Plants and insects have been interacting with each other for millions of years which have resulted in a coevolution, forcing both to maximize their fitness and not to be left behind in the race of survival. Insects select which individuals to graze on based on plant qualities that enhance their fitness, yet the factors influencing their choice remain understudied. This study aimed to elucidate why certain plant individuals suffer higher rates of herbivory within populations. Three plant species from different habitats in Scandinavia were surveyed: Sorbus aucuparia (rowan), Salix herbacea (dwarf willow), and Lactuca sibirica (Siberian lettuce). Using standardized protocols from the Herbivory Variability Network, 30 plant individuals were randomly selected in each site and surveyed for herbivore damage. Additionally, data were collected on the nearest neighbor of each plant (representing the same species), resulting in a total of 60 surveyed plants. Results revealed varied herbivory patterns among the species, indicating differential influences of plant size, growth stage, and neighboring plants on herbivory rates. An association between leaf and berry herbivory was found, suggesting that berries are less likely to sustain damage when leaves are already damaged. It suggests that trees retaining undamaged leaves are more proficient in photosynthetic processes and, thus capable of synthesizing berries enriched with higher concentrations of sugars and essential nutrients making them more attractive to insects. There is reason to believe that chemical defenses within the plants play an important role in the result seen in this study. This result provides insight into the behavior of insects, highlighting the complexity of plant-insect interactions and the need for further research to understand the factors driving herbivory patterns.

Plants adapt genetically and phenotypically to abiotic and biotic environmental conditions, and associated changes in their traits and investment strategies may affect their palatability to herbivores. This study aims to investigate if ecosystem retrogression results in heritable adaptation of Betula pubescens and how this impacts seedling growth, response to fertilizer, and palatability to the herbivore Spodoptera littoralis. Seeds were collected from a retrogressive island chronosequence for which nutrient availability increased with island size. Seeds were grown in a common garden and a fertilizer experiment was carried out to analyze genetic and phenotypic adaptations to nutrient availability. A bioassay using S. littoralis larvae was conducted to reveal the effect of adaptations to nutrient availability and herbivory on plant palatability. Only the root-to-shoot ratio indicated any heritable adaptation, being higher for seedlings originating from small islands. Seedlings showed highly plastic responses to fertilizer, indicative of an increased acquisition of resources. The palatability of B. pubescens was mainly determined by a tradeoff between leaf dry matter content and specific leaf area and was reduced by induced defenses. The acquisition of resources, growth, and reproduction of B. pubescens appears to be driven largely by phenotypic plasticity rather than prior genetic adaptation. Since all treatment responses were independent of island size, the whole population may be resilient to future changes in environmental conditions. The study revealed that ecosystem retrogression does not have to result in heritable plant adaptations, even if changes in ecosystem conditions can be substantial. It is of great importance to gain more knowledge on how species may adapt to future changes in environmental conditions over different timescales, both to naturally and anthropogenically induced changes.

Insect herbivory on forest canopies strongly affects ecosystem nutrient cycling and availability in a variety of ways, e.g. by changing the quantity, quality and timing of nutrient input to forest soils. A qualitative method for measurements of ingestion, egestion and exuviation rates of the insect Chrysomela tremulae on leaves of the hybrid Populus tremula x tremuloides were tested in this study with the aim to detect differences in relative nutrient cycling efficiencies. The assimilation efficiency (AD), efficiency of conversion of digested food (ECD) and efficiency of conversion of ingested food (ECI) increased from 1st, through 2nd and 3rd instar larvae with generally higher efficiencies for nitrogen than carbon. Effects on nutrient limitations for the insect were also tested by increasing the C:N ratio of insect diet. A carbohydrate solution was painted onto leaves which resulted in a significant increase in C:N (p<0.0001). This lead to a trend of lengthened developmental time for each ontogenetic stage, as well as higher ingestion rate and lower egestion- and exuviation rates. However, a different method of increasing the C:N ratio is recommended in future experiments since the leaves never truly absorbed the solution.

