Movement patterns in dung beetles and in the dung fly

Movements in coprophagous beetles between cow pats are discussed in relation to two hypotheses: (i) that the movement patterns are results of selection to maximize the net rate of energy intake; (ii) that the rates of immigration to and emigration from droppings are governed by simple stochastic rules of behaviour. Observations support the latter hypothesis, and contrast with predictions from the simplest optimization model. Reasons for this discrepancy are discussed. Spatio-temporal occurrence of the dung fly, Scatophaga stercoraria, around cow pats is re-analysed from Parker's data. A simple Markov chain model predicts the observations well, but it does not solve the question of the type of selection responsible for the values of the behavioural parameters. It is argued that difficulties in coping with a stochastic environment, and the consequences of movements being manifested on many spatial and temporal levels, favour evolution consisting of few key behavioural parameters being singled out and subsequently adjusted by selection.     

Use of habitat resources by scarab dung beetles in an savanna

In the Queen Elizabeth National Park, Uganda, we compared the scarab beetle assemblages in the dung of three wild ungulates (African buffalo, a ruminant foregut fermenter; hippopotamus, nonruminant foregut fermenter; and warthog, nonruminant hindgut fermenter). Dung was collected from two sandy-clay soils with different percentage of coarse sand. We aimed at investigating habitat resource selection by dung beetle species within a savanna natural contest with abundant and diverse food availability. Analyses were performed to detect differences for dung beetle assemblages in abundance, diversity, functional groups. Species richness in the three dung types and in the two soil types was similar. However, warthog dung and sandy-rich soil appeared the preferred habitat resources, in terms of abundance and biomass, while hippopotamus dung hosted the lowest values for these parameters. The analysis of functional groups revealed that slow-burying tunnellers held the major role, both in terms of abundance and biomass, and were mainly found in warthog dung.     

Monitoring the ecosystem service provided by dung beetles offers benefits over commonly used biodiversity metrics and a traditional trapping method

Surveying terrestrial invertebrates often requires lethal techniques that can also kill non-target vertebrates. Removing the desirable components of biodiversity is at odds with the philosophy of ecological restoration and biodiversity conservation more generally. Moreover, commonly used metrics generated by such survey approaches (e.g. abundance and species richness) are only indirectly related to the ecosystem services (e.g. pollination) that are often of primary interest. We examined the relationship between rates of dung removal (a direct measure of an ecosystem service) and dung beetle abundance and species richness in a temperate region of New South Wales, Australia, and examined if dung removal in revegetated riparian areas of different ages were trending monotonically toward rates in areas with mature native vegetation. Pellets of pig manure and conventional traps were left at study sites for 48 h to examine the relationships between rates of dung removal and dung beetle abundance and richness. Regressions of abundance and richness with average percent dung removal were positive and significant, demonstrating the potential of the method as a non-lethal proxy. While the dung removal method cannot determine the species responsible, percentage dung removal was more time-efficient, costing 4 min per sample, while abundance and richness cost 13 and 17 min, respectively. Despite variability among replicates of the same habitat type, the trajectory across the restoration gradient showed an increase from sites recently revegetated toward those with mature woody vegetation. We interpreted these results as a positive response of dung beetle activity and an indication of recovery of this ecosystem service. We argue that responses that can be collected efficiently such as dung removal should be used if restorationists have limited resources for data collection and analysis; non-specialists are involved; knowledge of ecosystem function is required, and animal ethics constrain options.     

Aggregated distribution of resources creates competition refuges for rainforest dung beetles

