The microbial ecology of tundra soils was studied at four contrasting sites on the sub-Antarctic island of South Georgia. Two main study sites were used - a deep Mossbank dominated by Polytrichum alpestre/Chorisodontium aciphyllum and a Festuca contracta Grassland, and two subsidiary sites - a dense stand of the deciduous Dwarf Shrub Acaena magellanica and a Tortula robusta/Rostkovia magellanica Mire included for certain aspects of this two year programme. The viable bacterial and fungal populations of the main sites were comparable to those of other tundra regions and showed a similar decrease with depth. Intra-site variability was correlated with vegetation cover and increased microbial populations associated with Juncus scheuchzerioides at the Mossbank and Festuca contracta at the Grassland. Seasonal variability of the microbial populations showed complex correlations with a range of edaphic variables of which temperature and moisture were the most important. Direct bacterial counts showed high numbers present. Variability in total numbers was reflected in the viable counts. Cellulolytic bacteria and fungi and ligninolytic fungi, a small but consistent part of the microbial populations, were correlated with depth, moisture and the heterotrophic populations but showed little association with the vegetation cover. Chrysosporium sp. and pycnidial fungi were important celluloytic organisms found at both main sites. Sterile mycelia were frequently isolated. The decomposition of moribund moss in the Mossbank was very slow (3-5% p.a.) while dead grass culms in the Grassland showed rates of 15-20% p.a. The decomposition rates of a pure cellulose material were compared at all four sites and showed the order of cellumlytic activity to be: Dwarf Shrub>Mire>Grassland>Mossbank. Patterns of cellulose decomposition revealed differences between the sites with depth and season and correlation analyses showed associations with vegetation at the Grassland and Mire sites. Total potential activity of the four sites was assessed by respirometry. The expression of results was complicated by the differing organic contents of the soils. The Dwarf Shrub and Mire sites showed consistently greater oxygen consumption than the Grassland or Mossbank and all sites showed reduced respiration with depth. Correlation analyses showed moisture to be the most important seasonal factor and at the Mossbank respiration was correlated positively with J. scheuchzerioides and negatively with P. alpestre. A general model linking decompositioA and nutrien~ cycling was created.

<p> Many southern California coastal salt marshes are urbanized and heavily impacted, but still provide important ecosystem services, including carbon and nutrient cycling. Salt marsh community structure and functions, such as decomposition, are essential for marsh ecosystems and are potentially vulnerable to inundation impacts created by sea level rise (SLR). The saltmarsh communities driving decomposition are comprised of invertebrates, fungi, and bacteria, which may be susceptible to SLR. In this project, inundation of saltmarsh sediments with associated plants and rhizosphere were manipulated using a marsh organ to assess the impacts of SLR on decomposer activity (leaf litter decay, anaerobic respiration) and community structure (bacterial and benthic invertebrate). Marsh organ samples across all inundation treatments showed altered decomposer community diversity and function compared to controls, indicating disturbance. However in some cases there were no significant differences between communities among SLR treatments. However, inundation effects may have been obscured by marsh organ artifacts.</p>

<p>Bees are essential for crop pollination services; however, the ecosystem services they provide by pollinating native plants are crucial for maintaining biodiversity in natural systems. This study analyzed bee community changes within, on the edge, and outside of forest fragments. Phenological variation over two seasons and modeling to predict bee abundance associated with forest characteristics was performed. Finally the genetic diversity of two species of Bombus was analyzed. Bowl traps and aerial sweep netting in and near forest patches were used to sample bee communities in northern Delaware between March and August, 2013 and 2014. Bee phenology stayed consistent between field seasons, but fewer bees were collected in 2014 compared to 2013. Abundance modeling (R: unmarked) predicted that bee abundance was negatively impacted primarily by agriculture surrounding the forest patch. Analyses using microsatellites revealed that B. impatiens lacked overt population genetic structure while B. bimaculatus showed two genetically distinct populations. Pesticide analysis revealed 17 pesticides observed on adult bees from seven urban and suburban forest patches. Further studies investigating natural bee fluctuations in response to multiple field seasons, floral diversity, and chronic pesticide exposure are crucial in order to assess native pollinator health.