Thesis (MSc (Conservation Ecology and Entomology))--Stellenbosch University, 2009. / ENGLISH ABSTRACT: An understanding of the interactions of herbivores, plant nutrients and soil properties is crucial for grazing management. Of particular interest are plant palatability and herbivore grazing preferences. These aspects, the focus of this thesis, were studied in a Swartland Shale Renosterveld and Swartland Alluvium Fynbos mosaic in the Western Cape of South Africa. This vegetation is classified as critically endangered due to the transformation of its landscape in favour of agricultural production and urban settlement. Pre-colonial herbivore vertebrates were hunted out by 1700, leading to a sparse knowledge of the early dynamics of the vegetation. However, currently game farmers and landowners are re-introducing selected species into the area. Thus, managers require knowledge on how to implement practical guidelines for best-practice grazing management. This study investigates, firstly, the relationship between plants and animals. This included seasonal assessment of seed germination from dung of bontebok and eland; the effect of stocking rates on plant palatability (crude protein, crude fibre, crude fat, moisture, tannin and mineral) of herbage was studied with the aim to understand how palatability influences herbivore forage decisions. Secondly, this study looked at how stocking rates influence soil nutrients (nitrogen, phosphorus), and others soil properties such as pH and soil moisture. The distribution of alien grasses was facilitated by grazers. About 58 % of grasses germinated from the dung of eland and Bontebok were alien species. Additionally, there was significant variation in palatability related to grazing pressure and plant maturity between sites and over seasons. Grasses on the high grazing site had higher carbohydrate (3%-5% higher) and protein content (1%-5% higher) than at the least grazed site. Mature grasses contained less water (10%-20%), but no obvious variation in tannin concentration than immature grasses. However, species such as Ficinia sp. showed variations with grazing pressure and maturity. Ficinia sp. on the high grazing site had higher tannin concentration (5mg/ml-22mg/ml) and crude protein (4%-9%) than at the least grazed site. When the plant ages, tannin concentration increase (ranging from 15% to19% higher). Two types of plant were recoreded according to their chemical response following grazing pressure. These types are 1) plants that are grazing tolerant and which produce more carbohydrate when grazed and 2) plants that are grazing intolerant under high grazing pressure and which produce chemical defence compounds such as tannin to deter herbivores attacks. The results indicate that in fynbos and renosterveld, the relationship between preference and plant chemical compounds is not consistent since no IV patterns emerged to explain what compounds drive preference. A combination of chemical compounds may be the reason for the selection by the grazers; alternatively, other compounds not included in the study may influence the forage selection by an herbivore. The second part of the study showed that stocking rates appeared to have a significant effect on soil properties investigated. Soil moisture was significantly affected by the stocking rate in autumn. The high grazing intensity site had the lowest soil moisture especially in autumn (10% lower than the control site), likely due to heavy trampling and soil compaction. pH was the lowest at the high grazing intensity site in all seasons compared to the control site. Likely reasons were the high deposition of nitrogen through dung and urine deposition, high removal of basic cations and animal exportation through hunting activities. Lastly, grazing maintains inorganic nitrogen at stable levels regardless of seasonal changes and increases the concentration of phosphorus especially under high grazing pressure compare to less grazed sites. The grazing dynamics of Swartland Shale Renosterveld - Swartland Alluvium Fynbos mosaic system are complex and multifaceted. Farmers need to pay attention to the nutritional status of plant species grazed to know whether they meet the nutritional requirements of the game in the area. Overstocking should be avoided in this system as it triggers the production of tanniferous compounds that could decrease the survivorship of herbivores. Moderate grazing 0.09 LAU/ha pressure provides the best stocking rates for effective grazing management. / AFRIKAANSE OPSOMMING: Vir suksesvolle weidingsbestuur is dit noodsaaklik om die interaksie tussen herbivore, plantvoedingstowwe en