Zoogeography Flashcards
Biogeography
– Study of the geographical distribution of living
things in time and space
– Zoogeography
is the study of animal distribution
Approaches
– Common question: Are current distributions the
result of dispersal or vicariance?
• Ecological – contemporary factors contribute to ranges
• Historical – phylogenetics, diversification
• Vicariance or dispersal might result in the disjunct
distribution of species
• Species’distributions are dynamic
– Former and present ranges differ
• Climatic shifts
• Facilitated dispersal
• Shared patterns can inform
– Earth history
– General evolutionary forces
Significant Patterns
- Distinct biogeographic regions
- Latitudinal diversity patterns
- Elevational diversity patterns
- Area relationships
- Island syndromes
Alfred Wallace (1823-1913)
“Father” of biogeography
• Traveled world documenting diversity and
distributions
Dispersal
• Occurs when an individual or population moves
from its place of origin to a new area
• Dispersal tendency due to
pressures exerted
by reproduction and necessity for the spacing
of individuals
Dispersal Depends on:
–Dispersal ability of species
– Breadth of tolerable environmental conditions
– Presence and permeability of barriers
Vicariance
• Species distribution patterns explained by splitting of
previously occupied region
• Emergent barriers divide species distribution
• Gene flow is restricted
• Geographic isolation and speciation
Avenues of Faunal Interchange
• Corridors – Pathway offering little resistance to movement • Filter route – Pathway allows passage of only certain species • Sweepstakes route – Pathway probably not crossed by large numbers of any given type of animal, but may be followed by an occasional individual
Wallace’s Zoogeographic Regions
Palearctic Region Nearctic Region Neotropical Region Afrotropical Region Indo-Malayan Region Australasian Region Antarctic Region Oceania
Palearctic Region
• Northern part of Old World
• Primarily temperate climate
– Shares 76% of families with Indo-Malayan region
Nearctic Region
• Includes nearly all of North America north of
the tropical sections of Mexico, and
Greenland
• Arctic tundra to semitropical thorn forest
Neotropical Region
• Americas from tropical Mexico south, Caribbean, southern tip
of Florida
• Tropical or subtropical (some deserts, alpine tundra, and
savannas)
• Characteristic mammals include marsupials, bats, primates,
xenarthrans, and hystricognath rodents
Afrotropical Region
• Africa south of Sahara, southern Arabian
Peninsula, Madagascar
• Deserts, tropical savannas, tropical forests,
montane forest, alpine tundra
• High diversity of ungulates
Indo-Malayan Region
• India, Indochina, southern China, Malay Peninsula,
Philippines, Indonesia west of Wallace’s line
• Tropical climate dominates
• Resembles Palearctic region (share 90% of families)
• Five families of primates, very high rodent and bat
diversity
Australasian Region
• Australia, Tasmania, Indonesian islands east of
Wallace’s line, New Guinea, islands of Melanesia,
New Zealand
• Tropical forests, savannas, and deserts
• 18 marsupial families and 9 native terrestrial eutherian
families (21 endemic). High rodent diversity in parts.
Antarctic Region
• Antarctica
• No land mammals since covered in ice in the
Neogene
– Seals only current terrestrial (semi) residents
Oceania
• Oceans of the world and isolated islands
– Relatively homogeneous from basin to basin
– Potential for global dispersal
• Marine mammals and bats
– Cetaceans and pinnipeds
– Verspertilionids and emballonurids
– Flying foxes on many Pacific Islands
Latitudinal Species Gradient
• Greatest diversity in the tropics
• Researchers have suggested that the
tropics:
– Have higher rates of evolutionary origination
(speciation) and act as a “diversity pump”
– Have lower rates of extinction and tend to
accumulate more species
Island Syndrome
• On islands:
– Competition reduced
– Fewer predators
– Flora may be depauperate
– Mammals tend to diverge from mainland stock
• Pattern of divergence is not consistent for all
species
• Mammals on islands tend to evolve toward a
fundamental or optimal body size for a particular
ecological strategy or body plan
Island Syndrome
• Island mammals different in size from
mainland
– Small mammals on islands generally larger
• Murids
– Large mammals on islands generally dwarfed
• Elephants
The History of Mammals in North and
South America
• Contemporary observations…
– Many mammalian families native to South America
– South America shares more families with North America
than any other continent
– But there are intriguing mammalian similarities with other
continents, too…
• Australian marsupials
• African and S. American rodents & primates
• Paleontologist George G. Simpson divided the history of
South American mammals into three “strata” (historical
groups)
Stratum 1: The Natives
• Original inhabitants when South America became isolated ~65 mya • Includes ancestors of modern armadillos, anteaters, sloths, and marsupials
Stratum 2: The Mystery Guests…from
Africa?
• Two types of mammals appear in the fossil record
of South America about 30 mya, and diversified
extensively since:
– New World rodents (guinea pigs, capybara, porcupines, etc…)
– New World monkeys (tamarins, spider monkeys, capuchins, etc…)
• Africa was ~1400km away from South America at
this time!
Evidence for Long-Distance Dispersal
from Africa
• Molecular evidence: closest relatives are still in Africa;
timing is after S. Am. and African continents split
• Fossil monkeys and rodents start to appear 30 mya in
South America, no earlier
• A floating island…It’s possible
– Paleoclimate and ocean models suggest ~ 10-15 day rafting
trip was possible
Stratum 3: The Great American Biotic
Interchange (GABI)
• GABI: Huge shuffling of species after sea levels fell,
continents moved, and isthmus of Panama formed
– From S. Am. to N. Am.: Sloths, opossums, armadillos,
porcupines, monkeys
– From N. Am. to S. Am.: Rodents, cats, weasels,
raccoons, horses, camels, deer, bears, dogs, skunks
