Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If You Use a Screen Reader

This content is available through Read Online (Free) program, which relies on page scans. Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.

Taxon Cycles in the West Indian Avifauna

Robert E. Ricklefs and George W. Cox
The American Naturalist
Vol. 106, No. 948 (Mar. - Apr., 1972), pp. 195-219
Stable URL: http://www.jstor.org/stable/2459928
Page Count: 25
  • Read Online (Free)
  • Download ($19.00)
  • Subscribe ($19.50)
  • Cite this Item
Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Taxon Cycles in the West Indian Avifauna
Preview not available

Abstract

Analysis of distribution patterns of land birds in the West Indies supports the empirical theory that once species invade islands they progress through a series of evolutionary changes that eventually greatly increase the probability of extinction. Species are arbitrarily assigned to four stages of the "taxon cycle" based on their distribution and differentiation within islands: (I) expanding or widespread, with little differentiation into morphologically distinct populations; (II) widespread but highly differentiated; (III) restricted, usually with a fragmented range; and (IV) endemic to one island. These stages are shown, beyond reasonable doubt, to represent a temporal sequence. Immigration has been observed to occur very rapidly, and expanding species usually reach most islands in a stepping-stone fashion. Recent colonists usually belong to species that are abundant and distributed in open habitats on the mainland. Once colonists reach islands, differentiation is usually rapid, although hampering effects of gene flow can be recognized. Changes in morphology and ecology also occur during the taxon cycle. In particular, habitat distributions are frequently restricted, often to mature forest. Extinction within recorded history has occurred with much higher frequency among Stage IV species than among species assigned to earlier stages. Slopes of species-area curves increase with stage of taxon cycle from 0.075 for Stage I species to 0.42 for Stage IV species, demonstrating that extinction rate is more sensitive to island size at progressively later stages of the cycle. Moreover, slopes vary with feeding behavior, from 0.04 for hummingbirds to 0.21 for flycatchers, swallows, and swifts. On the basis of these and other observations, we postulate that for a particular species the cycle results from progressively reduced competitive ability caused by counterevolution of the island biota toward that species. The cycle is driven by competition from newly arrived colonists that are initially free of a counteradaptive load. The presence of old populations on small remote islands rarely receiving new colonists attests to the importance of competition in the cycle. We expect groups with differing rates of immigration, differentiation, and extinction to exhibit different patterns of distribution among islands, but that suitable island groups, whose size and spatial patterns normalize these differences, can be found for any group of organisms. Moreover, the concept underlying the taxon cycle undoubtedly applies to mainland faunas and may help explain such patterns as variation in dominance and relative abundance of species.

Page Thumbnails

  • Thumbnail: Page 
195
    195
  • Thumbnail: Page 
196
    196
  • Thumbnail: Page 
197
    197
  • Thumbnail: Page 
198
    198
  • Thumbnail: Page 
199
    199
  • Thumbnail: Page 
200
    200
  • Thumbnail: Page 
201
    201
  • Thumbnail: Page 
202
    202
  • Thumbnail: Page 
203
    203
  • Thumbnail: Page 
204
    204
  • Thumbnail: Page 
205
    205
  • Thumbnail: Page 
206
    206
  • Thumbnail: Page 
207
    207
  • Thumbnail: Page 
208
    208
  • Thumbnail: Page 
209
    209
  • Thumbnail: Page 
210
    210
  • Thumbnail: Page 
211
    211
  • Thumbnail: Page 
212
    212
  • Thumbnail: Page 
213
    213
  • Thumbnail: Page 
214
    214
  • Thumbnail: Page 
215
    215
  • Thumbnail: Page 
216
    216
  • Thumbnail: Page 
217
    217
  • Thumbnail: Page 
218
    218
  • Thumbnail: Page 
219
    219