Abstract
We describe the abiotic factors affecting the distribution of black flies at a microhabitat scale, rather than at the regional scale usually present in the literature on the Neotropics. Black fly larvae were sampled from the Tocantins River and three tributaries, located in the Brazilian savanna (state of Tocantins, Brazil) during six bi-monthly sampling periods from October 2004-August 2005. At each sampling site, 15 random quadrats (30 x 30 cm) were sampled each period and for each quadrat were determined mean water velocity, predominant substrate type (rocks, riffle litter or riparian vegetation) and depth detrended correspondence analysis (DCA) was used to determine associations with current velocity, whereas correspondence analysis (CA) was used to estimate site specific current velocity associations. Canonical correspondence analysis (CCA) was used to identify general microhabitat associations. The CCA showed that most species had a trend towards riffle litter, except for Simulium nigrimanum associated with rocky substrate and Simulium cuasiexiguum associated with riparian vegetation. The DCA showed a well defined pattern of water velocity associations. The CA revealed that the species showed different speed associations from one site to another, suggesting different competitive pressures resulting in the occurrence of different realized niches.
Highlights
Hamada et al (2002) pointed out the relative scarcity of ecological studies on the black fly fauna of the Neotropical Region. In addition to this limited number of studies, most of the literature on this subject is restricted to a few geographical areas; in the specific case of Brazil, a large number of biomes lack ecological studies on their black fly fauna (Figueiró & Gil-Azevedo 2010), as most of the studies concentrate on the central Amazon (e.g., Hamada et al 2002), southeastern (e.g., AraújoCoutinho et al 2004, Figueiró et al 2006, Pepinelli et al 2005) and southern (Strieder 2004, Santos et al 2010) Mata Atlântica biomes
Another issue raised in Hamada et al (2002) is that most of the studies on Neotropical black flies approach the ecology of the individual species population (e.g., Hamada & McCreadie 1999), rather than the whole black fly community
Simulium pertinax Kollar, 1832 and Simulium dekeyseri Shelley & Py-Daniel, 1981 larvae are indistinct, as Simulium subnigrum Lutz, 1910 and Simulium inaequale (Paterson & Shannon, 1927) immature larvae. When we found both species in the localities, the pairs were treated as the same entity in this work
Summary
Hamada et al (2002) pointed out the relative scarcity of ecological studies on the black fly fauna of the Neotropical Region. Even though laboratorial studies have shown that variations in micro-scale water flow dynamics can create appropriate habitat for many specialized lotic organisms, playing a pivotal role in defining the spatial distribution of the benthic community (Statzner et al 1988), the number of field studies which quantified micro-velocities is extremely limited, due to the technical difficulties of such measurements (Hart et al 1996) In this present study we employ in our analyses the local macro-velocities, that is, the velocity within each habitat patch in a water course
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