Cladistic Biogeography: Interpreting Patterns of Plant and Animal Distributions (Oxford Biogeography Series)

Rating:
Summary: Cladistic Biogeography / Why the Controversy?
Review: In "Cladistic Biogeography," Christopher J. Humphries and Lynne R. Parenti offer a detailed but easily digestible analysis of the significance that geographic distributions of species have with respect to the history of those species and the geography that they inhabit. Despite the seeming harmlessness of the subject, the book touches upon very controversial notions. Anyone even skimming it may feel overcome by an avalanche of evidence that modern geological theories need some revising in order to account for a plethora of biogeographical facts.

The main thesis of cladistic biogeography is perhaps best described with an example. Imagine that several different species (involving plants, fish, insects, and animals) are restricted to two particular areas in South America that are separated by the Andes mountains. According to cladistic biogeography (or at least according to Parenti's and Humphries' view of it), the most reasonable conclusion is that these trans-Andes species are older than the Andes--and that the formation of the Andes separated them. This seems a more rational explanation for the pattern than the idea that each species evolved on one side of the Andes chain--and then each species managed to cross the Andes via various hypothetical, species-dependent methods of dispersal.

In general, the fundamental theory of cladistic biogeography can be stated as follows: If many different species are restricted to the same geologically separated areas (divided, for example, by oceans or mountains) then a single, general cause (e.g., a geological event) is a more preferable explanation for this pattern than a series of unfalsifiable theories of dispersal across the geological divide, with each dispersal theory designed for each organism. Despite the seeming obviousness of this argument, many geologists, ecologists, and other scientists are extremely critical of such biogeographical analyses because it often conflicts with current geological theories.

Perhaps, this explains the somewhat reaching criticism of Amazon-customer critic, Matthew L. Forister, who not only panned the book, "Cladistic Biogeography" but the entire science itself. (Forister also wrote a negative review of "Panbiogeography : Tracking the History of Life--Oxford Biogeography Series No 11" by Grehan, Heads, and Craw.) In his review of the Parenti and Humphries book, Forister dismisses cladistic biogeography because of its insufficiency when applied to the geographic distribution of his cousins throughout the United States. According to Forister, this would lead cladistic biogeographers to conclude that the extended Forister family "were split by the uplift of the Rockies and further rifted by the opening of the Grand Canyon." Obviously, Parenti and Humphries do not extend their arguments to families of humans who have access to modern transportation. And so Forister's criticism overlooks the elemental fact that the plants, worms, frogs, snakes, trees, fresh-water fish and other organisms that are the real subject of "Cladistic Biogeography" have a difficult time booking flights across mountains and are notoriously bad drivers.

As Parenti and Humphries point out, this is not the first time that biogeographical evidence conflicted with contemporary geological theory. In the early part of the 20th century, much of the evidence that Alfred Wegener used to support the theory of continental drift was biogeographical. Trans-Atlantic biogeographical patterns (as well as certain geological factors) suggested to Wegener that South America was at one time attached to Africa, while North America was connected to Europe. Geologists and others maintained that continents were always fixed and explained these patterns via various dispersal hypotheses for all of the species found on both sides of the Atlantic. These dispersal hypotheses involved cross-ocean land bridges, long-distance island hopping schemes, hitching rides on flotsam, etc. Wegener's hypothesis has now become the conventional view. So, in this instance at least, the seminal principle of cladistic biogeography was validated while all the seemingly fantastic methods of dispersal across the Atlantic have been rejected.

Interestingly, a more significant biogeographical pattern can be found across the Pacific. Cladistic biogeography suggests that some sort of general geological explanation for the distributions, like a past Asian/American and Australian/South-American juxtaposition, is required. Today this view is largely ignored by people who are not biogeographers--and, once again, popular explanations of the trans-Pacific patterns encompass a group of independent dispersal hypotheses that include cross-ocean land bridges, long-distance island hopping schemes, the hitching of rides on flotsam, etc.

