Print PageIncreased dominance by invasive grasses can alter the composition and structure of vegetation communities. These vegetation changes could affect many fauna, and arthropods may be impacted disproportionately due to their specialized relationships with certain plants for food resources and as reproduction sites. Changes in arthropod assemblages could affect a variety of ecosystem processes, such as pollination and decomposition, and modify availability of important prey species for many birds and small mammals. To better understand the effects of invasive plants, we compared diversity and abundance of arthropods in areas dominated by Kleberg bluestem, tanglehead, and a diversity of native grasses. Kleberg bluestem (Dichanthium annulatum) is an introduced Old World species that dominates grasslands in south Texas and tanglehead (Heteropogon contortus) is native to south Texas, but recently has been increasing in distribution and dominance in certain areas, behaving like an invasive species. We selected 90 1-m2 plots dominated by Kleberg bluestem, tanglehead, and diverse native grasses, 30 plots each, on the King Ranch, Kleberg County, Texas. We sampled arthropods using pitfall traps and vacuum sampling and quantified vegetation structure and composition in July and August 2009-2010. We sorted and identified arthropods to order and compared order richness, total abundance, and abundance of arthropod orders among the grassland types.
Results/Conclusions:
Areas dominated by native grasses had 50-130 (32-55%) more individual arthropods per plot during all sampling periods and one additional order (2-15%) of arthropods in three of four sampling periods, compared to areas dominated by invasive grasses. We also detected differences in abundance of specific arthropod orders; native grass-dominated areas had more plant-feeding bugs, spiders, grasshoppers/crickets, and beetles than areas dominated by invasive grasses, during at least some sampling periods. We detected 7-10% greater forb cover and 1-3 (18-40%) additional plant species in areas dominated by native grasses. Forbs are important food sources for certain arthropods, and a greater diversity of plant species may in turn increase the abundance and diversity of arthropods within a habitat; these changes in the arthropod community can have ecosystem-wide effects. Reductions in food resources could cause concomitant shifts in composition of animal communities, and disruption of ecosystem processes such as pollination and decomposition could result in subsequent changes in composition of plant communities. Although complete eradication of invasive grasses is unlikely, conservationists and managers can focus on maintaining or increasing vegetation heterogeneity to sustain diverse floral and faunal communities and critical ecosystem processes.
