A major trend in invasion biology is the development of models to accurately predict and define invasive species and the stages of their invasions. These models focus on a given species with an assumed set of traits. By doing so, they fail to consider the potential for differential success among different source populations. This study looked at the inland invasion of Rhithropanopeus harrisii in the context of a current invasion model. This species has been introduced worldwide, but has only invaded freshwater reservoirs within the state of Texas (United States) indicating a potential difference amongst source populations. Previous studies indicate that this species should not be capable of invading inland reservoirs due to physiological constraints in the larvae. A more recent study gives evidence to the contrary. To investigate whether the inland populations are in fact successfully established, I attempted to answer the following questions: Can inland populations successfully reproduce in the inland reservoirs and rivers? If so, what factors in the native environment could have led to the evolution of this ability? What are the impacts of this species in the inland reservoirs and what is its potential spread? I combined a larval developmental study, conspecific and heterospecific crab competition trials, field collections, gut content analysis, shelter competition trials with crayfish, and larval and adult dispersal study to answer these questions. I showed that Rhithropanopeus harrisii is established in the inland reservoirs and capable of spreading. I demonstrated that in the native populations along the Gulf coast of the United States, this species is the least aggressive and is therefore likely excluded into lower salinity waters during reproductive periods. This likely led to a lowered salinity tolerance in the larval stages, which predispose these populations to successful introductions in inland freshwater bodies. I showed that the crabs are capable of outcompeting juvenile crayfish for shelter at high densities and therefore warrant management in order to reduce their effect. This study indicates a need for the invasion models to take the source population into account in order to ensure effective and prudent management strategies.

While much evidence suggests that ecosystem functioning is closely related to biodiversity, present rates of biodiversity loss are high. With the emergence of the metacommunity concept ecologists have become increasingly aware that both local processes (e.g. competition, predation), and regional processes (e.g. dispersal and regional heterogeneity) affect ecological communities at multiple spatial scales. I experimentally investigated the effects of habitat connectivity and regional heterogeneity on biodiversity, community composition, and ecosystem functioning of artificial pond metacommunities of freshwater invertebrates at the local (α), among-community (β), and regional (γ) spatial levels. There was a significant effect of habitat connectivity on mean local richness, but mean local Simpson diversity, mean local functional diversity (FD), and all the three indices of ecosystem functioning investigated (regional abundance, invertebrate biomass, and chlorophyll a concentration) were unaffected by connectivity levels. Regional heterogeneity had no effect on local diversity, but enhanced both among-community richness and among-community Simpson diversity. Conversely, connectivity reduced among-community Simpson diversity. All indices of regional diversity were unaffected by either connectivity or heterogeneity. Despite expectations that there would be strong interactions between the effects of connectivity and heterogeneity on species richness, there were no interactions for any index of biodiversity at any spatial scale. Invertebrate community composition was unaffected by either connectivity or heterogeneity, though there was a significant effect of heterogeneity on its variance. Neither connectivity nor heterogeneity had significant effects on any index of ecosystem functioning, nor among-community coefficients of variation of ecosystem functioning. Connectivity appears to act mainly as a force homogenizing habitat patches in a region, as opposed to having strong effects in and of itself on communities. Conversely, heterogeneity acts largely as a diversifying force, maintaining differences between communities within a region, but, similar to connectivity, it does not have clear effects on communities at the local scale. Despite the different processes expected to act in homogeneous and heterogeneous regions, it does not appear that connectivity and heterogeneity interact strongly. / Thesis (Master, Biology) -- Queen's University, 2008-10-16 09:06:33.103

This study examines modern relationships among salt marsh plant species and their pollen in three salt marshes located on the northwest coast of the Bay of Fundy, New Brunswick. Linear regression analysis of pollen in 35 surface sediment samples and vegetation cover on small (<15 m) and broad (>15 m) scales show that, with the exception of Poaceae and Cheno Am, pollen corresponds well with fine-scale patterns of salt marsh vegetation. Scatter diagrams of paired pollen and cover data illustrate that cover of Triglochin is over-represented by its pollen, Glaux is under-represented, and Poaceae, Cheno Am, and Plantago are inconsistent. Tidal mixing and differential inputs from local, regional, and extra-regional sources with elevation limit the establishment of plant-pollen relationships for Cheno Am and Poaceae but not for other taxa. Comparison of 35 modern analogs from five vegetation zones using squared chord distance show that zones are distinct such that the marsh-terrestrial interface can be tracked with the greatest degree of certainty in a salt marsh paleo-ecological record and other marsh zones can be tracked when a conservative threshold of dissimilarity is used.

