Diversity of Life through Introductory article Time Article Contents . Diversification of Life Carl Simpson, Museum fu¨rNaturkunde,Berlin,Germany . Calibrating Global Diversity Trends . Patterns – Marine and Terrestrial Wolfgang Kiessling, Museum fu¨rNaturkunde,Berlin,Germany . What Causes Global-Scale Biotic Transitions? Based in part on the previous version of this Encyclopedia of Life Sciences . Limits to Diversity – Equilibrium and Expansion Models (ELS) article, Diversity of Life through Time by Arnold I Miller. Local and Regional Patterns . Sources of Biodiversity . Radiations Online posting date: 15th November 2010 Global diversity is the total number of taxa living in the biodiversity changes in the past will help us to understand present day or at any time in the geological past. Recon- fate of biodiversity in the face of human-induced changes structing the trajectory of global diversity by compiling to the planet. Many human-induced changes to the Earth data from the fossil record has been a major research have natural analogues in the geological past (e.g. intervals of global warming or ocean acidification); analyses of past agenda for palaeontologists for decades. The goal is to biodiversity during times of known environmental change produce an accurate reconstruction of the pattern of can help us predict how diversity will be affected by current global diversity that will ultimately allow us to under- environmental changes. Researchers seeking to determine stand the causes of diversity increases, decreases and whether the Earth is currently experiencing a mass extinc- transitions in the composition of the biota. The Paleo- tion of species have looked at the history of biodiversity biology Database, a new large-scale database based on for insights into levels of diversification and extinction individual collections of fossil taxa, allows palaeontolo- expected ‘naturally’, in a world not influenced unduly by gists to standardise sampling, thereby controlling for Homo sapiens. Palaeontologists unravel these processes vagaries of the fossil record. Collection-level data also by focusing on how global diversity changed over time and allows researchers to identify any asynchrony of changes applying statistical methods of sampling standardisation. in diversity among regions of the globe, with the ultimate See also: Adaptive Radiation; Conservation Biology and Biodiversity; Extinction; History of Biogeography; goal of identifying the habitats or environments that Macroevolution: Overview support biodiversity growth. Calibrating Global Diversity Trends Diversification of Life Sampling global diversity past and present Global diversity is a simple number to wrap our minds For decades, palaeontologists have worked hard to around. Arriving at this number, however, is challenging, reconstruct the pattern of global diversity through geo- even for taxa alive today. There is no way to count all logical time. This endeavour, when it produces biologically species without identifying each one; therefore, current meaningful trajectories, offers a plethora of insights not biodiversity estimates are done by extrapolating from well- only about the history of life but also about evolutionary sampled collections. Estimating biodiversity in the past has processes. The fossil record is the only source available for similar problems as well as others that come from the fossil understanding the long-term consequences to biodiversity record itself. Up to the end of the twentieth century, of physical perturbations to the Earth at local, regional and palaeontologists have largely taken the fossil record at face global scales. Because of this, understanding the causes of value and relied on compendia of the oldest and youngest known global occurrences of individual taxa to construct diversity curves. The results from these compilations have ELS subject area: Evolution and Diversity of Life shaped our view on the history of diversification and mass extinctions, which are depicted in most textbooks on evo- How to cite: lution. It has long been realised that a database of indi- Simpson, Carl; and Kiessling, Wolfgang (November 2010) Diversity of vidual fossil occurrences and their geological context Life through Time. In: Encyclopedia of Life Sciences (ELS). John Wiley & would offer superior opportunities to elucidate biologically Sons, Ltd: Chichester. meaningful diversity trajectories. But the task is huge. The DOI: 10.1002/9780470015902.a0001636.pub2 Paleobiology Database (PaleoDB, http://paleodb.org) was ENCYCLOPEDIA OF LIFE SCIENCES & 2010, John Wiley & Sons, Ltd. www.els.net 1 Diversity of Life through Time founded in 2000 to get a more reliable picture of diversity Counting methods and sampling through time as well as answer other questions that standardisation were previously impossible to address. The PaleoDB is currently being developed by the joint effort of approxi- The method used to count taxa in each time interval can mately 240 palaeontologists from 20 countries. The drastically influence the pattern of diversity. The role of primary data used to construct diversity curves with the counting methods in diversity curves was not fully appre- Paleobiology Database are the number of times a fossil ciated until occurrence-based data sets allowed a com- taxon is sampled in each time interval. This occur- parison of methods. Early compendia – which recorded rence-based approach is a powerful way to evaluate and only the oldest and youngest known global occurrences of control for any biases in sampling and led to a more robust individual taxa – assume that each taxon was extant for the estimate of global diversity. See also: Geological Time: entire interval between its first and last occurrences. With Dating Techniques; Geological Time: Principles; History this data structure, a simple tabulation of the number of of Palaeontology taxa alive in each interval will be strongly affected by what Experience has shown that it is usually not practical to palaeontologists know as the ‘Pull of the Recent’ (Raup, assess ancient diversity at the species level: there is too 1979). The record of extant taxa is many times better than much uncertainty about species-level identification in in any time of the past. Thus, all extant taxa with any fossil many cases, and the sheer number of fossil species cata- record, if only found in exceptionally preserved sites, will logued in the literature is daunting. Although there have contribute to the cumulative diversity after their oldest been attempts to construct global diversity curves at the occurrence, whereas extinct taxa can only contribute if species level (e.g. Janevski and Baumiller, 2009), these are both their oldest and youngest occurrences are known. The currently not deemed reliable because they are based on overprint of the Pull of the Recent can mask important either extrapolation or raw counts. Thus, global diversity changes in global diversity, so that even if diversity is truly compendia and curves have usually been constructed at unchanging or even declining, apparent diversity would the higher taxonomic levels of family or genus, with the seem to increase only due to the Pull of the Recent. A inference that their most salient features would also have primary concern in the development of counting methods been observed at the species level. However, in the new has been the elimination of these types of methodological occurrence-based databases, all taxonomic information is biases. recorded for each collection, and therefore, the diversity How global diversity patterns are tabulated depends on can be analysed at any taxonomic level. As the infor- the basic data recorded for each taxon. With occurrence- mation contained in the PaleoDB grows, our ability to based data, diversity in a time interval is simply the number obtain an accurate estimate of species-level diversity will of taxa that have actually been sampled, a method known increase. as ‘sampled-in-bin’ (Alroy et al., 2008). This counting The fossil record does not record always a high-fidelity method produces diversity curves with high short-term sample of taxa alive in the past. Because the pattern of variation, because taxa that actually lived during the taxonomic diversity through the Phanerozoic eon is interval but not sampled are not counted. Therefore, a derived from the fossil record, the quality of the fossil small correction is usually added; by counting taxa that are record itself can influence our estimates of diversity. found in the interval immediately before and after an Most notably, researchers interested in the diversity of interval but not inside it, we can account for those taxa that marine (ocean dwelling) organisms have long worried can be reliably inferred to be present in that time. Other that changes through time in the volume of sedimentary sampling issues, like variation in rock volume and research strata – the kinds of strata likely to contain fossils – are intensity, can be controlled for by using sample standard- correlated directly with perceived levels of biodiversity. ised sampled-in-bin counts. All else being equal, stratigraphic intervals containing In order to compare diversity counts between different larger volumes of sedimentary rock would be expected to time intervals, the amount of sampling in each interval contain more fossils and, therefore, a greater number of must be comparable. This is because the number of taxa fossil taxa. David Raup showed in 1976 that the Pha- found in a sample is not a linear function