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https://goo.gl/BUXfYV 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 Historical Biogeography Rearrangements of the continents and ocean basins Extinctions Proliferation of flowering plants Proliferation of fish, mollusks, & crustaceans Catastrophic collisions with asteroids ➊ ➋ ➌➍ ➎ Diversity has generally increased over the past several hundred million years 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 Related species: different places How to explain? Creation theory: Multiple centers of creation Evolution theory: common center for ancestor ? Historical Biogeography Historical Biogeography There are several fundamental processes in biogeography Isolation and Evolution Center of origin Evolution Speciation Extinction Dispersal Isolation and Evolution These are the processes by which organisms respond to changes in the geographic template. Isolation and Evolution The relative importance of movement, or dispersal, has been the subject of great debate. Historical Biogeography Historical Biogeography The early “dispersalists” included Darwin, Alfred Russel Wallace and Asa Gray. Wallace 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. Gray Darwin Historical Biogeography The dispersalists were opposed by the “extremists”, who believed that disjunctions had resulted from movement along ancient corridors that had disappeared. Historical Biogeography Lyell Hooker Among the leaders of the extensionist movement were Charles Lyell and Joseph Hooker. Historical Biogeography Historical Biogeography Historical Biogeography No evidence was ever discovered for the lost corridors proposed by the extensionists. Historical Biogeography Historical Biogeography However, evidence surfaced in the 20th Century for a new, powerful means of continental drift . dispersal: The movement of continents could raft populations away from each other and separate them in vicariant events (tectonic, climatic, or oceanographic occurrences that isolate previously connected populations). Historical Biogeography What is dispersal? Simply, the movement of organisms away from their birthplace. Often, confined to a particular life history stage. As a result, the debate between dispersalists and extensionists has been replaced by a debate between dispersalists and vicariance biogeographers Don’t confuse with dispersion, which refers to the position of individual organisms with respect to others in the population. Historical Biogeography The role of dispersal in biogeography is different. Dispersal Species B Species A’ 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. Ancestral population Geographic isolation Speciation Historical Biogeography Dispersal and Range Expansion In order to expand its range through dispersal, an organism must be able to: They are, however, critical to understanding the distribution of organisms. Historical Biogeography Dispersal and Range Expansion Biogeographers often distinguish three types of dispersal events that can accomplish this: • Reach a new area. • Survive the potentially harsh conditions occurring during the passage. 1. Jump dispersal (“sweepstakes”) • Survive and reproduce in the new area to the extent that a new population is established. 3. Secular migration. 2. Diffusion. How do they operate? Historical Biogeography Historical Biogeography Jump dispersal Definition: Movement of individual organisms across great distances, 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) Estuaries and mangrove swamps throughout the Caribbean 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. Historical Biogeography Historical Biogeography Contrast Jump dispersal is simply the colonisation of new areas over long distance. An example can be seen in the rapid recolonisation of Krakatau after all life was wiped out by the volcanic explosion of 1883 The many species of sunfish (Lepomis spp.) of the southeastern United States, lacking this tolerance, were unable to disperse to Caribbean islands. 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 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 Dispersal Dispersal of foraminifera Secular migration Paleogeographic reconstruction for late Pliocene (ca. Movement of species - may be active (flying) or passive (wind-transport, drifting on a log) 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. Sexton P F , Norris R D Geology 2008;36:899-902 ©2008 by Geological Society of America Historical Biogeography Historical Biogeography Diffusion and Secular migration 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. Historical Biogeography Vicariance Ancestral population Geographic isolation Speciation Shift happens Historical Biogeography Historical Biogeography VICARIANCE? VICARIANCE? Isthmus of Panama closed ~ 3.1 MYA Split ~150 “geminate” (twin) species Vicariance : Species distributions are determined by geological and climatological events: continental drift, Pleistocene glaciation etc Historical Biogeography Historical Biogeography A. formosus A. nuttingi P6 Knowlton et al.