Island Biogeography: Species Occurrence and Competition, Slides of Ecology and Environment

Download Island Biogeography: Species Occurrence and Competition and more Slides Ecology and Environment in PDF only on Docsity! Incidence Functions • Concept introduced by Diamond (1975) to describe the probability of occurrence of a species with respect to ordered site characteristics, such as species number Docsity.com Incidence Functions • The x-axis is the number of species on the island and the y axis is the proportion of islands in a given size class that were occupied by the species Docsity.com Incidence Functions • The IF may also simply reflect the distribution of habitat types among islands • For example, high-S species may be habitat specialists and those ‘specialized’ habitat may only exist on larger islands Docsity.com Incidence Functions • We can use null models to clarify what the proper interpretations of the IF should be • Whittam and Siegel-Causey (1981) examined Alaskan seabird colonies using IF Docsity.com Incidence Functions • They found examples of both high-S species (CM) as well as supertramps (GWG) Docsity.com Example • Schoener and Schoener examined 76 species of birds on 521 small islands in the Bahamas (as well as other vertebrate groups) • They also measured area, isolation, habitat availability and vegetation structure Docsity.com Occurrence Sequence • Lizards are perfectly ordered • Resident birds are highly structured • Migrant birds are more haphazard Docsity.com Results • Species occurrences were predictable, although different groups followed different assembly rule • Lizards and resident birds were ordered with respect to island area, migrant birds were more related to island isolation • The occurrence of both lizards and birds cold be predicted by vegetation and habitat structure Docsity.com Competition and Invasion History • The invasion history (the sequence and timing of arrival of different colonists in a community) has a significant effect on the their chances of establishment and on the resultant community structure Docsity.com Competition and Invasion History • Perhaps the best evidence that invasion sequence does affect the pattern of community development in this way comes from the growing number of experimental analyses of community development in laboratory microcosms Docsity.com Competition and Invasion History • E.g. Robinson and Dickerson (1984, 1987) ran a series of experiments using beakers and small aquatic organisms (e.g. algae, ciliates, rotifers, flagellate) • Species were added a in a specific sequence at two different rates • Differences were determined to be influenced by both sequence and introduction rate Docsity.com Competition and Invasion History • A series of small seasonal pools on a freshwater marsh offers additional insight • Natural colonization could occur in these identical pools… 50 former holes from concrete pillars removed (i.e. same size, depth, age, substrate) Docsity.com Competition and Invasion History • Pools were categorized based upon their isolation from source and extent of drying (tides) • Resulting communities within similar groups converged upon very homogeneous (with a total of 79 species) Docsity.com Competition and Invasion History • A number of species were recorded on only one or two occasions in only one or two pools • Jefferies divided species into two groups based on their relative occurrence (> or < 50% of pools) • He concluded that ‘expected’ species occurred at 79.6% and ‘unlikely’ species (occurring solely through deterministic processes) was 10.9% Docsity.com Competition and Invasion History • Differences of only a few days in the arrival times of mycophagus Drosophila in the communities that develop in decaying mushrooms can alter the outcome of competition Docsity.com Competition and Invasion History • We have a pretty good idea of the influence of communities that are relatively ephemoral, but long-lived organisms are much harder to understand Docsity.com Competition and Invasion History • Dragonfly community structure is a result of temporal variation, habitat selection, and predator-prey effects Docsity.com Competition and Invasion History • Similar experiments have been conducted using Odonates (Morin), but added fish to the system (strong predator of odonate larvae) Docsity.com Competition and Invasion History Fish reduce the abundance of odonates, reducing the intensity of competition and priority effects and changing the relative abundance of surviving dragonflies Docsity.com Competition and Invasion History • Other examples: many sessile-based communities (rocky shores, coral reefs) where competition for free-space is the major force structuring communities • Introduction of a predator into the system (predatory coral reef fish) can greatly impact subsequent community structure Docsity.com