A trait-based framework for dung beetle functional ecology

Abstract

Traits are key for understanding the environmental responses and ecological roles of organisms. Trait approaches to functional ecology are well established for plants, whereas consistent frameworks for animal groups are less developed. Here we suggest a framework for the study of the functional ecology of animals from a trait-based response-effect approach, using dung beetles as model system. Dung beetles are a key group of decomposers that are important for many ecosystem processes. The lack of a trait-based framework tailored to this group has limited the use of traits in dung beetle functional ecology. We review which dung beetle traits respond to the environment and affect ecosystem processes, covering the wide range of spatial, temporal and biological scales at which they are involved. Dung beetles show trait-based responses to variation in temperature, water, soil properties, trophic resources, light, vegetation structure, competition, predation and parasitism. Dung beetles' influence on ecosystem processes includes trait-mediated effects on nutrient cycling, bioturbation, plant growth, seed dispersal, other dung-based organisms and parasite transmission, as well as some cases of pollination and predation. We identify 66 dung beetle traits that are either response or effect traits, or both, pertaining to six main categories: morphology, feeding, reproduction, physiology, activity and movement. Several traits pertain to more than one category, in particular dung relocation behaviour during nesting or feeding. We also identify 136 trait-response and 77 trait-effect relationships in dung beetles. No response to environmental stressors nor effect over ecological processes were related with traits of a single category. This highlights the interrelationship between the traits shaping body-plans, the multi-functionality of traits, and their role linking responses to the environment and effects on the ecosystem. Despite current developments in dung beetle functional ecology, many knowledge gaps remain, and there are biases towards certain traits, functions, taxonomic groups and regions. Our framework provides the foundations for the thorough development of trait-based dung beetle ecology. It also serves as an example framework for other taxa.

Keywords: Scarabaeoidea; ecosystem engineers; ecosystem processes; effect traits; multifunctionality; response traits; trait-function relationships.

FIGURE 1

Dung beetle responses to the abiotic and biotic environment. Arrow titles in bold identify the main types of stressors or filters to which dung beetle traits respond, depicted as subsections in this review. Arrow titles in regular font identify some specific stressors.

FIGURE 2

Dung beetle effects on ecosystem functioning. Arrow titles in bold identify the main types of trait‐driven effects of dung beetles on the ecosystems, depicted as subsections in this review. Arrow titles in regular font identify some specific effects.

FIGURE 3

Relationships between dung beetle traits, responses to environmental factors and effects on ecosystem functions. Coloured bars identify the main types of traits, the environmental factors and/or evolutionary drivers to which they respond, and the ecosystem functions they perform (central, left and right columns, respectively). Bar heights indicate the number of traits within each category, and the width of the links between bars indicates the number of trait–response (to environmental factors) and trait–effect (on ecosystem functions) relationships identified during this review (see Table 1 and Supplementary Tables S1–S3).