Human presence as a determinant of the occurrence of mammals in a high diversity protected area of Cerrado-Caatinga ecotone in Brazil.

The Cerrado domain and its biodiversity has suffered several anthropogenic influences. Our objective was to evaluate the influence of biotic and anthropic variables on the mammal community in a protected area in the Cerrado-Caatinga ecotone. For this we sampled the mammals using camera traps (4,072 days/trap) for 16 months. We used generalized mixed linear models (GLMM) with model selection via Akaike's Information Criteria corrected for small sample size (AICc) to assess the influence of variables on richness, abundance and functional groups of mammals. We made a total of 663 photographic records of 16 species of medium and large mammals. The richness and number of mammals was negatively influenced by the distance to human settlements while carnivores were not affected by any of the variables evaluated, herbivores and generalists were more common in areas closer from human habitation. Despite the presence of large areas of native vegetation, our results show that there is a dominance of common and generalist species. The protected area is vulnerable to different sources of human pressure and the design and implementation of a management plan can be a key tool for protecting biodiversity and regulating the use of natural resources by local communities.

Soil contamination with permissible levels of lead negatively affects the community of plant-associated insects: A case of study with kale.

This study investigated whether lead (Pb), at concentrations allowed for soil, affects the community of insects that live in the aerial part of plants. We evaluated the effect of Pb concentrations on accumulated species richness, composition, and abundance of different functional groups of insects. Kale plants were grown in soil experimentally contaminated with four concentrations of lead nitrate: 0 (control), 144 (T1), 360 (T2), and 600 (T3) mg/kg of soil. The experiment was conducted in an open greenhouse for the natural colonization of insects. Insects were collected twice using trap bags attached to the plant leaf and by direct removal. The concentration of Pb in the stem and leaf samples increased with the increased soil contamination, even showing values above the limit allowed by the legislation for this plant species. Control plants showed a higher richness of accumulated insect species. In addition, the treatments had an effect on the community composition, in which Diaeretiella rapae (primary parasitoid) was found as an indicator of the control + T1 treatments and the top species Pachyneuron sp. (parasitoid of predators) was associated with the control. The abundance of chewing and sucking herbivores, their respective parasitoids, predators, and parasitoids of predators were negatively affected. Hyperparasitoid abundance was not affected, but their accumulated species richness was. This study was innovative in demonstrating that soil contamination by different concentrations of a heavy metal (Pb) can negatively affect the community of plant-associated insects, even at concentrations allowed for soil, reflecting possible damage to the ecosystem.

Trade-offs between growth, reproduction and defense in response to resource availability manipulations.

The Brazilian Cerrado is one of the most endangered biomes in the world. We evaluated the sustainability of leaf harvest in one of the most important Cerrado tree species, Stryphnodendron adstringens. The bark of this tree is used as a source of medicinal tannin. Harvesting bark, however, often kills the tree. In a manipulative field experiment, we tested the hypothesis that harvesting leaves, which might serve as an alternative source of tannin, would be less detrimental for tree survival, growth, reproduction, and defense than harvesting bark. In a two-way crossed experimental design, we either clipped 100% of a plant's leaves or applied NPK fertilizer to the soil. Our predictions of the experimental outcomes were based on plant resource and defense theory. Growth was determined by total leaf dry mass production, reproduction by inflorescence and fruit production traits, and defense by total phenolics, hydrolyzable tannins, and condensed tannins. Fertilization had a marginally positive effect on total leaf dry mass. Defoliation had no effect on subsequent leaf production, and most importantly, no plants died as a result of defoliation. We found high tannin amounts in leaves of S. adstringens produced both prior to and subsequent to clipping, further suggesting that leaves could serve as a sustainable alternative source of tannin. After clipping, plants invested more in tannin production and less in reproduction. Our results suggest that leaf harvest may be more sustainable than harvesting of bark in S. adstringens. We suggest the need for further investigation of the medicinal properties of leaf tannins to formulate a viable sustainable management plan for the exploitation of this plant species.

Morphological traits, allometric relationship and competition of two seed-feeding species of beetles in infested pods

Abstract Pair-wise competition produces asymmetric consequences for the interacting species, resulting in reduction of species fitness at the individual scale; however, little is known of the effects of competition on the allometric patterns of insects. In this study, we explored how competition, by means of pod infestation, affects the development of female and male individuals in the co-occurring bruchine beetles Merobruchus terani and Stator maculatopygus. We found differences between M. terani and S. maculatopygus in all morphometric traits, but no significant differences between males and females in either species. We also found, with an increasing degree of pod infestation, a positive trend in the pronotum, elytron and body weight of M. terani and a negative trend in morphological traits and body weight of S. maculatopygus. A negative allometry was maintained, suggesting that with increasing body weight, the body structures did not increase proportionally. On the other hand, we found that increasing the degree of pod infestation produced a wider variation in the individuals' body size than in low levels of infestation. Finally, we discuss how pod infestation can trigger competition between species, with both positive and negative impacts, even though the species function similarly in resource exploitation.

