Feature Paper: Crisci, JV (2001) Historical biogeography and patterns of diversity. Journal of Biogeography, 28(2):157-168.
Author Abstract: Historical biogeography is going through an extraordinary revolution concerning its foundations, basic concepts, methods, and relationships to other disciplines of comparative biology. There are external and internal forces that are shaping the present of historical biogeography. The external forces are: global tectonics as the dominant paradigm in geosciences, cladistics as the basic language of comparative biology and the biologist's perception of biogeography. The internal forces are: the proliferation of competing articulations, recourse to philosophy and the debate over fundamentals. The importance of the geographical dimension of life's diversity to any understanding of the history of life on earth is emphasized. Three different kinds of processes that modify the geographical spatial arrangement of the organisms are identified: extinction, dispersal and vicariance. Reconstructing past biogeographic events can be done from three different perspectives: (1) the distribution of individual groups (taxon biogeography) (2) areas of endemism (area biogeography), and (3) biotas (spatial homology). There are at least nine basic historical biogeographic approaches: centre of origin and dispersal, panbiogeography, phylogenetic biogeography, cladistic biogeography, phylogeography, parsimony analysis of endemicity, event-based methods, ancestral areas, and experimental biogeography. These nine approaches contain at least 30 techniques (23 of them have been proposed in the last 14 years). The whole practice and philosophy of biogeography depend upon the development of a coherent and comprehensive conceptual framework for handling the distribution of organisms and events in space.
Note to Readers: Follow links above for author email, full article text, or the publishing scientific journal. Author notes in my review are in quotes.
Review: Since this will be the first paper in a 12-week course on biogeography, I thought I'd take a moment to mention why this paper was chosen for week 1. Crisci (the author) provides a great summary of various kinds of historical biogeography, summarized in his table (below).
But before we get into interpreting Crisci's table (above, which should be referenced throughout this review whenever needed) I thought we'd take a moment to review biogeography in general, even though we've discussed it through multiple Science Corner posts in the past. Biogeography is a branch of science bridging "biology" and "geography" and concerns itself with trying to describe patterns of biodiversity and abundance of organisms of all kinds around the world… in essence, trying to describe how and why organisms occur in the populations they do in space and time. Different biogeographers study different groups of organisms as well as concentrate on whether they merely want to describe patterns of diversity or try to determine reasons why such patterns exist, as well as concerning themselves with various spatial scales. However, biogeographers, regardless of their organisms or focus, often have overlap in their findings, with one of the largest and most uniform (though not universal) observations being that there are distinct latitudinal gradients in species diversity, with tropical regions (at the most basic definition, regions between the Tropics of Cancer and Capricorn, or between 23.5º N or S of the equator) often being the centers of highest species diversity across a wide range of organisms (but not all).
Now that we know "what" biogeography is, we can start to focus, with this 12-week course aimed at discussing multiple ideologies of biogeography as a review before getting into applications of biogeography in "the real world." This first paper is an overview of historical biogeography, which is a branch of biogeography concerned with describing the historical reasons (often at geological timeframes) why organisms occur in their present patterns of diversity today (or within the recent, recorded past). As the author notes, there is a great debate over what factors are the most important in determining present patterns of biodiversity.
But why is this important? Managers use principles of historical biogeography to try to set up effective conservation zones (e.g., National Parks, Marine Protected Areas, etc.) that are able to provide protected areas where "seed populations" can reproduce and settle areas outside of such protected zones, thereby allowing sustainable harvest of environmental resources.
In essence, historical biogeography is a form of "comparative biology concerned with evolutionary processes over millions of years on a large, often global scale." Crisci notes his objectives for his paper being "to discuss the overall situation in which historical biogeography occurs, to outline the contemporary methodologies and to discuss several of the critical issues that need to be tackled."
In attempting to define the present state of historical biogeography, the author draws a comparison to Charles Dickens' opening paragraph of "A tale of two cities" in so much as there is a lot of debate, a lot of discovery, a lot of bias, etc. (i.e., "the best of times, the worst of times"). In essence, historical biogeography is still a young field that has only made its greatest progress since the 1970s.
