lajimäärä

Lajimäärä, or species richness, is a measure of the number of distinct species present in a defined area, sample, or time period. It is a basic indicator used in ecology to describe the biodiversity of a community or environment. Lajimäärä can refer to local (alpha) diversity, which counts species within a specific site, or to broader scales when aggregated across multiple habitats or regions.

Measuring lajimäärä involves field surveys and compilation of species lists from observations, captures, or identifications. The metric is sensitive to how intensively an area is sampled, the methods used, and the taxonomic resolution. Because more intensive sampling often reveals more species, comparisons between sites or times should account for sampling effort, for example through rarefaction, standardization by area, or by using complementary biodiversity metrics.

Lajimäärä is a component of biodiversity but does not capture species abundances or community evenness. Therefore it is commonly complemented by other measures such as diversity indices (e.g., Shannon, Simpson) and by assessments of evenness and community structure. In addition, lajimäärä can contribute to understanding ecosystem complexity and resilience, as greater species richness is often associated with a wider range of ecological roles and functions.

Applications include monitoring changes in biodiversity due to habitat alteration, climate change, pollution, or invasive species, informing conservation priorities, and assessing the ecological status of habitats. Limitations include its dependence on where and how sampling occurs, potential taxonomic inconsistencies, and the fact that it provides a snapshot rather than a complete picture of ecosystem diversity.