Quaking aspen (Populus tremuloides) is the most widely distributed tree in North America (Lindroth and St Clair 2013), and a keystone species in our western montane forests (Worrall et al. 2015). Aspen has become a model organism for studies of genetics and physiology in woody plants (Bradshaw et al. 2000, Taylor 2002). Aspen is also economicallyimportant (Worrall et al. 2015) – wood is harvested for various uses, its scenic beauty helps sustain the tourism economy in many areas, and it has recently been studied as a possible source of biofuel (Sannigrahi et al. 2010). Aspen is also a species of conservation concern, due to recent large-scale deterioration and decline of many aspen forests in the last two decades (Worrall et al. 2013). Several causal factors have been identified: fire suppression (Calder et al. 2011, Smith et al. 2011), increased ungulate herbivory (Kay and Bartos 2000), disease (Marchetti et al. 2011), and climate change (Worrall et al. 2013). My thesis focuses on two different biotic stressors of aspen: a fungal pathogen and ungulate herbivory. Understanding the relationship between aspen and their biotic stressors adds to our knowledge of aspen ecology and helps manage the increasing risk of decline in our aspen forests. Chapter 1 is a study of the relationship between aspen and a necrotrophic fungal pathogen (Drepanopeziza sp.) during a major disease outbreak in 2015. I quantified the relationship between Drepanopeziza infection severity and aspen leaf functional traits, including morphological, chemical and phenological traits. I found that severe Drepanopeziza infection was associated with low concentrations of a key class of herbivore defense compounds (phenolic glycosides), and strongly associated with early budbreak and leaf-out in aspen stands. The association between infection and early budbreak was likely caused by unusually rainy conditions in May of 2015, which may have exposed leaf tissue to wet conditions that favor thedispersal of Drepanopeziza spores. Chapter 2 is an experiment designed to determine whether the mode and timing of herbivory can influence aspen's defensive response. I specifically asked whether removing leaves, twigs and meristems together and removing leaves alone had unique effects on aspen sucker growth, survival, and phytochemistry. Additionally, I applied these simulated herbivory treatments to suckers on different dates to see whether early- or late-summer herbivory had greater effects on suckers. I found strong mode and timing effects on growth and survival, but not foliar chemistry.

Repeated polyploidization events are thought to be among the most important causes of sympatric speciation throughout evolutionary time. Changes in phenology and trait expressions that arise in polyploids have been shown to affect plant interactions with insect herbivores and pollinators. If these interactions are changed, selection subsequent to the polyploidization event could contribute to further divergence, or increased similarity, of cytotypes. This study was conducted to investigate plant interactions with insect herbivores and pollinators and patterns of selection in tetraploid and octoploid Cardamine pratensis L. (Brassicaceae), and to answer the following questions: i) Is there phenotypic selection on flowering phenology and number of flowers? ii) Is pollen limitation or herbivory most important for variation in reproductive output? iii) During what stages of ovary and ovule development do variation in fitness mainly arise? iv) Can the intensity of interactions be linked to phenology and number of flowers, suggesting that selection is mediated by pollen limitation or herbivory? v) Do intensity of interactions, and of interaction-mediated selection, differ between ploidy levels? From a combination of an observational study of herbivory and a hand pollination experiment, selection was found for earlier flowering in both subspecies. Intensity of herbivory was an important determinant of plant reproductive success, while hand pollination had little effect. Positive effects of flowering time on intensity of herbivory suggest that selection for earlier flowering was mediated by herbivores. Tetraploids initiated flowering later and suffered from more intense herbivory than did octoploids. The direction of selection was similar in both subspecies. However, differences strength of selection and intensity of herbivory suggest that there is a possibility of selection for their further divergence. / Polyploidisering anses vara en av de viktigaste orsakerna till artbildning inom populationer. Skillnader i blomningskaraktärer, såsom fenologi och blomantal, som uppstår i och med polyploidiseringen har visat sig påverka växters interaktioner med såväl pollinatörer som herbivorer. Förändringar i växt-insektsinteraktioner till följd av polyploidiseringen kan leda till selektion för ökade skillnader, eller likheter, mellan cytotyper. Studiens syfte var att undersöka växters interaktioner med insekter i form av pollinatörer och herbivorer, samt att undersöka selektionsmönster hos tetraploida och oktoploida Cardamine pratensis L. (Brassicaceae). Jag ville även besvara följande frågor: i) Sker selektion på blomningstid och blomantal? ii) Vilken växt-insektsinteraktion är viktigast för variation i reproduktionsframgång? iii) Under vilka utvecklingsstadier uppstår den största variationen i fitness? iv) Kan intensiteten av interaktionerna kopplas till blomningsfenologi och blomantal, vilket skulle indikera att selektion förmedlas genom pollenbegränsning eller herbivori? v) Skiljer sig styrkan av interaktionerna, och av interaktionsförmedlad selektion, mellan ploidinivåer? Studien utformades som en kombination av en observationsstudie av herbivori och ett handpollineringsexperiment, och jag fann selektion för tidigare blomning hos de två underarterna. Reproduktionsframgång styrdes av herbivori snarare än pollenbegränsing. Förlust av potentiell fitness genom att fröämnen inte utvecklades till frön var den faktor som starkast påverkade variation i fitness, och detta var också den fas i utvecklingen som bidrog i störst utsträckning till kvantitativ förlust av fitness. Ett positivt samband mellan blomningsfenologi och herbivoriintensitet indikerar att selektion för blomningstid var förmedlad av herbivorer. Tetraploider blommade senare och utsattes för mer intensiva herbivorattacker än oktoploider. Detta, samt skillnader i selektionsstyrka, indikerar att selektion skulle kunna leda till ökad divergens av underarterna.

