Review: Sherman, Duda (1999) An ecosystem approach to global assessment and management of coastal waters. Marine Ecology Progress Series, 190:271-287.

Feature Paper: DOWNLOAD * Sherman, Duda (1999) An ecosystem approach to global assessment and management of coastal waters. Marine Ecology Progress Series, 190:271-287.

Author Abstract: Since the Rio Summit in 1992 the public has become increasingly aware that coastal ecosystems are under signficant threat from pollution, overexploitation, and habitat loss. However, little progress has been made in sustained global actions to reverse their degraded state. It has been no small feat for the world community to come to agreement on international instruments identifying environmental and resource problems, but it is another matter altogether to muster the scientific community and the political will to enact necessary policy reforms and devote necessary funding to restore and protect valuable marine ecosystems. An ecosystems approach is emerging for the assessment and management of coastal waters around the globe utilizing modular strategies for linking science-based assessments of the changing states of large marine ecosystems to socioeconomic benefits expected from achieving long-term sustainability of their resources. To assist developing countries in implementing the ecosystems approach to marine resources development and sustainability in international waters, the Global Environment Facility and its $2 billion trust fund has been opened to universal participation that builds on partnerships with the United Nations Development Programme, the United Nations Environmental Programme, and the World Bank.

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: This week we'll look at some applications of biogeography aimed at applying global biodiversity analyses  towards conservation and management of those resources.

This week's paper was borne out of the 1992 Rio de Janeiro International Summit on Biological Diversity (variously called the Rio Convention, Rio Summit, or 1992 Biodiversity Convention) and a need to develop management strategies on a global level for cooperating countries bound by the Rio Summit. The three main goals of the Summit were:

    1)    "Conservation of biological diversity / biodiversity"
    2)    "Sustainable use of [biological] components [in ecosystems]"
    3)    "Fair and equitable sharing of benefits arising from genetic resources"

This paper was written to note that while many governments worldwide agreed in 1992 to protect biological diversity around the world, that by 1999 little had been done to find the "political will to enact necessary policy reforms and devote necessary funding to restore and protect valuable marine ecosystems."

The authors focus mainly on coastal marine ecosystems, which are being degraded more every year. The authors proposed a method to "link [modular] science-based assessments of the changing states of large marine ecosystems to socioeconomic benefits expected from achieving long-term sustainability of their resources."

The method specifically notes "paradigm shifts" are needed in the following ways: changing the focus from "individual species to ecosystems, small spatial scales to multiple scales, short-term perspectives to long-term perspectives, [the idea of] humans independent of ecosystems to [an understanding that] humans are integral parts of ecosystems, management divorced from research to adaptive management, and managing commodities to sustaining production potential for goods and services."

The authors noted that before the Rio Summit there was the "Global Environment Facility" program to note 4 focus challenges for environmental managers globally:

    1)    Climate change
    2)    Biodiversity conservation
    3)    Ozone depletion
    4)    International waters

In switching to a more global approach, the authors created a map of 50 "large marine ecosystems" worldwide, shown below:

This paper is the first of many that have come since its publication with the aim at mesosystem analyses and determining boundaries of large marine ecosystems. If you note the figure above, though, many isolated island nations (particularly in the Pacific Ocean) are missing from such schemes, but this can be explained for this paper with the understanding that the authors were mainly concerned with coastal marine ecosystems and thus the authors focused mainly on continental coastlines. The authors' criteria for defining LME boundaries focus on "ecosystem (1) productivity, (2) fish and fisheries, (3) pollution and ecosystem health, (4) socioeconomic conditions, and (5) governance."

The paper also outlines a United Nations trust fund developed to aid poorer nations in gathering the resources necessary to apply the agreements of the Rio Summit (funded by 161 countries worldwide at rates depending upon GDP of donor nations, whereby richer nations help subsidize poorer nations). This fund was developed because for most organisms, as we've seen in the past weeks, biodiversity is higher in tropical waters compared to temperate waters. And since many tropical nations are poor (in Asia, Africa, and Latin America) compared to temperate nations (in Europe and North America), some system must be developed to help manage resources where their management hasn't been a priority. In the authors' words "subsistence fishing for protein and income must be sustained for the support of coastal societies that have few economic alternative."

Once the framework is developed (large marine ecosystems), the authors developed various metrics, or "experimental measures of changing ecosystem states and health," noted below:

    1)    Biodiversity
    2)    Stability
    3)    Yields
    4)    Productivity
    5)    Resilience

The authors note that samples aimed at determining ecosystem health should be "focused on parameters relating to the resources at risk from overexploitation, species protected by legislative authority (marine mammals), and other key biological and physical components at the lower end of the food chain (plankton, nutrients, hydrography), including zooplankton composition, zooplankton biomass, water column structure, PAR, transparency, chlorophyll a, NO2, NO3, primary production, pollution, marine mammal biomass, marine mammal composition, runoff, wind stress, seabird community structure, seabird counts, finish composition, finish biomass, domain acid, saxitoxin, and paralytic shellfish poisoning."

The authors also note that "special consideration should be given to improved knowledge of how the natural system generates economic values" and that the interconnectedness of ecosystems should be focused upon, such as how "coastal wetlands [act] as nurseries for fisheries, natural pollution filters, and storm buffers" rather than having managers of individual ecosystems not share knowledge across areas of interest. In other words, if you have a specialist in a certain field, they will be excited and interested and knowledgeable about all aspects in their field, but they may be ignorant of other ecosystems or fields that don't concern their area of focus. However, scientists and specialists in other fields may know, for instance, that their ecosystem of focus is related to another ecosystem in ways that other specialists may not.

The authors also point out that while focus should be made on protecting ecosystems rather than individual species, that "keystone species in a valuable ecosystem" should not be "sacrificed through ignorance" and lack of management. A keystone species, as defined by Paine (1995), is "a species that has a disproportionate effect on its environment relative to its biomass."

The authors summarize their view by noting that managers should "include a generalized characterization of the ways in which human activities affect the natural marine system and the expected 'sensitivity' of these forcing functions to various types and levels of human activity." The authors also note that "natural and social scientists should concentrate further on resolving apparent effects that are confounded by cycles or complex dynamics in the natural system itself."

