<\/p>\n
In the last column, I wrote about the scientific classification of birds.\u00a0 I pointed out that the families and orders into which birds are classified are pigeonholes defined by scientists.\u00a0 The only taxonomic unit that is defined by nature is the species.\u00a0 Recognizing species is not as easy as one might think.\u00a0 We\u2019ll begin to explore this prickly subject today.<\/p>\n
A recent scientific review showed that there are over 60 definitions of species.\u00a0 I will collapse this list to three basic concepts and discuss the strengths and weaknesses of each.<\/p>\n
The morphological species concept is based on the idea that all members of a species should be similar.\u00a0 Of course similar is a subjective adjective.\u00a0 I like to show my introductory biology class a portrait of the basketball player Wilt Chamberlain next to the jockey Willie Shoemaker.\u00a0 An alien would scarcely suspect that these two mean, differing so much in height and skin color, belong to the same species.\u00a0 Strike one for the morphological species concept.<\/p>\n
Sibling species, species that are deceptively similar, also pose a problem for the morphological species concept.\u00a0 Prior to 1973, certain flycatchers with eye-rings and wing-bars were identified as Traill\u2019s Flycatchers.\u00a0 Fieldwork showed that some male Traill\u2019s Flycatchers gave a sneezy fitz-bew song and others gave a fee-bee-o song.\u00a0 Researchers found that some Traill\u2019s females responded only to the fitz-bew songs and others only to the fee-bee-o songs.\u00a0 Traill\u2019s Flycatcher is actually two very similar species: the Willow Flycatcher and the Alder Flycatcher.\u00a0 Distinguishing the two species in the field is nearly impossible and even in-hand identification is not always possible.\u00a0 Strike two for the morphological species concept.<\/p>\n
Ernst Mayr, one of the greatest biologists of the 20th century, developed the biological species concept, defining a species as a population of interbreeding organisms that are reproductively isolated from other populations.\u00a0 This concept is widely held and is the predominant view of the members of the American Ornithologists Union Check-list Committee that rules on taxonomic changes for the birds of the Americas.<\/p>\n
The critical aspect of this concept is the ability to breed with other individuals to produce viable offspring.\u00a0 Different species should be unable to hybridize; they should be reproductively isolated even if they are found in the same area.\u00a0 Isolating mechanisms include songs, displays and infertility that prevent members of different species from mating or producing viable young.<\/p>\n
Two problems arise with his concept.\u00a0 First, how do you treat populations that are geographically separate from each other?\u00a0 Consider the scrub jay complex.\u00a0 Scrub Jays are very common birds west of the Rocky Mountains, essentially occupying the ecological role of our Blue Jays.\u00a0 But there is a population of Scrub Jays in south Florida.\u00a0 Also, the Scrub Jays on Catalina Island, off the coast of Southern California, look a bit different from western Scrub Jays.\u00a0 How can you apply a test of the ability to interbreed for populations that are not in contact with each other?\u00a0 The answer is that it becomes a judgment call.\u00a0 Formerly, these jays were all treated as one species, the Scrub Jay.\u00a0 More recent work, based in part on DNA differences, has split the scrub jays into the Florida Scrub Jay, Western Scrub Jay and Island Scrub Jay.\u00a0 We still don\u2019t know if these different populations can interbreed.\u00a0 Strike one against the biological species concept.<\/p>\n
Another problem is that a lot of birds do hybridize.\u00a0 More than 10% of bird species care capable of creating viable offspring with members of other species.\u00a0 Ducks are the most notorious birds in this regard with over 400 hybrid combinations known.\u00a0 Mallards hybridize with over 50 species of ducks and geese.\u00a0 Wood Ducks hybridize with over 40 species.\u00a0 Over 10% of the American Black Ducks and Mallards in New England are hybrids.<\/p>\n
Hybrids occur regularly in wood warblers as well.\u00a0 Lawrence\u2019s Warbler is a well-known hybrid between a Golden-winged Warbler and a Blue-winged Warbler.\u00a0 The Cincinnati Warbler described by Audubon is now known to be a cross between a Blue-winged Warbler and a more distantly related species, the Kentucky Warbler.<\/p>\n
Even though hybrids often are capable of reproduction, in some cases their mixed-parentage offspring are not fertile.\u00a0\u00a0 Some hybrids capable of reproduction may have more difficulty in securing a mate than pure-breed individuals.<\/p>\n
But many hybrids can secure mates and produce offspring that are fertile.\u00a0 In such cases, ornithologists measure the proportions of hybrid to \u201cpure\u201d offspring where two populations overlap.\u00a0 The two populations are judged to be the same species if hybrids are common.\u00a0 In the next column, we will see this rule in action.\u00a0 I will also present a third, more controversial, species concept.<\/p>\n
In the last column, I wrote about the scientific classification of birds.\u00a0 I pointed out that the families and orders into which birds are classified are pigeonholes defined by scientists.\u00a0 The only taxonomic unit that is defined by nature is the species.\u00a0 Recognizing species is not as easy as one might think.\u00a0 We\u2019ll begin to […]<\/p>\n","protected":false},"author":146,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_s2mail":"","ngg_post_thumbnail":0,"footnotes":""},"categories":[425],"tags":[],"builder_content":"","_links":{"self":[{"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/posts\/95"}],"collection":[{"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/users\/146"}],"replies":[{"embeddable":true,"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/comments?post=95"}],"version-history":[{"count":8,"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/posts\/95\/revisions"}],"predecessor-version":[{"id":154,"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/posts\/95\/revisions\/154"}],"wp:attachment":[{"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/media?parent=95"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/categories?post=95"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/tags?post=95"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}