Crisci outlines "three external forces" as influencing the discipline of historical biogeography: "global tectonics as the dominant paradigm in geosciences, cladistics as the basic language of comparative biology and the biologist's perception of biogeography."
While many today might take for granted the existence of plate tectonics, debate existed into the 1960s on whether the continents on Earth were static or whether they had broken up and separated, as is known today. As Crisci states, "the biogeographical consequences of plate movements and interactions are enormous. The rearrangement of continental landmasses and island areas and the opening and closing of sea and ocean basins initiated by these movements and interactions have profoundly affected the distribution and history of organisms." It was during this era that Charles Darwin's theory of atoll formation (through gradual subsidence of volcanic islands combined with continuous growth upward of fringing reef systems) was also proved, though there is still debate about the universality of his basic principles for atolls around the world.
Crisci then goes on to not how "cladograms" became "a powerful language to communicate a system of relationships to other biologists" through defining the biological and historical "phylogenetic relationships between taxa and their geographical distribution" and noting how they are tied together. Currently, the integration of genetic cladograms with area cladograms (relationships about how different individuals, species / taxa, or localities are similar or dissimilar to each other) is serving an important role in "forcing biogeographers towards a more precise formulation of methodological practices and theoretical ideas and the exact quantification of their implications."
The final external force on historical biogeography outlined by the author is the perception of biogeography by biologists. Crisci notes that many biologists don't understand or like biogeography, either through its complexity or through the diversity of approaches and debates within the field of biogeography. This perspective is exemplified by Nelson (1978):
"Biogeography is a strange discipline. In general, there are no institutes of biogeography; there are no departments of it. There are no professional biogeographers -- no professors of it, no curators of it. It seems to have few traditions. It seems to have few authoritative spokesmen."
Of course, while a number of points are still valid (biogeographers tend either to be biologists or geographers who study organisms in space and time and therefore, necessitate an understanding of biogeographical principles), the science of biogeography has really matured over the last 30-odd years since Nelson's statements.
Crisci then describes the "internal forces shaping the present of historical biogeography" as "the proliferation of competing articulations (e.g. ecology vs. history, panbiogeography vs. cladistic biogeography, event-based methods vs. pattern-based methods); and recourse to philosophy and the debate over fundamentals (e.g. conceptions of space: absolute space vs. relative space)."
Crisci notes that "of the 30 techniques of historical biogeography currently in use, 23 (76%) have been proposed in the last 14 years." The mere presence of such internal debate within just one branch of the growing field of biogeography clearly shows an increase in interest on the subject and in quantifying distribution patterns of organisms around the world.
Crisci then goes on to describe current understanding of a main pillar of biogeography: the spatial arrangement of organisms geographically and throughout time.
There are "three different space-time processes that can modify the geographical spatial arrangement of organisms:
1) extinction (the death of all individuals in a local population, a species, or a higher taxon,
2) dispersal ([when an organism's] common ancestor originally occurred in one of the areas [studied] and later dispersed into other ones, where descendants survive to present day),
3) vicariance ([where an organism's] ancestor was originally widespread in greater areas, which became fragmented, and its descendants have survived in the fragments until now)."
Dispersalism as a doctrine came about through religious interpretations of the Bible's creation story where organisms dispersed from a "garden of Eden" throughout the world, backed up by an erroneous belief that the Earth was stable and that continents never moved. It wasn't until "two botanists, Stanley Cain and Léon Croizat, were among the first scientists to challenge vocally the dispersal explanation as the main process in biogeography and promote vicariance as an equally important process." Today, while debate still exists, some biogeographers push towards recognizing both dispersal and vicariance "as important processes by which organisms achieve their geographical distributions by applying a biogeographic model involving alternating cycles of dispersal and vicariance."
Cricsi then defines the three kinds of vicariance events known to exist:
1) "vicariance followed by speciation,
2) vicariance events that lack allopatric speciation, and
3) vicariance events followed by speciation after a previous speciation event indecent of the vicariance of the area."
Crisci then describes the "nine basic historical biogeographic approaches" summarized in his excellent table copied at the beginning of this review.
