Variations in dung beetle assemblages across a gradient of hunting in a tropical forest

Populations of large mammals are severely depleted by hunting in tropical forests, with direct effects on plant regeneration. But indirect consequences on commensal taxa depending on them for food resources, like coprophagous beetles, are less documented. Cascading effects of species loss across Scarabaeinae are expected, with likely significant negative implications for ecosystem functions. We examined dung beetle assemblages using pitfall traps at three rain forest sites in French Guiana ranging from intact mammalian fauna (Nouragues) to moderate (Kaw) and heavy (Matoury) defaunation. The site with the most depauperate mammalian fauna showed significantly lower dung beetle species richness than the two other two sites, which were not different from each other. Mean abundance and biomass per trap were not different across sites whereas community composition strongly differed among sites. A positive correlation was observed between body size and the individual contribution to dissimilarity between Nouragues and Kaw. The species contributing the most to dissimilarity were large. By contrast, one medium-sized species, dominant in Matoury, contributed the most to dissimilarity between Matoury and other sites. Diurnal genera of large tunnellers showed a higher diversity and abundance in Nouragues compared to other sites, whereas a nocturnal genus showed no differences. Large rollers were more abundant in Kaw compared to other sites. None of the groups of small beetles but one were affected by defaunation. Our results suggest that loss of large mammal populations affects dung beetle assemblage structure and causes decreasing abundance or disappearance of large tunnellers species that have a major impact on several dung beetle-mediated ecological processes.     

Turnover and nestedness in subtropical dung beetle assemblages along an elevational gradient

Aim

We investigated changes in dung beetle β‐diversity components along a subtropical elevational gradient, to test whether turnover or nestedness‐related processes drive the dissimilarity of assemblages at spatial and temporal scales.

Location

An elevational gradient (200–1,600 m a.s.l.) of the Atlantic Forest in southern Brazil.

Methods

We investigated the extent to which β‐diversity varied along the elevational gradient (six elevations) at both spatial (among sites at different elevations) and temporal (different months at the same site) scales. We compared both the turnover and nestedness‐related dissimilarity of species and genera using multiple‐site or multiple‐month measures and tested whether these measurements were different from random expectations.

Results

A mid‐elevation peak in species richness along the elevational gradient was observed, and the lowest richness occurred at the highest elevations. We found two different groups of species, lowland and highland species, with a mixing of groups at intermediate elevations. The turnover component of β‐diversity was significantly higher for both spatial (i.e. elevational) and temporal changes in species composition. However, when the data for genera by site were considered, the elevational turnover value decreased in relative importance. Nestedness‐related processes are more important for temporal dissimilarity patterns at higher elevation sites.

Main conclusions

Spatial and temporal turnover of dung beetle species is the most important component of β‐diversity along the elevational gradient. High‐elevation assemblages are not subsets of assemblages that inhabit lower elevations, but this relationship ceases when β‐diversity is measured at the generic level. Environmental changes across elevations may be the cause of the differential establishment of distinctive species, but these species typically belong to the same higher taxonomic rank. Conservation strategies should consider elevational gradients in case‐specific scenarios as they may contain distinct species assemblages in lowlands vs. highlands.

     

Forest complexity drives dung beetle assemblages along an edge-interior gradient in the southwest Amazon rainforest

1. The habitat heterogeneity hypothesis predicts that heterogeneous habitats may provide more niches and diverse ways of exploiting environmental resources, thereby allowing more species to coexist, persist and diversify. 2. We aimed to investigate how an edge-interior gradient related to forest complexity influences species composition, abundance and richness of dung beetles in the western Amazon rainforest. We expected dung beetle abundance and richness to increase along the forest edge-interior gradient, in accordance with the habitat heterogeneity hypothesis. We also expected strong changes in species composition driven by species turnover in the forest interior and nestedness along the forest edges. We sampled dung beetles using baited pitfall traps across an edge-interior gradient. We also assessed the variation in forest features along the edge-interior gradient to identify changes in forest complexity. 3. Both species richness and abundance of dung beetles increased along the forest edge-interior, following the gradient of forest complexity. The Sorensen dissimilarity of dung beetle assemblages was higher among sampling units placed near the forest edge, although neither turnover, nor nestedness was different between the extremes of the forest edge-interior gradient. There was a clear compositional change along the edge-interior gradient mostly driven by species turnover. Individual indicator value analysis revealed that species were strongly associated with the forest interior conditions. 4. The simplification of the Amazon rainforest near clearings causes compositional changes in dung beetle assemblages. These changes are characterised by species-poor and low-abundance assemblages and may impair dung beetle ecological functions and therefore forest recovery.     

Unexpectedly diverse forest dung beetle communities in degraded rain forest landscapes in Madagascar

Tropical forests, which harbor high levels of biodiversity, are being lost at an alarming speed. Madagascar, a biodiversity hotspot, has lost more than half of its original forest cover. Most of the remaining forests are small fragments of primary and secondary forest with differing degrees of human impact. These forests, as well as coffee and fruit plantations, may be important in supporting the forest-dependent biodiversity in Madagascar but this has been little studied. In Madagascar, dung beetles, which offer important ecosystem services, are largely restricted to forests. We examined the ability of fragmented and degraded forests to support dung beetle diversity, compared to the large areas of primary forest in eastern Madagascar. We found a general trend of a reduction of species with a loss of forest connectivity. In contrast, a higher level of forest disturbance was associated with higher species diversity. In several sites of low-quality forest as many or more species were found as in less disturbed and primary forests. The average size of dung beetles was smaller in the lower quality localities than in the primary forests. These findings suggest that many forest dung beetles in Madagascar are better adapted to forest disturbance than earlier expected, although they require some level of connectivity to surrounding forest.     

Trophic associations of a dung beetle assemblage (Scarabaeidae: Scarabaeinae) in a woodland savanna of Botswana

Species richness and abundance of dung beetles were assessed across a range of bait types that acted as surrogates for the food resources available in Chobe National Park, Botswana. These bait types were comprised of the dung of pig (omnivore), cattle (ruminant herbivore dropping fine-fiberd pads), sheep (pellet-dropping ruminant herbivore), and elephant (monogastric, nonruminant herbivore producing coarse-fibered droppings), and chicken livers (carrion). Species richness was similar between traps baited with pig, cattle, and elephant dung but was relatively lower in those baited with sheep dung and carrion. In traps baited with pig dung, abundance was relatively greater than in all other bait types. A cluster analysis of species abundance distributions for the 30 most abundant species identified four different patterns of bait type association at a 60% level of similarity. All but 1 of the 15 species in cluster A were attracted primarily to the dung of omnivores and pad-dropping ruminant herbivores (pig and cattle). All seven species of cluster B were attracted primarily to coarse-fibered, nonruminant herbivore dung (elephant). All four species of cluster C were primarily carrion and pig dung associated, whereas all four species of cluster D were carrion specialists. In conclusion, the most abundant species were attracted to all bait types, but most species were largely specialized to different dung types or carrion, with dung attracting the majority of the fauna in terms of both species richness and abundance.     

Fruit biomass availability along a forest cover gradient

Habitat loss is the main driver of the current high rate of species extinction, particularly in tropical forests. Understanding the factors associated with biodiversity loss, such as the extinction of species interactions and ecological functions, is an urgent priority. Here, our aim was to evaluate how landscape‐scale forest cover influences fruit biomass comparing different tree functional groups. We sampled 20 forest fragments located within landscapes with forest cover ranging from 2 to 93 percent in the Atlantic forest of southern Bahia, Brazil. In each fragment, we established five plots of 25 × 4 m and carried out phenological observations on fleshy fruit throughout 1 year on all trees ≥5 cm dbh. We estimated fruit availability by direct counting of all fruits and derived fruit biomass from this count. We used spatial mixed linear models to evaluate the effects of forest cover on species richness, abundance, and fruit biomass. Our results indicated that forest cover was the main explanatory variable and negatively influenced the total richness and abundance of zoochoric and shade‐tolerant but not shade‐intolerant species. A linear model best explained variations in richness and abundance of total and shade‐tolerant species. We also found that forest cover was positively correlated with the fruit biomass produced by all species and by the shade‐tolerant assemblages, with linear models best explaining both relationships. The loss of shade‐tolerant species and the lower fruit production in fragments with lower landscape‐scale forest cover may have implications for the maintenance of frugivore, seed dispersal service, and plant recruitment.     

Grassland area determines beetle assemblage dissimilarity from surrounding floodplain forest

Patch size is known to affect biodiversity in fragmented landscapes, but is usually examined in systems where the surrounding matrix habitat is unfavourable. We examined beetle diversity in a floodplain ecosystem that is characterised by naturally occurring grassland patches within a dominant matrix of contrasting yet habitable forest. We asked whether differences in the beetle assemblage between grassland and forest vegetation depended on the area of the grassland patch, which is a function of its flooding frequency and duration: smaller grasslands tend to be higher on the floodplain and are flooded less often and for shorter periods than larger grasslands. We found a negative relationship between grassland area and beetle abundance and species richness, and a positive relationship between grassland area and compositional dissimilarity from the surrounding forest. As expected, we found an overall difference in composition between forest and grassland assemblages, with five beetle species more common in the grasslands. Our study indicates that floodplain grasslands not only support beetle assemblages that are distinct from the surrounding forest, but that assemblages from the larger grasslands are compositionally more distinct than those from smaller grasslands. A likely cause of this pattern is the reduced edge effects and greater environmental contrast between forest and large grasslands that may be exposed to greater variation in local climate. Ongoing changes to flood regimes and potential encroachment of forest plants may decrease grassland area in the future, which may reduce spatial heterogeneity in the insect community in this unique floodplain ecosystem.     

Changes in the dung beetle community in response to restinga forest degradation

Restinga (forest formations on sandy substrates on the Brazil Atlantic coast) have declined from covering approximately 80 % of the coastline and continue to do so due to anthropogenic activity. This study compares the abundance, richness and species composition of conserved (CR) and degraded (DR) resting forest. We used six locations on the coast of Pernambuco, Brazil where there were paired CR and DR sites and used baited pitfall traps to sample dung beetles in the dry and wet seasons. We captured 1,724 individuals, which belonged to 25 species and 10 genera; 1,030 individuals (15 species) were from CR and 694 individuals (17 species) from DR. No significant differences was observed in the patterns of species richness or abundance between CR and DR sites but non-metric multidimensional scaling and similarity analyses revealed differences in species composition between CR and DR sites. Additionally DR sites had a higher beta diversity than CR sites. We found only seven of the 25 species identified in this study in both areas, indicating that few species from the original ecosystem remain in degraded sites. In addition, the forest species that were recorded in Degraded sites, such as Canthon nigripenne and Dichotomius schiffleri, had low abundance when compared to conserved restinga. We suggest that parts of the CR become areas under legal protection, in order to maintain the biodiversity of the remaining areas of restinga.     

Global dung webs: high trophic generalism of dung beetles along the latitudinal diversity gradient

At the global scale, species diversity is known to strongly increase towards the equator for most taxa. According to theory, a higher resource specificity of consumers facilitates the coexistence of a larger number of species and has been suggested as an explanation for the latitudinal diversity gradient. However, only few studies support the predicted increase in specialisation or even showed opposite results. Surprisingly, analyses for detritivores are still missing. Therefore, we performed an analysis on the degree of trophic specialisation of dung beetles. We summarised 45 studies, covering the resource preferences of a total of 994503 individuals, to calculate the dung specificity in each study region. Our results highlighted a significant (4.3‐fold) increase in the diversity of beetles attracted to vertebrate dung towards the equator. However, their resource specificity was low, unrelated to diversity and revealed a highly generalistic use of dung resources that remained similar along the latitudinal gradient.     

