Adriana M. Almeida

Seasonality of insects in the semi-arid Caatinga of northeastern Brazil

Seasonality of insects in the semi-arid Caatinga of northeastern Brazil. Insects are essential to tropical ecosystems functioning. In semi-arid regions, the increase in abundance and/or activity (e.g. reproduction and foraging behavior) of insects is usually associated with climatic variables. The present study investigates which climatic variables are best predictors of insect abundance in an area of Caatinga in northeastern Brazil. Individuals were sampled for 24 months using Malaise and pitfall traps, and beating trays. A total of 58925 individuals belonging to 20 insect orders were collected. The most abundant orders were Hymenoptera, Diptera, Collembola and Coleoptera. Most orders studied showed a clear maximum abundance in the rainy season. Rainfall and humidity were the best predictors of insect abundance in the Caatinga. However, no climatic variable could explain Psocoptera and Blattodea variance in abundance/activity. Our results suggest that climatic changes associated with rainfall patterns in the Caatinga may affect ecosystem processes and services that depend direct or indirectly on insect abundance/activity.

Diversidade e ocorrência de Asteraceae em cerrados de São Paulo

De abril a maio de 2000 a 2002 oito localidades com remanescentes de cerrados sensu stricto no estado de Sao Paulo foram amostradas para o levantamento das especies de asteraceas, uma das familias mais representativas da flora herbaceo-arbustiva nestas formacoes. Foram feitas 23 amostragens e cada area de estudo foi amostrada em media uma vez por ano durante o pico de floracao das plantas. Ao todo foram obtidas 399 amostras, nas quais foram reconhecidas 89 morfoespecies (74 foram identificadas como especies conhecidas). Quarenta por cento das especies foram registradas uma unica vez (unicatas), indicando um grande numero de especies raras. Apenas 10% das especies que ocorreram em mais de uma amostra foram obtidas de uma mesma area (sobreposicao espacial) ou de um mesmo ano de estudo (sobreposicao temporal). A riqueza de especies em cada area foi estimada por meio de transecoes e depois comparada a riqueza total observada em cada area de estudo, sendo esta na maioria das vezes mais alta que a estimada com base nas transecoes. A lista de especies obtida para os cerrados amostrados foi comparada a outras 24 listas publicadas para cerrados no Brasil. Embora a maioria das especies mais comuns tenha coincidido, oito especies (11% das especies identificadas) nao constam das listas publicadas. Concluimos que as areas de cerrado sensu stricto estudadas no estado de Sao Paulo encontram-se isoladas, com uma grande parte da flora herbaceo-arbustiva composta por varias especies raras e exclusivas. Diante deste quadro, sugerimos que a manutencao da biodiversidade de Asteraceae depende da conservacao de todo o conjunto de remanescentes de cerrado do estado de Sao Paulo.

Assemblages of endophagous insects on Asteraceae in São Paulo Cerrados

A survey of the endophagous insects fauna associated to Asteraceae capitula was carried out from 2000 to 2002 in eight cerrado sensu stricto sites located in the Brazilian state of Sdo Paulo. Sixty-four endophagous species of Diptera and Lepidoptera were recorded from 49 asteracean host plants. Approximately half of the species were obtained from a single locality, with a large proportion emerging from a single sample (unicates). Thirty percent of the species were singletons (i.e. only one individual was recorded). The large proportion of rare species suggests a high species turnover among localities. Lepidopteran species were recorded on more host species than dipterans, confirming their more polyphagous food habit, also observed in other Brazilian biomes and in Europe. We conclude that the studied cerrado localities, all within São Paulo State, are isolated with its invertebrate fauna composed of many rare and exclusive species. We suggest that the maintenance of Asteraceae biodiversity and their endophagous insects depend on the conservation of all cerrado remnants in the state.

Geographical distribution of Eupatorieae (Asteraceae) in South-eastern and South Brazilian Mountain Ranges

This study deals with the geographical distribution of Eupatorieae species in South-eastern and Southern Brazilian mountain ranges, with special emphasis on the Mantiqueira range (Serra da Mantiqueira). In the Mantiqueira range, five localities were sampled for two years during the flowering period of the plants. Species composition in the Mantiqueira localities was then compared to data from a central range (the Espinhaço) and a southern coastal range. Cluster and ordination analyses showed clear floristic differences among the three ranges. Nearer localities were more similar floristically only within the Espinhaço range and across all ranges, as shown by Mantel tests. The dendrogram in the Mantiqueira range clustered Itatiaia and Campos do Jordão, two non-adjacent localities with similar environment, landscape and topography. Different processes may be influencing the structure and composition of the Eupatorieae flora at different geographical scales. Historical and biogeographical processes may be more important in determining community composition of different mountain ranges, whereas factors such as climate and human impact may be determining differences among localities within each mountain range.

