The biological species concept defines a species as members of populations breeding or can interbreed in nature and not according to a similar appearance. Although the appearance is useful for species identification, does not define a species.
Looks are not everything
The agencies may look the same but be different species. For example, warblers turpiales (western meadowlark) and Eastern turpiales (Sturnella magna) look almost identical, but do not interbreed them – therefore are independent species under this definition.
Agencies can parecerdiferentes and still be of the same species. For example, when looking at these two ants might think they are distantly related species but are actually sisters are two ants of the species Pheidole barbataque perform different tasks in the same colony.
Within a single species can vary many characteristics. For example, hydrangeas may have “flowers” (actually are modified leaves) pink or blue, but that does not mean that we should classify the two forms as different species. In fact, it could make a plant blue “flowers” plant “flowers” roses back by simply changing the pH of the soil and the amount of aluminum absorbed by the plant.
The extent of the problem
We have already identified two of the difficulties posed by the biological species concept: what is done with asexual organisms and what is done with agencies hybridize to each other occasionally. Also it raises other difficulties: pelajaransekolahonline.com
What siginfica that “can interbreed them”? If a population of frogs it was divided by a highway, as shown below, which prevented the two groups from breeding frogs among them, should designate different species? Probably not, but what distance must separate them to us to set the limit?
Related species are species with a geographic distribution that forms a ring that matches at the ends. The many subspecies of salamanders of the genus California Ensatina show subtle genetic and morphological throughout its range differences. All of them are reproduced with its contiguous neighbors, with one exception: in the Southern California area in the overlapping the ends of the range, E. and E. eschscholtzii klauberi not interbreed them. So where do we draw the point of speciation?
Chronospecies are different stages of the evolutionary lineage that existed at different times. Obviously, chronospecies pose a problem for the biological species concept: for example, is not really possible (not very significant) find out whether a trilobite that lived 300 million years would have played with an ancestor that lived 310 million years ago .
Trilobite lineage below evolved gradually over time:
Should we consider trilobite A trilobite a separate species D ?, and if so, where should we divide the lineage in different species?