| Bromus inermis and Poa pratensis are invasive graminoids that are known to represent a threat to the biodiversity of prairie habitats through their impacts on vegetation. They are suspected of detrimental biodiversity effects that scale up trophically, but this was not previously confirmed via direct study. This study of invasive graminoid impacts centered on the insect community and diversity in small Northern Tallgrass Prairie remnants. A group of abundant target taxa were sampled extensively for two summers, 2006 and 2007, using pitfall and sweep sampling techniques. Statistically significant reductions in the species richness of target taxa in traps were observed during both summers and at both locations as the invasive component of surrounding vegetation cover increased, using categorical, regression, and diversity index measures. Shifts in abundance and community structure were also observed. This was a modest but measurable reduction in richness of about one common species per sample, proportionally 20-25% of richness. Brief examinations of spring burning impacts in 2007 indicate that burning may ameliorate the impact of invasive graminoids. This research also suggests that invasive graminoids may not produce measurable bottom-up effects until a certain 'threshold' level of cover at about 30% is reached. |
