Onshore-offshore gradient in metacommunity turnover emerges only over macroevolutionary time-scales

Area of Science:

• Paleontology
• Marine Ecology
• Evolutionary Biology

Background:

• Invertebrate lineages exhibit higher origination and extinction rates in onshore versus offshore habitats over geological timescales (>10 Myr).
• It is unclear if this onshore-offshore pattern in biodiversity turnover scales down to shorter durations (stages <5 Myr, sequences <0.5 Myr).

Purpose of the Study:

• To determine if onshore-offshore gradients in long-term turnover (Eocene to Plio-Pleistocene) can be extrapolated from short-term turnover.
• To investigate temporal turnover patterns of marine metacommunities across different depth gradients and timescales.

Main Methods:

• Analysis of molluscan species abundances from bulk samples in the northeast Atlantic Province.
• Comparison of short-term (<5 Myr) and long-term (~50 Myr) temporal turnover rates between onshore and offshore habitats.
• Assessment of extinction rates, abundance variability, and species range shifts across different time periods and depths.

Main Results:

• Temporal turnover of metacommunities did not significantly decline with depth over short durations (<5 Myr).
• A significant decline in turnover with depth was observed between the Eocene and Plio-Pleistocene (~50 Myr).
• This long-term decline was driven by higher onshore extinction of Eocene genera/families, increased onshore abundance variability, and onshore expansion of formerly offshore Eocene taxa.

Conclusions:

• The onshore-offshore decline in biodiversity turnover emerges only over long temporal durations.
• Abrupt climatic or oceanographic perturbations between the Eocene and Plio-Pleistocene likely triggered this long-term pattern.
• Net cooling and weaker thermal gradients in the Plio-Pleistocene may have facilitated the expansion of offshore specialists into onshore habitats.