Lecture 5 Mammal Zoogeography

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Lecture 5Mammal Zoogeography
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Phylogeny of Mesozoic Mammals
0 Yrs
CENOZOIC
MONOTREMES
MARSUPIALS
PLACENTALS
65 MY
K-T boundary
?
Ornithorhynchidae
CRETACEOUS
?
?
145 MY
Peramuridae
JURASSIC
Kuehneotheriidae
?
215 MY
TRIASSIC
(from Carroll 1988, pp. 415)
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What is Zoogeography?
Zoogeography is the study of the geographical
distributions of animals
Zoogeography seeks answers to questions
like Why are there marsupials in Australia and
South America? Why are members of the camel
family (Camelidae) found in north Africa and
South America? Why are there primates from
Japan to Africa, as well as South but not North
America?
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Principles of Ecological Zoogeography
Endemism
all species have a limited distribution on a
world scale. Some mammals are very well
dispersed - eg. Humans, their stock, and
commensuals like the house mouse (Mus
domesticus), whereas others have a very limited
distribution. Endemism (occurring nowhere
else), or being endemic - a taxon is restricted
to a limited geographical area. Endemism
depends on the scale you are referring to - it
might be a small area like an island, or an
entire continent. Endemism can refer to a single
species, genus, family, order, or other grouping.
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Principles of Ecological Zoogeography
Convergence
when groups of mammals become geographically
isolated, they usually diverge - meaning they
adapt (over a long time span) to the specific
climatological, geological and ecological
situation they are faced with. However -
sometimes convergence occurs - convergence occurs
when distantly related lineages inhabiting
regions with similar climatological, geological
and ecological situations evolve similar
morphologies, life history patterns or niche
characteristics. Numerous examples of
convergence exist among mammals
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Principles of Ecological Zoogeography
Mammals on Islands

• Islands can be the traditional sort (surrounded
  by water!), or isolated mountain ranges, deserts,
  parches of suitable vegetation etc - habitat
  islands
• Dispersal to islands is a problem for mammals -
  rodents and bats are the most successful island
  colonisers - eg. rodents and bats are the only
  terrestrial eutherians to reach Australia, and
  the Galapagos Islands.
• Different selective pressure on islands vs.
  mainland affects some characteristics of
  mammals
• niche expansion - competitive release
• body size - can be larger or smaller than
  mainland counterparts
• behaviour - predator aviodance, etc

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Principles of Ecological Zoogeography
Latitudinal Gradients Species diversity of
mammals (and most other life forms) increases
along a gradient from the poles to the Equator

• Several theories proposed
• higher productivity and stability in tropics
• greater habitat heterogeneity in tropics
• more spp. gt competition specialization
• harder to adapt to colder climates
• parasite loads gt in tropics

• Not always the case
• seals and baleen whales reach peak diversity at
  high latitudes
• Drylands in Sth America has gt diversity of
  endemics than lowland Amazon rforest

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Faunal Regions
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Plate Tectonics
Plate Tectonics - theory that the earths crust,
including the continents and ocean floors, is
made up of a series of plates, as plates collide
volcanoes occur, and may result in oceanic
islands, mountain ranges etc. Continental Drift
- movement over geological time of the earths
large land masses as a result of plate tectonics

• Wegener (1912, 1915) - but not accepted until
  1960s

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Marsupial Zoogeography
Marsupials evolved in North America (diverse
fossil evidence from southern Canada western
USA) Dispersed south to South America, Antactica
and Australia, and East to Europe north
Africa Gondwana split from Pangaea, and
marsupials underwent extensive radiation in
relative isolation Marsupials in North America
and Europe went extinct, possibly due to
radiation and expansion of the Eutherians Antarti
ca drifted south - massive extinction. Australia
drifted east, enormous radiation
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Dispersal and Centres of Origin
Passive Dispersal - movements in which the
dispersing organism plays no active role in the
movement Eg. rafting, or being transported by
humans Active Dispersal - involves an
accumulation of ecological dispersal events in
which individuals move by terrestrial locomotion
or flight active long-term species dispersal
movements, also called faunal interchanges, occur
via several routes.
Corridor Route - minimal resistance to the
passage of animals (eg. present interconnection
of Asia and Europe) Filter Route - allows only
certain species to pass through - eg. Beringia.
Only mammals adapted to the cold climate could
successfully cross between the continents. Sweeps
take Route - most restrictive pathway. Involves
movement of animals by swimming, flying, rafting
or other means . Unlikely to be crossed by large
numbers of a given type of animal, but occasional
one will make it. Eg. New Guinea to Australia to
New Zealand
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Glaciation and Refugia
During the Pleistocene several cool, dry glacial
periods, interspersed with warmer and wetter
interglacial periods have had a substantial
effect of mammal distributions There have been 4
glacial periods in the last 600,000 years, with
the most recent one ending approx. 12,000 years
ago. We are currently in an interglacial (warm,
wet) period During each glacial period, ice
sheets expanded and many species were displaced,
some driven to extinction. During glacial
periods, however, the sea level was lower and
some land bridges formed (eg. Bering land
bridge) During the interglacial periods,
episodes of recolonisation and resettlement
occurred, and sea level rose, isolating some
species
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Glaciation and Refugia Beringia
Beringia was a land mass which was largely
ice-free during the last glacial period (90,000 -
10,000 years ago) due to its arid climate It
acted as a refugium for several mammals, as well
as a land bridge for animals to cross between
Eurasia and North America
(from Pringle 1999)
Land bridge was submerged again approx. 11,000
years ago (to the present)
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Beringia Mammals
Steppe bison (Bison priscus)
American lion (Panthera leo atrox)
Others included short-faced bears
(Artodus) mastodon (Mammut americanum) woolly
mammoth (Mammuthus primigenius) Scimitar cat
(Hometherium serum) camels (several genera) first
humans in North America
Giant beaver (Casteroides ohioensis)
Jeffersons ground sloth (Megalonyx jeffersonii)
(from Pringle 1999)
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Beringia Immigrants
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Panamanian Land Bridge
Stopped by Filter
many bats most armadillos anteaters sloths most
histricomorphs
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Panamanian Land Bridge
porcupine nine-banded armadillo
Crossed Filter
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Panamanian Land Bridge
Stopped by Filter
shrews kangaroo rats pocket gophers beavers bobcat
s pronghorn antelope bison sheep
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Panamanian Land Bridge
Rabbits squirrels mice dogs bears raccoons weasels
otters skunks puma deer
Crossed Filter
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Panamanian Land Bridge
Cannot Recross Filter
coatis kinkajous tapirs peccaries camels
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Camelidae Zoogeography
Camelidae - Bactrian camels (Camelus bactrianus)
and dromedaries (C. dromedarius) occur in north
Africa, and llama (Lama glama), alpaca (L.
pacos), guanaco (L. guanicoe) and vicuna (Vicugna
vicugna) occur in South America Camelids arose
and diversified in North America, with some forms
eventually dispersing across the Bering Land
Bridge (Beringia) to Eurasia and Africa, and the
Panamanian Land Bridge to South America North
American camelids went extinct towards the end of
the last glaciation