grondeienskappe te verstaan. Van besondere belang is plantsmaaklikheid en herbivore se weidingsvoorkeure. Hierdie aspekte, wat die fokus van hierdie tesis is, is bestudeer in ‘n Swartland Shale Renosterveld en Swartland Alluvium Fynbos-mosaïek in die Wes-Kaap Provinsie van Suid-Afrika. Hierdie plantegroei word as kritiek bedreigd geklassifiseer weens die transformering van sy landskap ten gunste van landbou-aktiwiteite en stedelike vestiging. Pre-koloniale herbivoor vertebrata is teen 1700 deur jagters uitgeroei, wat gelei het tot min kennis oor die vroeë dinamiek van die plantegroei. Wildsboere en grondeienaars is egter besig om geselekteerde spesies in die area te hervestig. Bestuurders moet dus weet hoe om praktiese riglyne vir beste-praktyk weidingsbestuur te implementeer. Hierdie studie ondersoek eerstens die verhouding tussen plante en diere. Dit sluit seisoenale evaluering van saadontkieming uit die mis van bontebokke en elande in; die effek van veegetalle op plantsmaaklikheid (ruproteïen, ruvesel, ru-vet, vogpeil, tannien en minerale) van die weiveld is bestudeer om vas te stel hoe plantsmaaklikheid herbivore se weidingsbesluite beïnvloed. Tweedens het die studie die invloed van veegetalle op grondvoedingstowwe (stikstof, fosfor) ondersoek, asook ander grondeienskappe soos pH en grondvogpeile. Die verspreiding van uitheemse grasse is deur weidende diere gefassiliteer. Ongeveer 58% van alle grasse wat uit die mis van elande en bontebokke ontkiem het, was uitheemse spesies. Verder was daar beduidende variasie in plantsmaaklikheid verwant aan beweidingsdruk en plantvolwassenheid tussen verskillende persele en oor seisoene. Grasse op die hoogs beweide persele het 3%-5% hoër koolhidraatinhoude en 1%-5% hoër proteïeninhoude gehad as die minder beweide persele. Volwasse grasse het 10%-20% minder water bevat as onvolwasse grasse, maar het nie in terme van tannienkonsentrasie van die onvolwasse grasse verskil nie. Spesies soos Ficinia sp. het variasies getoon met beweidingsdruk en volwassenheid. Ficinia sp. het op die hoog-beweide perseel ‘n hoër tannienkonsentrasie (5mg/ml-22mg/ml) en meer ruproteïen (4%-9%) gehad as op die minste beweide perseel. Wanneer die plant verouder, verhoog die toename in tannienkonsentrasie (met tussen 15% en 19%). Twee tipes plante is aangeteken volgens hul chemiese response ná beweidingsdruk. Hierdie tipes is 1) plante wat beweidingstolerant is en wat meer koolhidrate produseer wanneer hulle as weiding dien en 2) plante wat onder hoë beweidingsdruk beweidingsintolerant is en wat chemiese verbindings VI soos tannien produseer om herbivooraanvalle af te weer. Die resultate dui aan dat die verhouding tussen voorkeur en plante se chemiese verbindings nie konstant bly in fynbos en renosterveld nie, aangesien geen patrone na vore getree het wat kon verklaar watter verbindings bepalend is vir voorkeur nie. ‘n Kombinasie van chemiese verbindings mag die rede wees waarom die herbivore sekere plante verkies; alternatiewelik mag ‘n herbivoor se plantseleksie beïnvloed word deur chemiese verbindings anders as dié wat in hierdie studie ondersoek is. Die tweede deel van die studie het aangetoon dat veegetalle blyk ‘n beduidende invloed te hê op die grondeienskappe wat ondersoek is. Grondvogpeile is in die herfs beduidend beïnvloed deur die veegetalle. Die perseel met die hoë beweidingsintensiteit het die laagste grondvogpeil gehad, veral in die winter (10% laer as dié van die kontrole-perseel), waarskynlik weens erge getrappel en grondkompaktering. Vergeleke met die kontrole-perseel was pH die laagste op die perseel met die hoë beweidingsintensiteit, in alle seisoene. Waarskynlike redes hiervoor is die hoë neeerslag van stikstof deur mis- en uriene-neerslae, hoë verwydering van basiese katione en dierevervoer wat deur jagaktiwiteite teweeg gebring word. Laatstens behou weiding anorganiese stikstof teen stabiele vlakke ongeag van seisoenale veranderinge en toenames in die konsentrasie van fosfor, veral onder hoë beweidingsdruk vergeleke met minder beweide persele. Die weidingsdinamiek van die Swartland Shale Renosterveld - Swartland Alluvium Fynbosmosaïeksisteem is kompleks en veelvlakkig. Boere behoort aandag te skenk aan die voedingstofstatus van die plantspesies wat as weiding dien, sodat hulle kan weet of die voedingsbehoeftes van die wild in die omgewing bevredig word. Die aanhou van te veel vee in hierdie sisteem behoort vermy te word aangesien dit as sneller dien vir die produksie van tannienbevattende verbindings wat die oorlewingsvermoë van herbivore kan verlaag. Matige beweidingsdruk (0.09 LAU/ha) bied vir effektiewe weidingsbestuur die beste veegetalle.

