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

• Published in: Paleobiology Vol. 49; no. 1; pp. 77 - 98
• Main Authors: Kearns, L. E., Bohaty, S. M., Edgar, K. M., Ezard, T. H. G.
• Format: Journal Article
• Language: English
• Published: New York, USA The Paleontological Society 01.02.2023; Cambridge University Press; Paleontological Society
• Subjects: Additives; Anthropogenic factors; Atlantic Ocean; Biodiversity; Cenozoic; Climate change; communities; Community structure; Divergence; Eocene; Expedition 342; faunal studies; Fluctuations; Foraminifera; Fossil foraminifera; Fossils; habitat; Human influences; Integrated Ocean Drilling Program; invertebrate; IODP Site U1406; IODP Site U1408; IODP Site U1410; microfossils; middle Eocene; North Atlantic; paleo-oceanography; paleoclimatology; paleoecology; Paleogene; Paleontology; planktonic taxa; Sampling; size; statistical analysis; Taxonomy; Tertiary
• ISSN: 0094-8373; 1938-5331
• DOI: 10.1017/pab.2022.24

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.