Biodiversity – Species
This Blog post #3 is entitled: Biodiversity – Species. It follows our last post #2: “Biodiversity – Variety of Life” of this Biodiversity series.
“The Hidden Universe”
This post #3, Biodiversity – Species, of our Biodiversity blog series is inspired by Chapter 1 of Part One of Alexandre Antonelli’s book, “The Hidden Universe: Adventures in Biodiversity“.
Part One of his book is entitled, “Biodiversity: More Than Meets the Eye’, and his Chapter 1 is entitled, ‘Species’.
Definitions of Species
What is a species?
Oxford English Dictionary
We refer to the definition in the “Concise Oxford English Dictionary“, Edition 12, for the biological sense of the word, ‘species’:
species n. (pl. same) 1 [Biology] a group of living organisms consisting of similar individuals capable of exchanging genes or of interbreeding, considered as the basic unit of taxonomy and denoted by a Latin binomial, e.g. Homo sapiens.
Wikipedia
Next, we go to Wikipedia to ask what a ‘species‘ is:
“a species is the eighth major taxonomic rank in Life’s hierarchy of biological classification” (as defined by biologists), “as well as being a unit of biodiversity.”
The Wikipedia article further explains:
“It can be defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction.”
But as the article goes on to explain, the definition is more complex than that.
Further Reading
We shall leave the reader to explore the details of the definition of ‘species’ in the Wikipedia article or other reliable research sources. But whether you investigate the definition of “species” further or not, we recommend that you read Antonelli’s definition in his book.
Our preoccupation here, in this post, is to consider the importance of species for biodiversity as we continue to review Antonelli’s book.
Biological Classification Hierarchy
Before continuing our post, perhaps we should ask the question, how do species fit into the biological scheme of things?
A ‘species’ is the eighth major taxonomic rank in the hierarchy of biological classification.
The eight major taxonomic ranks of Life are:
- Domain
- Kingdom
- Phylum
- Class
- Order
- Family
- Genus
- Species
We shall leave you to investigate these taxonomic ranks if you wish but it is not necessary for us to discuss them further here.
Species and Biodiversity
Antonelli begins his Chapter 1 “Species” with the following comment:
“Species are the bedrock of the living world. They are equivalent to the bricks of a house, the elements of the periodic table, the keys of a piano. All species have a place in nature; they exist in communities that depend on each other and their physical environment. Yet despite their vital importance, scientists cannot agree on a single definition of what a species is.”
Antonelli, Alexandre. The Hidden Universe: Adventures in Biodiversity (p. 31). Ebury Publishing. Kindle Edition.
Antoinelli’s final comment in his quote, above, is the reason that you may have found slightly differing definitions for “species” in the references that you may have consulted. But the fact that scientists may differ in their opinion does not affect the species themselves, obviously. This is our problem not that of the species.
Antonelli discusses this question of what is a species in more detail in his Chapter 1, giving examples to support his comments.
DNA
He also discusses DNA and its part in distinguishing between closely related species that may have previously been considered the same species.
He mentions that DNA can solve most questions of species identity. One exception is identifying extinct species. He says:
“DNA can now solve most problems of species identification, but not all. One important exception is for species that have gone extinct. DNA invariably degrades with time, and does so faster at higher temperatures. Even under the best preservation conditions, there is an upper theoretical ‘expiry date’ of some 1.5 million years, after which all its pieces will have broken apart.”
Antonelli, Alexandre. The Hidden Universe: Adventures in Biodiversity (p. 34). Ebury Publishing. Kindle Edition.
Antonelli gives several examples of projects involving identification of species, including using both DNA and non-DNA techniques. The examples include mammals, plants, insects, and fungi.
He also discusses the specific interactions between certain plants and their pollinators.
He also mentions that many bacteria species can exchange genes across species which makes DNA less reliable for identifying bacterial species. Some plants are also known to be able to exchange genes across species.
Geography of Life
Under the subheading of “The Geography of Life”, Antonelli tells us that there is work being done by scientists to identify where on the planet different species exist. This work may lead to a species richness database that would enable us to prioritise which regions we ought to protect. Thyis would not be an easy task, he tells us due to the large and complex logistics required. Currently available species information is apparently concentrated along road sides owing to the ease of access provided to investigating scientists by the road network.
He also discusses the “Theory of Island Biogeography” that links the size of an island or habitat to the richness of species possible within that defined area, for various reason that he mentions.
Latitudinal diversity gradient
Antonelli also discusses the “latitudinal diversity gradient“.
Antonelli, Alexandre. The Hidden Universe: Adventures in Biodiversity (p. 41). Ebury Publishing. Kindle Edition.
This is the observed effect that for “most groups of organisms, the closer you get to the equator, the more species you will find.”
He explains the reasons for this effect and gives examples.
End of post #3 of this Biodiversity Series.
Biodiversity – Genes
The next Blog post, #4 of this series, will be entitled: “Biodiversity – Genes” and will be inspired by chapter 2, “Genes”, of Antonelli’s book, “The Hidden Universe: Adventures in Biodiversity”.
(Post updated: 23/01/2026.)