Small but mighty: how overlooked small species maintain community structure through middle Eocene climate change

Abstract

Understanding current and future biodiversity responses to changing climate is pivotal as anthropogenic climate change continues. This understanding is complicated by the multitude of available metrics to quantify dynamics and by biased sampling protocols. Here, we investigate the impact of sampling protocol strategies using a data-rich fossil record to calculate effective diversity using Hill numbers for the first time on Paleogene planktonic foraminifera. We sample 22,830 individual tests, in two different size classes, across a 7 Myr time slice of the middle Eocene featuring a major transient warming event, the middle Eocene climatic optimum (MECO; ~40 Ma), at study sites in the midlatitude North Atlantic. Using generalized additive models, we investigate community responses to climatic fluctuations. After correcting for any effects of fossil fragmentation, we show a peak in generic diversity in the early and middle stages of the MECO as well as divergent trajectories between the typical size-selected community (>180 μm) and a broader assemblage, including smaller genera (>63 μm). Assemblages featuring smaller genera are more resilient to the climatic fluctuations of the MECO than those assemblages that feature only larger genera, maintaining their community structure at the reference Hill numbers for Shannon's and Simpson's indices. These results raise fundamental questions about how communities respond to climate excursions. In addition, our results emphasize the need to design studies with the aim of collecting the most inclusive data possible to allow detection of community changes and determine which species are likely to dominate future environments.

Paleoecology and evolutionary response of planktonic foraminifera to the mid-Pliocene Warm Period and Plio-Pleistocene bipolar ice sheet expansion

“…Their calcareous skeletons, or tests, preserve not only their entire life history, but also a biogeochemical expression of the surrounding water column (e.g., Edgar et al, 2017). These features allow for high-resolution species-specific quantification of physiological and ecological adaptation through periods of climate variability (e.g., Knappertsbusch, 2007;Wade et al, , 2016Hull and Norris, 2009;Wade and Olsson, 2009;Edgar et al, 2013a;Aze et al, 2014;Pearson and Ezard, 2014;Weinkauf et al, 2014Weinkauf et al, , 2019Brombacher et al, 2017aBrombacher et al, , 2021Falzoni et al, 2018;Si and Aubry, 2018;Fox et al, 2020;Todd et al, 2020;Kearns et al, 2021Kearns et al, , 2022Pearson and Penny, 2021;Shaw et al, 2021;Woodhouse et al, 2021;Friesenhagen, 2022;Hupp et al, 2022;Woodhouse and Swain et al, 2023).…”