Dans certains cas, la colonisation des zones humides par les espèces animales et végétales peut être une menace majeure pour la biodiversité. Il est donc primordial de mieux connaître l'écologie des espèces colonisatrices pour définir leurs relations avec le reste de l'écosystème. Nous avons étudié les conséquences de la colonisation relativement récente des étangs piscicoles français par le cygne tuberculé (Cygnus olor). Nous nous sommes intéressés à l'expression de cette colonisation dans l'espace par l'étude des processus de sélection de l'habitat. Nos résultats montrent que dans un paysage d'étangs, la répartition des cygnes tuberculés dépend à la fois de la configuration spatiale des étangs (aire isolement), des ressources disponibles et du statut de reproduction des cygnes tuberculés. Nous avons ensuite étudié les interactions entre le cygne tuberculé et les communautés animales et végétales des étangs. Sur les sites de cantonnement des couples, nous n'avons pas montré d'effet de la présence des cygnes tuberculés sur l'abondance des oiseaux d'eau, et aucune forme d'exclusion spatiale à l'échelle de l'étang. En revanche, les cygnes tuberculés peuvent générer une déplétion significative des herbiers de macrophytes aquatiques, suggérant des effets en cascade sur les autres communautés des étangs piscicoles. Comme toute perturbation générée par une espèce colonisatrice, celle associée à l'arrivée des cygnes doit néanmoins être replacée dans le contexte plus large des régimes de perturbations à l'oeuvre sur l'écosystème, ce qui importe particulièrement dans le cas d'écosystèmes aussi dépendants de l'activité humaine que les étangs piscicoles. / In some cases, wetland colonization by animals and plants may be a major threat to biodiversity. It is therefore crucial to better understand the ecology of colonizing species to assess their relationships with the other elements of ecosystems. We studied the consequences of the relatively recent colonization of French fishponds by mute swan (Cygnus olor). We especially considered how such colonization now translates into space, through the analysis of habitat selection processes. Our results show that swan distribution within a fishpond landscape depends on fishpond spatial configuration (area isolation), available resources as well as mute swan breeding status. We then analysed the relationships between mute swan and fishpond animal and plant communities. Where swan pair settle, we do not demonstrate any effect of swan presence on the abundance of other waterbirds, nor any spatial exclusion within fishponds. Conversely, mute swans can signif icantly deplete aquatic macrophyte beds, suggesting cascade effects on other fishpond communities are possible. Like any perturbation caused by a colonizing species, that associated with swan arrival however has to be considered in the broader context of perturbation regimes onto the ecosystem. This is especially crucial in ecosystems like fishponds, that are so much dependent upon human activity.

