Avoiding Competition: An Animal’s Guide
Whilst competition between animals can occur, whether between individuals of the same species or different, where possible competition is avoided. This is due to the energy expenditure and often risk of death associated with direct competition. Even the famous stag with their enlarged antlers always try to avoid competition before commencing. During the rut, stags will display behaviours such as parallel walking and roaring to assess dominance. If this does not assert one male as more dominant than another, fighting will commence.
Instead, particularly to avoid competition for food, animals have found another way of avoiding direct competition. This is related to niche theory developed by Hutchinson in 1957. Whereby all species have their own roles to play in an ecosystem and those with the same role cannot overlap to exist at the same time and have the same niche (described by Gause in 1934 known as the Competitive Exclusion Principle). MacArthur studied warblers in 1958 and found despite 5 species occupying the same tree, by splitting it into 16 cross sections, each species foraged in a slightly different area of the tree using slightly different techniques.
In 2011, Kiska et al. found 4 species of dolphin co-existing around Mayotte Island all with differing habitat and behavioural budgets, whether that be the depth in which they foraged or the area off the coast of Mayotte Island they were most likely found. In the Bay of Biscay, Das et al. found 2 distinct ecological niches for tuna based on the input of squid into their diets. These differing niches described allow animals to side-step competition and co-exist in the same areas.
From here, different methods of indirect competition were uncovered. The most common known as resource partitioning. This is where species occupying the same area will eat different prey to avoid competition. An example can be seen in bats as studied by Aldridge and Rautenbach in 1987. Mist-netting different species found a significant correlation between the size of the bat and the size of the prey where a large bat had a range of prey sizes, but small bats only fed on small prey. There are many explanations to this behaviour including the energy expenditure of the small bats being too great to justify the catch of large prey. However, the most widely accepted explanation is resource partitioning, to avoid competing with larger bats, whom given the size difference are most likely to win.
As a result of resource partitioning, over many generations character displacement occurs. This being where the animals change their anatomical or physiological structure to allow them to avoid competition. The most famous example being Darwin’s finches where the beak sizes evolved differently over time for the different species to feed on different size seeds. This method of side-stepping competition can also be seen in Fenchel’s study of mud snails in 1975 where snails feeding on larger food particles had evolved with larger body sizes when different snail species existed together.
Historical replacement whereby one species removes another species from its former range is often seen with invasive or introduced species. Such as the red and grey squirrels in the UK. The grey squirrels have spread vastly through the UK out-competing the red squirrels and taking over their habitat range, causing the red squirrel as a result to decrease its range and only occupy a handful of areas. This reduction in the niche size of the red squirrel is due to attempting to avoid competition with grey squirrels on account of their superior abilities of survival compared to the smaller red squirrels.
As a result of side-stepping competition, animals can also be seen to increase the size of the niches once a competitor has been removed. By studying 5 Caribbean islands in 1977, Cox and Richlefs found breeding birds of the same species occupied different sizes of niche on different islands due to there being a different composition of birds present. This difference was attributed to ecological release, where the bird species in one habitat were able to expand their range more than the same species residing in another habitat due to a competitor species not being present.
This animal’s guide to avoiding competition has walked through the basics of side-stepping competition by adopting techniques such as resource partitioning, character displacement, historical replacement, and ecological release.
All examples given in this text can be found, in full, using the information below:
Kiska et al. 2011. Ecological niche segregation within a community of sympatric dolphins around a tropical island. Marine Ecology Progress Series.
Das et al. 2000. Tuna and dolphin associations in north-east Atlantic: evidence of different ecological niches from stable isotope and heavy metal measurements. Marine Pollution Bulletin.
Aldridge and Rautenbach. 1987. Morphology, echolocation and resource partitioning in insectivorous bats. Journal of Animal Ecology.
Cox and Richlefs. 1977. Species diversity and ecological release in Caribbean land bird fauna. Oikos.
Fenchel. 1975. Character displacement and coexistence in mud snails. Oecologia
All photos are my own.
1,486 total views, 2 views today