Leaf litter input and electrical conductivity may change density of Phylloicus sp. (Trichoptera: Calamoceratidae) in a Brazilian savannah stream

Abstract

Aim Shredders are generally not abundant in tropical streams, and there is considerable evidence suggesting that the food supply drives this pattern in headwaters. The aim of this study was to assess the effect of variation in the availability of food resources, over one year, on the density of Phylloicus sp. (Trichoptera: Calamoceratidae), which is one of the main shredders in Neotropical headwaters. Methods We measured the relative importance of organic matter in terms of vertical input (VI) and benthic standing stock (BS) on Phylloicus sp. density from October 2012 to September 2013 in a preserved third order stream in the Cerrado savannah biome, Federal District, Brazil. Results Leaves were abundant (monthly biomass of 24.2 g.m–2 ±23.1 SD in VI and 46.1 g.m–2 ±76.7 SD in BS), increasing at the end of dry season (August to October) and comprised the most abundant fraction in VI and BS (~ 70%). Phylloicus sp. had a low density throughout the year (2.4 ind.m–2 ±4.9 SD) and its peak (13.7 ind.m–2 ±17.1 SD in October) was associated with greater leaf biomass in VI and high electrical conductivity in the stream. The well-defined peak of Phylloicus sp. density in October suggests interplay between the increase in Phylloicus density and the leaf litter that enters the stream at the end of the dry season. Electrical conductivity was also higher in October, reflecting an increase in nutrient concentrations in the water during this period. Conclusions The availability of leaf litter may be a determinant factor for the seasonal variation in Phylloicus sp. density in tropical streams, suggesting a bottom-up effect. Changes in the supply of allochthonous resources to the stream can lead to modification in populations of shredders, such as Phylloicus sp., and anthropogenic influences on the riparian vegetation can affect ecological processes of great importance to streams.

Effects of litter size and quality on processing by decomposers in a tropical savannah stream

“…, Leite et al . ). We have demonstrated that these differences can affect leaf decomposition rates and, consequently, ecosystem functioning of savannah streams.…”

“…, Leite et al . ). Our study supports the idea that the size and structural characteristics (quality) of litter are important factors that affect decomposer communities and litter breakdown rates in savannah streams.…”

“…In the same stream, Leite et al . () observed a leaf input of 24 g m 2 monthly and density of Phylloicus ranging from 2.4 to 13.7 ind/m 2 monthly. Extrapolating our results, the monthly leaf processing rates by Phylloicus would be 0.2–1.2 g m 2 , depending on density.…”

“…, Leite et al . ). The pattern in degradation rates for species was the same as that observed for microbial decomposition, with M. guianensis preferentially consumed over R. grandis and then I. laurina .…”

Biting midges (Diptera: Ceratopogonidae) from an urban forest fragment in Central Amazon (Brazil): Effects of opening areas on abundance, richness, and composition

“…Higher values of electrical conductivity result from increased ion concentrations and indicate increased nutrient concentrations in the water (Leite et al 2016). Thus, higher nutrient values may be associated with the decomposition of allochthonous organic matter (mainly leaves) in containers (Gessner et al 1999).…”