The arctic tundra has been warming disproportionately faster than the global mean. Although the tundra has historically been a carbon sink, the current state of its carbon balance is highly uncertain. Large warming induced changes to tundra ecosystems complicate our ability to model tundra carbon cycling. In this dissertation I explore the impact of herbivores on dry heath vegetation and carbon flux, herbivore impact on dry heath tundra canopy, and lastly, the impact higher vegetation has on the conditions under which the tundra transitions from a carbon sink to a carbon source. Chapter 1 presents a study on the impact long term herbivore absence has on dry heath tundra. I measured vegetation cover, abundances of plant growth forms and carbon flux. I demonstrate the herbivore exclusion in this tundra ecosystem results in higher vegetation abundance and greater carbon uptake. Moreover, under average environmental conditions during the measurement period, I show that excluding herbivores resulted in net carbon uptake under average temperature and light conditions during the measurement period. In chapter 2 I build upon my result from chapter 1. I quantify differences in canopy structure due to herbivore exclusion and integrate this into carbon flux estimates. I show that that different herbivore assemblages have significantly different effect on carbon fluxes. Specifically, exclusion of large herbivores results in higher carbon uptake compared to exclusion of large and small herbivores. I also demonstrate that incorporating canopy structure results in significantly lower carbon uptake during morning and evening hours than carbon flux estimates based on my results from chapter 1 would suggest. In chapter 3 I quantify the conditions under which tussock tundra transitions from a carbon sink to source and how that is impacted by increasing vegetation abundance. I show that under low light, tundra with higher vegetation abundance must surpass higher temperatures to become carbon sources compared to tundra with lower vegetation abundance. However, under high light, the conditions are reversed, and tundra with higher vegetation abundance become carbon sources at lower temperatures than tundra with lower vegetation.

Animal pollination represents one of the key innovations of the flowering plants, and constitutes an essential ecological service in most ecosystems. While pollinators are the main drivers of flower evolution, some floral traits are puzzling when viewed only in the context of this mutualistic interaction. In particular, the pollen of plants belonging to several families has spines or compounds with toxic effects on insects. Little is known about the causes and consequences of these enigmatic floral traits. Yet, pollen defences might play an important role in pollination given that pollen is the main source of food of the principal pollinators in most ecosystems: bees. My thesis investigates why plants sometimes have seemingly defended pollen and how these putative defences affect host-plant use by bees. Given the potential role of flower-colonizing microbes in pollination, I also investigate the potential for these microorganisms to influence flower evolution. I found that pollinators are unlikely to act as potential agents of selection on the concentration of defence compounds in the pollen of Lupinus argenteus. Rather, physiological spillover or pleiotropy from tissues highly defended against herbivores might be responsible for a baseline level of defence compounds in pollen, while such compounds could also mediate the interaction between plants and pollen-colonizing microbes. However, I did not find evidence that flower-colonizing microbes drive the evolution of floral traits in an experimental study. I also found that pollen chemical and mechanical defences likely restrict pollen-host use by Osmiini, a group of solitary bees exhibiting high interspecific variability in their pollen diet. Bees tolerated the defences of their pollen hosts, but were often harmed by the pollen defences of co-occuring plants exploited by other Osmiini species. This pattern provides a striking parallel with the evolution of host-use in herbivorous insects feeding on vegetative tissues, and suggests that pollen defences might play an important role in structuring plant–bee interactions. Overall, my thesis contributes to our understanding of the causes of the presence of chemical defences in pollen and their consequences for the pollination mutualism.

No description available.

No description available.

