Article: Impact of the Activity of Dung Beetles (Coleoptera: Scarabaeidae: Scarabaeinae) Inhabiting Pasture Land in Durango, Mexico
Author: Anduaga, S.
Published: Community and Ecosystem Ecology, October 2004
This study is an attempt to quantify a set of variables associated with the presence, diversity, and activity of dung beetles on the holistically managed El Jaralillo Ranch in Durango, Mexico. According to previous studies cited by the author, dung beetles enhance nutrient cycles by consuming and burying dung; they “also contribute to the control of fly and cattle-parasitizing nematode populations.”
Despite the importance of dung beetles, little formal research or monitoring has been conducted to ascertain the potential impact of holistic resource management on dung beetle populations and efficiency.
Because dung beetles are most active during periods of high rain, sampling was done during this time, in the months of July, September, and October of 1999. Sampling was done in three paddocks immediately after the removal of cattle. 10 traps were placed every 20 m along a 200 m linear transect, which was located 200 m from the central water supply.
The trap design itself provides a useful methodology for replication in future dung beetle studies and/or monitoring projects. Each trap was a 1000 cmplastic container with a 120 cmdiameter opening. These were filled with a detergent-water solution to 300 cmand buried to the rim along the transect. The trap was then covered with a 30 x 25 mm hexagonal mesh and baited with 1 kg of fresh cattle dung. Traps were emptied at 24-hour intervals for 72 hours and specimens were preserved in acid alcohol (90% alcohol and 10% acetic acid).
Results for abundance and biomass were summarized in the paper by month, but for the purposes of this article, only the totals were included in the table below.
Abundance and Biomass of dung beetles at El Jaralillo Ranch
*Exotic non-native species A similar dung-baited line transect method was used to evaluate dung beetle activity and dung processing percentage. The data show that over 90% of the dung bait showed some level of dung beetle activity; however, only 39% of the total dry matter was processed by the beetles. The author notes that overall abundance of the dung beetles is “rather poor compared with other dry-semidry locations. In Southern Texas, Nealis (1977) registered 19 species on 6 representative habitats.” Yet it is also noted that nearby areas in Mexico have shown a similarly low number of native species. No data is provided to compare overall biomass to other sites in Mexico, or other sites elsewhere in the world. Solar radiation and dung freshness seem to be the factors most associated with dung beetle activity. Indeed, most activity was observed within the first 24 hours of dung exposure, after which the number of specimens declined dramatically. The author notes that termites were observed colonizing and completely decomposing dry dung on the soil surface, but also notes the diminished effectiveness of termites to incorporate nitrogen-rich fresh dung below the soil surface. Unlike termites, dung beetles quickly bury fresh manure into the soil, which increases soil friability, aeration, and water retention capacity. Additionally, soil moisture is another critical variable associated with dung beetle activity. Larger native species are more effective at burying greater amounts of dung, yet the exotic species were much more abundant in both number and biomass. These larger species require high soil moisture for nesting and reproduction. A major flaw in this study is the lack of comparative data from nearby ranches. While the author concludes that the overall diversity and abundance of dung beetles is relatively poor, she draws this conclusion from comparison with a 30-year-old study conducted in Southern Texas. Much more useful would have been to apply the same methodology to surrounding, non-holistically managed ranches for a more direct and immediate comparison. In the absence of such data, the impact of Holistic Management on dung beetle populations is speculative. It is highly possible that Holistic Planned Grazing and Holistic Land Planning can be used to more effectively manage for dung beetle populations. To my knowledge, little formal effort has been directed towards this issue. The author takes a first step in this direction by establishing a strong monitoring protocol by which management and planning can be adjusted. Using Holistic Grazing Planning to reduce grass utilization and increase animal impact may increase litter cover and soil moisture, and also reduce solar radiation at the soil surface, thereby providing better overall environmental conditions for native species of dung beetle. Further work is required, but this paper along with the HM monitoring feedback loop provides the overall schema by which such an effort could be developed.