Biofilms are formed in aquatic environments by the attachment of bacteria to submerged surfaces, to the air/liquid interface, and to each other. Although biofilms are associated with disease and biofouling, the robust nature of biofilms; for example, their ability to tolerate chemical and physical stresses, makes them attractive for beneficial biotechnology applications such as bioremediation and biofuels. Based on an understanding of diverse signals and regulatory networks during biofilm development, biofilms can be engineered for these applications by manipulating extracellular/intercellular signals and regulators. Here, we rewired the global regulator H-NS of Escherichia coli to control biofilm formation using random protein engineering. H-NS variant K57N was obtained that reduces biofilm formation 10-fold compared with wild-type H-NS (wild-type H-NS increases biofilm formation whereas H-NS K57N reduces it) via its interaction with the nucleoid-associated proteins Cnu and StpA. H-NS K57N leads to enhanced excision of the defective prophage Rac and results in cell lysis through the activation of a host killing toxin HokD. We also engineered another global regulator, Hha, which interacts with H-NS, to disperse biofilms. Hha variant Hha13D6 was obtained that causes nearly complete biofilm dispersal by increasing cell death by the activation of proteases. Bacterial quorum sensing (QS) systems are important components of a wide variety of engineered biological devices, since autoinducers are useful as input signals because they are small, diffuse freely in aqueous media, and are easily taken up by cells. To demonstrate that biofilms may be controlled for biotechnological applications such as biorefineries, we constructed a synthetic biofilm engineering circuit to manipulate biofilm formation. By using a population-driven QS switch based on the LasI/LasR system and biofilm dispersal proteins Hha13D6 and BdcAE50Q (disperses biofilms by titrating cyclic diguanylate), we displaced an existing biofilm and then removed the second biofilm. Persisters are a subpopulation of metabolically-dormant cells in biofilms that are resistant to antibiotics; hence, understanding persister cell formation is important for controlling bacterial infections. Here, we engineered toxin MqsR with greater toxicity and demonstrated that the more toxic MqsR increases persistence by decreasing the ability of the cell to respond to antibiotic stress through its RpoS-based regulation of acid resistance, multidrug resistance, and osmotic resistance systems.

