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refers to a non-random pattern in the structure of insular communities
of, related to, or from an island
How are insular communities controlled by dispersal?
- Differences in dispersal ability through a filter.
- Reflects non-random pattern of insular species composition
- Although dispersal is biased in favor of taxa with superior immigration abilities, many insular forms have little or no ability to disperse to other islands
Can result from either dispersal abilities or different extinction probabilities
Two or more species with similar resource requirements on archipelagos that are similar islands result in [checkerboard] mutually exclusive distributions
Insular populations tend to exhibit ecological release, characterized by significantly broader niches and shifts to habitats, feeding strategies, activity periods, or other characteristics that would be non-typical.
Density compensation and niche shifts
- Competition influences the organization of communities by limiting species to only part of their fundamental niche, so populations expand their niches to increase density on islands where they interact with few species.
- Attributed to relatively low levels of interspecific competition
Hypothesized mechanisms and patterns of:
- The loss of avian flight on islands is associated with both a lack of predators and with increased body size.
- The absence of predators may have favored larger body sizes, without the cost of being stuck on the ground.
Loss of defenses/naivete (fearlessness/approachability)
- Many species on islands become fearless and approachable.
- Most of this is probably due to lack of predators.
- Dodos and other large land birds were quickly hunted to extinction because they were not afraid of humans when they arrived.
- Cactus on some Galapagos islands have soft spines.
- Many Galapagos animals were highly approachable when Darwin first arrived.
Size: optimum size
- Changes found on islands lower the overall energy expenditure and resource requirements for the island population.
- By minimizing resource requirements density can increase and therefore the probability of extinction decreases.
- Can explain flightlessness: flight requires large energy outputs, and even having the large pectoral flight muscles increases basal metabolic rate therefore requiring more resources for maintenance.
Harmonic and disharmonic biotas
Disharmonic biota: meaning the number and relative proportions of taxa living on the island differ significantly from the number and relative proportions of taxa on the nearest continental mainland area.
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