Travis Ingram today discussed coexistence. Sets of species can be found together because 1.) the local habitat requires a certain set of adaptations that all the species share, i.e. environmental filtering, 2.) some species have out competed others that are now absent from the community, i.e. assembly rules, 3.) the species coexist in a locality is entirely random, i.e. neutrality, 4.) the trials and tribulations of their evolutionary history selected for their ranges to overlap that locality, i.e. biogeography and species sorting. Ingram focuses on rockfishes from the Northeast Pacific finds that both mediated competition (2) and environmental filtering (1) are important. Interesting, he mentioned that similar patterns are found in plants suggesting generality across taxa.
Elizabeth Jones Sbrocco focuses on number 4 in the marine biodiversity hotspot that is the Indo-Pacific. During the last glacial maximum (LGM) the seas were 120m shallower. This is hypothesized to trap populations in shallow refugia, leading to genetic isolation, and eventually greater biodiversity. Her work demonstrates high levels of genetic structure in two species of clownfish through the region, partly due to contemporary currents but alls due to the localities of refugia during the LGM. The really cool part of the work, which made me wish her presentation could have been longer than 15 minutes, was that old refugia during the LGM were more environmental similar that those in habitats in the clownfish’s contemporary ranges. This implies at some level that adaptation to the refugial environment cannot explain the modern distribution.