1) Centre of origin and dispersal: "Originated in the Darwin-Wallace tradition" and believing that "species originate in one centre of origin, from which some individuals subsequently disperse by chance, and then change through natural selection" into different species.
2) Panbiogeography: "Originally proposed by Croizat, [it] basically plots distributions of organisms on maps and connects the disjunct distribution areas or collection localities together with lines called tracks. The area where two or more generalized tracks intersect is called [a] node, [meaning] that different ancestral biotic and geological fragments interrelate in space / time."
3) Phylogenetic biogeography: "The first approach [proposed by Brundin] to consider a phylogenetic hypothesis for a given group of organisms as the basis for inferring its biogeographic history [and] defined as the study of the history of monophyletic groups in time and space, applying two basic rules: (a) Progression rule (primitive members of a taxon found closer to its centre of origin [compared to variant forms on the periphery], (b) Devitation rule (in any speciation event, an unequal cleavage of the original population is produced [with peripheral populations being variant compared to conservative sister species]."
4) Cladistic biogeography: "Developed by Rosen, and Nelson & Platnick, [and[ assumes that the correspondence between phylogenetic relationships and area relationships is biogeographically informative. Analysis comprises two steps: the construction of area cladograms from different taxon cladograms and the derivation of general area cladogram(s)."
5) Phylogeography: "Proposed by Avise et al. (1987) and is the study of the principles and processes governing the geographical distribution of genealogical lineages at [the] intraspecific level using mitochondrial DNA in animals and chloroplast DNA in plants. In this approach the individuals are genotyped and assigned to maternal lineages and the resulting phylogeny is related to patterns of geographical distribution."
6) Parsimony analysis of endemicity: This approach uses "biota similarity" to classify "localities, quadrates or areas according to their shared taxa by means of the most parsimonious solution."
7) Event-based methods: "Postulates explicit models of the processes that have an effect on the geographical distribution of living organisms. The different types of processes (dispersal, extinction, and vicariance) are identified and assigned values of benefit-cost under an explicit model of functioning of nature."
8) Ancestral areas: "A cladistic procedure based on a dispersalist approach. The procedure (Bremer 1992) allows one to identify the ancestral area of a group from the topological information of its cladogram given the information of their presence on deep and numerous branches in that cladogram."
9) Experimental biogeography: "This approach exploits computers to model faunal build-up repeatedly against a fixed vicariate background over ecological and evolutionary time scales, [enabling] a biogeographer to know both vicariate history and actual phylogeny."
Again, look at Crisci's Table 1 (figure above) for a summary of the approaches compared to each other and look at his paper for greater details about each of the main approaches of historical biogeography, including citations for the main authors or proponents of each theory or approach.
Crisci points out, however, that despite the great growth in techniques aimed at understanding the distribution of organisms throughout the geological history of the Earth in an attempt to accurately describe why we see the current patterns that we do, and that "we have started to babble in the language with which the traces of the past are telling us the history of life on Earth," it is also likely that "this history is so complex that probably we will never see it totally revealed."
Does this mean that the pursuit of imperfect knowledge is a futile waste of time? While I suppose that answer is a deeply internal and personal one for every person in the world (since any of our actions or pursuits in life are likely to be forgotten relatively shortly after we die), I'll conclude with two quotes aimed at helping you determine the answer for yourself.
Karl Popper (1959): "Science never pursues the illusory aim of making its answers final, or even probable. Its advance is, rather, toward the infinite yet attainable aim of ever discovering new, deeper, and more general problems, and of subjecting its ever tentative answers to ever renewed and ever more rigorous tests."
Marcus Aurelius (167-168): "Do not act as if you were going to live ten thousand years. Death hangs over you. While you live, while it is in your power, be good. He who has a vehement desire for posthumous fame does not consider that all those who remember him will themselves also die very soon; then again also they who have succeeded them, until the whole remembrance shall have been extinguished as it is transmitted through people who foolishly admire and perish. But suppose that those who will remember are even immortal, and that the remembrance will be immortal, what then is this to you? And I say not what is it to the dead, but what is it to the living? What is praise except indeed so far as it has a certain utility? For you now reject unseasonably the gift of nature, clinging to something else…."
