Robert Whittaker (ecologist) in the context of Ecological Society of America

Lynn Margulis (born Lynn Petra Alexander; March 5, 1938 – November 22, 2011) was an American evolutionary biologist, who was the primary modern proponent for the significance of symbiosis in evolution. In particular, Margulis transformed and fundamentally framed biologists' understanding of the evolution of the Eukaryotes, organisms with nuclei in their cells. She proposed that they came into being by symbiotic mergers of bacteria. Margulis was the co-developer of the Gaia hypothesis with the British chemist James Lovelock, proposing that the Earth functions as a unified self-regulating system, and the principal defender and promulgator of the five kingdom classification of Robert Whittaker.

Throughout her career, Margulis' work could arouse intense objections, and her formative paper, "On the Origin of Mitosing Cells", appeared in 1967 after being rejected by about fifteen journals. Still a junior faculty member at Boston University at the time, her theory that cell organelles such as mitochondria and chloroplasts were once independent bacteria was largely ignored for another decade, becoming widely accepted only after it was powerfully substantiated through genetic evidence. Margulis was elected a member of the US National Academy of Sciences in 1983. President Bill Clinton presented her the National Medal of Science in 1999. The Linnean Society of London awarded her the Darwin-Wallace Medal in 2008.

Monera (/məˈnɪərə/) (Greek: μονήρης (monḗrēs), "single", "solitary") is historically a biological kingdom that is made up of unicellular prokaryotes. As such, it is composed of single-celled organisms that lack a nucleus.

The taxon Monera was first proposed as a phylum by Ernst Haeckel in 1866. Subsequently, the phylum was elevated to the rank of kingdom in 1925 by Édouard Chatton. The last commonly accepted mega-classification with the taxon Monera was the five-kingdom classification system established by Robert Whittaker in 1969.

Coccolithophores, or coccolithophorids, are single-celled organisms which are part of the phytoplankton, the autotrophic (self-feeding) component of the plankton community. They form a group of about 200 species, and belong either to the kingdom Protista, according to Robert Whittaker's five-kingdom system, or clade Hacrobia, according to a newer biological classification system. Within the Hacrobia, the coccolithophores are in the phylum or division Haptophyta, class Prymnesiophyceae (or Coccolithophyceae). Coccolithophores are almost exclusively marine, are photosynthetic and mixotrophic, and exist in large numbers throughout the sunlight zone of the ocean.

Coccolithophores are the most productive calcifying organisms on the planet, covering themselves with a calcium carbonate shell called a coccosphere. It is formed when a cell arrange a series of interlocking coccoliths to completely cover its surface. Coccoliths (minute calcium carbonate platelets) are generated within the cell, suggesting that the cell diameter cannot be exceeded by the maximum coccolith size. In addition, coccolith size and the orientation of calcite crystals forming coccoliths can vary among species. Although the interlocking structure of coccoliths offers strong mechanical protection for cell, the specific topology of the coccoliths (the way they interconnect within the coccosphere) and the mechanisms governing their arrangement remain unclear. One key function may be that the coccosphere offers protection against microzooplankton predation, which is one of the main causes of phytoplankton death in the ocean.

The initial version of a classification system of life by British zoologist Thomas Cavalier-Smith appeared in 1978. This initial system continued to be modified in subsequent versions that were published until he died in 2021. As with classifications of others, such as Carl Linnaeus, Ernst Haeckel, Robert Whittaker, and Carl Woese, Cavalier-Smith's classification attempts to incorporate the latest developments in taxonomy. Cavalier-Smith used his classifications to convey his opinions about the evolutionary relationships among various organisms, principally microbial. His classifications complemented his ideas communicated in scientific publications, talks, and diagrams. Different iterations might have a wider or narrow scope, include different groupings, provide greater or lesser detail, and place groups in different arrangements as his thinking changed. His classifications has been a major influence in the modern taxonomy, particularly of protists.

Cavalier-Smith has published extensively on the classification of protists. One of his major contributions to biology was his proposal of a new kingdom of life: the Chromista, although the usefulness of the grouping is questionable given that it is generally agreed to be an arbitrary (polyphyletic) grouping of taxa. He also proposed that all chromista and alveolata share the same common ancestor, a claim later refuted by studies of morphological and molecular evidence by other labs. He named this new group the Chromalveolates. He also proposed and named many other high-rank taxa, like Opisthokonta (1987), Rhizaria (2002), and Excavata (2002), though he himself consistently does not include Opisthonkonta as a formal taxon in his schemes. Together with Chromalveolata, Amoebozoa (he amended their description in 1998), and Archaeplastida (which he called Plantae since 1981) the six formed the basis of the taxonomy of eukaryotes in the middle 2000s. He has also published prodigiously on issues such as the origin of various cellular organelles (including the nucleus, mitochondria), genome size evolution, and endosymbiosis. Though fairly well known, many of his claims have been controversial and have not gained widespread acceptance in the scientific community to date. Most recently, he has published a paper citing the paraphyly of his bacterial kingdom, the origin of Neomura from Actinobacteria and taxonomy of prokaryotes.

In ecology, beta diversity (β-diversity or true beta diversity) is the ratio between regional and local species diversity. The term was introduced by R. H. Whittaker together with the terms alpha diversity (α-diversity) and gamma diversity (γ-diversity). The idea was that the total species diversity in a landscape (γ) is determined by two different things: the mean species diversity at the local level (α) and the differentiation among local sites (β). Other formulations for beta diversity include "absolute species turnover", "Whittaker's species turnover" and "proportional species turnover".

Whittaker proposed several ways of quantifying differentiation, and subsequent generations of ecologists have invented more. As a result, there are now many defined types of beta diversity. Some use beta diversity to refer to any of several indices related to compositional heterogeneity. Confusion is avoided by using distinct names for other formulations.

In ecology, gamma diversity (γ-diversity) is the total species diversity in a landscape. The term was introduced by R. H. Whittaker together with the terms alpha diversity (α-diversity) and beta diversity (β-diversity). Whittaker's idea was that the total species diversity in a landscape (γ) is determined by two different things, the mean species diversity in sites at a more local scale (α) and the differentiation among those sites (β). According to this reasoning, alpha diversity and beta diversity constitute independent components of gamma diversity: