Does the diversity of vegetation and diatoms correlate with soil and water factors in a tropical cloud forest's complex land use/land cover scenario?

Soil and water characteristics in micro basins with different land uses/land cover (LULC) can influence riparian vegetation diversity, stream water quality, and benthic diatom diversity. We analyzed 18 streams in the upper part of the La Antigua River basin, México, surrounded by cloud forests, livestock pastures, and coffee plantations. Concentrations of P, C, and N were elevated in the humus of forested streams compared to other land uses. In contrast, cations, ammonium, and total suspended solids (TSS) of water streams were higher in pastures and coffee plantations. These results indicate that LULC affects stream chemistry differently across land uses. Vegetation richness was highest (86-133 spp.) in forest streams and lowest in pastures (46-102), whereas pasture streams had the greatest richness of diatoms (9-24), likely due to higher light and temperatures. Some soil and water characteristics correlated with both true diversity and taxonomic diversity; soil carbon exchange capacity (CEC) correlated with vegetation diversity (r = 0.60), while water temperature correlated negatively (r = - 0.68). Diatom diversity was related to soil aluminum (r = - 0.59), magnesium (r = 0.57), water phosphorus (r = 0.88), and chlorophyll (r = 0.75). These findings suggest that land use affects riparian vegetation, while physical and chemical changes influence diatom diversity in stream water and soil. The lack of correlation between vegetation and diatom diversity indicates that one cannot predict the other. This research is an essential first step in understanding how land use changes impact vegetation and diatom diversity in mountain landscapes, providing valuable insights for environmental monitoring and conservation efforts in tropical cloud forests.

Antifungal capabilities of gut microbial communities of three dung beetle species (Scarabaeidae: Scarabaeinae).

Gut microbial communities are part of the regulatory array of various processes within their hosts, ranging from nutrition to pathogen control. Recent evidence shows that dung beetle's gut microbial communities release substances with antifungal activity. Because of the enormous diversity of gut microorganisms in dung beetles, there is a possibility of discovering novel compounds with antifungal properties. We tested the antifungal activity mediated by gut microbial communities of female dung beetles against nine phytopathogenic fungi strains (Colletotrichum asianum-339, C. asianum-340, C. asianum-1, C. kahawae-390, C. karstii-358, C. siamense-220, Fusarium oxysporum-ATCC338, Nectria pseudotrichia-232, Verticillium zaelandica-22). Our tests included the gut microbial communities of three species of dung beetles: Canthon cyanellus (roller beetle), Digitonthophagus gazella (burrower beetle), and Onthophagus batesi (burrower beetle), and we followed the dual confrontation protocol, i.e., we challenged each fungal strain with the microbial communities of each species of beetles in Petri dishes containing culture medium. Our results showed that gut microbial communities of the three dung beetle species exhibit antifungal activity against at least seven of the nine phytopathogenic fungal strains. The gut microbial communities of Onthophagus batesi significantly decreased the mycelial growth of the nine phytopathogenic fungi strains; the gut microbial communities of Canthon cyanellus and Digitonthophagus gazella significantly reduced the mycelial growth of seven strains. These results provide a basis for investigating novel antifungal substances within gut microbial communities of dung beetles.

Underlying and proximate drivers of biodiversity changes in Mesoamerican biosphere reserves.

Protected areas are of paramount relevance to conserving wildlife and ecosystem contributions to people. Yet, their conservation success is increasingly threatened by human activities including habitat loss, climate change, pollution, and species overexploitation. Thus, understanding the underlying and proximate drivers of anthropogenic threats is urgently needed to improve protected areas' effectiveness, especially in the biodiversity-rich tropics. We addressed this issue by analyzing expert-provided data on long-term biodiversity change (last three decades) over 14 biosphere reserves from the Mesoamerican Biodiversity Hotspot. Using multivariate analyses and structural equation modeling, we tested the influence of major socioeconomic drivers (demographic, economic, and political factors), spatial indicators of human activities (agriculture expansion and road extension), and forest landscape modifications (forest loss and isolation) as drivers of biodiversity change. We uncovered a significant proliferation of disturbance-tolerant guilds and the loss or decline of disturbance-sensitive guilds within reserves causing a "winner and loser" species replacement over time. Guild change was directly related to forest spatial changes promoted by the expansion of agriculture and roads within reserves. High human population density and low nonfarming occupation were identified as the main underlying drivers of biodiversity change. Our findings suggest that to mitigate anthropogenic threats to biodiversity within biosphere reserves, fostering human population well-being via sustainable, nonfarming livelihood opportunities around reserves is imperative.

