I compared the strength of bottom- up and top-down effects on insect herbivores along a natural salinity gradient in salt marsh communities in West - Central, Florida. I used a 2x2 factorial design with plots divided into four different treatments: 1) fertilizer applied to increase plant quality 2) sticky traps added to remove natural enemies (parasitoids) 3) fertilizer applied and sticky traps added and 4) control plots. These plots were placed on 7 different sites containing the salt marsh plant Borrichia frutescens along a natural stress salinity gradient. In each plot I determined the abundance of the sap sucker Pissonotus quadripustulatus, the gall maker Asphondylia borrichiae, spiders and the number of chewed leaves and bored stems. I also recorded leaf area, plant density, plant height and foliar nitrogen. Plants in fertilized plots exhibited increased height, density and leaf area.

<p>Plants commonly produce multiple, seemingly redundant defenses, but the reasons for this are poorly understood. The specificity of defenses to particular herbivores could drive investment in multiple defenses. Alternatively, genetic correlations between defenses could lead to their joint expression, even if possessing both defenses is non-adaptive. Plants may produce multiple defenses if putative resistance traits do not reduce damage, forcing plants to rely on tolerance of damage instead. Furthermore, resource shortages caused by herbivore damage could lead to compensatory changes in expression and selection on non-defense traits, such as floral traits. Natural selection could favor producing multiple defenses if synergism between defenses increases the benefits or decrease the costs of producing multiple defenses. Non-linear relationships between the costs and benefits of defense trait investment could also favor multiple defenses.</p><p>Passiflora incarnata (`maypop') is a perennial vine native to the southeast United States that produces both direct, physical traits (leaf toughness and trichomes) and rewards thought to function in indirect defense (extrafloral nectar in a defense mutualism with ants), along with tolerance of herbivore damage. I performed two year-long common garden experiments with clonal replicates of plants originating from two populations. I measured plant fitness, herbivore damage, and defense traits. I ran a genotypic selection analysis to determine if manipulating herbivore damage through a pesticide exclusion treatment presence mediated selection on floral traits, and if herbivore damage led to plastic changes in floral trait expression. To evaluate the role of selection in maintaining multiple defenses, I estimated fitness surfaces for pairwise combinations of defense traits and evaluated where the fitness optima were on each surface. </p><p>I found that resistance traits did not reduce herbivore damage, but plants demonstrated specific tolerance to different classes of herbivore damage. Tolerance was negatively correlated with resistance, raising the possibility that tolerance of herbivore damage instead of resistance may be the key defense in this plant, and that production of the two type of defense is constrained by underlying genetic architecture. Plants with higher levels of generalist beetle damage flowered earlier and produced proportionally more male flowers. I found linear selection for both earlier flowering and a lower proportion of male flowers in the herbivore exclusion treatment. I found that selection favored investment in multiple resistance traits. However, for two tolerance traits or one resistance and one tolerance trait, investment in only one trait was favored. </p><p>These results highlight the possibility of several mechanisms selecting for the expression of multiple traits, including non-defense traits. Resistance traits may have a non-defensive primary function in this plant, and tolerance may instead be a key defense strategy. These results also emphasize the need to consider the type of trait--resistance or tolerance--when making broad predictions about their joint expression.</p> / Dissertation

Although macroalgae usually are inconspicuous on pristine coral reefs, they often thrive on reefs that are subjected to various types of anthropogenic disturbance. This thesis consists of five papers and investigates how biomass and composition of macroalgal communities on coral reefs are affected by regulating factors, such as nutrient availability, herbivory, substrate availability and hydrodynamic forces. In addition, ecological functions and potential impacts of both wild and farmed macroalgal communities are evaluated. Paper I describes a method for using macroalgal tissue nutrient concentrations as bioindicator for nutrient availability, with the possibility to map nutrient loading from larger coastal cities. Papers II and III are manipulative studies comparing top-down and bottom-up regulation of macroalgal communities, where herbivore consumption seems to be the main regulator of biomass whereas nutrient availability mainly influences community composition. Exclosure of large-bodied herbivores had a positive influence on algal biomass in both studies, and during different climatic periods. Paper III also includes the influence of hydrodynamic forces on algal community biomass and structure by comparing a reef crest and a back reef-habitat. Alterations of top-down and bottom-up regulation generally had a stronger effect within the protected back reef-habitat, suggesting that such environments may be more sensitive to anthropogenic influence. Paper IV confirms the general conclusions from papers II and III by studying macroalgal biomass and composition on reef sites with different environmental prerequisites. This study also supports the notion that herbivorous fish can suppress accumulation of macroalgal biomass if substrate availability is low, but not where coral cover is reduced and plenty of substrate is open to macroalgal colonization. The study also found a large temporal variation of macroalgal standing stock and associated nutrients at sites with low top-down regulation. Paper V evaluates potential impacts of seaweed farming on coral reefs and nutrients in the seascape by experimentally studying growth, survival and nutrient binding capacity of Eucheuma denticulatum. This study showed that seaweed farms counteract eutrophication through nutrient extraction and that the risk of farmed algae colonizing local reefs seems to be small as they were rapidly consumed. In conclusion, the studies in this thesis contribute to the understanding of macroalgal regulation and function in tropical seascapes, thereby adding to the knowledge base for coastal management. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript. Paper 5: Manuscript.</p>

