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Browsing by Author "Adler, Lynn S."

Now showing 1 - 9 of 9
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    Attracting antagonists: does floral nectar increase leaf herbivory?
    Adler, Lynn S.; Bronstein, Judith L. (Ecological Society of America, 2004-06)
    Traits that are attractive to mutualists may also attract antagonists, resulting in conflicting selection pressures. Here we develop the idea that increased floral nectar production can, in some cases, increase herbivory. In these situations, selection for increased nectar production to attract pollinators may be constrained by a linked cost of herbivore attraction. In support of this hypothesis, we report that experimentally supplementing nectar rewards in Datura stramonium led to increased oviposition by Manduca sexta, a sphingid moth that pollinates flowers, but whose larvae feed on leaf tissue. We speculate that nectar composition may provide information about plant nutritional status or defense that floral visitors could use to make oviposition decisions. Thus, selection by floral visitors and leaf herbivores may be inextricably intertwined, and herbivores may represent a relatively unexplored agent of selection on nectar traits.
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    The dual role of floral traits: Pollinator attraction and plant defense
    Irwin, Rebecca E.; Adler, Lynn S.; Brody, Alison K. (Ecological Society of America, 2004-06)
    Plants are under siege from a diversity of enemies that consume both leaf and floral parts. Plants resist damage to leaves in a variety of ways, and we now have a rich literature documenting how plants defend themselves against herbivore attack. In contrast, the mechanisms by which plants resist enemies that consume floral parts or resources are much less known, even though damage to floral tissue usually has tighter links to plant fitness than damage to leaf tissue. Many plants experience nectar robbing, whereby floral visitors remove nectar from flowers, often without pollinating. Nectar robbers can reduce plant fitness to degrees comparable to, or even surpassing, reduction by herbivores. However, because nectar attracts both pollinators and nectar robbers, plants face a dilemma in defending against nectar robbers without also deterring pollinators. Here, we extend the conceptual framework of resistance to herbivores to include resistance to nectar robbers, focusing on nectar traits. We review published data and find that an array of nectar traits may deter robbers without deterring pollinators. Although resistance traits against robbers have been broadly identified, the costs and benefits of these traits in terms of plant fitness remain poorly understood. We present data showing that a nectar trait (dilute nectar) might directly, as well as indirectly, benefit plant fitness by deterring nectar-robbing bumble bees of Ipomopsis aggregata without deterring hummingbird pollinators. However, the magnitude of any plant fitness benefit will depend on the degree to which plants are pollen- vs. resource-limited in a given year. The results of our work offer both conceptual and empirical insight into how plants cope with attack by nonpollinating floral visitors through a relatively unexplored trait, nectar.
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    Ecological costs and benefits of defenses in nectar
    Adler, Lynn S.; Irwin, Rebecca E. (Ecological Society of America, 2005-11)
    The nectar of many plant species contains defensive compounds that have been hypothesized to benefit plants through a variety of mechanisms. However, the relationship between nectar defenses and plant fitness has not been established for any species. We experimentally manipulated gelsemine, the principal alkaloid of Carolina jessamine (Gelsemium sempervirens), in nectar to determine its effect on pollinator visitation, nectar robber visitation, and male and female plant reproduction. We found that nectar robbers and most pollinators probed fewer flowers and spent less time per flower on plants with high compared to low nectar alkaloids. High alkaloids decreased the donation of fluorescent dye, an analogue of pollen used to estimate male plant reproduction, to neighboring plants by one-third to one-half. However, nectar alkaloids did not affect female plant reproduction, measured as pollen receipt, fruit set, seed set, and seed mass. The weak effects of nectar alkaloids on female reproduction could represent a balance between the altered behavior of nectar robbers and pollinators, or it could be that neither of these interactions affected plant reproduction. Taken together, these results suggest that secondary compounds in nectar may have more costs than benefits for plants.
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    The effect of aphids in parasitoid-caterpillar-plant interactions
    Lentz, Amanda Jean (Virginia Tech, 2007-07-19)
    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.
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    The effect of larval diet and sex on nectar nicotine feeding preferences in Manduca sexta (Lepidoptera: Sphingidae)
    Sharp, David N.; Lentz-Ronning, Amanda J.; Barron, Johanna; Adler, Lynn S. (Florida Entomological Society, 2009-06)
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    Experimental study of an avian cavity-nesting community: nest webs, nesting ecology, and interspecific interactions
    Blanc, Lori A. (Virginia Tech, 2007-07-17)
    Cavity-nesting communities are structured by the creation of and competition for cavities as nest-sites. Viewing these communities as interconnected webs can help identify species interactions that influence community structure. This study examines cavity-nesting bird community interactions within the fire-maintained longleaf pine (Pinus palustris) ecosystem at Eglin Air Force Base, Florida. In chapter 1, I provide a background review of the ecology of my study system. In chapter 2, I use nest webs to depict the flow of cavity-creation and use at Eglin. I identified 2 webs into which most species could be placed. One web contained 6 species associated with pines. The second web contained 5 species associated with hardwoods. Red-cockaded woodpeckers (Picoides borealis) and northern flickers (Colaptes auratus) created most cavities used by other species within this community. In chapter 3, I describe snag densities and nest-site selection of the cavity-nesting bird community at Eglin. Large, mature pine snags were abundant, exceeding other reported densities for southern pine forests. Pine snags were heavily-used, despite the abundance of available red-cockaded woodpecker cavities in living pine. Hardwood snags accounted for 10% of nests found, and were used by 12 of 14 species. Diameters of nest-trees and available snags were below the range of optimal nest-snag diameters reported in other studies, indicating the need for site-specific snag management guidelines. In chapter 4, I combine a study of basic ecological principles with endangered species management to examine interactions within the cavity-nesting bird community at Eglin. I used a nest web to identify a potential indirect interaction between the red-cockaded woodpecker and large secondary cavity-nesters, mediated by the northern flicker. I used structural equation modeling to test a path model of this interaction. By experimentally manipulating cavity availability, I blocked links described in the model, confirming cavity creation and enlargement as mechanisms that influence this indirect relationship. I demonstrated that a red-cockaded woodpecker cavity-management technique could disrupt this indirect relationship by affecting northern flicker behavior, and provided an empirical example of how, in interactive ecological communities, single-species management can have indirect effects on non-target species.
