3 Current estimates of the total number of species

Over 1.8 million species have been described so far in the Catalogue of Life [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] , but estimates of the total number of species on Earth range very widely (Catalogue of Life, 2019). There have been estimates in the region of 8 million total species on Earth if microorganisms such as bacteria are excluded, rising to 1 trillion( NSF, 2016) or 2 billion if they are included (Brendan et al., 2017). The proportion of species that have so far been described compared with the total global estimate of the number of species varies between groups. For example, almost all mammals, birds and reptiles have been described but only about one in five insects have a description (Chapman, 2009).

Once an organism has been identified as being of a certain species, it is often possible to look up a whole range of ecological information about that species. You will learn more about this in Week 6. There are now many online databases and scientific publications that can provide detailed information on many of the named species. For example, a web search of the harlequin ladybird (Harmonia axyridis) not only shows a very wide range of colours and patterns displayed by this species but also indicates its life history, potential problems caused by its invasive nature, its native and non-native range, and links to many scientific papers on the species.