<p>Although we often study mutualisms (interactions in which both species benefit) at the level of the individual partners, mutualistic interactions take place in the context of populations and communities. Sharing mutualists with others in a population could result in indirect interactions in the form of mutualist-mediated competition or facilitation. In my dissertation work I asked whether intraspecific competition or facilitation for ants might occur in an extrafloral nectary-bearing (EFN) plant, and what the consequences would be for long-term population dynamics of the plant. My focal species was <italic>Colubrina spinosa</italic> (Rhamnaceae), a neotropical treelet on which I observed 69 ant species at La Selva Biological Station, Costa Rica. </p><p> Demonstrating intraspecific competition for mutualists requires that 1) neighbor densities affect mutualist visits to an individual, and 2) change in mutualist visits results in reduced benefit. To determine how mutualist density affects plant benefit, I experimentally manipulated ant abundances on plants over two years and measured growth and survival. To assess competition for mutualists, I excluded ants from conspecific neighbors and followed ant abundance on focal plants. To consider long-term facilitation, in which greater local nectar resources increase local ant abundance, I manipulated nectar resources in a two-year field experiment and estimated ant abundance on <italic>C. spinosa</italic> plants and on baits. </p><p> Considering local neighbor density both within a 1m radius and in 5x5 m plots, ant densities on <italic>C. spinosa</italic> plants showed evidence for a small-scale competition effect and a contrasting plot-level facilitation effect. The small-scale competition was sized-based; smaller plants lost ants to larger plants. Ant benefit to plants also depended on plant size. For larger plants, those with greater size-adjusted ant density had higher growth and survival than those with fewer ants than expected for their size. </p><p> To determine whether these contrasting competition and facilitation effects could impact population growth or densities, I modeled population dynamics with an integral projection model (IPM). Growth and survival were functions of ant density, which in turn depended on conspecific neighbors, plant size, and mean background ants. Results suggest that larger-scale facilitation of mutualists impacts long-term population growth more than small-scale competition. Population growth rate increased with increasing background ant density, which depended on facilitation at the 5x5m plot scale. In contrast, small-scale competition caused a redistribution of mutualist ants among plants of different sizes, but had very little effect on long-term population growth. </p><p> I thus conclude that on the scale of individuals there is evidence of intraspecific competition for ants as well as facilitation in the EFN plant <italic>C. spinosa</italic>, but only facilitation effects lead to appreciable changes in population dynamics. If mutualist-mediated facilitation effects tend to occur over long time scales in other systems as well, facilitation might prove to be more important than competition in other mutualisms.</p> / Dissertation

Despite a long history of investigations on protective ant-plant interactions, since the late 19century (Thomas Belt 1874), a comprehensive quantitative understanding of the adaptations that facilitate these associations between plants and ants and the differential importance of these adaptations in predicting the benefits and costs to each partner and in shedding light on the evolutionary trajectories of this ecologically widespread interaction is yet to be realized. In the present study we have experimentally shown that the identity of the ant species (T. albipes), the abundance of this ant species and the composition of EFN produced by floral buds and young leaves of H. brunonis plant populations contribute to facilitating protection of floral bud inflorescences and young leaves of H. brunonis populations in a particular site. Of all the 16 ant species that inhabit the domatia of H. brunonis at several sites, the plant has found its protective ant partner only in the dolichoderine ant T. albipes and that too, only in the southernmost site In our experimental set up of three populations of H. brunonis at three different latitudes, where each site is separated from another site by at least 200 km, we have shown that only the southernmost population (Solaikolli) in protected by the ant species T. albipes. Although T. albipes is found in two of the three populations used in the present study (Sampaji and Solaikolli), it is present in a relatively larger abundance both within the domatia of H. brunonis and in the terrestrial stratum only in the southernmost site Solaikolli and is hence able to protect the EFN producing structures of H. brunonis at this site. In comparison, T. albipes is found in low abundance both in the domatia and in the terrestrial stratum in the site Sampaji and does not protect EFN producing plant parts of H. brunonis at this site. We have also experimentally shown that the young leaves of H. brunonis at this southernmost site Solaikolli are protected to a greater extent than the floral bud inflorescences, since T. albipes preferentially utilized EFN produced by young leaves compared to EFN produced by floral buds at this site. Moreover, we have also shown that the floral buds of H. brunonis in the northernmost site are unprotected for two reasons: i. the absence of the protective ant species T.albipes at this site. ii. The EPN produced by some of floral buds at this site is differentially utilized to a much lower extent than floral buds from other sites due to EFN from Agumbe being > 400-fold more viscous than the EFN produced by floral buds at the other two sites (sampaji and Solaikolli) (at 30º C). Although previous studies have independently shown that the identity of the ant partner (Janzen 1966, Schemske 1980, Horvitz and Schemske 1984, Heads 1986, Oliveira et al. 1987a, b; Jaffe et al. 1989, RicoGray and Thien 1989, Davidson et al. 1991) and the abundance of the protective ant species (Koptur 1984, Rocha and Bergallo 1992, Di Giusto et al. 2001) are important in predicting the protective outcome of the interaction between a plant species and its interacting ants, few studies have examined these two factors along with an examination of the EFN volume and composition (Inouye and Inouye 1980, Rudgers and Gardener 2004) and differential utilization of these qualitatively different EFNs produced by different populations of the same ant plant. Humboldtia brunonis and its interacting ant species provides a unique system to address questions about the evolution of ecological specialization and the evolution of preadapted plant traits that facilitate interactions between plants and ants (especially domatia), due to its unique polymorphism for the presence of caulinary domatia and its widespread abundance in the low-elevation wet-evergreen forests of the Western Ghats.

