Lecture 16: Biogeography

Geographic dist’n of organisms (Wallace, Darwin)

Historical Ecological

Explanation complementary Explanation

- past - current

- large scale - small scale

Want to find distribution of monophyletic groups

Ratite Birds – Monophyletic• Once thought convergent

• But, movement of continents

cassowary kiwi tinamouAust. / N. Guinea N. Z. Neotropical

ostrich rhea emuAfrica S. America Aust.

Geographic Distribution

Endemic• Restricted Range

Cosmopolitan

• Wide Distribution

Description of distribution depends on taxonomic rank

e.g. Warblers

Relictual: very narrow range

e.g. Tuatara (only New Zealand)

Range Expansion

1. DispersalA) Active : locomotion B) Passive:

– edible fruit with resistant seeds – resistant eggs on feet of water birds. – parasitic stages in the life cycle.– wind, water currents– e.g. cockleburs

MobilityAll organisms are mobile at some stage

• Ferns & Fungi:fine spores: wide distribution

• Fresh-water Fish:motile: restricted in distributionneed geologic changes for dispersal

• Marine Fish :planktonic eggs & larvaewidely dispersed by ocean currents.

True Range Expansion

Peripheral Colonization (range expansion)

vs.

Satellite Populations (accidental dispersal)

Barriers to Dispersal1. unsuitable habitat 2. strong competitor 3. severe predation

Probability of accidental dispersal :mobility & type of border

maple seed

fern spore

Ways to Expand Range other than Dispersal:

2) Adaptive Radiation : adaptation to formerly unsuitable habitat

e.g. progressive drought resistance: eventual dispersal across desert

3) Geological & Climatological Changes: elimination of dispersal barrier

Dispersal vs. Vicariance

Dispersal • Range Expansion• Speciation

Vicariance• Splitting Range• Extinction of Middle

population

X

Vicariance: Pleistocene glaciations

• 2 million - 10,000 years ago

Cold adapted Cold adapted

Warm adapted Warm adapted

Refugia

Time

Continuity of Distribution

• Vicariance : disjunct

• Dispersal : disjunct or continuous

Disjuct Distributions:

• Tapir : Malaysia, neotropics

• Cacti : N & S. America, Madagascar

• Alligators: Asia, North America

Biogeographical Patterns

• Congruent Distributions are common among endemic taxa

• e.g. South America

• Suboscine Birds, Edentates, Platyrrhine Primates, Caviomorphs

Geographical History

• Patterns in biogeography often demonstrate history

• e.g. Biogeographical realms reflect breakup of supercontinent

• Wallace’s line

New Zealand

• Narrow endemism

New Zealand & New Caledonia from Australia.

~ 80 million years ago.

Australia from Antarctica:

~ 50 million years ago.

Antarctica from South America:

~ 60 million years ago

Convergence

Common in similar habitats across realms

• e.g. Desert Bipedal Rodents

North America Asia AustraliaHeteromyidae Dipodidae Muridae

Distributions

Elephantidae: • Origin: Africa (Pliocene 5mya)• Dispersed: N. Amer. (Bering land bridge)

mammoths: extinct

Camels:• Origin: N. Amer. (Eocene)• Dispersed: Eurasia (Bering)

: S. Amer. (Isthmus)• Extinct in all but S. Amer., N. Africa, Asia