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HISTORICAL BIOGEOGRAPHY
History of Biogeography
BARRIERS
VICARIANCE
DISPERSAL
HISTORICAL BIOGEOGRAPHY
Historical Biogeography
How do we reconstruct the origin, dispersal, and extinction of taxa?
Historical Biogeography
How historical events have affect the biology on the
planet?
Historical Biogeography
Changing climate and
physical conditions
Historical Biogeography
Rearrangements of the
continents and ocean basins
Historical Biogeography
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Catastrophic collisions with
asteroids
Extinctions
Diversity has generally increased over the past several hundred million years
Proliferation of flowering plants
Proliferation of fish, mollusks, & crustaceans
➋➊ ➌➍ ➎
Historical Biogeography
An exclusive focus on local environmental
conditions will yield an incomplete
understanding of diversity
Historical Biogeography
Where or how to find basic explanations for geographic patterns in species distributions and communities?
Historical Biogeography
Differentiation Speciation Extinction Dispersal Vicariance
There are several fundamental processes in biogeography
Historical Biogeography
Differentiation Speciation Extinction Dispersal
These are the processes by which organisms respond to changes in the geographic template.
There are several fundamental processes in biogeography
The relative importance of movement, or dispersal, has been the subject of great debate.
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Wallace
Gray
Darwin
The early “dispersalists” included Darwin, Alfred Russel Wallace and Asa Gray.
They argued that disjunctions (a situation in which two closely related populations are separated by a wide geographic distance) could be best explained as the result of long distance dispersal.
Historical Biogeography
The dispersalists were opposed by the “extremists”, who believed that disjunctions had resulted from movement along ancient corridors that had disappeared.
Lyell
HookerAmong the leaders of the extensionist movement were Charles Lyell and Joseph Hooker.
Historical Biogeography
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Historical Biogeography
No evidence was ever discovered for the lost corridors proposed by the extensionists.
Historical Biogeography
However,
Continental drift theory made a lot of sense
Historical Biogeography
As a result, the debate between dispersalists and extensionists has been replaced by a debate between dispersalists and vicariance biogeographers
Historical Biogeography
What is dispersal?
Simply, the movement of organisms away from their birthplace.
Often, confined to a particular life history stage.
Don’t confuse with dispersion, which refers to the position of individual organisms with respect to others in the population.
Dispersal
Ancestral population Geographic isolation Speciation
Species A’ Species B
Historical Biogeography
The role of dispersal in biogeography is different.
Biogeographers are interested in those dispersal events in which species change their range by dispersing over long distances.
These events are rare, and largely random.
They are, however, critical to understanding the distribution of organisms.
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In order to expand its range through dispersal, an organism must be able to:
• Reach a new area.
• Survive the potentially harsh conditions occurring during the passage.
• Survive and reproduce in the new area to the extent that a new population is established.
Dispersal and Range Expansion
Historical Biogeography
Biogeographers often distinguish three types of dispersal events that can accomplish this:
1.Jump dispersal (“sweepstakes”) 2.Diffusion. 3.Secular migration.
Dispersal and Range Expansion
How do they operate?
Historical Biogeography
Jump dispersal
Definition: Movement of individual organisms across large distances of inhospitable, followed by the successful establishment of a population of the original disperser's descendants at the destination.
This usually takes place over a time period less than the life span of the individual and often over inhospitable terrain.
Historical Biogeography
Jump dispersal
Species “skips” over area outside its range to new location Island colonisation
Some species lacking from islands – limited ability to disperse (mammals, amphibians, freshwater fishes)
Also occurs across continents
Historical Biogeography
The sheepshead minnow (Cyprinodon variegatus)
It has been able to colonize these habitats by dispersing many hundreds of miles across ocean water.
It’s ability to tolerate wide ranges of salinity makes this possible.
Estuaries and mangrove swamps throughout the Caribbean
Historical Biogeography
We can see the same thing over longer distances and greater time periods for many other archipelagoes.
The Galapagos lie 800 km west of Ecuador in the Pacific Ocean.
The Hawaiian Islands lie 4000 km west of Mexico.
In both cases, there is indisputable evidence of many groups of organisms reaching the islands by dispersal.
Historical Biogeography
Diffusion
Definition: Diffusion is the gradual movement of populations across hospitable terrain for a period of many generations. Species that steadily expand their ranges can be said to be diffusing.
Gradual spread of of individuals outward from the margins of a species’ range. It is a slower form of range expansion involving not just individuals, but populations.
Historical Biogeography
The cnidarians Velella and Physalia have sails or floats that allow them to drift across the surface of the ocean. In both cases, the orientation of the sail causes them to drift either to the right or left.
