Dung beetles as drivers of ecosystem multifunctionality: Are response and effect traits interwoven?

Abstract

Rapid biodiversity loss has emphasized the need to understand how biodiversity affects the provisioning of ecological functions. Of particular interest are species and communities with versatile impacts on multiple parts of the environment, linking processes in the biosphere, lithosphere, and atmosphere to human interests in the anthroposphere (in this case, cattle farming). In this study, we examine the role of a specific group of insects - beetles feeding on cattle dung - on multiple ecological functions spanning these spheres (dung removal, soil nutrient content and greenhouse gas emissions). We ask whether the same traits which make species prone to extinction (i.e. response traits) may also affect their functional efficiency (as effect traits). To establish the link between response and effect traits, we first evaluated whether two traits (body mass and nesting strategy, the latter categorized as tunnelers or dwellers) affected the probability of a species being threatened. We then tested for a relationship between these traits and ecosystem functioning. Across Scandinavian dung beetle species, 75% of tunnelers and 30% of dwellers are classified as threatened. Hence, nesting strategy significantly affects the probability of a species being threatened, and constitutes a response trait. Effect traits varied with the ecological function investigated: density-specific dung removal was influenced by both nesting strategy and body mass, whereas methane emissions varied with body mass and nutrient recycling with nesting strategy. Our findings suggest that among Scandinavian dung beetles, nesting strategy is both a response and an effect trait, with tunnelers being more efficient in providing several ecological functions and also being more sensitive to extinction. Consequently, functionally important tunneler species have suffered disproportionate declines, and species not threatened today may be at risk of becoming so in the near future. This linkage between effect and response traits aggravates the consequences of ongoing biodiversity loss.

Thermal niche helps to explain the ability of dung beetles to exploit disturbed habitats

“…Recent studies in the Atlantic forest (and in neotropical forests in general) have shown that land uses with complete loss of the canopy cover show a marked reduction in dung beetle abundance and diversity 2,3,5,65 and that those preserving the canopy cover (at least partially) are often used by native forest dung beetles 2,3,5,7,66,67 . While these differences have been explained by the hypothesis of physiological restrictions (particularly the tolerance to high temperatures) 3,5,14 , the results of this study are the first direct evidence to suggest that the thermal niche might be one of the main determinants of the ability of forest dung beetles to colonize open areas.…”

“…Differences in dung beetle diversity among land uses differing in canopy cover have been associated mainly with a marked increase in ground level temperature 2 , 8 – 10 and with the low tolerance of forest dung beetles to high temperatures (typical of open habitats during the day) 3 , 11 – 13 . Although previous studies have suggested that the physiological intolerance of forest dung beetles to high temperatures is a potential constraint to exploit disturbed habitats 2 , 3 , 14 , this hypothesis has never been tested. This knowledge gap on dung beetle thermal biology led us to ask the following question: can the thermal niche of dung beetles explain the occupation of disturbed habitats, and taxonomic and functional changes reported in previous studies?…”

Stronger dung removal in forests compared with grassland is driven by trait composition and biomass of dung beetles

“…This may explain the strong differences in dung removal between habitats due to the strongly changing abundance of large tunnellers in our study area. In Scandinavia, functionally important species suffered from disproportionate declines (Piccini et al, 2018) and this may also have occurred in Central Europe. High densities of dung beetles with low individual functional importance can support equivalent levels of functioning as provided by species with high individual functional importance .…”

Flower‐visitor communities of an arcto‐alpine plant—Global patterns in species richness, phylogenetic diversity and ecological functioning

“…A general positive link between biodiversity and ecosystem functioning (Allan et al, 2015;Butterfield, Camhi, Rubin, & Schwalm, 2016) has been variously ascribed to the effects of diversity per se (e.g., more species complement each other's use of available resources, thus allowing more complete resource use; e.g., Tilman et al, 2001) versus effects of species identity (with some species being particularly efficient from a functional perspective; e.g., Cardinale, Palmer, & Collins, 2002;Hooper, Chapin, & Ewel, 2005). Overall, species within a community often have varying impacts on individual ecosystem functions (Cardinale et al, 2006;Piccini et al, 2018;Slade et al, 2017).…”