An ecological analysis of lacustrine diatoms in Costa Rica

In many regions, the utility of diatoms as paleoenvironmental indicators is limited by insufficient ecological knowledge of the local modern species. We sampled 86 lakes in Costa Rica for limnological, chemical, and watershed characteristics, and we related these to diatoms using PCA, CCA, and other techniques. CCA using the 82 common species revealed relationships with evaporative concentration. Modeling of species frequencies revealed 82 significant relationships among 22 environmental parameters, especially calcium, elevation, lake depth, and pH. Species were also associated with watershed characteristics, including lake network number and maximum order of inflowing streams. At the species level, analyses supported Niche Theory: species differ in their preferences, and species distribution reflects biological process (e.g., species optima). Diatom assemblages, however, supported Neutral Theory: assemblages were often similar among lakes with dissimilar conditions, and dissimilar among lakes with similar conditions, even in nearby lakes; this suggests a limited role for biotic factors in community assembly. For these reasons the no modern analog problem may be an important challenge for paleoenvironmental reconstructions, and we recommend the use of species ecologies (e.g., optima) and multi-species transfer functions, along with ordination (e.g., CCA). Furthermore, such training sets for ordination should consider both watershed and lake characteristics.

Automated summary

The utility of diatoms as paleoenvironmental indicators is limited by a lack of ecological knowledge about local modern species. A study in Costa Rica examined 86 lakes to gather limnological, chemical, and watershed data and explored the relationships between these factors and diatoms. The analysis revealed significant associations between diatom species and environmental parameters such as calcium, elevation, lake depth, and pH. However, the study also found that diatom assemblages were often similar among lakes with different conditions and dissimilar among lakes with similar conditions, suggesting a limited role for biotic factors in community assembly.