This study examines the effects of resource distribution on colonisation, intra- and interspecific aggregation, and the occurrence of low-density, competition refuges for tropical dung beetles. In field experiments from central Peru, using dung pats (resource patches) of different volumes, the numbers of interacting species and total beetle biomass at individual pats increased with increasing pat volume. In two of three separate experiments (including an experiment that also varied patch density), this represented a decrease in the biomass of beetles per unit volume (biomass-density) at larger patches. The numbers of interacting tunneller species and tunneller biomass-density were also related to the distance between pats (patch density) in one of two experiments with constant numbers of pats. Closely positioned pats had generally fewer interacting species and a lower biomass-density of beetles. For the most abundant Dichotomius species, interspecific associations increased as distances increased between dung pats. The numbers of interacting species and biomass-density declined linearly under the combined effects of increasing patch density and local patch abundance in 25 m² plots. In experimentally placed grids with large numbers of pats, colonisation of pats at the edge of the grids was generally higher than at the centre of the grids for tunnellers and Eurysternus spp. but not for ball rollers; however, at least tunnellers did not readjust to avoid patches with high densities of competitors. These results indicate that an aggregated distribution of dung and natural variability in patch size contribute to species coexistence by creating low-density refuges for weaker competitors.     

Dung beetles ignore landmarks for straight-line orientation

Upon locating a suitable dung pile, ball-rolling dung beetles shape a piece of dung into a ball and roll it away in a straight line. This guarantees that they will not return to the dung pile, where they risk having their ball stolen by other beetles. Dung beetles are known to use celestial compass cues such as the sun, the moon and the pattern of polarised light formed around these light sources to roll their balls of dung along straight paths. Here, we investigate whether terrestrial landmarks have any influence on straight-line orientation in dung beetles. We find that the removal or re-arrangement of landmarks has no effect on the beetle’s orientation precision. Celestial compass cues dominate straight-line orientation in dung beetles so strongly that, under heavily overcast conditions or when prevented from seeing the sky, the beetles can no longer orient along straight paths. To our knowledge, this is the only animal with a visual compass system that ignores the extra orientation precision that landmarks can offer.     

蜣螂的生态价值和保护意义

蜣螂通常以粪便或腐殖质为食,在生态系统平衡中具有重要的作用。文章系统介绍蜣螂的生态价值,包括转将运粪便到地下、对种子二次传播的作用、传粉作用、对有害生物的控制作用和寄生虫的中间宿主,以及广阔的开发应用前景、重要仿生学意义和重大理论意义;并进一步提出蜣螂保护的迫切性和重要意义。     

Phenolic glucosides as feeding cues for willow-feeding leaf beetles

The effects of individual phenolic glucosides and total glucoside fractions on the feeding behaviour of three willowfeeding leaf beetles (Coleoptera: Chrysomelidae) were tested in the laboratory. Feeding preferences of the tested leaf beetles were strongly influenced by certain phenolic glucosides which are typical secondary compounds of willows (Salicaceae:Salix). Two of the tested leaf beetles,Galerucella lineola andLochmaea capreae showed rather similar responses to glucoside treatments. Both of them were strongly stimulated by total glucoside fractions fromSalix triandra and by its major glucoside salidroside. The third species,Phatora vitellinae, was attracted most by the fractions fromS. myrsinifolia andS. pentandra, and by two related salicylate glucosides, tremulacin and salicortin. Food selection pattern of the tested beetles in the laboratory concords fairly well with their distributions in the field and with the occurrence of phenolic glucosides in their host willows. Phenolic glucoside extracts stimulated more feeding than individual pure glucosides. This indicates that different compounds have synergistic effects in the feeding behaviour of leaf beetles. Our results clearly show that willow leaf beetles select their food based on phenolic glucosides of their host plants.     

Distribution and abundance of dung beetles in fragmented landscapes

Related species utilising similar resources are often assumed to show similar spatial population structures and dynamics. This paper reports substantial ecological variation within a set of Aphodius dung beetles occurring in the same patchily distributed resource, livestock dung in pastures. We show how variation in habitat and resource selectivity, in the rate of movements between pastures, and in the distribution of local population sizes all contribute to interspecific differences in spatial population structures. Local dung beetle assemblages are compared between two landscapes with different densities of pastures. In one of the landscapes, we contrast the abundances and regional distributions of Aphodius before and after 15 years of rapid habitat loss. Different species show very dissimilar responses to changes in the structure of the landscape. Our results suggest that generalist Aphodius species, and specialist species with high dispersal powers, occur as large "patchy" populations in the landscape. In contrast, a strict pasture specialist species with limited dispersal powers (A. pusillus) forms classical metapopulations. At the community level, interspecific differences in spatial population structures make the local community composition a function of the structure of the surrounding landscape.     

