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Finding Osama bin Laden with Biogeography

I saw the coolest thing ever on the Rachel Maddow Show tonight.  EverThomas Gillespie of the Geography Department at UCLA was on the show discussing his attempt to predict bin Laden’s location using satellite imagery and biogeographic theory!  It was so amazingly cool to hear him discussing distance-decay models and island biogeography theory to predict bin Laden’s location.  It’s all the cooler because Gillespie is, at least in part, a tropical forest ecologist, did his Ph.D. on tropical dry forests in Nicaragua, and has published on dry forest fragments in south Florida.

It also make me wonder.  This is fairly basic work as far as biogeography goes.  It seems like a much simpler, much more tractable problem than you tend to get in actual conservation biology.  Gillespie may not be right, and presumably if he was, bin Laden has moved by now.  You tend to think of the intelligence community having highly sophisticated tools for data analysis.  But then you hear things like the fact that they are overwhelmed by the sheer volume of data, and that they just don’t have enough analysts to deal with all the information they ‘capture’.  It makes me wonder whether the intelligence community should be hiring more community ecologists.  Community ecologists (and, apparently, environmental geographers) are faced with a “middle numbers” problem – they are faced with far too many data points to actually enumerate, but far too few to truly generalise. While this has posed a huge problem to the development of ecological theory, it hasn’t paralysed the field. Part of learning to function as an ecologist is learning to to deal with the issue.

Last month, after Karl’s funeral, Ryan reminisced about a recent interaction between him, Floyd and Karl.  He and Floyd had been counting and measuring the fish the had captured in their sampling.  After watching them measure and record several hundred fish, Karl pointed out to them that they should simply have put the fish into size classes and tallied the number in each size class.  It’s always hard to discard information that you’ve already gone to the trouble of collecting, but it’s often something you need to do in order to make sense of the data you have collected.  It’s something you learn to do as an ecologist…you learn to focus on that portion of the data that you can actually use.  It get the impression that it’s the kind of experience that might translate well into the world of intelligence analysis.

Gillespie, Thomas W., John A. Agnew, Erika Mariano, Scott Mossler, Nolan Jones, Matt Braughton, and Jorge Gonzalez. 2009. Finding Osama bin Laden: An Application of Biogeographic Theories and Satellite Imagery. MIT International Review. Online edition.


Evolution and conservation in Mexican dry forests

The characteristic peeling bark of <i>Bursera simaruba</i>.  Copyright Kurt Stueber, licensed under the GFDL

The characteristic peeling bark of Bursera simaruba. Copyright Kurt Stueber, licensed under the GFDL

Bursera simaruba has always been one of my favourite tree species. It’s a dry-season deciduous tree with compound leaves and a coppery peeling outer bark and a green (presumably photosynthetic) inner bark.  It’s a conspicuous element of tropical dry forests in Trinidad and Tobago, Puerto Rico and parts of southern Florida (where they call it the ‘gumbo limbo’ tree).  In all these places it’s the only representative of its genus.  In my experience, Bursera was Bursera simaruba, so I was surprised when I came across a Bursera that was grown from seed collected in Costa Rica that was obviously not B. simaruba.  Nonetheless, I still thought of Bursera as a relatively small genus.  Then I came across some information on the genus in Mexico which turned my picture of Bursera completely on its head.  There are 84 species of Bursera in Mexico – 80 of which are endemic – out of a total of approximately 100 species in the genus.  So why are 80% of the species of Bursera – a genus which ranges from Florida to Argentina – restricted to Mexico?