Influence of phylogenetic, environmental, and behavioral factors on the gut bacterial community structure of dung beetles (Scarabaeidae: Scarabaeinae) in a Neotropical Biosphere Reserve.

Gut bacteria help dung beetles metabolize nutrients contained and synthesize those unavailable in their food, depending on the ecological scenario in which they develop. However, less is known about the influence of environmental and behavioral factors on the taxonomic composition of bacterial gut communities in Scarabaeinae beetles. To address this research topic, we analyzed 13 tropical dung beetle species in the Los Tuxtlas Biosphere Reserve, Mexico, to understand how the beetle tribe, habitat, food preference, food relocation, and parental care influence the composition of gut bacterial communities. We found that the beetle tribe is the primary factor impacting the taxonomic composition of gut bacterial communities. Among them, Deltochilini displayed the highest variability in diversity due to the different combinations of habitat and food preferences among its species. On the other hand, the other tribes studied did not exhibit such variable combinations. Habitat emerged as the second most influential factor, with forest-dwelling beetles displaying higher diversity. This can be attributed to the heterogeneous environments within tropical forests, which offer a greater diversity of food resources. In contrast, grassland beetles, living in more homogeneous environments and relying on cow feces as their main food source, exhibited lower diversity. Our findings suggest a correlation between bacterial diversity and food resource availability in complex habitats, such as tropical forests, which offer a wider array of food sources compared to simpler environments like grasslands.

Land use scenarios, seasonality, and stream identity determine the water physicochemistry of tropical cloud forest streams.

Background: Land use is a major factor determining stream water physicochemistry. However, most streams move from one land use type to another as they drain their watersheds. Here, we studied three land use scenarios in a tropical cloud forest zone in Mexico. We addressed three main goals, to: (1) assess how land use scenarios generate different patterns in stream physicochemical characteristics; (2) explore how seasonality (i.e., dry, dry-to-wet transition, and wet seasons) might result in changes to those patterns over the year; and (3) explore whether physicochemical patterns in different scenarios resulted in effects on biotic components (e.g., algal biomass). Methods: We studied Tropical Mountain Cloud Forest streams in La Antigua watershed, Mexico. Streams drained different three scenarios, streams with (1) an upstream section draining forest followed by a pasture section (F-P), (2) an upstream section in pasture followed by a forest section (P-F), and (3) an upstream forest section followed by coffee plantation (F-C). Physicochemistry was determined at the upstream and downstream sections, and at the boundary between land uses. Measurements were seasonal, including temperature, dissolved oxygen, conductivity, and pH. Water was analyzed for suspended solids, alkalinity, silica, chloride, sulfate, magnesium, sodium, and potassium. Nutrients included ammonium, nitrate, and phosphorus. We measured benthic and suspended organic matter and chlorophyll. Results: Streams presented strong seasonality, with the highest discharge and suspended solids during the wet season. Scenarios and streams within each scenario had distinct physicochemical signatures. All three streams within each scenario clustered together in ordination space and remained close to each other during all seasons. There were significant scenario-season interactions on conductivity (F = 9.5, P < 0.001), discharge (F = 56.7, P < 0.001), pH (F = 4.5, P = 0.011), Cl- (F = 12.2, P < 0.001), SO42- (F = 8.8, P < 0.001) and NH4+ (F = 5.4, P = 0.005). Patterns within individual scenarios were associated with stream identity instead of land use. Both P-F and F-C scenarios had significantly different physicochemical patterns from those in F-P in all seasons (Procrustes analysis, m12 = 0.05-0.25; R = 0.86-0.97; P < 0.05). Chlorophyll was significantly different among scenarios and seasons (F = 5.36, P = 0.015, F = 3.81, P = 0.42, respectively). Concentrations were related to physicochemical variables more strongly during the transition season. Conclusion: Overall, land use scenarios resulted in distinctive water physicochemical signatures highlighting the complex effects that anthropogenic activities have on tropical cloud forest streams. Studies assessing the effect of land use on tropical streams will benefit from assessing scenarios, rather than focusing on individual land use types. We also found evidence of the importance that forest fragments play in maintaining or restoring stream water physicochemistry.