I conducted call-response surveys for Yuma clapper rails in the Colorado River delta, Mexico during the breeding seasons of 1999 and 2000 to estimate abundance, determine distribution, and identify patterns of habitat use. The maximum estimate of abundance was 6,629 individuals (95% C.I. 4,859 to 8,399). Rails were widely distributed in the delta, occupying almost all marshlands dominated by cattail. Rail density was higher in the Cienega de Santa Clara than in the other wetlands of the delta. High densities of clapper rails were associated with increased water depth, high cattail coverage, high vegetation coverage, low saltcedar coverage, proximity to shoreline, and increased salinity up to 8 ppt. As this is an endangered subspecies shared by Mexico and the U.S., the conservation of the delta ecosystem should be the interest of both countries, especially when management decisions upstream in the U.S. have an impact over natural areas downstream in Mexico.

Describing processes that lead to the distribution of parasites in space is important for understanding disease transmission and spread. Similarly, describing plant distribution patterns is important to understanding ecological processes. Indeed, distinguishing between dispersal and establishment limitation is central in plant ecology. Mistletoes allow doing both because they are plant parasites with clearly defined spatial distributions among hosts. Most mistletoes are dispersed by birds that consume mistletoe berries and defecate seeds onto host trees in a mutualistic relationship. I studied desert mistletoes, Phoradendron californicum (Viscaceae), which in the Sonoran desert, parasitize legume trees and are dispersed by Phainopepla nitens (phainopeplas). I examined patterns of spatial distribution and dispersal of P. californicum and the processes and mechanisms underlying these patterns at multiple scales. By counting mistletoes and deposited mistletoe-seeds, and watching phainopepla behavior, I found that mistletoes were aggregated within host trees, and that seed deposition was highest in tall and infected hosts. Likewise, phainopeplas perched preferentially in these trees, creating a positive feedback in which highly infected trees received many seeds and were likely to become reinfected. However, phainopeplas spent less time in trees than it takes for a seed to pass through their guts, which suggested interhost seed dispersal. I conducted a mistletoe removal experiment that confirmed a high degree of inter-host seed dispersal. These observations suggested that mistletoes would be aggregated at scales larger than individual trees. By mapping mistletoes and defecated seeds within a 4-hectare plot, I found that mistletoes were spatially correlated to at least 145 meters. Sampling at larger scales indicated that mistletoe prevalence was spatially correlated to approximately 1500 m and at scales larger than 4000 m. I also found that seed deposition increased with mistletoe prevalence in local neighborhoods. In conclusion, mistletoes are dispersal limited plants and are spatially correlated at several scales. Desert mistletoes are aggregated within hosts and their prevalence is spatially correlated at <1500 m and >4000 m. At the individual and local scales, their distribution is shaped by where birds defecate, which is influenced by host and neighborhood characteristics. At larger scales, their distribution may be primarily influenced by abiotic effects.

