Invasive species represent a major concern; they can result in serious ecological and economic losses and are recognised as one of the most serious threats to global species diversity. Plant invasions are of particular concern in New Zealand, which has high proportions of both naturalised and endemic plant species. In this thesis I focussed on the invasive plant Hieracium lepidulum, an exotic weed introduced from Europe to New Zealand prior to 1941. It is invasive in a variety of habitats in the South Island, where it has steadily increased in distribution and abundance over the last 50 years, and is thought to have detrimental impacts on native plant communities. I investigated factors influencing its invasion success and tested for impacts on native plant communities, making extensive use of existing plots into which H. lepidulum was experimentally introduced in 2003. I examined how community richness, turnover, resource availability and propagule pressure of the invader interacted to determine the invasion success of H. lepidulum. Results differed markedly above and below treeline. Above treeline, plots with higher richness and turnover were more invaded; below treeline, plots with higher available light were more invaded. In both habitats, these findings were modified by the influence of propagule pressure; at low propagule pressure, site characteristics were non-significant in explaining invasion success, while at higher propagule pressure these effects became significant. To test for impacts resulting in altered community composition and structure, I looked for changes in community richness, diversity and evenness subsequent to H. lepidulum introduction. As impacts may be more apparent at fine spatial scales, I made measurements at a 5 x 5 cm cell scale in addition to the established 30 x 30 cm plot scale. Plot species richness increased from 2003 to 2009 and a component of this increase was associated with H. lepidulum density. Other relationships between the plant community and H. lepidulum were generally non-significant. Results showed that H. lepidulum has had no negative effects on community richness, evenness or diversity. Despite being able to opportunistically colonise grassland sites with high turnover, and forest sites subject to canopy disturbance, dependant on propagule pressure, it appears H. lepidulum has not impacted community composition or structure.

Many regional and local factors can influence the distribution of native and exotic species in ecological communities. I examined the regional- and local-scale determinants of native and exotic vascular plant species richness and composition in a highly fragmented oak savanna ecosystem on southeastern Vancouver Island. In sharp contrast to most reported results, I found a negative relationship between native and exotic richness at the regional scale, and no relationship at the local scale. Two extrinsic factors, surrounding road density and climate, best explained the regional-scale relationship by each affecting natives and exotics in opposite ways. Road density and climate were also the dominant predictors of native and exotic composition at the regional scale. Patterns in the patch occupancy of individual species confirmed the importance of these factors but I found that low surrounding road densities and cool, wet conditions predicted the presence of many natives and the absence of many exotics. Environmental factors explained variation in richness and composition at the local scale, but these factors were different for natives and exotics. My results suggest that natives and exotics respond to roads and climate in fundamentally different ways. Roads increase both exotic propagule pressure and disturbance, which may facilitate exotic invasion. In contrast, disturbance from roads may increase the likelihood of local extinction for particular natives. Differing climatic preferences within the native and exotic species pools may also partially explain the observed patterns. There was no evidence that native diversity directly affects exotic diversity (or vice versa). Surprisingly, I found that connectivity was not an important predictor of richness or composition despite the high degree of habitat fragmentation in this ecosystem.

Invasive exotic species threaten biodiversity and ecosystem functions globally, creating need for and encumbering ecological restoration. When restoring exotic plant-dominated ecosystems, reinvasion pressure is the rate of new exotic recruitment following mature exotic removal. It can vary broadly among similarly invaded habitats and is crucial to restoration outcomes and costs, but is difficult to predict and poorly understood. Initial results from the experimental restoration of a wetland dominated by Triadica sebifera led us to develop the ‘outgrow the stress’ hypothesis. It holds: (1) Variation in reinvasion pressure is driven by differences in propagule abundance and spatiotemporal availability of realized recruitment windows, which are defined by abiotic conditions and biotic interactions. (2) Differences in reinvasion pressure become masked by exotic dominance when increases in niche breadth during development enable exotic persistence across sites where recruitment windows range from frequent to episodic. We validated this hypothesis. First, we used greenhouse and field experiments to quantify Triadica’s moisture niche early in development. By two months post-germination, seedling tolerances broadened to include conditions unsuitable for germination. This clearly demonstrated a rapid ontogenetic niche expansion, which could decouple mature Triadica density and average reinvasion pressure. Second, we used a greenhouse mesocosm experiment to quantify how recruitment window duration, competition and fertility impacted population-level Triadica establishment in stressful environments. As ‘outgrow the stress’ predicts, longer windows increased Triadica success and multi-factor interactions were common, with competition and fertility effects varying among environmental contexts. Third, we substantiated predictions of ‘outgrow the stress’ regarding propagule availability and soil moisture by manipulating these in a multi-site field experiment spanning eleven experimental restorations of Triadica-dominated habitats along a moisture gradient. Triadica reinvasion pressure varied broadly among sites but correlated with moisture and fertility. Propagule availability drove reinvasion in favorable environments, but availability of suitable conditions trumped propagules in extreme environments. Competition reduced Triadica performance and sometimes survival. Triadica prevalence reduced native plant prevalence. Six restorations require minimal Triadica management for success. This work advances our understanding and enables better predictions of reinvasion pressure and invasions in general. Accurate predictions enhance restoration efficiency by informing site selection and optimal management strategies.

