| dc.description.abstract | The knowledge of the role of physical and biological processes on animal community distribution is influenced
by the spatial scale adopted in ecological studies. Due the scarcity of studies of distributional patterns of benthic
macroinvertebrates in multiple scales in tropical and subtropical regions, this paper analyzes the structure of
benthic macroinvertebrate communities in different spatial scales (among small watersheds and different river
orders of each watershed) and the influence of certain environmental variables on these communities. The
sampling was performed with Surber sampler in the small watersheds of the Vacacaí-Mirim River (August,
2008), and the Ibicuí-Mirim and Tororaipí rivers (August 2009). In each watershed were selected four sampling
sites following the longitudinal gradient (stretches of 1st, 2nd, 3th and 4th orders. The environmental factors
analyzed were: water temperature, pH, electrical conductivity, dissolved oxygen, substrate granulometry and
presence of aquatic and riparian vegetation. A total of 10.985 individuals, 42 families and 129 taxa were collected
and, in general, the dominant taxa were Simuliidae (14%), Naididae (13%), Cricotopus sp. 1 (13%), Cricotopus
sp. 2 (8%) (Chironomidae), Paragripopteryx (5%) (Gripopterygidae) and Americabaetis (5%) (Baetidae)
representing 58% of the total specimens collected. There were no differences in macroinvertebrate richness
among watersheds, however, the community structure showed differences among the three watersheds. The
stretches of 3th and 4th orders showed higher richness than the stretches of 1st and 2nd orders. Additionally, there
was recorded difference among communities structure of different orders stretches (56%). In general the
environmental variables that influenced the distribution of the communities were granulometry, dissolved
oxygen, electrical conductivity and aquatic vegetation. The macroinvertebrates characteristic of 1st and 2nd order
stretches of the Vacacaí-Mirim River and of 1st order of the Tororaipí River watersheds where influenced mainly
by bigger granulometry and dissolved oxygen, while the macroinvertebrates associated to the 3th and 4th order
stretches were influenced by the higher electrical conductivity. The small watersheds of the Ibicuí-Mirim (except
the 2nd order stretch) and Tororaipí rivers (except the 1st and 4th order stretches) did not show difference
concerning the river orders, and were associated to the smaller electrical conductivity and absence of aquatic
vegetation. The 4th order stretches of the Tororaipí River was segregated of the other stretches due to its smaller
granulometry. The granulometry did not influence the small watershed of the Ibicuí-Mirim and Tororaipí rivers
(except the 4th order stretches) due to the presence of fine substrate, while the Vacacaí-Mirim River watershed
showed coarse substrate. This difference is probably determined by the fact that the Vacacaí-Mirim River
represents a tributary of a different and bigger hydrographic watershed, the Jacuí River Basin, while the others
small watersheds represents tributaries of the Ibicuí River Basin. Possibly, the Jacuí River Basin have higher
electrical conductvity, since this factor was high in all the sampled stretches, being encreased by the proximity to
urban areas with domestic sewage and agricultural activities near the river banks. In the small watersheds of the
Ibicuí-Mirim and Tororaipí rivers, the difference between the community structures is possibly related to
environmental features, such as finer substrate in both rivers and well developed riparian vegetation in the
Tororaipí River. | |
