. In such insects, maternal egg laying decisions may not only involve choosing optimal hosts based on their intrinsic qualities but also avoiding hosts occupied by conspecific brood. The ability to discriminate between previously exploited and unexploited hosts is often mediated by the use of a marking pheromone. Despite engaging in what appears to be host-marking behavior, the walnut fly Rhagoletis juglandis prefers to deposit clutches into previously exploited hosts. In this dissertation, I quantified host reuse in R. juglandis and assessed its impacts on offspring fitness. I also explored the role that marking pheromone plays in level of reuse. Host reuse by the walnut fly was common in the field, where trees were synchronously infested over a 14-17 day period. It was not unusual for individual fruit to bear 40-80 eggs; given that females laid clutches of ca. 16 eggs, each oviposition puncture probably contained ca. 1.6 clutches. The overall number of eggs deposited into fruit was positively correlated with fruit volume. Field and laboratory experiments showed that increases in larval densities within fruit reduced larval survival and pupal weight, the latter being strongly correlated with the number of eggs a female produced over her lifetime. The temporal staggering of clutches strongly and negatively impacted survival of later clutches. The effect of spatial patterning of clutches on offspring fitness depended on the number of clutches in the fruit: at higher densities, clutches performed better when deposited into the same puncture than when distributed uniformly over fruit. The evidence taken together suggests that host reuse by the walnut fly, R. juglandis, reduces per capita offspring fitness. Consistent with this inference was a final set of observations on female host-marking behavior. In field-cage experiments, fruit that were marked by females for longer durations were less acceptable to other females. Moreover, the duration of time that a female marked a fruit was positively correlated with the size of her clutch. These results indicate that, while females commonly reuse fruit, they nevertheless signal the level of larval competition associated with a fruit and adjust allocation of eggs to fruit accordingly.

Fragrances appear to act in conjunction with visual cues to attract specific pollinators. Besides the ecological influence of pollinator type on fragrance, as with many other attributes of organisms, phylogenetic history may also affect fragrance composition. In this dissertation I examine the quality and quantity of floral and vegetative fragrance, and explore the relationships among fragrance, pollinators, and phylogenetic history in the plant family Nyctaginaceae. Using DNA sequence data, I inferred phylogenetic relationships among and within the Nyctaginaceae genera Acleisanthes, Selinocarpus, and Mirabilis. There is a high incidence of hawkmoth pollination within these genera, in addition to multiple pollinator transitions. Results suggest that neither Acleisanthes nor Selinocarpus are monophyletic, but that together they comprise a monophyletic lineage. Because of this finding, I have taxonomically combined these two genera into a single genus. Analyses of floral and vegetative fragrance from Acleisanthes, Selinocarpus, and Mirabilis species included in the phylogenetic study show that each species has a unique fragrance profile. Further, although there is substantial variation among individuals within species, intraspecific variation is significantly lower than interspecific variation in fragrance profiles. Fragrances are composed of 5--108 different compounds from at least seven different biosynthetic classes. Some species produce most of their fragrance vegetatively, while floral emissions are the sole source of volatiles in other taxa. Results show that neither total amount of volatiles nor the amount of floral volatiles per mug floral tissue is correlated with pollinator type. However, the emission of nitrogen-bearing compounds appears to have been lost in those lineages that have also lost moth pollination, suggesting that the presence of nitrogen-bearing compounds may be important for moth attraction. Although the phylogenetic signal in the fragrance data is not entirely congruent with the signal in the DNA sequence data, certain compounds and biosynthetic pathways do support the independent phylogeny inferred using the DNA data. However, it is also clear that many compounds are highly homoplastic, yielding limited phylogenetic information. Overall results suggest that phylogenetic relationships rather than pollinator affinities are better predictors of fragrance composition among these Nyctaginaceae species.