Plant-soil feedback has been a well-studied mechanism in recent years of the success of invasive plants, the shift of species in succession, and the structure of plant communities in general. It is a process during which the plant affects the soil with its growth and these changes are reflected in the growth of other plants. Despite the large number of previous studies, relatively little attention is paid to the interaction of plant-soil feedback with other factors, which I consider important for understanding its role in natural plant communities. The aim of the work was to clarify the influence of plant-soil feedback on model species Arrhenatherum elatius and Centaurea scabiosa and to compare its influence with other factors - interspecific competition and herbivory (simulated loss of aboveground biomass). The influence of factors was investigated using biomass and changes in plant physiology, specifically chlorophyll fluorescence and the content of elements in aboveground biomass. The plant-soil feedback mechanism of the model species was assessed using the content of elements in the soil after cultivation. In the biomass of the species Arrhenatherum elatius, the factors of plant-soil feedback and competition manifested themselves in mutual interaction, when the presence of a competitor changed...

Herbivory by ungulates is a known agent of disturbance in many ecological systems around the globe. At high abundances and through a selective foraging behaviour herbivory may inflict significant direct and indirect effects on local plant and animal communities. Direct effects referto ungulates directly interacting with another species by foraging on plants and incidentally on insect eggs, larvae and/or adults. Indirect effects in this context describes ungulate feeding on plants which indirectly alters the availability and quality of food resources utilized by local insect fauna. Ungulates have even been considered as a potential conservation threat topersistence of some insect species. This aim of this thesis was to study the interaction between a common ungulate, the roe deer (Capreolus capreolus), and the rare butterfly Scolitantides orion by sharing the same plant resource, orpine (Hylotelephium telephium).  S. orion is a butterfly species of high conservation concern in Sweden. It is classified as endangered (EN) and has over the last decades experienced significant decrease in population size, mainly as a result of habitat loss and fragmentation. Roe deer has been considered as a potential threat to the population, but the magnitude of the threat has not been studied in detail. The objective of this thesis was to analyse the direct and indirect consequences of roe deer herbivory on S. orion population in the island of Mörtö, Stockholm archipelago. I predicted that roe deer alters the abundance of suitable host plants for oviposition and consumes egg and/or larvae, producing significant differences between protected and unprotected plants. The study was conducted in May-June 2020 in seven selected sites in Mörtö. At the onset of the butterfly season, 47 mesh cages were established sheltering 10.4% of the 1310 plants included in the study. Five inventories were conducted over a five-week time period, where each plant was examined by measuring the height, number of leaves, plant damage and the number of eggs and larvae. These data were used to examine the direct and indirect effect of roe deer foraging.  The results of this study could not confirm that roe deer has a significant direct or indirect effect on S. orion population in Mörtö. Hence, roe deer may not pose as large of a threat as initially expected, at least in this island at this time period. However, this was not the only result from this study. Plant properties such as leaf number and plant height (although not significant) as well as plant quality influenced the host choice for oviposition, with significantly more eggsbeing found on plants with more leaves and less plant damage. Hence, it seems that roe deer and other herbivores indirectly affects the host choice of S. orion by altering plant attractiveness. The reason for this behaviour needs to be studied in detail, but a proposed reason was that females choose plants with less damage to avoid competition and/or predation. Another finding was that a substantial number of eggs were lost over the season, some of which due to incidental feeding by roe deer and other herbivores. However, many eggs were lost without an identified reason, which likely is a result of disease or predators, but this needs to be studiedfurther. Finally, the cage experiment was successful in keeping the roe deer out but not able to cause a difference in egg survival between protected and unprotected plants. This was likely due to low roe deer herbivory in general.  Even though the effect of roe deer on S. orion population was not as significant as expected, it is still important to consider roe deer as a potential threat to the species at its most vulnerable stages as the species is dependent on the host plant for its survival. Hence, it would be interesting to do a similar experiment in a locality with higher deer density to further investigate the effect of roe deer on S. orion populations.