The ecology and evolution of a species is often considered only within the context of pairwise interactions even though a species' distribution and abundance may be determined by interactions with many species within and between trophic levels. Multiple herbivores often share the same host and may interact indirectly by altering the relationships between herbivores, their host plants and their parasitoids. However, the relationships between parasitoids and herbivore hosts have typically been studied in isolation of other herbivore species. I examined how the outcomes of species interactions change when multiple relationships are considered. Chapter 1 examined the potentially conflicting selection pressures Manduca sexta exerts on Nicotiana tabacum (tobacco), since M. sexta has pollinating adults but herbivorous larvae. I demonstrated that high nectar amino acids do not affect floral visitation, but increased oviposition of herbivores on leaves. Thus, the relative costs and benefits of nectar rewards may depend on the community of pollinators and their life histories. In the remaining chapters I examined how feeding on tobacco by the aphid Myzus persicae altered the interactions between a parasitoid (Cotesia congregata) and its hornworm host (M. sexta). Chapter 2 demonstrated that aphids reduced hornworm abundance and parasitism. Changes in hornworm abundance were not due to density-dependent changes in moth oviposition, but the proportion of caterpillars attacked by parasitoids was inversely density dependent with hornworm density. Chapter 3 examined whether changes in hornworm abundance and parasitism reflected aphid-induced changes in host plant quality or volatile emissions. Aphids increased hornworm mortality, did not affect parasitoid performance, and increased parasitoid search time. In combination with Chapter 2, results suggest that aphids can mediate parasitoid-caterpillar interactions through changes in host plants that reduce hornworm survival and alter parasitoid behavior. Chapter 4 addressed how the outcome of interactions that are altered by aphids changed with spatial scale, and found no effect spatial scale on hornworm abundance and parasitism. In this system, aphids alter parasitoid-caterpillar interactions through changes in plant quality that reduce hornworm performance and abundance, and in turn, influence parasitoid attack. This work demonstrates that the outcome of multispecies interactions may not be predictable from pairwise interactions. / Ph. D.

Invasive exotic species threaten native biodiversity, alter ecosystem structure and function, and annually cost over $100 billion in the US alone. Determining the ecological traits and interactions that affect invasion success are thus critical for predicting, preventing, and mitigating the negative effects of biological invasions. Native herbivores are widely assumed to facilitate exotic plant invasions by preferentially consuming native plants and avoiding exotic plants. Here, I use freshwater plant communities scattered broadly across the Southeastern U.S. to show that herbivory is an important force driving the ecology and evolution of freshwater systems. However, native consumers often preferentially consume rather than avoid exotic over native plants. Analyses of 3 terrestrial datasets showed similar patterns, with native herbivores generally preferring exotic plants. Thus, exotic plants appear defensively nave against these evolutionarily novel consumers, and exotic plants may escape their coevolved, specialist herbivores only to be preferentially consumed by the native generalist herbivores in their new ranges. In further support of this hypothesis, a meta-analysis of 71 manipulative field studies including over 100 exotic plant species and 400 native plant species from terrestrial, aquatic, and marine systems revealed that native herbivores strongly suppressed exotic plants, while exotic herbivores enhanced the abundance and species richness of exotic plants by suppressing native plants. Both outcomes are consistent with the hypothesis that prey are susceptible to evolutionarily novel consumers. Thus, native herbivores provide biotic resistance to plant invasions, but the widespread replacement of native with exotic herbivores eliminates this ecosystem service, facilitates plant invasions, and triggers an invasional meltdown. Consequently, rather than thriving because they escape their co-evolved specialist herbivores, exotic plants may thrive because their co-evolved generalist herbivores have stronger negative effects on evolutionarily nave, native plants.

Herbivores have a significant influence on their environment. Factors that influence herbivore distribution in a landscape are important for conservation. Artificial water provision is one such factor, with water sources being focal points of herbivore activity. Variation between herbivore utilisation of different waterhole types and habitat integrity surrounding the different waterholes is assessed in this study. Correlations are drawn between herbivore utilisation and habitat integrity to quantify the impact that artificial waterholes have on the landscape. A scoring system is devised to investigate the various factors affecting vegetation around artificial waterholes. Results show that there are significant variations between herbivore utilisation for different artificial waterhole types, as well as significant variation in habitat integrity surrounding the different waterhole types. Distance between waterholes and drainage lines, and utilisation by specific herbivore species have a significant impact on habitat integrity - specifically affecting veld condition and disturbance observed on woody plant species. A habitat score that was created by combining data from both the herbaceous and woody layers is not affected by waterhole type, distance from waterholes, or the different herbivore species utilising the different waterhole types. Earth dams have the greatest impact on surrounding vegetation and are the most utilised waterhole type. Closures of earth dams are not recommended due to their importance to herbivores. Less utilised waterhole types are also important, mitigating the impact of herbivore damage to vegetation at earth dams. / Environmental Sciences / M. Sc. (Nature Conservation)

