Download Information on SPECIES – How do we define them and how can we

Information on SPECIES – How do we define them and how can we
tell them apart
From “Understanding Evolution” website:
http://evolution.berkeley.edu/evosite/evo101/VADefiningSpecies.shtml
Defining a Species
A species is often defined as a group of individuals that actually or potentially interbreed in
nature. In this sense, a species is the biggest gene pool possible under natural conditions.
For example, these happy face spiders look different, but since they can interbreed, they are
considered the same species: Theridion grallator.
Also, many plants, and some animals, form hybrids in
nature. Hooded crows and carrion crows look
different, and largely mate within their own groups—
but in some areas, they hybridize. Should they be
considered the same species or separate species?
If two lineages of oak look quite different, but
occasionally form hybrids with each other, should we count them as different species? There are
lots of other places where the boundary of a species is blurred. It’s not so surprising that these
blurry places exist—after all, the idea of a species is something that we humans invented for our
own convenience!
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From “Encyclopedia of Life” website:
http://eol.org/info/468
What Is A Species?
Biodiversity can be measured in a number of ways, depending on what aspect is being examined.
There is the diversity of functions (e.g., decomposition, nutrient cycling, predation) that
organisms can perform in their ecosystems, the diversity of genes in a population of an organism,
or even the diversity of ecosystem types in a particular area. Most of the time when people talk
about biodiversity, though, they’re referring to the number of different species (or “types”) of
organisms. Biodiversity inventories, such as BioBlitzes,
or catalogues, such as the Encyclopedia of Life, are
organized by species.
Ursus americanus is the genus species name for the
American black bear. The first part of the name is the
genus, a group of related species (in this case bears); the
second part of the name is the species within the genus.
In some cases, a subspecies can also be designated to
further distinguish groups within a species, indicated by the addition of a third name. Ursus
americanus has several subspecies, for example, Ursus americanus californiensis and Ursus
americanus altifrontalis; these subspecies names refer to the geographical locations in which
they’re found.
Because evolution is an ongoing process, new species form continually over time, which means
that there is no perfect, definitive way of classifying organisms. However, taken together, there
are multiple “species concepts” that provide guidelines.
Biological species concept
Most broadly, a species is a group of
organisms with a shared, closed gene
pool. In many organisms, the way to
pinpoint a species is to apply the
biological species concept. According
to this definition, a species is made up
of all the organisms that are able to
mate with each other and produce
fertile offspring. For example, lions produce offspring with
other lions, and tigers with other tigers; if lions and tigers are
brought together in captivity they can occasionally produce a
hybrid called a liger or tigon, but these hybrids are not
themselves able to reproduce. It then follows that lions and
tigers are separate species. (Another term used for the inability
to interbreed is reproductive isolation.)
Morphological species concept
Another way that organisms can be classified is
on the basis of morphology, or physical features.
This definition is also often useful: sometimes it
is not possible to observe whether two organisms
interbreed (e.g., different types of whales in the
wild) but examining their physical features can
help determine how closely they’re related. In
general, if carefully chosen, morphological
features can indeed be an indicator of organisms
having the same common ancestor.
There are many problems with this approach: domestic dogs, for example, can look very
different but are actually all one species capable of interbreeding, whereas mouse lemurs look
very similar to each other but are actually at least 18 distinct species.
Genetic species concept
For organisms that have neither sexual reproduction nor many distinctive morphological features
in common—for example, bacteria—species are often defined as clusters of genetically similar
organisms (with “similar” somewhat arbitrarily defined). Using genetic markers as traits defining
species is also the principle behind DNA barcoding.
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From About.com
http://animals.about.com/od/s/g/species.htm
Species
By Laura Klappenbach
Some felids are capable of interbreeding but are still considered to be
separate species.
Definition: The term species can be defined as a group of individual
organisms that are capable of interbreeding to produce fertile offspring
in nature. A species is, according to this definition, the largest gene pool that exists under natural
conditions. Thus, if a pair of organisms are capable of producing offspring in nature, they must
belong to the same species.
Unfortunately, in practice, this definition is plagued by ambiguities. To begin, this definition is
not relevant to organisms (such as many types of bacteria) that are capable of asexual
reproduction. If the definition of a species requires that two individuals are capable of
interbreeding, then an organism that does not interbreed is outside of that definition.
Another difficulty that arises when defining the term species is that some species are capable of
forming hybrids. For example, many of the large cat species are capable of hybridizing. A cross
between a female lions and a male tiger produces a liger. A cross between a male jaguar and a
female lion produces a jaglion. There are a number of other crosses possible among the panther
species, but they are not considered to be all members of a single species as such crosses are very
rare or do not occur at all in nature.
Species form through a process called speciation. Speciation takes place when the lineage of a
single splits into two or more separate species. New species can form in this manner as a result
of several potential causes such as geographic isolation or a reduction in gene flow among
members of the population.
When considered in the context of classification, the term species refers to the most refined level
within the hierarchy of major taxonomic ranks (though it should be noted that in some cases
species are further divided into subspecies, but that term lacks clear and consistent definition).
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