How to address sampling issues in biodiversity measurement?

How to address sampling issues in biodiversity measurement? (NEW FORUM PAPER)

When sampling communities, we’re more likely to miss rare species than common ones. As a result, sampling issues pervade biodiversity measurement. For example, two of us could compare species richness along the same ecological gradient, using the same sampling techniques – but different effort – and find opposing patterns, simply because one of us sampled more, and the other less. For most ecological measures, our pictures get sharper with more data, but do not often radically reconfigure, as they can with species richness. Seeking methods that reflect ecological patterns, rather than sampling choices, we asked, “how can we best recognize and mitigate sampling limitations in biodiversity measurement?”

Our paper, “A conceptual guide to measuring species diversity” surveys current tools for measuring species diversity. We recommend two, coverage and Hill diversity, used together. Coverage is a measure of sampling completeness, and equalizing coverage can reduce bias in biodiversity comparisons. Hill diversity, a conceptually elegant spectrum of diversity metrics, allows ecologists to choose the sensitivity of their metric to the rarest species, the ones that bedevil richness estimation. To build up to our recommendations, we explore how each tool works under the hood.

For example, Hill diversities all measure an “effective number of species,” but that number depends on a choice to emphasize either more common or rarer species. “Emphasize how?” we asked, “how can we make the calculations concrete?” We (re-) discovered that Hill diversity measures average species rarity, and created balance plots. With our interactive balance plots, you can adjust species abundances and the scaling parameter, and see how the “effective number of species” is also a balance point: the mean species rarity.

Written for ecologists who seek biodiversity patterns in field data, our guide discusses how methods work and the tradeoffs among them. We argue that using Hill diversity and coverage together, ecologists can more robustly estimate biodiversity with meaningful measures, accounting for, and mitigating, sampling issues.

Written by: Michael Roswell
 

Comments