Seed predation food web, nutrient availability, and impact on the seed germination of Senegalia tenuifolia (Fabaceae) / Red alimentaria de depredación de semillas, disponibilidad de nutrientes e impacto sobre la germinación de las semillas de Senegalia tenuifolia (Fabaceae)

Abstract:Food web studies, which include qualitative and quantitative information about species interactions for all trophic levels in a specific community, are important tools to characterize the community structure, and to understand the role of species interaction in natural communities. With this aim, we collected fruits of Senegalia tenuifolia from a total of nine sites from three different areas in Minas Gerais, from June to August 2011. Fruits were collected and taken to the laboratory in special containers, to allow insect development and description. And then, we characterized the food web of insects associated with these seeds, and described interactions between these organisms and the host plant, and assessed the impact of insect attacks on seed germination with an experiment under controlled conditions. Additionally, we estimated the available NPK content and the Carbon:Nitrogen ratio in both fruits and seeds. In S. tenuifolia seeds, we have found 937 associated insects of 15 species structured in four trophic levels. We found two Bruchinae seed-feeders species: Merobruchus terani and Stator maculatopygus. We also have observed the seed-feeding hymenopteran species Allorhogas sp. 1 and Prodecatoma sp. 1, and hymenopteran parasitoids species such as Eupelmus sp.1, Lyrcus sp.1, Eurytoma sp.1, Horismenu s sp.1, Chelonus sp.1, Aprostocetus sp.1, Eiphosoma sp.1 and an unidentified Pteromalinae. Considering quantitative food web metrics, our data have suggested low values of generality and high values of trophic vulnerability, besides others, which demonstrated how species interactions are specialized. The impact of seed-feeding insects on seeds was found severe and prevented their germination. Lastly, seeds contained higher NPK content than fruits. In conclusion, the seed predation food web supported by S. tenuifolia has depicted two different features: specialized species interactions, considering parasitoids and seed-feeding species, and, generalized species interactions, considering host-plant and seed-feeding species. Indeed, seeds are resources with high nutrient concentration supporting a rich and complex food web. Finally, S. tenuifolia seeds are directly impacted by seed-feeding insects, preventing them from germination, which could result in a negative effect on host-plant population.

Resumen:Estudios de redes alimentarias, que incluyen información cualitativa y cuantitativa sobre las interacciones entre especies para todos los niveles tróficos en una comunidad específica, son herramientas importantes para caracterizar la estructura de la comunidad, y para comprender el papel de la interacción de las especies en las comunidades naturales. Con este objetivo, se recolectaron frutos de Senegalia tenuifolia de un total de nueve sitios de tres áreas diferentes, en Minas Gerais, entre junio y agosto 2011. Los frutos fueron recolectados y llevados al laboratorio en contenedores especiales, para permitir el desarrollo y descripción del insecto. Luego, se caracterizó la red alimentaria de los insectos asociados a estas semillas, se describieron las interacciones entre estos organismos y la planta hospedera, y se evaluó el impacto del ataque de insectos en la germinación de semillas mediante un experimento en condiciones controladas. Además, se estimó el contenido de NPK y la relación carbono:nitrógeno en frutos y en semillas. En semillas de S. tenuifolia, se encontraron 937 insectos de 15 especies estructuradas en cuatro niveles tróficos. Se encontraron dos especies de Bruchinae que se alimentan de semillas: Merobruchus terani y Stator maculatopygus. También se observaron especies de himenópteros que se alimentan de semillas: Allorhogas sp. 1 y Prodecatoma sp. 1, y especies de himenópteros parasitoides como: Eupelmus sp.1, Lyrcus sp.1, Eurytoma sp.1, Horismenus sp.1, Chelonus sp.1, Aprostocetus sp.1, Eiphosoma sp.1 y un Pteromalinae no identificado. Nuestros datos sugieren valores bajos de generalidad trófica y valores altos de vulnerabilidad trófica, además de otros, lo que demuestra cómo las interacciones entre especies son especializadas. El impacto en las semillas de los insectos que se alimentan de estas es severo e impidió su germinación. Por último, las semillas tenían un mayor contenido de NPK que los frutos. En conclusión, la red alimentaria de depredación de semillas con S. tenuifolia tiene dos características: interacciones de especies especializadas, considerando parasitoides y especies comedoras de semillas, e interacciones generalizadas entre especies, teniendo en cuenta la planta hospedera y las especies comedoras de semillas. De hecho, las semillas son recursos con alta concentración de nutrientes que proveen una rica y compleja red trófica. Por último, las semillas de S. tenuifolia se ven directamente afectadas por los insectos que se alimentan de semillas, que les impide la germinación, lo que podría resultar en un efecto negativo en la población planta-hospedero.

Fluctuations in density of an outbreak species drive diversity cascades in food webs.

Patterns in food-web structure have frequently been examined in static food webs, but few studies have attempted to delineate patterns that materialize in food webs under nonequilibrium conditions. Here, using one of nature's classical nonequilibrium systems as the food-web database, we test the major assumptions of recent advances in food-web theory. We show that a complex web of interactions between insect herbivores and their natural enemies displays significant architectural flexibility over a large fluctuation in the natural abundance of the major herbivore, the spruce budworm (Choristoneura fumiferana). Importantly, this flexibility operates precisely in the manner predicted by recent foraging-based food-web theories: higher-order mobile generalists respond rapidly in time and space by converging on areas of increasing prey abundance. This "birdfeeder effect" operates such that increasing budworm densities correspond to a cascade of increasing diversity and food-web complexity. Thus, by integrating foraging theory with food-web ecology and analyzing a long-term, natural data set coupled with manipulative field experiments, we are able to show that food-web structure varies in a predictable manner. Furthermore, both recent food-web theory and longstanding foraging theory suggest that this very same food-web flexibility ought to be a potent stabilizing mechanism. Interestingly, we find that this food-web flexibility tends to be greater in heterogeneous than in homogeneous forest plots. Because our results provide a plausible mechanism for boreal forest effects on populations of forest insect pests, they have implications for forest and pest management practices.