Co-declining mammals and dung beetles: an impending ecological cascade

Biodiversity loss can precipitate extinction cascades and impair ecological processes. These 'downstream' effects will be exacerbated if functionally important taxa are tightly linked with species threatened by extinction or population decline. We review the current evidence that such a scenario is currently playing out in the linked declines of persistently hunted mammal populations and the dung beetles communities (Coleoptera: Scarabaeidae: Scarabaeinae) that depend on them for adult and larval food resources. Through a close evolutionary association, mammal assemblages have played a fundamental role in structuring extant dung beetle communities. Today many game mammal species' populations are severely depleted by subsistence or commercial hunting, especially in tropical forest systems. Multiple lines of evidence from temperate and tropical systems indicate that the regional-scale decline or extirpation of medium and large bodied mammal faunas can severely disrupt the diversity and abundance of dung beetle communities through alterations in the composition and availability of dung resources. These observed community disassemblies have significant short- and long-term implications for the maintenance of key ecosystem processes including nutrient recycling and secondary seed dispersal. Identifying the species- and community-level traits that buffer or exacerbate these species and functional responses is essential if we are to develop a better understanding of the cascading ecological consequences of hunting in tropical forests.     

An old adaptive radiation of forest dung beetles in Madagascar

Adaptive radiations of mammals have contributed to the exceptionally high levels of biodiversity and endemism in Madagascar. Here we examine the evolutionary history of the endemic dung beetle tribe Helictopleurini (Scarabaeidae) and its relationship to the widely distributed Oniticellini and Onthophagini. Helictopleurini species are dependent on mammals for their resources. We date the single origin of the tribe at 37 to 23 MY ago, indicating overseas colonization of Madagascar. The main radiation occurred concurrently with the main radiations of lemurs. The ancestors of Helictopleurini are inferred to have been coprophagous species inhabiting open habitats. Subsequent evolution has involved a shift into forests, changes in resource use to a more generalized diet, and changes in body size. Four species of the extant 65 species have shifted to use the dung of the recently introduced cattle in open habitats, allowing these species to greatly expand their geographical ranges.     

Habitat fragmentation and the functional efficiency of temperate dung beetles

To understand how current patterns of habitat loss and fragmentation will ultimately affect ecosystem functioning, we need to match experimental manipulations of community structure with real changes occurring in the landscapes of today. In this study, we examine the consequences of habitat fragmentation on a key function: the decomposition of dung by invertebrates. In a microcosm experiment, we use previous observations of dung beetle assemblage structure in fragmented and intact landscapes to create realistic differences in assemblages of small, dung‐dwelling species in the genus Aphodius. We ask whether such differences will affect ecosystem functioning, and how their effects compare to those of removing full functional groups: dung‐dwelling Aphodius, tunnelling Geotrupes stercorarius, and/or earthworms. As measured by changes in dung fresh weight, we observe an overriding impact of removing G. stercorarius, with the amount of dung remaining at any one time doubling if the species is excluded. Compared to this major effect, there seem to be less effects of removing Aphodius, ambiguous effects of excluding earthworms, and no detectable effects of relatively minor changes in Aphodius assemblages as induced by current levels of fragmentation. Overall, our results support the general notion that different species contribute highly unevenly to overall ecosystem functioning. Most importantly though, our findings suggest that the functional consequences of habitat loss will depend on taxon‐specific responses to landscape modification. Only by addressing these responses may we predict the actual consequences of habitat loss.     