"Cladistic Biogeography" is a great step forward in trying to make sense of all the biogeographic data available to us today. It is an effort toward the development of rational, general principles for analyzing the geographic distribution of species, which hopefully will help geologists, ecologists, and biologists avoid the same mistakes that their counterparts made in the not-too-distant past regarding the very same subject.

--Dennis McCarthy

Rating:
Summary: Cladistic Biogeography / Why the Controversy?
Review: In "Cladistic Biogeography," Christopher J. Humphries and Lynne R. Parenti offer a detailed but easily digestible analysis of the significance that geographic distributions of species have with respect to the history of those species and the geography that they inhabit. Despite the seeming harmlessness of the subject, the book touches upon very controversial notions. Anyone even skimming it may feel overcome by an avalanche of evidence that modern geological theories need some revising in order to account for a plethora of biogeographical facts.

The main thesis of cladistic biogeography is perhaps best described with an example. Imagine that several different species (involving plants, fish, insects, and animals) are restricted to two particular areas in South America that are separated by the Andes mountains. According to cladistic biogeography (or at least according to Parenti's and Humphries' view of it), the most reasonable conclusion is that these trans-Andes species are older than the Andes--and that the formation of the Andes separated them. This seems a more rational explanation for the pattern than the idea that each species evolved on one side of the Andes chain--and then each species managed to cross the Andes via various hypothetical, species-dependent methods of dispersal.

In general, the fundamental theory of cladistic biogeography can be stated as follows: If many different species are restricted to the same geologically separated areas (divided, for example, by oceans or mountains) then a single, general cause (e.g., a geological event) is a more preferable explanation for this pattern than a series of unfalsifiable theories of dispersal across the geological divide, with each dispersal theory designed for each organism. Despite the seeming obviousness of this argument, many geologists, ecologists, and other scientists are extremely critical of such biogeographical analyses because it often conflicts with current geological theories.

Perhaps, this explains the somewhat reaching criticism of Amazon-customer critic, Matthew L. Forister, who not only panned the book, "Cladistic Biogeography" but the entire science itself. (Forister also wrote a negative review of "Panbiogeography : Tracking the History of Life--Oxford Biogeography Series No 11" by Grehan, Heads, and Craw.) In his review of the Parenti and Humphries book, Forister dismisses cladistic biogeography because of its insufficiency when applied to the geographic distribution of his cousins throughout the United States. According to Forister, this would lead cladistic biogeographers to conclude that the extended Forister family "were split by the uplift of the Rockies and further rifted by the opening of the Grand Canyon." Obviously, Parenti and Humphries do not extend their arguments to families of humans who have access to modern transportation. And so Forister's criticism overlooks the elemental fact that the plants, worms, frogs, snakes, trees, fresh-water fish and other organisms that are the real subject of "Cladistic Biogeography" have a difficult time booking flights across mountains and are notoriously bad drivers.

As Parenti and Humphries point out, this is not the first time that biogeographical evidence conflicted with contemporary geological theory. In the early part of the 20th century, much of the evidence that Alfred Wegener used to support the theory of continental drift was biogeographical. Trans-Atlantic biogeographical patterns (as well as certain geological factors) suggested to Wegener that South America was at one time attached to Africa, while North America was connected to Europe. Geologists and others maintained that continents were always fixed and explained these patterns via various dispersal hypotheses for all of the species found on both sides of the Atlantic. These dispersal hypotheses involved cross-ocean land bridges, long-distance island hopping schemes, hitching rides on flotsam, etc. Wegener's hypothesis has now become the conventional view. So, in this instance at least, the seminal principle of cladistic biogeography was validated while all the seemingly fantastic methods of dispersal across the Atlantic have been rejected.

Interestingly, a more significant biogeographical pattern can be found across the Pacific. Cladistic biogeography suggests that some sort of general geological explanation for the distributions, like a past Asian/American and Australian/South-American juxtaposition, is required. Today this view is largely ignored by people who are not biogeographers--and, once again, popular explanations of the trans-Pacific patterns encompass a group of independent dispersal hypotheses that include cross-ocean land bridges, long-distance island hopping schemes, the hitching of rides on flotsam, etc.

