Common species link global ecosystems to climate change: dynamical evidence in the planktonic fossil record

Abstract

Common species shape the world around us, and changes in their commonness signify large-scale shifts in ecosystem structure and function. However, our understanding of long-term ecosystem response to environmental forcing in the deep past is centred on species richness, neglecting the disproportional impact of common species. Here, we use common and widespread species of planktonic foraminifera in deep-sea sediments to track changes in observed global occupancy (proportion of sampled sites at which a species is present and observed) through the turbulent climatic history of the last 65 Myr. Our approach is sensitive to relative changes in global abundance of the species set and robust to factors that bias richness estimators. Using three independent methods for detecting causality, we show that the observed global occupancy of planktonic foraminifera has been dynamically coupled to past oceanographic changes captured in deep-ocean temperature reconstructions. The causal inference does not imply a direct mechanism, but is consistent with an indirect, time-delayed causal linkage. Given the strong quantitative evidence that a dynamical coupling exists, we hypothesize that mixotrophy (symbiont hosting) may be an ecological factor linking the global abundance of planktonic foraminifera to long-term climate changes via the relative extent of oligotrophic oceans.

Reliable estimates of beta diversity with incomplete sampling

“…In spite of its simplicity, this metric correlates well (albeit negatively) with other diversity indices that incorporate more information (Kowalewski et al 2006) but does not require identification and counting of all species in a community. The Berger-Parker index emphasizes dominance, and dominant species are widely recognized to control community structure and ecosystem functioning in modern (Caruso et al 2007) and fossil communities (Hannisdal et al 2017). Another aspect that supports our emphasis on the important role of abundant species is the volatility of species richness with respect to sampling technique and intensity.…”

“…For example, Shannon entropy is a widely used abundance-based diversity index that incorporates both species richness and evenness (e.g., Sanders 1968). The Berger-Parker index emphasizes dominance, and dominant species are widely recognized to control community structure and ecosystem functioning in modern (Caruso et al 2007) and fossil communities (Hannisdal et al 2017). For example, the Margalef index (Margalef 1958) only requires the total number of species and specimens in a community, assuming a log-series rank-abundance distribution.…”

How should we estimate diversity in the fossil record? Testing richness estimators using sampling‐standardised discovery curves

“…SQS has recently been criticised for tracking evenness (Hannisdal, Haaga, Reitan, Diego, & Liow, 2017). In fact, among-sample variation in evenness will confound any richness estimator that implicitly or explicitly utilises information about relative frequencies of taxa (see also Kosnik & Wagner, 2006).…”

Evidence for Trait-Based Dominance in Occupancy among Fossil Taxa and the Decoupling of Macroecological and Macroevolutionary Success

“…Note that this is essentially the numerator for measures of occupancy in other paleobiological studies (e.g., Carotenuto et al 2010;Liow 2013;Hannisdal et al 2017), which divide sites occupied by the total possible sites occupied for an interval. However, variation in how researchers delimit fossil localities and sample areas with fossils means that raw occurrence numbers might misrepresent occupancy.…”