Changes in food resources and conservation of scarab beetles: from sheep to dog dung in a green urban area of Rome (Coleoptera, Scarabaeoidea)
Introduction
Information about insect population decline is still scarce respect to that recorded for plant and vertebrate species. A low number of studies was conducted in North America and Europe to emphasise changes in composition of insect communities and their population decline through a long-term period (e.g., Desender and Turin, 1989, Lobo, 2001, Pyle et al., 1981, Turin and den Boer, 1988, van Swaay, 1990).
The conservation of dung beetle communities in green urban areas is strongly affected by reduction to complete disappearance of grazing herbivores. In many cases, the lands which were previously used as pastures were reconverted to green areas for recreational purposes while two species of carnivores, dogs and cats (both domestic and feral) became the most common large mammals.
The dung of carnivorous mammals is hardly colonised by Palaearctic scarab beetles (Barbero et al., 1999, Mysterud and Wiger, 1976, Carpaneto and Fabbri, 1984, Hancox, 1991, Halffter and Matthews, 1966, Martin-Piera and Lobo, 1996). Apart from a small number of truly generalist species, dung beetles usually avoid the faeces of wild carnivores because these are poor in cellulose content (M. Salonen in Landin, 1961). Only the brown bear (Ursus arctos Linnaeus, 1758), owing to its omnivorous diet, harbours a rich community of these insects (Carpaneto and Fabbri, 1984).
Data on the exploitation of dog scats as food resources for scarab beetles are few and scattered (e.g., Faithfull, 1992, Faithfull, 1994, Fincher et al., 1970, Huang et al., 2001, Oppenheimer and Begum, 1978). The study area of the present paper (the Urban Regional Park of Pineto) is a green patch entrapped within the town of Rome since many decades and was intensively grazed by sheep up to 1989, when it was reconverted into a public recreational area. As a consequence of the new management, grazing was suspended and dogs became the only large mammals. The elimination of livestock was the only great change operated in this area and around it during such passage from grazing to recreational use. In 1986, a one-year sampling was conducted in order to study the species composition and dynamics of the dung beetles community associated to ovine droppings (Carpaneto and Piattella, 1990) when the latter was the only steady resource of food available for dung beetles. Since then, dog scats are the only present source of food for dung beetles, as just occurred in other European and Australian capitals (Faithfull, 1992). Nowadays, some dogs are feral or vagrant, while the others are regularly brought there by their owners from the neighbouring houses.
The aim of the present study is to compare the past and present diversity of species in the dung beetle community of this area in order to discuss changes in their food resource. There have been few attempts to investigate the dung beetle preference for different types of dung, and the results are often contradictory (Barbero et al., 1999, Gittings and Giller, 1998, Lumaret et al., 1992). In particular, the objectives of this paper are: (1) to estimate the modifications in species assemblage with the change in resource quality and land use; (2) to test if changes in dung type produced variations in the proportional abundance of the species; (3) to understand if scarab beetle species are able to survive by exploiting dog dung as food resource in unchanged environmental conditions, after sheep removal.
Section snippets
Study areas
The main study area represents a fragment of Roman countryside entrapped by the unplanned urban development of the Fifties. It was preserved by the institution of the Urban Regional Park of Pineto, established in 24 September 1986. The area lies in the NW part of Rome and covers about 240 ha. The current landscape consists of small deciduous woodlands and grasslands extended over an undulated surface of low hills, including both volcanic and alluvial soils. Some perennial streams and ponds
Richness, diversity and dominance
Nine coprophagous species associated with dog scats were gathered during the sampling. The number of species associated with dog scats deals with 12% of the whole scarab dung beetle fauna (75 species) recorded still now from the urban area of Rome (Carpaneto and Piattella, 1997). Nevertheless, they represent 20% of the current dung beetle fauna of the urban area of Rome (45 species) as resulted by a recent and comprehensive research conducted in all the other nine Roman parks from 1999 to 2000.
Richness, diversity and dominance
The species richness recorded for dog dung in the Pineto Park (1999) is lower than that observed for sheep dung in the same area (1986). Moreover, it is also lower than the richness of all the other sheep dung assemblages in the nine Roman areas investigated.
A further evidence of the povery of species in dog dung is given by the low estimated number of species at the minimum number of individuals.
Values of Δ1 in the majority of the study areas are lower than Δ1 for the entire species pool, and
Conclusions
Dog faeces are not only a hygienic problem in urban areas (particularly if not dismantled by dung beetles), but also the most abundant resource for dung beetles. At present, dog dung in the Pineto Park is the sole food resource that can support a scarab dung beetle community, after the removal of both wild and domestic herbivores. Therefore, a reduced green area crossed by dogs could provide a temporary refuge for some species of dung eaters that otherwise may encounter local extinction in
Acknowledgements
We are grateful to Marco A. Bologna, scientific coordinator of the research line “Fauna and Zoocenosis” partially financed by the regional agency RomaNatura for the Management Plan of the Protected Areas of Rome. A special thank is also due to Simone Fattorini for his precious help in data elaboration. This research was also supported by a grant from MIUR (Ministry of Instruction, University and Research).
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