The Case For Pluralism
Let us start by introducing three prominent species concepts in biology. There are many more prominent species concepts, but introducing three is sufficient for providing the argument for pluralism. The most common species concept in the biological literature is Mayr’s Biological Species Concept. The Biological Species Concept defines a species taxon as a group of organisms that can successfully interbreed and produce fertile offspring. According to that concept, a speciesâ integrity is maintained by interbreeding within a species as well as by reproductive barriers between organisms in different species. The Ecological Species Concept defines a species taxon as a lineage of organisms maintained and segmented by ecological forces . Stabilizing selection maintains a speciesâ integrity, while disruptive selection can lead to new species. The Phylogenetic Species Concept defines a species taxon as a basal monophyletic lineage . A monophyletic lineage contains all and only the descendants of a common ancestor. Because monophyletic lineages occur up and down the Linnaean hierarchy, species are defined as basal monophyletic lineages â the smallest lineages represented in Linnaean classifications.
Figure 1. A branching event on a phylogenetic tree. If species must be monophyletic, then A+B cannot form a species. Some of the descendant’s of A+B’s ancestor are not contained in A+B but are in C.
M.N. Maunder, in, 2008
Exchange Of Genes Between Species
Horizontal gene transfer between organisms of different species, either through hybridisation, antigenic shift, or reassortment, is sometimes an important source of genetic variation. Viruses can transfer genes between species. Bacteria can exchange plasmids with bacteria of other species, including some apparently distantly related ones in different phylogenetic domains, making analysis of their relationships difficult, and weakening the concept of a bacterial species.
Louis-Marie Bobay and Howard Ochman suggest, based on analysis of the genomes of many types of bacteria, that they can often be grouped “into communities that regularly swap genes”, in much the same way that plants and animals can be grouped into reproductively isolated breeding populations. Bacteria may thus form species, analogous to Mayr’s biological species concept, consisting of asexually reproducing populations that exchange genes by homologous recombination.
Alternatives To The Traditional Properties
Among the most important consequences of adopting a unified species concept is that, by emphasizing separately evolving lineages over contingent properties of those lineages, it encourages biologists to shift their attention away from the traditional species criteria and develop new methods for species delimitation. Although properties such as intrinsic reproductive isolation, diagnosability, monophyly, and the like are certainly relevant to the issue of lineage separation, many of them represent somewhat artificial cutoffs in the continuous process of divergence. Moreover, most of these properties are not very useful for detecting lineage separation in the early stages of divergence. In this context, the development of new methods to test hypotheses of lineage separation that are no longer based on the traditional species criteria represents significant progress. For example, consider new methods for species delimitation being developed in the context of coalescent theory . These methods use information from gene trees, which is the same sort of information that is commonly used to assess monophyly under monophyletic and genealogical versions of the so-called phylogenetic species concept. However, in the case of these new coalescent-based methods, monophyly is not the focus. In fact, the methods in question can provide evidence for lineage separation even when none of the sampled loci exhibits monophyly within the sets of populations under consideration .
What Is Species Diversity
It is defined as the number of species and population of species that live in that particular environment. The population of species of that particular location is called species richness. There are approximately 1.8 million different species classified on Earth. Of all the total species, about one million belong to insects. New species are being discovered each year. Scientists estimate that there may be between 5 to 30 million species that actually live on Earth. Due to this wide diversity, there are different species diversity in different locations as different species are present in different locations depending upon their ability to adapt in that particular environment.
Saiga Antelope Case Study
We applied the framework to the Saiga Antelope . The species was listed as vulnerable when first assessed in 1996, lower risk in 2000, and critically endangered in 2002 . Its past history, diverse trajectories of its populations in different regions, and the potential it has for further recovery make this species particularly suitable for illustrating the nuances of the 4 conservation metrics. We also estimated the speciesâ past and future IUCN Red List categories under the same scenarios .
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Species: Definition Types And Examples
Content Curator| Updated On -Apr 13, 2022
Species are defined as a group of organisms made up of similar individuals capable of reproducing or exchanging genes with each other. The topic Species comes under the heading Taxonomic categories. A study of a group of individual organisms with fundamental similarities as a species is defined as Taxonomic.
Table of Content
Everyone must be able to differentiate between a species from other closely related species on the basis of distinct morphological differences. Lets have a look at Mangifera indica, Solanum Tuberosum , and Panthera leo . Indica, leo, tuberosum, these three names of species represent specific epithets, while the first words Mangifera, Solanum and Panthera are genera and represent another higher level of taxonomy or category. Different organisms can be represented by each genus that can have one or more epithets but with morphological similarities. Panthera can be considered as an example as it has another specific epithet called tigers, and Solanum includes species such as nigrum and melongena. The species in which the Humans belong to is sapiens, it is the genus Homo is which it is grouped together.