No description available.

abstract: Hydrological models in arid and semi-arid ecosystems can be subject to high uncertainties. Spatial variability in soil moisture and evapotranspiration, key components of the water cycle, can contribute to model uncertainty. In particular, an understudied source of spatial variation is the effect of plant-plant interactions on water fluxes. At patch scales (plant and associated soil), plant neighbors can either negatively or positively affect soil water availability via competition or hydraulic redistribution, respectively. The aboveground microclimate can also be altered via canopy shading effects by neighbors. Across longer timescales (years), plants may adjust their physiological (water-use) traits in response to the neighbor-altered microclimate, which subsequently affects transpiration rates. The influence of physiological adjustments and neighbor-altered microclimate on water fluxes was assessed around Larrea tridentata in the Sonoran Desert. Field measurements of Larrea’s stomatal behavior and vertical root distributions were used to examine the effects of neighbors on Larrea’s physiological controls on transpiration. A modeling based approach was implemented to explore the sensitivity of evapotranspiration and soil moisture to neighbor effects. Neighbors significantly altered both above- and belowground physiological controls on evapotranspiration. Compared to Larrea growing alone, neighbors increased Larrea’s annual transpiration by up to 75% and 30% at the patch and stand scales, respectively. Estimates of annual transpiration were highly sensitive to the presence/absence of competition for water, and on seasonal timescales, physiological adjustments significantly influenced transpiration estimates. Plant-plant interactions can be a significant source of spatial variation in ecohydrological models, and both physiological adjustments to neighbors and neighbor effects on microclimate affect small scale (patch to ecosystem) water fluxes. / Dissertation/Thesis / Doctoral Dissertation Biology 2015

Submitted by Ricardo Cedraz Duque Moliterno (ricardo.moliterno@uefs.br) on 2016-03-01T00:55:21Z No. of bitstreams: 1 DISSERTA??O augusto.pdf: 990945 bytes, checksum: 0ffa3c6ca52f5bfb881523a9ecb67d91 (MD5) / Made available in DSpace on 2016-03-01T00:55:21Z (GMT). No. of bitstreams: 1 DISSERTA??O augusto.pdf: 990945 bytes, checksum: 0ffa3c6ca52f5bfb881523a9ecb67d91 (MD5) Previous issue date: 2013-02-04 / The approach to the study of complex networks used for networks of interactions allows the identification of emergent properties such as nestdness, modularity and specialization. Consequently, we hypothesize that mutualistic networks between plants and butterflies visiting flowers in higher altitudes are characterized by few species, with low feeding selectivity. We developed the study using two organizational levels: local and global. The local level comprised mutualistic networks in two hills located in the Chapada Diamantina. The global level comprised mutualistic networks in different regions of the globe. For each network, we evaluated the relationship between altitude, modularity, nestdness and specialization. No network metric shoed a consistent change associated with altitudinal variation, not in the local and global levels. Thus, the structure of interaction networks between butterflies visiting the flowers and plants does not respond to changes in altitude, what we are left understand what factors may be determinants for this interaction. / A abordagem do estudo de redes complexas utilizada para as redes de intera??es permite a identifica??o de propriedades emergentes tais como o aninhamento, modularidade e especializa??o. Nesse sentido, propomos a hip?tese de que redes de intera??es entre borboletas visitantes florais e plantas em altas altitudes ser?o caracterizadas por poucas esp?cies, com baixa seletividade alimentar. Nossas expectativas s?o de que, ao longo de uma montanha (n?vel local), tais redes ser?o 1) menos modulares; 2) menos aninhadas e 3) compostas por esp?cies generalistas na regi?o do topo, quando comparadas com redes localizadas nas regi?es mais basais. Esperamos encontrar esse mesmo padr?o ao avaliar redes descritas em diferentes altitudes ao longo do globo (n?vel global). Realizamos o estudo utilizando dois n?veis organizacionais: local e global. O n?vel local envolveu dois morros situados na Chapada Diamantina e para cada morro, duas altitudes. O n?vel global envolveu redes de intera??es em v?rias partes do mundo com altitudes diferentes. Para cada rede avaliamos a associa??o entre altitude, modularidade, aninhamento e especializa??o. Nenhuma das tr?s m?tricas de rede revelou mudan?a consistente em rela??o ?s duas altitudes dos morros ou mesmo para a avalia??o global. Desta forma, a estrutura de redes de intera??o entre borboletas visitantes florais e plantas n?o responde a varia??es de altitude, o que nos resta entender quais os fatores que podem ser determinantes para essa intera??o.