Affinities of the Canthonini dung beetles of the Eastern Arc Mountains

The Eastern Arc Mountains (EAM) consist of 13 separate mountain blocks running from southern Kenya through eastern Tanzania in an arc shape. Organisms occurring in the forests of these mountains are known for their high levels of endemism. Some of these organisms have their closest relatives in distant geographic regions. In this study, molecular phylogenetic methods, based on partial sequences of one nuclear (28S) and two mitochondrial (COI and 16S) genes, are used to determine the relationships of three Scarabaeinae genera (tribe Canthonini) endemic to the EAM. Janssensantus and Tanzanolus are found to have a sister relationship within a lineage of south-eastern African genera, while Madaphacosoma’s closest ties are with Oriental and Madagascan taxa Ochicanthon and Epactoides, respectively. Divergence time estimates suggest a Miocene origin for the ancestral lineages of the three genera with Janssensantus and Tanzanolus separating in the Pleistocene. Our results provide evidence for a Madagascan origin for the EAM genera.     

Ancient origin of endemic Iberian earth-boring dung beetles (Geotrupidae)

The earth-boring dung beetles belong to the family Geotrupidae that includes more than 350 species classified into three subfamilies Geotrupinae, Lethrinae, and Taurocerastinae, mainly distributed across temperate regions. Phylogenetic relationships within the family are based exclusively on morphology and remain controversial. In the Iberian Peninsula there are 33 species, 20 of them endemic, which suggests that these lineages might have experienced a radiation event. The evolution of morphological adaptations to the Iberian semi-arid environments such as the loss of wings (apterism) or the ability to exploit alternative food resources is thought to have promoted diversification. Here, we present a phylogenetic analysis of 31 species of Geotrupidae, 17 endemic to the Iberian Peninsula, and the remaining from southeastern Europe, Morocco, and Austral South America based on partial mitochondrial and nuclear gene sequence data. The reconstructed maximum likelihood and Bayesian inference phylogenies recovered Geotrupinae and Lethrinae as sister groups to the exclusion of Taurocerastinae. Monophyly of the analyzed geotrupid genera was supported but phylogenetic relationships among genera were poorly resolved. Ancestral character-state reconstruction of wing loss evolution, dating, and diversification tests altogether showed neither evidence of a burst of cladogenesis of the Iberian Peninsula group nor an association between apterism and higher diversification rates. Loss of flight did not accelerate speciation rates but it was likely responsible for the high levels of endemism of Iberian geotrupids by preventing their expansion to central Europe. These Iberian flightless beetle lineages are probably paleoendemics that have survived since the Tertiary in this refuge area during Plio-Pleistocene climatic fluctuations by evolving adaptations to arid and semi-arid environments.     

Selecting dung beetles [Scarabaeinae] from spain for bushfly control in south-western Australia

The relative abundance of 16 dung beetle species (subfamilyScarabaeinae) was investigated at an annual pasture site near Olivenza in S.W. Spain in the spring of 1981. The night-flying speciesCopris hispanus which was the dominant species, made up 63 % and 81 % of the dry weight of beetles in traps set at dawn and dusk respectively and left open for 24 h. Further observations in 1982 and in 1983 confirmed thatC. hispanus and alsoBubas bison which flies during the day and night, were the 2 dominant species in spring. It is proposed that they should be introduced to S.W. Australia as part of an attempt to control bush fly.

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Résumé L'abondance relative de 16 espèces de beusiers (Scarabaeinae) a été étudiée au printemps 1981 dans un emplacement de pature annuelle près d'Olivenza dans le Sud-Ouest de l'Espagne. L'espèce nocturneCopris hispanus qui était l'espèce dominante représentait 63 % et 81 % du poids sec des coléopteres dans les pièges posés respectivement à l'aube et au crépuscule et laissés ouverts durant 24 h. Des observations ultérieures réalisées en 1982 et en 1983 confirmaient queC. hispanus et aussiBubas bison qui vole de jour comme de nuit étaient les 2 espèces dominantes du printemps. Leur introduction dans le Sud-Ouest de l'Australie est proposée comme un des éléments d'un essai de lutte contre la mouche de la brousse.

