GEOG20009 Lecture 7: Lecture 7 Detailed Notes Landscapes & Diversity GEOG 20009
15 May 2018
School
Department
Course
Professor
LECTURE 7: ISLAND BIOGEOGRAPHY
• Types of Islands: continental islands (part of continental shelf), continental fragments
(microcontinents – split off by tectonic drift) and oceanic islands (originating from volcanic
seamounts)
SPECIES-AREA RELATIONSHIP
• Small islands have fewer species than large
islands
• Independent of taxonomy and habitat
• One of the few mathematical relationships in
biogeography & ecology
• Not linear, but a power function
Species – Area Relationship Explanation
Sampling effect only? NO
• More species in greater areas is a result of getting more individuals in greater areas
o If you go out and measure a larger area, and compare it to a smaller area – larger will obviously have
more species
o Species diversity goes up passively with
number of individuals
• Because islands have steeper slopes than similarly
sized areas on continents, this suggests species-area
relations are not just a sampling phenomenon
Successful colonisation varies with area due to effects on
• Immigration & establishment
• Extinction
Other attributes vary with area
• Bigger islands offer a greater diversity of
environments suitable for many more species than
small islands
THEORY OF ISLAND BIOGEOGRAPHY
• Robert MacArthur & Edward Wilson in 1967, proposed a model to explain species-
area relation
• Model proposes that:
o Rates of immigration (I) (and establishment) are higher for islands closer
to a source pool of colonists (E.g. mainland) than those that are distant
o Rates of extinction (E) are higher on small islands (because population
sizes are smaller) than larger islands
o Number of species reaches an equilibrium number given sufficient time
that reflects a balance between rates of immigration & extinction
• Krakatoa island research: rate of new species immigrating to the island changed as
number of species increases
o Extinction of species from the island also changed with number of species
Questions/Concepts
• Islands are
mesocosms – patches
of habitat that have
been colonised by
species that have
travelled
• What determines the
diversity of species
on islands
• Species-area
relationship
• Theory of Island
Biogegraphy
Readings/Papers
•
S = cAz
S = number of species (species richness)
A = area of the island
C and z = empirically determined (from data) constants needed to fit area data to number of species – vary with
region & species pool
(c = a minimum area of island needed to sustain any species, z = a rate of increase on number of species for a unit
increase in area – comparing z can vary between taxa suggesting different mechanisms at play)
Lichens
• Comprise a series of algae and a species of fungus living
together (symbiotic relationship)
• Require sunlight & reasonably moist environments
• Live on soils, trees, rock
• Saxicolous: lichens living on rocks
• Colonise new surfaces via wind-blown spores & vegetatively
• Lichens establish more quickly on rough surfaces than smooth,
and respond to roughness of surfaces
• Lichens with spores will establish more quickly on new surfaces
lacking any lichens
• Exhibit species-area curves: no extinctions, no turnover
Document Summary
Types of islands: continental islands (part of continental shelf), continental fragments (microcontinents split off by tectonic drift) and oceanic islands (originating from volcanic seamounts) Small islands have fewer species than large islands. Independent of taxonomy and habitat: one of the few mathematical relationships in biogeography & ecology, not linear, but a power function. Islands are mesocosms patches of habitat that have been colonised by species that have travelled: what determines the diversity of species on islands. No: more species in greater areas is a result of getting more individuals in greater areas. If you go out and measure a larger area, and compare it to a smaller area larger will obviously have more species. Species diversity goes up passively with number of individuals. Lichens: because islands have steeper slopes than similarly sized areas on continents, this suggests species-area relations are not just a sampling phenomenon. Successful colonisation varies with area due to effects on.
