Vertical Distribution of Spiders (Araneae) on a Tropical Island Eric Brown Fall 2008 Advisor: Dr. Bruno Nyundo Academic Director: Helen Peeks Table of Contents TABLE OF CONTENTS - 2 - ACKNOWLEDGEMENTS - 3 - Deleted: - 3 - ABSTRACT - 5 -- 5 - Deleted: - 3 - INTRODUCTION - 6 -- 6 - Deleted: - 3 - STUDY AREA - 9 -- 9 - Deleted: - 3 - METHODS - 11 -- 11 - Deleted: - 3 - RESULTS - 14 -- 14 - Deleted: - 3 - DISCUSSION - 24 -- 24 - Deleted: - 3 - CONCLUSION - 27 -- 27 - Deleted: - 3 - RECOMMENDATIONS - 28 -- 28 - Deleted: - 3 - WORKS CITED - 29 -- 29 - Deleted: - 3 - APPENDICES - 31 -- 31 - - 2 - Acknowledgements This paper would not have been possible without the support of many people. In no particular order I want to thank: the four other Misali Island castaways—Matt, Lisa, Madeline, and Aisha—for keeping me entertained and in a good mood, as well as for an (almost) neverending supply of Nutella and peanut butter, Ilka for her help finding a stereoscope to use at IMS, Ali Said for information about staying on Misali and final approval for such, the Misali Rangers—Khamis, Said, Ali, Mohammed, Haji, Abbas—for food, bao, companionship, a never-ending supply of tea, boat rides, the generator, making who knows how many phone calls in order to set up all of the logistics for my return to Unguja, and extreme patience (and a good sense of humor) with my Kiswahili, the fishermen and ascaris for their assistance with my study (no matter what time of the night), Filbert and Hassan from Fundu Lagoon for leftovers, good conversation, and generosity that knows no bounds, Dr. Narriman Jiddawi for her assistance finding computer time at IMS, advice on advisors and a note to the fisheries department explaining my situation and asking permission for me to stay on Misali for my study, the Department of Fisheries for supporting me by allowing me free reign on Misali Island to perform my study, the guards at IMS for making it available all night, Robert Colwell for providing the EstimateS 7.5.1 population estimator software free of charge, Ali Seif at the Mkoani Guest House for allowing me to hang out there for half of a day while awaiting the ferry and for buying me my ferry ticket back to Unguja, Hamis for helping me find and purchase pipes to use as pitfall traps, Ali for his help getting zip-lock bags with which to catch spiders and for seeing me off at the ferry to Pemba, Helen for her patience with my work schedule, for supporting and approving my proposal, for extending office - 3 - hours to allow for more computer time, for help finding where to buy supplies, and for a semester’s worth of ISP ideas, Said for assistance finding an advisor, keeping the tax collectors at bay, advice on ferry tickets, and being available to answer ANY questions I had at ANY time—even if he was suffering—and always with his trademark sense of humor and good cheer, and finally my advisor, Dr. Bruno Nyundo from the University of Dar-es-Salaam, without whom I would have been lost, for agreeing to be my advisor, applying his expertise to my project, offering UDSM resources, being available at all times, being flexible and, in particular, helping me develop a valid methodology remotely, and with limited contact opportunities. Furthermore, I’d like to thank everybody who I have neglected to specifically mention above—believe it or not, there are many—who has helped me in any way during the study period. Your assistance has been invaluable and will not be forgotten. - 4 - Abstract The distribution of spiders into vertical layers was studied on Misali Island. In particular, differences in diversity, species richness, abundance, and body length were analyzed. A variety of collection methods were used in order to capture as many different species as possible from three levels of forest: leaf litter, groundcover (up to 1m), and understory (up to 3m). After being sorted to the morphospecies level, the spiders were cataloged and several statistical tests were run. These tests show that spiders do show species-level stratification between different levels of forest. They also pointed towards a particularly firm dividing line between species of the understory and those of the groundcover which discourages crossover. - 5 - Introduction Tropical islands are known as breeding grounds for both biodiversity and unique ecological situations because they combine two environments with already elevated levels of diversity and inimitability—the tropics and islands (Sadler, 1999). The vast distances of ocean separating islands acts as a biological barrier for many organisms. Over time, this barrier results in an ecosystem that develops unlike any other—no two islands have the same ecological situations, just as no two continents do. Since islands occur on a smaller scale than continents, however, their study allows a more complete look at a unique ecosystem. Furthermore, the vertical microhabitats of forests have been