Reindeer is an important factor influencing species composition and functions in Arctic ecosystems. However, our understanding of how the importance of reindeer varies among ecosystems is still limited. The aim of this study was to investigate how the vegetation has changed between 1995 and 2015 with and without large herbivores in an area with low herbivory. The study was conducted on Fulufjället in the Swedish mountain region. 16 plots were used, half of which excluded reindeer through fences. The effects of herbivory were generally quite small, which was expected since the density of reindeer is low in the area. However, crowberry (Empetrum nigrum) thrived better in the exclosures than in the grazed controls. In addition to that, the abundance of almost half of the investigated species had changed between 1995 and 2015, regardless of exclusion. Cladonia mitis, Schreber’s big red stem moss (Pleurozium schreberi) and common heather (Calluna vulgaris) were more abundant in 2015, while crowberry was less abundant in 2015. The report concludes that reindeer grazing has small but detectable effects on the vegetation in Fulufjället, and that substantial vegetation changes have occurred during the last 20 years, but that these changes cannot easily be explained by recent climate or land use changes.

Alpine and arctic treelines have been viewed as sensitive indicators of global climate change. While many treelines have advanced under warmer climate regimes in recent decades, the response has not been uniform. Some of this variability may be attributable to the impacts of herbivores. This study investigates the interacting effects of herbivory, climate, and understory vegetation on mountain birch establishment at treeline in the Scandes Mountains of northern Sweden. An extensive dendrochronological database was created to determine periods of establishment, which were then regressed against reindeer (Rangifer tarandus, L.) population data and historical climate data. Vegetation classifications were also created and analyzed to determine if establishment patterns vary by understory vegetation type. I have tested the hypothesis that tree establishment varies within the treeline ecotone and that high reindeer stocking levels negatively impact establishment. Weakly positive responses to herbivory were observed in patterns of tree establishment at treeline. This indicates that reindeer may modestly promote treeline advance at low densities, contradicting some previous research, but many of the results were not statistically significant. The climate variables found to have significant relationships with establishment were inconsistent across herding districts and aggregation levels. No connections between vegetation assemblages and establishment or between vegetation assemblages and reindeer use were observed.

Spiranthes Parksii Correll is an endangered orchid of Texas. Populations of S. parksii are threatened by habitat loss and degradation resulting from human population growth and attendant development and resource extraction. Conservation easements have been established for the protection of the species, but little is known about the population dynamics of S. parksii and the biotic and abiotic factors which drive them. A baseline of ecological information is necessary to the creation of effective management plans for the conservation of this species. The work presented here is an experimental investigation of the affects of large herbivores on S. parksii population dynamics. We explored direct impacts of herbivore browsing as well as indirect impacts resulting from removal of neighboring vegetation on S. parksii population fluctuations and the demographic parameters underlying them. To determine direct herbivore affects on demographic characteristics and their implications for S. parksii population dynamics, we established 32, 1.5mx1.5m plots in areas of high S. parksii abundance. Each of the plots was randomly assigned one of two treatments: herbivore exclusion and control. Demographic parameters were recorded for each individual located within the plots. The data suggest that large and small herbivore browsing affects different lifecycle transitions through removal of photosynthetic and reproductive tissue. These transition alterations have the potential to affect S. parksii population growth. To investigate the indirect impacts of herbivory on S. parksii population dynamics, we established 32 5mx5m plots. Each plot was randomly assigned one of four fertilizer treatments: control, nitrogen addition, phosphorus addition, and nitrogen and phosphorus additions. One half of each plot was randomly assigned one of two biomass removal treatments: unaltered control and biomass removal during orchid dormancy. Demographic data was collected for individuals within the plots. Plots with phosphorus and nitrogen phosphorus additions generally differed regarding orchid demographic variables from nitrogen addition plots and unfertilized controls. Also, available light tended to be greater during orchid flowering in plots with biomass removed than in unclipped controls. A complete understanding of both direct and indirect herbivore impacts on S. parksii population dynamics is necessary for effective conservation of this endangered orchid.

