Trogidae, MacLeay, 1819

Ratcliffe, Brett C., 2013, The Dung- and Carrion-Feeding Scarabs (Coleoptera: Scarabaeoidea) of an Amazonian Blackwater Rainforest: Results of a Continuous, 56 - Week, Baited-PitfallTrap Study, The Coleopterists Bulletin 67 (4), pp. 481-520 : 512-513

Trogidae

Trogid adults typically feed on carrion in the late stages of decay, although they are occasionally encountered on fresher remains. Only two species of Trogidae , Omorgus suberosus (F.) and Omorgus batesi (Harold) , were known from Brazil’ s Amazon Basin until Polynoncus juglans (Ratcliffe) was described ( Ratcliffe 1978) based upon 11 specimens captured during this study ( Table 1). Most trogids prefer drier habitats than those of Amazonia and, as necrophages, are typically outcompeted by ants and vultures in tropical rainforests, hence their rarity.

CONCLUSIONS

In this paper, I discuss trapping methodology and contrast the results from traps using two different solutions for preservation. I also review the species of scarabaeoids that were taken and relate their abundance and taxonomic diversity to local climatic factors. Concurrent with this study, I also conducted a similar trapping and inventory program for 43 weeks in a small remnant patch of secondary forest on the INPA campus 28 km from the Reserva Ducke site (unpublished data). As expected, fewer numbers (5,901 specimens) and fewer species (34) were collected on the INPA campus due to the lack of many dung producing mammals (agoutis were the largest), fewer number of traps (six as opposed to 20), and absence of a reservoir population of replacement scarabaeines. Eight species were collected on the INPA campus that were not taken in the Ducke study site, again reflecting the difference in biotopes as it affects species composition.

The guild of scarabaeoids in tropical rainforests relying on dung is more diverse in species and larger in numbers that those relying on carrion. The Reserva Ducke study supports that hypothesis with 100% of the species and 74% of the numbers collected in dung traps and 52% of the species and 26% of the numbers taken in carrion traps. The comparisons of picric acid and chloral hydrate solutions resulted in virtually no significant differences in species diversity or numbers of individuals, and so the preferred solution is chloral hydrate because it is more readily available and safer to use.

Dung and carrion in tropical rainforests are generally more limited in space and time because the biomass of mostly mammals producing the dung and carrion is less than in, for example, the tropical savannas of Africa (Cambefort and Walter 1991; Davis and Sutton 1997). Competitive success depends on the ability of a beetle to rapidly locate dung or carrion. Some beetles have evolved strategies that reduce competition. The most obvious is removal and burial of dung and carrion. Davis and Sutton (1997) observed that while most species are generalist coprophages, some species evolved to feed on fruit, fungi, carrion, and plant detritus or specialized on omnivore or herbivore dung to enhance coexistence of potential competitors with the result of increased species richness. Others developed arboreal lifestyles that may have evolved as a response to competition with the ground fauna for a common resource that is transitory and limited ( Ratcliffe 1980; Howden and Young 1981; Davis et al. 1997; Jacobs et al. 2008). Peck and Forsyth (1982) and Feer and Pincebourde (2005) concluded that most species use a spectrum of dung types, and it is the fine partitioning of different activity periods, foraging behaviors, body sizes, dung removal methods, feeding behaviors, and microclimate that contribute to so many species co-existing in the same habitat.

Subsequent to this study in the late 1970s, many large mammals were extirpated from the study area, thus reducing the dung resources needed for scarabaeine diversity. The total number of species (66 in the traps, others observed but not trapped) at the Reserva Ducke study site in the 1970s is today probably reduced due to the reduction in the populations of the dung producers. Removal of large-bodied mammals reduces dung resource availability that will then differentially affect dung beetles using either the “perch and wait” strategy observed in small-bodied species or the foraging on-the-wing strategy for locating large dung pats common to larger species of dung beetles (Peck and Howden 1984; Gill 1991). Perching species, primarily diurnal and smaller, usually feed on pelleted droppings typical of rodents and small ungulates, and so these species may persist after the larger mammals have been removed by hunting. Conversely, larger species that are primarily nocturnal (Cambefort and Walter 1991; Feer and Pincebourde 2005) may disappear because the larger dung pats upon which they rely will no longer be available ( Halffter et al. 1992; Nichols et al. 2009). Today, only the smaller species of mammals remain at Reserva Ducke ( Vulinec 2000), and the genera of large-bodied beetles most likely to be deleteriously affected would be Dichotomius, Phanaeus , Coprophanaeus , and Oxysternon . Nichols et al. (2009) concluded that this kind of restructuring of dung beetle communities has profound implications for the maintenance of several ecosystem functions, including reduction in nutrient recycling and reduction in burial of excreted seeds with concomitant change in plant associations and patterns of regrowth.

Chazdon et al. (2009) noted that degraded old-growth forests (affected by road building, selective logging, recurrent fires, fragmentation, and hunting) and secondary regrowth forests comprise roughly half of the world’ s remaining tropical forests. Quintero and Roslin (2005) suggested that the regrowth of fragments of secondary tropical vegetation in Amazonia a mere decade after clear cutting of forest supported dung beetle assemblages similar to those in formerly continuous forest. They did not mention what mammals remained in these fragments, but the dung beetles captured in their study were all smallbodied species with the exception of C. jasius . While they demonstrated that secondary forest growth can restore some conditions favorable for certain species of dung beetles, I believe the original fauna of large-bodied dung beetles cannot be restored due to the absence of larger mammals and the dung resources they provide. In another study in Amazonia, Gardner et al. (2008) concluded from their data that tropical secondary and plantation forests were of low value for restoring dung beetle populations. In view of the detrimental consequences for maintenance of dung beetlemediated ecosystem services by these impoverished dung beetle communities, they urged that conservation strategies prioritize the protection of remaining areas of primary forest rather than relying on secondary forests. I concur.

Some colleagues have expressed concerns to me of “trapping out” the beetles during such a long-term, intensive survey. I believe the species composition and abundance data clearly show that this did not happen, even though collecting was done for slightly more than a year. However, this could be a concern in forest fragments where the reservoir of dung-producing mammals and additional species or individuals of scarabs is limited by lack of suitable habitat or adequate food resources. In Reserva Ducke at the time of this study, the collecting grid represented only a tiny area of the forest, and so the reservoir of dung- and carrionfeeding scarabs was substantial and always available to replace the 19,000 specimens collected.

Goodland and Irwin (1975), Myers (1984), Klein (1989), Whitmore (1997), Fearnside (1990, 2009), and many others have observed that fragmentation of Amazonian rainforests, indeed all tropical forests, is continuing unabated at an alarming rate. The cascading consequences of selective extinction in remaining forest fragments results in a depauperate fauna and flora and a concomitant decrease in attendant ecosystem services. Unlike some of those disappearing dung beetles, humankind is in deep shit if this continues to happen. I am reminded of a sentiment from the World Wildlife Fund:

All that lives beneath Earth’ s fragile canopy is, in some elemental fashion, related.

Is born, moves, feeds, reproduces, dies.

Tiger and turtle dove; each tiny flower and homely frog; the running child, father to the man and, in ways as yet unknown, brother to the salamander.

If mankind continues to allow whole species to perish, when does their peril also become ours?

Humans need to step up and assume enhanced stewardship for the biota with which we share the planet... if it is not already too late. As H. G. Wells said long ago before there was a biodiversity crisis, “Human history more and more becomes a race between education and catastrophe”. And the answer to the WWF soliloquy above is NOW.