At the core of such a collaboration, the authors note that at the minimum there should be:

    1)    Integrated waste management
    2)    Water pollution abatement
    3)    Habitat improvement
    4)    Conservation of stressed mangrove and coral reef areas
    5)    Coastal tourism development
    6)    Improvements of the municipal fisheries

In creating such a collaboration, the authors note that their must be "complementarity among international agreements" and that "detailed rules and standards at the global level exist to control pollution from ships, including at-sea disposal of sates, and for whales."
The authors state that from best practices experience, there are several lessons that have been learned to help address ecosystem-level problems:

1. "Donor-driven rather than country-driven institutional arrangements have proved ineffective and recipient countries must take ownership of activities"
2. "Water quality must be considered together with water quantity and ecological considerations in any sectoral development project if sustainable development is to be achieved"
3. "Ecosystem-based approaches, which encompass overfishing, habitat loss, and biological diversity issues in addition to water quality / pollution abatement, are needed for improving management of transboundary water systems"
4. "Interministerial and subnational government involvement is necessary in these joint, multi-country regional initiatives if actual changes in sectoral activities causing the transboundary problems are to be achieved."

The authors conclude their paper with a good summary figure aimed at describing the main problems facing coastal marine ecosystems across political boundaries, noted below:

And while this paper is more than 10 years old now, the recommendations and problems outlined by the paper are just as relevant today as when first published.

Next we'll look at a classic paper on pacific island biogeography. Because the online version that I have a link to (below) is missing figures, and the figures are such an integral part of the paper, I think it is fair for me to host the images from the paper, particularly since the paper text is provided by the publisher (University of Hawaii) freely.

Review: Vega, Ayala, Morrone, Organista (2000) Track Analysis and conservation priorities in the cloud forests of Hidalgo, Mexico. Diversity, 6(3):137-143.

Feature Paper: DOWNLOAD Vega, Ayala, Morrone, Organista (2000) Track Analysis and conservation priorities in the cloud forests of Hidalgo, Mexico. Diversity, 6(3):137-143.

Author Abstract: A track analysis based on the distributional patterns of 967 species of vascular plant taxa (gymnosperms, angiosperms and pteridophytes) was performed to assess conservation priorities for cloud forests in the state of Hidalgo, Mexico, ranged in the municipalities of Chapulhuacán, Eloxochitlán, Molocotlán, Pisaflores, Tenango de Doria, Tlahuelompa and Tlanchinol, as well as five floristically equivalent areas in the states of Veracruz (Teocelo and Helechales), Tamaulipas (Gómez Faríias), Morelos-México (Ocuilan) and Oaxaca (Huautla de Jiménez). In order to detect generalized tracks we employed a new parsimony method, where clades (considered equivalent to generalized tracks) are defined forbidding homoplasy and acting like a compatibility algorithm. Several generalized tracks were found connecting these areas. Cloud forests of Chapulhuacán were connected according to three different generalized tracks and thus have a higher value, qualifying as a priority area of the conservation of cloud forests in the state of Hidalgo.

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: We'll finish up the week by examining how track analyses can be interpreted to determine areas to focus conservation efforts.

The authors restricted their analysis to a single ecosystem (cloud forests) over five states (Hidalgo, Veracruz, Tamaulipas, Morelos-México, and Oaxaca) in Mexico. Cloud forests were chosen because conservation has been difficult. They are a naturally fragmented ecosystem, often separated by lowlands between mountains (they require elevations of 600 to 3000 meters). As individual forests within a larger area are destroyed through "deforestation and agricultural exploitation," conservationists are tasked with determining which forest areas (often with different and unique floras) should be prioritized for conservation.

The authors first identified all the vascular plants within cloud forests surrounding Hidalgo, Mexico (specifics above). Presence-Absence data were constructed for the 967 species of plants identified for all cloud forests. Instead of taking a normal panbiogeographic approach for identifying "generalized tracks" (remember to look at Week 3's review of panbiogeography for all terms), the authors proposed a new analysis based on cladistic parsimony. Cladograms were generated for all taxa and then converted to generalized tracks "by joining together their minimal geographical distance [to] the areas included in the same clade." In other words, the authors used cladistics to determine clustering and relatedness of taxonomic compositions within each cloud forest locality in the study, then used those cladistic clusters to create generalized tracks rather than relying on minimal spanning tree algorithms from a purely geographical perspective.

The authors continued their analysis in a stepwise fashion, whereby they first used all species presence and absence data to determine an original cladogram, then determined which species in the matrix "defined" the outcome of the cladogram (the species comprising the basal branches of the cladogram). Those species records were then removed from subsequent analyses to determine secondary cladograms, and so forth until only isolated localities remained.

The authors converted each cladogram into generalized tracks as described above, and by "comparing the different generalized tracks obtained, we found that Chapulhuacán is a panbiogeographic node according to three different connections between generalized tracks; and Huautla de Jiménez, Gómez Farías, Eloxochitlán and Pisaflores are panbiogeographic nodes according to one connection between generalized tracks. For this reason, Chapulhuacán turned out to be the most important area for conservation because it has different biotic affinities, so it should have the first priority when protecting the cloud forests of Hidalgo."

The authors were faced with a situation where there is a fragmented community of ecosystems, with each isolate containing a fairly unique composition of species and where many endemic plants existed for each area, coupled with no protection for any of the forests in the study. Rather than conserving all cloud forests (the ideal but impractical situation), the authors used science to determine the area with "species dorm different ancestral biotas" that represented the greatest uniqueness of all isolated cloud forests in a region.

The authors' approach differs from typical conservation approaches that only look at total species richness. The authors note that "instead of the species-richness criterion, which considers that all species are equivalent, track methods measure the distinctiveness among biotas, weighting those areas with representatives of different ancestral biotas. The track approach allows conservationists to integrate distributional data efficiently, which could be a complement to… other analyses, e.g. phylogenetic indices or complementarity."

The authors conclude with the take-home message that "the biodiversity crisis is far from being a simple matter, and different approaches should be applied and tested in order to allow its appropriate conservation" and that the general public should be educated in better understanding "the interrelationship between biology, geology, history and conservation."

