Determinants of Biotic Resistance to Invasion in Plant Community Assembly PDF Download

Author: Chaeho Byun
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Languages : en
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Book Description
"Biotic resistance refers to the ability of species in a resident community to restrict invasion. Biotic resistance is central to our understanding of how a community recruits/repels new species. From a practical perspective, biotic resistance is relevant to the restoration of communities and/or the management of invasive species. Fundamental ecological mechanisms regulating biotic resistance are not fully understood. This research investigates determinants of biotic resistance to invasion. Its overall objectives were to identify the characteristics of species and communities making them more or less resistant to species invasion and to quantify the contribution of other biotic and abiotic factors to the regulation of biotic resistance. I hypothesized that (1) functional group identity of wetland species would be a good predictor of their biotic resistance, while species identity effect would be redundant within functional group; (2) mixtures of species would be more invasion resistant than monocultures; (3) abiotic constraints (flooding in this case) would influence biotic resistance both through direct effect on invaders and indirect effect on resident wetland species, and (4) propagule pressure of invading species would interact with wetland plant density to influence biotic resistance. I chose an introduced lineage of Phragmites australis as a model invasive species to test biotic resistance, but used emergent functional groups of wetland species based on trait similarity to facilitate generalizations to other species. I conducted a series of rigorous community assembly experiments both in pots and in wetland to simulate a situation where P. australis seeds land on bare soil along with other wetland species, a common occurrence in the field after disturbances or wetland restoration. I used advanced statistical approaches based on diversity-interaction models to disentangle species interaction mechanisms underlying diversity effect and structural equation models to estimate effect of flooding on invasion.Strong resistance of short fast-growing annual plants to restrict P. australis emergence was one of the most consistent findings across several experiments. This result suggests priority effect as a mechanism regulating biotic resistance to prevent seed-mediated invasion of P. australis. Regarding the diversity-invasibility relationship in community assembly, combining certain functional groups in specific ratio led to complementarity diversity effect which strengthened biotic resistance. This result implies species interactions between functional groups are key mechanisms generating diversity effect. Structural equation model supported a partial mediation hypothesis in which both direct flooding effect on P. australis and indirect flooding effect on wetland plants determined invasion success. Abiotic constraint and biotic resistance worked synergistically or antagonistically in controlling invasion depending on the fitness of the wetlands species involved. Finally, propagule pressure increased invasion success up to a threshold beyond which additional P. australis seeds did not increase invasion proportionally. This threshold was controlled by the species recruitment rate (i.e., seed density) of wetland plants, decreasing with increased density of wetland plants. By embracing complex invasion processes and multiple drivers, my research not only advances our comprehension of early community assembly and response to invasion, but also proposes a useful analytical framework that I hope will inspire future investigations and experimentations in community ecology. The fields of restoration ecology and invasion ecology, in particular, are in dire need of strong quantitative evidence to support ecological management approaches. This study can be an important step toward predicting invasion risk and impact as well as designing native community assembly for invasive plant management. " --