Secondary production dynamics of shredder chironomids under the effect of resource food availability of two litter leaf species with different decomposition rates.

Abstract

Diverse shredder chironomid species have been already described in Brazil, and studies with larvae species have pointed out that they manifest an important role in accelerating the biomass decomposition rates of leaf-litter species. Nonetheless, the effects of leaf-litter biomass availability in secondary production of adult shredder chironomids are unknown. This study will aim to estimate the aspects of growth rate, secondary production and changes in the community structure of adult shredder chironomid species under the influence of the availability of leaf-litter biomass in a colonisation experimente of two leaf species with diferente decomposition rate decay. The colonisation experiment will be performed in Savana headwater streams (n = 10) located in the central region of São Paulo state, Brazil. The adult shredder chironomid collection will occur using an adapted trap model (n = 60) under colonisation leaf bags (mesh 0.5 mm) containing Magnolia ovata and Licania tomentoda dried leaves (10 g) through 90 days of colonisation period. Temporal analyses will be performed after10, 30, 50, 70 and 90 colonisation days. Different classes of body length of adult chironomids will be obtained using stereomicroscope measurements. An aliquot of 10 specimens per body length class will be dried on the stove (50º C) for 24 hours until they reach the dry weight. The biomass as well as celulose and lignina of leaf species will be determined. The biomass of chironomid species will be determined using the length-mass regression model. The growth rate of species throughout different colonisation periods will be analysed using the linear growth equation model. The secondary production of species will be determined using the instantaneous production (PR) and integrated production (IP) rate equations. Significant differences between PR values of species will be analysed using the variance analysis (ANOVA, p < 0.05). The effect of leaf species biomass loss between different colonisation days on IP' of shredder chironomid species will be analysed using a simple regression analysis with the significant differences compared using the MANOVA (p < 0.05). The changes in the structure community of shredder chironomids and other functional feeding groups throughout the colonisation days will be analysed using non-metric multidimensional scaling (MDS) analysis, with similarity distances calculated trough Bray-Curtis index. The significant differences in community composition among colonisation days will be analysed through similarity analysis (ANOSIM) using the Bray-Curtis index. To do this, the abundance values of taxa will be used. The results obtained from studies of secondary production will help to gain knowledge about the population dynamics and structure community of adult species that compose this aquatic insect group in headwater streams. The results would highlight the importance of maintaining biodiversity as well as the ecological process in freshwater systems.