Measures of species diversity and levels of endemism are important components in determining conservation priorities. In numerous countries, islands and biomes, biological exploration has advanced considerably since 1980 and ongoing field inventories, combined with systematic studies using classical techniques and more modern molecular biology, are modifying previous estimates of biotic diversity, such as those concerning endemism and species richness. With almost unparalleled levels of endemism, species diversity and human threat, Madagascar is one of the most critical global priorities for conservation, and has been designated one of the most important biodiversity hotspots (Myers et al., Reference Myers, Mittermeier, Mittermeier, da Fonseca and Kent2000; Groombridge & Jenkins, Reference Groombridge and Jenkins2002). This island nation, with a surface area of 594,150 km², retains, depending on definitions and analyses, between 15% and < 10% of the natural forests that existed before human colonization (Vieilledent et al., Reference Vieilledent, Grinand, Rakotomalala, Ranaivosoa, Rakotoarijaona, Allnutt and Achard2018; Global Forest Watch, 2022), estimated by some scholars to have been > 10,000 years ago (Hansford et al., Reference Hansford, Wright, Rasoamiaramanana, Perez, Godfrey and Errickson2018; Godfrey & Douglass, Reference Godfrey, Douglass and Goodman2022). Of particular importance associated with conserving the forest-dwelling biota of Madagascar is that the annual deforestation rate during 2010–2014 was nearly 100,000 ha/year, and nearly half of the remaining forest area is located < 100 m from the forest edge (Vieilledent et al., Reference Vieilledent, Grinand, Rakotomalala, Ranaivosoa, Rakotoarijaona, Allnutt and Achard2018).

Since the 1980s, considerable advances have been made in biological research on Madagascar, including the exploration of scientifically unknown or poorly known areas, and subsequent studies of associated specimens. As previously summarized by Goodman & Benstead (Reference Goodman and Benstead2005) based on The Natural History of Madagascar (Goodman & Benstead, Reference Goodman and Benstead2003), for a country such as Madagascar, with its considerable and poorly documented levels of biotic diversity and endemism, the measures used in biodiversity analyses are in constant need of revision. However, given the remarkable number of new species being described across a wide variety of taxonomic groups and considerable changes in geographical distribution, it is difficult for any single research team to maintain up-to-date data for the island. The recalculation of these values depends on the hundreds of specialists working on the island's biota. The recent publication of The New Natural History of Madagascar (Goodman, Reference Goodman2022), a synthesis by 539 contributors from a range of disciplines, provides the means to update these estimates. Here, I give revised data for species richness and endemism of a wide variety of marine and terrestrial taxonomic groups on Madagascar (Table 1; comparisons between the 2003 and 2022 books are only for groups treated in both volumes).

Table 1 Estimates of species richness and endemism (where available) of Malagasy plants and animals over the course of nearly 2 decades. The 2003 data are from The Natural History of Madagascar (Goodman & Benstead, Reference Goodman and Benstead2003), and those of 2022 from The New Natural History of Madagascar (Goodman, Reference Goodman2022), and sources (author names and associated page numbers) within each of these volumes are given. Species tallies from 2022 that are preceded by an asterisk (*) include confirmed candidate species. In most cases the 2022 data were tabulated in 2020 or the first half of 2021 and for certain groups there has been the subsequent description of new species, the majority being endemics.

¹Concerns bamboos in the Bambusoideae.