Species diversity patterns reflect several underlying processes – those that generate diversity, and those that maintain that diversity.  When species are grouped into a genus, the assumption is that they are more closely related to one-another than are they to any species in a different genus.  To get from that one ancestral species to its modern descendants, something must occur that allows the single ancestral lineage to split into several daughter lineages (a process known as speciation).  This figure from the Wikipedia article on speciation summarises the different modes of speciation.speciation_modes

In order to generate the type of pattern seen in Bursera, you need one of two evolutionary processes to be active.  Either Bursera originally diversified in Mexico, and a few species have spread beyond that ancestral range (giving rise to their own daughter species along the way) or something happened in Mexico that led to the diversification in a limited portion of the range of a widespread genus.  In the former case, Mexican diversity should be old, and the splits between the Mexican species should lie deep in the ancestry of the genus.  In the latter case, Mexican diversity is newer, and the splits between the Mexican species are likely to have been derived from more widespread species.

ResearchBlogging.orgIn a paper published in PLoS ONE in October, Judith Becerra and Lawrence Venable of the University of Arizona looked at the case of Bursera in Mexico.1 Bursera is an old genus – molecular phylogenies based on ribosomal DNA suggest that modern species share a common ancestor about 66-74 million years ago, and fossil evidence suggests that the genus was once ranged over a much wider portion of North America.2 It turns out that most of the Mexican species are more recent.  The number of lineages increased substantially within the last 30 million years3 and peaked between 10 and 17 million years ago (which coincides with the formation of the Western Sierra Madre and the Neovolcanic belt).1 Becerra suggested that the diversification of Bursera is likely to have coincided with the expansion of dry forests in central and southern Mexico.3 These dry forests were made possible by the uplift of the mountains which provided appropriate climatic conditions for the establishment of tropical dry forests by sheltering them from northern cold fronts.1

In previous work, Becerra has built a detailed phylogeny of the Mexican species of Bursera.  Using this phylogeny, she was able to show that the diversification of these species coincided with the formation of the Western Sierra Madre and the Neovolcanic belt.  In the PLoS ONE article she and Venable used this phylogeny and the distribution of existing Bursera species to predict where the various species are likely to have originated.  Despite the fact that it ranks third in Bursera species richness today, they found that the Southwest was actually the source of the largest number of species.  The Balsas River basin, on the other hand, has the most species (and the largest number of endemic species), but was the site fo relatively few diversifications.  Continued mountain-building led to an expansion of dry forest, into which new species wer able to spread.  Other new species were able to invade the Mexican highlands, the Sonoran Desert, upland oak forests or subhumid tropical forests.

Becerra and Venable termed the diversity-generators “source” areas and the non-dry forest habitats as “diversity sinks”.  Personally, this bothered me, as it felt like they were borrowing terminology from population ecology (where it applies to individuals within populations) and applying it to species in a way that is likely to bring unwanted baggage.  Sink populations recruit fewer individuals than are required to replace losses to the population, and as such will go extinct if they don’t continue to receive immigrants from the source population.  There’s nothing to indicate that Becerra and Venable are using ‘sinks’ to mean anything beyond the fact that these areas are occupied by species that evolved elsewhere.  Using this borrowed terminology is likely to mislead readers who are more familiar with the concept of source-sink dynamics in population ecology.

Since certain areas have been superior generators of diversity, Becerra and Venable suggest that prioritising them for conservation should yield superior long-term outcomes.  Protecting areas that can generate diversity should be more important than simply protecting areas that harbour greater diversity.  They write:

The differences between diversity and diversification mean that this may be transitory in the long run, analogous to protecting species in zoos. While it might sound unusual to try to conserve diversity based on events happened in the past, there may be cases in which the aerographic patterns of diversification have occurred repeatedly for a long time, giving us some kind of assurance that it will continue happening in the same way for at least the near future. In the case of Bursera, diversification seems to have been higher in one area for a long time, starting 15 million years ago or perhaps even longer. If not greatly perturbed, there is no reason not to believe that these same patterns of diversification will continue. This approach could be especially useful if there are no other stronger criteria to decide where conservation efforts should be directed. If we had to choose between conserving one of two areas and everything is equal except their history of being sinks or sources of diversification, there would be no harm and perhaps much gain in choosing the source. The long-term maintenance of biodiversity require us preserve its sources, to the extent that these can be accurately determined [8].

