Bottom-up controls, ecological revolutions and diversification in the oceans through time

Abstract

Animals originated in the oceans and evolved there for hundreds of millions of years before adapting to terrestrial environments. Today, oceans cover more than two-thirds of Earth and generate as much primary production as land. The path from the first macrobiota to modern marine biodiversity involved parallel increases in terrestrial nutrient input, marine primary production, species' abundance, metabolic rates, ecotypic diversity and taxonomic diversity. Bottom-up theories of ecosystem cascades arrange these changes in a causal sequence. At the base of marine food webs, nutrient fluxes and atmosphere-ocean chemistry interact with phytoplankton to regulate production. First-order consumers (e.g., zooplankton) might propagate changes in quantity and quality of phytoplankton to changes in abundance and diversity of larger predators (e.g., nekton). However, many uncertainties remain about the mechanisms and effect size of bottom-up control, particularly in oceans across the entire history of animal life. Here, we review modern and fossil evidence for hypothesized bottom-up pathways, and we assess the ramifications of these processes for four key intervals in marine ecosystems: the Ediacaran-Cambrian (635-485 million years ago), the Ordovician (485-444 million years ago), the Devonian (419-359 million years ago) and the Mesozoic (252-66 million years ago). We advocate for a clear articulation of bottom-up hypotheses to better understand causal relationships and proposed effects, combined with additional ecological experiments, paleontological documentation, isotope geochemistry and geophysical reconstructions. How small-scale ecological change transitions into large-scale evolutionary change remains an outstanding question for empirical and theoretical research.

Resilience of infaunal ecosystems during the Early Triassic greenhouse Earth

“…Bioturbation influences the distribution of planktonic organisms by controlling the dormancy of resting/larval stages of planktonic organisms and thus essentially influences the base of the food web in a marine ecosystem ( 20 ). “Bottom-up control” mechanism of ecosystem cascades connects nutrient concentrations to primary producers to first-order consumers and has positive feedbacks on higher-order consumers such as nekton ( 35 ). Both peaks of the diversity of infaunal ecosystem engineers and nekton in the Smithian may also be a result of the amelioration of environmental conditions in the aftermath of the extinction.…”

Terrestrial forcing of marine biodiversification

“…The exact pathways by which trophic resources are transmuted into biological diversity remain poorly-understood 79 . Nutrient availability and productivity nevertheless undoubtedly play significant roles in biodiversification on different time scales, like those associated with stoichometric theory: enhanced metabolism, increased grazing and predation, all of which would have impacted biogeochemical cycles; enhanced resources available for reproduction, population increase and potential dispersal leading to genetic isolation; and life cycle changes 8 , 9 , 13 , 21 .…”

Beyond functional diversity: The importance of trophic position to understanding functional processes in community evolution

“…The decrease in slope of ntp ∼ log bs for progressively younger communities was driven by the appearance of increasingly large body-sized guilds of top consumers throughout the Mesozoic, culminating in the Aptian (Figure 5). Larger body sizes of high level consumers must be supported by enhanced production and biomass at lower trophic levels; therefore the decreasing slope of ntp ∼ log bs is likely an ecological signal of the secular increase in primary production observed over the course of the Mesozoic (Knoll and Follows, 2016;Lowery et al, 2020;Martin and Servais, 2020;Antell and Saupe, 2021;Rojas et al, 2021). Thus, results presented here provide direct evidence for escalation, and agree with broad taxonomic patterns reported for the MMR, even considering early examples of megafaunal predation in the Early Triassic (Jiang et al, 2020;Liu et al, 2021).…”