Assessing the Arthropod Diversity Along an Urban Gradient Using Spiders as a Model William Kish & Sujan Henkanaththegedara Department of Biological & Environmental Sciences Longwood University, Farmville, Virginia Background Urbanization generally cause loss of native species diversity (Blair 1996). Urbanization may also promote a few urban- adapted taxa and lead to biotic Southern House Spider (Kukulcania hibernalis) homogenization (Blair 1996). Little attention has been given to explore how urban development affects the diversity and abundance of arthropods including spiders (Shochat et al. 2004). Common House Spider (Parasteatoda tepidariorum) Intermediate Disturbance Hypothesis The highest diversity is reported in moderately disturbed locations (Connell 1978). Background The United States supports a considerable diversity of spiders (~4,000 species, Bradley, 2013). Tuft-legged Orbweaver Many aspects of spider habitat use, and niche (Mangora placida) specialization are poorly documented (Howell and Jenkins 2004). Additionally, the species diversity of spiders in the eastern United States is poorly documented (Howell and Jenkins 2004). Canopy Jumping Spider (Phidippus otiosus) Effects of Urbanization Compared bird species distribution and abundance across urban gradient Species richness, Shannon diversity and biomass was highest at moderately disturbed habitats Support for intermediate disturbance hypothesis (Blair 1996) Effects of Urbanization Diversity was highest in desert remnants habitat (dominated by native vegetation, no built structures) Diversity was lowest in mesic yards (>50% lawns, exotic plants, and irrigation) (Shochat et al. 2004) Research Objectives 1) Study spider diversity and abundance along an urban gradient - Test the Intermediate Disturbance Hypothesis 2) Explore the relationships between environmental conditions and the diversity of spiders. 3) Compile a checklist of spiders in the Longwood Lancer Park flood plain. Study Area Longwood University in Farmville, Virginia at the Lancer Park Flood Plain. This ~30-acre area with both aquatic and terrestrial habitats containing: Third order stream Seasonal pools and several man-made ponds Eastern deciduous forests Grasslands and hedge habitats Buffer habitat with parking lots and roads Research Design Three 5m x 5m study plots representing forested habitat (non- urban), grassy habitat (transitional), and urban habitat. Field Data Collection • Fall 2018 (N=5) and Spring 2019 (N=7) • Collected using visual observations and sweep nets. • Photographed and released back to the original capture location. • Environmental data were also collected (temperature, humidity, light intensity and height) Distribution of the experimental plots Field Data Collection Spiders were identified using field guides and identification keys provided by Bradley (2013), Gaddy (2009), and Howell and Jenkins (2004) Reported to iNaturalist online species repository (https://www.inaturalist.org) Data Analysis Diversity was determined using the Shannon-Wiener Diversity Index. Data was analyzed statistically using R statistical software program. Two way ANOVAs and Simple Linear Regressions were used. Results • 11 Families, 51 Genera, 76 Taxa, and 345 Individuals • Most abundant families and Taxa: A B • Salticidae (17.4%); White-jawed Jumping Spider (Hentzia mitrata) (20) (A) • Lycosidae (16.2%); Rabid Wolf C D Spider (Rabidosa rabida)(8) (B) • Oxyopidae (15.7%); Lynx Spider (Oxyope sp.) (48) (C) • Araneidae (13.0%); Humped Trashline Orbweaver (Cyclosa turbinate) (20) (D) Results: Species richness Fall 2018: Highest number of species in grassland habitat. 