Author Abstract: Historical biogeography is going through an extraordinary revolution concerning its foundations, basic concepts, methods, and relationships to other disciplines of comparative biology. There are external and internal forces that are shaping the present of historical biogeography. The external forces are: global tectonics as the dominant paradigm in geosciences, cladistics as the basic language of comparative biology and the biologist's perception of biogeography. The internal forces are: the proliferation of competing articulations, recourse to philosophy and the debate over fundamentals. The importance of the geographical dimension of life's diversity to any understanding of the history of life on earth is emphasized. Three different kinds of processes that modify the geographical spatial arrangement of the organisms are identified: extinction, dispersal and vicariance. Reconstructing past biogeographic events can be done from three different perspectives: (1) the distribution of individual groups (taxon biogeography) (2) areas of endemism (area biogeography), and (3) biotas (spatial homology). There are at least nine basic historical biogeographic approaches: centre of origin and dispersal, panbiogeography, phylogenetic biogeography, cladistic biogeography, phylogeography, parsimony analysis of endemicity, event-based methods, ancestral areas, and experimental biogeography. These nine approaches contain at least 30 techniques (23 of them have been proposed in the last 14 years). The whole practice and philosophy of biogeography depend upon the development of a coherent and comprehensive conceptual framework for handling the distribution of organisms and events in space.
Note to Readers: Follow links above for author email, full article text, or the publishing scientific journal. Author notes in my review are in quotes.
Review: Since this will be the first paper in a 12-week course on biogeography, I thought I'd take a moment to mention why this paper was chosen for week 1. Crisci (the author) provides a great summary of various kinds of historical biogeography, summarized in his table (below).
But before we get into interpreting Crisci's table (above, which should be referenced throughout this review whenever needed) I thought we'd take a moment to review biogeography in general, even though we've discussed it through multiple Science Corner posts in the past. Biogeography is a branch of science bridging "biology" and "geography" and concerns itself with trying to describe patterns of biodiversity and abundance of organisms of all kinds around the world… in essence, trying to describe how and why organisms occur in the populations they do in space and time. Different biogeographers study different groups of organisms as well as concentrate on whether they merely want to describe patterns of diversity or try to determine reasons why such patterns exist, as well as concerning themselves with various spatial scales. However, biogeographers, regardless of their organisms or focus, often have overlap in their findings, with one of the largest and most uniform (though not universal) observations being that there are distinct latitudinal gradients in species diversity, with tropical regions (at the most basic definition, regions between the Tropics of Cancer and Capricorn, or between 23.5º N or S of the equator) often being the centers of highest species diversity across a wide range of organisms (but not all).
Now that we know "what" biogeography is, we can start to focus, with this 12-week course aimed at discussing multiple ideologies of biogeography as a review before getting into applications of biogeography in "the real world." This first paper is an overview of historical biogeography, which is a branch of biogeography concerned with describing the historical reasons (often at geological timeframes) why organisms occur in their present patterns of diversity today (or within the recent, recorded past). As the author notes, there is a great debate over what factors are the most important in determining present patterns of biodiversity.
But why is this important? Managers use principles of historical biogeography to try to set up effective conservation zones (e.g., National Parks, Marine Protected Areas, etc.) that are able to provide protected areas where "seed populations" can reproduce and settle areas outside of such protected zones, thereby allowing sustainable harvest of environmental resources.
In essence, historical biogeography is a form of "comparative biology concerned with evolutionary processes over millions of years on a large, often global scale." Crisci notes his objectives for his paper being "to discuss the overall situation in which historical biogeography occurs, to outline the contemporary methodologies and to discuss several of the critical issues that need to be tackled."
In attempting to define the present state of historical biogeography, the author draws a comparison to Charles Dickens' opening paragraph of "A tale of two cities" in so much as there is a lot of debate, a lot of discovery, a lot of bias, etc. (i.e., "the best of times, the worst of times"). In essence, historical biogeography is still a young field that has only made its greatest progress since the 1970s.