Parasitoid Wasps in Flower Heads of Asteraceae in the Brazilian Cerrado: Taxonomical Composition and Determinants of Diversity

This study provides the first survey of the parasitoid fauna reared in flower heads of Asteraceae in the Brazilian cerrado. We investigated the relative importance of herbivore richness and plant species commonness to differences in parasitoid species richness among the plant species. A total of 15,372 specimens from 192 morphospecies belonging to 103 genera of Hymenoptera were reared from the flower heads of 74 Asteraceae species. Chalcidoidea and Ichneumonoidea were the most common superfamilies, with Eulophidae and Braconidae as the main families of parasitoid wasps. Singletons and doubletons accounted for 45% of total parasitoid species richness. The number of parasitoid species per plant species ranged from 1 to 67, and the variation in parasitoid species richness among plants was mainly explained by the number of sites in which the plants were recorded. This study shows that there is a highly diversified fauna of Hymenoptera parasitoids associated with flower heads of Asteraceae in the Brazilian cerrado. Our findings suggest that the accumulation of parasitoid species on plants is mainly determined by the regional commonness of plant species rather than the number of herbivore species associated with the plants.

Disentangling the influence of plants and herbivores on the local diversity of parasitoids in the Brazilian Cerrado

This study investigated the extent to which host plants and their associated herbivores determine the local diversity of parasitoids, which depend, directly or indirectly, on these two groups as food resource or shelter for their development. The tritrophic system studied here is composed of Asteraceae, endophagous herbivores associated with their flower heads and parasitoid wasps. Samplings were undertaken in 18 remnants of the Brazilian Cerrado. Path analysis was used to unveil the direct and indirect effects of species richness, average taxonomic distinctness (AvTD), and sampling effort of plants and herbivores on parasitoid richness and AvTD. Plant species richness had only an indirect effect – mediated by herbivores – on parasitoid species richness. On the other hand, there were both direct and indirect effects of plant species richness on the AvTD of parasitoids. An implication of our findings is that the local extinction of plant species promotes not only the local loss of their herbivores but also the loss of parasitoid species and a decrease in the phylogenetic diversity of parasitoids, which can jeopardise their future evolutionary history.

Connectivity and Nestedness in Bipartite Networks from Community Ecology

Bipartite networks and the nestedness concept appear in two different contexts in theoretical ecology: community ecology and islands biogeography. From a mathematical perspective nestedness is a pattern in a bipartite network. There are several nestedness indices in the market, we used the index �. The indexis found using the relation � = 1 � where � is the temperature of the adjacency matrix of the bipartite network. By its turnis defined with help of the Manhattan distance of the occupied elements of the adjacency matrix of the bipartite network. We prove that the nestedness indexis a function of the connectivities of the bipartite network. In addition we find a concise way to findwhich avoid cumbersome algorithm manupulation of the adjacency matrix.

Measuring Asymmetry in Insect-Plant Networks

In this work we focus on interaction networks between insects and plants and in the characterization of insect plant asymmetry, an important issue in coevolution and evolutionary biology. We analyze in particular the asymmetry in the interaction matrix of animals (herbivorous insects) and plants (food resource for the insects). Instead of driving our attention to the interaction matrix itself we derive two networks associated to the bipartite network: the animal network, D1, and the plant network, D2. These networks are constructed according to the following recipe: two animal species are linked once if they interact with the same plant. In a similar way, in the plant network, two plants are linked if they interact with the same animal. To explore the asymmetry between D2 and D1 we test for a set of 23 networks from the ecologic literature networks: the difference in size, ΔL, clustering coefficient difference, ΔC, and mean connectivity difference, Δ . We used a nonparametric statistical test to check the differences in ΔL, ΔC and Δ . Our results indicate that ΔL and Δ show a significative asymmetry.