Convergent and divergent character displacement

Abstract

Consideration of the possibilities and difficulties of detecting character displacement leads to a re‐definition of the phenomenon; character displacement is the process by which a morphological character state of a species changes under Natural Selection arising from the presence, in the same environment, of one or more species similar to it ecologically and/or reproductively. This incorporates the principal ideas in the original definition given by Brown & Wilson (1956), but eliminates the restriction of making comparisons of the character states of a species in sympatry and allopatry. The evidence for the ecological (competitive) aspect of character displacement is assessed by analyzing in detail the best documented and well publicized examples in the literature. Some of the examples either do not exhibit displaced characters or, if they do, the “displacement” can be interpreted in other and perhaps simpler ways; this applies to the so‐called classical case of character displacement, Sitta tephronota and S. neumayer in Iran. Other examples, involving lizards and birds, constitute better evidence for character displacement, but in no single study is it entirely satisfactory. It is concluded that the evidence for the ecological aspect of character displacement is weak.

REPRODUCTIVE CHARACTER DISPLACEMENT IN CALOPTERYX (ODONATA: CALOPTERYGIDAE)

“…The search for examples of reproductive character displacement (as redefined by Grant, 1972) is motivated by the desire to reveal the role natural selection plays in the establishment and/or improvement of premating barriers to gene exchange between speciating populations. The search is severely limited by the need to examine closely related species whose geographic ranges overlap extensively but not completely (Walker, 1974) and by the difficulty in documenting expected examples (Grant, 1972).…”

“…The search is severely limited by the need to examine closely related species whose geographic ranges overlap extensively but not completely (Walker, 1974) and by the difficulty in documenting expected examples (Grant, 1972). Considerable attention has been focused on the acoustical pair-forming signals of birds, anurans, and singing insects.…”

“…Considerable attention has been focused on the acoustical pair-forming signals of birds, anurans, and singing insects. Despite the suitability of these signals in quantitative surveys for patterns suggesting reproductive character displacement, few examples have been found (Alexander, 1969;Blair, 1974;Fouquette, 1975;Grant, 1972;Thielcke, 1969;Walker, 1974). To date only a few studies have focused on the displacement of: 1) pair-forming displays (Ferguson, 1973),2) morphology associated with species discrimination (Grant, 1975), or 3) discrimination abilities within a species (Waage, 1975;Wasserman and Koepfer, 1977).…”

“…Despite the suitability of these signals in quantitative surveys for patterns suggesting reproductive character displacement, few examples have been found (Alexander, 1969;Blair, 1974;Fouquette, 1975;Grant, 1972;Thielcke, 1969;Walker, 1974). To date only a few studies have focused on the displacement of: 1) pair-forming displays (Ferguson, 1973),2) morphology associated with species discrimination (Grant, 1975), or 3) discrimination abilities within a species (Waage, 1975;Wasserman and Koepfer, 1977). This paper presents an example of displacement of morphological characters used in species discrimination for two species of damselflies, Calopteryx maculata (De Beauvois) and C. aequabilis (Say), and deals with the problems affecting previous efforts to document character displacement.…”

“…This paper presents an example of displacement of morphological characters used in species discrimination for two species of damselflies, Calopteryx maculata (De Beauvois) and C. aequabilis (Say), and deals with the problems affecting previous efforts to document character displacement. Grant (1972Grant ( , 1975 provided a critical review of these problems and presented an example of careful documentation in the classic case of the rock nuthatches (Sitta).…”