chapter 14 april 18th, 2012. island biogeography loss of dispensability, the development of...

Chapter 14

April 18th, 2012

Island Biogeography

• Loss of dispensability,

• the development of gigantism or dwarfism,

• the loss of antipredator defensive features and behaviors,

• the development of woody shrubs and trees from species that occur as soft-stemmed herbs on continents,

• and the development of highly specialized niches

Theory of Island Biogeography• MacArthur and Wilson 1967

• Constructs linkages between species-area relationships on islands to dispersal and extinction processes

• Large islands support more plants and animals than smaller islands

• Examples: Hawaii and Caribbean

• Nested pattern of insular communities

• Endemics

• Islands that are closer to continents have higher species richness than those farther away

Theory of Island Biogeography

Theory of Island Biogeography

• Immigration balanced by extinction

• Species turnover

• Small Island Effect – islands are too small to impact extinction rates

• Rescue Effect – populations of species on islands on the brink of extinction are rescued by the arrival of new immigrants of the same species

• Target Area Effect – size matters as much as distance

Theory of Island Biogeography

• Problems with Theory:– Treats all species the same in terms of immigration

and extinction– Doesn’t take into account the impact that plants

and animals might have in facilitating immigration by other species

– Extinction of some species may make immigration for other impossible

– Excludes speciation and evolution

Theory of Island Biogeography

• Problems with Theory:– Volcanic disturbances, invasive species,

competition, ocean and wind currents, historical land connections, doesn’t account for humans not taken into account

– Doesn't take migratory animals into account

Theory of Island Biogeography

Island Rule• The smaller the mammal, the larger it gets on

islands; the larger the mammal, the smaller it gets on islands– Massive rodents on islands– Dwarf elephants on Mediterranean Islands