Biogeography Flashcards
Australia
strange mammal fauna eg monotremes, giant flightless birds (emus)
Galapagos land mammals
only galapagos rice rat
dominant land mammals in galapagos
herbivorous turtles and iguanas
is the environment in the galapagos just not conducive to mammals?
no- once introduced to the galapagos, goats thrived, almost destroying the ecosystem
Darwin’s mistake
collected turtles for eating on the voyage, didn’t realise there were many different species of turtles and that he had eaten a new species
Could tell where the turtles came from just from the shape of their shell
Endemicity in the galapagos
islands just a few miles apart have same habitats but very different turtle species
what is primarily responsible for the distribution of different groups
geographical barriers- oceans and mountains
as opposed to environmental conditions eg species on plains of S America aren’t similar to species on plains of Europe, N America or Africa- they’re similar to things in mountains and forest of S America
Wallace’s contribution related to
biogeography
What were the biogeographic realms wallace broke the world into
palearctic nearctic neotropical ethiopian oriental australian
fact that physical barriers to movement controlled distributions suggests
groups of animals and plants, had moved to occupy their present ranges until they couldn’t move
dispersal mechanisms
land bridges
oceanic dispersal
land bridges
existence of similar species on different land masses
Bering land bridge
Russia and Alaska separated by 50 miles water
Geological record of UK shows marine rocks on land- implied sea level could change and/or land could be lifted up- could let land mammals pass what used to be ocean
discovery of ice ages where lots of water locked up in glaciers- explained how sea levels van be vastly reduced to make bridge
How can climate change act as a filter on bridges
climate determines how far N/S a species can spread
species that can only inhabit warm climates can’t spread across high-latitude land bridges
Paleocene-Eocene thermal maximum
55 m years ago, already warm climate became suddenly much warmer
What happened when the poles were subtropical
because high latitudes subtropical, warmth loving species could move north
Meant Beringia and other high latitude land bridges no longer had a climatic filter
who moved from asia into europe and n america through beringia/greenland
warmth loving primates
55m years ago
ancestors of horses spread into n america and later spread back across bering bridge into asia, europe and africa
what implies the and bridge is v recent
fishes and marine life on either side of the isthmus of panama very similar
great American interchange
fossils show that a few million years ago S America was an island continent- different fauna: giant armadillos, rodents, giant flightless birds.
N America: bears, cats, horses etc
Isthmus formed: southern species moved north and N moved S
How are the Galapagos colonised without land bridges?
flight
Flight mechanisms
birds blown out to se by storms, lost while migrating
Birds travels in flocks so a viable pop can colonise an island at once
Insects also blown long distances
Birds also dispersal vectors- carry seeds in crops/guts, invertebrates on their feet
Fern spores and plant seeds float on wind for long distances
What does flight explain
why island fauna often dominated by birds
Mammals outcompete them usually- can’t compete if can’t access the environment
Why do birds become large and flightless when access islands
exploit abundant food
Water dispersal
species of plant adapted to float e.g. coconut- distributed in tropics all over the world
Floating of plants by other means
icebergs trap rocks and soil
Soil trapped in tree roots can also carry seeds
Animals that float/swim
tortoises have a lighter weight shell than turtles to move on land- v buoyant
Can survive months without food/water
Crocs good swimmers and can drink saltwater- colonise distant islands
What is required for dispersal of animals to be successful
multiple individuals, or a female with a clutch of fertilised eggs
Animals that can’t fly/float long distances?
Rafting
trees and vegetation rafts drift long distances so animals clinging can travel too
Works better for lizards than mammals: go long without food and water
Galapagos rice rate anomaly: most offshore island have lizards, but not mammals
amphisbaenia
worm lizards
poor candidates for dispersal: live in burrows, don’t swim/float
However they’re widespread- continental drift
Pangea evidence
coasts of Africa and S America fit together, geology on either sides of Atlantic matches
Rocks on one coast similar in age and composition to on the other coast
Fossils from the Permian similar in Africa and S America
Hence land masses once joined into one giant continent
Seafloor spreading and plate tectonics
Discovery of seafloor spreading and subduction found that ocean crust near mid ocean ridges younger than crust further away
- seafloor splits along mid ocean ridges and new crust generates as crust split apart
Old crust thrown down into the earth in trenches and melted- created conveyer belts which drove continents apart
Gondwanaland
200m years ago
S America, Africa and India joined
Pangea
250 m ya
All continents united
What else does continental drift explain the distribution of
marsupials and flightless birds
Problems with CD explanation for dispersal of worm lizards
don’t diversify till after continental breakup (shown by evol tree, made from fossil evidence and molecular clock/data), so distribution can’t be explained by CD
SO must involve dispersal
Must have crossed the Atlantic
So how did worm lizards disperse?
Travelling in soil carried by floating vegetation (same as seeds)
Trees- fallen of eroding cliffs, washed out to sea by rivers or tsunamis, could have carried them in their roots
Ratites
fossils and molecular data also reject CD as explanation for dispersal
Oldest fossils of ratites don’t appear until Palaeocene (after CD, after Gondwana broken up) And they can fly.
Ratites flew then evolved large, flightless forms to take adv of niches left by Dino extinction
Mammals
most are recent, radiate after cretaceous in response to Dino extinction
S America was a island continent till Isthmus of Panama formed
Madagascar and Aus isolated since the cretaceous
SO inhabitants had to cross water
Fossil marsupials
Oldest not from Gondwana, instead Cretaceous of China and N america
First appearance in southern hemisphere is in the paleocene of s america
Immigrated when dinos went extinct maybe by rafting
Recent spread of marsupials from N america to S america to Australia = dispersal
