THE INFLUENCE OF STOLONIFEROUS REPRODUCTION ON EDIACARAN ECO-EVOLUTIONARY DYNAMICS

Competition and reproduction are two of the most fundamental mechanisms of evolutionary theory, but the effects of competition and reproductive modes on early animal diversification are not well understood. To understand the impact of reproductive mode on resource competition and Ediacaran diversity, the presence and strength of intra-specific competition, reproductive variables (dispersal cluster size and spatial directionality) were quantified using spatial point process analyses from 20 taxa populations across 9 Ediacaran Avalonian early animal communities (572-560 Ma). Binomial regressions found spatial directionality was a significant predictor for the presence of intraspecific competition. General linear regression models found significant association between the strength of intra-specific competition (minimum PCF value) with stoloniferous reproductive variables (48%). In the three communities that exhibited inter-specific competition, there were five out of eight heteromyopic interactions whereby inter-specific competition occurs at smaller spatial scales than intra-specific competition. For Mistaken Point E surface and Bed B Charnwood Forest, these interactions included the most abundant taxa, implying that heteromyopia patterns dominated these communities. Heteromyopia enables co-existence of sub-optimal competitors because the dispersal limitation of the dominant species means that they do not inhabit all the optimal habitat, so that lesser competitors can still exist within the same community, operating under reduced selection pressure. We explored the consequences of this scenario on community diversity with a spatially explicit model: within communities with limited dispersal and reduced selection pressure, alpha and beta diversity were low; but when dispersal distances and selection pressure increased both alpha and beta diversity doubled. These diversity patterns mirror those found in the Avalon and White Sea assemblages. Thus, the presence of stolon-induced heteromyopia may underpin the relatively slow diversification rates found within the Avalon assemblage, limiting early animal evolution prior to the onset of widespread mobility and sexual reproduction (specifically wide dispersal ranges) in the White Sea assemblage.