Species Richness and Composition Assessment of Spiders in a Mediterranean Scrubland

View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Estudo Geral J Insect Conserv DOI 10.1007/s10841-007-9116-3 ORIGINAL PAPER Species richness and composition assessment of spiders in a Mediterranean scrubland Pedro Cardoso Æ Se´rgio S. Henriques Æ Clara Gaspar Æ Luis C. Crespo Æ Rui Carvalho Æ Jesper B. Schmidt Æ Pedro Sousa Æ Tama´sSzuts} Received: 9 May 2007 / Accepted: 21 September 2007 Ó Springer Science+Business Media B.V. 2007 Abstract Intensive fieldwork has been undertaken in influence richness, abundance or composition of the sam- Portugal in order to develop a standardized and optimized ples to some extent, although sampling method had the sampling protocol for Mediterranean spiders. The present strongest influence whereas ‘‘collector’’ showed no effect at study had the objectives of testing the use of semi-quanti- all. The results support the idea that the only variables that tative sampling for obtaining an exhaustive species richness need to be controlled in similar protocols are the sampling assessment of spiders and testing the effects of day, time of methods and the time of day when each method is executed. day, collector and sampling method on the collected species We conclude that populations in structurally simple habitats richness and composition of a Mediterranean scrubland. present narrower peaks of adult abundance, which implies The collecting summed 224 samples corresponding to one higher percentages of juveniles in samples. Finally, results person-hour of effective fieldwork each. In total, 115 spe- also indicate that habitats with a relatively simple structure cies were captured, of which 110 were recorded inside a like scrublands may require as much sampling effort, in delimited one-hectare plot, corresponding to more than 70% order to reach similar proportions of captured species in of the about 160 estimated species. Although no estimator relation to the estimated richness, as habitats that are much reached the asymptote, the Michaelis-Menten curve more complex. behaviour indicates that the estimated richness should be accurate. Most different sampling approaches (day, time of Keywords Araneae Á Biodiversity assessment Á day, collector and sampling method) were found to Estimators Á Inventory Á Sampling protocol P. Cardoso Á J. B. Schmidt Á T. Szuts} C. Gaspar Natural History Museum of Denmark, Zoological Museum, Biodiversity and Macroecology Group, Department of Animal University of Copenhagen, Universitetsparken 15, Copenhagen and Plant Sciences, University of Sheffield, Sheffield S10 2TN, 2100, Denmark UK P. Cardoso L. C. Crespo Centre for Macroecology, University of Copenhagen, Department of Zoology, Faculty of Sciences and Technology, Universitetsparken 15, Copenhagen 2100, Denmark University of Coimbra, Largo da Se Nova, Coimbra 3000, Portugal P. Cardoso (&) Á C. Gaspar Agricultural Sciences Department – CITA-A, University of P. Sousa Azores, Terra-Cha˜, Angra do Heroismo 9701-851, Portugal CIBIO, Centro de Investigaçaõ em Biodiversidade e Recursos e-mail: [email protected] Gene´ticos, Campus Agra´rio de Vairaõ, Vairao 4485-661, Portugal S. S. Henriques Á R. Carvalho Department of Biology, University of E´ vora, Nućleo da Mitra, P. Sousa Evora 7002-554, Portugal Departamento de Zoologia e Antropologia, Faculdade de Cieˆncias da Universidade do Porto, Porto 4099-002, Portugal S. S. Henriques Institute of Botany and Zoology, Masaryk University, Kotlarska 2, Brno 61137, Czech Republic 123 J Insect Conserv Introduction method) could influence the collecting efficiency and the composition of samples. Arthropods, as a megadiverse group, have always presented a formidable challenge for taxonomists, ecologists and conservationists alike. Their sheer numbers make it Methods usually impossible to fully assess their richness and geographical patterns, even in restricted taxa or geographical Study site areas. In a world where global biodiversity is diminishing, rapid biodiversity assessment (RBA) programs have been The study was developed in a scrubland, located in Po- developed in order to try to gather as much information as maraõ, Vale do Guadiana Nature Park, in southeastern possible with the scarce time and resources usually avail- Portugal, at an altitude of 120 m (N 37°34.500, W able for the task (e.g. Duelli 1997; Jones and Eggleton 007°32.100). The site was dominated by a variety of 2000). Such programs usually have two main issues, sclerophilous plants, including rockrose (Cistus sp.), lav- comparability and efficiency. Comparability between ender (Lavandula sp.), gorse (Ulex sp.) and plants that areas, instances or even taxa, can only be guaranteed by the remained from the former agricultural use of the site or use of standardized sampling protocols. Efficiency, so that from surrounding areas, mainly oat (Avena sativa L.). No scarce resources are not wasted, can only be guaranteed by plants surpassed the height of 1 m, and in the majority of the