Interglacials and Glacials - Natural Experiments in Biodiversity Dynamics

There are three major ecological hypotheses to explain plant community composition and structure: 1) external, or extrinsic, environmental control (e.g. climate change), 2) internal, or intrinsic, species interactions (e.g. competition, facilitation), and 3) neutral dynamics, random processes, and historical legacies. Testing of these hypotheses requires long-term observational data on community composition over several hundred thousand years or even the last 1-2 million years. During such periods, Earth has experienced major climatic shifts from temperate interglacial stages (we live in the latest interglacial) to cool, often dry, glacial 'ice-age' stages. Due to advances in our knowledge about past vegetation and improvements in Quaternary chronology, continuous records of vegetation change through alternating interglacial and glacial stages from Greece, France, and Colombia are now available. Each of these records provides a unique long-term ecological observatory. The changes from glacial to interglacial conditions are a series of 'natural experiments' on the vegetation and ecology. The IGNEX project used numerical methods to detect major recurring patterns of vegetation change, taxonomic diversity, and compositional turnover for each interglacial, for each glacial-interglacial pair, and for all interglacials. Results from these analyses have permitted testing of three previously unexplored hypotheses: 1) that 'historical legacies' are important in long-term vegetation dynamics - they are, 2) that interglacials differ in their composition and biodiversity - they do, and 3) that plant communities have long temporal continuity - no, they do not. Testing these hypotheses is important in establishing 'baseline conditions' for restoration ecology, in predicting biotic responses to future environmental change, and in providing a factual basis for future conservation. The project involved 18 researchers from eight countries.

The creation by Dr Blas Benito of three R packages that have scope beyond the IGNEX project 1) distantia: assessing dissimilarity between multivariate time series. https://cran.r-project.org/web/packages/distantia/index.html 2) memoria: quantifying ecological memory in palaeoecological datasets and other long time-series. https://CRAN.R-project.org/package=memoria 3) virtualPollen: simulating pollen curves from virtual taxa with different life and niche traits. https://CRAN.R-project.org/package=virtualPollen

There are three major ecological hypotheses to explain community structure - extrinsic environment control, intrinsic interactions, and neutral dynamics. Testing of these requires long-term data that, thanks to major advances in Quaternary science and geochronology, are available from continuous sequences of alternating interglacial and glacial stages from Greece, NE Russia, and Colombia, covering the last 3.5 million years. Numerical methods are used to detect major compositional patterns, taxonomic, functional, and phylogenetic diversity, and compositional turnover for each interglacial and glacial-interglacial couplet. Results from these analyses will permit the testing of the three major ecological hypotheses: 1) that contingency ('historical legacies') is important in long-term dynamics, 2) that interglacials differ in their composition and biodiversity, and 3) that vegetational assemblages have no long temporal continuity. The project consists of 14 researchers and two MSc students from six countries.