Research Proposal

Dung beetles (Scarabaeinae): Diel flight activity, response to bait size, bait type, and habitat structure in central Zambia

Introduction

Dung beetle research is a current hot topic in the field of entomology. Dung beetles play a keystone role in the removal of dung, via relocation for feeding and oviposition. This behaviour substantially increases soil fertilisation and aeration, and enhances soil nutrient recycling rates. It has also been suggested that dung beetles play a pivotal role in reducing the transmission of a number of parasites, and removal of dung from intensive farmland is essential in order to prevent pasture fouling. Furthermore, dung beetles have an important role as secondary seed dispersers, and thus in plant regeneration.

More than 7,000 species of dung beetle have been described worldwide with over 2,000 species from Africa, south of the Sahara. Abundance is highest during the summer months of September and October, when up to one hundred dung beetles may be found in a singly cattle pat. However, despite such a vast resource, very little published data exists on dung beetles in southern Africa. Indeed, no studies appear to have been carried out in Zambia.

It has been shown that dung beetle ‘trapability' depends on bait size. However, optimum bait size is not known. Convention states to use 30g bait, however, this appears to vary between studies, and in some studies bait size is not even considered. Those few studies concerned with bait size generally agree that larger bait size will increase dung beetle abundance in the catch. However, an optimum bait size does not appear to have been established in any one of the aforementioned studies. There is as yet no standard protocol for the baited pitfall trapping of dung beetles, and thus studies are often difficult to compare. This is also true of bait type. What is the optimum bait type? Again, very few studies exist on this topic, and none from Zambia. Some studies suggest that cattle dung ensures optimum catch, while other studies rely on carrion, or rotting fruit. However, bait type may be varied at each site to ensure optimum catch, as even an ‘optimum' bait type would not attract all species.

Agricultural intensification is increasing drastically in Zambia, and as it snowballs, the role that scarabs play will become increasingly important. The few published studies show that habitat transformation affects dung beetle assemblages. Disturbance caused by increasing intensification of grazing cattle adversely affects predominantly species of large body size. It is these large scarabs that are most important in dung removal due to their potential to clear large volumes in a short time period. Thus, agricultural intensification, and poor farming practice may have negative consequences on ecosystem stability. Yet again, no studies appear to have been carried out in Zambia.

Temporal variation in the activity of dung beetles has been cited as a mechanism of ecological segregation between potentially competing species. Dung beetles exploit a patchy resource, therefore there is strong competition is probable. Yet no study has provided clear evidence of competition in dung beetles. Resource partitioning has been suggested through exploitation of diel activity, soil type, vegetation cover, dung type, age of dung, and seasonality. Diel activity studies are again rare (non-existent in Zambia), and provide controversial, often conflicting results. Thus, this is another area in need of more study to provide a clearer picture of proposed competition in dung beetles.

Methods and materials

Dung beetles will be sampled using standard trapping procedure: baited pitfall traps, over a 3-day trapping period, at three sites. Five separate experiments will be conducted, and the data from all will be used to assess the difference in community assemblage due to habitat structure. Data will also be collected on the efficiency of dung removal at different farming intensity. The trapping period will be September-October 2005, when dung beetle abundance has found to be highest, thus maximising catch.

Experiments

1.       Optimum Bait Size: 6 categories of bait size, (and one bait-free control) will be used: 30g, 60g, 120g, 240g, 480g, and 960g. Traps will be emptied once every 24 hours over a 3-day trapping period. Dung beetle specimens will be counted, and bait size used in subsequent trapping will be based on that which yielded the highest dung beetle abundance (all sites summed).

2.       Bait Type: 5 categories of bait type, (and one bait-free control) will be used: cattle dung, elephant dung, human faeces, chicken carrion, and fruit. Traps will be emptied once every 24 hours over a 3-day trapping period.

3.       Diel Flight Activity: Traps will be emptied over a 24 hours period, which will be divided into the major flight periods (e.g. crepuscular (dawn/dusk), morning diurnal, afternoon diurnal etc).

4.       Dung Clearance Rates. 5 fresh cattle pats will be marked (with a small flag) at each farm site, on each day of trapping. Observations of percentage remaining will be recorded per hour, until dung is removed completely.

5.       Comparison between sites: the 3 habitat types: Site 1 - intensive grazing land; Site 2 - non-intensive grazing land; Site 3 - grassveld (semi-natural).

The samples will be stored and sorted at the Hope Entomological Department, with the help of D.J. Mann.

Materials: preserving fluid (saturated salt solution or alternative), 70% alcohol, storage bags, plastic buckets, gauze, bait.

Results

The Scarabaeinae Research Network, or ScarabNet is presently coordinating the development of the Scarabaeinae as an invertebrate focal taxon for use in rapid biodiversity assessments. This experiment ties into the dung beetle research at the Hope Entomological Collections, Oxford University Museum, and will be entered into the ScarabNet database. A large amount of baseline data will result from this study to be utilised by Scarab Net. ScarabNet is in the process of collecting data to produce a ‘handbook of standard methods', to be published in 2009. It is thus vital that data is collected on both optimum bait size and bait type. No published data exists from Zambia, and the data collected will be used to provide the Scarabaeinae Research Network with information enabling them to produce a geographically correct protocol. The diel flight pattern experiment will provide an additional resource on a topic with very little published data. Less than ten papers have been found on this subject and thus additional experimental data is vital. The effect of farming intensification on dung beetle community structure, and efficiency in dung removal is yet again another topic not widely studied. Using dung beetles as a focal taxon, will allow extrapolation to the possible widespread ecological implications of farming intensification.

Budget

Flights ~ £600, visa ~ £30, living costs (Zambia) ~£840, accommodation (Oxford) ~ £1,120 = £ 2,590 (Consumables for specimen preparation in Oxford provided by University Museum).

Referees

Darren J. Mann, Curatorial Officer, Hope Entomological Collections, Oxford.

Dr Robin McCleery, Wadham College, Oxford.

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