What Is A Species
The most famous definition of a species comes from the 20th century German-born biologist Ernst Mayr, who emphasised the importance of interbreeding. The idea is that two organisms are of the same species if they can breed with one another to produce fertile offspring. That is why a donkey and a horse arent the same species: they can breed and produce offspring, but not fertile offspring.
Mayrs way of thinking about species has some amazing consequences. Recently, due to rising temperatures in the Arctic, polar bears and grizzly bears have been coming into increased contact, and have been producing fertile offspring. The offspring are called grolar or pizzly bears. What this suggests is that polars and grizzlies may actually be the same species after all, despite radical differences in size, appearance, hibernation behaviours, diet and so on.
But it wasnt long before the problems with Mayrs approach became apparent. The definition makes use of the notion of interbreeding. This is all very well with horses and polar bears, but smaller organisms like bacteria do not interbreed at all. They reproduce entirely asexually, by simply splitting in two. So this definition of species cant really apply to bacteria. Perhaps when we started thinking about species in terms of interbreeding, we were all just a bit too obsessed with sex.
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Mayr’s Biological Species Concept
Most modern textbooks make use of Ernst Mayr‘s 1942 definition, known as the Biological Species Concept as a basis for further discussion on the definition of species. It is also called a reproductive or isolation concept. This defines a species as
groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups.
It has been argued that this definition is a natural consequence of the effect of sexual reproduction on the dynamics of natural selection. Mayr’s use of the adjective “potentially” has been a point of debate some interpretations exclude unusual or artificial matings that occur only in captivity, or that involve animals capable of mating but that do not normally do so in the wild.
The Lineage Species Concept
Due to the limitations of the biological species concept described above, other species concepts have been developed. The lineage 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 . This concept focuses more on the evolutionary history that has shaped the species as we see it today, and increasingly relies on genetic data to assign individuals to species. The lineage species concept resolves some of the problems of the biological species concept since it can be applied to asexual species and those for which detailed reproductive behavioral data are unavailable. Its reliance on genetic data makes it also difficult to apply to long-extinct species however, recent advances in genetic analysis have allowed scientists to extract DNA from recently extinct organisms such as Neanderthals and wooly mammoths. Scientists using the lineage species concept must still consider what type and magnitude of genetic differences, and in what portions of the genome, constitute different species and must employ modern computational tools to manage the increasingly large datasets produced in genetic analyses.
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Phylogenetic Evolutionary And Genealogical Species Concepts
Other more recently derived species concepts rely more heavily on a retrospective view by defining a species in a strictly historical sense as a separate evolutionary lineage that is internally connected through time , the âevolutionary species conceptâ , and the âgenealogical species conceptâ for a good overview, see Harrison article in Howard and Berlocher, 1998 likewise, de Queiroz, 2007). These species concepts are less oriented toward process and identifying specific biological traits that maintain cohesion within species or promote divergence between species and instead are more oriented toward the final evolutionary result â lineage divergence. That is not to say that process cannot be usefully inferred from looking at historical patterns of lineage sorting and splitting , but the emphasis in these particular species concepts is clearly on pattern rather than on trying to incorporate a variety of biological processes into the species definitions themselves.
Marc Ereshefsky, in, 2007
Examples Of Species In A Sentence
speciesspeciesspeciesspecies San Antonio Express-Newsspecies WiredspeciesCNNspeciesalspecies USA TODAYspecies Smithsonian Magazinespecies Country LivingspeciesNBC Newsspecies The Salt Lake Tribunespecies Longreadsspecies Chicago Tribunespecies NBC Newsspecies ABC Newsspecies CBS Newsspecies New York Timesspecies STAT
These example sentences are selected automatically from various online news sources to reflect current usage of the word ‘species.’ Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.
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Relevance Of Diverse Properties
Another consequence of a unified species concept is that many different properties are relevant to the issue of species delimitation. Under most of the alternative species concepts, in which various properties acquired by diverging lineages were viewed as necessary properties of species, a different one of these properties was considered necessary under each alternative concept. This practice created the undesirable situation in which each alternative species concept unduly emphasized only one of the various properties at the expense of the others , with biologists engaged in an ongoing battle over which property was to be considered the most important.
In contrast, under a unified species concept, most of the properties emphasized under the alternative concepts should be considered relevant to the issue of species delimitation. In the context of a unified species concept, any property that provides evidence of lineage separation is relevant to inferring the boundaries and numbers of species. Considering the properties that have previously been adopted as secondary species criteria , either the property itself , or its converse , provides evidence of lineage separation. Thus, all of those properties are relevant to the problem of species delimitation.
