Character Displacement - Examples

Examples

While studies on character displacement have been performed in a wide variety of taxa, a few groups have disproportionately contributed our understanding of this principle: mammalian carnivores, Galapagos finches, Anolis lizards on islands, three-spined stickleback fish and snails (Dayan and Simberloff 2005).

In the initial explication of character displacement, many of the examples they set forth as potential evidence for character displacement were observations between multiple pairs of birds. These included rock nuthatches in Asia, Australian honey-eaters of the genus Myzantha, Australian parrots, shearwaters in the Cape Verde Islands, flycatchers of the Bismarck Archipelago and notably, Darwin's finches in the Galapagos (Brown and Wilson 1956). Lack (1947) found that when the two species Geospiza fortis and G. fuliginosa occurred on large islands together, they could be distinguished unequivocally by beak size. When either one occurred by itself on a smaller island, however, the beak size was intermediate in size relative to when the two co-occurred.

The lizard genus Anolis on the islands in the Caribbean has also been the subject of numerous studies investigating the role of competition and character displacement in community structure (e.g., Losos 1990). Lesser Antilles islands can only support Anolis species of different sizes, and the relative importance of character displacement versus size at colonization in determining invasion success has been explored and debated.

Threespine sticklebacks (Gasterosteus spp.) in post-glacial lakes in western Canada have contributed significantly to recent research of character displacement (e.g., Schluter 1993, Schluter 1995). Both observations of natural populations and manipulative experiments show that when two recently evolved species occur in a single lake, two morphologies are selected for: a limnetic form that feeds in open water and a benthic form that feeds at the lake bottom. They differ in size, shape and the number and length of gill rakers, all of which is related to divergence in their diet. Hybrids between the two forms are selected against. When only one species inhabits a lake, that fish displays an intermediate morphology. Studies on other fish species have shown similar patterns of selection for benthic and limnetic morphologies (Dayan and Simberloff 2005), which can also lead to sympatric speciation (e.g., Barluenga et al. 2006).

The Appalachian salamanders Plethodon hoffmani and P. cinereus displayed no trophic, morphological or resource use differences among allopatric populations; when the species occurred in sympatry, however, they displayed morphological differentiation that was associated with segregation in prey size (Adams and Rohlf 2000). Where these two species co-occurred, P. hoffmani had a faster closing jaw required for larger prey, and P. cinereus had a slower, stronger jaw for smaller prey. Other studies have found Plethodon salamander species that demonstrate character displacement from aggressive behavioral interference rather than exploitation (Adams 2004). That is, morphological character displacement between the two species is due to aggressive interaction between them rather than the exploitation of different food resources. It is often assumed that closely related species are more likely to compete than are more distantly related species, and hence many researchers investigate character displacement among congeners (Dayan and Simberloff 2005). While character displacement was originally discussed in the context of very closely related species, evidence suggests that even interactions among distantly related species can result in character displacement. Finches and bees in the Galapagos may provide an interesting example (Schluter 1986). Two finch species (Geospiza fuliginosa and G. difficilis) exploit more flower nectar on islands where the lager carpenter bee (Xylocopa darwini) is absent than on islands with the bees. Individual finches that harvest nectar are smaller than conspecifics that do not (Schluter 1986).

Introduced species have also provided recent “natural experiments” to investigate how rapidly character displacement can affect evolutionary change (Dayan and Simberloff 2005). When American mink (Mustela vison) was introduced in north-eastern Belarus, the native European mink (Mustela lutreola) increased in size, and the introduced mink decreased in size (Sidorovich et al. 1999). This displacement was observed within a ten-year study, demonstrating that competition can drive rapid evolutionary change.