Testing ecological theory at macroecological scales may be useful for disentangling abiotic influences from anthropogenic disturbances, and thus provide insights into fundamental processes that structure ecological communities. In tropical coral reef systems, our understanding of community structure is limited to small-scale studies conducted in moderately degraded regions, while larger regional or ocean scale analyses have typically focused on identifying human drivers of reef degradation. In this thesis, my collaborators and I combined stable isotope specimens, underwater visual censuses, and remote sensing data from 43 Pacific islands and atolls in order to examine the relative roles of natural environmental variation and anthropogenic pressures in structuring coral reef fish and benthic communities. First, at unexploited sites on Kiritimati Atoll (Kiribati), isotope estimates indicated that trophic level increased with body size across species and individuals, while negative abundance ~ body size relationships (size spectra) revealed distinct energetic constraints between energy-competing carnivores and energy-sharing herbivores. After demonstrating size structuring of reef fish communities in the absence of humans, we then examined evidence for size-selective exploitation impacts on coral reefs across the Pacific Ocean. Size spectra 'steepened' as human population density increased and proximity to market center decreased, reflecting decreases in large-bodied fish abundance, biomass, turnover rate, and mean trophic level. Depletion of large fish abundances likely diminishes functions such as bioerosion by grazers and food chain connectivity by top predators, further degrading reef community resilience. Next, we considered the relative strengths of abiotic, biotic and anthropogenic influences in determining reef benthic state across spatial scales. We found that from fine (0.25 km2) to coarse (1,024 km2) grain scales the phase shift index (a multivariate metric of the relative cover of hard coral and macroalgal) was primarily predicted by local abiotic and bottom-up influences, such that coral-dominated reefs occurred in warm, productive regions at sites exposed to low wave energy, irrespective of grazing or human impacts. Our size- based analyses of reef fish communities revealed novel exploitation impacts at ocean-basin scales, and provide a foundation for delineating energetic pathways and feeding interactions in complex tropical food webs. Furthermore, we demonstrate that abiotic constraints underpin natural variation among fish and benthic communities of remote uninhabited reefs, emphasizing the importance of accounting for local environmental conditions when developing quantitative baselines for coral reef ecosystems. / Graduate / 0329

Increasing temperatures resulting from climate change have within recent years been shown to advance phenological events in a large number of species worldwide. Species can differ in their response to increasing temperatures, and understanding the mechanisms that determine the response is therefore of great importance in order to understand and predict how a warming climate can influence both individual species, but also their interactions with each other and the environment. Understanding the mechanisms behind responses to increasing temperatures are however largely unexplored. The selected study system consisting of host plant species of the Brassicaceae family and their herbivore Anthocharis cardamines, is assumed to be especially vulnerable to climatic variations. Through the use of this study system, the aim of this thesis is to study differences in the effect of temperature on development to start of flowering within host plant species from different latitudinal regions (study I), and among host plant species (study II). We also investigate whether different developmental phases leading up to flowering differ in sensitivity to temperature (study II), and if small-scale climatic variation in spring temperature influence flowering phenology and interactions with A. cardamines (study III). Finally, we investigate if differences in the timing of A. cardamines relative to its host plants influence host species use and the selection of host individuals differing in phenology within populations (study IV). Our results showed that thermal reaction norms differ among regions along a latitudinal gradient, with the host plant species showing a mixture of co-, counter- and mixed gradient patterns (study I). We also showed that observed differences in the host plant species order of flowering among regions and years might be caused by both differences in the distribution of warm days during development and differences in the sensitivity to temperature in different phases of development (study II). In addition, we showed that small-scale variations in temperature led to variation in flowering phenology among and within populations of C. pratensis, impacting the interactions with the butterfly herbivore A. cardamines. Another result was that the less the mean plant development stage of a given plant species in the field deviated from the stage preferred by the butterfly for oviposition, the more used was the species as a host by the butterfly (study IV). Finally, we showed that the