Macromeria viridiflora is an herbaceous perennial in which floral traits vary geographically. In my dissertation research, I analyzed geographic variation in plant morphology and pollinator assemblages. I conducted experiments to determine the breeding system of the plants, and used visitation rate and pollen deposition to compare effectiveness of floral visitors as pollinators. I analyzed aspects of pollinator attractants and rewards in the flowers and placed this into the context of pollinator syndromes. In addition, I used phylogenetic analysis of the genus to determine polarity of change in corolla size within the species. Analysis of morphometric data from eight sites across the range of the species revealed significant among-population variation in vegetative and floral traits. Flower size variation is particularly strong and follows a latitudinal cline. Hawkmoths and hummingbirds were the main floral visitors throughout the range. The large-bodied hummingbirds visiting plants in the southern regions are not present in the northern regions, where flowers are visited by hummingbirds with barely half the body size and much shorter bills. This difference in bill size of hummingbird pollinators mirrors the geographic variation in flower size in M. viridiflora, suggesting that pollinator-mediated selection may be acting upon the species. Flowers of M. viridiflora have several characteristics that fit both the hummingbird and hawkmoth pollinator syndromes, namely copious sucrose-rich nectar and long floral tubes. However, they also have characteristics that correspond with a single major pollinator. This plant therefore presents a compromise floral syndrome that attracts two classes of pollinators. Breeding system studies showed that whereas plants are self-compatible and occasionally produce seed autogamously, pollinators are important for reproductive success in the plants. Combining visitation rate and pollen deposition as measures of pollinator effectiveness, hummingbirds were found to be the most effective pollinators at both sites. Phylogenetic analysis produced a single most parsimonious tree that supports the monophyly of the genus. Mapping of corolla size onto the phylogeny indicates that floral size has changed many times within the genus, and that very large corolla size in southern populations of Macromeria viridiflora has been derived from a smaller-flowered ancestor.

No description available.

A study of the floristic structure of the bracken community indicated a continuum from high frond densities with a species-poor sward, growing on an organic and acidic soil, to lower frond densities with a relatively species-rich sward on a more mineralised, less acid soil. An analysis of the biomass structure of the community showed that an increase in frond density, litter deposition and long shoot rhizome length, together with a decrease in soil pH, were correlated with a decrease in turf biomass. Excluding livestock appeared to be associated with a decrease in bracken frond mortality but also significantly fewer frond buds and unemerged fronds were found below ground. This suggests that frond damage caused by livestock stimulates the production of frond buds and, paradoxically, may lead to higher frond densities. Asulam reduced frond production, in the year after spraying, by approximately 80 per cent. However, the rates of recovery were very variable such that full recovery or no recovery were observed after three years. The percentage recovery was most rapid in areas with the highest frond densities prior to treatment and may be due to proportionally more rhizome remaining alive after spraying. No significant effect of bracken control was seen on the productivity of the underlying native sward. Furthermore the application of lime and phosphate and the restriction of grazing failed to significantly increase sward cover. The application of agricultural seed mixtures indicated that those containing Agrostis tenuis appeared to have the most potential for rapid sward development, with the removal of bracken litter and restriction of grazing being unnecessary. A model was constructed to suggest two appropriate management strategies for long-term bracken control after spraying. For sparse turf, reseeding and the application of lime and phosphate are necessary but for reasonably well-developed turf no further management is required.

The ecology of the natural enemies of coroal aphids was investigated at field sites near Norwich, Norfolk during the period when aphids were found on cereals. Field work was supplemented with laboratory studios on one group of predators, the Cioccinollidao. The field studies from 1976 to 1978 had the objective of determining the relative importance of the following natural enemies of cereal aphids, Coccinollidao, Syrphidao, Chrysopidao, . Aphidiidao, polyphagous ground predators and fungal pathoCons. in 1976 Coccinollidao voro the most important predators, followed by Syrphidao and the parasitic Aphidiidao, in 1977 Coccinollidao were again most important, followed by Aphidiidao, fungal pathogons and : "Syrphidao, while in 1978 Aphidiidno and fungal pathogens were the most important cereal aphid natural onomios. Predators were most effective in warm, sunny weather conditions as in 1976, while tunal opizootics occurred in humid weather, Mortality from aphid specific natural enemies was at a maximum late in the aphid population cycle on cereals, honco natural onomios worn unable to prevent economically oignificant outbreaks in 1976 and 1977i though they reduced peak aphid populations and hastened the 'crash' in aphid numbers. The role of polyphagous prodators was difficult to assess because of their low numbers, but exclusion experiments in 1977 showed significantly hij; hor aphid numbers in plots whore thoso prodators were excluded early in the season, though those differences disappeared later, Laboratory studios on Coccinolliclao (mainly Coccixlelln 7-riinetnta with soMo obsorvationa on C'n ac3nQlla 11-runctntn) Cavo inforºaeation on coroal aphid consumption ratos soarchint capacity under different environmento. 1 conditions, ability of adults to survive starvations fecundity of fomalars in relation to aphid conssumptiong and tho effoct of solar radiation on the internal body tewporaturo of adult