"Cladistic Biogeography" is a great step forward in trying to make sense of all the biogeographic data available to us today. It is an effort toward the development of rational, general principles for analyzing the geographic distribution of species, which hopefully will help geologists, ecologists, and biologists avoid the same mistakes that their counterparts made in the not-too-distant past regarding the very same subject.

--Dennis McCarthy

Rating:
Summary: The Peculiar Science of Cladistic Biogeography
Review: Scattered throughout the western United States, I have a handful of cousins: one in Oregon, two in Wyoming, and two in Arizona (along with an aunt and uncle in the latter state). Including myself as a resident of California, this is a distribution of Foristers, and from it could be made an area cladogram, which would look like a four-branched tree, with one state perched at the top of each branch. I happen to know that the Foristers have been in Wyoming the longest, for only slightly less time in Arizona, and only recently in California and Oregon. Therefore, I would arrange the area cladogram with Wyoming in an ancestral position, then Arizona, and finally Oregon and California bunched together as sister groups. Countless area cladograms could be made by inquiring into the family histories of other people-if at all possible, we might also construct some cladograms for the family dog and the starling that frequents the windowsill, just to be broad-minded.

Then (and this is the raison d'être of the book in question), a collection of these area cladograms could be compared, and a kind of compromise cladogram would be derived which represented the common features of all the family histories. To do this right, some math and computer programs could be used, as described by the authors of Cladistic Biogeography; for now, however, let us focus on the consequences of our cladograming, and not be distracted by the glamor of the process. So what can we say about our compromise tree? For a moment suppose the best of all worlds: a clear pattern arises, with various people, dogs, and starlings showing ancestral groups in Wyoming and Arizona, and sister groups in various other western states. With a little common sense, we might say that our Homo sapiens reflect a history of westward movement and that the dogs and house sparrows moved from Wyoming to the other states with the humans (we probably had to throw out a couple of native American cladograms that would have confused the obvious "signal"). But wait! Parenti and Humphries tell us that dispersal is not an explanation for biogeographical patterns. Since any species can disperse according to its own unknowable caprice, we had better assume that the distributions of all organisms are crafted by the same processes. In our case, humans and dogs and starlings might have been widespread across the west in large populations that were split by the uplift of the Rockies and further rifted by the opening of the Grand Canyon.

The case is not closed, however. According to Cladistic Biogeography, geology can only "illuminate" the patterns derived from area cladograms, but can never test them. Without confirmation from other sciences, we can only gain confidence in out pattern by throwing in more and more cladograms from diverse groups-the more agreement we find, the more assuredly we may speak of the history of the "biotas" of Wyoming, Arizona, and the other western states. Within this seemingly scientific iteration lies the fatal flaw of cladistic biogeography as presented by Parenti and Humphries. I described an oversimplification of the process of arriving at a compromise cladogram. In the analyses done in Cladistic Biogeography, all possible combinations of areas are considered for each organism, a process which can produce hundreds of trees. However, if one of the organisms in question, through a peculiarity of its history, presents only one possible cladogram, that organism will dictate the entire analysis. The possible trees for each organism are then searched for patterns that do not disagree with that one peculiar cladogram. How do we know that one organism it not a fluke, some kind of historical freak unrelated to all other members of the "biota"? We do not know any such thing. In fact, Parenti and Humphries forbid us from knowing any specific natural history, for, they say, such biological questions as age of arrival or dispersal ability are precisely what area cladograms are designed to test!