The present study compared Sand Forest bird assemblages found in a communal land area with that of the Tembe Elephant Park, and determined the habitat preference and status of selected herbivore species within the park. The study forms part of the Maputaland Conservation-based and Integrated Rural Development Programme of the Centre for Wildlife Management from the University of Pretoria and is linked to the activities of the Lubombo Transfrontier Conservation Area (LTFCA). The main purpose of the study was to compare Sand Forest bird assemblages found in the Tshanini Community Conservation Area, which is characterised by low levels of human utilisation, with that of the Tembe Elephant Park, which is characterised by wildlife utilisation. This approach was used to determine the biological importance of this communal land area in contributing towards the conservation of the rare Sand Forest habitat. Visual and auditory bird surveys revealed that the communal land area contains unique Sand Forest bird assemblages, which demonstrated the biological importance of the communal land for Sand Forest conservation, especially from an avian perspective. The second purpose of the study was to identify possible competition between selected herbivore species within the Tembe Elephant Park and/or a decrease in numbers of rare species. Herbivores that might be adversely affected by the destruction of the Sand Forest, or who may themselves have a destructive effect on the Sand Forest were also identified. Target herbivores included the nyala Tragelaphus angasii, impala Aepyceros melampus, Burchell’s zebra Equus burchellii, greater kudu Tragelaphus strepsiceros, red duiker Cephalophus natalensis and suni Neotragus moschatus. Road transects were used to record the spatial distribution of the target herbivores, and the vegetation types that were used more or less often than expected were subsequently determined. None of the target herbivores showed a preference for the Sand Forest or appeared to have a destructive effect on the Sand Forest. The suni, however, reached its highest density within the Sand Forest and the destruction of this habitat will therefore negatively affect the suni population. In several parks and reserves that aim to conserve a variety of species, it has been necessary to control the populations of highly competitive species. Both the nyala and the impala are highly competitive and occur in relatively high numbers within the Tembe Elephant Park, and consequently their population numbers should be kept sufficiently low in order not to have a negative influence on the vegetation or the survival of less competitive ungulates. Total aerial counts and transect distance sampling counts indicated an increase in the numbers of all the target herbivores. It is important to protect a viable portion of the preferred habitat of every target species within a reserve, and to keep competition with rare species to a minimum for the long-term survival of the regional biodiversity. Key aspects of wildlife and their habitat should be monitored so that trends are noted in time, and management adjustments can be made accordingly. / Dissertation (MSc (Wildlife Management))--University of Pretoria, 2007. / Centre for Wildlife Management / unrestricted