Experimental Crosses Between Two Dung Beetle Lineages Show Transgressive Segregation in Physiological Traits.

Physiological traits in insects are intrinsically related to their behavior, fitness, and survival and can reflect adaptations to ecological stressors in different environments, leading to population differentiation that may cause hybrid failure. In this study, we characterized five physiological traits related to body condition (body size, body mass, amount of fat, total hemolymph protein, and phenoloxidase activity) in two geographically separated and recently differentiated lineages of Canthon cyanellus LeConte, 1859 within their natural distribution in Mexico. We also performed experimental hybrid crosses between these lineages to better understand the differentiation process and explore the presence of transgressive segregation over physiological traits in them. We found differences between lineages in all traits except body mass, suggesting selective pressures related to different ecological pressures. These differences were also apparent in the transgressive segregation of all traits in F1 and F2 hybrids, except for phenoloxidase activity. Protein content was sexually dimorphic in both parental lineages but was reversed in hybrids, suggesting a genetic basis for the differences between sexes. The negative sign of transgressive segregation for most traits indicates that hybrids would be smaller, thinner, and generally unfit. Our results suggest that these two lineages may undergo postzygotic reproductive isolation, confirming the cryptic diversity of this species complex.

Next-generation sequencing, isolation and characterization of 14 microsatellite loci of Canthon cyanellus (Coleoptera: Scarabaeidae).

BACKGROUND: We used Illumina paired-end sequencing to isolate and characterize microsatellites of Canthon cyanellus, a Neotropical roller dung beetle, encompassing several lineages within its distribution range. METHODS AND RESULTS: We examined C. cyanellus specimens collected at eight different localities in Mexico (two or three specimens per locality). We initially performed amplification tests with 16 loci, but two of which were unsuccessful. The 14 remaining microsatellites were polymorphic, with 2-16 alleles each. The expected and observed heterozygosity ranged from 0.11 to 0.76 and from 0.20 to 0.78, respectively. CONCLUSIONS: These microsatellites will help to assess structure at the population and lineage levels, identify zones of potential hybridization between lineages, and draw a more precise geographic delimitation of C. cyanellus lineages.

Mechanisms of diversity maintenance in dung beetle assemblages in a heterogeneous tropical landscape.

BACKGROUND: Anthropized landscapes play a crucial role in biodiversity conservation, as they encompass about 90% of the remaining tropical forest. Effective conservation strategies require a deep understanding of how anthropic disturbances determine diversity patterns across these landscapes. Here, we evaluated how attributes and assembly mechanisms of dung beetle communities vary across the Selva El Ocote Biosphere Reserve (REBISO) landscape. METHODS: Community attributes (species diversity, abundance, and biomass) were assessed at the landscape scale, using spatial windows and vegetation classes. Windows were categorized as intact, variegated, or fragmented based on their percent cover of tropical forest. The vegetation classes analyzed were tropical forest, second-growth forest, and pastures. RESULTS: We collected 15,457 individuals and 55 species. Variegated windows, tropical forests, and second-growth forests showed the highest diversity values, while the lowest values were found in intact windows and pastures. Landscape fragmentation was positively and strongly related to dung beetle diversity and negatively related to their abundance; biomass was positively associated with forest cover. Beta diversity was the primary driver of the high dung beetle diversity in the landscape analyzed. DISCUSSION: The landscape heterogeneity and its biodiversity-friendly matrix facilitate the complementarity of dung beetle assemblages in the Selva El Ocote Biosphere Reserve. Random processes govern beta diversity patterns in intact and variegated windows. Therefore, vegetation cover in the region is sufficient to maintain a continuous flow of dung beetles between forested landscape segments. However, intense anthropic disturbances acted as deterministic environmental filters in fragmented windows and pastures sites, leading to biotic homogenization processes. Our results suggest that increasing habitat variegation in highly fragmented sites is an effective strategy to prevent or buffer homogenization processes in the REBISO landscape.