[Emphasis added]

I’m not sure if I agree, or disagree.  On one hand, there’s a lot of evidence that suggests that species assemblages are more transient than they were assumed to be in the past.  The simple fact that an area supports a large assemblage of species may reflect chance as much as some special property of the site.  So from that perspective, the areas that have generated diversity should be more important than the areas that harbour diversity.  On the other hand, why should we assume that an area that generated a lot of diversity in the past will continue to do so in the future?  The rate at which new species are being generated appears to have declined sharply in past 10 million years.3 If, as has been suggested, the generation of diversity was related to mountain-forming, is it reasonable to expect the process to continue?  It’s difficult to say what it is that generates a species flock in one area and not in another.

The other big question I found myself with was what is the purpose of conservation?  At what point will we be able to stop protecting species and environments?  When will the threats recede, or will they recede at all?  What will the world look like when the current human-driven extinction event has run its course?

This post is my contribution to PLoS ONE @ Two, a celebration of the second birthday of PLoS ONE.

  1. Judith X. Becerra, D. Lawrence Venable (2008). Sources and Sinks of Diversification and Conservation Priorities for the Mexican Tropical Dry Forest PLoS ONE, 3 (10) DOI: 10.1371/journal.pone.0003436
  2. Judith X. Becerra (2003). Synchronous coadaptation in an ancient case of herbivory.  Proceedings of the National Academy of Sciences USA 100 (22): 12804-12807 DOI: 10.1073/pnas.2133013100
  3. Judith X. Becerra (2005). Timing the origin and expansion of the Mexican tropical dry forests.  Proceedings of the National Academy of Sciences USA 102 (31): 10919-10023 DOI: 10.1073/pnas.0409127102

Oekologie #19

Edition #19 of the Oekologie blog carnival is up at Greg Laden’s blog.  There’s lots of great stuff there, like Grrlscientist’s post on the evolution of poisonous birds, or a post from Sustainable Design Update on using coffee grounds as a source of biodiesel, or Greg Laden’s Congo Memoirs, or… Go.  Read.

Ideas in Ecology and Evolution

Ideas in Ecology and Evolution is a new open-access journal which “publishes only short forum-style articles that develop new ideas or that involve original commentaries on any topics within the broad domains of fundamental or applied ecology or evolution”.  They also have an interesting review process:

Referees for Ideas in Ecology and Evolution are not anonymous; they are paid – not just for their reviewing services, but importantly, they are paid to forfeit their anonymity.  In other words, in the event that the paper is published, payment of referees secures their consent to reveal their identities – directly within the published paper – as having refereed the paper.  Referee identity is also revealed to authors of rejected papers.  Referees must agree to these conditions in advance, before receiving the paper for review.  This is done on-line, and the referee is paid upon receipt of the review.

The author pays for the review process and publication.  It costs $400 to submit an article ($300 to pay two reviewers, $100 for the rest of the process) and an additional $300 upon acceptance. That’s the drawback of most open-access systems – that they require authors to incur substantial costs.  Not that ‘closed-access‘ journals publish your articles for free…but it can still be a barrier for some authors.  Granted, many of them are willing to waive their fees for authors who are unable to pay.  I haven’t seen anything of the sort here, but that isn’t surprising in a journal this new.

H/T Bora.

Speciose or species-rich?

As a graduate student I came across the word “speciose”.  It had an alluring sound to it that was lacking in its more pedestrian synonym “species-rich”.  Equally appealing, I suspect, was the fact that it supplied a formal-sounding alternative that was less accessible to the average person.  (If you’re lucky, you outgrow that affectation and learn that clear communication is what matters most.)

