Dung Beetles (Coleoptera: Scarahaeidae ...

COMMUNITYAND ECOSYSTEMECOLOGY

Dung Beetles (Coleoptera: Scarahaeidae, Geotrupidae) Attracted to Fresh Cattle Dung in Wooded and Open Pasture EDUARDO

GALANTE, JAVIER MENA, AND CARLOS LUMBRERAS

Departamento de Ciencias Ambientales y Recursos Naturales, Universidad de Alicante, 03080 Alicante, Spain

Environ. Entornol. 24(5): 1063-1068 (1995)

ABSTRACT The biomass of dung beetles attracted to fresh cattle dung was studied in a Mediterranean holm oak pasture ecosystem with a continental Mediterranean climate (supramediterranean level). Results indicated a nonuniform biomass distribution of dung beetles throughout the year. Major peaks of species activityand biomassconcentration of dung beetles occurred in open areas of the pasture in the spring followedby minor peaks in the fall. Beetle biomass in the open pasture was greater than that in the wooded pasture. The species of dung beetles comprising the greatest amount of biomass and the most important species available to destroy cattle dung pats in Mediterranean ecosystemswith a continental climate were Bubas 1m1millS Olivier, OntllOphagus opacicollis d'Orbigny, Copris hispanus (L.), Carris lunaris (L.), and Onthopha{!.us vacca (L.). KEY WORDS

dung beetles, biomass, holm oak, pastureland, Mediterranean ecosystem

IN PASTURELAND ECOSYSTEMS,dung beetles play an important role in the rapid recycling processes of dung (Bornel11issza 1960, Breymeyer 1974, Ml'rrit and Anderson 1977, LUl11aret1980, Fincher et al. 1981, Lumaret and Kirk 1987). Many species of Scarabaeidae and Geotrupidae have developed spl'cial feeding and breeding strategies that allow them to remove dung rapidly from pashlre surfaces by digging burrows below the dung pad to store fragments of dung into tunnels or form dung into balls and roll them away from the pat for burial far from the food source (Halffter and Matthews 1966, Halffter and Edmonds 1982, Doube 1990, CambefOlt and Hanski 1991). In countries that historically had a greater number of grazing animals, many species of dung beetil'S evolved that are now capable of burying the dung of livestock within a few days after deposited on pasture (Ridsdill-Smith and Kirk 1985, Lumaret and Kirk 1987). Several species of dung beetles have been introduced into areas of Australia and the United States to improve dung burial on pasture (Waterhouse 1974, Bornemissza 1976, Fincher 1981, Kirk and Lumaret 1990) and to reduce breeding of pest flies (Hughes et a!. 1978, Hughes

and Morton 1985, Fincher 1986, Ridsdill-Smith et a!. 1986). As part of the program to introduce dung beetles into areas of Australia, insects were selected from southwestern Spain and southern France (Kirk 1983, Ridsdill-Smith and Kirk 1985, LUl11aret and Kirk 1987). Selection of dung beetles for introduction into various countries should be based on phenology, activity, and bioclimate classification. In Mediterranean climate areas, dung beetles have developed

traits that enable them to exploit dung (Kirk and Lumaret 1990). In these ecosystems, dung beetles show greatly diversified activity in space and both annual and daily periods (Galante et a1. 1991, 1994) and the result should be an irregular distribution of dung beetle biomass in both space and time. The overall activity of dung beetles in Mediterranean ecosystems is seasonal and dependent on temperature and precipitation (Lumaret et. a!. 1992). To select species to be introduced into other areas, specific bioclimatic studies must also be considered. Adaptations and restriction to particular bioclimates determined the distribution of beetles in the Iberian Peninsula (Kirk and Ridsdill-Smith 1986) and it should be compared with bioclimate considerations such as the Rivas-Martinez (1987) classification to prevent the failure of introduction in some countries. The purpose of the current study was to determine the biomass of dung beetles attracted to cattle dung during the 1st few hours of exposure (05 h) in a holm oak pasture ecosystem with a Mediterranean climate. The 3 objectives were (1) to confirm that the distribution of dung beetles biomass was not uniform throughout the year, (2) to quantify the spatial and temporal concentration of the biomass of dung bettles attracted to cattle dung, and (3) to verify the most important species that are present in the pasture and available for the breakdown of cattle dung pats. Materials and Methods Experimental Site. A survey of dung beetles was conducted in a Mediterranean holm oak pas-