Although rather inconspicuous on healthy coral reefs, macroalgae form the basis of coral food webs. Today, macroalgae are generally increasing and many reefs undergo transitions from coral to macroalgal dominance resulting from e.g. enhanced nutrient loading or increased fishing. This thesis aims to investigate the relative importance of top-down and bottom-up regulation, and different herbivore types, on macroalgal distribution, fecundity and community composition on coral reefs. Papers I and II indicate that macroalgal abundance in a coral reef system is largely governed by top-down regulation through grazing by herbivores, while bottom-up regulation through enhanced nutrient availability rather influence algal species composition. Paper II also shows that these regulating effects are not as evident in an area with relatively strong water motion, suggesting that impacts of anthropogenic disturbance may be site-specific. Paper III shows that herbivory is an important factor influencing macroalgal growth and subsequent reproduction. Furthermore, Paper IV and V conclude that efficiency in removing macroalgal biomass is dependent on the type of dominant herbivore, where sea urchins seem to be more effective than fish. Paper IV indicates a seasonal variation in macroalgal biomass and distribution in a small geographic scale but with relatively high temporal resolution. Paper V on the other hand shows these same effects, but with a focus on geographic variation, including a large part of the East African region, as well as between year temporal variations in Kenya. Together, results from the two latter studies indicate that herbivory by fish may not be able to prevent a macroalgal bloom in a degraded system where substrate availability for algal colonization is high, but that it may still facilitate coral recovery over time. Thus, a large algal biomass may not necessarily indicate a reef beyond the possibility of recovery. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Accepted. Paper 4: Manuscript. Paper 5: Manuscript.</p>

Aircraft strikes are a significant safety hazard on airports worldwide. Wildlife management at airfields is the most effective tactic to reduce airstrike risk – to modify the habitat to be undesirable to animals. Tall fescue grasses containing a fungal symbiont may serve that purpose. They produce alkaloids that convey resistance to some grass-feeding invertebrates, which might in turn reduce incidence of insectivorous birds. A commercial endophytic grass (Avanex™) consisting of ‘Jackal’ tall fescue infected with a unique endophyte (AR 601) is purported to contain especially high levels of alkaloids and to reduce bird populations if planted at airports. I evaluated it against the common KY31 tall fescue with its wild-type endophyte for invertebrate and vertebrate deterrence. Invertebrate abundance, survival, growth, and development were generally similar on Jackal E+ or KY31 E+. Spanish goats and wild birds showed no avoidance of Jackal E+, nor did Jackal E+ contain significantly higher levels of alkaloids than did KY31 E+. The Avanex™ tall fescue was not any better than KY31 in deterring herbivores but the concept is sound. However, better understanding of the relationship between grass, endophyte, alkaloid, and herbivore is needed to inform how such grasses might be used to reduce bird strike hazard.

Global warming and increasing atmospheric nitrogen deposition are ranked as second and third most important global drivers of biodiversity loss. Widespread species losses have deep implications for the functioning of ecosystems, the delivery of essential ecosystem services and their resilience to future environmental perturbations. There is growing recognition that interactions between species play a crucial role in determining the response of ecosystems to global environmental changes. Moreover, evidence of synergistic effects between global change drivers has prompted numerous calls to integrate multiple drivers in ecological research. Nevertheless, empirical studies assessing the impacts of temperature and nitrogen on communities at multiple trophic levels are largely absent. This thesis explores the effects of temperature and nitrogen on a tri-trophic system comprising plants, herbivores and natural enemies. The first chapter shows impacts of the drivers on the composition and phenology of an herbivore community. The second chapter highlights changes in biomass under the treatments at three trophic levels. The third chapter explores, for the first time, the impacts of temperature and nitrogen on quantitative food webs. Finally, the last data chapter uses body size as an important species trait to gain insights on the mechanisms causing shifts in food web structure. The key findings of this thesis were i) trophic interactions largely mediated the effects of both global change drivers ii) In particular, strong bottom-up effects determined the system response, with herbivores responding positively and consistently more so than plants and parasitoids in particular. However, iii) this contrasting response was not explained by a phenological mismatch. iv) Food-web structure responded to the changes in composition of herbivores and parasitoids, but shifts in interaction structure did not affect the resilience of the food. However, temperature and nitrogen impacted host-parasitoid food-web structure by altering the response of parasitoid species to host density and size structuring, which is likely to bear consequences on host-parasitoid co-evolution and future food-web architecture and stability. Finally, v) we found frequent, non-additive interactions between the global change drivers. We conclude that co-occurring temperature and nitrogen are likely to alter food-web structure and overall ecosystem balance, with increasing herbivore dominance likely to have important implications for ecosystem functioning and food-web persistence.

