A good indicator species should be easy to sample, identify and measure, and be informative about its ecological context. We analysed data from a nation-wide dung beetle survey in Venezuela in order to assess the indicative response of Oxysternon festivum (Coleoptera: Scarabaeinae) to vegetation and climatic condition in the Orinoco river basin. Our approach consisted of two steps: estimating habitat suitability (HS) from historical records and mean environmental conditions, and analysing four different properties measured during a nationwide survey (occurrence, total abundance, individual body size, and total biomass), in relationship with HS and current environmental covariates measured from remote sensors. O. festivum population status could not be completely explained by historical or current conditions alone, but rather by combinations of both. It was strongly associated with forest vegetation, but abundance, biomass and body size increased under harsher (hotter and drier) climatic conditions. Thus, O. festivum seems to be sensitive to changes in vegetation cover, but tolerant to certain levels of perturbance, where it probably replaces other, more sensitive species. Fully understanding the role of O. festivum requires the analysis of its relationships to other species. We strongly recommend the development of similar protocols for the analysis of other potential ecological indicator species, drawing information from historical and contemporary sources and exploiting the available statistical tools to reveal complex patterns. Given the high diversity of dung beetles, and the growing interest in this group, several candidates will probably be found in most tropical countries.
Oxysternon festivum is a species of dung-beetle of the scarab beetle family.
Oxysternon festivum has a colored dorsum and black head and underside, the pronotum is smooth. As most Oxysternon species, it has considerable variation in color, ranging from the typical coppery-red to entirely black, and including yellow-red and green forms. The black form is apparently restricted to the Island of Trinidad and thus considered as a separate subspecies (O. festivum nigerrimum Arnaud, 2002).[1]
The species reaches a length of about 16–31 millimetres (0.63–1.22 in) and shows sexual polymorphism. Major males are horned and substantially bigger than the hornless female, while minor males are hornless and often smaller than females. Females and small males differ in the form of the transverse carina.[1]
Oxysternon festivum was among the first dung beetle species studied by zoologist in the early 18th century. The first illustration of an "exceedingly beautiful shining gold and red, three horned beetle" was published in 1747 by August Johann Rösel von Rosenhof, and a first description was done by Laurens Theodorus Gronovius in 1764, but the names applied were non-binomial and therefore invalid for nomenclatural purposes.[3][4][5] It was later re-described by Carl Linnaeus under the name of Scarabaeus festivus, and was subsequently included in most publications regarding exotic insects in the late 18th and early 19th centuries.[6][7][8][9][10]
O. festivum was once assigned to the genus Sternaspis, but the name was preoccupied and thus invalid. Laporte, writing under the pen name of Le Compte de Castelnau, proposed the genus Oxysternon to include several species of Phaneus-like species with a long, spiniform extension of the anterior angle of the metasternum. O. festivum was later designated as the type species of this genus.[6][11]
Two color forms were described as aberrations by Olsoufieff, and later formalised as subspecies by Arnaud, using the names O. festivum viridanum for the green form and O. festivum nigerrimum for the black form. However the green coloration is apparently part of the phenotypical variation of the species and thus is not recognized as a separate subspecies.[1]
The distinct male morphotypes are associated to different reproductive tactics: major males fight for females and guard and defend burrows actively, while minor males evade fights and try to sneak to the burrows to mate with females.[12]
This species is attracted to dung, carrion and fruits as food resources, but are only known to breed on dung and carrion.[11][13]
This species is mostly restricted to the Guiana Shield and can be found in French Guiana, Guyana, Suriname, Venezuela, Brazil, Colombia, and Trinidad.[14][15]
Oxysternon festivum lives in forest but can tolerate certain degree of habitat perturbation.[15]
Oxysternon festivum is a species of dung-beetle of the scarab beetle family.
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