Early colonization patterns of diatoms across time and among three freshwater lakes.

Abstract

Diatoms (Bacillariophyta) form stable colonies on artificial substrates in less than 21 days (Cairns et al., 1983), but the factors that affect such colonization have not been rigorously studied. In our study we explored different factors of diatom colonization in three different-sized freshwater lakes--Douglas (large), Munro (medium), and Lancaster (small). We used the MacArthur-Wilson equilibrium theory of island biogeography (1963) to explain our findings. This theory predicts that species should increase in number and diversity over time until an equilibrium is reached between colonization and extinction rates of species. This theory also predicts that larger islands should be more diverse and rich than smaller islands. In all three lakes, we found that species diversity and richness tended to increase on day 6, peak on day 15, and remain stable through day 21. Doulgas also generally had higher species richness and diversity than Munro and Lancaster. These results support predictions made by island theory. With regard to species in relative high abundance (>5%), Douglas and Munro showed a trend of succession from planktonic to 'attaching' and motile diatoms. In contrast, euplankton remained abundant across the 21-day period in Lancaster, and periphyton species colonized sooner than in the other two lakes. Lancaster's distinct littoral zone and smaler species pool may account for these differences. In looking at number of species from 1975 to 2005, Douglas had more types of genera and species than Munro and Lancaster. This result further supports island theory since species richness increased relative to island size. Finally, Lancaster was less similar over the 30-year period than Douglas and Munro, supporting the idea that smaller islands tend to change more than larger lakes.