Seed dispersal in New Zealand relies on a different guild from the one present before the arrival of humans into the islands. Post-dispersal biotic and abiotic filters have also changed due to the introduction of seed predators and herbivores. The aim of this thesis was to evaluate the actual contribution of seed dispersers to the patterns of seed fall and to understand the effects of biotic (seed density, predators, distance from conspecifics) and abiotic (pH, canopy openess, etc) factors on seed and seedling survival. I expected that tree species with different fruit sizes would be selected by different assemblages of dispersers, therefore being deposited and recruiting differentially on the forest floor. I analyzed the changes in small-scale seed diversity with the use of seed traps during two seasons in two 0.36 ha plots in a mixed broadleaf-podocarp temperate forest. The diversity of seeds was lower for in-fruit seeds (1.40 species per grid-cell) than for bird-dispersed seeds (2.62). The dominant species D. cupressinum was dispersed towards con- and heterospecific canopies (wind-dispersed trees Weinmannia racemosa and Metrosideros umbellata), giving a probable mechanism for the observed increase in finescale seed diversity. Then, using a 12-year dataset on seed fall I analyzed the changes in ground-level seed heterogeneity generated by bird-dispersed seed rain (propagule-scale) relative to the canopy composition (adult-scale) on six tree species. A Non Metric Multidimensional Scaling analysis demonstrated that the differences in species composition between sampling points (seed traps) were larger for tree canopies than for dispersed seeds. Different tree species acted as seed importers and/or exporters, although these patterns were not explained by fruit size or the richness of the disperser assemblages. I also investigated the effects of seed and seedling density on seed predation, seedling emergence and seedling survival to 12 months of five tree species. Seed predation increased with seed size, and it was higher at high density only for the largest-seeded species Beilschmiedia tawa and Prumnopitys ferruginea. Access of seed and seedling predators to the propagules was the main factor affecting seedling emergence and seedling survival. Abiotic variables were important for germination and seedling survival of the two small-seeded species, but only biotic predictors (mammalian exclosure and density) were important for medium and large-seeded species. Finally, using a split-plot experimental design I measured the effects of (a) the presence of conspecific canopy, (b) high conspecific seed densities and (c) introduced (or invasive) mammal access on seedling emergence and seedling survival (Janzen-Connell effects). Distance effects were stronger than density effects, and mediated by native and exotic predators. Final survival under conspecifics was strongly reduced in both species, with zero survival of B. tawa under conspecifics, and near zero (2/896) under D. dacrydioides. Seed dispersal service in New Zealand is still enough to produce changes in the spatial pattern of seed deposition in the forest. Post-dispersal processes such as seed predation and herbivore are having strong impacts on the survival and potential recruitment of plant species. Large-seeded trees are the most affected in terms of the impact of introduced mammals on seed predation, but seedling survival is affected independent of seed size. However, it is unknown how different these ecological processes are from the original situation without pests in New Zealand. The results of my research can contribute with valuable information for future research trying to understand the consequences of seed dispersal for recruitment, as well as inform complex models that try to predict the long-term impacts of the exotic mammals introduced in New Zealand.

Flexible life-history traits and dispersal may allow generalist populations to persist across a range of habitats despite experiencing contrasting selection pressures. Invertebrates exploiting temporary ponds must develop quickly and disperse as adults, or have wide environmental tolerances. Conversely, permanent-pond invertebrates must avoid a suite of predators (e.g., fish and dragonflies). This gradient of pond permanence can result in life-history trade-offs that influence fitness, population dynamics, and genetic structure. In addition, recruitment between habitats may balance juvenile life-history trade-offs and be crucial to sustain generalist invertebrate populations in ponds with unpredictable hydrology. Through a multi-year survey of three pond complexes in the Canterbury high-country and a series of mesocosm experiments using two generalist pond invertebrates, Xanthocnemis zealandica damselflies and Sigara arguta waterboatmen, I found these two species had alternative life-history strategies that influenced their distributions across the pond-permanence gradient. With longer juvenile development, X. zealandica benefited from flexible life-history traits: temporary-pond X. zealandica had accelerated development and short-term desiccation tolerance, but were excluded from ponds with long dry periods, whereas, permanent-pond X. zealandica had extended development and predator avoidance behaviours (e.g., reduced movement and refuge-use). In contrast, S. arguta had an opportunistic life-history strategy with a fixed, rapid development response that allowed them to inhabit more temporary ponds, but they were intolerant of drying and limited to permanent ponds that contained shallow refuges from fish. These results illustrate how alternative life-history strategies enabled two generalist species to achieve broad realised niches. Recruitment between habitats also appeared to be important for balancing trade-offs and maintaining meta-populations across the pond-permanence gradient. To evaluate the importance of X. zealandica dispersal among and within pond complexes I used microsatellite analyses. While there was unique genetic population structure between the North and South Islands, at lower spatial scales there was little variability in genetic diversity and limited genetic structure in populations, likely due to gene flow among different habitat types. Overall, this work shows how an interaction of juvenile strategies and adult dispersal could reduce life-history trade-offs, resulting in weak selection pressures across an unpredictable disturbance gradient. Whether increasingly unpredictable hydrological patterns under climate-warming favour generalist species will likely depend on how well generalist life-history traits and dispersal allow exploitation of a range of habitat types and resilience to variable selection pressures. Higher mean summer rainfall in New Zealand may allow both species to exploit more temporary ponds, whereas longer dry periods between extreme precipitation events could limit X. zealandica distributions. Thus, species with generalist strategies are likely to be favoured under warming, but their specific life-history strategies will likely promote or limit their ability to exploit more unpredictable habitats.

