MODULE 13 Effects of Road Disturbance on Arthropod Diversity

1. MODULE 13Effects of Road Disturbance on Arthropod Diversity SEE-U 2001Biosphere 2 Center, AZ Professors: Danoff-Burg, James Kittel, Tim TA: Erika Geiger Yuko Chitani Mei Ying Lai Lily Liew Asma Madad Adam Nix Eli Pristoop J.C. Sylvan

2. Introduction Primary Questions: How are arthropod morphospecies richness and abundance affected by road intensity in a desert environment? Hypothesis: Arthropod morphospecies richness and abundance are more reduced along a high intensity road than a low intensity road in a desert environment.

3. Methods • We sampled three transects in two treatments: one along a high intensity road (Treatment A), and one along a low intensity road (Treatment B). • Each transect ran 50 meters perpendicular to the road. • Along each transect, we sampled at three points 3m, 10m, and 50m. This was the basis for our distance gradient. • At each point, we sampled using quadrat design using a beat sheet and a single aspirator. • We labeled specimens according to sampling points. • At the lab we catalogued the arthropod morphotaxa.

4. Results • The statistical analysis does not support our initial hypothesis. Instead, the two 2-way ANOVA test reveals the following: • Abundance - Arthropod abundance was greater along a high intensity road than a low intensity road in a desert environment. (Distance, F2,12 = 10.659, S; Road, F1,12 = 6.566, S) • Species Richness - Arthropod richness was also greater along a high intensity road than a low intensity road in a desert environment. (Distance, F2,12= 10.667, S; Road, F1,12 = 4.167,NS) • Our graphs in Excel (figures 1, and 2) demonstrate the following trends.

7. Discussion Hypothetically, the impact of roads on biodiversity in desert environments should be less severe than in the denser habitats like a temperate forests, because: • Desert environments have more bare ground and no tree canopy. • Arthropod species may be more adapted to openings; fragmentation of their habitats like road cuts may not affect them. • There should be little or no significant change in species richness along roads. However, both richness and abundance decreases with distance from the road regardless of road intensity. • In both treatments, arthropod morphospecies richness increases along a 50 meter distance gradient approaching the road. • In both treatments, the abundance of arthropods also increases along a 50 meter distance gradient approaching the road. • While we found more samples and in a greater variety along the higher intensity road than the lower one, the difference in abundance and richness taken together is not great enough to be statistically significant. We have a few hypotheses to explain this trend: • Vehicles introduce new species to the areas surrounding roads. • Climatic factors such as temperature, wind, and humidity can create a suitable environment for exotic species. Our sampling method may have introduced biases: • We sampled only creosote trees. • We did not account for changes in topography. To improve our study: • We need to include more samples.

8. Conclusion • Species richness is not significantly affected by road intensity. • However, it is significantly affected by distance from road. • Abundance is not significantly affected by road intensity. • However, it is significantly affected by distance from road. • Effects of fragmentation are not restricted to dense forests.

9. References Floyd Werner and Carl Olson. 1994. Insects of the Southwest. Fisher Books. Tucson. Robert L. Smith. Venomous Animals of Arizona. College of Agriculture, University of Arizona. Tucson.. Lorus J. Milne and Margery Milne. 1995. National Audubon Society Field Guide to North American Insects and Spiders. Alfred A. Knopf. New York. Darryl P. Saunders. A Pictorial Key to the Orders of Adult Insects. Purdue University. West Lafayette, IN. Donald J. Borror and Richard E. White. 1970. A Field Guide to Insects: America North of Mexico. Houghton Mifflin. New York.