Biological Species Concept
What makes an animal or plant a unique? The answer lies in what is called the biological species concept. This idea helps us understand how different groups of organisms are classified. We will explore how the biological species concept works and how it relates to reproductive barriers. We will also examine other species concepts and compare them to the biological species concept.
What Is the Definition of Species According to the Biological Species Concept?
The biological species concept is a way to define what a species is. According to this concept, individuals belong to the same species if they can mate and produce healthy offspring. In contrast, individuals from different species cannot interbreed or produce viable, fertile offspring. For example, dogs in Canada and Japan are considered members of the same species because they can mate and their offspring can survive and reproduce. However, horses and donkeys are considered separate species because even though they can interbreed, their offspring, mules, cannot have babies of their own. This concept is important in understanding how different species are classified in nature.
How are Reproductive Barriers Related to the Biological Species Concept?
Gene flow is the movement of genetic information between populations of the same species. This means that organisms or gametes can enter a population and bring new or existing alleles with them. However, gene flow does not occur between populations of different species since members of different species cannot interbreed and share genetic information. Reproductive barriers are responsible for limiting or preventing gene flow between different species. These barriers can be either prezygotic, which prevent the formation of a zygote, or postzygotic, which prevent gene flow after the formation of a zygote. Prezygotic barriers include mechanisms such as temporal isolation, geographic isolation, behavioral isolation, and gametic barrier. Postzygotic barriers include hybrid inviability and hybrid sterility. Reproductive barriers are important in defining the boundaries of a species as a reproductive community and gene pool, and they help to maintain the cohesion of the species as a genetic system. They are the reason why members of a species share more similarities with each other than 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.
The biological species concept is advantageous because it focuses on reproductive isolation, which is a clear and objective criterion for defining species. This criterion is easy to apply in many situations, such as with the western meadowlark and eastern meadowlark. Even though these two species look very similar, they are considered distinct species because they do not interbreed despite having overlapping breeding ranges. The fact that they do not interbreed is a clear indication that they belong to different species, as they are reproductively isolated from each other. The biological species concept is a useful tool for understanding the diversity of life and how different species are defined in nature.
The biological species concept has some limitations that make it difficult to apply in certain situations. For instance, it cannot be applied to fossils because their reproductive isolation cannot be evaluated. Additionally, it does not apply to asexual organisms or self-fertilizing organisms. Finally, there are cases where sexual organisms hybridize in the wild, yet they are still able to maintain their cohesion as distinct species.
Because of these limitations, the biological species concept is considered a working definition. Other species concepts have been developed to address these limitations and are useful in different situations. For example, the phylogenetic species concept defines species based on shared evolutionary history, which can be applied to both sexual and asexual organisms. The morphological species concept defines species based on physical characteristics, which can be applied to fossils and organisms with limited biological data. Overall, it is important to use multiple species concepts to best understand and define the diversity of life.
What Are Other Definitions of Species?
Let's take a look at each of these species concepts in more detail and compare them to the biological species concept.
- Morphological species concept: This concept defines species based on physical characteristics, such as size, shape, and color. It assumes that individuals belonging to the same species share similar morphological traits and that individuals belonging to different species have different traits. This concept can be applied to both living and fossil organisms, making it a useful tool for studying evolutionary history.
Compared to the biological species concept, the morphological species concept is more inclusive, as it does not require reproductive isolation to define species. However, it may not accurately reflect genetic differences between populations and may lump together populations that are reproductively isolated but have similar morphological traits.
- Ecological species concept: This concept defines species based on their ecological roles in a particular environment. It assumes that individuals belonging to the same species occupy similar ecological niches and interact with their environment in similar ways. This concept can be applied to both living and extinct organisms and provides insight into the role of species in their ecosystem.
Compared to the biological species concept, the ecological species concept is more inclusive and flexible, as it does not require reproductive isolation to define species. However, it may not accurately reflect genetic differences between populations and may not apply to species that have similar ecological roles but are genetically distinct.
