What is the importance of reproductive isolation to the biological species concept?

Recommended textbook solutions

Applications and Investigations In Earth Science

9th EditionDennis G. Tasa, Edward J. Tarbuck, Frederick K. Lutgens

1,295 solutions

Environmental Science for AP

2nd EditionAndrew Friedland, Rick Relyea

965 solutions

Essentials Of Geology

13th EditionDennis G. Tasa, Edward J. Tarbuck, Frederick K. Lutgens

743 solutions

Environmental Science

15th EditionBradley Smith, Eldon D. Enger

427 solutions

Journal Information

TAXON is the leading international journal devoted to systematics, phylogeny and taxonomy of algae, fungi, and plants. It also publishes papers on methodology, botanical history, biography, bibliography and related subjects, opinion pieces, commentaries and new perspectives, and publishes a number of regular columns including Plant Systematics World. TAXON is the only place to publish proposals to amend the International Code of Nomenclature for algae, fungi and plants (except Chapter F - fungi) or nomenclatural proposals.

Publisher Information

Wiley is a global provider of content and content-enabled workflow solutions in areas of scientific, technical, medical, and scholarly research; professional development; and education. Our core businesses produce scientific, technical, medical, and scholarly journals, reference works, books, database services, and advertising; professional books, subscription products, certification and training services and online applications; and education content and services including integrated online teaching and learning resources for undergraduate and graduate students and lifelong learners. Founded in 1807, John Wiley & Sons, Inc. has been a valued source of information and understanding for more than 200 years, helping people around the world meet their needs and fulfill their aspirations. Wiley has published the works of more than 450 Nobel laureates in all categories: Literature, Economics, Physiology or Medicine, Physics, Chemistry, and Peace. Wiley has partnerships with many of the world’s leading societies and publishes over 1,500 peer-reviewed journals and 1,500+ new books annually in print and online, as well as databases, major reference works and laboratory protocols in STMS subjects. With a growing open access offering, Wiley is committed to the widest possible dissemination of and access to the content we publish and supports all sustainable models of access. Our online platform, Wiley Online Library (wileyonlinelibrary.com) is one of the world’s most extensive multidisciplinary collections of online resources, covering life, health, social and physical sciences, and humanities.

Rights & Usage

This item is part of a JSTOR Collection.
For terms and use, please refer to our Terms and Conditions
Taxon © 1964 Wiley
Request Permissions

What makes a species a species? In the following, we will discuss the concept of the biological species, then elaborate on how reproductive barriers relate to the biological species concept, and, finally, compare the concept of the biological species to other species concepts.

What Is the Definition of Species According to the Biological Species Concept?

The biological species concept defines species as populations whose members interbreed and produce viable, fertile offspring.

In nature, members of two different species are reproductively isolated. They may not consider each other as potential mates, their mating may not lead to the formation of a zygote, or they cannot produce viable, fertile offspring.

Viable: Able to sustain life.

Fertile: Able to produce offspring.

Let's Discuss Some Examples in Which the Biological Species Concept is Applied

Despite being an unlikely pair to meet, a dog in Canada and a dog in Japan have the potential to interbreed and produce viable, fertile puppies. They are considered members of the same species.

On the other hand, horses and donkeys can interbreed, but their offspring–mules (Figure 1)–will be infertile and cannot produce offspring. Therefore, horses and donkeys are considered separate species.

Figure 1. Mules are the sterile hybrid offspring of horses and donkeys. Source: Dario urruty, Public domain, via Wikimedia Commons.

How are Reproductive Barriers Related to the Biological Species Concept?

Gene flow is the movement of genetic information from one population of organisms to another. When organisms or gametes enter a population, they may bring new or existing alleles in varying amounts compared to those already present in the population.

Gene flow occurs between populations of the same species but not between populations of different species. Members of a species can interbreed, so the species in its entirety shares a common gene pool. On the other hand, members of different species might be able to interbreed, but they will produce sterile offspring, unable to pass on their genes. Hence, the presence or absence of gene flow can distinguish one species from another.

Reproductive barriers limit or prevent gene flow between different species. Biological species are defined by their reproductive compatibility; we can say that different biological species are distinguishable by their reproductive isolation. Reproductive isolation mechanisms are categorized as either prezygotic or postzygotic barriers:

1. Prezygotic barriers prevent the formation of the zygote. These mechanisms include temporal isolation, geographic isolation, behavioral isolation, and gametic barrier.
2. Postzygotic barriers prevent gene flow after the formation of the zygote, leading to hybrid inviability and hybrid sterility.

Reproductive barriers help define the boundaries of the species as a reproductive community and as a gene pool and maintain the cohesion of the species as a genetic system. Reproductive barriers are why members of a species share more similarities than they do with members of other species.

What are the Advantages and Limitations of the Biological Species Concept?

The biological species concept provides the most widely accepted definition of species.

An advantage of the biological species concept is that it focuses on reproductive isolation, making it simple and easy to apply in some situations. For example, the western meadowlark (Sturnella neglecta) and the eastern meadowlark (S. magna) look very similar. Still, they are two distinct species because, despite their overlapping breeding ranges, the two species do not interbreed (Figures 2-3).