Contests over reproductive resources in female roller beetles: Outcome predictors and sharing as an option.

Fights among females are frequent, although less attention has been placed on them than on male fights. They arise when females compete for food, oviposition, mates, brooding sites, or access to resources which increase offspring survival. It has been shown that the outcome of female fights may be less predictable by asymmetries in resource holding power, than in male fights. Male roller beetles fight over food resources, food balls, needed for mating and nesting, and it has been show in some species that asymmetries in reproductive experience and resource holding power in terms of size predict fight outcome, including ties in which contenders cut and split the food ball. In this study, we tested the influence of asymmetries in reproductive status (experience) and body size on female fight outcome in the carrion roller beetle Canthon cyanellus cyanellus. As predicted, and as previously found for males of the same species, female reproductive status of both contenders and relative size predict fight outcome. Larger and reproductively experienced contenders have a higher probability of winning. Furthermore, ties are more likely in fights involving opposing asymmetries (vgr. Large reproductively naïve owner versus small reproductively experienced intruder). Also as predicted, food ball splitting is more likely to be started by the predicted loser. This mode of resource sharing may be the result of a fighting strategy in which the costs of continuing to fight are greater than the benefits of not splitting, if a fraction of the disputed resource is more than the minimum needed for the present reproductive needs, and reduces costs associated to a longer fight.

Phylogeographic structure of Canthon cyanellus (Coleoptera: Scarabaeidae), a Neotropical dung beetle in the Mexican Transition Zone: Insights on its origin and the impacts of Pleistocene climatic fluctuations on population dynamics.

Canthon cyanellus is a roller dung beetle with a wide distribution range in the tropical forests of the New World. In Mexico, it inhabits the Pacific and the Gulf coasts, the Yucatan Peninsula and the south mainly in the State of Chiapas. This species shows a wide geographical variation in cuticle color, which has been used as defining trait for subspecies. In this study we analyzed the phylogeographic and demographic history of the Mexican populations of C. cyanellus using DNA sequences of the nuclear ITS2, and the mitochondrial COI and 16S genes. We found that not all the current valid subspecies are supported by the molecular analysis. The populations are genetically and geographically structured in five lineages. The diversification events that gave origin to the main lineages within this species complex occurred during the Pleistocine in a time range of 1.63-0.91Myr. The demographic history of these lineages suggests post-glacial expansions toward the middle and the end of the Pleistocene. The combined data of mitochondrial and nuclear DNA suggest that the phylogeographic structure and demographic history of the C. cyanellus populations are the result of: the geological and volcanic activity that occurred from the end of the Pliocene to the Pleistocene; and the contraction and expansion of tropical forests due to the glacial and inter-glacial cycles during the Pleistocene. Landscape changes derived from historical events have affected the demographic history of the populations of this species. The results presented here point to the need to review the taxonomic status and delimitation of the lineages encompassed in the Canthon cyanellus complex.

Dung removal by dung beetles (Coleoptera: Scarabaeidae) and macrocyclic lactone use on cattle ranches of Yucatan, Mexico / Remoción de estiércol por escarabajos estercoleros (Coleoptera: Scarabaeinae) y uso de lactonas macrocíclicas en ranchos ganaderos de Yucatán, México

