Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Alien invasive species are a global concern not only threating biodiversity, but also negatively impacting regional economies. Consequently research aimed at understanding the invasion process is crucial for management of invasive alien species to reduce these impacts. Identifying accurate natal ranges is the key first step for efficient alien plant management, especially biological control. Such knowledge may assist in selecting host-specific biological control agents and help prevent non-target impact on native species. A case in point is the genus Cardiospermum of which species have been extensively moved around the globe with two species now being possible widespread invaders (C. grandiflorum and C. halicacabum), and a third species (C. corindum) having significant invasion potential. However, in some regions the native statuses of these species are not clear, hampering management. In order to minimize potential non-target impacts it is prudent to determine the relationships between Cardiospermum taxa in unknown native ranges prior to the release of biological control agents. With this thesis I aim to review available literature on the genus Cardiospermum, determine potential spread to suitable habitats globally for selected taxa, resolve unknown native ranges in southern Africa, and investigate rapid speciation of an endemic Namib Desert species of balloon vine. Through exhaustive searches for available literature on the genus Cardiospermum I report on the biology and ecology of selected species within the genus, with special focus on the most widespread species. Specifically, using species distribution modelling I investigate the potential spread of C. halicacabum, C. corindum and C. grandiflorum globally and assess the accuracy with which this can be determined using known native ranges to predict current alien ranges. Results indicate that these species have significant potential to spread, though highlighting that species distribution modelling over-fit predicted suitable ranges when using native range data alone. To resolve uncertain native ranges of selected species within the genus I reconstructed a dated multi-gene phylogeny and chloroplast haplotype network to investigate relationships within and among Cardiospermum species. I conclude that C. halicacabum is non-native in southern Africa due to polyphyletic relationships among accessions, while C. corindum is native due to natural long distance dispersal as indicated by a single monophyletic southern African clade. The close relationship observed between C. corindum and the African species, C. pechuelii, lead to a population-level genetic investigation of these two taxa. For this, I constructed a multi-gene phylogeny, chloroplast haplotype network and conducted population genetic diversity analyses which all indicated that the African arid adapted taxa, C. pechuelii, endemic to the Namib Desert of Namibia, evolved from C. corindum following long distance dispersal from South America. This study firstly provides insights into the ecology and biology of Cardiospermum, warning against further introduction due to potential spread. Secondly I resolved the unknown native statutes of Cardiospermum species in southern Africa and, lastly, illustrated the origin of African C. pechuelii. My research findings have major implications for on-going biological research against C. grandiflorum in South Africa and cautions strongly against the release of already-identified biological control agents due to their potential non-target impacts. / AFRIKAANSE OPSOMMING: Indringerspesies is 'n wêreldwye probleem as gevolg van hul direkte bedreiging van biodiversiteit asook hul negatiewe impakte op streeksekonomieë. Gevolglik is navorsing aangaande die indringingsproses van uiterste belang om doeltreffende beheer van indringerspesies te verseker. Die bepaling van die inheemse herkoms van indringerpopulasies is die eerste belangrike stap tot doeltreffende beheer, veral biologiese beheer. Hierdie informasie kan help met die identifisering van gasheer-spesifieke biologiese agente en om potensiële nie-teiken impakte op inheemse plant spesies verhoed. ‘n Voorbeeld is ballon rankplante in die genus Cardiospermum, waarvan verskeie spesies wêreldwyd verspreid is, met die gevolg dat minstens twee spesies (C. halicacabum en C. grandiflorum) nou moontlike wydverspreide indringers is en ‘n derde spesie (C. corindum) ook potensiaal toon as ‘n indringerspesie. In sommige streke is die in- of uitheemse statusse van hierdie spesies onbekend en belemmer gevolglik hul doeltreffende beheer. Met hierdie tesis streef ek om die genus Cardiospermum te hersien en potensiële verspreiding van geselekteerde spesies na geskikte habitatte te bepaal, om onbekende inheemse streke binne Suider-Afrika op te los en