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    Host species affects herbivory, pollination, and reproduction in experiments with parasitic castilleja
    Adler, Lynn S. (Ecological Society of America, 2003-08)
    The relative performance of a parasitic plant on different host species will depend on both direct and indirect effects of hosts on parasite interactions with mutualists and antagonists. Host species could affect parasite interactions with both herbivores and pollinators due to the uptake of defensive compounds and nutrients. However, the effects of different host species on parasitic plants have not been experimentally tested in the field. I determined the effect of two native host species, an alkaloid-producing, nitrogen-fixing lupine and non-alkaloid, non-nitrogen-fixing grass, on herbivory, pollination, and reproduction of the hemiparasitic plant Indian paintbrush (Castilleja indivisa). Within this experiment, I manipulated herbivory and pollination to determine their effects on Indian paintbrush reproduction. Indian paintbrush parasitizing lupines produced three times as many seeds and were more attractive to pollinators than Indian paintbrush parasitizing grass. However, there was no effect of host species on early season or floral herbivory. In addition, MANOVA revealed that host species influenced the response of Indian paintbrush female reproduction to experimentally manipulated herbivory and pollination treatments. Thus, the effect of hosts on parasites is mediated by interactions with herbivores and pollinators, and both direct and indirect effects may shape the selective pressures mediating interactions between hosts and parasites.
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    Nymphaea odorata (Water-lily, Nymphaeaceae): Analyses of molecular and morphological studies
    Woods, Kristi Yvonne (Virginia Tech, 2003-02-06)
    Molecular and morphologic studies were used to determine the evolution, classification and differentiation of Nymphaea odorata. Molecular analyses of the nuclear internal transcribed spacer (ITS) region, the chloroplast trnL-F region, and inter-simple sequence repeat (ISSR) markers determined the variation present between and within two species of Nymphaea. The ITS region resulted in a phylogeny depicting strong separation between species (N. mexicana and N. odorata) and some separation between N. odorata's subspecies. The ITS region contained polymorphisms, which upon SAHN clustering and principle coordinate (PCOA) and minimum spanning tree (MST) analyses produced groups similar to the clades in the ITS phylogeny. Sixteen accessions were chosen for trnL-F analysis, where a subspecies-specific molecular marker was found. In most accessions the marker confirmed the original subspecies classification. Molecular analyses using ISSRs characterized among population variation in N. odorata and N. mexicana using five primers. ISSR markers among populations were highly variable within a species and were used in UPGMA, PCOA and MST analysis, which resulted in separation between the subspecies. Both univariate and multivariate analyses were performed on quantitative and qualitative morphological characters. An analysis of variance resulted in six morphological characteristics that were statistically significant (P< 0.05), the majority being leaf blade characteristics. Multivariate statistics of principle component analysis and discriminate analysis resulted in groups for each subspecies, both emphasized the importance of quantitative leaf blade characteristics. Overall, both morphology and molecular characteristics supported the classification of subspecies for ssp. odorata and ssp. tuberosa, due a lack of strong segregation of characteristics.
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    Trophic dynamics in the fine-root based food web: integrating resource heterogeneity, root herbivores, and root foraging
    Stevens, Glen N. (Virginia Tech, 2005-05-24)
    Resources in the soil are heterogeneously distributed. We know that plant species differ in their root responses to nutrient patches and that these differences in foraging can influence plant competition. However, most studies of root-resource interactions overlook the potential top-down influence of root herbivores. While root herbivores can influence plant community structure, the extent to which they influence ecosystem-scale factors such as net primary production is unclear. In addition, little is known regarding root herbivore foraging behaviors and, more importantly, whether these foraging behaviors can actually influence species interactions. In this dissertation, I present a conceptual model of soil-root-herbivore interactions in which soil resource heterogeneity structures both root dynamics and the abundance and influence of root herbivores. I conducted two field and one greenhouse experiment examining this proposed model. The dissertation includes an introductory chapter (Chapter 1), a field study examining root responses to manipulations of soil fertility and root herbivory (Chapter 2), a greenhouse study that used plant species responses to heterogeneity to develop predictions about the role of root herbivores in mixed-species neighborhoods (Chapter 3), and a field study of planted communities examining soil fertility and fauna effects on above- and belowground structure and function (Chapter 4). In all cases, there were significant effects of root herbivores on community structure and components of net primary production. Resource distribution had a strong effect in studies conducted in sandy, nutrient-poor soils (Chapter 2 and 3), but had a reduced effect in the study conducted at Kentland Farm in loamy soils (Chapter 4). Interactions between resource availability and root herbivory were common. These results support the theory that the potential benefit of resource-rich patches may be constrained by root herbivores. This research complements recent findings that demonstrate other potential costs of species foraging behaviors (such as exposure to soil anoxia and increased drought stress), as well as potential effects of root herbivores and other soil fauna on plant diversity.