Title: Phytoplankton diversity and strategies in regard to physical disturbances in a shallow, oligotrophic, tropical reservoir in Southeast Brazil
Abstract: Phytoplankton diversity and strategies in regard to physical disturbances in a shallow, oligotrophic, tropical reservoir in Southeast BrazilThe IAG Lake is a small, oligotrophic, and shallow reservoir located in the Parque Estadual das Fontes do Ipiranga Biological Reserve, south of Municipality of São Paulo, southeast Brazil.The study of the phytoplankton community dynamics is based on samples collected along the vertical proſle of the water column in the pelagic region of the reservoir (Z max = 4.7 m), 3 times a day (7 h, 13 h, and 19 h) during 7 consecutive days of the dry period (20-26 August 1996) and of the rainy period (22-28 January 1997), but at 5 depths during the dry period and at 4 depths during the rainy one.The relationships among species richness, diversity, evenness, and dominance were discussed within the Connell's Intermediate Disturbance Hypothesis (IDH).The responses of the descriptive species in the community and C-R-S strategies were studied.The variation of the mixing zone was the main factor responsible for the changes in the community structure as well as for the maintenance of the diversity during both climate periods.The disturbance was considered of high frequency during the dry period and of intermediate frequency during the rainy one.The diversity was higher during the rainy period, conſrming the IDH, at least during the present study.Peridinium gatunense Nygaard was dominant in most sample units during the dry period.During the rainy one, Chlamydomonas debaryana Goroschankin and Oocystis lacustris Chodat were the species that contributed the most.Regarding the functional groups, S-strategists dominated the dry period, differing from the rainy one, when the functional diversity was higher.In conclusion, changes in the phytoplankton community structure were well explained by Connell's IDH.