Biogeography, Evolution, and Island Biodiversity: Key Concepts and Processes

evolutionary history

when and where did a species originate, and what has happened to it since then

influenced by geological history

boundaries occur where

species composition drastically change over short distances

the barriers include bodies of water, mountains, etc

earth has many biogeographical areas

these different areas are separated by barriers

- barriers that prevent dispersal create these regions

major process controlling formation of biogeographic regions is

plate tectonics (continents rifting apart)

fossil help us reconstruct tectonic plate positions and movements over time

if fossils were present on x supercontinent, it must be at least as old as that continent

evolutionary separation of species can be attributed to 2 basic processes

variance and dispersal

variance

a physical barrier that forms that prevents dispersal and divides a species into 2 or more discontinuous populations

dispersal

when members of a species cross an existing barrier and establish a population some place else

individuals from the original population cross over an existing barrier

a lineage split due to vicariance was present in the whole area

before the barrier arose

biodiversity is higher in some groups compared to others

more biodiversity in areas closer to the equator except for some species like the seabird

species diversification rate

in the tropics, speciation rate is higher and extinction rate is lower because, the climate is much more consistent allowing more species to thrive in those areas

species time hypothesis

in the tropics, there is more time for speciation to occur, because that region has been climatically stable over time (no ice sheets)

productivity hypothesis

diversity is promoted by higher productivity which allows more resources which lowers extinction rate due to competition

have more species diversity

larger islands and smaller islands close to mainlands

the smaller and further away an island is

the less species that will be on it

the number of species on an island is

the rate at which species become extinct and also the rate the species immigrate

the turnover will always result in an equilibrium number of species

habitat fragmentation

large connected natural habitats are broken into smaller "island habitats" and this disrupts the natural wildlife, limits resources, threatens diversity and species that resided there

edge effects

are one of the reasons why smaller islands house less species

also are much less habitable because fragmentation exposes species in a fragment to much higher temps, hunting, hazards, predators, and diseases that make it unsuitable for animals to live and also reduces the immigration rate from patch to patch