Elevational zonation of afrotropical forest bird communities along a homogeneous forest gradient

Aim This study analyses the distribution and abundance of birds from a forested tropical gradient in order to determine whether elevationally distinct communities are detectable in this habitat. Location An avifaunal census was carried out on a single transect within the tropical forest of the Udzungwa Mountains in the Eastern Arc, Tanzania, covering a range in elevation from 300 to 1850 m. Methods Two complementary data sets on forest birds were analysed, encompassing (1) data derived from standardized 20‐ha spot‐mapping censuses performed at nine elevations over 175‐m intervals from 400 to 1800 m a.s.l., and (2) all observations of birds binned into 32 data points at 50‐m intervals, from 300 to 1850 m a.s.l. The degree of zonation in the avian community along the elevational gradient was examined using the chronological clustering method, an agglomerative hierarchical clustering method that can be carried out with a range of similarity indices. Results The chronological clustering analysis of the data set based on standardized spot‐mapping revealed a clearly defined boundary at c. 1200 m a.s.l., separating lowland from montane communities. Most bird species could be categorized as belonging to one of these two communities. The data set based on all observations revealed a number of potential secondary boundaries, although these boundaries delimited the entire elevational ranges of individual species in only relatively few cases. Main conclusions In contrast to previously published studies, we find evidence of an elevational zonation of distinct communities within a seemingly homogeneous habitat. Although similar boundaries have been assumed to arise as a result of vegetational ecotones, or because of interspecific competition, these mechanisms are poorly corroborated. We suggest that the causes of patterns of zonation are not well understood, and that the interplay among species distributions, species richness, and environmental factors needs more consideration. The chronological clustering method is proposed as an appropriate tool for studying these specific patterns.     

Changes in riparian forest composition along a sedimentation rate gradient

Riparian forests are highly valued for maintaining water quality through the retention of sediments and nutrients. They also provide some of the most diverse and species-rich habitats in the world. What is largely unknown, however, is how sediment deposition affects plant community composition in these forests. The objective of this study was to examine changes in plant community composition across a gradient of increasing rates of sedimentation in riparian forests in the southeastern Coastal Plain, USA. Seventeen plots were established within riparian forests receiving between 0 and 5.5 cm year⁻¹ of sediment deposits. Species density and biomass estimates were collected annually from 2002 to 2006 for overstory and mid-story plant species within each plot. Percent cover and nested frequency of understory plant species were determined annually during 2004–2006. Measures of community composition in the understory, mid-story, and overstory layers of forests were compared to changes in environmental factors associated with increased sedimentation. In the understory, annual, exotic, and upland species had higher importance values in plots receiving high sediment deposition. The densities of shade-intolerant and N-fixing species in the mid-story also increased with increasing sedimentation rates. Increased overstory mortality was associated with high sedimentation rates, though increases in understory light levels in these gaps were not the main driver of understory species changes. Edaphic factors, such as soil texture, moisture, and temperature, were significantly correlated to species composition in all three forest layers, suggesting that changes in soil physical structure due to sedimentation may drive community-level changes in these forests.     

Amphibian communities along a forest degradation gradient in an East African forest reserve

The amphibian communities in Africa's tropical forests are of global conservation importance, but disturbances derived from anthropological activities threaten to dismantle this irreplaceable diversity. We explored the impacts of forest degradation on the amphibian community in Mabira Central Forest Reserve, Uganda. We sampled amphibians from March to July of 2015 in plots that were positioned along a gradient of forest degradation. We conducted visual encounter surveys across three categories of forest degradation with six 300-m transects in each (four surveys per transect). From 216 h of surveyor effort, we detected 3563 individual frogs representing 30 species from eight families and 13 genera. Hyperoliidae was the most diverse family represented by 13 species in four genera. Hyperolius had the highest number of species (nine) followed by four genera each represented by three species (Phrynobatrachus, Pytchadena, Leptopelis, and Sclerophrys). Comparisons among plots along a gradient of forest degradation revealed differences in species richness, composition, and frequency of encounters. The regenerating and degraded forest plots were similar in species composition to each other and were dominated by mostly widespread, open-canopy species. Several forest-dependent species were recorded in both the regenerating and mature forest plots but were absent from the degraded plots. In the regenerating and mature forests, species presence was significantly associated with high canopy cover, high relative humidity, and dense leaf litter, whereas the microhabitat variables of high grass cover and high temperature were most influential in the degraded forests. Our study provides important data on an Afrotropical amphibian community and suggests that forest degradation has dramatically altered the habitat to the detriment of forest specialist species.     

