Trond H. Larsen

Extinction order and altered community structure rapidly disrupt ecosystem functioning

By causing extinctions and altering community structure, anthropogenic disturbances can disrupt processes that maintain ecosystem integrity. However, the relationship between community structure and ecosystem functioning in natural systems is poorly understood. Here we show that habitat loss appeared to disrupt ecosystem functioning by affecting extinction order, species richness and abundance. We studied pollination by bees in a mosaic of agricultural and natural habitats in California and dung burial by dung beetles on recently created islands in Venezuela. We found that large-bodied bee and beetle species tended to be both most extinction-prone and most functionally efficient, contributing to rapid functional loss. Simulations confirmed that extinction order led to greater disruption of function than predicted by random species loss. Total abundance declined with richness and also appeared to contribute to loss of function. We demonstrate conceptually and empirically how the non-random response of communities to disturbance can have unexpectedly large functional consequences.

Degraded lands worth protecting: the biological importance of Southeast Asia's repeatedly logged forests

Southeast Asia is a hotspot of imperilled biodiversity, owing to extensive logging and forest conversion to oil palm agriculture. The degraded forests that remain after multiple rounds of intensive logging are often assumed to be of little conservation value; consequently, there has been no concerted effort to prevent them from being converted to oil palm. However, no study has quantified the biodiversity of repeatedly logged forests. We compare the species richness and composition of birds and dung beetles within unlogged (primary), once-logged and twice-logged forests in Sabah, Borneo. Logging had little effect on the overall richness of birds. Dung beetle richness declined following once-logging but did not decline further after twice-logging. The species composition of bird and dung beetle communities was altered, particularly after the second logging rotation, but globally imperilled bird species (IUCN Red List) did not decline further after twice-logging. Remarkably, over 75 per cent of bird and dung beetle species found in unlogged forest persisted within twice-logged forest. Although twice-logged forests have less biological value than primary and once-logged forests, they clearly provide important habitat for numerous bird and dung beetle species. Preventing these degraded forests from being converted to oil palm should be a priority of policy-makers and conservationists.

Extreme Trophic and Habitat Specialization by Peruvian Dung Beetles (Coleoptera: Scarabaeidae: Scarabaeinae)

Abstract Resource partitioning strategies can help us understand the origin and maintenance of highly diverse communities. We collected 205 dung beetle species (Coleoptera: Scarabaeidae: Scarabaeinae) associated with many different kinds of resources in southeastern Peru. We focus only on extreme cases of resource specialization of species occupying unusually narrow ecological niches, rather than the broad range of specialists which exists. The natural history of most of these species is previously unknown, and several have been considered very rare. Although dung beetles were captured with all types of dung, including avian, reptile and invertebrate dung, species did not specialize exclusively on certain dung types. Ten species appeared to specialize exclusively on a single non-dung food resource, including fruit, fungus, carrion, dead invertebrates, and live millipedes. The diets of 15 species captured only by hand or with passive flight intercept traps are unknown, and these included species in unusual genera such as Anomiopus, Bdelyrus, Canthonella, Dendropaemon, and Sinapisoma. Eleven species appeared to specialize exclusively on a restricted habitat or microhabitat such as riverine beach, Guadua bamboo patches, river alder forest (Tessaria), attine ant nests, or abandoned termite nests. Four species of Canthon were forest canopy specialists. The apparent rarity of some of these species, such as Canthonidia rubromaculata Blanchard, Deltochilum valgum Burmeister, Ontherus laminifer Balthasar, and Ontherus raptor Génier, may only be due to their unusual habits, while other species, such as Megatharsis buckleyi Waterhouse, appear to be genuinely rare. We also discuss the implications of these findings for sampling methodology and assessment of species abundance distributions.

Understanding Trait-Dependent Community Disassembly: Dung Beetles, Density Functions, and Forest Fragmentation

Anthropogenic disturbances such as fragmentation are rapidly altering biodiversity, yet a lack of attention to species traits and abundance patterns has made the results of most studies difficult to generalize. We determined traits of extinction-prone species and present a novel strategy for classifying species according to their population-level response to a gradient of disturbance intensity. We examined the effects of forest fragmentation on dung beetle communities in an archipelago of 33 islands recently created by flooding in Venezuela. Species richness, density, and biomass all declined sharply with decreasing island area and increasing island isolation. Species richness was highly nested, indicating that local extinctions occurred nonrandomly. The most sensitive dung beetle species appeared to require at least 85 ha of forest, more than many large vertebrates. Extinction-prone species were either large-bodied, forest specialists, or uncommon. These explanatory variables were unrelated, suggesting at least 3 underlying causes of extirpation. Large species showed high wing loading (body mass/wing area) and a distinct flight strategy that may increase their area requirements. Although forest specificity made most species sensitive to fragmentation, a few persistent habitat generalists dispersed across the matrix. Density functions classified species into 4 response groups on the basis of their change in density with decreasing species richness. Sensitive and persistent species both declined with increasing fragmentation intensity, but persistent species occurred on more islands, which may be due to their higher baseline densities. Compensatory species increased in abundance following the initial loss of sensitive species, but rapidly declined with increasing fragmentation. Supertramp species (widespread habitat generalists) may be poor competitors but strong dispersers; their abundance peaked following the decline of the other 3 groups. Nevertheless, even the least sensitive species were extirpated or rare on the smallest and most isolated islands.

From coprophagy to predation: a dung beetle that kills millipedes

The dung beetle subfamily Scarabaeinae is a cosmopolitan group of insects that feed primarily on dung. We describe the first case of an obligate predatory dung beetle and contrast its behaviour and morphology with those of its coprophagous sympatric congeners. Deltochilum valgum Burmeister killed and consumed millipedes in lowland rainforest in Peru. Ancestral ball-rolling behaviour shared by other canthonine species is abandoned, and the head, hind tibiae and pygidium of D. valgum are modified for novel functions during millipede predation. Millipedes were killed by disarticulation, often through decapitation, using the clypeus as a lever. Beetles killed millipedes much larger than themselves. In pitfall traps, D. valgum was attracted exclusively to millipedes, and preferred injured over uninjured millipedes. Morphological similarities placing D. valgum in the same subgenus with non-predatory dung-feeding species suggest a major and potentially rapid behavioural shift from coprophagy to predation. Ecological transitions enabling the exploitation of dramatically atypical niches, which may be more likely to occur when competition is intense, may help explain the evolution of novel ecological guilds and the diversification of exceptionally species-rich groups such as insects.