Abstract:The expanded use of macrocyclic lactones (ML) to treat endo- and ectoparasites in cattle in tropical regions, can reduce dung beetle populations, and thus interrupt the dung removal process in cattle pasture ecosystems. During the reproductive period (the rainy season) of two functional groups of dung beetles (paracoprid and telocoprid Scarabaeinae), we compared dung removal amount in ranches where ML are and are not used in Yucatan, Mexico, through exclusion traps baited with 500 g of ML-free cow dung. On each ranch, two transects (separated by 500 m) with six traps each, were set up for 24 hours. After this time, all the dung remnants in each trap were obtained and weighed in order to record the dung removal. Results showed that dung removal amounts were similar in ranches with and without ML use. Dung beetles removed 40.1 % of all cow dung weighed. Paracoprids removed 87.46 % and telocoprids 12.54 % of all the dung that was removed. Our results indicated that the ecological function of dung beetles in the pastures studied, does not seem to be affected by the ML use, and that paracoprid species removed most of the dung. For both types of ranch, further studies that take into account the population dynamics and movement of the most important dung beetle species in the region are required, coupled with laboratory studies evaluating the effect of ML on their reproductive success. This could give some light on the effect of ML on the ecological function of this important insect group in the sustainability of cattle production systems. Rev. Biol. Trop. 64 (3): 945-954. Epub 2016 September 01.

ResumenLa expansión en el uso de lactonas macrocíclicas (LM) para el tratamiento de endo y ectoparásitos del ganado en las regiones tropicales puede reducir las poblaciones de escarabajos del estiércol, interrumpiendo así el proceso de eliminación de estiércol de ganado en los pastizales. Durante el período reproductivo (época de lluvias) de dos grupos funcionales de escarabajos coprófagos (paracópridos y telecópridos), se comparó la cantidad removida de estiércol usando trampas de exclusión cebadas con 500 g de estiércol de vaca libre de LM en dos ranchos donde se usan y en dos donde no se usan LM, en la península de Yucatán, México. En cada rancho se establecieron dos transectos (separados por 500 m) con seis trampas cada uno, las cuales estuvieron activas durante 24 horas. Después de este tiempo, todos los restos de estiércol en cada trampa se pesaron para registrar la remoción. Los resultados mostraron que las cantidades de remoción fueron similares en ranchos con y sin uso de LM. Los escarabajos estercoleros removieron 40.1 % del peso total del excremento. Los paracópridos removieron 87.46 % y los telecópridos 12.54 % del total de excremento removido. Los resultados indican que la función ecológica de los escarabajos estercoleros en los potreros estudiados no parece verse afectada por el uso de LM y que las especies paracórpidas remueven la mayor parte del excremento. Se requiere hacer más estudios en ambos tipos de ranchos, en los que se tome en cuenta la dinámica poblacional y el movimiento de las especies más importantes de la región, acoplados a estudios de laboratorio que evalúen el efecto de las LM sobre el éxito reproductivo, y de esta manera esclarecer el efecto de las LM sobre la función ecológica de este grupo de insectos tan importante para la sustentabilidad de los sistemas ganaderos.

Dung removal by dung beetles (Coleoptera: Scarabaeidae) and macrocyclic lactone use on cattle ranches of Yucatan, Mexico.

The expanded use of macrocyclic lactones (ML) to treat endo- and ectoparasites in cattle in tropical regions, can reduce dung beetle populations, and thus interrupt the dung removal process in cattle pasture ecosystems. During the reproductive period (the rainy season) of two functional groups of dung beetles (paracoprid and telocoprid Scarabaeinae), we compared dung removal amount in ranches where ML are and are not used in Yucatan, Mexico, through exclusion traps baited with 500 g of ML-free cow dung. On each ranch, two transects (separated by 500 m) with six traps each, were set up for 24 hours. After this time, all the dung remnants in each trap were obtained and weighed in order to record the dung removal. Results showed that dung removal amounts were similar in ranches with and without ML use. Dung beetles removed 40.1 % of all cow dung weighed. Paracoprids removed 87.46 % and telocoprids 12.54 % of all the dung that was removed. Our results indicated that the ecological function of dung beetles in the pastures studied, does not seem to be affected by the ML use, and that paracoprid species removed most of the dung. For both types of ranch, further studies that take into account the population dynamics and movement of the most important dung beetle species in the region are required, coupled with laboratory studies evaluating the effect of ML on their reproductive success. This could give some light on the effect of ML on the ecological function of this important insect group in the sustainability of cattle production systems.