Next we'll review two papers, one tying in with today's review by focusing on conservation, and the other examining the biogeography of the Pacific ocean (and island floras and faunas) based on multiple biogeographic schemes and approaches.

Review: Gallo V, Cavalcanti MJ, da Silva HMA (2007) Track analysis of the marine palaeofauna from the Turonian (Late Cretaceous). Journal of Biogeography, 34:1167-1172.

Feature Paper: DOWNLOAD Gallo V, Cavalcanti MJ, da Silva HMA (2007) Track analysis of the marine palaeofauna from the Turonian (Late Cretaceous). Journal of Biogeography, 34:1167-1172.

Author Abstract: Aim To analyse the worldwide distribution patterns of Turonian marine biotas using a panbiogeographical approach. 

Location Turonian localities of southern and north-eastern Brazil, Mexico, Canada, central Europe, England and Morocco. 

Method Panbiogeographical track analysis. 

Results Nine generalized tracks and six nodes were found. The generalized tracks comprise two vicariant track patterns (one northern and one mid-southern) across the Atlantic. 

Main conclusions The generalized tracks show clearly two separate marine biotas, which were associated with the proto-South Atlantic and the proto-North Atlantic oceans. These generalized tracks, as well as the two vicariant track clusters between the north and south Atlantic, are identified by vicariant relationships shared by most of the taxa analysed, and illustrate the final break up of the Gondwana and Laurasia supercontinents and the consequences of vicariant events for the biogeography of the Atlantic Ocean.

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: This week we start looking at specific examples of applied biogeography now that we have an understanding of several schools of biogeography. The first paper we looked at this week dealt with historical biogeography. This paper uses panbiogeographical track analyses to analyze the global distribution patterns of fossil marine taxa.

The specific fossil group looked at included "marine palaeofauna" from the Turonian (Late Cretaceous, 94 - 89 million years ago) strata. Taxa examined included "foraminifera, ostracods, sponges, brachiopods, molluscs, crustaceans, echinoids, fishes from a variety of taxonomic levels, turtles, crocodiles, lizards, and mosasaurs" though the final analysis involved only those groups with diverse fossil records at all locations examined by the authors worldwide: molluscs, crustaceans, and fishes. 

The panbiogeography analysis used by the authors follows the more rigorous approach of biogeographers today compared to the beginnings of panbiogeography. Locality records are first plotted on a map and then they are connected using mathematical formulas based on minimum spanning trees (minimum distances between points required to connect all points on the plotted map).

To elaborate on our week three seminar series on panbiogeography, the authors sum up their approach to panbiogeography with the following definitions. For further information about panbiogeography, look to the week three papers.

"The panbiogeographical method of track analysis consists of plotting locality records or areas of distribution of various taxa on maps and connecting them using lines following a criterion of minimum distance. These lines are named individual tracks and they correspond to the geographical coordinates of the taxon or the place in the sector of geographical space where the evolution of this taxon occurred. The coincidence of individual tracks of groups not phylogenetically related corresponds to a generalized track, implying a common history (spatial homology). If two or more generalized tracks intersect in an area, the intersection determines a node, which may predict distinct ancestral biotas and geological fragments interrelated in space and time."

Twelve localities worldwide were chosen based on the quality of the fossil record coupled with necessary geographical information: Brazil (2 locations), Morocco, Europe (4), Canada (2), Mexico (4). Data were missing for Asia, so while the study can't really be considered global, it is certainly the largest-scale panbiogeographic survey of the fossil record to date. The result of the authors' track analysis is shown in their figure below.

The authors then go on to explain how each track could have been created from a palaeogeographic standpoint, meaning how various events (such as rising sea levels, plate tectonic rifting of continents, or connection of various seas) resulted in the ability of organisms from one area to expand their ranges into another area.

The authors conclude their interpretations with the observation that "Generalized tracks found in this study illustrate the final break up of the Gondwana and Laurasia supercontinents and the consequences of vicariant events for the biogeography of the Atlantic Ocean. The nodes and main massing correspond to the Mesoamerican gate, identified by Croizat (1958) as one of the main centres of global biological diversity. In this context, it is interesting to note that the world network of generalized tracks for the modern biota illustrated in Croizat (1958, p. 1018, Figure 259) also shows a northern and mid-southern track connection across the Atlantic, and also emphasizes trans-Atlantic connections between the same general localities as included in the present study. This suggests that centres of diversity in the modern world may date at least from Mesozoic times, and that the factors affecting the diversity of past and present terrestrial biotas may also have affected biotas in the marine realm."

We'll finish up next by seeing how track analysis can influence conservation priorities for living taxa today.

Review: Crame JA (2001) Taxonomic diversity gradient through geological time. Diversity and Distributions, 7:175-189.

Feature Paper: DOWNLOAD Crame JA (2001) Taxonomic diversity gradient through geological time. Diversity and Distributions, 7:175-189.

Author Abstract: There is evidence from the fossil record to suggest that latitudinal gradients in taxonomic diversity may be time-invariant features, although almost certainly not on the same scale as that seen at the present day. It is now apparent that both latitudinal and longitudinal gradients increased dramatically in strength through the Cenozoic era (i.e. the last 65 my) to become more pronounced today than at any time in the geological past. Present-day taxonomic diversity gradients, in both the marine and terrestrial realms, are underpinned by the tropical radiations of a comparatively small number of species-rich clades. Quite why these particular taxa proliferated through the Cenozoic is uncertain, but it could be that at least part of the explanation involves the phenomenon of evolutionary escalation. This is, in essence, a theory of biological diversification through evolutionary feedback mechanisms between predators and prey; first one develops an adaptive advantage, and then the other. However, there may also have been some form of extrinsic control on the process of tropical diversification, and this was most likely centred on the phenomenon of global climate change. This is especially so over the last 15 my. Various Late Cenozoic (Neogene) vicariant events effectively partitioned the tropics into a series of high diversity centres, or foci. It has been suggested that, in the largest of these in the marine realm (the Indo-West Pacific or IWP centre), a critical patterns of islands acted as a template for rapid speciation during glacioeustatic sea level cycles. The same process occurred in the Atlantic, Caribbean and East Pacific (ACEP) centre, though on a lesser scale. Tropical terrestrial diversity may also have been promoted by rapid range expansions and contractions in concert with glacial cycles (a modified refugium hypothesis). We are beginning to appreciate that an integrated sequence of Neogene tectonic and climatic events greatly influenced the formation of contemporary taxonomic diversity patterns.

