Comparison of spider guilds found in various oilseed crops of Pakistan

Transcription

1 BIOLOGIA (PAKISTAN) 2010, 56 (1&2), PK ISSN Comparison of spider guilds found in various oilseed crops of Pakistan MUHAMMAD MOHSIN, ABDUL QAYYUM KHAN SULEHRIA, IFTIKHAR YOUSUF, MUHAMMAD EJAZ, MUHAMMAD JAMEEL YOUSUF & ALTAF HUSSAIN Department of Biology, Govt. Post Graduate College, Satellite Town, Gujranwala (MM, MJY); GC University, Lahore (AQKS, AH); AMC, Department of Physiology, Rawalpindi (IY); Govt. Degree College, Peoples Colony, Gujranwala (ME) ABSTRACT Spiders utilize similar resources in different ways in agro-ecosystems. This assemblage of spiders is known as guild. Here spiders have been classified into guilds by using quantitative analysis of ecological characteristics of spider families occurring in six major oilseed crops of Pakistan. The similarity in spider species richness among crops was evaluated with the Sørensen qualitative coefficient while similarity in spider guild composition was calculated with the proportional similarity index. Clusters were constructed using the unweighted average linkage method. While total species richness varied widely among crops, the proportion of the total species within each guild was remarkably even across crops. The relative abundance of guilds varied greatly, which may reflect availability of resources within a crop type. Patterns of resemblance in guild lay out suggest the possibility of plant habitat structure as an influence on the spider community. Key words: Species richness, Spider guild composition, Oilseed crops, Spider guild. INTRODUCTION Invertebrate fauna is present in every agro-ecosystem in which insects and their relatives predominate. Higher spider species diversity is found in natural and agricultural areas, however, their specific diversity is generally lower than that of insects (Marc & Ysnel, 1999). A larger number of spider species are associated with oilseed crops as compared to any other agro-ecosystem. Among oilseed crops cotton shows the maximum spider species richness (Schoeman et al., 1999). Unfortunately spiders have largely been ignored because of the human tendency to favor some organisms over others of equal importance because they lack a universal appeal (Humphries et al., 1995). Spiders are among the numerically dominant insectivores in terrestrial ecosystem and exhibit a very diverse range of life style and foraging behaviors. They are important predators of insect pests. They form a major component of the generalist predator fauna and are potentially able to restrict pest population growth (Harwood et al., 2001). Though they are mostly generalist predators but some spider species are specialist predators (Whitecomb, 1962). Spiders can be considered as an ideal biological control agents because besides being generalist predators they are capable of propagating their population rapidly (Slansky & Rodriguez, 1989). They feed on a wide range of different animal

2 70 M. MOSHIN ET AL BIOLOGIA (PAKISTAN) groups, however, in general they tend to concentrate on insect prey. The significance of spider assemblages as biological control of pest is cosmopolitan (Pearce et al., 2004). Interest has been developed to help growers and consultants to understand spiders and their true value in crops: so that they begin to incorporate them in IPM strategies. Among beneficial species in crops, spiders are usually ignored and only predatory insects are considered. The information regarding their predatory role would allow spiders to become an integral part of IPM strategies. Favorable results can be achieved by using spiders as biological control agents in combination with selective and non-persistent insecticides and restricting the number of their applications to only specific times so as to protect them (Mushtaq et al., 2003, 2005). The indiscriminate use of insecticides in agro-ecosystems has been increased many folds resulting in ecological imbalance and appearance of more resistant pest strains in oilseed crops. Spiders as an excellent bio-control agent offer an opportunity and provide an alternative means of control for insect pest. Prior to this attempt in Pakistan various studies on biodiversity, relative abundance of spiders and ecology of oilseeds crops were carried on cotton, maize and canola by Saleem (1999); Ghafoor (2002) and Tahir (2008) from Faisalabad. The objective of present research is to review the work of various researchers on spider fauna of oilseed crops so that we may be able to identify spiders into families, genera and species that will help us to know about species composition, relative abundance and spider guilds found in oil seed crops after analyzing data statistically that is likely to increase the production of oils from oilseeds crops in Pakistan. MATERIALS AND METHODS A number of studies have been done in previous years by the workers of Araneae laboratory, Department of Zoology and Fisheries, U. A. F. on the biodiversity of spiders found in oilseed crops such as cotton, maize, peanut, canola, soybean etc. In the present study the data provided in these research dissertations has been used and is re-evaluated to know about the spider guilds residing in different oil seed crops and highlight the spider assemblage found in the form of spider guilds which will provide an appropriate parameter for the selection and justification of spider species. Guild concept refers to a group of species utilizing the same resource in similar ways (Uetz., 1991). Therefore guilds form the basis of community and reflect taxonomic relationships. Each guild will be comprised of most dominant families, genera and species found in foliage as well as on ground surface. In this way an excellent combination in the form of most appropriate spider species guild found in ground and upper surface of plants will be identified for use in IPM. Different collection methods for ground and foliage spiders were used. In the case of ground spiders mostly pitfall traps were used in grid and trap line fashion and for the foliage spiders mostly jarring, net sweeping and hand picking methods were employed which resulted into a good number of species recorded by students.

