Novel Herbivore-plant Interactions PDF Download

Author: Ian Seth Pearse
Publisher:
ISBN: 9781267239402
Category :
Languages : en
Pages :

Get Book Here

Book Description
Understanding ecological invasions and the impacts of novel species interactions is one of the most important issues in modern ecology and evolution. Novel plants, including weeds, crop plants, and ornamentals are a common, almost ubiquitous feature of modern, human-influenced ecosystems. A striking observation is that in almost all cases, some herbivores adopt these non-native host plants, while other herbivore species do not. Conversely, some non-native plants accumulate many herbivores in their invaded range, while others accumulate few --a tenet of the longstanding Enemy Release Hypothesis. Understanding the variation in herbivore use of exotic plants is thus an issue of major importance, as it will impact ecological dynamics including extinctions, colonizations, range expansions, patterns of biodiversity, evolutionary processes such as host-shifts, and ultimately speciation. Variation in host use also has a strong influence on two of the most critical applied ecological problems of today: plant invasions and sustainable agriculture. The question of which non-native plants will get colonized by which herbivores is inextricably linked to the evolution of plant traits that affect herbivore colonization and the evolution of herbivore traits that affect their host-affiliations. As such, a comparative approach in understanding relevant traits of non-native plants, herbivore traits, and herbivore associations with non-native plants may help to create a framework for understanding the assembly of herbivore communities on non-native plants. This dissertation attempts to create a framework for predicting establishment of herbivore communities on non-native plants and to develop non-native oaks as a system for understanding the colonization of non-native plants. In the first chapter, I describe in depth the theoretical bases for predicting herbivore communities on novel plants. I suggest that the basis for predicting novel herbivore-plant interactions must take into account the host-breadth of an herbivore, the defensive investment of the novel plant, and trait matching between the novel interactors. In the second and third chapters, I apply this theory to oak taxa planted outside of their range using observations from oaks planted in arboreta. The amount of damage that non-native oak species experience was strongly predicted by the evolutionary relationship between the non-native oak and a local native oak species. Interestingly, the damage to these non-native trees was not related to the typical defensive traits that people commonly survey in oaks, suggesting that a more subtle suite of traits accounts for the ability of most herbivores to switch hosts between oak species. In contrast, the fourth chapter, I report the results of feeding trials with a common, generalist herbivore, which do respond strongly to typical oak defenses (such as tannins and leaf toughness). This suggests that very generalist herbivores may track "defensive" leaf traits to a greater degree than the rest of the herbivore community when establishing novel host-affiliations. A novel interaction between a plant and an herbivore is at least in part determined by plant traits. In the fifth and sixth chapters, I describe the evolution of oak traits that affect herbivore associations considering both normal macro-evolutionary processes as well as hybridization. I find that oak defensive traits have undergone strong convergence during the evolution of the genus Quercus. Moreover, these traits track aspects of the abiotic environment such as temperature seasonality and drought intensity. When hybridization occurs between oak species, the resulting hybrid's leaf traits were typically intermediate of its parental species indicating that these traits are inherited additively even during hybridization. In the final chapter, I focus on leaf phenology as a particularly important trait in driving the association of herbivores with non-native plants. I found that oak species, which retained only a portion of their leaves throughout winter, accumulated a higher abundance of leaf miners than oak species that were either totally deciduous or evergreen. I attribute trend to the observation that evergreen trees had very tough leaves over summer and accumulated few leaf miners late in the season. Completely deciduous trees lost all of their leaves in winter and had to be recolonized each year by a new set of leaf miners.