later seasonal appearance of the butterflies relative to their host plants, the higher butterfly preference for host plant individuals with a later phenology, corresponding to a preference for host plants in earlier development stages (study IV). For our study system, this thesis suggest that climate change will lead to changes in the interactions between host plants and herbivore, but that differences in phenology among host plants combined with changes in host species use of the herbivore might buffer the herbivore against negative effects of climate change. Our work highlights the need to understand the mechanisms behind differences in the responses of developmental rates to temperature between interacting species, as well as the need to account for differences in temperature response for interacting organisms from different latitudinal origins and during different developmental phases in order to understand and predict the consequences of climate change. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript.</p>

Em resposta aos danos ocasionados por insetos, as plantas emitem voláteis que atraem os inimigos naturais desses herbívoros. Embora essa relação tritrófica venha sendo intensamente estudada, muitos mecanismos envolvidos nesta interação ainda permanecem inexplorados. Dentre os compostos voláteis induzidos por herbivoria e emitidos pelas plantas, os terpenos são os mais expressivos e abundantes. Em resposta ao dano ocasionado por um inseto, cascatas bioquímicas são iniciadas na planta, as quais podem alterar a expressão de genes envolvidos na resposta a tal dano. Este trabalho analisou as mudanças na expressão gênica e produção de compostos voláteis em plantas de milho, Zea mays (Poaceae)promovidas por lagartas Spodoptera frugiperda (Lepidoptera: Noctuidae) ao longo do tempo. Utilizando a técnica de PCR em tempo real (qRTPCR) foram verificadas respostas no nível da expressão gênica das plantas submetidas à indução por herbivoria. Foram analisados os genes de uma lipoxigenase e de três terpeno sintases, enzimas envolvidas na produção de compostos voláteis que atraem parasitóides de S. frugiperda. As plantas submetidas à herbivoria apresentaram níveis de expressão gênica e emissão de voláteis maiores do que as plantas sadias. Os resultados fornecem bases para o entendimento dos mecanismos endógenos responsáveis pela liberação de voláteis nas plantas visando o estabelecimento de novos fundamentos para o controle biológico de pragas. / In response to insect damage, plants emit volatiles that attract natural enemies of herbivores. Although this tritrophic interaction has been intensively studied, many mechanisms involved in this interaction remain unexplored. Among the herbivore-induced volatile compounds, terpenes are the most abundant and significant ones. In response to insect damage, biochemical pathways are activated, which can alter the expression of genes involved in the response to that damage. This study examined changes in gene expression and volatile compounds production in maize plants, Zea mays (Poaceae) promoted by Spodoptera frugiperda (Lep.: Noctuidae) caterpillars through time. Using the real-time PCR technique (qRT-PCR) we verified responses on the level of gene expression of plants subjected to herbivores feeding. We analyzed genes of lipoxygenase and three terpene synthases, enzymes involved in the synthesis of volatile compounds that attract parasitoids of S. frugiperda. Plants subjected to herbivory had higher levels of gene expression and volatile emission when compared to healthy plants. Results provide basis for better understanding of plant volatile emission endogenous mechanisms in order to set new foundations for biological control of pests.

As plantas, produtores da base das cadeias tróficas, apresentam diversos tipos de defesas contra a ação de consumidores, os herbívoros, podendo ser defesas físicas, químicas e bióticas. Nas defesas bióticas, plantas fornecem recursos alimentares (e.g. néctar extrafloral) e/ou moradia para predadores que em troca podem fornecer proteção contra herbívoros. Assim, a partir de comportamentos agressivos e/ou de patrulha, formigas são consideradas os principais protetores de plantas. Nessa perspectiva, a presente dissertação buscou investigar a influência que o néctar extrafloral tem sob a interação formiga-planta em uma área de Cerrado. O estudo foi realizado na Reserva Ecológica do Clube Caça e Pesca Itororó de Uberlândia, no município de Uberlândia, MG, em uma área com fitofisionomia de cerrado sentido restrito. A espécie de planta utilizada neste estudo foi Qualea multiflora (Vochysiaceae), uma das espécies mais abundantes do Cerrado, a qual apresenta nectários extraflorais (NEFs) na base do pecíolo foliar e nas inflorescências. Nossas hipóteses principais foram: a) que formigas visitantes dos NEFs de Q. multiflora impactam positivamente a planta, reduzindo a ação de herbívoros; b) que essas interações formigas-plantas são modificadas ao longo do desenvolvimento fenológico das folhas das plantas; c) que diferentes níveis de herbivoria nas plantas produzem também diferentes reações nas formigas visitantes; e d) que diferentes estruturas das plantas apresentam diferentes níveis de defesas. Os resultados demonstrados no Capítulo 1 comprovam que