Arthropod surveys on Bioko, Equatorial Guinea
Charles E. Griswold Schlinger
Curator of Arachnida California Academy of Sciences
Research Professor of Biology San Francisco State University
Presented to Central African Regional Programs for the Environment
Arthropods (Insects, arachnids, and myriapods) offer a unique perspective in biodiversity surveys. Arthropods are the most diverse animal group on earth: perhaps 90% of metazoan species richness at any given site comprises arthropods. Arthropod richness may be 1-2 orders of magnitude greater than the next richest group. Arthropod species tend to have narrow distributions than vertebrates, allowing a more fine-grained sampling of geography. They show higher rates of endemism (Scharff 1992) than other taxa at a given site. Taxonomic richness of arthropods offers numerous biotic opportunities for replication of patterns of geography and evolution. This promise is largely unrealized due to what is sometimes called the ‘taxonomic impediment.’ Most arthropod species are effectively unidentifiable, and many, perhaps most, may be still undescribed. For example, the recorded spider fauna of Madagascar is close to 400 species (Roth 1992a). Yet nearly 400 species were collected in a 6-month survey at one mid elevation site in the southern part of the island (Roth 1992b). Clearly, the arthropod fauna is imperfectly known. Arthropod biologists working in the tropics are usually forced to use the ‘morphospecies’ concept, i.e., those species that are diagnosable at a given site, whether identifiable or not. Arthropod biologists recognize this problem and realize that the solution will be long-term. General collections are made and maintained for study now and for generations well into the future. Some advantages of surveying arthropods may be realized now by targeting selected groups that are well known and/or the subject of special study. Spiders are a good example of such a group (Dippenaar-Schoeman & Jocqué 1997). Cladistics has been applied to spider phylogeny since the early 1970’s so the taxonomy is reasonably mature (Coddington & Levi 1991; Coddington in press). A research program aimed at understanding the diversity, phylogeny, and geography of African montane rainforests has been ongoing for more the 15 years (Griswold 1991 and references cited therein). The arthropod survey of Bioko requires a general collection but at this time can offer a detailed analysis of the spiders families Cyatholipidae, Migidae, Phyxelididae, and Zorocratidae. Other arthropod groups were also targeted to take advantage of interest and expertise at California Academy of Sciences (CAS). Diptera (flies) were collected generally and reports planned for the Acroceridae, Blepharoceridae, and Therevidae. Ground beetles of the family Carabidae were also targeted.
Coddington, J. in press. Progress in spider systematics. Systematic Biology.
Coddington, J. & Levi, H. 1991, Systematics and evolution of spiders (Araneae). Annual Review of Ecology and Systematics 22: 565--592.
Dippenaar-Schoeman, A., & Jocqué, R. 1997. African spiders: an identification manual. Plant Protection Research Institute Handbook 9: 1--392.
Griswold, C, 1991. Cladistic Biogeography of Afromontane Spiders. Australian Systematic Botany, 4(1): 73-89.
Roth, V, 1992a. Preliminary list of spiders recorded from Madagascar with synonymies, present placement of species, and a partial bibliography. Unpublished Technical Report for Parc Nacional Ranomafana, pp.1--18.
Roth, V, 1992b. Spiders of Ranomafana National Park and immediate area. Unpublished Technical Report for Parc Nacional Ranomafana, pp.1--13.
Scharff, N. 1992. The linyphiid fauna of eastern Africa (Araneae: Linyphiidae) -- distribution patterns, diversity, and endemism. Biological Journal of the Linnean Society, 45: 117-154.
ARTHROPOD SURVEY PERSONNEL:
Dabney, Mr. Keith D.—Curatorial Assistant, Department of Entomology, California Academy of Sciences (fieldwork and specimen preparation)
Griswold, Dr.Charles E.—Schlinger Curator of Arachnida, Department of Entomology, California Academy of Sciences, and Research Professor of Biology, San Francisco State University (specimen preparation and data analysis: spiders).