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: Today we start looking at specific examples of applied biogeography now that we have an understanding of several schools of biogeography. The first paper we look at this week falls into the applied historical biogeography category. This paper looks at the case of latitudinal diversity gradients (the observation that the majority of taxonomic groups have a higher proportion of species in tropical, lower latitudes than higher latitudes) throughout the fossil record to determine whether "latitudinal gradients in taxonomic diversity may be time-invariant features."

The author found that both for the "marine and terrestrial realms" that a high profusion of tropical species today compared to higher, temperate latitudes is the result of "the tropical radiations of a comparatively small number of species-rich clades."

The author examined the fossil record over the last 100 million years to come to his conclusions. While he found a gradient throughout the past, the author notes that only from the Cenozoic era (i.e. the last 65 million years) did major shifts in the diversity gradient occur, particularly as a result of new radiation and speciation "following the K-T mass extinction event." What is interesting in this paper is the finding that "taxonomic diversity gradients must have steepened substantially" since that die off of organisms.

The model marine taxonomic group chosen by the author to examine latitudinal gradients throughout the last 100 million years and to compare to present-day latitudinal gradients of extant (living) taxa is the molluscs. They were chosen in part because of their excellent fossil record as well as because they are one of the largest living groups (in terms of diversity, or numbers of species) of marine organisms today. The model terrestrial taxonomic group examined by the author is the angiosperms (flowering plants).

In both groups examined, the author shows that large percentages of total group diversity today are reflected in relatively few family clades within each major group, with those clades being relatively young (< 65 million years since first fossil record) and principally lower latitude, tropical groups.

The author makes a small note about other taxonomic groups with major latitudinal diversity gradients showing highest diversity in tropical, lower latitudes (especially equatorial): "all major insect groups," birds, mammals, teleost fish, and snakes.

All groups discussed show a latitudinal diversity gradient in the fossil record, though none to the extent seen in the present day. As a result, the author concludes that "there must have been a dramatic increase in the scale of this [latitudinal diversity gradient] feature between the latest Cretaceous and Recent."

One hypothesis the author presents for why the diversity gradient is more pronounced today than in the fossil record (besides noting that the fossil record is still incomplete and not entirely understood) is linked to Global Climate Change, where a "temperature maximum occurred between 19.5 and 17 Ma, followed by an abrupt cooling trend between 17 and 14 Ma linked to the rapid expansion of the East Antarctic ice cap." 65 million years ago there were no polar ice caps, so it is suggested that perhaps a major die off of organisms occurred in the poles as "polar temperatures deteriorated rapidly to their present day levels" compared to the tropics, which "were much less affected." As major clades of organisms "continued to expand" in the tropics, the same radiation wasn't seen in areas of rapidly deteriorating temperatures.

The author concludes a continued tropical radiation "is of considerable significance because it suggests that the process of tropical diversification was a prolonged one that coincided with phases of both global warming and cooling."

And tying in with our panbiogeography seminar series last week, the author also notes that "over the last 100 my [million years] the continental land masses have become unusually emergent, fragmented and dispersed; long, north-south-trending continents and continental shelves have become progressively partitioned along latitudinal environmental gradients" [as a result of plate tectonic movements]. As populations of organisms became geographically fragmented, speciation increased in part due to reproductive barriers between populations from such geographic separation.

The author focuses on abiotic factors (such as continental movement and climate change) because he notes that "it is still open to question as to precisely how local ecological interactions scale up to determine origination and extinction rates. Many biotic replacements [die-offs of some groups and radiation of others] within the fossil record could equally well be interpreted as the replacement of incumbent taxa by fundamental environmental change as by ecological interactions [e.g., predator-prey interactions or feedback mechanisms]."

The author also notes "one further important phenomenon to bear in mind. Rather than being evenly spread geographically throughout the tropics, diversity is very strongly concentrated within discrete centres, or foci. This is particularly so within the marine realm, where two major foci are traditionally recognized: an Indo-West Pacific (IWP) one and an Atlantic, Caribbean and East Pacific one (ACEP)."

From a fossil perspective, the author brings a fresh view on whether the IWP is "an evolutionary centre of origin." The author disagrees with such a view, noting that "there is now an increasing volume of evidence to suggest that what we may in fact be looking at is a homogenous, early Cenozoic, pan-tropical (Tethyan) fauna that has been disrupted by a series of essentially Neogene tectonic and climatic events."

The author notes that "rapid speciation" is often linked in the fossil record with "rapid climate change" and that as sea levels rose and fell or tropical regions expanded or contracted, the most tropical and climatically-stable regions (equatorial) would have acted as a "refugium" that would periodically be infused with new species on the peripheries of the tropics as climatic conditions were favorable.

The author concludes that "latitudinal gradients in taxonomic diversity can be traced back in the geological record to well within the Palaeozoic era (i.e. at least 400 my, and perhaps substantially more" but that "all the available evidence suggests that, from the Late Palaeozoic to Early Cenozoic, they were on nothing like the scale of those seen today in either the marine or terrestrial realms." Examining the fossil record and comparing diversity to today, the author suggests that present day levels are at a "maximum or near-maximum" for diversity.

Next we'll continue our seminar series with a look at track analysis on the fossil record, followed by a  track analysis of forests in Mexico and how applying the results of such analyses can influence conservation priorities.

Review: Holloway (1992) Croizat's Panbiogeography: a New Zealand perspective. Journal of Biogeography, 19(3):233-238.

Feature Paper: DOWNLOAD Holloway (1992) Croizat's Panbiogeography: a New Zealand perspective. Journal of Biogeography, 19(3):233-238.

Author Abstract: This panbiogeography special issue of the New Zealand Journal of Zoology represents a significant milestone in the development of biogeography. It has already earned plaudits in this journal, and it illustrates a nodal fusion of the biogeographic philosophy of Leon Croizat with a critical mass of mainly young biologists seeking to go beyond the traditional in addressing the biogeography of one of the more intriguing land masses in the world, New Zealand. The 'Croizatian' tradition of iconoclasm is alive and well.

