Year: 2016
Type: dissertation
Abstract: The fossil record offers unique insights into the environmental and geographic partitioning of biodiversity during global diversifications. Global (gamma) diversity can be decomposed into local (alpha) and turnover (beta) components. Relationship of alpha and beta diversity in deep time during major evolutionary radiations has seldom been studied in paleobiology. Pathways of alpha- and beta- diversity in diversifying ecosystems notably differ depending on the relative role of various ecological interactions and environmental parameters. By combining the analysis of macroecological patterns of taxonomic composition and spatial distribution, we can assess the question which factors primarily controlled the diversification of life over geological times. Here I explore biodiversity patterns during the Cambrian radiation, the most dramatic radiation in Earth’s history. That the main pulse of the Cambrian radiation was in the early Cambrian has long been known, but defining the time of peak diversity has been hampered by problems with stratigraphic correlations. Many mechanisms of the Cambrian Explosion have been proposed, which can be subsumed as abiotic change, biotic interactions and genetic. This thesis aims at elucidating the role of biotic interactions using rigorous quantitative analyses of Ediacaran-Cambrian biodiversity dynamics. I use data from the Paleobiology Database (http://paleobiodb.org), which is a core infrastructure for modern paleobiological analyses. Based on well-established biostratigraphic correlation charts, I revised the stratigraphic assignments of all collections from the Ediacaran into the earliest Ordovician. I use sampling-standardized analyses of fossil occurrence data to derive accurate time series of alpha, beta, and gamma diversity. The vetted data demonstrate a prominent diversity peak in Stage 3, which is roughly equivalent to the Siberian Atdabanian and most of the Siberian Botomian. As diversity stabilized or declined subsequently, I conclude that Cambrian radiation only spanned the first three Cambrian stages in terms of biodiversity at the genus level. I assess how the overall increase in global diversity was partitioned between within-community (alpha) and between-community (beta) components and how beta diversity was partitioned among environments and geographic regions. Alpha and beta diversity increased from the Fortunian to Stage 3, and fluctuated erratically through the following stages. Changes of Cambrian gamma diversity were chiefly driven by changes in beta diversity. The pattern of diversity partitioning along onshore-offshore gradients demonstrate that there is no clear trend. Major ecological innovations appeared randomly with respect to bathymetric gradients and the variation of genus turnover between communities was not governed by environmental heterogeneity. My study elucidates that global biodiversity during the Cambrian radiation was driven by niche contraction at local scales and vicariance at continental scales. At local scales, the combined trajectories of alpha and beta diversity during the initial diversification suggest low competition and high predation within communities. At continental scales, the increase of beta diversity was controlled by the high rate of community turnover among adjacent continents. Beta diversity has similar trajectories both among environments and geographic regions, but turnover between adjacent paleo-continents was probably the main driver of diversification. This finding supports the general importance of plate tectonics in large-scale diversifications.
Author: Na Lin
Language: English
Subfield: Paleontology
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W3213974595