- Phylogenetic species concept: This concept defines species based on shared evolutionary history, as determined by molecular data, such as DNA sequences. It assumes that individuals belonging to the same species share a common ancestor and that individuals belonging to different species have different ancestors. This concept can be applied to both living and extinct organisms and provides insight into the evolutionary history of species.
Compared to the biological species concept, the phylogenetic species concept is more specific, as it focuses on genetic differences between populations. However, it may be difficult to apply in cases where molecular data is limited, and it may not accurately reflect unique ecological roles of species.
Overall, each of these species concepts has its advantages and limitations compared to the biological species concept, and they are useful in different situations for understanding the diversity of life.
The Morphological Species Concept
The morphological species concept is particularly useful for studying fossils and extinct organisms because it is based solely on physical characteristics. This allows researchers to distinguish between species even when reproductive behavior cannot be inferred.
Trilobites are a great example of how the morphological species concept can be applied to fossils. With over 20,000 species, trilobites are one of the most diverse groups of extinct arthropods. By examining the cephalon or cranidium of trilobite fossils, researchers can distinguish between different species based on their form and structural features.
This is in contrast to the biological species concept, which relies on reproductive isolation to define species. Since this cannot be observed in fossils, the biological species concept cannot be applied in this case. However, the morphological species concept provides a valuable alternative for studying the diversity of life throughout history.
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
According to 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. 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. Therefore, according to the ecological species concept, grizzly bears and polar bears are two distinct species, even though there is potential gene flow between them because they occupy two different ecological niches.
The ecological species concept is indeed applicable to both sexual and asexual species, and it considers how the environment can influence the morphological development of organisms. However, as you mentioned, there are some limitations to this approach.
One of the main challenges with the ecological species concept is that there are organisms whose interactions with resources in their environment are overlapping. This means that different species may occupy similar ecological niches, making it difficult to distinguish between them based solely on their ecological roles. Additionally, some organisms may switch to other resources when their preferred resources become scarce or unavailable, which could further complicate the identification of species based on their ecological niches.
Despite these limitations, the ecological species concept remains a valuable tool for understanding the diversity of life on Earth and the complex relationships between organisms and their environments. By studying the ecological niches of different species, researchers can gain insights into the factors that shape the evolution of life and the ways in which species interact with one another in ecosystems.
The Phylogenetic Species Concept
The phylogenetic species concept defines species as a group of individuals that share a common ancestor and possess similar defining traits. This approach is based on the evolutionary history of organisms and often relies on genetic evidence to identify and classify species. In a phylogenetic tree, species are represented by branches that emerge from a common ancestor, with each branch representing the emergence of a new, distinct species. Figure 7 provides a visual representation of how species can be represented as branch points in a phylogenetic tree.
One of the advantages of the phylogenetic species concept is that it allows for a more objective and quantitative approach to species classification. By using genetic data to reconstruct evolutionary relationships between organisms, researchers can identify and classify species based on their genetic relatedness and evolutionary history. Additionally, the phylogenetic species concept can help to resolve taxonomic confusion and clarify the relationships between different groups of organisms.
However, this approach can also be challenging because it requires a significant amount of genetic data and computational resources to construct accurate phylogenetic trees. Additionally, there may be cases where genetic data is not available or is difficult to obtain, which could limit the applicability of the phylogenetic species concept in certain contexts. Despite these challenges, the phylogenetic species concept remains a valuable tool for understanding the evolution and diversity of life on Earth.
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.
Biological Species Concept
What is the biological species concept?
The biological species concept defines species as populations whose members interbreed and produce viable, fertile offspring.
How do reproductive barriers relate to the biological species concept?
Biological species are defined by their reproductive compatibility, so we can say that different biological species are distinguishable by their reproductive isolation. 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.
What are some examples of biological species concept?
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 as defined by the biological species concept.On the other hand, horses and donkeys can interbreed, but their offspring–mules –will be infertile and cannot produce offspring. Therefore, horses and donkeys are considered separate species.
which is true about 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.
What does the biological species concept not apply to?
The biological species concept does not apply to fossil evidence, asexual organisms, and sexual organisms that freely hybridize.
