Biology and Biomedical Sciences: Evolution, Ecology and Population Biology
Date of Award
Doctor of Philosophy (PhD)
Chair and Committee
Tiffany M Knight
Although introduced plant species are often considered to be one of the most notable anthropogenic threats to biodiversity, their influence on biodiversity remains controversial. Some studies have shown large declines in biodiversity in plant-invaded areas, whereas others have noted that plant invasions are rarely implicated as the cause of species extinctions. This dissertation aims to synthesize this seemingly conflicting literature on the effects of invasive plants on biodiversity. The overarching hypothesis in this research is that the effect of invasive plant species on biodiversity is scale-dependent, and the discrepancy among studies can be explained by a difference in the scales of investigation at which these studies take place. In addition, the processes by which invasive plants influence community structure leads to slow, long-term extinction dynamics that mask likely future plant extinctions.
In Chapter 1, I used a meta-analysis to examine the influence of invasive plants on plant biodiversity. The meta-analysis showed a negative relationship between the effect size of an invasive plant on biodiversity: i.e., species richness) and the spatial scale at which the data were collected. Next, in Chapter 1 and 2, I developed a framework that generated testable predictions about why invasive plants cause scale-dependent biodiversity loss. This framework linked the shifts in plant biodiversity to scale-dependence by using the species-area relationship. In Chapter 2, I tested the framework by conducting surveys of species-area relationships in habitats with and without invasive plants in three disparate ecosystems--a temperate forest, sub-tropical forest, and tropical forest. In all three ecosystems, species in invaded habitats accumulated faster with area than species in uninvaded habitats, revealing smaller effects of invasive plants on the loss of biodiversity with increasing spatial scale. Results showed that scale-dependent biodiversity loss was due to sampling effects: i.e., a loss of individuals), as well as larger negative effects on the abundance of common species compared to the abundance of rare species. In Chapter 3, I further investigated changes in community structure by exploring the demographic processes that result in differential effects on common versus rare native species in habitats invaded by Lonicera maackii: Caprifoliaceae) in Missouri, United States. The overall population growth of common species was consistently more negatively affected than that of rare species. This was due to larger declines in common species' reproduction and greater sensitivity of their population growth to declines in the proportion of reproductive individuals. Finally, in Chapter 4, I established field and greenhouse experiments to test which abiotic conditions are altered by the presence of L. maackii. The results of these experiments showed that L. maackii significantly reduce light levels that reach the forest floor and that rare species tend to be more shade-tolerant than common species.
This dissertation synthesizes literature on the effects of invasive plants on biodiversity and provides a framework for how to approach biodiversity loss and predict future extinctions in the context of species commonness and rarity. Overall, my research reconciles the differences observed among local and broad-scale effects of invasive plant species on biodiversity.
Powell, Kristin Irene, "The Effects of Invasive Plants on Biodiversity Across Spatial Scales" (2013). All Theses and Dissertations (ETDs). 1200.