In the December issue of TREE, Michael Hart delves into the origin and use of the word speciose.  Although similar to “species”, speciose actually shares a root derives from “specious” in ‘beautiful’ or ‘lovely’.  Hart sees value in speciose – it’s no longer than “species-rich” and solves the hyphenation problem (i.e., the problem of not knowing when to join the words “species” and “rich” with a hyphen).  Both “species-rich” and “speciose” first show up in the Web of Knowledge database in 1957, and use of both terms has grown fairly consistently.  Although he cites Gill’s plea to cease ‘the misuse of ‘‘speciose’’ in the evolutionary biological literature,’ Hart sees value in this “lovely word” and urges “deliberate consideration” as to its future and fate.

I embraced “speciose” in my first or second year as a grad student.  I happily embraced it, using it both in writing and conversation.  And then, to my horror, I discovered Gill or some other pedant who insisted that “speciose” was being misused by ecologists.  With that discovery, I discontinued use of speciose immediately.  The only thing worse than using big words is misusing them.  Granted, it had been wearing thin already – my doctoral advisor, for example, had seen no inclination to adopt the word despite my repeated use of it.

And that’s where it’s stood ever since, for me, until now.  Granted, Al Gentry used to word, and being as amazing a biologist as he was, he had the right to use whatever word he wanted, however he wanted to…and be right.  After all, he was Al Gentry.  (And he had tragically passed away, doing a rapid assessment of biodiversity.)

Reading Hart made me re-think my opposition to “speciose”.  We have the right to re-define words from time to time.  This might be a good candidate.  I’m not sure if it’s for me, but I should be willing to accept that it is, after all, an acceptable term.

Hart, Michael W. 2008. Speciose versus species-rich. Trends in Ecology & Evolution, 23 (12):660-661 doi:10.1016/j.tree.2008.09.001

Seeking sustainability in Amazonian palm production

buritizal-1Mauritia flexuosa, commonly known as the Moriche palm, aguaje, burití (and a variety of other names) is a large palm which is native to tropical South America and Trinidad. It grows in permanently or temporarily flooded forests, and often forms monodominant stands.  In parts of South America these stands cover thousands of hectares at densities which can exceed 300 trees per hectare.  Moriche palms are important as a source of “food, fiber, oil, medicinals, materials for construction and fishing equipment, and fallen stems serve as a substrate for raising of edible larvae of the palm beetle (suri, Rhynchophorus palmarum)”1

433px-buriti_fruchtPalm fruits are important food sources both for humans and wildlife.  The outer surface of the Moriche fruit is reddish-brown and scaly.  Beneath this is a thin layer of yellowish pulp which covers a large seed.  This pulp is used in Peru to make ice cream, popsicles and cold drinks.  Consumption in Iquitos ranges from 22-150 tonnes/month.  The harvest and sale of the fruit is an important source of income for rural people in the Peruvian Amazon.1

The idea of a non-timber product from the rainforest with a well-established market…it seems too good to be true.  And in a sense, it is.  While it would seem to be the perfect tool for forest conservation, demand for aguaje has led to the degradation or destruction of extensive areas of Moriche swamps.  You see, the normal way to harvest the fruit is to cut down the tree.  Aguaje production around Iquitos, Peru, is estimated to lead to the destruction of at least 24,000 trees annually.1 It takes 7-8 years for an individual to reach maturity, so the rate of replacement of cut trees is pretty slow.  Add to that the fact that the most productive trees are cut (it takes the same effort to cut down a tree with a large fruit crop as it does a tree with few fruit) and the end result is pretty obvious.  Not only do aguaje collectors have to travel to more and more remote sites in order to harvest fruit, the trees left behind to re-seed the area are the ones that produce the least attractive crops.  In addition, moriche swamps are important food resources for wildlife.1

