Studies have been performed in a wide variety of taxa—a few groups having disproportionately contributed to the understanding of character displacement: mammalian carnivores,
Galapagos finches,
anole lizards on islands,
three-spined stickleback fish, and snails. 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. Most character displacement studies focus on morphological differences in feeding apparatus rather than on those relating to habitat use. However, comparisons of micro-habitat use and morphological adaptations of Western and Eastern Rock Nuthatches indicate that these two species show spatial niche segregation in addition to trophic niche segregation. 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 species in the same
genus. 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 members of the same species that do not. Many studies have measured niche (often seen in diet) overlap between closely related species, sometimes finding strong niche divergence; seen even in broad niche overlaps. The specific periods of diet divergence are seen as the main cause of adaptive divergence in morphology and performance of a bird species; which can be connected to periods of scarcity. Between the sets of Finches there were low competition. These results are due to correlation between the vast differences in diet coupled with large and adaptive differences in beak morphology. However, with similar levels of Finch phylogeny showed ongoing divergence, diet overlap and competition.
Reptiles 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.
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.
Amphibians The Appalachian salamanders
Plethodon hoffmani and
P. cinereus display no morphological differences, eating habits, or resource use exploitation differences among allopatric populations; when the species occurs in sympatry; however, they exhibit morphological differentiation that is associated with segregation in prey size. Where these two species co-occur,
P. hoffmani has a faster closing jaw required for larger prey, and
P. cinereus has 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. That is,
morphological character displacement between the two species is due to aggressive interaction between them rather than the exploitation of different food resources.
Molluscs On
Okinawa Island, the snail species
Satsuma largillierti lives on the eastern half of the island, while
Satsuma eucosmia lives on the western half. Both populations overlap in sympatry along the middle of the island, where the penis length of the species differs significantly where they meet in sympatry. The snails' penis lengths exhibit divergence, suggesting reproductive character displacement of this trait.
Fish Threespine sticklebacks (
Gasterosteus spp.) in post-glacial lakes in western
Canada have contributed significantly to recent research of character displacement. 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,
Mammals Introduced species have also provided recent "natural experiments" to investigate how rapidly character displacement can affect evolutionary change. This displacement was observed within a ten-year study, demonstrating that competition can drive rapid evolutionary change. == See also ==