established as containing unique organisms that only exist at certain different vertical levels. This has been proven for a variety of organisms, including butterflies (Fermon et al., 2003), moths (Brown, 1997), and bats (Bernard, 2001). Since vertical layering works with butterflies, moths, and bats it is likely that some vertical stratification will be detected in this study. Only a few past studies have focused specifically on vertical spider distribution. These include Sorensen (2001), Pekar (2005), Wagner et al. (2003), and Schipper er al. (2007). However, none of these studies attempt to look at vertical spider stratification within a microhabitat itself—an island. Because this reduces variables and simplifies the working ecosystem, an island is a good place to start in order to begin building knowledge about vertical spider distribution. Researchers have determined that the tropical canopy holds a high proportion of the number of arthropod species existing in the forest (Erwin, 1982). Furthermore, - 6 - researchers have identified the vertical distribution of spiders to be similar to that of other arthropods (Sorensen, 2001). We can use this information to develop informed hypotheses about the vertical microhabitats. In that vein, this study endeavors to unveil the vertical distribution of spider species and spider attributes that vary on a vertical basis. It attempts to answer the following questions in an effort to uncover information about the vertical zones that spiders segregate themselves into on Misali Island: 1) Is the vertical distribution of spiders on Misali Island different in different vertical zones? 2)Does spider diversity differ based on vertical zones? 3) Does species richness differ based on vertical zones? 4) Does spider abundance differ based on vertical zones? 5) Does spider body length differ based on vertical zones? This study is important because it adds to the existing scholarship on spiders of Tanzania. This topic is not widely studied, and the gaps in knowledge are much larger than the pieces filled in. For example, Sorensen (2001) found that 80% of his collected spiders were not taxonomically defined yet. This presents a large unknown in the area of scholarship. Learning about these undiscovered and barely-discovered organisms can be potentially beneficial to humans for reasons yet undiscovered or for a variety of discovered reasons: direct—such as medical treatment—and indirect—such as mosquito population control. These reasons more than justify the time and expense put into this - 7 - project. - 8 - Study Area Spiders were collected on Misali Island, an island in the Zanzibar archipelago, over the course of three weeks. The island is located ~10 km off of the west coast of Pemba Island, centered at coordinates XXXXXXX (Abdullah et al., 2000). The entirety of the island, along with a portion of adjacent coral reef, is designated a Marine Protected Area, and is part of the Pemba Channel Conservation Area (PECCA). At .9 km, the island represents all of the terrestrial protected area within PECCA (Abdullah et al., 2000). The island is uninhabited except for the four rangers, several soldiers and fishermen who camp in two areas on the island at any one time. The island is covered with sections of sandy beach, verdant forest, and coral rag, and has little elevation change, with a maximum elevation of 6m (Google Earth). Sampling was performed in November, 2008, during the short rainy season of November/December in three vertical layers—leaf litter, groundcover and understory—within three separate 400 m2 plots on the island. The three plots deliberately represent three different vegetation zones on Misali in order to collect the widest variety of spider fauna. The sites had the following characteristics: Site #1: Canopy height ~10 m, understory density ~40%, groundcover ~30%, leaf litter depth ~3 cm. This site was located near (but did not include) the Bendera caves on the west side of the island. The area was entirely covered with topsoil. Site #2: Canopy height ~6 m, understory density ~35%, groundcover ~25%, leaf litter depth ~2 cm. This site was located on the north end of the island and a portion of - 9 - it included the edge of a mangrove area. However, it was not an intertidal area. The soil makeup was partially coral rag, partially topsoil. Site #3: Canopy height ~8m, understory density 85%, groundcover ~50%, leaf litter depth ~4 cm. This site was located in the southwest portion of the island, close to the Ranger Station and Visitor’s Center. This was the most topographically varied of the sites, with a coral rag wall raising part of the area ~1.5 m above the rest. The area was mostly covered with a thin layer of topsoil, but there were several portions where coral rag peeked through. In all sampled areas the forest showed no evidence of disturbance by humans, save for the nature trails that run adjacent to the sampling areas.