ARTICLE IN PRESS Journal of Arid Environments Journal of Arid Environments 56 (2004) 303–327 www.elsevier.com/locate/jnlabr/yjare Dung-insect communitycomposition in arid zones of south-eastern Spain Francisco Sanchez! Pin˜ ero*, Jose M. Avila Departamento de Biolog!ıa Animal y Ecolog!ıa, Facultad de Ciencias, Universidad de Granada, 18071 Granada, Spain Received 14 February2002; received in revised form 23 September 2002; accepted 2 April 2003 Abstract Dung-insect communitycomposition was studied at three sites for 1 year,and for a further 8 months at one site, in an arid region of Spain. The insect communitywas dominated byants, dung flies and beetles. Ants were abundant and flies relativelyscarce at all three sites, whereas beetle diversityand abundance differed among sites and between years.Community composition varied along the year in species richness, abundance and biomass. Although dung-insect communities of arid Spain share some traits with dung-insect assemblages in other deserts, diversityand trophic structure of these communities are highlyvariable, a common but underappreciated feature of communities in arid regions. r 2003 Elsevier Ltd. All rights reserved. Keywords: Desert; Dung-insect community; Inter-annual variability; Seasonality; Spain; Spatial variability 1. Introduction Insects associated with dung form a highlydiverse communityincluding specialized coprophagous and predatoryspecies of beetles and flies, as well as an arrayof generalist consumers, which colonize feces during the different stages of decomposition (Koskela and Hanski, 1977; Hanski, 1987, pp. 837–884, 1990, pp. 127–145, 1991, pp. 5–21). The activityof these insects, speciallyscarab beetles, is crucial to dung decomposition (Anderson and Coe, 1974; Holter, 1977, 1982; Gitting et al., 1994) and therebysignificantlyenhances primaryproductivity( Bornemissza *Corresponding author. Tel.: +34-958-242-309; fax: +34-958-243-238. E-mail address: [email protected] (F. Sanchez! Pin˜ ero). 0140-1963/03/$ - see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0140-1963(03)00057-0 ARTICLE IN PRESS 304 F. Sanchez! Pin˜ero, J.M. Avila / Journal of Arid Environments 56 (2004) 303–327 and Williams, 1970; Fincher et al., 1981; Rougon and Rougon, 1983; Ricou and Loiseau, 1984). Plant productivityis increased byintegration of nutrients into the soil (Guillard, 1967; Edwards and Aschenborn, 1987) and byseed burial, which provides adequate microclimates for germination and reduces the risk of seed predation (Estrada and Coates-Estrada, 1991). In addition, the beetles’ burrowing activities aerate and soften the soil (Brusaard, 1987; Herrick and Lal, 1996). Thus, dung insects are keyorganisms in systems with grazing mammalian herbivores, particularlyin nutrient poor systems such as deserts. Manyarid regions are used as rangelands for livestock. In shrubsteppes of the Mediterranean Basin livestock (principallysheep and goats) consume about 1500 kg/ ha/year (dry weight) of vegetal matter, producing ca. 600 kg/ha/year of dung (Le Houreou,! 1981, pp. 479–521). Although dung-associated fauna are potentiallyan important part of these ecosystems, dung insects have been scarcely studied in arid zones. Some studies have described dung-beetle assemblages (Nealis, 1977; Rougon and Rougon, 1980, 1981, 1982a–c, 1983; Dajoz, 1994) and the role of termites during late stages of dung decomposition (Havertyand Nutting, 1975 ; Johnson and Whitford, 1975; Kingston, 1977; Whitford et al., 1982; Rougon and Rougon, 1991; Whitford, 1991). However, the composition and structure of entire dung-insect communities have been investigated onlyin the Chihuahuan desert ( Schoenly, 1983) and the Sahelian region (Rougon and Rougon, 1991). These studies show the diversityof insects that exploit dung but few general patterns emerge: whereas the most abundant insects exploiting dung in the Chihuahuan Desert are ants (although scarabaeids and tenebrionids were still the most important dung consumers), beetles (principallystaphylinid and scarabaeoid beetles) are the dominant species in dung communities in Sahel. Schoenly(1983) and Rougon and Rougon (1991) described dung-insect communities at single sites and over a period of a few months to 1 year. Neither studyaddressed among site, inter-annual or seasonal variabilityin community composition and structure, which are crucial to the understanding of desert communities (Polis, 1991, pp. 1–26; Sanchez-Pin! ˜ ero, 1997). The present study analysed the structure of dung-insect communities in three sites and 2 years (at one site) in an arid region of south-eastern Spain. The goals of this studywere to: (1) describe the taxonomic and trophic composition of the community; and (2) analyse the spatial, inter-annual and seasonal variabilityin communitystructure (taxonomic and trophic composition, abundance and biomass). 