O PAPEL DOS TRAÇOS FUNCIONAIS NA ECOLOGIA DO FITOPLÂNCTON CONTINENTAL

Abstract

THE  ROLE  OF  THE  FUNCTIONAL  TRAITS  ON  THE  PHYTOPLANKTON  ECOLOGY  IN INLAND WATERS. To cluster species based on their functional traits has been a growing trend in ecology due  to  its  ability  to  predict  or  explain  the  structure  of  communities  and  their  responses  to  environmental conditions. The  aim  of  this  review  is  to  discuss  the  foundations  of  approach  based  on  functional  traits  in the ecology of freshwater phytoplankton. First, we identify the functional traits relevant to phytoplankton; then we provide a review of the functional approach literature and, finally, we analyze Brazilian freshwater ecosystems  using  the  functional  groups  (FG)  proposed  by  Reynolds  et  al.  (2002).  Functional  traits  affect the fitness of species through their effects on reproduction and survival. These traits can be: morphological (i.e. size, shape), physiological (i.e. concentration and composition from photosynthetic pigments, capability of  nitrogen  fixation,  toxin  production),  behavioral  (i.e.  mixotrophy,  motility)  and  life  history  (i.e.  asexual/sexual reproduction, production of resting stages). Results from a multivariate analysis based on data from 33 aquatic ecosystems indicate that different types of ecosystems (rivers, lakes, estuaries and reservoirs) share similar FG across similar trophic states. Oligotrophic systems were dominated by small organisms or larger one equipped with functional traits, such as flagella or mixotrophy behavior, that allow them to live in poor nutrient conditions. In mixed hipertrohic lakes, both the enriching in nutrient condition (that provide matter enough to allow the increase in the size of the organisms), and the decrease in water transparency favor the dominance of large organisms with high surface/volume ratio, such as filamentous cyanobacteria. Although the scheme proposed by Reynolds et al. has been a potential tool to sum up the community types in Brazilian aquatic  ecosystems,  it  presents  some  limitations,  such  as:  (i)  some  FGs  have  been  added  on  the  intuitive grounds, (ii) the need of taxonomic knowledge from a specialist, and (iii) cyclic reasoning. Other schemes have been proposed due to these limitations. Thus, future studies should give emphasis to test the scheme which better predict the community composition of phytoplankton in relation to environmental conditions.

Keywords: Phytoplankton; community structure; functional groups; functional traits.