Foster's Island Rule SPECIFICALLY Flashcards
What is island biogeography?
Provides some of the best evidence in support of natural selection and the theory of evolution.
Describes an ecosystem that is isolated by being surrounded by different ecosystems.
What is island dwarfism?
The process of large animals evolving and reducing body size when population range is limited to a small environment. This is caused by a niche of resources, causing stunted growth and reduced reproduction.
Example of dwarfism?
Channel Island Fox (Urocyon Littoralis):
- One third smaller than its mainland ancestor the gray fox.
- Decline in 1990’s was attributed to predation by golden eagles which inhabited island after alien prey base (feral pigs and mule deer fawns) along with absence of native bald eagle due to extripation via chemical contaminans and direct persecution.
- Also declined due to canine distemper virus caused by a mainland raccoon (Coonan et al. 2010)
- Due to being geographically isolated, it has no immunity to parasites and diseases brought in from the mainland.
- Solution: USFWS draft recovery plan inn 2012 to remove disease and predation using monitoring strategies and managing captive fox populations.
What is island gigantism?
Size of a species grows rapidly in comparison to mainland species, due to the absence of predators, size is used for competitive resources.Can withstand harsher conditions
What is Foster’s island rule? 1964
Members of a species get smaller or bigger depending on the resources available in the environment
FOSTER 1964
Example of gigantism?
Giant rat (Papagomys Amandvillei), Flores (Indonesia):
- Due to smaller landmass and limited food resources as well as absence of predators such as hawks falcons and owls as the predators on Flores are kimodo dragons, marabou stork and vultures, meaning rats had no reason to remain small
- IUCN Red List, near threatened threatened by deforestation, dogs and cat predation and hunting from locals.
- Solution = Rutong Protection Forest
(Suyanto 1998)
Biddick et al. 2019 (plant counter to Foster’s island rule)
Island plant species follow the island rule in terms of stature and leaf size, however seed size is not affected.
Although, the island rule is intended for animals to follow and not plants, research has not been intended to apply to plants, could be a different set of factors rather than resource, island size etc.
Biddick et al. 2019
Dunlop and Morris, 2018 (Dwarf Golden Bandicoot)
Dwarf golden bandicoot taken from Barrow island and four generations later the offspring adapted to be the size of mainland golden bandicoot. Therefore this is not a genetic response and is a phenotypic response to resource availability and in this case ecological processes that limit resources are the cause of island dwarfism.
Dunlop and Morris, 2018
Karagkouni 2016 (Terrestrial Isopods)
Island species of isopods do not differ greatly in size compared to the mainland species. This is due to an isopods ability to adapt and eat almost all vegetation, therefore there is no limiting factor to their resources and they remain the same as well as having a wide range of predators which result in no predation pressure.
Karagkouni, 2016
What are the processes that cause island gigantism? (in depth)
Predators are absent from the island which can be a result of difficulties during dispersal. (i.e pre-historic Cuba, only apex predators are owls, eagles and falcons which are less efficient and allow herbivores to grow bigger without the need to hide.)
Allows species to compete for niche and can survive for prolonged periods without resources.
Terratorialism - Anaho island, Nevada, terratorial reptiles are larger compared to mainland (keehn et al. 2013)
What is a niche?
Limited resources and tolerance levels
What are the processes that cause island dwarfism? (in depth)
Reproductive benefits - gestation period is shorter (development time as an embryo) and generation times are shorter
Carnivores get smaller because of size and availability of prey, as competition is low priority - i.e. Tiger snakes (Notechis Scutatus) namely on Carnac Island, are smaller on islands because small snakes are more adapted to take small prey (Keogh et al. 2005)