Many regional and local factors can influence the distribution of native and exotic species in ecological communities. I examined the regional- and local-scale determinants of native and exotic vascular plant species richness and composition in a highly fragmented oak savanna ecosystem on southeastern Vancouver Island. In sharp contrast to most reported results, I found a negative relationship between native and exotic richness at the regional scale, and no relationship at the local scale. Two extrinsic factors, surrounding road density and climate, best explained the regional-scale relationship by each affecting natives and exotics in opposite ways. Road density and climate were also the dominant predictors of native and exotic composition at the regional scale. Patterns in the patch occupancy of individual species confirmed the importance of these factors but I found that low surrounding road densities and cool, wet conditions predicted the presence of many natives and the absence of many exotics. Environmental factors explained variation in richness and composition at the local scale, but these factors were different for natives and exotics. My results suggest that natives and exotics respond to roads and climate in fundamentally different ways. Roads increase both exotic propagule pressure and disturbance, which may facilitate exotic invasion. In contrast, disturbance from roads may increase the likelihood of local extinction for particular natives. Differing climatic preferences within the native and exotic species pools may also partially explain the observed patterns. There was no evidence that native diversity directly affects exotic diversity (or vice versa). Surprisingly, I found that connectivity was not an important predictor of richness or composition despite the high degree of habitat fragmentation in this ecosystem.

Les invasions biologiques sont reconnues comme un facteur évolutif important sur une échelle de temps courte. Elles affectent notamment la structure génétique des populations, les patrons d'évolution phénotypique et la richesse des faunes de parasites associées aux populations envahissantes. Cette étude se propose de quantifier les conséquences d'une invasion biologique suivant ces trois niveaux (génétique, phénotypique et parasitologique) en prenant pour exemple le cas du tilapia du Mozambique Oreochromis mossambicus. Ce cichlidé africain présente un statut remarquable en biologie de la conservation puisqu'il est à la fois (i) l'une des espèces les plus envahissantes au monde car dispersée à l'échelle globale au cours du XXème siècle et (ii) une espèce " quasi-menacée " (UICN) sur son aire native (partie du sud-est de l'Afrique) du fait de son hybridation massive avec d'autres Oreochromis sp. introduits. La démarche générale employée ici est de décrire l'histoire récente des populations à l'aide de marqueurs nucléaires (AFLP) et des séquences de l'ADN mitochondrial (ADNmt), puis de mettre en relation ces résultats génétiques avec la diversité morphologique et la parasitologie des populations. Deux systèmes différents ont été étudiés : Au sein de l'aire native, l'étude se focalise sur le Limpopo inférieur et le sous-bassin de la Changane (Mozambique). Des patrons d'introgression incluant trois espèces en présence sont détectés, mais les hybrides sont peu fréquents et leur expansion limitée. Ces résultats sont de plutôt bonne augure pour la conservation d'O. mossambicus et ils permettent d'identifier deux zones de conservation prioritaires. L'étude des parasites indique une plus grande diversité parasitaire mais de faibles prévalences dans les sites de moindre valeur en conservation, ce qui pourrait favoriser le succès des espèces introduites et de leurs hybrides. Parmi les territoires envahis, les AFLP et l'ADNmt soutiennent une homogénéité générale et une diversité génétique faible, qui sont interprétées comme le résultat d'un fort goulot d'étranglement précédant l'expansion à l'échelle mondiale. Une structure des populations en lien avec la géographie à large échelle (Nouvelle-Calédonie, Guadeloupe, Jamaïque) est cependant détectée. La variation de la forme du corps est également structurée à large échelle géographique, ce en dépit des fortes variations environnementales enregistrées à l'échelle locale. Cela suggère un effet des contraintes génétiques sur la diversification morphologique contemporaine. L'absence de parasites monogènes sur les populations introduites en Nouvelle-Calédonie peut être mise en relation avec un évènement fondateur, et est proposé comme l'un des facteurs ayant pu favoriser le succès de l'espèce. En conclusion, une faible diversité génétique ne contraint vraisemblablement pas un potentiel envahissant élevé et une diversification rapide chez les tilapias.