laastens, om die herkoms van ‘n ware Afrika spesie (C. pechuelii) te ondersoek. Na deeglike ondersoek van beskikbare literatuur doen ek verslag omtrent die biologie en ekologie van spesies binne Cardiospermum, met spesiale fokus op die mees wydverspreidste spesies. Deur gebruik te maak van spesies verspreidings modelle bestudeer ek die potensiaal van verdere verspreiding wêreldwyd vir C. halicacabum, C. corindum en C. grandiflorum en rapporteer ook omtrent die akkuraatheid van hierdie tegniek. Resultate toon dat alle spesies aansienlike potensiaal toon om verder te versprei, maar beklemtoon ook dat hierdie metode inheemse streek data “oor-aanpas”. Om enige onsekerhede aangaande inheemse streke op te los, het ek ‘n gedateerde multi-geen filogenie en ‘n chloroplas haplotipe netwerk opgetrek om die verhoudings binne en tussen geselekteerde Cardiospermum spesies te bepaal. Ek kom tot gevolgtrekking dat C. halicacabum nie inheems in Suider-Afrika is nie, as gevolg van polifiletiese verhoudings, en dat C. corindum inheems is en moontlik ook ‘n voorbeeld van natuurlike langafstand verspreiding, soos aangedui deur ‘n enkele monofiletiese groep. Die naverwante filogetiese verhouding tussen C. corindum en C. pechuelii het daartoe gelei dat ek die herkoms van C. pechuelii in Afrika ondersoek het. ‘n Multi-geen filogenie, chloroplas haplotipe netwerk en populasie genetiese diversiteit analises het aangedui dat C. pechuelii endemies is tot die Namib Woestyn van Namibië, en die produk is van lang afstand verspreiding van C. corindum vanaf Suid-Amerika. Hierdie studie gee eerstens insig tot die ekologie en biologie van Cardiospermum en waarsku teen verdere verspreiding. Tweedens dui my studie ook die opgeloste inheemse streke in Suider-Afrika aan van sekere Cardiospermum spesies, en laastens, illustreer ek die herkoms van C. pehuelii. My navorsing het baie belangrike gevolge vir die huidige biologiese beheer program teen C. grandiflorum in Suid-Afrika en waarsku teen die vrystelling van reeds geïndentifiseerde biologiese beheer agente weens potensiële nie-teiken impakte op inheemse spesies.

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: I investigated the impacts of the invasive wattle species (Acacia mearnsii, A. dealbata, A. decurrens), on the ecological function and productivity of rangelands in South Africa and their ability to sustain livestock production. More specifically, this study set out to: (1) assess grazing areas at a national scale; (2) identify evidence of progressive impacts of these species on livestock production across a selection of magisterial districts; (3) determine the effects of A. mearnsii density on growth form dominance of indigenous plant species, and highlight how this translates into impacts in forage quality and quantity; (4) determine the effects of A. mearnsii invasion on soil resources and conditions (key determinates of ecological function) required to support grazing production; and finally (5) determine to effects that clearing operations have had on the provision of grazing resources. My results indicate that the level of overlap between wattle invasion and areas with a high grazing potential, at the national scale, is relatively low (2.9%). However, at a magisterial district scale, areas with a high grazing potential have a moderate (approximately 35.1% high grazing potential area under wattle invasion for highest invaded district) level of invasion. Scattered and moderate levels of invasion currently dominate or characterise these species invasion patterns. Both light and dense A. mearnsii invasions reduce grazing capacity. Dense invasion had the most severe effect reducing grazing capacity from 2 ha, required to support one large stock unit, to 8 ha. The clearing of this species was found to improve grazing capacity within 5 years. The reduction in grazing capacity following invasion was largely due to reduced basal cover and herbaceous biomass. The clearing of invaded sites was found to increase both basal cover and herbaceous biomass to pre-invasion levels. Acacia mearnsii invasion was found to affect certain soil properties. Under an A. mearnsii canopy, plant litter, carbon content of the soil and nitrogen concentrations were all found to be elevated. Overall, this study demonstrates that Acacia invasions have a significant effect on grazing resources at a local or site scale, and that for the eastern region of South Africa, these effects are ultimately scaled up to a district level. This is likely to have important financial and human well-being repercussions. However clearing and restoration programs are clearly able to reverse or mitigate these effects. This study therefore lends support to or complements other ecosystem service provision arguments for clearing alien invasive species. / AFRIKAANSE OPSOMMING: Die impak van die