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: For our final paper on panbiogeography this week, we'll look at how panbiogeography has developed in New Zealand, a country with some of the strongest proponents of the panbiogeography school of biogeography. This paper is a review (guest editorial) of multiple papers from a conference on panbiogeography that aims to describe the then current state of panbiogeography in New Zealand.

Besides describing how different researchers used panbiogeographic principles, the author gives the following excellent summary (and unique perspective compared to the other panbiogeography papers discussed) of how panbiogeography sits within the field of biogeography as a whole:

"Connor's description of panbiogeography as R-mode biogeography (relationships of taxonomic pattern) is the one I would accept as offering a clear distinction from cladistic (or vicariance) biogeography (Q-mode, relationships of areas), but what is the requisite methodology? It will involve the objective recognition of statistically-significant [my emphasis] generalized tracks in the distribution of taxa, incorporating information on areas of endemism involved, the massing centres of higher taxa (foci of species richness) and the cladistic structure within them in relation to the areas of endemism. Major problems to be addressed [in future work on panbiogeography] include: (1) initial selection of areas of endemism; (2) accumulation of a sample of cladograms sufficiently large to provide statistically-significant results; (3) handling of the cladogram sample in a manner that will optimize recognition and test the significance of recurrent pattern; (4) development of a philosophy for assessing patterns so recognized in terms of process hypotheses. …. Solution of the third problem may also involve an element of phonetics: to devise a measure that will compare clades in a pairwise manner not just on aspects of range or richness, but incorporating information on the representation of areas over the structure of the clade, and then apply a clustering method to recognize groups."

The author notes that addressing such problems (still not fully resolved almost two decades later from the publication of this paper) will allow a "more probabilistic methodology for track analysis, and in the related methods of spanning tree analysis and construction and comparison of biogeographic graphs, both of which attempt to incorporate cladistic structure into track analysis."

This paper also gives a much better (or more refined) definition of "baseline" (introduced earlier this week) as "features of tracks such as the crossing of an ocean or sea basin, or a major tectonic structure, that is interpreted as a diagnostic character uniting individual tracks that may otherwise have little in common." This paper mentions that instead of the "significant subjective element" that some panbiogeographers use in constructing baselines and tracks, that panbiogeographers should rather apply "stricter protocols for track construction and baseline identification… particularly with regard to utilization of Great Circle minimal distances rather than straight lines on Mercator-type projections." In other words, rather than using rectangular maps, researchers should recognize that the Earth is (essentially) spherical and that distances along tracks (important in constructing a minimum spanning tree as one needs to determine minimal distances traversed) should take that point into account.

The author also suggests using archipelagos or groups of islands "such as the Indo-Australian tropics or the Caribbean [as] an opportunity to assess geological hypotheses of [their] evolution in relation to any statistically-significant clusters of patterns." In taking such an approach, the author suggests incorporating the principles of island biogeography (laid out by MacArthur and Wilson in 1967) into panbiogeography theory.

The paper concludes with the words that perhaps biogeographers should take "a more complex view emphasising interacting mutually contingent networks of causes. In practice achieving such a synthesis will require a breakdown of the conceptual and methodological boundaries between biogeography, evolutionary biology, systematics, ecology and geology. Achieving such a dissolution could be seen as the aim of the panbiogeographic synthesis."

Next we'll look at some specific examples of taxonomic gradients and track analyses with the following three papers. As usual, I encourage reading ahead

Review: Grehan, Stace (1990) Panbiogeography: beyond Dispersal versus Vicariance? Journal of Biogeography, 17(1):99-101.

Feature Paper: DOWNLOAD Grehan, Stace (1990) Panbiogeography: beyond Dispersal versus Vicariance? Journal of Biogeography, 17(1):99-101.

Author Abstract: In a recent guest editorial Stace (1989) expressed concern at the preoccupation of vicariance biogeography with vicariance events at the expense of migration to explain distributions. I take this opportunity to draw attention to the emergence of panbiogeography as a programme of synthesis between ecology, geology, systematics, and biogeography that does not require a priori adherence to specific doctrines of vicariance and dispersal while making positive and productive contributions to biogeographic methodology and theory. 

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: We will continue our examination of panbiogeography this week with a discussion of how panbiogeography can be applied specifically to tackling biogeographic problems where vicariance or dispersalism don't seem capable of resolving distributions.

This paper is a little different that other papers we've reviewed in that it is written by one author (Grehan) as a response to another author (Stace) and therefore provides lengthy quotations from Stace with comments or rebuttals by Grehan.

Stace begins his view by stating that dispersal (or migration) and vicariance (separation of populations by barriers) are both important means through which disjunct distributions are created. A disjunct distribution is where certain taxa are found in multiple locations that are widely separated from each other but where those taxa are not (necessarily) found at all locations between known sites. In Stace's view, as with many biogeographers, either vicariance occurs in a given situation for a certain group of taxa, or dispersal occurs… but each are mutually exclusive of the others.

Grehan points out that panbiogeography does not consider vicariance or dispersalism in determining biogeographic affinities and therefore "should be of some considerable interest to Stace as it may represent an alternative solution to his stated concern." Grehan continues to note that "Stace's presentation of vicariance and dispersal places biogeography firmly within the jaws of a methodological dilemma that can be recognized as a 'binary opposition' where the main outcome is simply to present a negative image of the alternative." With panbiogeography "rejecting the terms of the debate (that vicariance and dispersal have equal and independent existence) as a false opposition" Grehan aims to prove in a short rebuttal that panbiogeography can provide a new basis as a major school of biogeography in resolving distributions.

Grehan discusses the late Joseph Hooker (a great past botanist), who recognized that in certain circumstances, either vicariance or dispersal could both be considered valid answers to individual distributions. Hooker (in the 19th century) realized that "the problem lay not in the lack of 'facts' but the absence of an appropriate method." Grehan argues that panbiogeography is the modern method that can resolve current biogeographic problems.

