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I'm a doctoral student in evolutionary ecology; D & T is my personal 'blog, and my top topics are science, religion, and politics, with particular interest in the interface between science and religion.
Jeremy Yoder
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- August 14, 2010
- 06:59 PM
- 5,915 views
Cite more papers, get more citations?
by Jeremy Yoder in Denim and Tweed
Nature News is reporting some interesting results presented as a paper at a meeting of the International Society for the Psychology of Science & Technology last week: articles published in the journal Science with longer "Works Cited" sections are themselves more frequently cited [$$]. A plot of the number of references listed in each article against the number of citations it eventually received reveal that almost half of the variation in citation rates among the Science papers can be attributed to the number of references that they include. And — contrary to what people might predict — the relationship is not driven by review articles, which could be expected, on average, to be heavier on references and to garner more citations than standard papers.The same authors did a similar analysis of papers published in the journal Evolution and Human Behavior over 30 years, and found similar results [PDF]. Here's the relevant figure from that paper:
.flickr-photo { }.flickr-framewide { float: right; text-align: left; margin-left: 15px; margin-bottom: 15px; width:100%;}.flickr-caption { font-size: 0.8em; margin-top: 0px; } Cite more, be cited more. Figure 2 from Webster et al. (2009) [PDF].
The lack of a "review effect" is surprising, but I don't think this overall result is. Academia, as much as we might describe it as cutthroat, also runs on reciprocal altruism. Authors notice when their papers are cited, and are more likely to cite papers that build on or relate to their own work. I'd be interested to see the network of citation underlying the pattern Webster et al. have found—I suspect that there's a lot of clustering around disciplines and sub-disciplines and sub-sub-sub-disciplines that contributes to all this mutual back-scratching citing.
Reference
Webster, G.D., Jonason, P.K., & Schember, T.O. (2009). Hot topics and popular papers in evolutionary psychology: Analyses of title words and citation counts in Evolution and Human Behavior, 1979-2008. Evolutionary Psychology, 7 (3), 348-348 Other: http://www.epjournal.net/filestore/ep07348362.pdf
... Read more »
Webster, G.D., Jonason, P.K., & Schember, T.O. (2009) Hot topics and popular papers in evolutionary psychology: Analyses of title words and citation counts in Evolution and Human Behavior, 1979-2008. Evolutionary Psychology, 7(3), 348-348. info:other/http://www.epjournal.net/filestore/ep07348362.pdf
- October 19, 2008
- 03:07 PM
- 1,490 views
Towards an empirical morality
by Jeremy Yoder in Denim and Tweed
Andrew Sullivan links to a thought-provoking 1998 essay by E.O. Wilson, in which the champion of sociobiology delves into the question of whether morality arises from divine revelation or natural selection. Wilson takes an interesting position, attempting to turn the question around by ninety degrees:But the split is not, as popularly supposed, between religious believers and secularists. It is... Read more »
J.D. Greene, R.B. Sommerville, L.E. Nystrom, J.M. Darley, & J.D. Cohen. (2001) An fMRI Investigation of Emotional Engagement in Moral Judgment. Science, 293(5537), 2105-8. DOI: 10.1126/science.1062872
- August 31, 2008
- 11:33 AM
- 1,463 views
Big herbivores shape plant community response to global warming
by Jeremy Yoder in Denim and Tweed
The cover article from this week's PNAS has important implications for how we plan for, and deal with, climate change. Post and Pedersen report that the way an arctic plant community changes in response to warming depends heavily on the presence of large herbivores [$-a], like muskoxen and caribou.
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E. Post, & C. Pedersen. (2008) Opposing plant community responses to warming with and without herbivores. PNAS, 105(34), 12353-8. DOI: 10.1073/pnas.0802421105
F.L. Russell, D.B. Zippin, & N.L. Fowler. (2001) Effects of white-tailed deer (Odocoileus virginianus) on plants, plant populations and communities: A review. The American Midland Naturalist, 146(1), 1-26. DOI: 10.1674/0003-0031(2001)146[0001:EOWTDO]2.0.CO;2
- September 7, 2008
- 02:45 AM
- 1,409 views
Christ Church as it is: Creationist Credentials
by Jeremy Yoder in Denim and Tweed
A couple of weeks ago, I introduced Christ Church, Moscow, Idaho's friendly neighborhood theocracy-in-embryo, which weds garden-variety Christian Right hypocrisy with creepy, racist Neo-Confederate overtones. Today, I'm going to have a look at the Christ Church-affiliated New Saint Andrews College.