indringer- wattelbome spesies ( A. mearnsii , A. dealbata , A. decurrens) , op die ekologiese funksie en produktiwiteit van weivelde in Suid-Afrika en hul vermoë om vee produksie te onderhou was ondersoek. Meer spesifiek, is hierdie studie uiteengesit om: (1) ondersoek in te stel na die mate van oorvleueling tussen indringing deur wattelbome spesies en belangrike weidingsgebiede op 'n nasionale skaal; (2) bewyse te verskaf van die progressiewe impak van hierdie spesies op vee-produksie oor 'n seleksie van politieke distrikte, (3) die gevolge van A. mearnsii digtheid op groei vorm en oorheersing van inheemse plante te wys, en hoe dit voer kwaliteit en kwantiteit affekteer; (4) die gevolge van A. mearnsii indringing op grond hulpbronne sowel as die kondisie (sleutel bepalende faktore van ekologiese funksie) wat benodig word om weiding produksie te ondersteun vas te stel, en uiteindelik (5) om die gevolge van skoonmaak bedrywighede op die voorsiening van weiding hulpbronne te bepaaal. My resultate dui daarop dat die vlak van oorvleueling tussen die wattelbome indringing en gebiede met 'n hoë weiding potensiaal, by die nasionale skaal, relatief laag is (2’9 %). Maar op 'n landdrosdistrik skaal, het gebiede met 'n hoë weiding potensiaal 'n matige (ongeveer 35.1 % weiding potensiaal area onder wattelbome indringing vir die hoogste binnegevalde distrik ) vlak van indringing. Verspreide en matige vlakke van indringing oorheers tans of kenmerk hierdie spesies se indringings patrone. Beide lig en digte A. mearnsii besettings verminder dravermoë. Digte inval het die mees ernstige uitwerking en verminder dravermoë van 2 ha, wat nodig is om een grootvee-eenheid te ondersteun na 8 ha. Bevindinge wys dat die verwydering van hierdie spesies weiding kapasiteit kan verbeter binne 'n tydperk van 5 jaar. Die afname in dravermoë na indringing is grootliks te wyte aan die afname in basale bedekking en kruidagtige biomassa. Na die skoonmaak van indringer persele is bevind dat beide basale bedekking en biomassa weer verhoog tot voor- indringings vlakke. Acacia mearnsii indringing beïnvloed sekere grondeienskappe. Onder A. mearnsii blaredak, is alle blaarafval, koolstof-inhoud van die grond en stikstof konsentrasies verhef. In die algeheel, toon hierdie studie dat die Acacia indringings 'n beduidende uitwerking op weidings hulpbronne by 'n plaaslike of perseel skaal het, en vir die oostelike streek van Suid-Afrika, is hierdie effekte ook uiteindelik vertaalbaar tot 'n distrik vlak. Dit sal waarskynlik belangrike finansiële en menslike welsyn gevolge hê, maar die skoonmaak en herstel programme is duidelik daartoe instaat om die gevolge te keer of te verminder. Hierdie studie leen dus ondersteuning aan of komplimenteer ander ekostelsel dienslewering argumente (soos dié van die Werk vir Water program) vir die verwydering van indringerspesies.

The species of two genera in Insecta: Hemiptera: Adelgidae were investigated through the lenses of genetics, morphology, life cycle and host species. The systematics are unclear due to complex life cycles, including multigenerational polymorphism, host switching and cyclical parthenogenesis. I studied the hemlock adelgids, including the nonnative invasive hemlock woolly adelgid on the east coast of the United States, that are currently viewed as a single species. I used multivariate morphometric analyses to identify morphological differences among hemlock adelgid lineages. With principal component analyses and MANOVA, the six lineages that were used in this study were found to be significantly different from each other. The findings of this project provide evidence for taxonomic designation of different hemlock adelgid lineages, which will hopefully inform regulation of these distinct lineages, as these distinctions between the lineages of hemlock adelgids could equate to other biological differences, ex. cold tolerance, host specialization, fecundity and dispersal ability. I also investigated the relationship between species Pineus similis, Pineus abietinus through phylogeny, genetic distances, life cycle and host species. This was done through using three mitochondrial (COI, COII, cytB) and one nuclear (EF1a) gene, in Maximum Parsimony, Maximum Likelihood and Bayesian analyses, along with genetic distance measurements. The P. similis and P. abietinus on Pinus could not be separated within the Bayesian analyses, and P. similis and P. abietinus on Abies had low calculated distance measurements (2.98%) compared to the average distance between species within the genus (28.07%). These two studies emphasize the current confusion within the Adelgidae family, and the results presented in this thesis stress the importance of using components of multiple species concepts to better understand the systematics of these lineages.

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.