Crisci outlines "three external forces" as influencing the discipline of historical biogeography: "global tectonics as the dominant paradigm in geosciences, cladistics as the basic language of comparative biology and the biologist's perception of biogeography."
While many today might take for granted the existence of plate tectonics, debate existed into the 1960s on whether the continents on Earth were static or whether they had broken up and separated, as is known today. As Crisci states, "the biogeographical consequences of plate movements and interactions are enormous. The rearrangement of continental landmasses and island areas and the opening and closing of sea and ocean basins initiated by these movements and interactions have profoundly affected the distribution and history of organisms." It was during this era that Charles Darwin's theory of atoll formation (through gradual subsidence of volcanic islands combined with continuous growth upward of fringing reef systems) was also proved, though there is still debate about the universality of his basic principles for atolls around the world.
Crisci then goes on to not how "cladograms" became "a powerful language to communicate a system of relationships to other biologists" through defining the biological and historical "phylogenetic relationships between taxa and their geographical distribution" and noting how they are tied together. Currently, the integration of genetic cladograms with area cladograms (relationships about how different individuals, species / taxa, or localities are similar or dissimilar to each other) is serving an important role in "forcing biogeographers towards a more precise formulation of methodological practices and theoretical ideas and the exact quantification of their implications."
The final external force on historical biogeography outlined by the author is the perception of biogeography by biologists. Crisci notes that many biologists don't understand or like biogeography, either through its complexity or through the diversity of approaches and debates within the field of biogeography. This perspective is exemplified by Nelson (1978):
"Biogeography is a strange discipline. In general, there are no institutes of biogeography; there are no departments of it. There are no professional biogeographers -- no professors of it, no curators of it. It seems to have few traditions. It seems to have few authoritative spokesmen."
Of course, while a number of points are still valid (biogeographers tend either to be biologists or geographers who study organisms in space and time and therefore, necessitate an understanding of biogeographical principles), the science of biogeography has really matured over the last 30-odd years since Nelson's statements.
Crisci then describes the "internal forces shaping the present of historical biogeography" as "the proliferation of competing articulations (e.g. ecology vs. history, panbiogeography vs. cladistic biogeography, event-based methods vs. pattern-based methods); and recourse to philosophy and the debate over fundamentals (e.g. conceptions of space: absolute space vs. relative space)."
Crisci notes that "of the 30 techniques of historical biogeography currently in use, 23 (76%) have been proposed in the last 14 years." The mere presence of such internal debate within just one branch of the growing field of biogeography clearly shows an increase in interest on the subject and in quantifying distribution patterns of organisms around the world.
Crisci then goes on to describe current understanding of a main pillar of biogeography: the spatial arrangement of organisms geographically and throughout time.
There are "three different space-time processes that can modify the geographical spatial arrangement of organisms:
1) extinction (the death of all individuals in a local population, a species, or a higher taxon,
2) dispersal ([when an organism's] common ancestor originally occurred in one of the areas [studied] and later dispersed into other ones, where descendants survive to present day),
3) vicariance ([where an organism's] ancestor was originally widespread in greater areas, which became fragmented, and its descendants have survived in the fragments until now)."
Dispersalism as a doctrine came about through religious interpretations of the Bible's creation story where organisms dispersed from a "garden of Eden" throughout the world, backed up by an erroneous belief that the Earth was stable and that continents never moved. It wasn't until "two botanists, Stanley Cain and Léon Croizat, were among the first scientists to challenge vocally the dispersal explanation as the main process in biogeography and promote vicariance as an equally important process." Today, while debate still exists, some biogeographers push towards recognizing both dispersal and vicariance "as important processes by which organisms achieve their geographical distributions by applying a biogeographic model involving alternating cycles of dispersal and vicariance."
Cricsi then defines the three kinds of vicariance events known to exist:
1) "vicariance followed by speciation,
2) vicariance events that lack allopatric speciation, and
3) vicariance events followed by speciation after a previous speciation event indecent of the vicariance of the area."
Crisci then describes the "nine basic historical biogeographic approaches" summarized in his excellent table copied at the beginning of this review.
