Vol. 43 No. 3, 2004

Spider Diversity on Orchid Island, Taiwan: A Comparison between Habitats Receiving Different Degrees of Human Disturbance

Kuan-Chou Chen and I-Min Tso*

Department of Biology, Tunghai University, Taichung, Taiwan 407

Kuan-Chou Chen and I-Min Tso (2004) Tropical forests exhibit very high spider diversity, but most related studies have examined a particular functional group or layer of the habitat and few have assessed the impacts of disturbance on tropical Araneae diversity. Orchid I. is 92 km off the southeastern coast of Taiwan, and its forests are the northernmost tropical forests in East Asia. In this study, the spider diversity was compared in 4 types of habitats with different degrees of human disturbances on this island. Habitat types examined in this study included primary forest, cultivated woodlands with a small degree of disturbance, firewood plantations with an intermediate level of disturbance, and grasslands generated from the clear-cutting of forests. We used 2 replicates for all habitat types, each containing four 5 x 5 m sample plots. Spiders from the ground, understory shrubs, and canopy were collected to obtain a comprehensive representation of diversity from all microhabitats in the sample plots. From the 1718 adult specimens obtained, 123 species from 19 families were identified. The abundance was the highest in the primary forest and lowest in the grassland plots. Plots in the 4 habitat types did not differ in Margalef species richness, Shannon-Weaver function, or Simpson index. However, plots in the primary forest had significantly lower evenness due to the high relative abundance of dominant orb weaver species. Results of a UPGMA analysis using pair-wise Euclidean distances showed that the sample plots could be clustered into 4 distinct groups, indicating that the composition of spiders among habitat types considerably differed. Plots in the primary forest, cultivated woodland, and firewood plantation habitats were dominated by space web builders and orb weavers, while those in the grasslands contained a much-higher proportion of wandering sheet weavers and ground runners. Results of this study suggest that various forest management activities conducted by the indigenous Yami people seemed to have increased the habitat heterogeneity of Orchid I., thus maintaining a high diversity of spiders.

Key words: Biodiversity, Araneae, Lanyu, Yami people.

*Correspondence: Tel: 886-4-23590121 ext. 3240-37. Fax: 886-4-23590296. E-mail: spider@mail.thu.edu.tw