The occurrence of compensatory photosynthesis was examined in the field during the spring for all foliage elements on two Agropyron bunchgrass species that differ in their evolutionary history of grazing pressure. Compensatory photosynthesis did occur in many individual foliage elements during at least part of their ontogeny. For both species, compensatory photosynthesis was related primarily to delayed leaf senescence and increased soluble protein concentrations, but not to an improvement in the water status of clipped plants. Photosynthetic water use efficiency and photosynthetic rates per unit soluble protein of foliage on partially defoliated plants were not increased following the clipping treatments. Light and temperature dependencies of gas exchange measurements were usually very similar between the two Agropyron species. However, gas exchange rates per unit foliage area of leaves exserted late in the spring on~ spicatum plants were significantly different from those on A. desertorum plants when these leaves were senescing. To determine the ecological significance of these differences between species for light and temperature dependencies, the average carbon gain and water loss rate per tiller were estimated. The differences between species for carbon gain and water loss rates per tiller in this environment were substantially less than the individual leaf gas exchange differences between species. Photosynthetic activity and survival of leaves were also determined during the fall, winter, and early spring for the two Agropyron species in the field. A large proportion of the leaves of both species survived the winter. Photosynthetic rates of both species declined as air temperature dropped during the fall, were slightly positive during the winter between periods of snow cover, and increased during the early spring. Even though there is potential for photosynthesis during a winter with intermittent snow cover, total plant saccharide pools were barely maintained over such a winter. Although A. desertorum and A. spicatum were exposed to different levels of grazing pressure during their evolutionary history, the phenology, water status, and gas exchange rates of foliage and tillers were very similar both for undefoliated as well as partially defoliated plants. Therefore, we conclude that compensatory photosynthesis does not appear to be an important ecological component of herbivory tolerance for these species.

The giant panda (Ailuropoda melanoleuca) subsists on bamboo, but lacks gastrointestinal modifications for fiber digestion. Pandas display dietary selectivity for certain plant parts; however, cues for selection are unknown, and few have examined panda feeding behavior and bamboo nutrient composition simultaneously. Bamboos are clonal plants, with seasonal cycles of nutrient accumulation related to peak photosynthesis and recruitment. These cycles can be destabilized by aboveground disturbance; however, effects of disturbance on nutritional quality and sustainability of bamboo for primary consumers have not been studied. I examined 4 factors that may contribute to bamboo nutritional quality or sustainable harvest: season, ramet maturity and age, and disturbance. I conducted a 3-year study with Phyllostachys aureosulcata (PLLAU), P. glauca (PLLGL), and P. rubromarginata (PLLRU), at the Shelby County AgriCenter, Memphis TN, applying 3 disturbance treatments in a replicated split-plot design: control, 3% and 20% annual removal of biomass. Bamboo was sampled 8 times/year and divided into shoot, leaf, and culm (central stem) for analysis of crude protein (CP), neutral- and acid-detergent fiber (NDF and ADF), ash, lipid, minerals, and acid-insoluble ash (AIA). I quantified bamboo-stand production, maturity, recruitment and mortality. Biomass removed from PLLAU was used in diet-selection trials with 2 giant pandas, observing consumption of plant parts and bamboo from different disturbance treatments, and sampling bamboo for allelochemical and starch analysis. Disturbance effects were evident only for branch and culm dry mass in PLLRU. In Year 2, drought conditions and peak roosting blackbird populations confounded results. Defoliation and guano deposition preceded changes to soil chemistry, bamboo composition, and stand structure; recruitment increased for PLLRU. After accounting for confounding factors, less-mature bamboo had greater concentrations of most nutrients, but less NDF, ADF, and K. Two-year-old ramets had greater CP, NDF, lipid, P, K, S, and Cu, but less Ca and Fe, than 1-year-old ramets. I confirmed seasonal plant-part selection by pandas, but found no correlation between leaf consumption and AIA concentration. Culm starch analyses were insufficient to establish a clear pattern. I recommend further investigation of non-structural carbohydrates in bamboo, and palatability testing of undisturbed versus disturbed bamboo, which I was unable to examine.