Roles of environmental variables and land usage as drivers of dung beetle assemblage structure in mopane woodland

Colophospermum mopane woodland covers large areas of dry lowland savanna in southeastern Africa. Dominant land usage is conservation (45%) with the remainder mostly modified by farming. Dung beetle responses to environment (dung type, habitat, weather) and land usage (conservation, farming, mining) were examined at Phalaborwa (23.9431°S 31.1411°E) in the Phalaborwa‐Timbavati Mopaneveld, South Africa. Partitioning of gamma species richness and diversity showed lower alpha values in mine areas than in farm and conserved areas. However, between‐land usage differences in species richness, alpha diversity, abundance and biomass, showed lower significance than those between dung type and different weather. At two sampling scales, three multivariate techniques variously separated assemblages according to land usage, dung type and weather. Analysis of 21 mean samples separated clusters according to dung type (Canonical Correspondence Analysis, CCA) or mine assemblages, conserved plus farm assemblages on pig plus elephant, or cattle dung (NMDS, Factor Analysis) with shared variance of >80% and unique variance of 16–18% per cluster. In analysis of 188 samples (CCA), each overlapping dung type cluster was offset in ordinal space with congruent patterns of separation according to land usage and weather (drier days distant from moister days; conserved plus farm areas distant from early succession mine areas, which were distant from disturbed and later succession mine areas). Mining, dung types, and moist conditions were the strongest contributors to between‐assemblage differences. Compared with conserved areas, dung beetle diversity is appreciably altered by mining but only slightly altered by intensive game farming or livestock ranching with subsistence agriculture.     

Interspecific and intraspecific variation in diet preference in five Atlantic forest dung beetle species

1. Dung beetles are commonly assumed to be generalist feeders, but there has been limited work in identifying whether there is interspecific variation in feeding preference. Equally, there has been no work exploring whether generalist feeding behaviour in a species is a result of within‐species specialisation. 2. This study identified the individual and species‐level feeding preferences of five dung beetle species towards human, jaguar and pig dung using a choice experiment. 3. It was found that species varied in their preference for the dung types, but there was no evidence that within a species, individual beetles varied in their dung choice. These findings were similar to results from field experiments that are more typically used to assess feeding preferences in dung beetles. 4. The results suggest that individual specialism in feeding may not be common in dung beetles. However, there is variation in feeding preferences among species, which is often overlooked and can have implications for the ecosystem functions they provide. It is suggested that choice arenas can be used to assess feeding preferences in dung beetle species that are not abundant enough to reliably estimate dietary choice from field studies.     

Testing for seasonal displacement in a dung beetle guild

The temporal overlap between seasonal distribution of adults of 14 congeneric dung beetle species ( Aphodius spp) was determined during one year, based on 11122 captures The mean seasonal distribution of adults (mean of the sampling dates weighted by the abundance value) was analyzed to elucidate deviations from ram-domness In addition, the effect of the shape of seasonal distribution of adults was investigated In both analyses randomization methods were used A clear trend exists maximizing the temporal displacement between middle points of chronologically consecutive species newly emerging species appear every 26 ± 16 days This trend minimizes the number of species pairs with no or very little temporal overlap In contrast, the mean temporal overlap of the whole guild seems unaffected, with some species pairs showing a large temporal overlap Whether the observed pattern can be attributed to interspecific competition must be addresed experimentally     

