Comparative phylogeography - the role of history in the structuring of aquatic communities

Aquatic community structure is, in part, a mosaic resulting from dispersal and extinction events.  Some events occur on short time scales (weeks, months, or years), while others take place over geological time periods.  Understanding the role of geological time often requires studying broad geographical areas.  Historic dispersal pathways may have varied between taxa due to physical constraints unique to each taxon.  Dispersal can be ordered by such physical constraints.  Our work has focused on fish which exhibit what we term conservative dispersal, requiring active lotic or lentic connections through which to move.  Their phylogeographical associations show potential invasion routes for large obligate aquatic invertebrates with similar dispersal constraints.  But other invertebrates, such as snails and amphipods, may also disperse through more ephemeral connections, including isolated ponds and spring seeps.  Overland flight facilitates more avenues of dispersal in aquatic insects but a gradient in flight capacity exists between taxa that may generate differences in dispersal rates.  These examples imply a hierarchy of mechanisms.  A better understanding of the importance of different dispersal mechanisms will arise through comparative phylogeographic studies.