Figures 2The western meadowlark

Figure 3. the eastern meadowlark

In Figures 2-3. The western meadowlark (left) and the eastern meadowlark (right) look similar but are considered two distinct species according to the concept of biological species. Source (left): English: NPS Photo, Public domain, via Wikimedia Commons. Source (right): gary_leavens, CC BY-SA 2.0, via Wikimedia Commons.

However, in other situations, the biological species concept is difficult to apply. The major limitations of the biological species concept are summed up as follows:

1. It is inapplicable to fossil evidence because their reproductive isolation cannot be evaluated.
2. The biological species concept defines species in terms of sexual reproduction, so it does not apply to asexual organismslike prokaryotes or self-fertilizing organismslike parasitic tapeworms.
3. The biological species concept is challenged by the ability of sexual organisms that freely hybridize in the wild but are able to maintain their cohesion as distinct species.

Because of the limitations of the biological species concept, it is considered a working definition. Alternative species concepts are useful in other situations.

What Are Other Definitions of Species?

There are over twenty species concepts, but we will focus on three: the morphological species concept, the ecological species concept, and the phylogenetic species concept. We will also compare each one with the biological species concept.

The Morphological Species Concept

As defined by the morphological species concept, species are distinguished based on their form and structural features.

Biological vs. Morphological Species Concept

Compared to the biological species concept, the morphological species concept is easier to apply in the field because it is based only upon appearance. Additionally, unlike the biological species concept, the morphological species concept is applicable to both asexual and sexual organisms, as well as to fossil evidence.

For example, trilobites are a group of extinct arthropods with over 20,000 species. Their existence can be traced back to around 542 million years ago. The cephalon (head region) or cranidium (central part of the cephalon) of trilobite fossils (Figure 4) are used to distinguish between species. The biological species concept cannot be used to distinguish them because reproductive behavior cannot be inferred from fossil evidence.

Figure 4. Species of trilobites are often identified using their cephalon or cranidium. Source: James St. John, CC BY 2.0, via Wikimedia Commons.

The downside to this approach is that morphological evidence can be interpreted subjectively; researchers may disagree on what structural features can set species apart.

The Ecological Species Concept

As defined by the ecological species concept, species are distinguished based on their ecological niche. An ecological niche is a role that a species plays in a habitat based on its interactions with the resources available in its environment.

For example, grizzly bears (Ursus arctos) are often found in woodlands, prairies, and forests, while polar bears (U. maritimus) are often found in Arctic Seas (Figures 5-6). When they interbreed, they can produce fertile offspring. However, this rarely happens in the wild because they mate in different habitats. According to the ecological species concept, they are two distinct species, even though there is potential gene flow between them because they occupy two different ecological niches.

Figure 5 Polar bears

Figure 6 Grizzly bears

Figures 5-6. Polar bears and grizzly bears can produce fertile offspring but are considered two distinct species. Source: (Left) Susanne Miller, U.S. Fish and Wildlife Service, Public domain, via Wikimedia Commons. (Right) Steve Hillebrand, U.S. Fish and Wildlife Service, Public domain, via Wikimedia Commons.

Biological vs. ecological species concept

An advantage to the ecological species concept is that it is applicable to both sexual and asexual species. It also takes into consideration how the environment can influence the morphological development of organisms.

The downside to this approach is that there are organisms whose interactions with resources in their environment are overlapping. There are also organisms that switch to other resources due to external factors. For example, feeding habits can change when food becomes scarce.

The Phylogenetic Species Concept

As defined by the phylogenetic species concept, species are a group whose members share a common ancestor and possess similar defining traits. In a phylogenetic tree, species would be represented by branches in a lineage. A lineage that branches off represents the emergence of a new, distinct species. This approach focuses on the evolutionary history of organisms and often relies on genetic evidence. Figure 7 shows how species can be represented as branch points in a phylogenetic tree.

Biological vs. phylogenetic species concept

An advantage of the phylogenetic species concept is that it is applicable to asexual organisms and organisms whose reproductive behaviors are unknown. It is also less restrictive in terms of morphological changes within the history of a species, as long as there is continuity of sexual fertility. It is applicable to both extinct and extant organisms.

The downside to this approach is that phylogenies are hypotheses that are open to revision. The discovery of new evidence could lead to species reclassification, making it an unstable basis for identifying species.

Biological Species Concept - Key takeaways

• The biological species concept defines species as populations whose members interbreed and produce viable, fertile offspring.
• The biological species concept provides the most widely accepted definition of species, but it has limitations. It is inapplicable to fossil evidence, asexual or self-fertilizing organisms, and sexual organisms that freely hybridize.
• Other species concepts include morphological, ecological, and phylogenetic species concepts.
• The morphological species concept distinguishes species based on their form and structural features.
• The ecological species concept distinguishes species based on their ecological niche.
• The phylogenetic species concept is a group whose members share a common ancestor and possess similar defining traits.

What is the importance of reproductive isolation to the biological species concept quizlet?

What is the importance of reproductive isolation?

Why reproductive isolation is central to the biological species concept?

Why is reproductive isolation important in natural selection and biological evolution?