optimization of sampling protocols. the area, the cover was much lower. The density of bushes As a megadiverse taxon, spiders share these constraints was relatively low, with large areas of bare ground being with most other arthropods. Despite their diversity, only covered by oat and low herbaceous vegetation or even importance in ecosystems, and the fact that probably many rocky patches. No trees were present in the delimited risk extinction or are already extinct, our enormous sampling area, and only a few holm oaks (Quercus ilex L.) knowledge gap does not allow knowing the true extent of were scattered in the region. Litter had a very thin, dry these considerations. Yet, no standardized and optimized layer, when existent. Average minimum temperature of the protocols have yet been proposed for spiders in natural region in January is 6°C and maximum temperature in habitats. August is 31°C, although peaks above 40°C are common. Most studies involving spider diversity assessment have Annual mean temperature is 17°C and precipitation is used a limited number of methods, leaving many species 500 mm, mostly occurring during autumn and winter undetected due to the failure of covering many microhab- months and with almost null precipitation during summer. itats. Spiders are very diverse in their ways of life, and sampling them requires a combination of methods. In Design of the study addition, many sampling programs neglect to consider the time of day or collector experience as important variables. We delimited a square sampling plot 100 m wide (1 ha), For spiders, complete protocols or sampling packages that where most of the sampling effort was applied. Additional gather information from a series of semi-quantitative effort was made around the sampling plot, up to a distance methods have proved to be the most effective (Coddington of about 100 m and an overall sampling area of about 10 ha. et al. 1991). Exhaustive sampling protocols directed at Sampling was made from May 9 to 23 of 2006, although spiders, mainly based on semi-quantitative methods, have most effort was concentrated from May 19 to 22 (hereafter been trialled in several parts of the world, i.e. Bolivia days 1 to 4). This period was chosen because it is the richest (Coddington et al. 1991), Peru (Silva and Coddington annually in Mediterranean areas (Cardoso et al. 2007). 1996), the USA (Coddington et al. 1996; Dobyns 1997; In total, 224 samples were taken. Each sample consisted Toti et al. 2000), Tanzania (Sørensen et al. 2002) and in one person-hour of work independently of the method. Denmark (Scharff et al. 2003). However, they were never From these, 128 samples were made inside the delimited fully standardized and optimized. plot over 4 days, both day and night, by eight collectors, From 2001 to 2006, systematic fieldwork has been using two different methods. Sampling followed a balanced undertaken in Portugal in order to reach a RBA protocol for design, that is, the same effort was applied for each sam- Mediterranean spiders (e.g. Cardoso et al. 2004a, b, 2007). pling day, time of day, collector and sampling method. The work now presented focused on a scrubland area in southern Portugal representative of this habitat type. The objectives were to determine if it was possible to conduct Sampling days an exhaustive semi-quantitative sampling of the spider community present in the habitat at the time of sampling, Since sampling was concentrated in 4 days, in a relatively and which factors (day, time of day, collector and sampling simple habitat with a scarce variety of microhabitats, this 123 J Insect Conserv continuous collecting was considered sufficient to provide a vegetation. Eighty samples were collected, 64 of which close to complete representation of the community. Besides, inside the plot. both the trampling of the ground and the continuous sweeping of plants certainly disturbed the habitat to a certain extent. We wanted to know if such sampling and disturbance Pitfall would cause the number of species and specimens to decrease from the beginning to the end of the fieldwork and if Two hundred and fifty six pitfall traps were used next to the the species composition would change with time. delimited plot in a square of 16 by 16 traps. Each trap was 5 meters from the nearest traps. A sample was considered as a 2 by 2 square of four traps so that we had 64 samples Time of day in total. The clumping of traps made individual sample effort reasonably comparable with time-based samples In both tropical (e.g. Sørensen et al. 2002) and Mediter- (being the effort applied to put and collect four traps ranean (Cardoso et al. unpublished results) forests, night equivalent to one person-hour of work) and reduced sto- sampling was found to perform considerably better than chastic heterogeneity among samples. The traps were set day sampling, as most spiders are night active. We wanted outside but next to the plot to avoid interference with the to test if night collecting would differ in the richness, collectors.

Load more