This dissertation addresses the question of how leaf litter from trees affects animals that live in aquatic environments, with an emphasis on the effect of Chinese tallow (Triadica sebifera) leaf litter on anuran larvae (i.e., frog tadpoles). This question is important to our understanding of how allochthonous inputs to aquatic habitats drive biodiversity in wetlands. It also addresses a timely conservation concern in southeastern Louisiana where invasion by Chinese tallow trees (Triadica sebifera) is displacing native trees. The invasion process is homogenizing forest composition and changing the quantity and quality of litter inputs to ponds from those produced by a mixture of native species to that of a single invasive species. This change in litter quality may have important effects on aquatic animals because leaf litter that falls into ponds is an important source of nutrients and energy in wetland foodwebs. Leaf litter also affects water quality via effects on dissolved oxygen and leaching of defensive compounds, which may subsequently affect the diversity and performance of aquatic animals. Herein I address these issues by presenting a series of studies in which tadpole and aquatic invertebrate responses were tested using leaf litter from Chinese tallow leaves and three native tree species. The major findings of this research are: (1) Leaf litter has a direct effect on water quality (2) Chinese tallow can cause differential survival and performance of tadpoles (3) Differences in water quality due to leaf litter can cause changes in tadpole behavior (4) Chinese tallow leaf litter breaks down much faster than litter from native trees (5) Difference in litter breakdown rates influence aquatic community composition.

Invasões biológicas estão entre as principais causas da perda de biodiversidade no planeta. Ambientes isolados como as ilhas oceânicas e ambientes sujeitos a distúrbio antrópico são considerados mais propensos à invasão. Para as plantas, o sucesso na invasão pode ter relação com a superioridade na competição com as espécies nativas, que pode ocorrer através da produção de substâncias alelopáticas. Dentre as 100 principais espécies invasoras do planeta está a Leguminosa Leucaena leucocephala, que produz substâncias com potencial alelopático e está estabelecida em ilhas oceânicas tropicais em todo o mundo. No Brasil, a invasora foi introduzida na ilha de Fernando de Noronha, onde ocupa vastas áreas. Apesar da relevância desta ilha para a conservação da biodiversidade, não há informações essenciais para o manejo da invasora, como a situação da invasão e seus fatores determinantes. Neste trabalho, realizado em Fernando de Noronha, utilizamos experimentos para investigar a alelopatia como mecanismo associado à invasão e para avaliar o efeito de L. leucocephala sobre o estabelecimento de Erythrina velutina (Leguminosae), espécie nativa comum na ilha, mas frequentemente excluída das áreas invadidas por L. leucocephala. Não encontramos indícios de efeitos alelopáticos de L. leucocephala sobre a germinação de E. velutina, mas a exótica reduziu o crescimento e a sobrevivência da nativa. O efeito negativo é potencializado quando L. leucocephala está associada à Capparis flexuosa (Capparaceae), única espécie nativa frequentemente encontrada em áreas invadidas. Isoladamente, o efeito de C. flexuosa sobre E. velutina varia de positivo a neutro, evidenciando que o saldo das interações entre espécies nativas é alterado na presença de uma exótica. Adicionalmente, diagnosticamos a extensão atual da invasão e sua expansão nos últimos 20 anos, seus fatores determinantes e o impacto sobre a comunidade de plantas nativas em Fernando de Noronha. O diagnóstico da invasão mostrou que L. leucocephala está amplamente distribuída pela ilha, povoando densamente a maioria dos locais onde ocorre. A área ocupada pela espécie aumentou cerca de 40% nos últimos 20 anos, e não há restrições ambientais para o estabelecimento da exótica, embora ela seja favorecida pela atividade agropecuária. Em áreas invadidas o número de espécies nativas diminui quase pela metade e observamos uma tendência à homogeneização da comunidade. É provável que o alto grau de perturbação antrópica em Fernando de Noronha gere limitações à dispersão e modifique os ambientes tornando-os desfavoráveis para o estabelecimento de espécies nativas. Entretanto, há fortes evidências de que L. leucocephala causa mudanças ecológicas na ilha influenciando na perda espécies nativas. Considerando a importância biológica de Fernando de Noronha, ações de controle da expansão da exótica e restauração das áreas invadidas demonstram-se urgentes / Biological invasions are among the main causes of biodiversity loss on the planet. Isolated environments such as oceanic islands and disturbed environments are considered more prone to invasion. For plants, the invasion success may be related to advantages in competition with native species, which may occur through the production of allelopathic substances. Among the 100 most invasive species on the planet is the legume Leucaena leucocephala, which produces substances with putative allelopathic effects and is established on tropical oceanic islands worldwide. In Brazil, the invader was introduced on the island of Fernando de Noronha, where it occupies vast areas. Despite the relevance of this island for biodiversity conservation, important information for the management