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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
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(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 14 C in winter (October–April), and reach 60 C 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