Perennial grass vegetation dynamics of heavy grazing, moderate grazing and ungrazed treatments were analyzed during two extreme drought events: the drought of 1951 to 1956 and the drought events centered on the year 2000. Analysis of each drought event from weather records and Palmer Drought Severity Index values showed that the intensity, duration and pattern of each drought event were structurally unique. Grazing intensity was the primary driver of perennial grass species composition and community structure both during and between each drought event. Total basal area for each drought event was driven primarily by variation in precipitation pattern. Basal area per plant dynamics were significantly influenced by grazing intensity while plant density was driven by both precipitation and grazing intensity. Topo-edaphic variation significantly influenced the persistence and distribution of perennial grass species during an extreme drought event centered on the year 2000. The presence of large or abundant surface rock features facilitated the survival of perennial grasses during this drought event by creating a positive soil microenvironment. Sites with large surface rock features acted as drought refugia for perennial grass populations. Sites with abundant surface rock features had 10 times greater perennial grass basal area and 5 times greater plant density than sites with few surface rock features. Grazing intensity was the primary driver of species composition and community structure within both refugia and non-refugia sites. Grazing intensity had no effect on perennial grass basal area. However, grazed treatments had two times greater perennial grass density than non-grazed treatments. Species response to grazing intensity and surface rock cover was individualistic. Grazing response groups (intolerant, intermediate, and tolerant) separated along a gradient of surface rock cover and grazing intensity. Abundant surface rock features act as refugia for perennial grasses by facilitating their persistence during extreme drought events on the Edwards Plateau.

In contrast to the much that is known about herbivory and its consequences, lichenovory has seldom been studied. Recently, studies confirming the anti-feedant role of lichen secondary metabolites were brought out and hypotheses considering the nature of these interactions were introduced. Also, a few papers dealing with the ecological consequences of lichenovory were published lately. My thesis was aimed on the secondary metabolites issue and the preferences of the lichen feeders in the natural conditions. Six epiphytic lichen species containing secondary compounds (Parmelia sulcata, P. saxatilis, Parmelina tiliacea, Melanelixia glabratula, M. subaurifera, M. glabra), two without them (Melanohalea exasperata, M. exasperatula) and two species of gastropods that naturally climb the trees to feed on lichens (Lehmannia marginata, Cochlodina cerata) were selected for grazing experiments. The deterring role of the lichen compounds was proven. These were also identified using thin-layer chromatography. Subsequently, a transplantation experiment was carried out. It was focused on specifying the preferences of lichen grazers in their natural habitat. The genus Melanohalea that does not contain any secondary metabolites was strongly prefered. No significant preferences among the other species used in the...

Herbivory produces direct and indirect effects on plants and at different spatial scales will have varied consequences. Consumption of plants by vertebrate grazers may affect the plants on an organismal level through direct mortality, on a community level by changing species composition or by altering the rate of succession, and even at a whole ecosystem level by altering nutrient cycles. The majority of the scientific literature has focused extensively on herbivory by mammals and birds. With regard to mammals, studies have shown how folivory affects individual plants, plant populations, and communities of plants. Mammals, as well as birds, also ingest and disperse seeds. This dispersal of seeds by animal consumption, known as endozoochory, allows the non-motile parent plant to disperse seeds to otherwise unreachable locations. Endozoochory may also have an effect on the germination of seeds. Attempts to quantify the effects of non-avian reptiles on plants and plant communities through folivory and frugivory is lacking, despite the prevalence of some form of herbivory in many non-avian reptile groups. I examined the effect of the gopher tortoise (Gopherus polyphemus) herbivory on plant community composition on Egmont Key, Florida by direct experimentation with folivory and frugivory (chapter 1). This species was chosen because of its relatively large size, high density on the proposed field site, and because it is easy to locate due to the presence of large conspicuous burrows in the ground. These burrows provide a central location by which the tortoise begins and ends a foraging activity. Tortoise exclosure plots were used to directly measure the effects of grazing on plant counts and biomass, species richness, biodiversity, and species dominance and evenness. At the conclusion of these exclosure experiments, cafeteria-feeding trials were conducted to relate dietary preference to the plant abundance results found in the field. Seeds from the plant species found on Egmont Key were also fed to tortoises to determine the effects that passage through the tortoise gut had on seed germinability (chapter 2). Seeds that passed through the gut were collected from scat, and planted alongside control seeds that were not consumed by tortoises. Each treatment also was planted with and without tortoise scat to determine if altered germinability post ingestion was from physiological effects from gut passage, or simply being in the presence of scat. Finally, a meta-analysis was conducted looking at the effects of gut passage on seed germinability across different animal taxa and several other moderators (chapter 3). Tortoise exclosure plots had lowered species richness, and significantly lowered diversity and evenness, but significantly higher dominance than in controls. Heliotropium polyphyllum, the most highly preferred local species by tortoises, was the most dominant plant in exclosure and control plots and became even more dominant in exclosure plots. The abundance and biomass of the next two most common plant species, Fimbristylis cymosa and Polypremum procumbens, which are not preferred by tortoises, were reduced in the exclosures, probably due to increased competition with Heliotropium. Several rare plant species were eliminated in the exclosure plots. I conclude that tortoise herbivory may directly influence plant community assembly by reducing preferred plant species and promoting the growth of non-preferred species. Ingested seeds from two fleshy-fruited plant species germinated in greater proportions and in less time than control seeds. The presence of scat also increased germination proportion following gut passage and decreased time to germination in both these species. Germination proportions in five dry-fruited native species were either not affected, or lowered, and time to germination was either not affected, or slower following gut passage. Similarly, the effects of scat had no effect on germination percentage in these species, or decreased it, and had no effect on time to germination, or increased it. One nonnative dry-fruited species was also tested and while germination percentage following gut passage was unaffected, time to germination decreased. Similarly, while the addition of scat increased germination percentage, there was no effect on time to germination. In summary, only seeds from fleshy-fruited plant species were consistently positively affected by passage through gopher tortoise guts and by gopher tortoise scat. Utilizing meta-analyses, I found non-flying mammals, but no other herbivores, enhance the percentage of seeds germinating compared to uningested seeds, and non-avian reptiles were found to decrease the time to germination. Seeds from fleshy fruits, despite being evolved for vertebrate herbivore consumptions, did not germinate faster or in greater proportions than did seeds from dry-fruited plant species. Seeds dispersed by animals native to the same areas as the plants displayed enhanced germinability compared to uningested seeds, as did those dispersed by herbivores or omnivores, and seeds passed by herbivores and omnivores cause increased germination proportions in faster times than those passed by carnivores.