1. Population differentiation was studied in the halophytic annuals Salicornia and Suaeda maritima at Stiffkey, Norfolk, England. 2. The salt marsh at Stiffkey shows considerable spatial and temporal heterogeneity. The gradient in height across the marsh results in extreme differences in tidal regime and edaphic conditions, while physiographic features such as salt pans, creeks and their associated levees, impose smaller-scale heterogeneity. Salicornia and Suaeda maritima occur throughout the marsh and exhibit striking variations in phenotype associated with particular microhabitats. 3. Monitoring of field populations of these annuals during successive phases of the life cycle showed that morphologically distinct populations differed in aspects of their life-histories. These differences included the control of dormancy and germination, the phenology of growth and development, and fecundity. 4. The genetic and environmental components of these differences were examined in reciprocal transplant experiments of both seed and seedling material and in uniform growth conditions in growth cabinets and in a glasshouse. Survival and many aspects of both vegetative and reproductive performance were measured throughout the life cycle. 5. Much of the variation in natural populations was attributable to differences in plant density. Plant size and fecundity were extremely plastic in their response to density. Phenological features were more stable and structural characters were most stable. Survival was density independent. 6. Environmental differences between sites also had profound effects on growth and survival of the plants. In particular, some aspect of hypersaline edaphic conditions and the presence of perennial vegetation reduced considerably the survival and growth of annual plants. 7. When the density dependent components of performance were removed, and plants from different parts of the marsh were grown under the same environmental conditions, significant differences remained between them in morphology and life-history. This applied both to plants grown on the same site in the field and to those grown under uniform conditions. These differences between populations were likely to be genetic. 8. Three sorts of explanation of the adaptive significance of genetic differences between populations were examined. First, the relative performance and survival of local and foreign populations planted on the same site were examined at all stages of the life cycle. These differences were expressed as relative selection coefficients. The relative success of populations was also measured over an entire generation by comparing numbers of seeds sown with those produced. This gives an estimate of the relative fitness of the local and foreign populations at each site. Second, correlations were examined between life history characteristics of the populations and features of their environment that were likely to act as selective agents. Third, parallel variation was examined between Salicornia and Suaeda maritima populations within the same zone of the marsh. 9. All three of these approaches were adopted to achieve a concensus of information. Each approach suffers different limitations and the interpretation of information obtained from each is discussed critically. 10. Selection usually favoured the survival and growth of local relative to that of foreign populations at all sites and at all stages in the life cycle. The highest selection coefficients were for survival of the lower marsh 1 t" ... upper morsn 1 . popu a lon ln competltlon wlth the~perennla vegetatlon during the growth phase (ca 0.7) and for seed production of upper marsh Suaeda maritima on the lower marsh (ca 0.9). 11. Measures of the intensity of selection at specific stages of the life cycle did not predict accurately the magnitude of selection over an entire generation. All populations planted as seeds on their native site were relatively fitter than foreign populations transplanted to same site. Relative fitness is likely to have been underestimated because the local and foreign populations at each site were not grown in competition with one another. 12. Chromosome numbers were counted in Salicornia plants typical of the populations recognized by their morphologies and life histories. Three tetraploid and three diploid Salicornia populations and three diploid Suaeda maritima populations were identified at stiffkey. 13. The breeding systems and possible genetic structures of Salicornia and Suaeda maritima populations are discussed in relation to population differentiation. salicornia populations appear to be largely inbreeding and consist of many predominantly homozygous lines. occasional outcrossing provides sufficient variability to allow divergence of the populations under selection. population differentiation in Suaeda maritima apears to be maintained by restriction of gene flow between populations by divergence in flowering times, as well as by intense selection.