Lecture 5
Mammal Zoogeography
145 MY
JURASSIC
215 MY
?
Multiturberculata
Amphilestidae
Triconodontidae
Docodontidae
?
?
Dryolestidae
Paurodontidae
Peramuridae
PLACENTALS
MARSUPIALS
‘K-T boundary’
Amphitheridae
Shuotherium
Spalacotheriidae
Kuehneotheriidae
CRETACEOUS
Morganucodontidae
65 MY
Ornithorhynchidae MONOTREMES
CENOZOIC
Haramiyoidea
Sinoconodontidae
Phylogeny of Mesozoic Mammals
0 Yrs
?
TRIASSIC
(from Carroll 1988, pp. 415)
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?
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.
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
echidna (Tachyglossus)
pangolin (Manis)
aardwolf (Protoletes)
Giant anteater (Myrmecophaga)
aardvark (Orycteropus)
numbat (Mymecobius)
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
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. = > competition & specialization
•harder to adapt to colder climates
•parasite loads > in tropics
40
50
50
80
100
110
110
110
140
150
150
150
160
Not always the case
•seals and baleen whales reach peak diversity at high latitudes
•Drylands in Sth America has > diversity of endemics than lowland Amazon r’forest
Faunal Regions
Palearctic
Nearctic
Neotropical
Ethiopian
Oriental
Australian
Plate Tectonics
Plate Tectonics - theory that the earth’s 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
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
Antartica drifted south - massive
extinction.
Australia drifted east,
enormous radiation
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.
Sweepstake 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
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
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)
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
Jefferson’s ground sloth
(Megalonyx jeffersonii)
Giant beaver
(Casteroides ohioensis)
(from Pringle 1999)
Beringia Immigrants
1.8 million years ago
Mammuthus (mammoth)
Synaptomys (bog lemming)
Microtus (vole)
Ondatra (muskrat)
1.2 million years ago
Clethrionomys (red-backed vole)
Phenacomys (vole)
Synaptomys (bog lemming)
Microtus (vole)
Bison (Bison)
Gulo (wolverine)
Smilodon (saber-tooth cat)
170,000 years ago
Dicrostonyx (collared lemming)
Lemmus (lemming)
Lagurus (vole)
Microtus (vole)
470,000 years ago
Microtus pennsylvanicus (meadow vole)
M. montanus (montane vole)
Cervalces (extinct stag moose)
Rangifer (caribou)
Oreamnos (mountain goat)
Ovibos (musk ox)
Ovis (sheep)
Alces (moose)
Bos (yak)
Saiga (antelope)
Bootherium (extinct bovid)
70,000 years ago
Clethrionomys rutilis (red-backed vole)
Microtus oeconomus (tundra vole)
Panamanian Land Bridge
Stopped by Filter
many bats
most armadillos
anteaters
sloths
most histricomorphs
Panamanian Land Bridge
porcupine
nine-banded armadillo
Crossed Filter
Panamanian Land Bridge
Stopped by Filter
shrews
kangaroo rats
pocket gophers
beavers
bobcats
pronghorn antelope
bison
sheep
Panamanian Land Bridge
Rabbits
squirrels
mice
dogs
bears
raccoons
weasels
otters
skunks
puma
deer
Crossed Filter
Panamanian Land Bridge
Cannot Recross Filter
coatis
kinkajous
tapirs
peccaries
camels
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