What Is a Species Flock?
What Is a Metaflock?
|The anal fin of a sexually active male Protomelas spilopterus, showing yellow egg-dummy spots of the type characteristic of the "Hap" species flock. The numerous spots are not surrounded by transparent rings. They appear three- dimensional because of gradations of color from the edge of the spot to the center. Photo copyright © by M. K. Oliver.||In contrast, the anal fin of a mature male Cyathochromis obliquidens, representative of the Mbuna species flock, has fewer, more specialized egg-dummies. Each spot is surrounded by a narrow transparent ring (here appearing as a darker zone where the blue photo background shows through the fin), enhancing the 3-D effect. Photo copyright © by M. K. Oliver.|
species flock is a group of closely related species all living in the same ecosystem. As Greenwood (1974: 19) emphasized, "The term 'species flock' . . . should, strictly speaking, be applied to a species assemblage of monophyletic origin." The clear implication, then, is that a species flock evolved within the ecosystem from a single ancestral species by repeated speciation events. Thus, for an assemblage to merit the term "species flock," theoretically it should be possible to point to one or more synapomorphies (shared specialized characters) in all members of the assemblage, characters lacking in relatives outside the flock.
The haplochromine cichlids of Lake Malawi have long been called a species flock. It appears to me, however, that there are actually two haplochromine species flocks in the lake, one comprising the 11 genera of mbuna, the other including all the remaining endemic haplochromines (Oliver, 1984). Although it has not been possible to show that either Lake Malawi flock is monophyletic, it does appear that each flock is more closely related to different cichlids outside of the lake than it is to the other flock. The mbuna have specialized, ocellate egg dummy spots on the anal fin, much like those of haplochromines of the assemblage in Lakes Victoria, Edward, and Kivu, including the gradal "genus" Astatotilapia (which lacks any defining synapomorphy). The other Malawi haplochromines, in contrast, have less-specialized, nonocellate egg dummies, like the (not necessarily closely related) genus Serranochromis and its relatives.
Thus, the entire endemic haplochromine fauna of Lake Malawi constitutes what I would call a species metaflock a complex of two or more closely related species flocks (within the same subfamily or tribe), each at least presumptively monophyletic, that do not together make up a monophyletic group.
|Last Update: 8 April 2002
Web Author: M. K. Oliver, Ph.D.
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