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2014-09-29T14:10:59Z No. of bitstreams: 2 Teixeira, Laura Helena Marcon-2013-tese.pdf: 2830610 bytes, checksum: 659f08910c5e986bd655384eca69bff1 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2014-09-29T15:12:12Z (GMT) No. of bitstreams: 2 Teixeira, Laura Helena Marcon-2013-tese.pdf: 2830610 bytes, checksum: 659f08910c5e986bd655384eca69bff1 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2014-09-29T15:12:13Z (GMT). No. of bitstreams: 2 Teixeira, Laura Helena Marcon-2013-tese.pdf: 2830610 bytes, checksum: 659f08910c5e986bd655384eca69bff1 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2013-08-30 / Fundação de Amparo à Pesquisa do Estado de Goiás - FAPEG / Pneumonia is of the main causes of death of children under 5 years of age. Several health organizations worldwide, public and private, are engaged in investigating the disease and evaluate the effectiveness of mechanisms to prevent and combat existing. Infections causing pneumonia can be avoided. However, especially in poor countries, the resources to promote prevention are scarce. Thus the combat actions need to be very efficient and effective. To ensure the effectiveness of these actions, such as vaccines, are necessary statistical information like age range, region, period, social status and history obtained through field research. This paper proposes and implements a software architecture for the construction, use and maintenance of research of childhood pneumonias. The techniques, technologies, tools and services used in defining the architecture were chosen with a focus on low cost. This way is much more feasible to use software for automated search systems by healthcare entities that have few financial resources. / As pneumonias estão entre as principais causas de morte das crianças com menos de 5 anos de idade. Várias entidades de saúde no mundo todo, públicas e privadas, estão empenhadas em investigar a doença e avaliar a eficiência dos mecanismos de prevenção e combate existentes. As infecções que causam pneumonia podem ser evitadas. No entanto, principalmente em países pobres, os recursos para promover a prevenção são escassos. Assim as ações de combate precisam ser muito eficientes e eficazes. Para garantir a efetividade dessas ações, como as vacinas, são necessárias informações estatísticas como faixa etária, região, época, condição social e histórico obtido através de pesquisa em campo. Este trabalho propõe e implementa uma arquitetura de software para construção, uso e manutenção de sistemas de pesquisa das pneumonias na infância. As técnicas, tecnologias, ferramentas e serviços utilizados na definição da arquitetura foram escolhidos com foco no baixo custo. Dessa forma fica muito mais viável a utilização de softwares para sistemas de pesquisa automatizados por entidades de saúde que possuem poucos recursos financeiros.

For decades scientists believed that herbivory had minimal impact on freshwater ecosystems. We now know that herbivory in freshwater systems equals or exceeds herbivory in terrestrial and marine systems. In extreme cases, herbivores can change clear, macrophyte dominated ecosystems into turbid plankton dominated ecosystems. Even though research on plant-herbivore interactions in freshwater systems has increased, there is still much that is unknown. This thesis is comprised of four studies investigating freshwater plant-herbivore interactions across multiple spatial scales. The first study investigated how induced chemical defenses in Cabomba caroliniana suppress herbivore consumption and growth as well as how this herbivore-generated change in plant chemistry affects the growth of plant associated microbes. At the spatial scale of individual ponds or lakes, consumers that induce their host plants may also be indirectly affecting other consumers and microbial pathogens via changes in this shared resource. The second study moves to an ecosystem scale and investigates how exotic versus native apple snails may impact Everglades' habitats. We investigated plant preference, consumption, growth and conversion efficiencies in the singly native apple snail to occur in the U.S. (Pomacea paludosa) versus four introduced species (P. canaliculata, P. insularum, P. haustrum and P. diffusa). We found that even though plant preferences are similar, invasive snails tend to eat more, grow more rapidly, and sometimes more efficiently than natives. This suggests that invasive species could have a large impact on the environment, especially the abundance of submerged plants. The third study investigated how palatability of freshwater plants varies with latitude (i.e. geographic scale). Increased herbivory at lower latitudes is hypothesized to select for increased plant defenses, which has been shown to be true for tropical forests, salt marshes, and seaweeds. When we contrasted eight confamilial plants collected in Indiana versus Southern Florida, three of four herbivores significantly preferred northern plants. When we evaluated a second set of plants collected from Indiana versus Central Florida, only one of three herbivores preferred the northern plants. Overall, our results suggest a preference for northern plants, but the strength of this relationship was variable. We hypothesize that this variability may be driven by 1) local variance in herbivore pressure that creates variance in plant defenses, and/or 2) the effect of winter length on the survival and feeding rate of herbivores. The final study expanded to a world scale, and investigated herbivore preference for native vs exotic plants. We found that both N. American crayfish and S. American snails preferred exotic plants over confamilial natives, despite responding to different plant characteristics. The single species of apple snail that occurs in N. American showed no preference for native or exotic plants from a N. American perspective, but instead exhibited preferences that correlated with its history of evolution in S. America. As the N. American species is a sister species of the S. American snails, feeding by the N. American snail appears more affected by its S. American lineage than its recent history in N. America. This suggests that phylogenetic legacy will affect choices of the herbivore as well as resistance or susceptibility of plants.