Operation COBRA: Developing a new protocol for measuring spider biodiversity in New Zealand pastures

Abstract

Research in conservation biology, ecology, and agroecology requires accurate knowledge of species distributions. Arthropods are often ignored or under-sampled in biodiversity and conservation assessments due to the large amount of effort caused by their large diversity, small size and lack of taxonomic guides. To assess these groups accurately, rapid biodiversity assessment programmes have been established. These programmes are based on sampling protocols that are required to be standardised to allow for comparison and optimised to obtain the maximum possible data with the minimum amount of effort. This research project aims to develop a new protocol for measuring spider biodiversity in pastures in New Zealand. A COBRA (Conservation Oriented Biodiversity Rapid Assessment) protocol consists of an intense sampling of an ecosystem by using the optimal combination of sampling methods. This study intensively sampled dairy and cropping pastures in the Canterbury area, and used ground sampling, suction sampling, sweeping, and pitfall traps to assess spider biodiversity. The minimum amount of effort and combination of methods required to record different levels of taxonomic and functional diversity was calculated. A total of 2767 spiders were caught, which included 1384 adults (50%) representing 12 families and 28 species. Pitfall traps collected 92% of the estimated number of species for all sampling methods. Ground hand collection collected 80.7% and suction sampling collected 22.5% of the estimated number of species. Sweeping collected the lowest estimated number of species with 17.8%. Therefore, of the four sampling methods used pitfall traps and ground hand collection were far more efficient at collecting spider species. Pitfall traps collected 12 unique species. Ground hand collection collected four unique species. Sweeping collected one unique species and suction sampling collected no unique species. Pitfall traps and ground sampling are the best methods to use to quickly assess spider diversity in pasture. Sweeping and suction sampling have limitations. Neither method can be used if the pasture is wet and suction sampling is not cost-efficient. Night sampling yielded more species compared to day sampling. Using a standardised protocol in pasture allows biodiversity to be measured over time to accurately assess whether it has increased or decreased as farming strategies change. For monitoring, ultimately, these tools will be used for assessing biodiversity on farms.