Quantifying Species Recovery With A Green
where s is each spatial unit, Ws the weight of the state in the spatial unit , WF is the weight of the functional category, and N is the number of spatial units. The denominator is the maximum possible score attained when all spatial units are assessed as functional. The states are based on this formula and thus are calculated as a percentage of the fully recovered state. The conservation metrics are calculated as differences between 2 states.
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When Mayr’s Concept Breaks Down
A simple textbook definition, following Mayr’s concept, works well for most multi-celled organisms, but breaks down in several situations:
- When organisms reproduce asexually, as in single-celled organisms such as bacteria and other prokaryotes, and parthenogenetic or apomictic multi-celled organisms. DNA barcoding and phylogenetics are commonly used in these cases. The term quasispecies is sometimes used for rapidly mutating entities like viruses.
- When scientists do not know whether two morphologically similar groups of organisms are capable of interbreeding this is the case with all extinct life-forms in palaeontology, as breeding experiments are not possible.
- When hybridisation permits substantial gene flow between species.
- In ring species, when members of adjacent populations in a widely continuous distribution range interbreed successfully but members of more distant populations do not.
The evolutionary biologist James Mallet concludes that
there is no easy way to tell whether related geographic or temporal forms belong to the same or different species. Species gaps can be verified only locally and at a point of time. One is forced to admit that Darwin’s insight is correct: any local reality or integrity of species is greatly reduced over large geographic ranges and time periods.
A Unified Species Concept
The situation I have just described suggests a simple solution to the species concept problem. The solution involves a relatively minor yet still fundamental shift in the way that species are conceptualized. It retains the element that is common to all contemporary species concepts, and it eliminates the conflicts between those rival concepts without denying the importance of the properties that underlie their obvious differences. In short, it represents a unified species concept.
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Typological Or Morphological Species
Eurasian blue titsmorphospecies
A typological species is a group of organisms in which individuals conform to certain fixed properties , so that even pre-literate people often recognise the same taxon as do modern taxonomists. The clusters of variations or phenotypes within specimens would differentiate the species. This method was used as a “classical” method of determining species, such as with Linnaeus early in evolutionary theory. However, different phenotypes are not necessarily different species . Species named in this manner are called morphospecies.
In the 1970s, Robert R. Sokal, Theodore J. Crovello and Peter Sneath proposed a variation on the morphological species concept, a phenetic species, defined as a set of organisms with a similar phenotype to each other, but a different phenotype from other sets of organisms. It differs from the morphological species concept in including a numerical measure of distance or similarity to cluster entities based on multivariate comparisons of a reasonably large number of phenotypic traits.
Species Concepts In Phytoplankton
The species concept for most phycologists is based on the morphological characters and hence the term âspeciesâ means morphospecies. On the other hand, for evolutionary biologists the term means biological species that can be defined as a reproductive community of populations that occupy a specific niche in Nature. If we accept the above definition of species, any talk about biological species in groups where sexual reproduction has not been observed yet is meaningless. Nevertheless, recent concepts argue that it would be unproductive and inconvenient to restrict the term âspeciesâ exclusively to one or the other.
James H. Thorp, … Walter W. Dimmick, in, 2015
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The Death Of Essentialism
Since Aristotle, species have been paradigmatic examples of naturalkinds with essences. An essentialist approach to species makes sensein a pre Darwinian context. God created species and an eternal essencefor each species. After Gods initial creation, each species isa static, not an evolving group of organisms. Darwinism offers adifferent view of species. Species are the result of speciation. Noqualitative featuremorphological, genetic, orbehavioralis considered essential for membership in a species.Despite this change in biological thinking, many philosophers stillbelieve that species are natural kinds with essences. Let us startwith a brief introduction to kind essentialism and then turn to thebiological reasons why species fail to have essences.
Kind essentialism has a number of tenets. One tenet is that all andonly the members of a kind have a common essence. A second tenet isthat the essence of a kind is responsible for the traits typicallyassociated with the members of that kind. For example, goldsatomic structure is responsible for golds disposition to meltat certain temperatures. Third, knowing a kinds essence helpsus explain and predict those properties typically associated with akind. The application of any of these tenets to species isproblematic. But to see the failure of essentialism we need onlyconsider the first tenet.
Recognition And Cohesion Species
A mate-recognition species is a group of sexually reproducing organisms that recognise one another as potential mates. Expanding on this to allow for post-mating isolation, a cohesion species is the most inclusive population of individuals having the potential for phenotypic cohesion through intrinsic cohesion mechanisms no matter whether populations can hybridise successfully, they are still distinct cohesion species if the amount of hybridisation is insufficient to completely mix their respective gene pools. A further development of the recognition concept is provided by the biosemiotic concept of species.
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