material

1. 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

2. Ratite Birds – Monophyletic
• Once thought convergent
• But, movement of continents
cassowary kiwi tinamou
Aust. / N. Guinea N. Z. Neotropical
ostrich rhea emu
Africa S. America Aust.

3. 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)

4. Range
Expansion
1. Dispersal
A) 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

5. Mobility
All organisms are mobile at some stage
• Ferns & Fungi:
fine spores: wide distribution
• Fresh-water Fish:
motile: restricted in distribution
need geologic changes for dispersal
• Marine Fish :
planktonic eggs & larvae
widely dispersed by ocean currents.

6. True Range Expansion
Peripheral Colonization (range expansion)
vs.
Satellite Populations (accidental dispersal)

7. Barriers to Dispersal
1. unsuitable habitat
2. strong competitor
3. severe predation
Probability of accidental dispersal :
mobility & type of border
maple seed
fern spore

8. 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

9. Dispersal vs. Vicariance
Dispersal
• Range Expansion
• Speciation
Vicariance
• Splitting Range
• Extinction of Middle
population
X

10. Vicariance: Pleistocene glaciations
• 2 million - 10,000 years ago
Cold adapted Cold adapted
Warm adapted Warm adapted
Refugia
Time

11. Continuity of Distribution
• Vicariance : disjunct
• Dispersal : disjunct or continuous
Disjuct Distributions:
• Tapir : Malaysia, neotropics
• Cacti : N & S. America, Madagascar
• Alligators: Asia, North America

12. Biogeographical Patterns
• Congruent Distributions are common
among endemic taxa
• e.g. South America
• Suboscine Birds, Edentates, Platyrrhine
Primates, Caviomorphs

13. Geographical History
• Patterns in
biogeography often
demonstrate history
• e.g. Biogeographical
realms reflect breakup
of supercontinent
• Wallace’s line

14. 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

15. Convergence
Common in similar habitats across realms
• e.g. Desert Bipedal Rodents
North America Asia Australia
Heteromyidae Dipodidae Muridae

16. 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