Kavanaugh, Dr. David—Curator, Department of Entomology, California Academy of Sciences, and Research Professor of Biology, San Francisco State University (specimen preparation and data analysis: carabid beetles)
Ubick, Mr. Darrell—Curatorial Assistant, Department of Entomology, California Academy of Sciences (fieldwork, specimen preparation, and data analysis: spiders)
SURVEY LOCALITIES ON BIOKO
Parque Nacional de Pico Basile is the highest (elev. 3011) of two volcanic massifs dominating the landscape of Bioko. Vegetation ranges from lowland forest through montane (800 m 1400 m) and mossy/cloud forest (1500 m - 2500 m). Forest gives way to shrub formations above 2500 m and alpine meadow at the summit. Collecting was done at three sites (sites 1--3) along the road and along hunter’s trails into the forest.
Reserva Cientifica de la Caldera de Luba is located in the southern highlands, which rise to an elevation of over 2500 m. Precipitation of over 11,000 mm is typical on the south end of Bioko. A continuous gradient of forest exists on the south slopes of the southern highlands (Reserva Cientifica de Caldera de Luba), from lowland forest through montane and mossy forest. Collections were made at 2 sites (sites 4--5) at Moca Valley, a montane forest site with some intrusion of agricultural lands.Four sites were sampled in the Luba region (sites 6--9). The Luba region is a coastal lowland rainforest with swampy areas and much intrusion of cacao plantation.
1--Pico Basilé: 3°36’9”N, 8°46’38”E, ca.2300 m, 26--27 Sep.1998 - mossy/cloud forest (collecting by beating and sweeping foliage, searching at night, and sifting leaf litter)
2--Pico Basilé: 3°37’38”N, 8°48’15”E, ca.1750 m, 27--29 Sep. 1998 - mossy/cloud forest (collecting by beating and sweeping foliage, searching at night, and sifting leaf litter)
3--Pico Basilé: 3°41’44”N, 8°52’17”E, ca.700m, 17 Sep. 1998 - montane forest (collecting by beating and sweeping foliage, searching at night, and sifting leaf litter)
4--Moca: 3°21’36”N, 8°39’49”E, ca.1300-1400 m, 1--11 Oct. 1998 - mossy/cloud forest (collecting by beating and sweeping foliage, searching at night, and sifting leaf litter)
5--Moca: 3°22’0”N, 8°39’57”E, ca.1500 m, 5--10 Oct. 1998 - mossy/cloud forest (collecting by beating and sweeping foliage, searching at night, sifting leaf litter, and pitfall traps)
6--5 km W Luba: 3°27’54”N, 8°31’17”E, ca. 0-50 m, 12--14 Oct. 1998 - cacao plantation with fig trees (collecting by beating and sweeping foliage, searching at night, and sifting leaf litter)
7--3.5 km W Luba: 3°28’54”N, 8°34’58”E, ca. 0-50 m, 13 Oct. 1998 -swampy forest (collecting by beating and sweeping foliage, searching at night, and sifting leaf litter)
8--Arena Blanca: 3°31’21”N, 8°35’0”E, ca. 0-50 m, 14 Oct. 1998 (collecting by beating and sweeping foliage, and sifting leaf litter)
9--Punta Becrof: 3°43’18”N, 8°39’41”E, ca. 0-50 m, 18 Oct. 1998 (collecting by beating and sweeping foliage, and searching at night)
Arthropods were collected by hand searching during both day and night, beating and sweeping of foliage, sieving leaf litter, and pitfall trapping. Flying insects were sampled with malaise traps during the day, and with ultraviolet and mercury vapor light traps at night. Specimens are currently being sorted, labeled, and stored at the California Academy of Sciences, where they will be available to qualified researchers from all over the world.
CONSERVATION IMPORTANCE OF BIOKO
Insofar as can be estimated at this time, the arthropod fauna of Bioko is as rich and diverse at that of mainland Cameroon. The island shows no impoverishment associated with isolation. For those spider taxa that can be identified endemism is low (though an assessment of carabid beetles may show otherwise) and so Bioko cannot be considered a 'center of endemism.' Perhaps the most valuable aspect of Bioko is that it may harbor a rich and diverse biota, comparable to any on the mainland, for which a complete transect from low to high elevation (lowland forest through montane and mossy forest) is preserved on the south slopes of the southern highlands (Reserva Cientifica de Caldera de Luba). Only Mount Cameroon is comparable, and both population pressure and volcanic activity threaten this gradient. The Reserva Cientifica de Caldera de Luba is a biodiversity treasure that deserves top conservation priority.
Created by Heather Tennison April 10, 2001