'Species' is just a word, one that can be defined in many different ways. This lessons defines biological, ecological, morphological, and phylogenetic species concepts.
What Is a Species?
What is a species? This seems like a really silly question. I mean, we've all come to expect that a species is basically a group of individuals with some sort of common characteristics or qualities or something similar to that. Of course, therein lies the problem: it's some sort of common quality. But, which one quality, characteristic, or factor unites a group of living things into a species? It turns out, there's more than one answer! And, thus, there's more than one way to look at and define a species.
Biological Species Concept
The most common way biologists define a species is known as the biological species concept, a concept where a species is defined as a population or a group of populations whose members have the potential to interbreed in nature and produce viable as well as fertile offspring, but are not able to breed with or produce viable offspring with members of another species.
One key word is potential - the potential to interbreed and produce viable offspring. This doesn't mean they have to do so. What I mean is, if you live in London, but a member of the opposite sex lives in Buenos Aires, you may never meet to have kids, but you theoretically do have the potential to have children.
But, if you live in sub-Saharan Africa next to a multitude of wild animals, you might be right next to them, but for various reasons will not be able to breed with or produce viable offspring with all of these different animals. The potential doesn't exist even though the proximity is not an issue.
Ecological Species Concept
Another kind of definition of species is the ecological species concept, a concept that defines species as a set of organisms that exploit or are adapted to a particular niche, meaning it's how members of a species interact with all aspects of their environment, be it living or nonliving. What this means is that two species of pine may have different sizes, growth rates, and ability to tolerate droughts or heat based on their particular resources and environment, but they can still interbreed with one another on occasion.
Another example may be two species of mice that look the same, but eat different foods and tolerate different levels of heat based on their ecological niche. Even though gene flow during reproduction may occur in these two examples between the respective species in question, because they live in different ecological niches, they are considered different species in this concept nonetheless.
Morphological Species Concept
Sometimes, the information on gene flow within and between species is unknown. In these cases, biologists may use the morphological species concept, a concept that characterizes a species based on its structural features like body shape. When is this beneficial? Fossils are a good example. We may not have enough information about a long-extinct species to figure out gene flow patterns or even the ecological niches the extinct species may or may not have shared.
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All scientists may have to go on is how a skull was shaped or how the pelvis was shaped or how the teeth were arranged, or something similar. And so, the species are arranged based on morphology, their looks. While this species concept is great in classifying fossils or even asexual organisms, it is quite subjective, and scientists may disagree on which structural features should actually identify a species.
Phylogenetic Species Concept
And, finally, for our lesson, the last kind of species concept I want to define is the phylogenetic species concept, a concept that defines species as the most irreducible group of individuals that share a common ancestor, meaning this group of individuals forms a single branch on the tree of life and, thus, views a species as a group of individuals that share a recent and unique evolutionary history with one another.
There are tons of other ways a species can be define, but we covered four big ones:
The biological species concept is a concept where a species is defined as a population or a group of populations whose members have the potential to interbreed in nature and produce viable, as well as fertile, offspring, but are not able to breed with or produce viable offspring with members of another species.
The ecological species concept is a concept that defines species as a set of organisms that exploit or are adapted to a particular niche.
The morphological species concept is a concept that characterizes a species based on its structural features, like body shape.
The phylogenetic species concept is a concept that defines species as the most irreducible group of individuals that share a common ancestor.
What Makes a Species?
When a group of individuals share common characteristics, they are often identified as a species, but the word itself is vague. What characteristics link them together? Which aspects will prevent them from belonging to a species? In biology, the categorization of species has different criteria around which to organize.
After reviewing this lesson, you should be able to describe the four different species concept models.
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