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The hierarchy of biological classification's eight major taxonomic ranks. A genus contains one or more species. Minor intermediate ranks are not shown. A species (pl.: species) is a population of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. [1]
That is, the splitting of an existing species into two separate species, or the budding off of a new species from a parent species, both driven by a biological "fashion fad" (a preference for a feature, or features, in one or both sexes, that do not necessarily have any adaptive qualities).
Over 1.5 million living animal species have been described—of which around 1 million are insects—but it has been estimated there are over 7 million in total. Animals range in size from 8.5 millionths of a metre to 33.6 metres (110 ft) long and have complex interactions with each other and their environments, forming intricate food webs .
The species' appearance is among the most variable in North America. Once considered different species, numerous varieties of juncos have been lumped together over the years.
Quinarianism gets its name from the emphasis on the number five: it proposed that all taxa are divisible into five subgroups, and if fewer than five subgroups were known, quinarians believed that a missing subgroup remained to be found. [2] Nicholas Aylward Vigors's Quinarian classification of birds. The missing entries represented groups that ...
The two forms hunt different prey species and have different diets, vocal behaviour, and social structures. Some divergences between species could also result from contrasts in microhabitats. A population bottleneck occurred around 200,000 years ago greatly reducing the population size at the time as well as the variance of genes which allowed ...
More than 99 percent of all species, amounting to over five billion species, [7] that ever lived on Earth are estimated to be extinct. [8] [9] Estimates on the number of Earth's current species range from 10 million to 14 million, [10] of which about 1.2 million have been documented and over 86 percent have not yet been described. [11]
The most curious fact is the perfect gradation in the size of the beaks in the different species of Geospiza, from one as large as that of a hawfinch to that of a chaffinch, and (if Mr. Gould is right in including his sub-group, Certhidea, in the main group) even to that of a warbler.