Doctor of Philosophy (PhD)
Research in invasion ecology has focused on developing ecological theory that can predict how invasive species interact with invaded communities. However, empirical support for theoretical predictions has been inconsistent. Inconsistencies may be attributed to the lack of data in three core areas; (1) field data with enough resolution to determine population dynamics of invasive species in relation to native species, (2) manipulative field experiments that encapsulate natural variation found among micro-habitats, and (3) field data that incorporate effects of invasive species within and among spatial scales. This dissertation has addressed these concerns by examining the mechanisms responsible for the successful invasion and ecological impacts of the invasive grass smooth brome (Bromus inermis) within the prairies of North Dakota and Minnesota. GIS analyses revealed that native Spartina pectinata patch growth was two times greater in non-invaded areas versus areas heavily invaded with brome. The probability of extinction of native Spartina pectinata averaged 8 times more likely in areas of high versus low brome coverage. Field experiments determined differences in germination between invasive smooth brome and native prairie cordgrass were not driven by habitat differences or soil conditions. Following initial germination, invasive smooth brome had a negative impact on cordgrass establishment, which was primarily due to a 78% and 47% reduction in native cordgrass plant height and stems density, respectively. Throughout the field experiment invasive smooth brome was a dominant competitor under all habitats and soil conditions except in areas where soil salinity levels were highest. Results from the herbivore study indicated that smooth brome has the potential to have negative effects on local herbivore assemblages. Despite the large differences in herbivore species richness, diversity and evenness at our larger spatial scales, my results indicated no statistically significant effects of invasive smooth brome. Results indicated that plant species richness had a larger effect than invasive smooth brome on herbivore assemblages (i.e. plant species richness, predator abundances, landscape surroundings). Future directions for research concerning the impact of smooth brome on native herbivore assemblages should include incorporating herbivore community composition, predator abundances and landscape features (i.e. surrounding matrix, prairie isolation and management history).
Document Availability at the Time of Submission
Release the entire work immediately for access worldwide.
Dillemuth, Forrest Paul, "Invasion of smooth brome into North American tall-grass prairies: impact on native plant/herbivore species and mechanisms responsible for successful invasion" (2012). LSU Doctoral Dissertations. 3788.
Cronin, James T.