Grehan points out that Croizat (the founder of panbiogeography) "demonstrated that patterns of dispersal (= evolution of distribution) are correlated with neither the migratory abilities of organisms (their different means of dispersal) or current world geography. Croizat's analysis suggested that tracks [discussed in the previous two papers this week] were correlated on a global scale with ocean basins and he identified tectonics as the nexus between geology and biology. This finding resulted in novel geological predictions that have since been independently corroborated by geological research."

Grehan then discusses a specific example of a disjunct population and shows how the problem is solved using panbiogeography. Stace concludes the article by pointing out that many panbiogeographers are very dogmatic and more critical of other biogeographic schools than the alternative schools of thought are to panbiogeography.

Of course, any good student or researcher will examine all schools of thought in their field and make their own determinations based upon thoughtful analyses of different perspectives.

Review: Grehan (2001) Panbiogeography from tracks to ocean basins: Evolving perspectives. Journal of Biogeography, 28:413-429.

Feature Paper: DOWNLOAD Grehan (2001) Panbiogeography from tracks to ocean basins: Evolving perspectives. Journal of Biogeography, 28:413-429.

Author Abstract: Misconceptions arising from efforts to translate panbiogeography into terms used in other biogeographic and evolutionary theories are discussed with respect to Cox's (1998, Journal of Biogeography, 25, 813-828) critique of panbiogeography. Croizat's rejection of 'Darwinian dispersal' applies only to efforts to utilize this concept as a general explanation for biogeographic patterns. The conceptual difference between distribution and panbiogeographic dispersal maps is illustrated to show that Croizat did not synonymize distribution and dispersal. Croizat's position on continental drift and plate tectonics does not support Cox's (1998) claim that Croizat 'for long time' refused to accept the theory of plate tectonics. The methodological relationship between panbiogeographic analysis and geology suggests an independence of methodology that prevents geological theory from falsifying panbiogeographic predictions. Panbiogeographic predictions for the eastern Pacific are shown to be in agreement with current historical geological models. Claims by Cox (1998) that the panbiogeographic method is variable and questionable are evaluated with respect to the biogeographic homology of primitive frogs, ratite birds, and southern beeches to demonstrate the consistent application of minimal distance, main massing, phylogenetic affinity and baseline criteria. Panbiogeographic classification concepts are contrasted with the Darwinian system (supported by Cox) utilizing a concept of unitary geographical area based on the language of Roman military rule. Inconsistent positions expressed in recent critiques of panbiogeography may indicate an underlying and implicit acceptance of the empirical and theoretical progress generated by panbiogeography within modern biogeography. 'The formation of groups has an invigorating effect in all spheres of human striving, perhaps mostly due to the struggle between the convictions and aims represented by the different groups' (Einstein, 1938. Collier's, 26 November).


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: We will continue our examination of panbiogeography this week with a more updated paper from Grehan (the author of our first review this week). Like Grehan's first paper we reviewed, we'll continue our definition of panbiogeography.


As the author notes, "panbiogeography is the only research program in historical biogeography based on the analysis of spatial or geographical relationships [and] it is perhaps for this reason more than any other that panbiogeography remains so controversial among biogeographers."


What we hope to achieve with paper 2 is to build on the foundation of understanding of panbiogeography that we covered on February 28 with the first paper. As such, I won't go into a big discussion of reiterating facts or arguments or points by this author (the same author as our first paper this week) that were already covered with the first paper. I'll only bring up new points or facts that I feel can help clarify an understanding of panbiogeography.


While spatial relationships are integral to all biogeography analyses, what the author means is that "with most historical biogeographers trained as biologists and having a primary interest in biological systematics [how organisms are related to each other], a fundamental shift in perspective is required to accept geography as an integral element of biogeographic analysis."


In other words, our training and preconceptions can affect how we interpret biological data in a geographical context. When approaching panbiogeography, one must be interested more in the geographical connection of areas than merely the similarity of species checklists. For panbiogeographers, Darwinian evolution alone is insufficient to explain the "many facts of world biogeography."


In a Darwinian context, speciation occurs through isolation of individuals and populations sexually to the point where one original population or species becomes several populations of the same species, that when exposed to various environmental factors, makes it favorable from a reproductive standpoint for certain features of the original population to perpetuate through the generations while other features are lost. When enough divergence of features occurs, and where the two (or more) populations are no longer reproducing together naturally, then the populations are considered by taxonomists to be separate species.


What panbiogeography emphasizes is how geographic separation is often paramount in speciation and therefore, to determine ancestral source populations, one must consider the geographic history and connectivity of various populations.


As we discussed last week, when the various populations are plotted on a map and connected by minimum-spanning trees, it is possible to create a map of a most conservative dispersal route, illustrated by the author below.

As an example illustrating the above figure, the author uses the case of the eastern Pacific ocean and how Baja (Mexico) was once separate from North America, and how the Caribbean plate (in plate tectonic theory) helped form Central America through compression during the movement of North and South America towards each other. The author points out how Croizat's original theory of panbiogeography as it relates to the formation of the Americas has, in recent years, been supported by plate tectonic theory.


The rest of the paper is concerned with how panbiogeography evolved after its foundation by Croizat. The greatest contribution to panbiogeography occurred in 1987 with the "introduction of graph theory [a branch of mathematics] by Page providing a new analytical context for tracks, nodes and baselines that was compatible with Croizat's earlier definitions and applications."


Two new terms in panbiogeography were introduced by Craw in 1988: "orientation" and "ocean baseline." Orientation refers to "the origin and direction of flow of migration with respect to a baseline" and includes "arrows on figures [of tracks] to designate directionality to the tracks." The term "ocean baseline" was introduced to emphasize "Croizat's assignment of major global baselines to ocean basins." A third new term was introduced by Henderson in 1990: "antinode." Antinodes "identify geographical centers of significant absence of taxa that may also be informative for track analysis." Sometimes, the absence of species or groups is just as important as the presence of species or groups. As we'll see in the future in another paper of Pacific Island biogeography, biogeographical regions were discovered when one ignored the floras and faunas of atolls compared to larger, "high" islands.

Review: Grehan (1994) The beginning and end of Dispersal: the representation of 'Panbiogeography'. Journal of Biogeography, 21(5):451-462.