Made available in DSpace on 2014-12-17T14:33:09Z (GMT). No. of bitstreams: 1 AlexanderCFR_TESE.pdf: 2277990 bytes, checksum: fde046b8c7771a53154cf0f53839f90c (MD5) Previous issue date: 2014-07-08 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / This study aimed to compare the development of crab and tree communities of two restored mangrove areas, one planted with Rhizophora mangle and the other naturally recovered, and also to compare the predation of Grapsid crab Goniopsis cruentata and the Ocypodid Ucides cordatus over the propagules of three mangrove trees: Rhizophora mangle, Avicennia schaueriana e Laguncularia racemosa. Specifically, we tested the hypothesis that Goniopsis predation is more important that Ucides predation, and that these consumers have antagonist effects over propagule consumption. In each area, 10 quadrates were selected at random to analyze tree richness, diameter, height, tree biomass and crab richness and density five years after restoration experiment start. Results show that tree height, biomass and crab density were significantly higher in artificially restored area. No significant differences were observed in crab species richness between areas, but higher tree richness was observed in self-recovered area. Results suggest that planting propagules of Rhizophora can significantly increase tree recovering if the aim was increase tree biomass and crab density, which can accelerate return of ecological functionality. Goniopsis is a more important propagule predator than Ucides both in natural and restored areas. The effects of Goniopis were higher in absence of Ucides, due to negative interactions among these two predator species. The preference of Goniopsis by Avicennia and Laguncularia can favor the dominance of Rhizophora observed in Neotropical mangroves. This study suggests that propagule predation by Goniopsis should be controlled in restoration programs, if dominance of Rhizophora is undesirable respect to more rich tree communities / O presente estudo teve como objetivo comparar o desenvolvimento das comunidades de ?rvores e caranguejos de duas ?reas de mangue restauradas, uma plantada com Rhizophora mangle e outra naturalmente recuperada, al?m de comparar a magnitude da preda??o do Graps?deo Goniopsis cruentata e do Ocypod?deo Ucides cordatus sobre os prop?gulos de tr?s esp?cies de mangue: Rhizophora mangle, Avicennia schaueriana e Laguncularia racemosa. Em particular, foi testada a hip?tese de que a preda??o de Goniopsis ? mais importante que a preda??o por Ucides e que esses consumidores possuem efeitos antag?nicos sobre a preda??o de prop?gulos. Em cada ?rea, 10 quadrantes foram aleatoriamente selecionados para analisar a riqueza arb?rea, di?metro, altura, biomassa arb?rea e riqueza e densidade de caranguejos cinco anos ap?s o in?cio do experimento de restaura??o. Os resultados mostraram que tanto a altura e biomassa arb?reas quanto a densidade de caranguejos foram significativamente maiores na ?rea artificialmente restaurada. N?o foram observadas diferen?as significativas na riqueza de esp?cies de caranguejos entre as ?reas, mas houve uma maior riqueza de esp?cies de ?rvores na ?rea auto-recuperada. Estes resultados sugerem que o plantio de prop?gulos de Rhizophora pode aumentar significativamente a recupera??o da cobertura vegetal, se o objetivo for elevar a biomassa arb?rea e a densidade de caranguejos, o qual pode acelerar o retorno da funcionalidade ecossist?mica. Goniopsis foi um predador de prop?gulos mais importante que Ucides tanto em ?reas naturais quanto restauradas. Os efeitos de Goniopsis foram maiores na aus?ncia de Ucides devido a intera??es negativas entre estas esp?cies de predador. A prefer?ncia de Goniopsis por Avicennia e Laguncularia pode favorecer a domin?ncia de Rhizophora observada nos mangues Neotropicais. Este estudo sugere que a preda??o de prop?gulos por Goniopsis em programas de restaura??o de mangue deveria ser controlada se a domin?ncia de Rhizophora ? indesej?vel em rela??o a comunidades com mais esp?cies de ?rvore

Many regional and local factors can influence the distribution of native and exotic species in ecological communities. I examined the regional- and local-scale determinants of native and exotic vascular plant species richness and composition in a highly fragmented oak savanna ecosystem on southeastern Vancouver Island. In sharp contrast to most reported results, I found a negative relationship between native and exotic richness at the regional scale, and no relationship at the local scale. Two extrinsic factors, surrounding road density and climate, best explained the regional-scale relationship by each affecting natives and exotics in opposite ways. Road density and climate were also the dominant predictors of native and exotic composition at the regional scale. Patterns in the patch occupancy of individual species confirmed the importance of these factors but I found that low surrounding road densities and cool, wet conditions predicted the presence of many natives and the absence of many exotics. Environmental factors explained variation in richness and composition at the local scale, but these factors were different for natives and exotics. My results suggest that natives and exotics respond to roads and climate in fundamentally different ways. Roads increase both exotic propagule pressure and disturbance, which may facilitate exotic invasion. In contrast, disturbance from roads may increase the likelihood of local extinction for particular natives. Differing climatic preferences within the native and exotic species pools may also partially explain the observed patterns. There was no evidence that native diversity directly affects exotic diversity (or vice versa). Surprisingly, I found that connectivity was not an important predictor of richness or composition despite the high degree of habitat fragmentation in this ecosystem. / Science, Faculty of / Botany, Department of / Graduate