0046-225X/95/1063-1068$02.00/0

© 1995 Entomological Society of Anu'fica

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ENVIRONMENTAL

TobIe 1. Doily capture perio"" Hours

Morning Spring Summer Autumn

Winter

0530-1030 0500-1100 0700-1200 0730-1200

Afternoon 1030-1630 1100-1700 1200-1600 1200-1530

Evening 1630-1930 1700-2000 1600-]800 1530-]730

Night 1930-0530 2000-0500 1800-0700 1730-0800

ture with a predominance of Quercus rotundifolia Lam. near Salamanca in western Spain. The 400ha pasture was dedicated to year-round grazing for "=200 adult cattle with varying numbers of yearlings and calves. During the year, the cattle are herded from one place to another within this area. The ecosystem consisted of clear-felled savannalike woodland (dehesa), with areas transformed by human activity into open pasture land with no trees or shnlbs. The climate was continental and showed a period of severe drought with high temperatures from the end of June to mid-September and very cold winter temperatures (Galante et a!. 1991). The period of highest precipitation was in early fall but there are also 2 peaks of precipitation in early spring and winter (Galante et a!. 1991). Rivas-Martinez (1983) defined the thermicity index as It = (T + m + M)10, \ovithT = average of annual temperatures; m = average of minimum temperatures in the coldest month; M = average of the maximum temperatures in the coldest month. The study area was in the Supramediterranean level \ovithan It from 60 to 210 (Rivas-MartInez 1987). Collection of Beetles. Dung baited pitfall traps according to Hanski (1980) and CSR (Cebo-Superficie-Rejilla)-type traps (Lobo et a!. 1988) placed 20 m apart were used to monitor dung beetle activity (Mena et al. 1989). Each trap consisted of a plastic bucket 21 cm in diameter, buried to its rim in the soil. As a preserving fluid, 300 ml of 50% ethylene glycol was used. The bait consisted of 1,000 cm3 (±200 g) of fresh cattle dung for each trap, supported on a wire grill on the top of the buckct. Two parallel rows of 4 traps each (4 traps + 4 replicates) were placed from the holm oak woodland area of the pasture to tlIe open pasture, with a total of 4 traps (2 + 2) in the wooded area and 4 traps (2 + 2) in the open area. The traps were baited monthly for 2 d (48-h periods) from April 1987 to March 1988. According to Mena et al. (1989) the daily biomass distribution for each day was divided into 4 periods of capture: morning, afternoon, evening/crepuscular, and night (Table 1). The dung used as bait and the preserving fluid containing trapped beetles were removed at the end of each of the 4 periods. As a result, 128 samples were collected every month (4 traps X 4 periods X 2 d X 4 replicas). After collection of beetles, the traps were reset with fresh dung and preserving fluid. Thus, the sequence of the annual and daily biomass distribution of the

Vol. 24, no. 5

ENTOMOLOGY

dung beetles (Scarabaeidae and Geotmpidae) was followed in open and wooded pasture. Biomass of Insects. The dry wcight per species \Vas obtained by calculating the mean weight of 20 specimens (10 males and 10 females) of each species. These were dehydrated at 60°C for 72 hand were subsequently weighed on a precision balance. The total dry weight of beetles of each species was calculated from the number of beetles trapped. Statistical Analysis. The Stat-Views II SE Program was used for data analysis (Abacus, 1988). Data were compared using analysis of variance (ANOVA) to test the a priori hypotheses that there would be differences in dung beetle biomass, (1) between seasonal distribution, (2) between daily distribution biomass, and (3) between habitats distribution (wooded and open areas). Results

Seasonal Biomass. In total, 6,331 individuals belonging to 17 species of Scarabaeidae and 3 species of Geotrupidae were captured (Table 2). Highly significant differences among seasons were found (F = 26.78, df = 3, P < 0.001). A major peak of species activity and biomass concentration of dung beetles attracted to the cattle dung bait occurred in the spring and again in the fall. The recorded biomass in spring contributed >50% of the biomass for the entire year (Table 2) and differences from the other seasons were highly significant (spring/summer, P < 0.001; spring/fall, P = 0.015; spring/winter, P = 0.011). No significant differences were found between summer and winter biomass. In late spring (MaYlJune), Bubas hubalus Olivier, Copris hispallus (I..), and Copris ltmaris (L.), because of their large size and together with numerous individuals of the small Ollthophagus opacicollis d'Orbigny, were the dominant group in biomass (73%) (Table 2). Although fewer in numbers (2.6% of the total), B. bllbalus formed tlle dominant species in biomass (23.7%), because of its large size. O. opacicollis constituted the dominant species in numbers of individuals (55.9%), but equaled only 21.5% of the total biomass of dung beetles (Table 2). The increase in dung beetle biomass in the early hlll was the result of the emergence of B. huhallls and peak activity of Geotrupes mutator Marsham and 0. opacicollis. During the fall, the dung beetle biomass showed a sharp decline and in winter, minimal biomass was registered. Throughout the year, except during summer months, B. buballls made up a higher percentage of the total biomass in both open and wooded pasture land during the 1st few hours after deposit. In the fall, and especially in spring, C. lUllaris made an important contribution to the biomass in the wooded pasture (16% of annual biomass). Also in summer, Geotrupes ihericus Baralld was relatively important (17% of summer biomass) (Table 2).

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