a herbivoria foliar em Q. multiflora foi baixa e similar nos diferentes estágios de desenvolvimento da folha, mostrando que as defesas expressas pela planta são eficientes. Das três defesas foliares avaliadas durante o desenvolvimento foliar, observou-se que a densidade de tricomas apresenta pico de efetividade no início do desenvolvimento, a defesa biótica (produtividade dos NEFs) apresenta pico de efetividade no período intermediário do desenvolvimento, e a dureza foliar apresenta pico de efetividade no período em que a folha já está adulta. Esses resultados comprovam a eficiência da variação temporal nas defesas foliares de Q. multiflora, o que interfere diretamente na interação formiga-planta. No Capítulo 2, foi mostrado que NEFs localizados em inflorescências produzem néctar mais volumoso e energético que atrai maior quantidade de formigas comparado ao néctar produzido pelos NEFs foliares. A produtividade e a atratividade dos NEFs, assim como o forrageamento de formigas, também foram afetados por variações na herbivoria (simulada experimentalmente). Esses resultados demonstram que Q. multiflora sincroniza suas defesas foliares ao longo do tempo garantindo a proteção contra herbívoros e que essas defesas (como evidenciado para defesa biótica) podem ser alteradas de acordo com o valor e probabilidade de ataque de suas estruturas. / Plants, producers of food chains, have different types of defenses against action of consumers, herbivores, which can be physical, chemical and biotic defenses. In biotic defenses, plants provide food resources (e.g. extrafloral nectar) and/or shelter for predators, which in turn may provide protection against herbivores. Thus, from patrol and/or aggressive behavior, ants are considered main plants protectors. From this perspective, the present work aimed to investigate the influence that extrafloral nectar has under ant-plant interaction in an area of Cerrado. The study was conducted in Reserva Ecológica do Clube Caça e Pesca Itororó de Uberlândia, in Uberlândia, MG, in an area with cerrado stricto sensu vegetation. The plant species used was Qualea multiflora (Vochysiaceae), one of the most abundant species of Cerrado, which has extrafloral nectaries (EFNs) at the base of leaf petiole and in inflorescences. Our main assumptions were: a) EFNs visitors ants of Q. multiflora positively impact the plant reducing the herbivore action; b) these ants-plants interactions are modified along the phenological development of plant leaves; c) different herbivory levels in plants produce different reactions in visitors ants; and d) different plant structures have different defenses levels. Results presented in Chapter 1 show that foliar herbivore in Q. multiflora was low and similar to different stages of leaf development, showing that expressed plant defenses are effective. Of the three foliar defenses evaluated during leaf development, it was observed that density of trichomes presents effectiveness peak in early development, biotic defense (EFNs productivity) in intermediated period of development and leaf toughness in the period in which the leaf is adult. These results show the efficacy of temporal variation in foliar defenses in Q. multiflora, which directly affects ant-plant interaction. In Chapter 2, it was shown that EFNs located in inflorescences produce nectar more quantitative and qualitative, which attract large amount of ants, than EFNs located in leaves. EFNs productivity and attractiveness, as well as ants foraging, were also influenced by herbivory variation (experimentally simulated). These results show that Q. multiflora synchronizes its leaf defenses over time ensuring protection against herbivores and that these defenses (as evidenced for biotic defense) can be changed according to value and attack probability of their structures.

Conventional Appalachian surface-mine reclamation techniques repress natural forest regeneration, and tree plantings are often necessary for reforestation. Reclaimed Appalachian surface mines harbor a suite of mammal herbivores that forage on recently planted seedlings. Anecdotal reports across Appalachia have implicated herbivory in the hindrance and failure of reforestation efforts, yet empirical evaluation of herbivory impacts on planted seedling vitality in this region remains relatively uninitiated. First growing-season survival, height growth, and mammal herbivory damage of black locust (Robinia pseudoacacia L.), shortleaf pine (Pinus echinata Mill.), and white oak (Quercus alba L.) are presented in response to varying intensities of herbivore exclusion. Seedling survival was generally high, and height growth was positive for all species. The highest herbivory incidence of all tree species was observed in treatments offering no herbivore exclusion. While seedling protectors lowered herbivory incidence compared with no exclusion, full exclusion treatments resulted in the greatest reduction of herbivore damage. Although herbivory from rabbits, small mammals, and domestic animals was observed, cervids (deer and elk) were responsible for 95.8% of all damaged seedlings. This study indicates that cervids forage heavily on planted seedlings during the first growing-season, but exclusion and tree species selection is effective at reducing herbivory.