The depletion of moriche stands is apparent to local people, especially those who earn income by harvesting the fruit.  In the interest of sustainable harvest, a climbing system was developed that made it possible to harvest fruit without destroying the tree.  Maya Manzi of Clark University and Oliver Coomes of McGill looked at the effect of the introduction of the climbing system to the village of Roca Fuerte in Peru.  Since 1999 Fuerte Roca has been located on the north bank of the Marañón River in the Peruvian Amazon.  Prior to that it was located on the south bank.  Relocation across the river allowed them to exploit new stands of Moriche palms.  In 1999 the stands had been nearby, but four years later it took almost three hours to reach productive stands.  Seeing this change, and being aware that a similar thing had happened when the village was located on the south bank, the villagers were willing to work with an NGO to try to find a way to sustainably harvest the palm fruit.  Purchase of the climbing system led to the designation of an extractive reserve where fruit could only be harvested by climbing, not by cutting.

Manzi and Coomes looked at the socioenomic characteristics of the villagers and tried to determine which factors made them more likely to adopt the new means of harvest.  Unsurprisingly, younger people were more likely to adopt the new technology, as were those who were more successful hunters.  Families with “fewer non-land assets” and less hunting experience were less likely to adopt the newer technology.

One constraint on the adoption of the new technology was the fact that the village had only been able to afford to purchase four sets of climbing gear.  Since climbing requires a fair amount of manual dexterity and strength, it’s probably harder for older people to learn.  (Now, granted, I’ve seen old men climb coconut trees, but they have probably been doing it all their lives.)  I would tend to assume that younger people would also be more likely to adopt new technology, but I have no idea whether my assumptions translate to rural Peru.

I found it interesting that hunting success correlated with a greater willingness to adopt the climbing techniques.  The authors explained this as follows:

Our second model reveals that participation in harvesting by climbing instead of felling tends to be higher among younger households and those with higher forest knowledge, as reflected by success in hunting large bodied animals (mainly ungulates). Hunters are well aware that large ungulates depend on the availability of aguaje palm fruit and that they play an important role in the regeneration of aguaje palm forests through seed dispersal. As such, hunters have a strong incentive to protect aguaje stands.

Other factors like having “fewer non-land assets” are interesting, but less well explained.  The paper also discusses factors related to the willingness of people to cultivate the palms – interesting stuff, perhaps for another time.

Photo credits: The first photograph, copyright Eurico Zimbres, is from Wikimedia Commons and is licensed under the Creative Commons Attribution 2.5 License.  The second photograph was related into the public domain by its creator Frank Krämer.

Manzi, M., O.T. Coomes (2008). Managing Amazonian palms for community use: A case of aguaje palm (Mauritia flexuosa) in Peru Forest Ecology and Management DOI: 10.1016/j.foreco.2008.09.038

The importance of habitat area in conservation: a look at the species-area relationship

Species conservation has always been intimately linked with the idea of habitat conservation. While habitat quality determines the amount of habitat required to protect a viable population of a given species, it’s only a modifier – the determining factor is area. Habitat quality can determine whether you need more or less area, but area is still the critical factor. While protected areas can be set aside for specific species, more commonly protected areas seek to protect as many species as possible. More land is likely to protect more species, but there are other factors that influence conservation decisions like the cost of land acquisition and the competing interests such as agriculture, mining or housing development.

One way to maximise the number of species in a protected area is to include as many habitat types as possible. If you include a forest, a meadow, a marsh and a lake in your protected area, you are likely to get a lot more species than you would if you only had forest habitat. The heterogeneity of the area increases the number of species. (After all, you don’t find a lot of fish in a pine forest, or field mice in a lake.) But again, this overlays a simple factor of area. A larger tract of forest will probably have more species than a smaller tract of forest. A larger section of a marsh will probably have more species than a smaller section of marsh. This fact, known as the species-area relationship is fundamental in both ecology and conservation biology. The existence of a relationship between species richness and area is obvious to anyone who has taken the time to think about it, but it is still interesting enough that it has attracted the attention of generations of ecologists.

[Read the rest of the post at ScientificBlogging]

This is the first in a series of posts in which I plan to examine one of the fundamental concepts in ecology – the species-area relationship