(1993) created a phylogeny of Pacific (P) and Caribean (C) species pairs of Alpheus P6 C6 P3 In 6 out of 7 cases, the closest relative of a species was on the other side of the Isthmus Atlantic Ocean C3 C3 P5 C5 Isthmus of Panama P4 C4 Pacific Ocean Allopatric speciation in snapping shrimp Alpheus – sibling species P7 P7 A. panamensis A. millsae 53 P1 C1 P2 C2 Historical Biogeography Historical Biogeography VICARIANCE? 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. Cox, C. B. & Moore, P. D. (2005). Biogeography. An ecological and evolutionary approach. Oxford: Blackwell Scientific Publications, London. The final results of vicariant speciation and of jump dispersal are identical. Historical Biogeography BARRIERS The nature of long-distance dispersal means that organisms often have to survive for periods of time in environments that are hostile to them. These environments constitute physical and biological barriers to dispersal. The effectiveness of such barriers in preventing dispersal depends not only on the nature of the barrier, but also on the organism dispersing. Historical Biogeography Pacific Pacific Pacific Rise of the Isthmus of Panama Atlantic Atlantic Atlantic 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 VICARIANCE / DISPERSAL Bannerfishes(Chaetodontidae) IAA:Indo-AustralianArchipelago PeterF.Cowman BIOTIC EXCHANGE AND DISPERSAL ROUTES Corridors Filters Sweepstake routes DISPERSAL: OVERCOMING BARRIERS dispersal corridor dispersal filter sweepstakes dispersal A A A B B B corridor habitats A to B dispersal wide variety easy limited array (oases) difficult; only certain organisms make it none occasional migrants 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. Corridors are dispersal routes that allow movement of most taxa from one region to another. They do not selectively discriminate against one form, but rather allow a balanced assemblage of plants and animals to cross them. The areas at the two ends of a corridor should contain a fairly similar assemblage of organisms. The Bering Land Bridge which existed some 20,000 years ago likely functioned as a corridor which allowed organisms to pass from northern Eurasia to North America with very little selection of the types that could pass. Conditions along the corridor would have differed little from those on either end. Historical Biogeography A filter is a dispersal route that exercises some selection over the types of organisms that can pass through it. As a result, the colonists are a somewhat biased subsets of those that could potentially pass. The Arabian subcontinent acts as a filter in that only certain mammals, reptiles and ground birds can disperse between northern Africa and central Asia. 1. species originate in “centers of origin” The Lesser Sunda Islands form a twoway filter for the reptilian fauna of southeastern Asia and Australia. This region is sometimes known as “Wallacea”, and is bisected by Wallace’s Line. Historical Biogeography Historical Biogeography 1. species originate in “centers of origin” 1. species originate in “centers of origin” 2. speciation follows 2. speciation follows 3. new species evolve and disperse, thus displacing more primitive species to the periphery of the center of origin Historical Biogeography 1. species originate in “centers of origin” 2. speciation 3. new species evolve and disperse, thus displacing more primitive species to the periphery of the center of origin. 4. organisms disperse as far away as permitted by their abilities and their physical conditions. Historical Biogeography Relationships between geological and ecological properties of environment Patterns of morphological variation Coincided with Modern Synthesis Linking lead to formulation of biological species concept (Ernst Mayr) Also identified allopatric speciation Historical Biogeography Burgeoning info from Paleontology Origin, dispersal, radiation, and decline of terrestrial vertebrates Development of phylogenies New groups rise Increase in number of species Radiate to fill niches and expand range Still – question of how dispersed Historical Biogeography Earth’s crust believed fixed until 1960s Continental drift 1st proposed 1858 Resurfaced by Wegener and Taylor using geological and ecological evidence Criticized and denied until evidence became overwhelming Changed dispersal from land bridges to movements of continents Historical Biogeography Continental drift lead to study of disjunctions Vicariance biogeography Examination and revision of phylogenies Approaches to investigating historical biogeographic patterns Phylogeography or historical biogeography 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 Historical Biogeography Computers Geographic information systems Geostatistics HISTORICAL BIOGEOGRAPHY VICARIANCE DISPERSAL END