LAKE FAUNAS THROUGH TIME—THE ESTUARY EFFECT AND HOW LIFE INVADED LAND

The timing and mechanisms of how faunas established themselves on land is critical to our understanding of clade origination, radiation, and derivation through time. In addition, determining the conditions and physiological traits necessary for clades to invade continents allows us to better characterize the nature of these invasions and understand the requirements for survival in non-marine environments as well as informing on the possible cause of diversity disparity across the tree of life.

The early history of lake faunas is one of opportunity and amelioration. Feedback loops created by the establishment of vascular land plants altered the terrestrial nutrient cycle and impacted lacustrine regimes by increasing the nutrient availability and loading, allowing more complex trophic interactions to develop. Trophic levels were established early and became increasingly complex throughout the Paleozoic.

Continental faunas established themselves through estuarine gateways via multiple invasions during maximum flooding events when ecosystem space expanded on the shelf margin. Characterizing the clades that were subsequently successfully established on land reveals a diversity disparity between exclusively marine clades and those that are both marine and continental in distribution. With the exception of the echinoderms, clades on continents are more diverse than those metazoans occurring exclusively in the marine realm. This salinity divide is likely due to differing osmoregulation strategies.

Clades invading the continents via the “estuary effect” did so numerous times via the episodic establishment of marine-freshwater connections along continental margins. The invasion occurrences and subsequent diversification demonstrates a dramatically different diversification pattern on continents than in the marine realm. The global tectonic and geochemical cycling that has occurred throughout the Phanerozoic may have influenced continental colonization and subsequent diversification of those clades through time.