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HISTORICAL BIOGEOGRAPHY

History of Biogeography

BARRIERS

VICARIANCE

DISPERSAL


Historical Biogeography

How do we reconstruct the origin, dispersal, and extinction of taxa?


How historical events have affect the biology on the

planet?


Changing climate and

physical conditions


Rearrangements of the

continents and ocean basins


Historical Biogeography Historical Biogeography


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


An exclusive focus on local environmental

conditions will yield an incomplete

understanding of diversity


Where or how to find basic explanations for geographic patterns in species distributions and communities?


Differentiation Speciation Extinction Dispersal Vicariance

There are several fundamental processes in 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.


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.


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.




No evidence was ever discovered for the lost corridors proposed by the extensionists.


However,

Continental drift theory made a lot of sense


As a result, the debate between dispersalists and extensionists has been replaced by a debate between dispersalists and vicariance biogeographers


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


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.



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


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?


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.


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


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


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.


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.


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.


Range expansion


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.


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


Shift happens Vicariance

Ancestral population Geographic isolation Speciation


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?


A. formosus A. nuttingi

A. panamensis A. millsae

Atlantic Ocean

Isthmus of Panama

Pacific Ocean

Alpheus –

sibling species53

Allopatric speciation

in snapping shrimp


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


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



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.


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


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