Effects of Large-scale Wildfires on the Scorpion and Solifugid Communities of the San Diego MSCP Region Data Summary Prepared for: San Diego Association of Governments U. S. DEPARTMENT OF THE INTERIOR U. S. GEOLOGICAL SURVEY WESTERN ECOLOGICAL RESEARCH CENTER Effects of Large-scale Wildfires on the Scorpion and Solifugid Communities of the San Diego MSCP Region By Christopher W. Brown, Milan J. Mitrovich, Carlton J. Rochester, and Robert N. Fisher U. S. GEOLOGICAL SURVEY WESTERN ECOLOGICAL RESEARCH CENTER Data Summary Prepared for: San Diego Association of Governments San Diego Field Station USGS Western Ecological Research Center 4165 Spruance Road, Suite 200 San Diego CA, 92101 Sacramento, California 2010 i U.S. DEPARTMENT OF THE INTERIOR KEN SALAZAR, SECRETARY U.S. GEOLOGICAL SURVEY Martia McNutt, Director Suggested citation: Brown, C. W., M. J. Mitrovich, C. J. Rochester, and R. N. Fisher. 2010. Effects of large-scale wildfires on the scorpion and solifugid communities of the San Diego MSCP region. U.S. Geological Survey Data Summary prepared for San Diego Association of Governments. 45 pp. The use of firm, trade, or brand names in this report is for identification purposes only and does not constitute endorsement by the U. S. Geological Survey. For additional information, contact: Dr. Steven Schwarzbach, Center Director Western Ecological Research Center 3020 State University Dr. East Modoc Hall, Room 3006 Sacramento, CA 95819 ii TABLE OF CONTENTS ABSTRACT..................................................................................................................... 1 INTRODUCTION ........................................................................................................... 2 METHODS ...................................................................................................................... 5 Study areas. .........................................................................................................................5 Scorpion and solifugid sampling.........................................................................................7 Statistical analyses ..............................................................................................................8 RESULTS ...................................................................................................................... 10 DISCUSSION................................................................................................................ 12 ACKNOWLEDGEMENTS........................................................................................... 15 LITERATURE CITED .................................................................................................. 16 TABLES ........................................................................................................................ 19 Table 1. Species capture rate by site and condition .........................................................19 Table 2. Results from the hierarchical linear modeling analyses.....................................20 Table 3. Vegetation associations of scorpion and solifugid species ................................20 Table 4. Occupancy models for Anuroctonus p. pococki.................................................21 Table 5. Occupancy models for Vaejovis puritanus.........................................................21 FIGURES....................................................................................................................... 22 Figure 1. Schematic of the study areas.............................................................................23 Figure 2. Study plot design ..............................................................................................24 Figure 3. Vegetation composition by site.........................................................................25 Figure 4. Monthly activity patterns of the Solifugae and Scorpiones ..............................26 Figure 5. Pre-fire species composition at Little Cedar Ridge ..........................................28 Figure 6. Post-fire species composition at Little Cedar Ridge.........................................29 Figure 7. Pre-fire species composition at Elliott Chaparral Reserve................................30 Figure 8. Post-fire species composition at Elliott Chaparral Reserve..............................31 Figure 9. Pre-fire species composition at Rancho Jamul (reference)...............................32 Figure 10. Post-fire species composition at Rancho Jamul (reference) ...........................33 Figure 11. Pre-fire species composition at Rancho Jamul (impacted) .............................34 Figure 12. Post-fire species composition at Rancho Jamul (impacted)............................35 Figure 13. Pre-fire species composition at Santa Ysabel Preserve (reference)................36 Figure 14. Post-fire species composition at Santa Ysabel Preserve (reference) ..............37 Figure 15. Pre-fire species composition at Santa Ysabel Preserve (impacted) ................38 Figure 16. Post-fire species composition at Santa Ysabel Preserve (impacted)...............39 APPENDIX I. Scorpion species accounts .................................................................... 40 iii ABSTRACT To investigate the role of large-scale wildfires on the scorpion and solifugid species within San Diego County of southern California, we examined specimens that had been collected from four study sites distributed across the region from both before and after the 2003 wildfires: 1) Santa Ysabel Preserve, 2) Rancho Jamul Ecological Reserve-Hollenbeck Canyon Wildlife Area, 3) Little Cedar Ridge, and 4) Elliott Chaparral Reserve. In October and November of 2003, large-scale fires burned approximately 130,000 ha of San Diego County. We collected data to assess fire impacts on the local solifugid and scorpion communities using drift fence arrays with pitfall traps. Sampling prior to the fires was conducted between May 1998 and June 2003. Post-fire sampling was conducted between January 2005 and September 2007 with the objective of identifying impacts of wildfire on the scorpion and solifugid communities. We calculated monthly detection frequencies of each species to test for differences in seasonal activity patterns between scorpions and solifugids. We compared total species richness, rates of species accumulation, and average species richness detected per sample occasion between pre- and post-fire sample periods to describe major differences in the pre- and post-fire datasets. To test for the effects of wildfire on the community, we compared pre- to post-fire differences in the average species richness per sample occasion between burned and unburned plots, as well as modeled the effects of vegetation, plot condition (burned or unburned), and their interaction on the species richness measures for post-fire periods. We also tested for associations between vegetation types and individual scorpion and solifugid species and for the two most dominant species, constructed site occupancy models to compare occupancy among sites, vegetation types, and between burned and unburned plots. Seven scorpion and 14 solifugid species were detected across all of our trapping efforts. The scorpions Vaejovis puritanis and Anuroctonus pococki pococki were the most commonly detected species, occurring in 14.6% and 8.9% of the sample collections, respectively. The most abundant solifugid was Eremochelis andreasana, which we found in 1.7% of the samples. The majority of the species that we observed were only found in 1% or less of the samples that we collected. Of all of the species collected, three scorpions, A. p. pococki, V. puritanis, and Superstitionia donensis, and three solifugid species, Ammotrechula wasbaueri, E. andreasana, and Eremochelis kastoni, were detected at all four study sites. Our monthly detection frequencies showed that scorpions and solifugids reached their peak activity levels at different times of the year. Solifugids were most active in June while scorpions reached peak activity in August. Species richness and rate of species discovery increased in post-fire samples compared to pre-fire. The difference in average species richness per sample occasion between pre- and post-fire samples did not vary between burned and unburned plots. In the post-fire period, species richness per sample occasion for scorpions and solifugids varied by vegetation type but not plot condition, meaning there was a measured effect of vegetation but not fire on the average number of species detected. Approximately half of the scorpions and solifugids tested had a positive association between detection and vegetation type. Occupancy analyses revealed that the scorpions A. p. pococki and V. puritanus varied by site. A. p. pococki also varied by vegetation, but neither species varied by condition (i.e., burned or unburned) or across years. The overall absence of a negative effect of wildfire on the scorpion and solifugid communities in our analyses of pre- and post-fire sample data is not surprising given the biology 1 of both scorpions and solifugids is well suited to surviving both the short and long-term effects of fire. Both species groups are nocturnally active and readily use below-ground retreats during the daytime needing less shade cover. Scorpions and solifugids largely inhabit xeric environments, with seasonal peaks in activity occurring during the hottest and driest periods of the year. Both species-groups are comprised of generalist predators that