The ecological factors that maintain defensive chemical variation within and between plant species have intrigued ecologists for decades. While theory posits that polymorphisms may be maintained different forms of balancing selection, relatively few experimental studies have tested whether such balancing selection can maintain defensive chemical trait polymorphisms in nature. Further, evidence demonstrating balancing selection is rare for any trait. Here, I investigated a stereochemical trait polymorphism in Xanthium strumarium. This species is polymorphic with respect to the stereochemistry of the lactone ring junction of a prominent defensive compound class ? the sesquiterpene lactones. Individual plants typically produce only cis-fused or trans-fused lactones across their entire suite of compounds. Sesquiterpene lactones are known to influence feeding behavior and growth rates of various herbivores, but nothing is known about the ecological implications of variation in this stereochemical trait. I first examined whether sesquiterpene lactone stereochemical variation can influence folivore feeding behavior in the laboratory. Using pure sesquiterpene lactones in controlled feeding experiments, I found that laboratory-reared grasshoppers were less deterred by the cis-fused compounds than the trans-fused compounds. I then found that these patterns extended to the field: in common gardens, plants producing cis-fused lactones received more damage than plants producing trans-fused lactones. Additionally, folivore damage was negatively correlated with plant fitness. Taken together, these results indicate that herbivores can impose natural selection on this stereochemical trait polymorphism in nature. Finally, I found evidence that spatially variable selection leads to fitness patterns conducive to the maintenance of this polymorphism. Further, I found that the intensity of folivore damage across spatial scales predicted in which environments each morph outperformed the other, with plants producing cis-fused lactones achieving higher fitness than plants producing trans-fused lactones when herbivore pressure was low (and the reverse being true when herbivore pressure was high). This work demonstrates that relatively minor defensive chemical variation can have far-reaching impacts on the ecology and evolution of plant populations.