A size-distribution-based model of forest dynamics along a latitudinal environmental gradient

A geographically extended model of the dynamics of tree size structure of forests is proposed to simulate the change of forest zonation along latitude in response to global environmental change. To predict the response of forests to global change, it is necessary to construct functional models of forest tree populations. The size-structure-based model requires far less memory and steps of calculation compared with individual-based models, and it is easy to incorporate the dimension of geographic locations into the model to describe large-scale dynamics of forest-type distributions. The effect of increasing size growth rate, expected from increasing atmospheric carbon dioxide, was diminished at the stand-level basal area density, because of regulation by one-sided competition. Model simulations of a century-long global warming at around 3 °C predicted that (1) biomass changed in resident forests rather simultaneously in response to warming, and that (2) there was a considerable time lag in movement at the boundaries of different forest types, particularly under the existence of resident forest types that would be finally replaced. It required several thousand years after a century-long warming spell for forest types to attain new steady-state distributions after shifting. As a consequence, global warming created a zigzag pattern of biomass distribution along a latitudinal gradient, i.e., an increase in the cooler-side boundary of forest types and a decrease in the warmer-side boundary.     

Edge effects on dung beetle assemblages in an Andean mosaic of forest and coffee plantations

In landscapes dominated by agriculture, conspicuous edges often occur between landscape elements. However, there is disagreement about the existence and intensity of edge effects, and information about species‐specific responses remains scarce. Studying such edge effects can help elucidate functional landscape connectivity and contribute to agricultural management. We, therefore, assessed whether sun‐grown coffee represents a barrier to dung beetles in an Andean agricultural landscape. We also evaluated whether the response to edge effects differs among species. We found that diversity and abundance tend to decrease from forest to sun‐grown coffee and that there are sharp increases in species turnover at the forest–coffee edge. We detected several different species‐specific responses to the forest–coffee edge, suggesting differences in the mobility of the species (or spillover) and in the degree of penetration that takes place from forest patches to sun‐grown coffee plantations. This study demonstrates that the sun‐grown coffee matrix constitutes a barrier to forest species and suggests that the forest–coffee ecotone is more complex than expected. Our results support the notion that the conservation value of native forest patches in agricultural scenarios depends on the functional connectivity of forest units in the landscape to maximize the opportunities species have to disperse through the agricultural matrix.     

Effects of forest fragmentation on the beetle assemblage at the relict forest of Fray Jorge, Chile

Habitat fragmentation is recognized as one of the main factors associated with species extinction and is particularly acute in South American forest habitats. In this study, we examined the effects of forest fragmentation on the beetle assemblage at the relict temperate forest of Fray Jorge (Chile). We evaluated the following hypotheses: (1) there is a strong edge effect, so that the number of beetle species and individuals increases away from the edge, towards the inner part of each fragment, (2) this pattern should be apparent in the larger fragments but not in the smaller ones, where edge effects are expected to be stronger, and (3) there should be a significant interaction between number of species/individuals found inside and outside fragments (i.e., in the matrix) and season, because of an increase in aridity and water stress during austral summer months. We found that the relationship between the number of individuals and number of species vs distance from the matrix towards the forest interior was affected by fragment size and season. In general, both number of species and individuals tended to increase from the matrix towards the forest edge and then either decrease, increase or maintain a constant level, depending on fragment size and season. The result of an ANOVA analysis, which used season, size, and position (inside vs outside fragments) as factors and number of individuals as the response variable, showed a significant effect of fragment size, position, and season and a significant interaction between fragment size and season, season and position, and size and position. ANOVA analysis using number of species as the response variable showed that area, season, and position all had significant effects. The results also showed a significant interaction between size and season and between season and position. Our results emphasize the existence of strong fragment-size and seasonal effects modulating both the response of beetles to fragmentation and their abundance and distribution in temperate areas. Thus, seasonal dynamic effects can be of paramount importance to demonstrate and understand the effect of habitat fragmentation upon arthropod assemblages in temperate areas.