Secondary tropical forests recover dung beetle functional diversity and trait composition

Secondary forests dominate some human-modified tropical biomes, and this is expected to increase via both abandonment of marginal agricultural land as well as forest and landscape restoration programmes. A key question is whether promoting the recovery and protection of secondary tropical forests will return invertebrate functional diversity and associated functional traits. Dung beetles are ideal for assessing functional diversity as they play vital roles in several ecosystem functions, including seed dispersal, nutrient cycling and bioturbation. We examined how taxonomic and functional diversity, and the functional trait composition of native dung beetle species recovers in naturally regenerating secondary forests in comparison to both cattle pastures and primary forest in the Colombian Choco-Andes, a global hotspot of threatened biodiversity. Using a space-for-time approach, we found that taxonomic and functional diversity recovered to levels comparable to primary forest within approximately 30 years of secondary forest regrowth. Functional richness and FD, measures of the diversity of traits present in a community, were similar in secondary and primary forest, but significantly lower in pasture. Rolling dung beetle species were positively associated with forest habitats, particularly primary, while dwelling species were more common in pasture. Thus, the functional trait composition of secondary forests was more similar to primary forest than to pasture. The ability of secondary forests to rapidly accumulate primary-forest dung beetle functional diversity, and a representative suite of functional traits, provides an opportunity to protect biodiversity and ecosystem functioning, especially in regions where marginal agricultural land allows cost-effective conservation actions.