The geographic mosaic theory of coevolution predicts that spatial differences in species interactions result in a patchwork of evolutionary hot and cold spots across a landscape. We used horsenettle (Solanum carolinense L.), a perennial weed with a diverse insect community found in old fields and meadows, to examine local adaptation and resource-mediated selection. The goals of this study were to (1) determine the potential for a selection mosaic by identifying local adaptation through trait-interaction matching with herbivores, pollinations and plant competitors, and (2) determine the potential for indirect selection through resource allocation tradeoffs. The potential for local adaptation was determined by measuring interactions in four populations and relating those findings to plant traits measured on offspring grown from those populations in a ‘common garden.’ Allocation tradeoffs between growth, herbivore resistance, and floral traits were also assessed in the common garden. We found high herbivore damage in the field associated with decreased root:shoot ratios in greenhouse-grown plants, which may indicate an herbivore-mediated effect on life-history through selection for a more annual strategy. By examining allocation tradeoffs we found evidence of two distinct reproductive strategies in this perennial plant. Negative correlations between reproductive traits and both growth and defense suggest that individuals either favor current growth and reproduction over defense, or invest in current survival and defense while delaying reproduction. Overall, this study sheds light on how selection changes over space and time, which are of many of the fascinating traits we find in plants and animals today.

No description available.

Currently the size and frequency of wildfires are increasing at a global scale, including arid ecosystems that exhibit great sensitivity to disturbance. Fire effects on plant pollination and reproductive success in deserts are largely unknown. Plant dependence on animal pollinators for reproduction can increase the risk of reproductive failure if pollination services are hindered or lost. Species that depend on few taxonomically related pollinator species are expected to be most negatively affected by disturbances that disrupt pollination interactions. To assess fire and isolation effects on reproductive success in desert plant communities, and how wildfire influences the pollination success of generalist and specialist pollinated plants, the number of flowers, fruits, and viable seeds produced by plants surviving in burned and unburned desert landscapes were compared. Fire increased flower production for wind and generalist pollinated plants, and did not affect specialist plant flower production. Increases may be associated with positive physiological responses exhibited by plants surviving in burned areas. Fire did not affect pollination services. Wildfire effects on fruit production were neutral or positive, and overall seed:ovule ratios varied by 3% or less in burned and unburned areas for each pollination strategy. Increasing isolation within burned areas did not affect fruit production for generalist or specialist pollinated plants, suggesting that pollination services are functional across expansive burned desert landscapes. Annual reproductive output varied between years in burned and unburned areas, and shifts likely resulted from variation in annual precipitation patterns. Reductions in landscape reproductive output may be partially compensated by increased per plant fruit and seed production and maintaining pollinator services across burned landscapes, providing native shrub communities the possibility to naturally recover from fire disturbances. Habitat disturbances can influence plant interactions with herbivores, in addition to pollinators. To understand how fire and ungulate herbivory affect reproductive success of specialist pollinated desert plants, reproductive effort, floral herbivory, and pollinator visitation and success, were compared for Yucca baccata, and Yucca brevifolia in burned and unburned areas of the Mojave Desert. Fire increased Y. baccata flowering from 12% to 22% of plants in burned areas, but had no effect on the number of flowers or fruits produced per plant. Fruit set and pollinator collection failed at all sampled Y. baccata individuals, while fire and herbivory had no effect on Y. brevifolia flower, fruit, and pollinator collection. Herbivores consumed 50% and 67% of floral stalks produced by Y. baccata in unburned and burned areas. Herbivores pose a clear threat to successful sexual reproduction for Y. baccata. Removal of ungulate herbivores during important flowering periods may still result in failed fruit and seed production if local pollinator reserves have been drastically reduced or lost.

Human activities and rapid global climate change are altering fire regimes with potential threat to the stability of aspen ecosystems in North America. Aspen is an early successional species that plays an important role in post-fire forest reestablishment, but chronic browsing on juvenile aspen by large ungulate herbivores after fire can be detrimental and lead to regeneration failure. Although larger and more severe fires are expected to become more prominent, whether and how this may influence aspen and ungulate communities remains unclear. The objective of this research was to examine how the relationship between aspen and ungulate communities might be influenced by variation in fire severity and size. In 2012, we examined browse patterns, growth responses and defense chemistry (phenolic glycoside and condensed tannins) concentrations of regenerating aspen that experienced variable burn severity in the 2010 Twitchell Canyon Fire, Utah, USA. We found that greater light availability in higher severity burn environments enhanced aspen tolerance and resistance against herbivory by increasing growth potential and defense chemistry concentrations of aspen. These results suggest that burn severity influences plant-herbivore interactions through bottom-up and top-down forces, and that higher fire severity increases post-disturbance vegetation recruitment potential by increasing resilience to herbivory. In 2013, we characterized aspen and ungulate patterns of 25 fires that spread across five National Forests (Uinta-Wasatch-Cache NF, Ashley NF, Fishlake NF, Dixie NF, and Manti-La Sal NF) in the state of Utah. We identified interaction effects between fire size and severity that strongly influenced aspen and ungulate densities. Fire size and severity are important ecological filters that can interact to affect forest reestablishment and community response. This information is useful in developing decision-making tools for wildfire and ungulate management that can more effectively increase the long-term resilience of forests systems.