For many marine organisms occurring within Malagasy waters, with a few exceptions, the current state of knowledge is still insufficient to estimate species richness. There appear, however, to be few local marine endemics, although at a regional level (western Indian Ocean) the numbers are higher. Earlier assessments of the vascular plant diversity suggested 10,000–12,000 species (Koechlin et al., Reference Koechlin, Guillaumet and Morat1974; Phillipson, Reference Phillipson, Davis, Heywood and Hamilton1994; Schatz et al., Reference Schatz, Lowry, Lescot, Wolf, Andriambololonera, Raharimalala, Raharimampionona, van der Maesen, van der Burgt and van Medenbach de Rooy1996), with rates of endemism of c. 85%. A more recent estimate is 14,000 species and endemism of nearly 87% (Lowry et al., Reference Lowry, Phillipson, Andriamahefarivo, Schatz, Rajaonary, Andriambololonera, Goodman, Raherilalao and Wohlhauser2018), with even higher endemism amongst trees and large shrubs. On the basis of the nine plant families covered in both books (Table 1), the level of endemism in 2003 for these groups was 92%, and 90% in 2022. For these nine families, 677 species new to science have been described, with 573 endemic. For the 21 non-marine invertebrate groups covered in both books, endemism in 2003 (slightly > 5,800 species) was 86% and in 2022 (slightly < 10,570 species) it was 91%. For virtually all groups covered in both books, there were notable increases in species diversity, but these were most dramatic in ants, with an additional 859 species (93% endemics), and in terrestrial snails, with 452 new species (93% endemics). With these increases in species diversity, as well as in other invertebrate groups such as spiders, millipedes and caddisflies, it is clear that large-scale inventories and subsequent systematic studies of the island's invertebrates (Fisher, Reference Fisher and Goodman2022) are making important contributions to improving knowledge of these groups.

Madagascar's vertebrate fauna has received considerable attention from field biologists, taxonomists and the conservation community. The data from the 2003 book included 879 land vertebrates, with 739 (84%) endemic. In the 2022 book, the total is 1,234, of which 1,100 (89%) are endemic; when breeding birds (52% endemic) are excluded from these comparisons, rates of endemism rise to 97%. A total of 339 new species of endemic Malagasy land vertebrates were described as new to science between 2003 and 2022 (Fig. 1). For terrestrial vertebrates, rates of endemism are 95–100%, and those for flying vertebrates (bats and birds) are 52–78%.

Fig. 1 The number of endemic non-marine vertebrate species described as new to science between 2003 and 2021, in 5-year intervals (4 years for 2018–2021). The levels of endemism for each group and associated acronyms are: F, freshwater fishes (69%); A, amphibians (99%); R, reptiles (95%); B, birds (52%); TM, non-primate terrestrial mammals (100%); P, primates (100%); Bt, bats (78%). Confirmed candidate species are not included in these calculations.

Since 2003, there has been a dramatic increase in the number of Malagasy researchers undertaking field studies and students presenting higher degrees in the national university system in fields related to conservation biology. For example, in the botany chapter of the 2003 book, the number of contributions with Malagasy authors was 6 of 45 (13%), with a total of 15 Malagasy co-authors; in the 2022 book, these figures are, respectively, 20 of 45 (40%) and 47 Malagasy co-authors (Gautier et al., Reference Gautier, Lowry, Goodman and Goodman2022). The same pattern occurs in the mammal chapters, with < 12% of the contributors being Malagasy in the 2003 book, and 45% in the 2022 book (Goodman & Soarimalala, Reference Goodman, Soarimalala and Goodman2022).

The data presented here further highlight Madagascar as a critical component of our global biological heritage. An overwhelming majority of the island's terrestrial species occur in the original and widely differing forest formations. These forests are shrinking at an alarming rate (Vieilledent et al., Reference Vieilledent, Grinand, Rakotomalala, Ranaivosoa, Rakotoarijaona, Allnutt and Achard2018; Global Forest Watch, 2022) and are clearly in need of conservation action, which needs a multifaceted approach to be effective (Jones et al., Reference Jones, Rakotonarivo, Razafimanahaka and Goodman2022). Major advances in the park and reserve system have been made over the past 2 decades, which in 2003 included 46 legally protected areas, comprising c. 17,000 km² or 3% of the island's land area (Randrianandianina et al., Reference Randrianandianina, Andriamahaly, Harisoa, Nicoll, Goodman and Benstead2003). By 2018 the number of protected areas increased to 122, comprising nearly 12% of the island (Ranivo Rakotoson & Razafimahatratra, Reference Ranivo Rakotoson, Razafimahatratra, Goodman, Raherilalao and Wohlhauser2018). Although it is important not to disregard various historical and modern problems in the maintenance of the unique biodiversity of Madagascar represented in these protected areas (Gardner et al., Reference Gardner, Nicoll, Birkinshaw, Harris, Lewis, Rakotomalala and Ratsifandrihamana2018; Jones et al., Reference Jones, Rakotonarivo, Razafimanahaka and Goodman2022), remarkable progress has been made over the past 2 decades in the network of marine and terrestrial sites.