of the invasion, as its extension and determinants, do not exist. In this work we use experiments to investigate allelopathy as a mechanism associated with the invasion and to evaluate the effect of L. leucocephala on the establishment of Erythrina velutina, a native species common on the island, but often absent from invaded areas. We found no evidence of allelopathic effects of L. leucocephala in the germination of E. velutina, but the exotic reduced the growth and survival of the native. The negative effect is enhanced when L. leucocephala is associated with Capparis flexuosa, the only native species often found in heavily invaded areas. When alone, the effect of C. flexuosa on E. velutina varies from positive to neutral, indicating that the balance of interactions between native species is altered in the presence of an exotic. Additionally, we describe the current distribution of L. leucocephala and its expansion in the last 20 years in Fernando de Noronha. We also investigate the environmental and anthropic factors determining the invasion and the impact of L. leucocephala on the plant community. We found that L. leucocephala is widely distributed throughout the island, densely populating most places where it occurs. The area occupied by the species increased about 40% in the last 20 years, and there are no environmental restrictions for the establishment of exotic, although it is favored by farming. In invaded areas, the number of dominant native species decreased by almost half and we observed a tendency towards homogenization of the community. It is likely that the high degree of human disturbance in Fernando de Noronha poses dispersal limitations and modifies the environments making them unsuitable to the establishment of natives. However, there are strong evidences that L. leucocephala is driving ecological changes on the island that influence in native species loss. Considering the biological importance of Fernando de Noronha, actions to control the expansion of exotic and to restore the invaded areas are urgent

O uso de animais de montaria em áreas naturais tem gerado grande preocupação, pois podem gerar impactos ambientais. Um dos problemas que precisa ser investigado é a relação entre animais de montaria e a presença de plantas exóticas em áreas de alto valor ecológico. Assim, o presente trabalho teve como objetivo testar um protocolo de germinação para sementes de duas espécies de gramíneas, braquiária (Urochloa decumbens) e capim gordura (Melinis minutiflora) que passaram pelo trato digestório de cavalos. As sementes foram ofertadas aos animais junto com a ração com posterior coleta das fezes. No experimento foram realizados três tratamento. No tratamento \"braquiária\" foram ofertadas sementes de Urochloa decumbens, no tratamento \"capim gordura\" foram ofertadas sementes de Melinis minutiflora e o \"sem tratamento\" foi ofertada apenas a ração. Parte das sementes foram retiradas das fezes e submetidas a testes de germinação e o material restante foi utilizado para testar a capacidade germinativa das sementes diretamente nas fezes em um ambiente controlado. Na germinadora verificou-se que as sementes que passaram pelo trato digestório dos cavalos tiveram uma menor taxa de germinação comparadas com as sementes com tratamento de quebra de dormência. No tratamento feito em casa de vegetação as sementes que foram retiradas das fezes e que germinaram foram identificadas. Não houve diferença na taxa de germinação entre os cavalos, o que ocorreu entre os tratamentos. No tratamento braquiária predominou a germinação de Urochloa decumbens, no tratamento capim gordura a maior taxa de germinação de Melinis minutiflora e no sem tratamento predominou o nascimento de outras espécies. As sementes estudas tem potencial de germinar, crescer e frutificar, porém não se sabe se as espécies podem formar uma população capaz de colonizar novas áreas. / The use of riding animals in natural areas has caused great concern because their use cause environmental impacts. One of the problems that needs to be investigated is the relationship between the use of riding animals and the presence of exotic plants in natural areas. This study aimed to test a germination protocol for the of two species Urochloa decumbens and Melinis minutiflora that has passed through the digestive tract of the horse. The seeds were offered to horses and their feces were collected. Tree treatments were set, in \"braquiaria\" treatment seeds Urochloa decumbens were offered to the horses, in the \"capim gordura\" treatment seeds of Melinis minutiflora offered and the untreated were offered only horse food. Part of the seeds were removed from the feces and undergo germination test and the remain of the feces were used to test in a green house. The germination rate of the seed from de horse dung was lower than germination rate of the dormancy breaking treatment seeds. The seeds that germinate on the greenhouse were identified. There were no difference between the germination rate between treatments, but there was between species in braquiaria treatment predominated the germination of Urochloa decumbens in the grass fat treatment most Melinis minutiflora germination rate and the untreated predominated the germination of other species. Seeds from horse dung has the potential to germinate, grow and bear fruit, but it is not known if this species can form a population able to colonize new areas.

The introduction of a species to areas outside its native range can result in ecological and genetic changes of evolutionary significance. The frog Eleutherodactylus coqui was introduced to Hawaii, from Puerto Rico, in the late 1980s and has lost genetic variation in mitochondrial DNA. The extent to which founder effects have influenced phenotypic variation in the introduced range is unknown. In this study I compared phenotypic variation in life-history traits, advertisement calls, and stripe patterns among introduced and native populations of the frog Eleutherodactylus coqui. I also conducted laboratory experiments to determine the influence of genetics and temperature on trait variation. Body size in wild populations was positively correlated with elevation in both ranges, but the slope of elevation on body size was greater in Puerto Rico than in Hawaii. Advertisement call frequencies and rates were negatively correlated with elevation but duration was positively correlated with elevation. Frequencies were correlated with body size, but rate, duration, and intensity were not. Color patterns are more variable in Puerto Rico than Hawaii and appear to be maintained by balancing selection in Puerto Rico. Lab results indicate that body size is negatively correlated with temperature, which may explain Bergmann's rule in the field, but patterns of intrinsic growth rate may explain differences in the effect of elevation between Hawaii and Puerto Rico. Body size appears to explain most of the variation in call frequencies, whereas temperature explained most of the variation in rate and duration. Color patterns appear to be determined by a single locus with five alleles. Founder effects appear to explain the difference between Hawaii and Puerto Rico in color pattern variation and in clinal variation in body size and call frequencies. The loss of genetic variation in these traits is likely to have evolutionary consequences for this species in Hawaii.

This study investigated the role of an invasive tall cane, Arundo donax L. (Arundo), in the riparian water cycle. Four 100 meter transects were arrayed perpendicular to the lower Rio Grande in southwest Texas. The first objective was to determine the primary water source for Arundo by using naturally occurring stable isotopes. Surface soil, river water, groundwater, precipitation and rhizome samples were collected every month during 2010 and 2011 growing seasons, which coincided with a major flood that saturated soils in the first year followed by extreme drought in the second year. The second objective was to characterize how Arundo water use varied with water availability gradients in the riparian zone. Leaf gas exchange and leaf delta13C were measured along potential moisture gradients. The third objective was to understand the interaction between groundwater and surface water, and whether Arundo water use affected daily groundwater fluctuations. The isotope ratio of rhizome water was consistent with shallow soil moisture uptake and with previous observations of a relatively shallow, fibrous root system. Floodwater from July 2010 persisted in the soil for at least a year despite a severe drought, and became the dominant water source for Arundo during much of the study period. Although the alluvial water table in this floodplain was shallow (< 6 m) and subject to changes in river level, groundwater seemed not to be an important source for Arundo, so long as the soil moisture was sufficient. In this study, Arundo was not found to experience soil moisture limitation, and the spatial variability of Arundo transpiration was not associated with any soil moisture availability gradients. Arundo was found to close its stomata in response to increasing vapor pressure deficit (VPD), causing declining transpiration rate and increasing leaf delta13C composition. Significant exchange between the river and the alluvial groundwater was reflected in the similarity of isotopic compositions and the high correlation between river and groundwater elevations. Cross correlation analysis showed that over 50% of the diurnal groundwater fluctuations were caused by river stage changes. Consistent with the above ecophysiological and stable isotope results, Arundo water use was not found to influence daily groundwater fluctuations.

Integrating mutualism into the study of ecological communities is likely to be critical to understanding community dynamics and to predict the consequences of anthropogenic changes to ecosystems. Invasive species are among the greatest of these threats to global biodiversity. Throughout the Pacific, the invasive ant Anoplolepis gracilipes associates mutualistically with Morinda citrifolia , a native plant with extrafloral nectaries (EFN). I tested the hypothesis that these interactions can mediate invader impacts Anoplolepis gracilipes abundances were positively correlated with the dominance of EFN-bearing plants per site and negatively correlated with the species richness of native ants. Additionally, A. gracilipes displayed a higher magnitude of responses to nectar than other dominant ants. Mutualisms also had significant impacts on the structure of arthropod communities. These effects were strongest when A. gracilipes dominated local ant assemblages. These results suggest that novel mutualisms between invasive and native species can facilitate the impacts of invasions on communities.