2. Study area The studywas conducted at Barranco del Espartal (750 m elevation, hereafter Baza), Rambla del Grao (900 m, hereafter Grao) and Llanos de Guadix (1100 m, hereafter Llanos), located 10–40 km apart in the Guadix–Baza Basin (Granada Province, SE Spain). The three sites had similar grazing pressures (ca. 1.4–1.6 sheep/ ha). Sites included the characteristic landscapes of these arid zones: ramblas (occasional watercourses) with a substrate composed of silt and gypsum sediments ARTICLE IN PRESS F. Sanchez! Pin˜ero, J.M. Avila / Journal of Arid Environments 56 (2004) 303–327 305 (Baza) or sandyclaysoils (Grao); and the plateau, with a substrate composed of limestone plates and claysoil (Llanos). The climate is Mediterranean continental and highlyseasonal, with strong dailyand seasonal temperature fluctuations. Tempera- tures are usuallybetween zero and À14C in winter (October–April), and reach 60C at ground level in summer (Epypsa, 1985). Temperature records from the two main towns in the area (Guadix and Baza, 6–10 km to the studysites) showed that similar seasonal trends occur across the studyarea (maximum temperature: r ¼ 0:981; p ¼ 0:0001; minimum temperature: r ¼ 0:988; p ¼ 0:0001; n ¼ 36; Pearson’s correlation; Fig. 1). Precipitation is irregular and occurs mainlyduring the cold months. During the studyperiod, annual rainfall was lower in 1991 (227.3 mm) than in 1992 (304.9 mm), showing a similar seasonal distribution pattern across the studyarea 100 (A) 90 1990 1991 1992 80 Precipitation 70 T Max T min 60 50 40 30 20 10 0 -10 J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D 100 (B) 90 80 Precipitation/Temperature 70 60 50 40 30 20 10 0 -10 J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D Month Fig. 1. Monthlymean maximum ( TMax) and minimum (Tmin) temperature ( C) and total amount of precipitation (mm) at the two main towns of the studyarea (A=Baza, B=Guadix) during 1990–1992. ARTICLE IN PRESS 306 F. Sanchez! Pin˜ero, J.M. Avila / Journal of Arid Environments 56 (2004) 303–327 (r ¼ 0:783; p ¼ 0:0001; n ¼ 36; Fig. 1). The potential evapo-transpiration exceeds annual rainfall bythree times ( Sierra et al., 1990). The studyarea corresponds to a middle arid system (Le Houreou,! 1989). The vegetation consists of savannas with holm–oak trees (4% cover), grasses (30% cover) and Artemisia shrubs (12% cover) at Llanos, and typical arid open shrubsteppes (46–54% bare soil, 12–17% shrub cover) dominated by Artemisia (Compositae) and Salsola (Chenopodiaceae) shrubs, Stipa (Gramineae) tussock grasses and Retama sphaerocarpa (L.) Boissier (Fabaceae) brushes at Baza and Grao. 3. Methods We used dung-baited pitfall traps to studythe arthropod fauna associated with excrements (see Southwood, 1978; Lobo et al., 1988). Traps consisted of a plastic cylinder (10 cm diameter  20 cm high) buried in the ground and containing a collecting cup (6.5 cm diameter  9 cm high) with a preservative (a solution of 10 g/l cloral hydrate and soap). A funnel on top of the cylinder was connected to the collecting cup in the interior of the cylinder. A baited grill (2.5  2.5 cm mesh) rested on the funnel. Bait was fresh sheep dung (200 g) collected in a sheep stockyard at Barranco del Espartal. We carried out sampling from March 1991 to February1992 at the three sites. We were also interested in inter-annual variation in dung arthropod assemblages, so we carried out additional sampling in Baza from March 1992 to October 1992. We established five pitfall traps at each site. Pitfall traps were baited with fresh dung at 15-dayintervals. Contents of the pitfall traps were collected at 2 and 15 daysafter baiting. After 15 days, due to the dry conditions in the zone, dung was completely dried and was no longer attractive to insects, but five drydung-pats were left on the ground in each site to examine for termite activity. We have classified insects into five trophic groups: predators, opportunistic predators, coprophages, opportunistic coprophages and omnivores. Predators (histerid and staphylinid beetles; Appendix A) eat only live prey, whereas coprophages (dipteran larvae and scarabeid, aphodiid, hydrophylid beetles) eat (exclusivelyor principally)dung. Omnivores (Formicidae) feed both on live preyand dung. Opportunists appear in dung as predators or coprophages, but are not restricted to excrement (e.g., carabid, tenebrionid, and some staphylinid and aphodiid beetles; Appendix A). Classification of species into trophic groups was based on direct observations in the studyarea and literature (e.g., Koskela and Hanski, 1977; Schoenly, 1983; Cambefort, 1991, pp. 156–178). Biomass was estimated from bodylength (0.01 mm accuracy)using allometric equations calculated from specimens from the studyarea ( Hodar,! 1996). 3.1. Statistical analysis To analyse species turnover between sites and years, beetles were identified to species level (Appendix A). Alpha species diversitywas calculated using Shannon H 0 ARTICLE IN PRESS F. Sanchez! Pin˜ero, J.M. Avila / Journal of Arid Environments 56 (2004) 303–327 307 index of evenness, and differences in diversityvalues were compared using a t-test (Magurran, 1988).