Influência de fatores ambientais sobre a composição de espécies de baratas (Insecta: Blattaria) na Reserva Ducke, Manaus, Amazonas, Brasil

Abstract

Cockroaches (Hexapoda; Blattaria) are abundant and well adaptable to the environment, cause a significant impact on the distribution of the nutrients, and are components of the diet of invertebrates and small vertebrates. In a gradient of 5 x 5 km in an ombrophilous dense terra firme forest, we evaluated the morphospecies richness and abundance of cockroaches and the role of environmental variables (clay content, slope, concentration of aluminum in the soil, litter height and number of trees) on the assembly of morphospecies. Aiming at reducing the effort of collecting and sorting we also verified if the ecological relationships captured with the total community of morphospecies of cockroaches could be captured with the reduced community, after the exclusion of very common and very rare morphospecies. The gradient studied has 30 plots of 250 m, installed in contour line and are evenly distributed. We sampled in two periods: November/December 2010 and May 2011. From 18:30 an active sampling with one hour of effort was undertaken in each plot, totaling 30 hours of effort per amostral period. Each plot was sampled by two collectors, distant 30 meters from each other and inspecting one meter at each side of the plot. A total of 979 specimens was recorded, identified in 19 genera and 40 morphospecies. The 40 morphospecies are within the estimated number of morphospecies provided and we suppose that the meso-spatial scale of 5 X 5 km of sampling effort positively influenced this number. Redundancy Analysis (RDA) showed that the litter height, clay content, and soil aluminum were the variables that contributed most to capture the pattern of cockroaches distribution in the forest at both total and reduced community to ten morphospecies levels. This pattern was most clearly shown for species presence-absence data. The total variation explained in all cases was less than 20% for data abundance and presence/absence. This may be due to the high mobility of the cockroaches, making it difficult to establish the boundaries of their territories. Multiple linear regression analyzes indicated that these variables were also important in explaining the distribution of 10 selected morphospecies. The relathionship of soil aluminum in with cockroaches can be indirect, because herbivorous cockroaches may be feeding on leaves of plants with higher concentrations of this element in their leaves. Both the concentration of aluminum and the clay percentage in the soil exerted the same effect on the assembly of cockroaches since these variables are highly correlated. The reduced community, comprising 10 morphospecies can be selected to elaborate a research protocol that will result in the reduction of the time of sampling, sorting, and identification. The economy can be used to expand the collection at other sites and in the monitoring of biodiversity and environmental impacts.