Feature Paper: DOWNLOAD Grehan (1994) The beginning and end of Dispersal: the representation of 'Panbiogeography'. Journal of Biogeography, 21(5):451-462.

Author Abstract: The contrast in theory and method between Croizat's panbiogeography and traditional approaches to biogeography presents traditional biogeographers with a significan hurdle when attempting to portray panbiogeography. This epistemological barrier can result in panbiogeography being misrepresented when attempting to categorize panbiogeography within traditional frameworks that are not applicable in a panbiogeographic context. The conflict between the traditional contexts presented in Cox & Moore (1993) and the alternative methods and concepts developed in panbiogeography are illustrated here with respect to the following issues: (1) standard tracks as vicariance events rather than biogeographic (spatial) homologies, (2) Croizat opposing tectonics rather than integrating tectonics with biogeographic patterns, (3, 4) Croizat giving little attention to fossils and climate rather than extensively discussing their relationships with biogeography, (5) ocean baselines being inappropriate to terrestrial patterns rather than representing the spatial homologies, and (6) treating main massings as Darwinian centres of origin rather than spatial criteria for orienting tracks.

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: We are now into week 3 of our 12-week course in biogeography, and this week we'll look at the biogeography subdiscipline of panbiogeography, which was created by the biogeographer Croizat (1950s) and has been controversial over the years because panbiogeography started out just as plate tectonic theory was being accepted, but before a full knowledge of continental movements and plate tectonics occurred. As the author of this week's paper notes, much confusion surrounds panbiogeography because it is concerned mostly with geographical connections, which we'll discuss, rather than emphasizing "ecological and evolutionary approaches to biogeography," resulting in "the unintentional result [of] a mis-representation of panbiogeographic concepts that conflicts with actual panbiogeographic texts." In other words, ecologists and evolutionary biologists approach panbiogeography from the context of their fields, causing some errors.

Today we'll start a discussion on what exactly panbiogeography is as well as ensuring that misunderstandings don't occur.

To start, panbiogeography deals with certain terms. As the author notes, "the track method represents one of the most well known aspects of panbiogeography. Individual locations are linked together as line graphs or 'tracks' and those tracks sharing the same biogeographic homologies (baselines) are grouped together into standard or generalized tracks."

Croizat was concerned primarily with "the geological background upon which the ancestral range [for organisms] was established, not Darwinian barriers with respect to the current isolates." In other words, Croizat was not concerned with reproductive barriers or natural selection but rather where individual groups of organisms originated ancestrally.

Another point where panbiogeography typically differs from other branches of biogeography is that "major geographic features widely regarded as 'barriers' in conventnal biogeography (e.g. oceans) become 'centres of origin' in panbiogeography. These panbiogeographic centres of origin are not of the Darwinian kind from which taxa migrate according to their different means of disperseal, but are the baseline that orient or center the geographic sectors involved with the evolution of particular taxa." Because panbiogeography is "interested in biogeographic centers and biogeographic origins" it differs from vicariance biogeography, which eschews "any concept of center of origin."

Now that we understand the concept of a "track" (a biogeographic connection between locations) we can discuss the concept of a "node," which is a geographic area that has served as an originating point for two or more other geographic locations (with their respective groups of organisms). In Croizat's terms, a node is a "region where more than [one[ biogeographic system had converged." However, when starting a panbiogeographic analysis, one looks at "plant and animal distributions" first in attempting to reconstruct historical patterns rather than looking at geological theory. This is likely a result of Croizat working concurrent with the beginnings of plate tectonic theories.

The author then goes into a discussion refuting a number of the negative claims against Croizat, such as whether he paid enough attention to plate tectonics, the fossil record, or climate change. As such a discussion isn't pertinent to defining panbiogeography, I'll leave it to interested readers to follow up in the full paper. Suffice it to say however that the author provides multiple examples where Croizat did give due attention to all three areas.

The third key definition for panbiogeography is the "baseline." A baseline is, in essence, a large track, particularly through an ocean basin, that connects the "biogeography of the group so that it may be compared and analyzed in relation to other distributions that may or may not share the same spatial homology." Baselines are typically drawn through ocean basins to connect the majority of common organisms on landmasses, as illustrated below.

When baselines, tracks, and nodes are represented graphically, a kind of "minimum spanning tree" (MST) is created. The MST is a mathematics problem (combinatorics and graph theory) to represent the shortest graphical space (most conservative representation) needed to connect multiple points. From a panbiogeography perspective, a MST represents the most conservative "route" by which organisms traveled geographically to become separate populations today. Panbiogeography then adds the concept of a "main massing" to try and determine the base of the MST such that it becomes a "directed graph." In other words, it isn't important merely to connect the floras and faunas of various geographical regions, but also to attempt to determine the origins of disparate groups today.

After defining the key terms of panbiogeography and giving several examples, the author notes that while "Croizat established these methods and concepts over 40 years ago [50 years ago today], they do remain relevant in the context of modern research on geology, paleontology, ecology and systematics." The author also notes that "panbiogeographic methods can lead to novel predictions about evolution that can be tested by independent disciplines such as systematics."

The author concludes the paper by noting that many biogeographers are concerned with "the dichotomies of ecology vs history, and dispersal vs vicariance. The imposition of binary oppositions requires the selection of one alternative as if this choice represents the real, natural, world. Panbiogeography represents a research program that is working to deconstruct the strict demarcation between these artificial dichotomies."

This paper is from 1994. Since then, biogeography has continued to grow as a science and many environmental scientists are recognizing the importance of multidisciplinary research and approaches in order to solve ever-complex biological problems. No theory is static in science. Only laws are such. As a result, panbiogeography should be recognized for its value and not just as a precursor to vicariance biogeography.

The rest of this week, we'll continue our examination of "panbiogeography" (the remaining papers on the reading list are noted below). As usual, I encourage downloading the articles in advance and reading them before the summaries. Panbiogeography is a complex and misunderstood branch of biogeography, so I wanted to provide several papers that note the growth of the science over the last 20 years.

Review: Weir JT, Schluter D (2007) The latitudinal gradient in recent speciation and extinction rates of birds and mammals. Science, 315:1574-1576 + supplement.

