Abstract:
The literature on species diversity of phytoplankton of tropical
lakes is scarce, and for the main part comes from studies of the big
lakes in Africa, or deep lakes in South America, leaving a gap in the
information about small shallow tropical lakes. In the present work
the phytoplankton species composition and diversity of 27 shallow
lakes and ponds in Costa Rica (Central America) was studied.
The species composition was found to agree with other studies of
tropical lakes, with a dominance of Chlorophyta, Cyanophyta, or in
some cases Bacillariophyta or Euglenophyta; and a general paucity of
Chrysophyta and Cryptophyta.
Species richness varied considerably among the lakes, and tended
to decrease with an increase in lake elevation. A low evenness in the
species abundances was found, with one or more species outnumbering
the rest by several orders of magnitude.
Individual species abundances and species composition was found
to vary with time in Rio Cuarto Lake, a meromictic lake situated in a
region with low seasonal change in precipitation.
In comparison with the phytoplankton of temperate lakes, the
phytoplankton of the tropical lakes studied tended to have a lower
evenness of species abundances, although species richness may be
similar to temperate figures in some cases. Diversity indices
sensitive to changes in the abundance of rare species tend to be
higher in the tropical lakes studied; diversity indices sensitive to
changes in the numbers of abundant species tend to be similar between
the temperate and tropical lakes examined.