In the author's defense, it is possible that their method could generate one area cladogram that could then be confirmed by patterns from many other organisms. For example, they work their magic on a collection of distributions from the Atlantic and Mediterranean, and conclude that the Mediterranean biota is more closely related to far northern biotas than to mid-latitude Atlantic or Caribbean groups of organisms. However, I remain unconvinced that another method of pattern generation (perhaps even a random method) might not have produced an area cladogram that could have been similarly confirmed by dozens of different examples from the same waters. Simply put, the biodiversity is immense, and even the devil can quote scripture for his own ends.

Rating:
Summary: The Peculiar Science of Cladistic Biogeography
Review: Scattered throughout the western United States, I have a handful of cousins: one in Oregon, two in Wyoming, and two in Arizona (along with an aunt and uncle in the latter state). Including myself as a resident of California, this is a distribution of Foristers, and from it could be made an area cladogram, which would look like a four-branched tree, with one state perched at the top of each branch. I happen to know that the Foristers have been in Wyoming the longest, for only slightly less time in Arizona, and only recently in California and Oregon. Therefore, I would arrange the area cladogram with Wyoming in an ancestral position, then Arizona, and finally Oregon and California bunched together as sister groups. Countless area cladograms could be made by inquiring into the family histories of other people-if at all possible, we might also construct some cladograms for the family dog and the starling that frequents the windowsill, just to be broad-minded.

Then (and this is the raison d'être of the book in question), a collection of these area cladograms could be compared, and a kind of compromise cladogram would be derived which represented the common features of all the family histories. To do this right, some math and computer programs could be used, as described by the authors of Cladistic Biogeography; for now, however, let us focus on the consequences of our cladograming, and not be distracted by the glamor of the process. So what can we say about our compromise tree? For a moment suppose the best of all worlds: a clear pattern arises, with various people, dogs, and starlings showing ancestral groups in Wyoming and Arizona, and sister groups in various other western states. With a little common sense, we might say that our Homo sapiens reflect a history of westward movement and that the dogs and house sparrows moved from Wyoming to the other states with the humans (we probably had to throw out a couple of native American cladograms that would have confused the obvious "signal"). But wait! Parenti and Humphries tell us that dispersal is not an explanation for biogeographical patterns. Since any species can disperse according to its own unknowable caprice, we had better assume that the distributions of all organisms are crafted by the same processes. In our case, humans and dogs and starlings might have been widespread across the west in large populations that were split by the uplift of the Rockies and further rifted by the opening of the Grand Canyon.

The case is not closed, however. According to Cladistic Biogeography, geology can only "illuminate" the patterns derived from area cladograms, but can never test them. Without confirmation from other sciences, we can only gain confidence in out pattern by throwing in more and more cladograms from diverse groups-the more agreement we find, the more assuredly we may speak of the history of the "biotas" of Wyoming, Arizona, and the other western states. Within this seemingly scientific iteration lies the fatal flaw of cladistic biogeography as presented by Parenti and Humphries. I described an oversimplification of the process of arriving at a compromise cladogram. In the analyses done in Cladistic Biogeography, all possible combinations of areas are considered for each organism, a process which can produce hundreds of trees. However, if one of the organisms in question, through a peculiarity of its history, presents only one possible cladogram, that organism will dictate the entire analysis. The possible trees for each organism are then searched for patterns that do not disagree with that one peculiar cladogram. How do we know that one organism it not a fluke, some kind of historical freak unrelated to all other members of the "biota"? We do not know any such thing. In fact, Parenti and Humphries forbid us from knowing any specific natural history, for, they say, such biological questions as age of arrival or dispersal ability are precisely what area cladograms are designed to test!

In the author's defense, it is possible that their method could generate one area cladogram that could then be confirmed by patterns from many other organisms. For example, they work their magic on a collection of distributions from the Atlantic and Mediterranean, and conclude that the Mediterranean biota is more closely related to far northern biotas than to mid-latitude Atlantic or Caribbean groups of organisms. However, I remain unconvinced that another method of pattern generation (perhaps even a random method) might not have produced an area cladogram that could have been similarly confirmed by dozens of different examples from the same waters. Simply put, the biodiversity is immense, and even the devil can quote scripture for his own ends.