A good hypothesis is a matter of scale

Submitted by editor on 1 September 2014.
Old-growth longleaf pine vegetation in the Croatan National Forest, North Carolina. Photograph by Kyle Palmquist.

By Jes Coyle. Read full study here.

Graduate students at the University of North Carolina (UNC) at Chapel Hill used data from over 52 000 forested locations in the eastern USA to show that there is no regional level support for a widely held ecological hypothesis. The hypothesis, termed the stress-dominance hypothesis, posits that as the physical environment becomes less stressful, the presence of different species at a particular location should shift from being determined by the environmental stressor to being determined by competition. The researchers tested this hypothesis using two large forest datasets from the eastern USA, combined with information about tree physiological traits and phylogenetic relationships. Although trees in different environments had different traits, there was no evidence for the predictions of the hypothesis. The researchers concluded that while the stress-dominance hypothesis may operate at smaller spatial scales, it is not generally applicable across larger regions.

Basic cove forest in Pisgah National Forest, North Carolina. Photograph by Kyle Palmquist.

The research project developed from a National Science Foundation distributed graduate seminar aimed to encourage biodiversity research that extended beyond traditional metrics, such as species counts. It enabled graduate students studying ecology at UNC and thirteen other universities to learn the challenges and opportunities of combining traditional biodiversity research with functional, phylogenetic, and genetic diversity data. The inter-institutional and collaborative nature of the seminar allowed the UNC team to learn from their peers around the world while developing the hypotheses and statistical techniques used in the study.