Historical Biogeography
Range expansion
Historical Biogeography
Secular migration
Definition: Secular migration is diffusion taking place so slowly that the diffusing species undergoes appreciable evolutionary change during the process. The range of the species expands or shifts over long time intervals (thousands or millions of years). The environments themselves may change and natural selection acts on the descendant populations.
Evolutionary divergence through range expansion. Evolutionary time scale.
Historical Biogeography
Range extension:
the species is at first found only in area A. It later gradually extends its range of distribution into the neighbouring area. However, in the absence of any barrier between the two areas, it cannot differentiate into a new separate species.
Cox, C. B. & Moore, P. D. (2005). Biogeography. An ecological and evolutionary approach. Oxford: Blackwell Scientific Publications, London.
Diffusion and Secular migration
Historical Biogeography
Shift happens Vicariance
Ancestral population Geographic isolation Speciation
Historical Biogeography
Vicariance :
Species distributions are determined by geological and climatological events: continental drift, Pleistocene glaciation etc
VICARIANCE?Historical Biogeography
Isthmus of Panama closed ~ 3.1 MYASplit ~150 “geminate” (twin) species
VICARIANCE?
Historical Biogeography
A. formosus A. nuttingi
A. panamensis A. millsae
Atlantic Ocean
Isthmus of Panama
Pacific Ocean
Alpheus –
sibling species53
Allopatric speciation
in snapping shrimp
Historical Biogeography
Knowlton et al.(1993) created a phylogeny of Pacific (P) and Caribean (C) species pairs of Alpheus C6
C3
C5
C4
C1
C2
P6P6
P3
P5
P4
P1
P2
P7
C3
P7
Historical Biogeography
Knowlton et al.(1993) created a phylogeny of Pacific (P) and Caribean (C) species pairs of Alpheus
In 6 out of 7 cases, the closest relative of a species was on the other side of the Isthmus
C6
C3
C5
C4
C1
C2
P6P6
P3
P5
P4
P1
P2
P7
C3
P7
Historical Biogeography
Historical Biogeography
Vicariance: a species originally occupies the whole of area A and B, but these
two areas become separated from one another by a barrier. The original
species then differentiates, by gradual genetic change, into two
separate species that are separated by the barrier.
Jump dispersal: the species is at first restricted to area A by a barrier that separates if from area B, and only
later disperses across the barrier. The two populations of the species now
each diferentiate into separate species.
The final results of vicariant speciation and of jump dispersal are identical.
Cox, C. B. & Moore, P. D. (2005). Biogeography. An ecological and evolutionary approach. Oxford: Blackwell Scientific Publications,
London.
Molecular phylogeny and geographical distribution of the intertidal snails, Cerithideopsis californica and C. pliculosa. A maximum-likelihood tree was constructed based on 873 bp of the CO1 gene. The major clades are categorized as clades A, B and the detailed subclades are within. Numbers near nodes are the support values for the clade from the different analyses (ML/BI). The scale bar represents the phylogenetic distances expressed as units of expected nucleotide substitutions per site. The distributions of the major genetic clades are shown at the right side of the figure. Numbers near the geographical points indicate sample size. Letters indicate sampling sites.
Historical Biogeography
Corridors Filters
Sweepstake routes
Biogeographers often distinguish three kinds of dispersal routes based on how they effect biotic interchange.
1. Corridors. Allow dispersal by permitting movement Contemporary examples. Historical – account for related of different species or even same species in widely separated regions
2. Filters. Conditions fall outside range of physiological tolerance. Restrictive dispersal pathway. Conditions restrictive to some species, not others. Can be biotic or abiotic
3. Sweepstakes routes. Hazardous or accidental dispersal mechanisms by which animals move from place to place. The standard examples are island hopping and natural rafts. Many land vertebrates live in the Caribbean Islands, and (if their biogeography is correctly explained by dispersal) they might have moved from one island to other, perhaps being carried on a log or some other sort of raft.
BIOTIC EXCHANGE AND DISPERSAL ROUTES
DISPERSAL: OVERCOMING BARRIERS
A B
A B
A B
dispersal corridor
dispersal filter
sweepstakes dispersal
wide variety
limited array (oases)
none
easy
difficult; only certain organisms make it
occasional migrants
corridor habitats
A to B dispersal
Area Cladogram Example
Approaches to investigating historical biogeographic patterns
1. Emphasizes hypothesis testing 2. Uses phylogenies (many of which are
developed with molecular data) 3. Uses area cladograms 4. Uses fossil and geological data
Phylogeography or historical biogeography
History of Biogeography
BARRIERS
VICARIANCE
DISPERSAL
HISTORICAL BIOGEOGRAPHY