Spider biodiversity related to bund habitat and insecticide use in Hainan

by
Alberto Barrion, S Villareal, J Catindig, International Rice Research Institute, Los Baños, Philippines and Ducheng Cai, Hainan University, Danzhou, Hainan, China

Map of Hainan Island showing locations of the 4 sampling sites

In the first exploration, we collected 10,424 spider individual using various sampling methods and have sorted them out to species. Spider biodiversity is impressive and several species had never been described (Read:New species described). The spider samples were obtained from Hai Kou, Lingshui, Sanya and Danzhou rice fields.  We have also interviewed farmers in these 4 collection sites and obtained their insecticide use patterns. To determine species richness we used the rarefaction method available in ECOSIM and EstimateS (Gotelle and Entsminger, 2005 and Colwell 2009) and  The rarefaction technique was applied to compute species richness to avoid the sample size sensitivity.

There is very high spider biodiversity in Hainan Island. Photo credit: S. Villareal.

Spider species richness seems more related to bund vegetation.  In Haikou and Sanya where farmers in the sampling sites had applied herbicides in the bunds, species richness, S were extremely low, 35.7 for Sanya and 37 for Haikou.  Highest species richness was found in Danzhou (69.7), where insecticide sprays were lowest and rice fields were richly surrounded by vegetation.  Bunds were not sprayed with herbicides. In Lingshui, an area with intensive rice cropping and bunds were not applied with herbicides and often planted with vegetables and fruits the spider species richness was intermediate at 54.5.  The rarefaction curves are shown below.

Rarefaction curves of the spider species richness and abundance. Species richness was compared at abundance equal 1231.

The analysis indicated that spider species richness is probably highly dependent on bund vegetation as these habitats can provide the refugia between rice crops for hiding and reproduction. Thus the two sites that farmers applied herbicides to the bunds had the lowest spider richness.  In the sites where bund integrity was not destroyed by herbicide sprays, spider species richness was higher. Insecticide sprays also have effects as in Danzhou where much less insecticides were used in the rice fields, spider species richness was significantly the highest.

References

Colwell, R.K. 2009. EstimateS: Statistical estimation of species richness and shared species from samples. Version 8. http://viceroy.eeb.uconn.edu/estimates

Gotelli, N.J. and Entsminger, G.L. 2005. Ecosim: Null Models Software for Ecology. Version 7.72. Acquired Intelligence Inc, & Kesey-Bear. http://www.garyentsminger.com/ecosim/index.htm

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