Evaluation of the infestation rate of Blaesoxipha alcedo in the carrion roller scarab Canthon cyanellus cyanellus and its effect on reproductive behavior.

This study documents Blaesoxipha alcedo (Aldrich; Diptera: Sarcophagidae) parasitizing the necrophagous ball roller beetle Canthon cyanellus cyanellus LeConte collected over 2 yr, and evaluates the reproductive behavior of parasitized beetles. Up to 52% of the beetles collected in the field had been parasitized and exhibited modified sexual behavior. In general, 21% of the males and 24% of the females had been parasitized. The number of parasitized males peaked in August 2000 (52%), but that of females peaked in May 2001 (52%). The lowest percentage of parasitized males (7%) was recorded in September 2000, June 2001, and July 2001; for females, parasitism was lowest in June 2000 (10%). The larva of this sarcophagid fly penetrates the host through the tegumentary membrane, leaving a scar. The larvae feed on the gonads of male and female C. c. cyanellus, castrating them, causing the loss of their ability to recognize individuals of the opposite sex, preventing reproduction, and lowering overall reproductive success.

[Generic diversity of Trichoptera (Insecta) of Paramo Rabanal (Cundinamarca-Boyacá, Colombia)]. / Diversidad genérica de Trichoptera (insecta) en dos microcuencas del Páramo Rabanal (Cundinamarca-Boyacá, Colombia).

Trichopterans are considered an important and diverse biotic element in continental aquatic ecosystems. The purpose of this study was to evaluate the assemblages of the order Trichoptera in two subwatersheds with a gradient of disturbance. Four sampling events were conducted in two subwatersheds in the Eastern Mountain Range of the Colombian Andes. For the analysis we used rarefaction curves, Bray-Curtis Index and Partitioning Diversity and total richness and Shannon's diversity as metrics. Although total richness was similar between both subwatersheds, abundance was always highest in streams within the conserved subwatershed. Each subwatershed was dominated by different genera, except Ochrotrichia, which was abundant at all sites. Alpha diversity was similar among streams in the conserved watershed, while a reduction in diversity potentially associated with the disturbance gradient was observed in streams of the disturbed subwatershed. Beta diversity (0Dbeta and 1Dbeta) between subwatersheds and among conserved streams was similar, while in disturbed streams a similar gradient to that of alpha diversity was found. The similitude analysis clustered streams according to their conservation status. Differences found in trichopteran assemblages do confirm that the use of their attributes is adequate to assess the conservation status of stream ecosystems. Rev. Biol. Trop. 62 (Suppl. 2): 97-110. Epub 2014 April 01.

Diversidad genérica de Trichoptera (Insecta) en dos microcuencas del Páramo Rabanal (Cundinamarca-Boyacá, Colombia)

Generic diversity of Trichoptera (Insecta) of Paramo Rabanal (Cundinamarca-Boyacá, Colombia). Trichopterans are considered an important and diverse biotic element in continental aquatic ecosystems. The purpose of this study was to evaluate the assemblages of the order Trichoptera in two subwatersheds with a gradient of disturbance. Four sampling events were conducted in two subwatersheds in the Eastern Mountain Range of the Colombian Andes. For the analysis we used rarefaction curves, Bray-Curtis’ Index and Partitioning Diversity and total richness and Shannon’s diversity as metrics. Although total richness was similar between both subwatersheds, abundance was always highest in streams within the conserved subwatershed. Each subwatershed was dominated by different genera, except Ochrotrichia, which was abundant at all sites. Alpha diversity was similar among streams in the conserved watershed, while a reduction in diversity potentially associated with the disturbance gradient was observed in streams of the disturbed subwatershed. Beta diversity (0D and ¹D) between subwatersheds and among conserved streams was similar, while in disturbed streams a similar gradient to that of alpha diversity was found. The similitude analysis clustered streams according to their conservation status. Differences found in trichopteran assemblages do confirm that the use of their attributes is adequate to assess the conservation status of stream ecosystems. Rev. Biol. Trop. 62 (Suppl. 2): 97-110. Epub 2014 April 01.

