FUNCTIONAL DIVERSITY OF EARLY EDIACARAN COMMUNITIES

The first macrofaunal communities emerged in the late Ediacaran ~574-564 Ma, recorded in relatively deep-water continental slope deposits exposed around the Avalon Peninsula in Newfoundland. These communities contain taxa belonging to several clades/morphogroups, which may represent a mixture of stem- and eumetazoan organisms. There is, however, little evidence for biotic interactions in the Avalon. Height may have facilitated propagation but the interactions between body plans, body size, and feeding strategies (i.e., key ecological traits) are not understood. Understanding the structure and function of these early communities is key to understanding the origin of marine ecosystems.

Functional diversity, which quantifies species’ ecological roles from the distribution of functional traits within communities independent of taxonomy, may provide insight into how Avalon communities were structured and developed. To estimate functional diversity, we compiled trait and occurrence data for Avalon genera from museum collections, primary literature, and the Paleobiology Database. Functional traits included feeding, vertical orientation, body plan, and body size (estimated as mean log biovolume). Three functional diversity indices were calculated for each community: functional richness (which estimates the total trait space occupied by a community), functional evenness (which quantifies how regularly traits are distributed within communities) and functional divergence (which captures how traits are distributed relative to a point of central tendency for that community).

We show that functional richness among Avalon communities was relatively low, which likely corresponds to limited taxonomic richness and available traits. However, functional evenness and divergence were high. Genera were distributed very evenly and widely according to their functional traits, rather than clustering around central values. Moreover, different taxonomic groups showed minimal overlap in trait space with body size playing an important role in niche separation. The first macrofaunal communities, though long-thought to be comprised of morphologically ‘simple’ organisms, thus contained remarkable functional diversity, with ecological roles potentially distinguishable through body size.