Size, weapons and armor as predictors of competitive outcomes in fossil and contemporary marine communities

Inter- and intraspecific competition are usually observed over a few generations but their patterns and consequences are seldom tractable in natural systems over longer timescales relevant to macroevolutionary change. Here, we use win-draw-lose competitive overgrowths for a marine benthic community of encrusting bryozoans that have evolved together in New Zealand for at least 2.3 million years to investigate battles for substrate space, a resource that is limiting for these colonial organisms. Using more than 6000 fossilized and contemporary battles, we explored what combination of traits – including relative zooid (module) size, weapons, armor and relative abundance –best predict battle outcomes, and if these are time-varying. In simpler models where we disregard trait-trait interactions, we find that the effects of larger zooid sizes and three-dimensional growth on battle outcomes are both positive, while that of relative abundance is negative, such that more common species are more o...