Herbivory can have many effects on plant fitness, including altering plant-pollinator interactions and sexual reproduction in angiosperms. Pollinator-mediated interactions may be impacted when herbivores alter plant traits, such as floral display size, that can influence pollinator visitation rates, and, ultimately, the reproductive component of plant fitness. Here I describe an investigation into the indirect effects of feeding by beetles released as a biological control agent, Galerucella calmariensis and G. pusilla, on plant-pollinator interactions and reproductive output in the invasive plant Lythrum salicaria L. (purple loosestrife). During the summer of 2011, three treatments (low, ambient and mechanical herbivory) were applied to 105 plants during the pre-flowering period of growth. At the onset of flowering, a series of pollinator observations were conducted over the course of approximately 1.5 weeks. Several aspects of floral display were affected by the herbivory treatments, including increased inflorescence and flower production in the ambient and mechanical herbivory treatments, relative to the low herbivory treatment. Treatment type did not have a significant effect on the number of pollinator foraging bouts, but had marginally significant effects on the number of flowers probed per pollinator foraging bout and per 30-minutes. Moreover, treatment had a significant effect on the number of switches among the inflorescences on a single plant. I discuss the possibility that the differences in pollinator visitation were mediated by differences in the architecture and the size of floral display. There were no detectable differences in fruit or seed production (i.e., female fitness) among treatments. However, as I discuss, differences in pollinator visitation may affect other unmeasured aspects of fitness, such as the level of inbreeding or the number of seeds sired through male function.

Plant populations near the northern limits of their geographic distribution may experience different biotic pressures than southern populations. For instance, if herbivores are scarce in northern populations, performance of their host plants may benefit. In this study, I looked at populations of burdock (Arctium minus) along an 815 km latitudinal gradient from the northern range limit to more southern populations. I found that plant height, stem diameter, and number of seeds all increased on approaching the northern limit. In addition, I also found significant decreases in herbivory by generalist and specialist leaf and seed predators, even though northern plants invested less in physical and possibly chemical defenses. In an experiment in which seeds were planted in different soils, marginal soil initially produced smaller plants, but subsequently larger plants than soil from southern populations. These results indicate northern populations experience relaxed pressure from natural enemies and may benefit as a result.

Plant populations near the northern limits of their geographic distribution may experience different biotic pressures than southern populations. For instance, if herbivores are scarce in northern populations, performance of their host plants may benefit. In this study, I looked at populations of burdock (Arctium minus) along an 815 km latitudinal gradient from the northern range limit to more southern populations. I found that plant height, stem diameter, and number of seeds all increased on approaching the northern limit. In addition, I also found significant decreases in herbivory by generalist and specialist leaf and seed predators, even though northern plants invested less in physical and possibly chemical defenses. In an experiment in which seeds were planted in different soils, marginal soil initially produced smaller plants, but subsequently larger plants than soil from southern populations. These results indicate northern populations experience relaxed pressure from natural enemies and may benefit as a result.

