GEOG20009 Lecture Notes - Lecture 18: Allopatric Speciation, Ocean Current, Ratite
15 May 2018
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LECTURE 18: DIVERSIFICATION & REGIONALISATION cont.
• Geographic patterns – must show some information of evolution/link to the past
• Biogeographic regions indicate the pervasive influence of geography, geology and climate on the historical origins,
diversification and spread of lineages
o History of place and lineage preserved in the distributions of contemporary taxa
DISUNCTION
• Disjunction: closely related organisms that occur in (widely) separated areas, absent in intervening areas
• Amphitropical vs small-scale/local
• Can be continental or hemispherical
• Usually inhabit similar environments, morphologically similar – not always the case through (Ratite (flightless) birds)
• Explaining this disjunction – a major goal in biogeography
o By tectonics: carried to distant sites on crustal plates as they drift apart
o By dispersal: dispersed long distances over geographic barriers (plants)
o By intervening extinction: surviving remnants of once-widespread taxon
o Or a combination of the above
• Porcupine: Brazil, Malaysia, African and North American – similar morphology, yet not all share genetics = not
disjunction unless they share genetics
LONG-TERM DYNAMICS V STABILITY
• Evolutionary pattern following long-term isolation – allopatric speciation
o If groups are isolated in regions of different area, geology and climate, these differences promote
ecological divergence
Convergent Evolution
• If physical environments are similar – distantly related organisms may independently evolve to similar adaptations
• Analogous (functionally similar) traits arise when different species live in similar ways or environments
• Homologous structures or traits have a common origin, but can have dissimilar functions
• Convergence in some traits, yet differences in others – at a species level
• Convergence of assemblages/biota
What attributes keep distinct biotas separated (biogeographic provincialism)?
• Land Bridges: but no complete biotic interchange
• Barriers between biogeographic regions: oceans, mountains, deserts
o Selective – provide a filter
• Resistance to invasion: (biotas of large landmasses)
o Adapted to tolerate environment and interactions (inertia)
o Most exotic species have failed
o Diverse & saturated ecosystems more resistant
Birds
• Good dispersers – yet show provincialism
• 2 functional groups: limited dispersal v long-distance migration
• Limited possibilities to develop new breeding/wintering area
• Dependence on seasonal productivity
What happens when barriers erode or disappear?
• Biotic Interchange: A melding of 2 distinct, previously isolated biotas
• Such contacts have occurred historically – yet poor record due to limited fossil record
GREAT AMERICAN BIOTIC EXCHANGE
• A large-scale ecological and evolutionary event
• Combined effect of dispersal, interaction, extinction and evolution on diversity
• Chain of islands between N and S America formed – kept growing and finally formed a land bridge
• Closure of the isthmus (3-4ma) – changes in ocean circulation & allows migration of terrestrial animals
o Evidence of closure 15 Ma
• S. America endemic fauna – mainly marsupials
Document Summary
Disunction: disjunction: closely related organisms that occur in (widely) separated areas, absent in intervening areas, amphitropical vs small-scale/local, usually inhabit similar environments, morphologically similar not always the case through (ratite (flightless) birds) Explaining this disjunction a major goal in biogeography. Porcupine: brazil, malaysia, african and north american similar morphology, yet not all share genetics = not disjunction unless they share genetics. Evolutionary pattern following long-term isolation allopatric speciation. If groups are isolated in regions of different area, geology and climate, these differences promote ecological divergence. If physical environments are similar distantly related organisms may independently evolve to similar adaptations. Convergent evolution: analogous (functionally similar) traits arise when different species live in similar ways or environments, homologous structures or traits have a common origin, but can have dissimilar functions. Convergence in some traits, yet differences in others at a species level. What attributes keep distinct biotas separated (biogeographic provincialism): barriers between biogeographic regions: oceans, mountains, deserts.
