If you need an accessible version of this item please contact JSTOR User Support

Competitive Interactions and the Evolution of Ecological Niches as Illustrated by the Australian Honeyeater Genus Melithreptus (Meliphagidae)

Allen Keast
Evolution
Vol. 22, No. 4 (Dec., 1968), pp. 762-784
DOI: 10.2307/2406902
Stable URL: http://www.jstor.org/stable/2406902
Page Count: 23
  • Download PDF
  • Cite this Item

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 need an accessible version of this item please contact JSTOR User Support
Competitive Interactions and the Evolution of Ecological Niches as Illustrated by the Australian Honeyeater Genus Melithreptus (Meliphagidae)
Preview not available

Abstract

A genus of Australian birds (Melithreptus, Meliphagidae) shows no significant geographic variation over extensive continental ranges but marked morphological shifts with isolation. The changes are investigated with respect to shifts in basic ecology of the species and relative to the associated avifauna in each case. The following findings were reached: 1) Commonly a larger, and a smaller, species of Melithreptus occur together, differing in mean linear measurements by 10%. In isolated Tasmania the differences are greatly exaggerated. In southwestern Australia (isolated forest segment) and on Kangaroo Island, from which the larger species is absent, a smaller species (different one in each case) has a longer bill and tarsus. 2) The smaller species are either foliage gleaners (M. lunatus, M. affinis), or else feed in the branches (M. brevirostris). The larger species (M. gularis, M. validirostris) are much less specialized in their choice of feeding zones. 3) Evolutionary shifts can only, in part, be explained by ecological shifts and interrelationships within Melithreptus. Significantly, they occur under conditions of marked impoverishment in the associated avifauna, e.g., Tasmania, Kangaroo Island, and southwestern Australia have only half the number of passerine species as the mainland of southeastern Australia. These faunas, particularly Tasmania, prove to be lacking, or deficient in, certain basic types of birds. Thus creepers (Climacteris) and nuthatches (Neositta) are absent. 4) Detailed feeding zone studies show that, in Tasmania especially, various species of birds have moved into the resultant vacant niches. Pre-eminent among these are Melithreptus validirostris, that has now become in part a trunk-prober and in part a bark-prizer, and has acquired corresponding morphological attributes. M. affinis, a foliage-gleaner, becomes more warbler-like in its shorter bill and hallux. Apart from M. validirostris three other species of birds have become part trunk-feeders in Tasmania and show morphological changes adapting them for this. These are another honeyeater, a thrush, and a warbler. The present study shows how impoverished insular faunas come to reach a state of ecological balance by a redivision of ecological niches and ways of life among the component species. This is achieved not by species abandoning their former way of life when they enter a new niche but by their becoming increasingly diversified, i.e., they occupy a wider spectrum. The changes in bill, tarsus, and hallux length that characterize insular populations of birds in different parts of the world are interpreted relative to this.

Page Thumbnails

  • Thumbnail: Page 
762
    762
  • Thumbnail: Page 
763
    763
  • Thumbnail: Page 
764
    764
  • Thumbnail: Page 
765
    765
  • Thumbnail: Page 
766
    766
  • Thumbnail: Page 
767
    767
  • Thumbnail: Page 
768
    768
  • Thumbnail: Page 
769
    769
  • Thumbnail: Page 
770
    770
  • Thumbnail: Page 
771
    771
  • Thumbnail: Page 
772
    772
  • Thumbnail: Page 
773
    773
  • Thumbnail: Page 
774
    774
  • Thumbnail: Page 
775
    775
  • Thumbnail: Page 
776
    776
  • Thumbnail: Page 
777
    777
  • Thumbnail: Page 
778
    778
  • Thumbnail: Page 
779
    779
  • Thumbnail: Page 
780
    780
  • Thumbnail: Page 
781
    781
  • Thumbnail: Page 
782
    782
  • Thumbnail: Page 
783
    783
  • Thumbnail: Page 
784
    784