Los tricópteros son considerados un componente biótico importante y diverso de los ecosistemas acuáticos continentales. Este estudio tuvo como objetivo evaluar la comunidad del orden Trichoptera en dos microcuencas con diferente grado de perturbación. Se realizaron cuatro campañas de muestreo en dos microcuencas de la Cordillera Oriental de los Andes colombianos. Se realizaron análisis mediante curvas de rarefacción, el índice de Bray Curtis y partición de la diversidad, usando como medidas la riqueza y la diversidad de Shannon. Se encontró que, aunque la riqueza fue similar entre las dos microcuencas, la abundancia siempre fue mayor en los arroyos de la microcuenca conservada. En cada microcuenca dominaron géneros diferentes, excepto Ochrotrichia que fue abundante en todos los sitios. La diversidad alfa entre los arroyos de la microcuenca conservada fue similar, mientras que en la perturbada se observó una reducción de la diversidad asociada a un gradiente de perturbación de los arroyos. La diversidad beta (0D y ¹D) entre microcuencas y entre arroyos conservados fue similar, mientras que en los perturbados también mostró un gradiente similar al de la diversidad alfa. El análisis de similitud agrupó los arroyos según su estado de conservación. Las diferencias encontradas en los atributos de los comunidades de tricópteros confirman que su uso es adecuado para conocer el estado de conservación de los sistemas que habita.

The role of body size and shape in understanding competitive interactions within a community of Neotropical dung beetles.

Geometric morphometrics is helpful for understanding how body size and body shape influence the strength of inter-specific competitive interactions in a community. Dung beetles, characterized by their use of decomposing organic material, provide a useful model for understanding the structuring of ecological communities and the role of competition based on their size and morphology. The relationship between body size and shape in a dung beetle community from the Atlantic Forest in Serra do Japi, Brazil was analyzed for 39 species. Fifteen anatomical landmarks on three-dimensional Cartesian coordinates were used to describe both the shape and the size of the body of each species on the basis of the centroid located along homologous points in all of the species. The first vector of a principal components analysis explained 38.5% of the morphological variation among species, and represents a gradient of body shape from elongated, flattened bodies with narrow abdomen to rounded or convex bodies. The second component explained 17.8% of the remaining variation in body shape, which goes from species with an abdomen that is larger than the elytra to species with constricted abdomens and large elytra. The relationship between body size and shape was analyzed separately for diurnal and nocturnal species. In both guilds not only were there differences in body size, but also in body shape, suggesting a reduction in their level of competition.

Removal rates of native and exotic dung by dung beetles (Scarabaeidae: Scarabaeinae) in a fragmented tropical rain forest.

Many studies have evaluated the effect of forest fragmentation on dung beetle assemblage structure. However, few have analyzed how forest fragmentation affects the processes carried out by these insects in tropical forests where their food sources consist mainly of dung produced by native herbivore mammals. With the conversion of forests to pastures, cattle dung has become an exotic alternative and abundant food for dung beetles. This study compares dung removal rates of native (monkey) and exotic (cow) dung in different-sized fragments of tropical rain forests, during the dry and rainy seasons at the Los Tuxtlas Biosphere Reserve. Dung removal rates were affected by season, dung type, and the interaction between resource type and season. During the dry season, the removal rates of monkey dung were somewhat similar than during the rainy season, whereas the removal rates of cow dung were much higher during the rainy season. Dung beetle biomass and species richness were almost three times greater in monkey dung than in cow dung. Monkey dung attracted species belonging to the dweller, roller, and tunneler guilds; cow dung attracted mostly tunnelers. Therefore, the use of exotic dung may result in a biased misconception of the rates of dung removal in tropical forest and an underestimation of dung beetle diversity. This study highlights the importance of working with natural tropical forest resources when attempting to identify realistic tendencies concerning processes in natural habitats and those modified by fragmentation and by other human activities.