     

Visual cues for the retrieval of landmark memories by navigating wood ants

BACKGROUND: Even on short routes, ants can be guided by multiple visual memories. We investigate here the cues controlling memory retrieval as wood ants approach a one- or two-edged landmark to collect sucrose at a point along its base. In such tasks, ants store the desired retinal position of landmark edges at several points along their route. They guide subsequent trips by retrieving the appropriate memory and moving to bring the edges in the scene toward the stored positions. RESULTS: The apparent width of the landmark turns out to be a powerful cue for retrieving the desired retinal position of a landmark edge. Two other potential cues, the landmark's apparent height and the distance that the ant walks, have little effect on memory retrieval. A simple model encapsulates these conclusions and reproduces the ants' routes in several conditions. According to this model, the ant stores a look-up table. Each entry contains the apparent width of the landmark and the desired retinal position of vertical edges. The currently perceived width provides an index for retrieving the associated stored edge positions. The model accounts for the population behavior of ants and the idiosyncratic training routes of individual ants. DISCUSSION: Our results imply binding between the edge of a shape and its width and, further, imply that assessing the width of a shape does not depend on the presence of any particular local feature, such as a landmark edge. This property makes the ant's retrieval and guidance system relatively robust to edge occlusions.     

A simple assay to determine the nutritional suitability of cattle dung for coprophagous beetles

An assay using extracted dung fluid was developed to provide an objective method of assessing the suitability of cattle dung for beetle Euoniticellus intermedius. Fluid was extracted from whole dung by twisting gauze-wrapped samples by hand, or by use of an hydraulic press set sequentially at 2 MPa, 6 MPa and 10 MPa. Artificial dung was made by adding dung fluid to shredded fibre-board in a 15:1 weight ratio. The rate of brood-ball (= egg) production by female E. intermedius fed on the artificial dung made from fluid extracted by the hydraulic press at 2 MPa was the same as that on natural whole dung. Reproductive performance on all artificial dungs was significantly correlated with the percent dry matter content of the dung fluid used in the mixture. Thus the percent dry matter in the fluid extracted at 2 MPa pressure provides an objective measurement for comparing the quality of different dungs as food for adult E. intermedius, without the need for performing bioassays. The results confirm that the fluid component of dung is the major source of nutrition for adult dung beetles.Deceased February 1986.     

Discontinuous gas exchange in dung beetles: patterns and ecological implications

This study correlates a distinctive pattern of external gas exchange, referred to as the discontinuous gas exchange cycle (DGC), observed in the laboratory, with habitat associations of five species of telecoprid dung beetles. The beetles were chosen from a variety of habitats that would be expected to present different amounts of water stress. All five species exhibited DGC. Sisyphus fasciculatus has been recorded only in woodland areas, and does not have strict spiracular control during its DGC. Anachalcos convexus and Scarabaeus rusticus are associated with open mesic habitats. Both species exhibit a distinct DGC, previously found in some other insect species, but intermediate within this study group. Sc. flavicornis and Circellium bacchus are typically found in arid regions, and have the most unusual form of DGC, with spiracular fluttering during the burst phase. These results support the hypothesis that spiracular fluttering reduces respiratory water loss. From this study we conclude that the DGC is an ancestral adaptation, most probably as a result of anoxic environments in underground burrows, but that spiracular control is enhanced to reduce respiratory water loss in beetle species that live in arid habitats. Received 4 August 1999 / Accepted: 7 October 1999     

Visual discrimination of cues differing as for their number of elements, their shape or their orientation, by the ant Myrmica sabuleti

Using operant conditioning as a method, we study if Myrmica sabuleti workers can discriminate figures made of different numbers of the same element, different filled shapes or hollow forms and elements differently oriented. The ants effectively discriminate figures containing different numbers of the same element but without counting the elements: their distinguishing is based on the global aspect (dimensions, area) of the figures. They distinguish filled shapes as well as hollow forms when these look different if seen with convexity. For instance, they differentiate well between concave filled shapes or concave hollow forms. They see distinctly an element and the same one rotated if this element, seen with convexity, looks different after its rotation. They perceive until a 30° rotation of a vertical segment and until a 15° rotation of a horizontal segment. In conclusion, M. sabuleti workers are sensitive to the number of elements, dimension, shape, form and orientation of visual cues with the restriction that they probably see them with convexity.