1) Centre of origin and dispersal: "Originated in the Darwin-Wallace tradition" and believing that "species originate in one centre of origin, from which some individuals subsequently disperse by chance, and then change through natural selection" into different species.
2) Panbiogeography: "Originally proposed by Croizat, [it] basically plots distributions of organisms on maps and connects the disjunct distribution areas or collection localities together with lines called tracks. The area where two or more generalized tracks intersect is called [a] node, [meaning] that different ancestral biotic and geological fragments interrelate in space / time."
3) Phylogenetic biogeography: "The first approach [proposed by Brundin] to consider a phylogenetic hypothesis for a given group of organisms as the basis for inferring its biogeographic history [and] defined as the study of the history of monophyletic groups in time and space, applying two basic rules: (a) Progression rule (primitive members of a taxon found closer to its centre of origin [compared to variant forms on the periphery], (b) Devitation rule (in any speciation event, an unequal cleavage of the original population is produced [with peripheral populations being variant compared to conservative sister species]."
4) Cladistic biogeography: "Developed by Rosen, and Nelson & Platnick, [and[ assumes that the correspondence between phylogenetic relationships and area relationships is biogeographically informative. Analysis comprises two steps: the construction of area cladograms from different taxon cladograms and the derivation of general area cladogram(s)."
5) Phylogeography: "Proposed by Avise et al. (1987) and is the study of the principles and processes governing the geographical distribution of genealogical lineages at [the] intraspecific level using mitochondrial DNA in animals and chloroplast DNA in plants. In this approach the individuals are genotyped and assigned to maternal lineages and the resulting phylogeny is related to patterns of geographical distribution."
6) Parsimony analysis of endemicity: This approach uses "biota similarity" to classify "localities, quadrates or areas according to their shared taxa by means of the most parsimonious solution."
7) Event-based methods: "Postulates explicit models of the processes that have an effect on the geographical distribution of living organisms. The different types of processes (dispersal, extinction, and vicariance) are identified and assigned values of benefit-cost under an explicit model of functioning of nature."
8) Ancestral areas: "A cladistic procedure based on a dispersalist approach. The procedure (Bremer 1992) allows one to identify the ancestral area of a group from the topological information of its cladogram given the information of their presence on deep and numerous branches in that cladogram."
9) Experimental biogeography: "This approach exploits computers to model faunal build-up repeatedly against a fixed vicariate background over ecological and evolutionary time scales, [enabling] a biogeographer to know both vicariate history and actual phylogeny."
Again, look at Crisci's Table 1 (figure above) for a summary of the approaches compared to each other and look at his paper for greater details about each of the main approaches of historical biogeography, including citations for the main authors or proponents of each theory or approach.
Crisci points out, however, that despite the great growth in techniques aimed at understanding the distribution of organisms throughout the geological history of the Earth in an attempt to accurately describe why we see the current patterns that we do, and that "we have started to babble in the language with which the traces of the past are telling us the history of life on Earth," it is also likely that "this history is so complex that probably we will never see it totally revealed."
Does this mean that the pursuit of imperfect knowledge is a futile waste of time? While I suppose that answer is a deeply internal and personal one for every person in the world (since any of our actions or pursuits in life are likely to be forgotten relatively shortly after we die), I'll conclude with two quotes aimed at helping you determine the answer for yourself.
Karl Popper (1959): "Science never pursues the illusory aim of making its answers final, or even probable. Its advance is, rather, toward the infinite yet attainable aim of ever discovering new, deeper, and more general problems, and of subjecting its ever tentative answers to ever renewed and ever more rigorous tests."
Marcus Aurelius (167-168): "Do not act as if you were going to live ten thousand years. Death hangs over you. While you live, while it is in your power, be good. He who has a vehement desire for posthumous fame does not consider that all those who remember him will themselves also die very soon; then again also they who have succeeded them, until the whole remembrance shall have been extinguished as it is transmitted through people who foolishly admire and perish. But suppose that those who will remember are even immortal, and that the remembrance will be immortal, what then is this to you? And I say not what is it to the dead, but what is it to the living? What is praise except indeed so far as it has a certain utility? For you now reject unseasonably the gift of nature, clinging to something else…."
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