The global effort to rehabilitate and restore destroyed mangrove forests is unable to keep up with the high mangrove deforestation rates which exceed the average pace of global deforestation by three to five times. Our knowledge of the underlying processes of mangrove forest regeneration is too limited in order to find suitable techniques for the restoration of degraded mangrove areas. The general objective of my dissertation was to improve mangrove restoration by understanding regeneration processes and local plant-plant interaction in a regenerating Avicennia germinans forest. The study was conducted in a high-shore mangrove forest area on the Ajuruteua peninsula, State of Para, Northern Brazil. The dwarf forest consisting of shrub-like trees is recovering from a stand-replacing event caused by a road construction in 1974 which interrupted the tidal inundation of the study area. Consequently, infrequent inundation and high porewater salinity limit tree growth and canopy closure. All trees and seedlings were stem-mapped in six 20 m x 20 m plots which were located along a tree density gradient. Moreover, height, crown extent, basal stem diameter of trees were measured. The area of herbaceous ground vegetation and wood debris were mapped as well. The mapped spatial distribution of trees, seedlings and covariates was studied using point pattern analysis and point process models, such as Gibbs and Thomas point process, in order to infer underlying ecological processes, such as seed dispersal, seedling establishment, tree recruitment and tree interaction. In the first study (chapter 2), I analyzed the influence of abiotic and biotic factors on the seedling establishment and tree recruitment of A. germinans during the recolonization of severely degraded mangrove sites using point process modeling. Most seedlings established adjacent to adult trees especially under their crown cover. Moreover, seedling density was higher within patches of the herbaceous salt-marsh plants Blutaparon portulacoides and Sesuvium portulacastrum than in uncovered areas. The higher density of recruited A. germinans trees in herb patches indicated that ground vegetation did not negatively influence tree development of A. germinans. In addition, tree recruitment occurred in clusters. Coarse wood debris had no apparent effect on either life stage. These results confirm that salt-marsh vegetation acts as the starting point for mangrove recolonization and indicate that the positive interaction among trees accelerates forest regeneration. In the second study (chapter 3), I analyzed how intraspecific interaction among A. germinans trees determines their growth and size under harsh environmental conditions. Interaction among a higher number of neighboring trees was positively related to the development of a focal tree. However, tree height, internode length and basal stem diameter were only positively associated in low-density forest stands (1.2 trees m-2) and not in forest stands of higher tree density (2.7 trees m-2). These results indicated a shift from facilitation, i.e. a positive effect of tree interaction, towards a balance between facilitation and competition. In the third study (chapter 4), I used point process modeling and the individual-based model mesoFON to disentangle the impact of regeneration and interaction processes on the spatial distribution of seedlings and trees. In this infrequently inundated area, propagules of A. germinans are only dispersed at a maximum distance of 3 m from their parent tree. Furthermore, there is no evidence that the following seedling establishment is influenced by trees. I was able to differentiate positive and negative tree interactions simulated by the mangrove model mesoFON regardless of dispersal processes based on static tree size information using the mark-correlation function. The results of this dissertation suggest that mangrove forest regeneration in degraded areas is a result of facilitative and not competitive interactions among mangrove trees, seedling and herbaceous vegetation. This has important implications for the restoration of degraded mangrove forest. Degraded mangrove areas are usually restored by planting a high number of evenly spaced seedlings. However, high costs constrain this approach to small areas. Assisting natural regeneration could be a less costly alternative. Herbaceous vegetation plays a crucial role in forest recolonization by entrapping propagules and possibly ameliorating harsh environmental conditions. So far only competition among mangrove trees has been considered during restoration. However, facilitative tree interactions could be utilized by planting seedling clusters in order to assist natural regeneration instead of planting seedlings evenly-spaced over large areas. This dissertation also showed that point pattern analysis and point process modeling can enable forest ecologists to describe the spatial distribution of trees as well as to infer underlying ecological processes.