O presente estudo apresenta uma re-análise dos registros de interação inseto-planta na “Flora Glossopteris”, relativos ao Permiano Inferior da Bacia do Paraná, no Rio Grande do Sul e Santa Catarina. O material preservado na forma de impressões/compressões foliares é proveniente do topo do Grupo Itararé, do Grupo Guatá (Formação Rio Bonito) e do Grupo Passa Dois (Formação Irati), e dos afloramentos Morro do Papaléo, Rio da Estiva, Mina do Faxinal, Quitéria e Minas do Leão. O principal objetivo foi analisar os registros existentes e as novas evidências de interações inseto-planta em megáfilos do Permiano Inferior da Bacia do Paraná, nos Estados do Rio Grande do Sul e Santa Catarina, a fim de verificar possíveis padrões de distribuição dos danos. O trabalho foi dividido em três etapas, sendo a primeira uma revisão da coleção DPE-IG-UFRGS, para levantamento de novas amostras com evidencias de fitofagia e exame do material já descrito na literatura. A segunda etapa consistiu na descrição do material inédito, proveniente do afloramento Rio da Estiva (SC), cedido pela coleção GSA-IG-USP, a qual culminou na elaboração do artigo que compõe o primeiro capítulo desta dissertação. A terceira e última etapa correspondeu à análise da existência de especificidade entre os padrões de herbivoria e os distintos gêneros foliares e da importância do sítio deposicional na ocorrência das interações inseto-planta no registro fóssil. Para tanto, foram utilizadas ferramentas estatísticas multivariadas (PCoA, MANOVA). Essa última etapa resultou no artigo apresentado no segundo capítulo da dissertação. Como resultado, encontrou-se no afloramento Rio da Estiva apenas 10 amostras de com sinais de consumo por artrópodes, que apresentaram somente três padrões de danos: consumo de margem foliar e remoção ovóide e linear de lâmina foliar. As folhas herbivorizadas foram classificadas como Glossopteris sp., Glossopteris communis, Glossopteris occidentalis e Gangamopteris obovata. Quanto à especificidade dos danos, a análise de variância indicou diferença significativa entre os gêneros foliares em relação aos padrões de fitofagia (P = 0.006). Glossopteris sp. e Cordaites sp diferiram entre si (P = 0.008), assim como Gangamopteris sp. e Cordaites sp. (P = 0.04). Entretanto, Glossopteris sp. não diferiu de Gangamopteris sp. Os afloramentos também diferiram em relação aos tipos de danos encontrados (P = 0.001). A evidência de consumo de tecidos foliares indica que as glossopterídeas eram herbivorizadas predominantemente por insetos mandibulados. Os resultados sugerem a existência de especificidade entre os insetos herbívoros e a vegetação permiana. As diferenças encontradas entre os padrões de consumo entre as diferentes localidades sugerem que a herbivoria era mais intensa em certas comunidades de plantas do que em outras. / The present study offers a re-analysis of plant-insect interaction records in “Glossopteris Flora”, from Paraná Basin (Lower Permian), found in Rio Grande do Sul e Santa Catarina states. The material preserved as leaf impressions/compressions come from Itararé Group, Guatá Group (Rio Bonito Formation) and Passa Dois Group (Irati Formation), and from five localites: Morro do Papaléo, Faxinal Mines, Rio da Estiva, Faxinal, Quitéria and Minas do Leão outcrops. The main goal was study the records of plant-insect evidences in megaphylls of Lower Permian, from Paraná Basin, in states of Rio Grande do Sul e Santa Catarina, to verify possible patterns of damages distributions. The work was divided in three stages: the first was a reviewed of DPE-IG-UFRGS collection, to survey new samples with evidence of phitophagy and examine the material described in literature. The second stage consisted in the description of the material from Rio da Estiva outcrop (SC), hand over by GSA-IGUSP collection. These results can be found in the first chapter of this dissertation. The third and last stage was the analysis of existence of specificity between the damage types and the leaf genera, and the importance of deposicional site in the presence of insect-plant interactions in the fossil record. For this, a Principal Coordinate Analyses (PCoA) and a multidimensional analysis of variance (MANOVA) was carried out. This last step resulted in a paper present at second chapter of the dissertation. As a result, in Rio da Estiva outcrop we found only ten samples with signs of consumption by arthropods, showing just three patterns of damages: removal of foliar edge, and ovoid and linear removals of foliar lamina. The leaves were classified as Glossopteris sp., Glossopteris communis, Glossopteris occidentalis and Gangamopteris obovata. As to damage specificity, the analyses of variance indicated that foliar genera differed significantly in relation to herbivory patterns (P = 0.006). Glossopteris sp. and Cordaites sp differed to each other (P = 0.008), as well as Gangamopteris sp. in relation to Cordaites sp. (P = 0.04). However, Glossopteris sp. did not differ from Gangamopteris sp. Sites also differed significantly in relation to damage types (P = 0.001). The evidence of consumption of foliar tissues indicates that glossopterids hosted a functional feeding group of predominantly mandibulate insects. The results suggest the existence of specificity between insects and the Permian vegetation. The differences found in the patterns and frequencies of consumption in different localities suggest that herbivory was more intensive in some plant communities than in others.