Gretchen Brownstein and company have an accepted paper in the Journal titled “Chance in plant communities: a new approach to its measurement using the nugget from spatial autocorrelation ”. Read the abstract here.
The authors have provided a short synopsis of the paper and a photo of one of their study sites on the South Island, New Zealand.
Community composition, i.e. species presence or absence, is controlled by two types of factor: deterministic ones and random ones. There is a large body of work examining both types of factors, with evidence supporting both. Generally this work has looked for evidence of either random factors or deterministic factors, but it seems increasingly clear that both are at work simultaneously.
The discussion has now shifted towards examining whether random or deterministic factors are more important in structuring communities. Do different community or habitat types differ in their degree of randomness? Does species richness or time since disturbance influence the degree of randomness? These are fundamental ecological questions, however until now there has been no clear way to quantify the degree to which randomness or ‘chance variation’ determines community composition.
In our paper we describe a method for quantifying randomness using the distance/dissimilarity relation. We tested our method in 16 sites around the South Island of New Zealand, including forests, shrublands, grasslands and wetlands, to see if and how chance varied across plant community types and at different spatial grains (scales).
We found that randomness was not related to community type but rather that randomness was correlated with the species richness of the whole community: communities with more species have a greater degree of randomness. Our method provides ecologists with a tool to quantify randomness in communities and our analysis lends support to the idea that chance, redundancy and the size of the species pool are all connected.