Dung beetles increase plant growth: A meta-analysis

The ecosystem services provided by dung beetles are well-known and valued. Dung beetles bury dung for feeding and breeding, and it is generally thought that the process of burying dung increases nutrient uptake by plant roots, which promotes plant growth. Many studies have tested the effects of dung beetles on plant growth, but there has been no quantitative synthesis of these studies. Here we use a multi-level meta-analysis to estimate the average effect of dung beetles on plant growth and investigate factors that moderate this effect. We identified 28 publications that investigated dung beetle effects on plant growth. Of these, 24 contained the minimum quantitative data necessary to include in a meta-analysis. Overall, we found that dung beetles increased plant growth by 17 %; the 95 % CI for possible values for the true increase in plant growth that were most compatible with our data, given our statistical model, ranged from 1 to 35 %. We found evidence that the dung beetle–plant growth relationship is influenced by the plant measurement type and the number of beetles accessing the dung. However, beetles did not increase plant growth in all quantitative trials, as individual effect sizes ranged from -72 % – 806 %, suggesting important context-dependence in the provision of ecosystem services.

Methods
On 3rd November 2023, we conducted a literature search on the Scopus and Web of Science databases with the following search terms:

(("dung beetle*" OR scarabaei*) AND (herb* OR pasture OR plant* OR primary OR seedling*) AND (growth OR increase* OR product* OR yield))

From this literature search, we identified 26 studies (containing 677 study outcomes) that compared the difference in plant growth between areas with untouched dung (dung only) and areas with dung colonised solely by dung beetles (dung+beetles).

The reported results and experiment parameters from the 677 study outcomes were recorded in the meta_analysis_data.csv dataset.