Variação espacial na densidade, riqueza e composição de especies de insetos associados a capitulos de Senecio brasiliensis (Asteraceae)

AUTOR(ES)
DATA DE PUBLICAÇÃO

2000

RESUMO

This thesis was divided in two chapters. In chapter I, I investigated the factors responsible for the variation of insects density per plant in Senecio brasiliensis populations. I also related the insects local density and its geographic distribution. In chapter 11,I ana1yzedthe factors responsible for the variation of insect richness per plantoI also investigatedthe effect of the distance among patches and the patches size on the similarity of the insects composition. The field work was carried out in two regions in Southem Brazil. I sampled four sites in the region named North (Minas Gerais state), and five in the region named South (São Paulo and Paraná states). In each locality I sampled a pair of patches (discrete populations) of Senecio brasiliensis, one large and one sma1l.In each patch I sampled 30 plants and ftom each one 30 flowerheads were dissected. Ten species of insects were obtained: eight endophagous, one galler and one predator species. The species belong to the families Cecidomyiidae, Agromyzidae (Diptera), Pyralidae, Tortricidae and Pterophoridae (Lepidoptera). I analyzed the variation of insect density and richness per plant in relation to region, locality, vegetation complexity surrounding the patch, patch size, plant density in the patches, and plant size. The two main factors explaining the insects density variability were the complexity of the vegetation surrounding the p~tches and loca1ity,which reflects characteristics of each area. The variables that estimate the plant resource concentration (patch size, plant density and plant size) did not interfere in most of the insect species densities, probably because of their generalist habit and the saturation on the reproductive capacity. OnlyMelanagromyza erechtitidis (Agromyzidae),the most specialist insect species, was significantly influencedby plants density and size. I detected a significant positive relationship between the average density of insects per plant, per patch and its geographic distribution (number of localities in whiçh they occurred) for each insect species. Both the complexity of vegetation surrounding the patches and locality also presented a significant effect on the insects richness per planto There !S a higher insect richness in plants surrounded by more complex vegetation. This result may be related to the generalist habit of these species. The loca1ityvariable reflects, for each arca, its particularities variations and colonization history. The variables reflecting resource concentration in the host plant (patch size,plant density and plant size) did not interfere with the insects richness per planto I found a significant effect of the distance among patches on their faunistic similarity, with more distant patches showing less similarity. Similar sized patches showed a higher faunistic similarity than different sized patches. The results show that both plants local characteristics and large scale factors related to the spatial distribution of the host plant and insects are important in determining the local density, richness and composition of insects inhabiting Senecio brasiliensis flowerheads

ASSUNTO(S)

compostas insetos - ecologia senecio

ACESSO AO ARTIGO

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