Variation in dispersal and competitive ability mediate realized connectivity in two benthic marine invertebrates

For marine species with complex lifecycles, linking dispersal with local species interactions to predict spatial patterns of realized connectivity is an enduring challenge. So far, because the scale of dispersal in many species exceeds our ability to manipulate it, theoretical and modelling developments outpace empirical support, and reconciling theory with direct experimental evidence is understandably rare. With two species of marine invertebrate (Botrylloides violaceus and Bugula stolonifera), the goal of this study was to experimentally test whether within and among species variation in larval dispersal and post-settlement competitive interactions determine spatially explicit differences in colony performance and population structure for each species. For B. stolonifera, the results showed incorporating the origins of larvae with post-settlement competitive interactions can qualitatively predict the establishment and performance of individuals among spatially discrete habitat patches. However, dispersal and competition were poor predictors of spatial population structure and individual performance for B. violaceus indicating for some species relationships between dispersal and competition can be more complex than isassumed. The results highlight the often acknowledged but rarely tested need to predict realized connectivity we must follow individuals from spawning to reproductive maturity to encompass well studied, but implicit mechanisms (such as competition and settlement behaviour), that may mediate connectivity.