Character displacement

Character displacement is a phenomenon in evolutionary biology where differences among similar species whose distributions overlap geographically are accentuated in regions where the species co-occur, but are minimized or lost where the species' distributions do not overlap. This pattern of variation is attributed to the evolutionary process of natural selection, which acts to minimize competitive interactions between the species. When two species compete for the same resource, natural selection favors individuals in each species that can exploit different resources or utilize common resources in different ways. Over time, this can lead to changes in the traits of the species involved, such as differences in body size, beak shape, or coloration, which reduce competition and allow for coexistence.

Mechanisms

Character displacement can occur through two main mechanisms: ecological character displacement and reproductive character displacement.

• Ecological character displacement involves changes in traits that affect the resource use of the species. For example, if two species of finch compete for seeds of similar sizes, natural selection may favor birds with beaks better suited to different seed sizes in areas where the species coexist. This can lead to a divergence in beak size or shape between the populations of the two species that co-occur, compared to populations that do not overlap.

• Reproductive character displacement involves changes in traits that affect mating, such as differences in mating calls or breeding times. This form of character displacement helps to reduce hybridization between species by promoting reproductive isolation. For instance, if two closely related frog species mate in the same pond, but one species evolves a unique mating call, this can reduce the likelihood of mating between the species, thus reducing competition for mates.

Evidence

Evidence for character displacement has been observed in a variety of organisms, including birds, mammals, insects, and plants. One of the classic examples involves the Galápagos finches, studied by Peter and Rosemary Grant. They found that beak size and shape in these finches were influenced by the types of seeds available on their specific islands, leading to a divergence in these traits where species co-occurred, compared to islands where each species lived in isolation.

Implications

Character displacement is an important concept in ecology and evolution because it provides insight into how species coexist and how biodiversity is maintained in ecosystems. It also illustrates the dynamic nature of evolutionary processes, showing how species can adapt to their environments and to each other over time. Understanding character displacement can help in the conservation of species by highlighting the importance of maintaining the ecological processes that allow for species divergence and coexistence.

See also

• Adaptive radiation
• Competition (biology)
• Evolutionary biology
• Natural selection
• Speciation