Isabella Carter
The concept of a species is a useful tool for scientists and conservationists to study life on Earth. While there is no single definition that satisfies all naturalists, a species is often defined as a group of organisms that can reproduce with one another and create fertile offspring. This is known as the biological species concept. However, this definition becomes problematic when considering organisms that reproduce asexually, such as bacteria, or in cases where similar species hybridize in the wild, like polar bears and grizzly bears. To address these issues, scientists have proposed other species concepts, such as the phylogenetic species concept, which defines species based on their evolutionary history and genetic data, and the morphological species concept, which focuses on similarities in structure. Ultimately, the classification of a species can be difficult and controversial, and our understanding of species is constantly evolving as we make new discoveries about life on Earth.
| Characteristics | Values |
|---|---|
| Biological Species Concept | Individuals belong to the same species if they can interbreed in nature and produce viable, fertile offspring |
| Prezygotic and postzygotic barriers ensure that members of different species do not reproduce with one another | |
| Phylogenetic Species Concept | Groups of organisms that share a pattern of ancestry and descent and which form a single branch on the tree of life |
| Lineage Species Concept | Similar to the phylogenetic concept, but can be applied to asexual species and those without detailed reproductive behavioural data |
| Morphological Species (Morphospecies) Concept | Relies on similarities in structure |
| Typological Species | Organisms conform to certain fixed properties (a type, which may be defined by a chosen 'nominal species') |
| Phenetic Species | Defined as a set of organisms with similar phenotypes |
| Conservation | Conservation laws in many countries make special provisions to prevent species from going extinct |
| Naming | Scientists follow the guidelines of the International Code of Zoological Nomenclature (ICZN) or the International Code of Nomenclature for Algae, Fungi and Plants (ICN) |
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What You'll Learn
The biological species concept
However, the biological species concept has limitations and is difficult or impossible to use in certain cases. For example, it cannot be applied to asexual organisms, such as bacteria, as they reproduce without sexual reproduction and do not fit into the concept's focus on interbreeding. It also cannot be applied to long-extinct species for which reproductive data does not exist and can no longer be obtained.
Another limitation arises when organisms occasionally form hybrids with one another. For example, hooded crows and carrion crows look different and mostly mate within their groups, but they hybridize in some areas. It becomes unclear whether they should be considered the same or separate species.
Despite these limitations, the biological species concept is still a useful tool for scientists and conservationists studying life on Earth. It provides a basis for categorizing and identifying organisms, which is necessary for research and conservation efforts.
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The phylogenetic species concept
The PSC differs from the biological species concept (BSC), which defines species as groups of individuals that can interbreed in nature and produce viable, fertile offspring. The BSC does not account for cases where organisms have separate evolutionary histories but can still hybridize. The PSC, on the other hand, considers groups with distinct evolutionary histories as separate species, regardless of their ability to hybridize.
The PSC has been supported by biologists as it provides a logical framework that accords primacy to patterns of historical diversification. It also offers an objective approach to reconstructing the evolutionary histories of species and higher-level groupings. Additionally, the PSC accommodates asexual reproduction, making it applicable to a wider range of organisms.
However, the use of the PSC has been associated with "taxonomic inflation," where surveys using this concept reported a higher number of species and smaller populations and ranges compared to non-phylogenetic concepts. This inflation can create political and practical difficulties, especially in conservation efforts.
In conclusion, the phylogenetic species concept offers a distinct approach to species identification by focusing on shared traits and evolutionary history. While it provides advantages over the BSC, particularly for asexual organisms and evolutionary understanding, it also presents challenges and complexities in conservation efforts due to taxonomic inflation.
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The morphological species (morphospecies) concept
The morphological species concept is often used when other species concepts cannot be applied or in conjunction with other concepts. For example, it is frequently applied in palaeontology, where breeding experiments are not possible, or when genetic data is limited or unavailable. In these cases, morphology can provide valuable information for species identification. Carl Linnaeus, who began formally naming and categorizing species in 1735, used the morphological species concept. He developed the binomial nomenclature system, which is still used today, where each species is given a two-word Latin name.
However, the morphological species concept has limitations and potential drawbacks. Morphology can be misleading, as organisms with similar physical traits may not be closely related. For example, sharks and dolphins have similar body shapes and coloration but genetic analyses reveal that sharks are more closely related to rays and other fish, while dolphins are more closely related to whales and other mammals. Additionally, the concept has been criticized for allowing the description of new species based on limited sampling or aberrant forms that may not accurately represent the species as a whole.
Furthermore, the morphological species concept may not account for natural variation within a species. Different phenotypes or clusters of variations within a species, such as longer or shorter tails, do not necessarily indicate different species. For example, a four-winged Drosophila born to a two-winged mother is not a different species. This concept also breaks down in cases where organisms reproduce asexually, as each clonal lineage could potentially be considered a separate microspecies.
Despite these limitations, the morphological species concept remains a useful tool for scientists and conservationists studying life on Earth. It provides a way to categorize and identify organisms, which is necessary for research and conservation efforts. However, it is important to consider multiple lines of evidence, such as genetic data and reproductive behaviour, in conjunction with morphological data to fully understand species boundaries.
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The lineage species concept
Scientists using the lineage species concept must consider what type and magnitude of genetic differences, and in what portions of the genome, constitute different species. They must employ modern computational tools to manage the large datasets produced in genetic analyses.
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The typological species concept
The concept of species is a human invention used for convenience in categorising and identifying organisms. There is no single definition that satisfies all naturalists, and there are several alternative species concepts, each with its own strengths and limitations.
However, the typological species concept has its limitations. For example, different phenotypes are not necessarily different species. Large differences in phenotype may not always reflect large differences in relatedness among organisms, and it can be difficult to discern small but significant differences. Large differences in morphology may be due to single-locus colour polymorphisms, as seen in snow geese and king snakes. Small differences in morphology may be difficult to detect, as with the slight brown coloration on the flank and shorter claw on the hind toe of the short-toed treecreeper.
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Frequently asked questions
A species is often defined as a group of organisms that can reproduce with one another and create fertile offspring.
The biological species concept defines a species as a group of individuals that actually or potentially interbreed in nature.
The phylogenetic species concept defines species as groups of organisms that share a pattern of ancestry and descent and which form a single branch on the tree of life.
A typological species is a group of organisms in which individuals conform to certain fixed properties (a type, which may be defined by a chosen 'nominal species').
Scientists follow the guidelines of the International Code of Zoological Nomenclature (ICZN) or the International Code of Nomenclature for Algae, Fungi and Plants (ICN). These codes provide strict rules for Latinizing names and descriptive terms used in species names.