Feature Paper: DOWNLOAD * Weir JT, Schluter D (2007) The latitudinal gradient in recent speciation and extinction rates of birds and mammals. Science, 315:1574-1576 + supplement.

Author Abstract: Although the tropics harbor greater numbers of species than do temperate zones, it is not known whether the rates of speciation and extinction also follow a latitudinal gradient. By sampling birds and mammals, we found that the distribution of the evolutionary ages of sister species — pairs of species in which each is the other’s closest relative — adheres to a latitudinal gradient. The time to divergence for sister species is shorter at high latitudes and longer in the tropics. Birth-death models fitting these data estimate that the highest recent speciation and extinction rates occur at high latitudes and decline toward the tropics. These results conflict with the prevailing view that links high tropical diversity to elevated tropical speciation rates. Instead, our findings suggest that faster turnover at high latitudes contributes to the latitudinal diversity gradient.

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: This is the third paper of our 12-week course in biogeography, and the second paper of week 2. As with the first paper this week, this paper deals with approaches meant to discover, map, and quantify patterns of diversity of various organisms in space. This week we'll discuss the latitudinal species diversity gradient, meaning the concept that there is a distinct non-random pattern of species accumulation and diversity as one moves latitudinally from the equator to the poles.

As the authors state, "the tropics possess many more species than temperate regions, yet the underlying causes of this latitudinal gradient in species diversity are poorly understood."

So here we are left with two points to discuss.

First, that there is a nonrandom gradient in species diversity, with the tropics (at the bare minimum the region bounded between the Tropic of Cancer (23º26' north of the equator) and the Tropic of Capricorn (23º26' south of the equator), but more realistically dependent upon climatic conditions as a result of upwelling (in the case of marine environments) or altitude and precipitation (in the case of terrestrial environments).

Second, not only does such a pattern exist (for the majority of species and taxonomic groups in nature, both for plants and animals, though there are some distinct exceptions), but this pattern is poorly understood and there is a lot of speculation among scientists as to why such a pattern exists. Over the coming weeks, we'll discuss some of these theories, but if you also recall our Week One lecture on historical biogeography, a quick summary of some of the more important theories was provided.

The paper this week deals with two terrestrial groups (birds and mammals) and tries to describe and explain their latitudinal diversity gradient. And while broad generalizations are almost never possible in biological sciences (sometimes, exceptions to the rule are the rule), the mere fact that most species studied show a similar pattern of diversity (aquatic and terrestrial) suggests that similar principles apply.

This is a lesson that one should learn when starting out in science: find principles that apply for one group of organisms and perform a similar study to determine whether such principles apply for other groups of organisms. If enough organisms follow the same pattern, then theories can be proposed and mechanisms underlying such patterns can be discussed.

In performing their study, the authors chose to look at speciation and extinction rates as a mechanism to "cause" the observed distribution patterns today. How did they do this since it is probably impossible to be present for a speciation or extinction event? The answer lies in genetics.

The authors looked at the "genetic distances of mitochondrial DNA from the cytochrome b gene" in 309 sister species pairs ("most closely related pair of extant species descended from an immediate common ancestor") of "New World birds and mammals." As mtDNA is passed down through females (mothers) only and is fairly conservative over time, mapping genetic mutations within the mtDNA of individuals and assuming (based on past studies for wide groups of organisms) a certain constant rate of random mutation allows one to determine the amount of time that two species have existed separately since they last shared a common ancestor (the point where no mutations in the mtDNA existed between individuals in each species examined.

One interesting finding for the authors was that age of divergence (and by proxy, speciation rate) differed latitudinally, with species near the equator having diverged up to "10 million years ago, with a mean age of 3.4 million years ago" and that "as distance from the equator increased, the upper limit and mean ages of sister species declined significantly" such that "at the highest latitudes, all of the sister species diverged less than 1.0 million years ago."

The authors point out that "this pattern of declining age with latitude is opposite to the pattern that would occur if faster rates of speciation had driven the buildup of Neotropical diversity, because the ages of sister species should be youngest where speciation rates are highest."

The authors then suggest that "it may be possible to extract information about speciation and extinction rates from the distribution of sister-species ages… because speciation and extinction can be inferred by the shape of the age distributions of sister species." The authors explored various mathematical models to fit speciation and extinction rates across a latitudinal gradient.

The authors found that "estimated speciation and extinction rates were lowest at the equator and increased significantly toward the poles." The authors note that "these results are surprising because the latitudinal gradient in estimated speciation rate is opposite to the gradient in net rate of diversification estimated by many studies to be highest in tropical taxa."

This finding is important because one theory meant to explain higher species diversity in the tropics is that speciation rates are higher in the tropics than in temperate latitudes and therefore, more species are "created" in the tropics as a result of faster speciation rates.

In reconciling their findings the authors suggest the following explanations:

"These quantitative estimates are based on the assumption that speciation and extinction can be approximated by a continuous birth-death process as latitude becomes higher or lower. Yet, we know that there have been fluctuations in the opportunities for speciation and extinction over the past few million years. For example, extensive climatic fluctuations that occurred at high latitudes during the late Pliocene and Pleistocene (2.5 Ma to present) may have concentrated speciation and extinction events in time, resulting in episodic species turnover. In contrast, the bursts of diversification in tropical faunas may predate the late Pliocene and Pleistocene, and the patterns observed today may be the result of a subsequent decline in diversification either because the geological processes that promoted diversification (e.g., formation of Isthmus of Panama, marine incursions, orogeny, and river formation) have slowed or because diversification rates declined as the number of tropical species approached a “carrying capacity." Given such variability, our estimates are best regarded as averages over the periods studied. These results suggest that extinction rates are greatest where species diversity is lowest [in Temperate regions for most species]. Whereas most efforts have aimed at identifying the geological, climatic, and ecological factors that might have elevated tropical speciation rates, our results suggest that both speciation and extinction vary with latitude and contributed importantly to the latitudinal diversity gradient."

As we look at other groups of organisms over the "semester" we'll see how well the authors' findings apply to other taxonomic groups, especially in a marine context.

Next we'll be looking at the biogeography subdiscipline of "panbiogeography" with the reading list noted below. As usual, I encourage downloading the articles in advance and reading them before the summaries.

Cheers and happy studies.