3 Vol. 56 (1&2) Spider Guilds Found in Various Oilseed Crops 71 The similarity in spider species has been evaluated with Sorensen qualitative coefficient (Southwood, 1992). The spider guild composition was calculated with proportional similarity index (Price, 1984; Smith, 1996). The clusters have been constructed using the un-weighted average method (Pielou, 1984). Cluster analysis was performed with STATISTICA (StatSoft, 1997). RESULTS The hierarchical cluster analysis produced a dendrogram which was used to construct spider guilds (Fig. 1). The breakdown of successive clusters appeared to be based primarily on web use, web-type, and microhabitat, resulting in 5 to 7 clusters of spider families that can be considered as guilds. Araneidae and tetragnathidae are 100% similar. Dictynidae and theridiidae also showed 100% resemblance. Among philodromidae and thomicidae there existed 93.5% similarity. 85.4% is the similarity level between the oxyopidae and salticidae. Corinnidae and erignoidae resemble 72%. Gnaphosidae and lycosidae show 83.3% similarity. Scytodidae, oonopidae, clubionidae and linyphiidae show similarity of 54.6%, 66.6%, 73.2% and 81.4% with their respective spider guild correspondingly. Cotton, maize and canola support the highest number of spider species followed by peanut and soybean. Sunflower is the most species-poor crop (Fig.2). Besides vast differences in species richness, spider faunas of individual crops were also distinctly dissimilar. Soybean, maize and canola share similarity of 99.7%. Sunflower has similarity of 98.7% with its respective spider guild. 96.4% similarity exists among cotton and its respective spider guild. Peanut share similarity of 82.3% with spider guild formed by all other crops. In soybean a total of 276 spiders were captured, out of which 260 are ground runners and 16 are foliage runners. In sunflower there are 165 specimens of spiders found, out of which are 23 ambushers, 119 ground runners, 20 foliage runners and 3 stalkers. In canola 445 were ground runners, 40 stalkers, 14 foliage runners and 25 ambushers. The total number of spiders caught from canola was 524. In maize a total of 3079 spiders were caught, out of which 2705 were ground runners, 20 foliage runners, 101 stalkers, 39 ambushers, 213 orb-weavers and 1 wandering. In peanut there were stalkers 213, ground runners 127, ambushers 71, orb-weavers 18 and 16 foliage runners. Total number of spiders caught from peanut was 445. From cotton 5769 spiders were collected, in them were ground runners 2899, foliage runners 906, ambushers 291, stalkers 1036, orb-weavers 545, wandering 47 and space web 45. Proportional similarity in the relative species richness of spider guilds of oil seed crops indicate that there exists 98.6% similarity among soybean and canola as far as their species richness is concerned (Fig. 3). Maize share 97.9% similarity with its respective guild of soybean and canola. Sunflower, soybean, canola and maize share 94.4% similarity. Peanut and cotton share 97.2% similarity and their guild share similarity of 87.3% with the guild formed by all other crops. In soybean there were 88% ground runners and 12% foliage runners. On the other hand in sunflower there were ambushers 26%, ground runners 53%, foliage runners 16% and stalkers 5%. In canola there were 64% ground runners, 12% foliage runners, 11% ambushers and 13% stalkers. Maize

4 72 M. MOSHIN ET AL BIOLOGIA (PAKISTAN) had ground runners 59%, stalkers 17%, orb-weavers 9%, foliage runners 7%, ambushers 6% and wandering 2%. In peanut stalkers were 34%, ground runners 40%, ambushers 13%, foliage runner 5% and orb-weaver 8%. Spider guild structure (proportional abundance) varied among individual crops (Fig. 4). The dendrogram represents that soybean, peanut, canola and sunflower show similarity of 77.3%. Cotton had the similarity of 62.9% with the guild formed by these four crops. On the other hand maize had the similarity of 41.6% with guild formed by all other crops. Spider guild composition represented that in soybean there are 94% ground runners and remaining 6% were foliage runners. In sunflower there are ambushers 13%, ground runners 72%, foliage runners 12% and stalkers 3%. There are 84% ground runners, 7% stalkers, 2% foliage runners and ambushers 7% in canola. In maize there are ground runners 87%, foliage runners 1%, stalkers 4%, ambushers 2%, orb-weavers 5 % and

5 Vol. 56 (1&2) Spider Guilds Found in Various Oilseed Crops 73 wandering 1%. In peanut there are stalkers 34%, ground runners 35%, ambushers 20%, orb-weavers 5% and foliage runners 6%. In cotton there are ground runners 50%, foliage runners 15 %, ambushers 5 %, stalkers 17 %, orbweavers 9%, wandering 1 % and space web 3%. DISCUSSION Various spider species utilize similar resources in different ways and form an assemblage in an ecosystem. Not only different spider species are associated with different oilseed crops but their composition also varies (Luczak, 1979; Nyffeler, 1982). The occurrence of particular spider species in specific crops is due to their response to particular features of the habitat or complex community interactions (Moran & Southwood, 1982). It has also been observed that habitat structure maintain diverse spider assemblages (Wise, 1993). Neighboring habitats also directly influence spider species and their abundance particularly in patchy agricultural landscapes (Alvarez et al., 1997).

6 74 M. MOSHIN ET AL BIOLOGIA (PAKISTAN) Many early workers stated that there was no evidence of a particular prey preference in spiders. However spiders show preference to certain pests (Bristowe, 1941). Some spider species clearly dominate over the others because their preferred prey reside in that particular ecosystem (Pekar, 2005). There are some specialist predators among spiders such as Pardosa milivina feeds predominately on the pink boll worm (Clark & Glick, 1961). It is very good to use spiders as biological control agents because some species are specialist predators. For a particular crop spider guilds can be used as excellent biological control agents for targeting specific pest species. The present study provides an ample evidence that spiders can be used in a better way in IPM strategies.

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