The Cameroon Highlands that run along the Cameroon-Nigeria border are an important source of biodiversity. Not only are they rich in species and high in endemics, but biota from West Africa have not been studied as extensively relative to other parts of the Afrotropics, or the tropics in general. Threatening these rare and diverse habitats is anthropogenic pressure, which fragments forests and changes local animal communities. This thesis wished to address the impact of humans on seed dispersal and recruitment processes on selected tree species in forests on the Mambilla Plateau - a montane region in Nigeria's north-east. Research was conducted at Ngel Nyaki Forest Reserve, a conservation area established by the Nigerian Montane Forest Project. The reserve comprises a moderately-large forest patch (Ngel Nyaki Forest) and many small riparian fragments embedded in a grassland matrix. Cattle grazing and burning of this grassland are major threats to the survival of forest in this area.Hunting of local wildlife for bushmeat is also of concern, considering many of the region’s large-mammalian fauna are now locally extirpated (e.g. elephants) or at low abundances (many primate species). Loss of large-bodied frugivorous species has the potential to negatively impact the recruitment of large-seeded tree species that solely rely on them as seed dispersers. In this study, the ability for scatterhoarding rodents to act as surrogate dispersers for large-seeded species is tested. While much research has been carried out on secondary rodent dispersal in the Neotropics, work in the Afrotropics is still in its infancy. Because the outcome of plant-rodent interactions (i.e. predated or dispersed) may vary with season, habitat, or traits of the seed species in question, a number of experiments were established to quantify how local rodents at Ngel Nyaki may or may not be acting as effective dispersers. Additionally, the benefits of rodent dispersal were examined by creating an experiment that simulated secondary dispersal on seedling recruitment. The results of this study demonstrated that rodents can act as effective dispersers in Afromontane forests, but this is influenced by habitat, seasonal abundance of resources, and palatability of seed species. Furthermore, it was demonstrated that burial of seeds by rodents can increase the establishment probability of a seed by protecting it from removal by other rodents. However, while rodents play a strong driver of seed survival, it was also demonstrated that seedling mortality factors (such as herbivory) can also be heavy filters to seedling success. It is hoped that the results of this study will help to inform better management decisions and understand how the composition of the forest might change in the future.

The November 2004 explosive eruption of Grímsvötn volcano, Iceland (G2004) commenced as a subglacial event within the interior of the Vatnajökull ice cap before breaking through the ice cover to generate a 6-10 km high eruption column. This produced a tephra apron extending >50 km across the ice surface northwards from the eruption site, incorporating 0.047 km3 (DRE) of plagioclase-bearing, sparsely porphyritic, basaltic tephra. This study focuses on quantifying the key eruption parameters and evaluating the stratigraphy, grain size and geochemical characteristics of the proximal facies of the subaerial deposit with a level of detail and precision that has never previously been possible for a modern glacio-volcanic event. The G2004 deposit consists of a finely layered sequence which is subdivided into seven units (A-G) on the basis of differences in texture, grain size and componentry and the presence of sharp contacts between the layers. It is poorly sorted and finegrained with a median clast diameter of 1.5 Φ. The grain size characteristics and clast morphologies are indicative of intense phreatomagmatic fragmentation, despite a significant component of highly vesicular juvenile glass. A wide range in thicknesses and geometries of depositional units reflects variations in intensity and style of activity. Units C and E account for 80% of the total deposit volume, including the entire distal portion, and are interpreted to represent a mixture of (i) a widely dispersed component that fell from the upper margins of a strongly inclined (~45°) 6-10 km high plume and (ii) a locally dispersed (<3 km from source) component originating from (1) pyroclastic density currents generated by shallow explosions and tephra jets and (2) sedimentation from the jet region and lower convective column margins. The other units are only locally dispersed around the vent. A significant proportion of fine material was deposited in the near-vent region due to particle aggregation processes. The bulk of the G2004 deposit is therefore identified as the product of continuous incremental deposition during the passage of a single quasi-steady current supplied by a sustained explosive phreatomagmatic eruption, with a variable contribution of material from concurrent tephra fallout. Major oxide, trace element and volatile composition of the G2004 tephra were analysed and compared with that of the G1998 and Laki events. Results indicate that the G2004 magma originated within a shallow-level, compositionally stratified chamber and was discharged through an independent plumbing system. The parent magmas for each of these three Grímsvötn events were produced by different degrees of partial melting within a similar lower-crust or mantle source, but are not related by fractional crystallization or magma mixing. Despite episodic intense vesiculation, the G2004 magma was fragmented at very shallow levels by almost exclusively phreatomagmatic mechanisms – the effect of which was to arrest the degassing process such that only 75% of the potential magmatic sulphur budget escaped to the atmosphere.

