Ecological functions and ecosystem services provided by Scarabaeinae dung beetles

Abstract

Clear understanding of the links between ecological functions and biodiversity is needed to assess and predict the true environmental consequences of human activities. Several key ecosystem functions are provided by coprophagous beetles in the subfamily Scarabaeinae (Coleoptera: Scarabaeidae), which feed on animal excreta as both adults and larvae. Through manipulating feces during the feeding process, dung beetles instigate a series of ecosystem functions ranging from secondary seed dispersal to nutrient cycling and parasite suppression. Many of these ecological functions provide valuable ecosystem services such as biological pest control and soil fertilization. Here we summarize the contributions of dung beetles to nutrient cycling, bioturbation, plant growth enhancement, secondary seed dispersal and parasite control, as well as highlight their more limited role in pollination and trophic regulation. We discuss where these ecosystem functions clearly translate into ecosystem services, outline areas in critical need of additional research and describe a research agenda to fill those gaps. Due to the high sensitivity of dung beetles to habitat modification and changing dung resources, many of these ecological processes have already been disrupted or may be affected in the future. Prediction of the functional consequences of dung beetle decline demands functional studies conducted with naturally assembled beetle communities, which broaden the geographic scope of existing work, assess the spatio-temporal distribution of multiple functions, and link these ecosystem processes more clearly to ecosystem services.

Introduction

Human economy, health and wellbeing are intimately linked to functionally intact ecosystems (MEA, 2005), and well characterized relationships between biodiversity and ecosystem function are key to predicting the ecological and economic impacts of human activities (Armsworth et al., 2007). In terrestrial systems, insects play important ecological roles in diverse ecological processes such as nutrient cycling, seed dispersal, bioturbation and pollination. Dung beetles in the coleopteran subfamily Scarabaeinae mediate several of these processes.

Dung beetles are a globally distributed insect group, with their highest diversity in tropical forests and savannas (Hanski and Cambefort, 1991). Largely coprophagous, dung beetle species feed on the microorganism-rich liquid component of mammalian dung (and less commonly that of other vertebrates, as well as rotting fruit, fungus and carrion) and use the more fibrous material to brood their larvae (Halffter and Edmonds, 1982, Halffter and Matthews, 1966).

Most dung beetles use one of three broad nesting strategies, each with implications for ecological function. Paracoprid (tunneler) species bury brood balls in vertical chambers in close proximity to original deposition site. Telocoprid (roller) species transport balls some horizontal distance away, before burial beneath the soil surface. Endocoprid (dweller) species brood their young inside the dung mass itself (Halffter and Edmonds, 1982). Ecological linkages between dung beetles and mammals have played an important role in shaping the evolution of the Scarabaeinae and the structure of extant dung beetle communities for at least the last 40 million years (Cambefort, 1991). Recent fossil evidence of dung-provisioned burrows strongly suggests that dung beetles evolved coprophagy through association with dinosaurs even before the diversification of mammals (Chin and Gill, 1996).

The amount of dung buried by a beetle species is primarily related to mean female body size (Horgan, 2001), though factors such as soil type and moisture (Sowig, 1995), pair cooperation (Sowig, 1996) and dung quality (Dadour and Cook, 1996) also play a role. These varied patterns of consumption and relocation of dung by beetles drive a series of ecological processes that include nutrient cycling, soil aeration, secondary seed burial, and parasite suppression.

Where they are directly relevant to humans, these ecosystem functions often provide important and/or economically beneficial ecosystem services (De Groot et al., 2002). Here we summarize our current knowledge about dung beetle ecosystem functions. We outline the circumstances wherein these functions become ecosystem services and highlight areas in need of further empirical study. We frame the importance of these ecological processes with a discussion of the numerous threats to dung beetle persistence.