12 P = 0.0188 F = 6.217 10 8 6 4 2 Number of Species 0 Urban Grassland Forest High Disturbance Low Disturbance Results: Abundance Fall 2018: Highest abundance was in the grassland habitat P < 0.001 35 F = 15.00 30 25 20 15 Abundance 10 5 0 Urban Grassland Forest High Disturbance Low Disturbance Results: Shannon-Wiener Diversity Fall 2018: No significant differences among habitats. 2 P = 0.172 1.8 F = 1.99 1.6 1.4 1.2 1 Wiener Wiener Index (H') 0.8 - 0.6 0.4 0.2 Shannon 0 Urban Grassland Forest High Disturbance Low Disturbance Results: Species Richness Spring 2019: Highest number of species in forested habitat 7 6 P = 0.832 F = 0.186 5 4 3 2 Number of Species 1 0 Urban Grassland Forest Results: Abundance Spring 2019: Highest abundance was in the grassland 10 9 P = 0.689 8 F = 0.38 7 6 5 4 Abundance 3 2 1 0 Urban Grassland Forest High Disturbance Low Disturbance Results: Shannon-Wiener Diversity Spring 2019: No significant differences among habitats. 1.8 1.6 1.4 P = 0.405 F = 0.951 1.2 1 0.8 Wiener Wiener Index (H') - 0.6 0.4 0.2 Shannon 0 Urban Grassland Forest Results: Effects of humidity Abundance had a significant positive correlation with relative humidity. 45 40 R² = 0.1283 P = 0.0273 35 30 25 20 15 Abundance 10 5 0 0 20 40 60 80 100 Humidity (%) Results: Effects of light intensity Abundance had a significant negative correlation with light intensity 45 R² = 0.1478 40 P = 0.0188 35 30 25 20 Abundance 15 10 5 0 0 50000 100000 150000 Light Intensity (Lux) Results: Effects of height Abundance had a significant negative correlation with height 45 R² = 0.1195 40 P = 0.0335 35 30 25 20 15 Abundance 10 5 0 0 50 100 150 200 Height (cm) Results: Effects of light intensity Number of species had a significant negative correlation with light intensity 14 R² = 0.1245 P = 0.0322 12 10 8 6 4 Number of Species 2 0 0 50000 100000 150000 Light Intensity (Lux) Conclusions and Discussion 11 Families, 51 Genera, 76 Taxa, and 345 Individuals Rural habitats support diverse spider communities Less diversity and abundance in urban habitats in fall 2018 Provides evidence for negative impacts of urbanization Support for IDH with fall 2018 data but not with spring 2019 Possibly due to lack of “mature spider community” after winter More spiders in humid, low elevation and dark habitats Discussion Limitations Seasonality of spiders Extreme weather Spotted Orbweaver (Neoscona crucifera) Future Directions Yellow Garden Spider Continue sampling to increase sample size (Argiope aurantia) Analyze the seasonal variation Sample throughout the year https://www.inaturalist.org/projects/lancer-park-spiders-fall-2018 https://www.inaturalist.org/projects/lancer-park-spiders-spring-2019 Acknowledgments We would like to thank, Data collection: Griffin Mayo and Zachary Taylor Funding: Longwood CURIO Program and Virginia Academy of Science (Undergrad Research Scholarship) This study was conducted as an extension of Longwood BioBlitz (https://blogs.longwood.edu/longwoodbioblitz/) under VDGIF Scientific Collecting Permit # 059601. References Blair, R.B. 1996. Land use and avian species diversity along an urban gradient. Ecological Applications 6:506-519. Bradley, R. A. 2013. Common Spiders of North America. University of California Press, Berkeley and Los Angeles, CA. Connell, J.H. Diversity in Tropical Rain Forests and Coral Reefs. Science199: 1302- 1310. Gaddy, L.L. 2009. Spiders of the Carolinas. Stensaas + Kollath Publishing, Duluth, Minnesota, USA. Howell, W. M., and Jenkins, R. L. 2004. Spiders of the Eastern United States. Pearson Education, Boston, Massachusetts, USA. Shochat, E, W.L. Stefanov, M.E.A. Whitehouse, S.H. Faeth. 2004. Urbanization and spider diversity: influences of human modification of habitat structure and productivity. Ecological Applications 14: 268–280 Questions?.