Butterflies fulfill a unique role among insect pollinators as long-distance flyers. This makes butterflies particularly valuable as vectors of genetic diversity among spatially isolated plant populations. Like many insects, though, butterfly populations have experienced significant declines in recent years. To help inform conservation efforts, and to investigate community and species level dynamics, I studied butterflies and their floral resources as part of a three year pollinator survey across the state of North Dakota. At the community level, I analyzed butterfly-flower interaction networks across space and time. I then examined the specialization of individual species within those networks and their contributions to network structure. I also evaluated spatial and temporal distribution patterns of monarch butterflies, regal fritillaries, and their plant resources. Results revealed dynamic spatiotemporal relationships between butterflies and their plant resources that have important implications for conservation efforts and the study of ecological communities.

A project involving shrub removal was undertaken by the United States Forest Service in the Spring Mountains National Recreation Area (SMNRA) to reduce accumulated woody fuels, which can pose risks to human communities. This research focuses on the interactions between shrubs and the perennial forb Palmer's penstemon (Penstemon palmeri), one of many nectar sources for the endemic Spring Mountains Acastus Checkerspot Butterfly (Chlosyne acastus ssp robusta). Initial observations revealed that P. palmeri (`penstemon') seemed to grow almost exclusively under shrubs. Such spatial associations are often indicative of a history of positive interactions between plants, and led to the research presented here. These studies investigate and discuss the interactions between this penstemon and shrubs in the arid shrublands of the SMNRA. Spatial patterns between populations of penstemon and shrubs were measured during November 2008-May 2011, and the consequences of shrub-association for individual penstemon emergence, survival, growth, and reproduction were documented (Chapter 2). The results suggest that although shrubs reduced penstemon emergence, they increased seedling survival (a seed-seedling conflict) resulting in a strong shift toward association between shrubs and penstemon over time. Further, while no differences in growth were detected between microhabitats, the results suggest that shrubs inhibited P. palmeri flowering but improved the successful maturation of fruits when flowering occurred. The mechanisms driving these patterns were elusive, but seed-sowing and seedling transplant experiments suggested that shrub soils, rather than their canopies, alter the nature of seed-seedling conflicts in a way that may promote seed-bank persistence in penstemon populations (Chapter 3). To provide a detailed description of the reproductive response of penstemon to shrubs, structural equation modeling was used to describe the importance of shrubs for penstemon seed production (Chapter 4). The results suggest that competition with shrubs reduced penstemon seed production, but that shrubs simultaneously facilitated penstemon water balance and altered the foraging behavior of its pollinators, indirectly increasing seed production. I conclude by discussing the importance of these studies, and studies of plant interactions in general, for helping land managers balance the objectives of fuel load reduction with protecting desirable species (Chapter 5).

Aloe mites are herbivores of the genus Aloe (ALOACEAE) and are associated with hyperplastic growth in various aloe species, but the biochemistry of this interaction is poorly understood. In an effort to characterize plant defense responses to herbivory in the genus Aloe, a salivary extract was isolated from aloe mites (Aceria aloinis Keifer) and its bioactivity was tested using a hypocotyl elongation assay. Subsequently, Aloe striata plants were treated with jasmonic acid (JA), salicylic acid (SA), and the mite salivary extract. Using water and methanol, compounds of different polarity were extracted from aloe tissues that had been frozen and crushed at 4, 12, and 24h after treatment. Extracts were analyzed by HPLC and three compounds were found. One of these compounds was SA (mean concentration of 4µg/mL), and this is the first time that this aloe species has been found to produce SA. Two additional peaks of unknown identity were observed in JA- and SA-treated plants. These results suggest that A. striata may in fact undergo a JA-mediated change in secondary metabolism as part of a plant defense response.

Exotic invasive plant species can alter aquatic habitats potentially influencing the macroinvertebrate community and foraging fishes. Therefore, I investigated the hypothesis that Hydrilla verticillata will alter habitat important to macroinvertebrate community structure and bluegill foraging efficiency. Studies were conducted in ponds and aquaria. At the pond level, macroinvertebrate abundance, richness, and biomass in a hydrilla-dominated habitat did not differ significantly from a diverse plant habitat. Indicator taxa did differ significantly between respective treatments. The data suggest hydrilla beds may not provide increased macroinvertebrate abundance and richness compared to diverse plant beds as previously thought. In aquaria, habitat complexity (Ihv) and light transmittance were influenced by increasing the homogeneity of hydrilla in an aquatic bed habitat. In addition, bluegill foraging efficiency was affected negatively by increasing spatial complexity of a hydrilla dominated habitat. Therefore, a shift to a monotypic hydrilla habitat can alter macroinvertebrate community composition and impact bluegill foraging success.

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.