The failure of regeneration of oak (Quercus spp.) and other hardwood species has been noted throughout eastern North America as well as on the eastern Edwards Plateau of central Texas. Previous research has suggested that two factors—prolonged periods of fire suppression and high densities of white-tailed deer—may be particularly influential in preventing seedlings of certain species from reaching the adult size class. It is also possible that these two factors interact, and the success of reintroducing fire to promote hardwood regeneration may depend on local deer density. This study, composed of observational and experimental components, first compared browsing frequency on woody plants in burned and unburned plots at six sites in central Texas. We found that although fire history did not affect browsing frequency, browsing frequency varied significantly among sites (likely due to differences in local deer densities) and among species. In our experimental study, we used cages to protect woody plants from deer herbivory in burned and unburned areas and compared growth after one year to plants of similar size and species that were exposed to herbivory. Plants in burned areas were significantly more likely to increase in height than plants in unburned areas. Similarly, plants protected from herbivory were more likely to increase in height after one year than plants that were browsed. There were no significant differences in the amount of growth woody plants in burned and unburned areas or plants that were caged or uncaged put on during one year. This is likely due to the extreme hot and dry weather that occurred across central Texas during the course of this study. These results support previous research showing that deer are currently limiting hardwood growth of multiple species on the eastern Edwards Plateau. Further, although it appears that fire can be used to stimulate hardwood growth (particularly during a non-drought year) successful hardwood regeneration is unlikely at current deer densities. / text

Despite their difference in body size and morphology, the moose (Alces alces) andthe mountain hare (Lepus timidus) sustain themselves during winter on similar plantspecies and plant parts in in subarctic environments, namely apical twigs ofmountain birch (Betula pubescens ssp. czerepanovii). Herbivores must select areas anditems of food that provide sufficient intake rates and food nutritional quality whilebalancing this against their intake of dietary fiber and potentially detrimental plantsecondary metabolites. This selection takes place simultaneously at multiple spatialscales, from individual plants and plant parts to patches of food and parts of the wider landscape. While the herbivores must consider their need for food to sustaindaily activities, for body growth and reproduction it is also necessary to avoid predators and harsh environmental conditions. For managers, an understanding of key factors for animal foraging distributions is pivotal to reach intended goals ofmanagement and conservation plans. Knowledge in this area is also important formodels to make accurate predictions of foraging responses of herbivores to resource distributions. The mountain birch forest displays a naturally heterogeneous distribution of trees and shrubs which presents herbivores with a challenge to findgood feeding areas. In an investigation of the spatial distribution of moose browsing on birch and willows (Salix spp.) in two winter seasons separated in time by 14 years,it was found that moose browsing patterns in 1996 were correlated to those observed in 2010. It was also found that moose browsing was spatially clustered within the same distances (1000-2500 m) as densities of willow and birch, but at other spatial scales, browsing was mostly randomly distributed. It was concluded that foragedensity is a cue for moose but only at certain spatial scales. Similarly, a comparison of foraging distribution by hare and moose showed that high birch density was a key factor for both species. In spite of this, hares and moose used different parts ofthe same environment because they respond to food resource distribution at different spatial scales. Hares fed from smaller plants, and focused their foraging activity on smaller spatial scales than moose. These results emphasize the importance of taking into account the distribution of food resources at spatial scales relevant for each species in plans for conservation and management. In an experimental study it was found that intensified browsing on natural forage by mountain hares can be induced locally through placement of food. The induced browsing varied with the amount and quality of the added food, but also with thedensity of natural food plants and natural foraging distribution by hares. Finally, ina last experiment habitat preference of mountain hares across edges between open and forested areas was studied. The results were not consistent; hares utilized baitto a greater extent within forested areas than bait placed on a nearby lake ice, butbait on mires and heaths was either preferred over bait in nearby forest, or utilizedto a similar extent. A possible explanation is that hares have knowledge of their environment such that both forested areas and subarctic mires and heaths are partof its natural home range, whilst the extreme environment on the lake ice is not. During recent decades arctic areas have had an increase in vegetation density andwill be affected by future climate warming and therefore, factors that determineforaging ecology of key herbivores need to be identified. This thesis sheds some light on these factors in relation to spatial scale and forage distribution for two high profile herbivores in the subarctic.

The herbivory experienced by non-native invasive plants may depend on their local environments, such as herbivore abundance. In this study, I performed a common garden experiment with plants sampled from 11 populations of Arctium minus, from southern Ontario to near its northern range limit. I also compared performance and herbivory of burdock in open and understory habitats. Finally, I conducted freezing tolerance experiments with the lepidopteran seed predator Metzneria lapella, and palatability tests with plants from different populations. Results suggested that the previously described latitudinal trends in herbivore damage among populations are due to environmental differences rather than genotypic differences among populations. At a local scale, plants of open habitat were less damaged and had better performance than understory plants. Burdock has not escaped damage by herbivores in its invaded range; instead variation among sites in herbivore populations and impacts may significantly affect the invasiveness of this species.