ON THE APPLICATION OF THE THEORY OF ISLAND BIOGEOGRAPHY AND ITS MODERN EXTENSIONS TO SUBMARINE BANK COMMUNITIES

Abstract

This thesis explores the application of a traditionally terrestrial-based ecological theory, the Theory of Island Biogeography (TIB), to a large marine ecosystem. Decades of testing of this theory have led to various extensions acknowledging that the slope of the Species-Area Relationship (SAR) reflects species traits related to dispersal capacity, and species’ competitive and predatory interactions. Until recently, it was largely believed that marine ecosystems were too large and interconnected for this body of theory to apply. My research indicates that this is not true. I tested the applicability of TIB and its derivatives to the structure and dynamics of fish and macroinvertebrate communities inhabiting ten highly productive offshore banks (ranging 500 to 10’500 km2) located on the Scotian Shelf, NW Atlantic Ocean. In Chapter 2, I found support for the TIB: there was a positive SAR for the fish species of the offshore banks. I also found support for predictions of the Trophic TIB concerning the role of predators in controlling the SAR of lower trophic levels: prey and mesopredator SAR slopes increased following the collapse of largebodied predatory groundfish populations due to overfishing. In Chapter 3, I tested for a positive SAR across the macroinvertebrate assemblages of the banks. I found a significant SAR slope only for the least dispersive taxon, supporting early predictions of a negative relation between dispersal capacity and SAR slope. I also found that oceanographic processes play an important role in connecting these assemblages, most-so for highly dispersive taxa. In Chapter 4, across the fish assemblages of the banks, I found support for the original predictions of TIB that, on average over the long-term, bank-specific colonization and extinction events are at equilibrium. However, I also found a dramatic increase in interannual turnover of prey fish species following predator collapse, particularly on the coldest, largest banks, suggesting an extension of the Trophic TIB linking increased SAR slopes to reduced temporal stability may be warranted. My research supports the continued application of TIB and its modern derivatives in large marine ecosystems to elucidate variation of insularity and temporal stability among species assemblages under different disturbance regimes.