Terrestrial Insect Survey and the capacity of assemblages change on Dongsha Island

Project Duration	2011-12-31 ~ 2012-12-30
Research Title	Terrestrial Insect Survey and the capacity of assemblages change on Dongsha Island
Contracted Organization	National Chung Hsing University
Principal Investigator	Yang Man-Miao
Project Participants	Chiang Tung-Chuan, Liu Che-Yuan, Teng Ying-Hsuan, Chiu Chun-Yi, Fan-Chiang Chun-Cheng, Wu Tsung-Tse, Lai Bao-Cheng, Chen Chih-Wei
Keywords	Dongsha Island, insect resource survey, monitoring, functional groups, conservation, indicator insects
Abstract	This study conducted a comprehensive survey of insect fauna and monitoring assessments of indicator insect species. Building upon the 2008 study, six sampling sites were established across different environments and vegetation zones on Dongsha Island, including the main island area, the northern sand ridge, and the southern sand ridge. Quantitative insect sampling was carried out using Malaise traps, pitfall traps, and sweep nets, supplemented with qualitative collections through visual hand-picking and light trapping. Surveys were conducted at a baseline frequency of once every two months. A total of more than 710 morphospecies belonging to 18 orders and over 159 families were collected. Of these, 110 species from 53 families were identified to species level, bringing the cumulative number of species identified to species level over the years to 141 species. Dominant taxa across sampling sites included Hymenoptera, Diptera, and Lepidoptera. Functional group analysis recorded 244 herbivorous species, 99 carnivorous species, and 62 detritivorous species. Together with plants as primary producers, the trophic structure resembles a food pyramid with a broad middle and apex. Indicator monitoring focused on herbivorous insects and their natural enemies. Large Lepidoptera were selected as herbivorous indicator species, including Cephonodes hylas, Macroglossum nigricans, and Euploea mulciber. The two hawk moth species maintained stable and widespread populations, whereas Euploea mulciber showed signs of local extinction, with newly colonizing populations struggling to establish. For natural enemy monitoring, predatory lady beetles, lacewings, and mantises were selected. Populations of lady beetles and lacewings increased in response to rising prey abundance. Overall, although the small size of Dongsha Island limits the number of insects that can be sustained at any given time, the cumulative number of recorded species continues to grow. This suggests ongoing colonization by external insect species, accompanied by continuous processes of immigration and local extinction. Dongsha Island thus serves as a living laboratory for island biogeography, highlighting its importance for both academic research and environmental education, and underscoring the value of long-term study and development.