To test competing hypotheses about the relative roles of vicariance and dispersal in the freshwater fishes in Galaxiidae, a phylogenetic framework and a time scale for species divergence were estimated using mitochondrial and nuclear DNA sequences. Relaxed clock dating revealed that the Galaxiidae originated in Gondwana in the late Cretaceous and thus vicariance cannot be ruled out for the two basal lineages, Galaxiella and Brachygalaxias. These two lineages are ancient relicts that rafted to their present distributions or were fragmented by the separation of Australia from South America via Antarctica. The opening of the Drake passage between South America and Antarctica initiated the proto-Antarctic Circumpolar Current (pACC) and counter-clockwise circulation in the South Atlantic, on which marine stage ancestors could have dispersed to South Africa and New Zealand via Australia during the late Eocene. Thus dispersal explains the disjunct distribution of the clade comprised of G. platei, G. zebratus and Neochanna spp. in South America, South Africa, and Australasia. The narrowing of the Drake passage and collapse of the pACC from about 24-14 Mya likely prevented further contact between South America and South Africa. Tectonic events around the globe produced an anomalous warming event, which along with the uplift of New Zealand provided empty niches and promoted the radiation of Galaxias. Most of the speciation in the other clades occurred during this time. When the Antarctic Circumpolar Current was reactivated at the end of the Mid-Miocene Climatic Optimum (MMCO) about 15–14 Mya, it provided a marine conveyor belt for the dispersal of the ancestor of Galaxias maculatus from Australia to South America, and later to Australia and New Zealand. The integration of divergence times estimated on the phylogeny with ancestral area reconstruction supports an origin in Gondwana and subsequent oceanic dispersal as the explanation for the distribution of the Galaxiidae across the southern continents.

To test competing hypotheses about the relative roles of vicariance and dispersal in the freshwater fishes in Galaxiidae, a phylogenetic framework and a time scale for species divergence were estimated using mitochondrial and nuclear DNA sequences. Relaxed clock dating revealed that the Galaxiidae originated in Gondwana in the late Cretaceous and thus vicariance cannot be ruled out for the two basal lineages, Galaxiella and Brachygalaxias. These two lineages are ancient relicts that rafted to their present distributions or were fragmented by the separation of Australia from South America via Antarctica. The opening of the Drake passage between South America and Antarctica initiated the proto-Antarctic Circumpolar Current (pACC) and counter-clockwise circulation in the South Atlantic, on which marine stage ancestors could have dispersed to South Africa and New Zealand via Australia during the late Eocene. Thus dispersal explains the disjunct distribution of the clade comprised of G. platei, G. zebratus and Neochanna spp. in South America, South Africa, and Australasia. The narrowing of the Drake passage and collapse of the pACC from about 24-14 Mya likely prevented further contact between South America and South Africa. Tectonic events around the globe produced an anomalous warming event, which along with the uplift of New Zealand provided empty niches and promoted the radiation of Galaxias. Most of the speciation in the other clades occurred during this time. When the Antarctic Circumpolar Current was reactivated at the end of the Mid-Miocene Climatic Optimum (MMCO) about 15–14 Mya, it provided a marine conveyor belt for the dispersal of the ancestor of Galaxias maculatus from Australia to South America, and later to Australia and New Zealand. The integration of divergence times estimated on the phylogeny with ancestral area reconstruction supports an origin in Gondwana and subsequent oceanic dispersal as the explanation for the distribution of the Galaxiidae across the southern continents.