The spread of exotic species is considered to be one of the most significant threats to ecosystems and emphasises the need for appropriate management interventions. The majority of marine non-indigenous species (NIS) are believed to have been introduced via ship biofouling and their domestic spread continues to take place via this mechanism. In some countries, biosecurity systems have been developed to prevent the introduction of NIS through biofouling. However, implementing biosecurity strategies is difficult due to the challenges around identifying high-risk vectors. Reliable predictors of risk have remained elusive, in part due to a lack of scientific knowledge. Nonetheless, invasion ecology is an active scientific field that aims to build this knowledge. Propagule pressure is of particular interest in invasion ecology as it describes the quantity and quality of the propagules introduced into a recipient region and is considered to be an important determinant in the successful establishment of NIS. Environmental history affects health and reproductive output of an organism and, therefore, it is beneficial to examine this experimentally in the context of biofouling and propagule pressure. The aim of this thesis was to examine how voyage characteristics influence biofouling recruitment, survivorship, growth, reproduction and offspring performance through the ship invasion pathway. This was to provide fundamental knowledge to assist managers with identifying high-risk vessels that are likely to facilitate the introduction or domestic spread of NIS, and to understand the processes affecting biofouling organisms during long-distance dispersal events. Chapter One provides an introduction to the issues addressed in this thesis. Each data chapter (Chapters Two – Five) then focused on a stage of the invasion process and included field experiments using a model organism, Bugula neritina. Finally, Chapter Six provides a summary of key findings, discussion and the implications to biosecurity management. Throughout this thesis, the effect of donor port residency period on the success of recruits was highlighted. Chapter Two focused on recruitment in the donor region. As expected, recruitment increased with residency period. Importantly, recruitment occurred every day on vulnerable surfaces, therefore, periods as short as only a few days are able to entrain recruits to a vessel hull. The study presented in Chapter Three showed that there was high survivorship of B. neritina recruits during 12 translocation scenarios tested. In particular, the juvenile short-residency recruits (1-8 days) survived voyages of 8 days at a speed of 18 knots; the longest and fastest voyage simulated. Interestingly, variation in voyage speed and voyage duration had no effect on the survivorship of recruits, but did have legacy effects on post-voyage growth. Again, B. neritina which recruited over very short residency periods of 1 day continued to perform well after translocation and had the highest level of reproductive output after the voyage scenarios (Chapter Four). Recruits that were older (32-days) and reproductively mature at the commencement of the scenarios failed to release any propagules. Even though the number of ‘at sea’ and ‘port residency’ days were equal, reproductive output was higher after short and frequent voyages than after long and infrequent voyages. Finally, the study presented in Chapter Five examined transgenerational effects of B. nertina. Results showed that although the environmental history of the parent colony had a carry-over effect on offspring performance, it was the offspring environment that was a stronger determinant of success (measured by reproductive output and growth). Although cross-vector spread is possible (i.e. parent and offspring both fouling an active vessel), offspring released from a hull fouling parent into a recipient environment will perform better. In combination, these studies have provided new insights into NIS transport via vessel biofouling. Although shipping pathways are dynamic and complex, these results suggest that juvenile stages that recruit over short residency periods and are then translocated on short voyages, may pose a higher risk for NIS introduction than originally assumed. This has implications for marine biosecurity management as short residency periods are common and short, frequent voyages are typical of domestic vessel movements which are largely unmanaged.