NSA cultivates a reputation as the ivory tower's ivory tower - the curriculum includes lots of... Read more »
W. Godsoe, J.B. Yoder, C.I. Smith, & O. Pellmyr. (2008) Coevolution and Divergence in the Joshua Tree/Yucca Moth Mutualism. The American Naturalist, 171(6), 816-23. DOI: 10.1086/587757
R. Gomulkiewicz, D.M. Drown, M.F. Dybdahl, W. Godsoe, S.L. Nuismer, K.M. Pepin, B.J. Ridenhour, C.I. Smith, & J.B. Yoder. (2007) Dos and don'ts of testing the geographic mosaic theory of coevolution. Heredity, 98(5), 249-58. DOI: 10.1038/sj.hdy.6800949
G.L. Wilson, & C.H. Ernst. (2005) Reproductive Ecology of the Terrapene carolina carolina (Eastern Box Turtle) in Central Virginia. Southeastern Naturalist, 4(4), 689. DOI: 10.1656/1528-7092(2005)004[0689:REOTTC]2.0.CO;2
J.B. Yoder, & B. Shneiderman. (2008) Science 2.0: Not So New?. Science, 320(5881), 1290-1. DOI: 10.1126/science.320.5881.1290
- August 29, 2008
- 01:50 PM
- 1,355 views
The evolution of offspring size
by Jeremy Yoder in Denim and Tweed
The question of offspring size - that is, how big a child is relative to its parent - can seem downright absurd. In fact, it was the subject of the only paper (to my knowledge) ever published in the journal Evolution that ends with a punch line. That piece, written by Ellstrand in 1983, pretended to seriously address the question of why juveniles are smaller than their parents [$-a]. It was... Read more »
N.C. Ellstrand. (1983) Why are juveniles smaller than their parents?. Evolution, 1091-4. DOI: http://www.jstor.org/pss/2408423
D.S. Falster, A.T. Moles, & M.Westoby. (2008) A General Model for the Scaling of Offspring Size and Adult Size. The American Naturalist, 172(3), 299-317. DOI: 10.1086/589889
C.C. Smith, & S.D. Fretwell. (1974) The optimal balance between size and number of offspring. The American Naturalist, 499-506. DOI: http://www.jstor.org/stable/2459681
- October 30, 2008
- 03:57 PM
- 1,325 views
Why do butterflies have four wings?
by Jeremy Yoder in Denim and Tweed
In this week's PNAS is a tidy result that demonstrates what you ca get away with when you study invertebrates: butterflies and moths can still fly if their hindwings are amputated, but they can't take evasive action [$-a]. That summary tells you just about all you need to about the reported experimental result; but the rest of the article has some interesting speculation.
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B. Jantzen, & T. Eisner. (2008) Hindwings are unnecessary for flight but essential for execution of normal evasive flight in Lepidoptera. PNAS, 105(43), 16636-40. DOI: 10.1073/pnas.0807223105
- January 2, 2009
- 10:19 AM
- 1,262 views
Evolution applied: Biological warfare against mosquito-borne disease
by Jeremy Yoder in Denim and Tweed
This week's issue of Science starts the new year with an exciting application of evolutionary dynamics: a sort of biological warfare agent to control disease-bearing mosquitoes.
Even in the twenty-first century, mosquito-borne diseases like malaria and Dengue fever remain major public health challenges, particularly in the developing world. When vaccines are not available, the only way to... Read more »
C.J. McMeniman, R.V. Lane, B.N. Cass, A.W.C. Fong, M. Sidhu, Y.-F. Wang, & S.L. O'Neill. (2009) Stable introduction of a life-shortening Wolbachia infection into the mosquito Aedes aegypti. Science, 323(5910), 141-4. DOI: 10.1126/science.1165326
A.F. Read, & M.B. Thomas. (2009) MICROBIOLOGY: Mosquitoes cut short. Science, 323(5910), 51-2. DOI: 10.1126/science.1168659
- August 22, 2008
- 02:28 PM
- 1,251 views
How the chili got its hots
by Jeremy Yoder in Denim and Tweed
In this week's PNAS: capsaicin, the stuff that makes chili peppers hot, may have originally evolved as an anti-fungal agent [$-a].
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Photo by bleu celt.Tewksbury et al. examine variation in "pungency" (that is, concentration of... Read more »
J. J. Tewksbury, D. J. Levey, M. Huizinga, D. C. Haak, & A. Traveset. (2008) Costs and benefits of capsaicin-mediated control of gut retention in dispersers of wild chilies. Ecology, 89(1), 107-17. DOI: 10.1890/07-0445.1
J. J. Tewksbury, & G. P. Nabhan. (2001) Seed dispersal: Directed deterrence by capsaicin in chilies. Nature, 412(6845), 403-4. DOI: 10.1038/35086653
J. J. Tewksbury, K. M. Reagan, N. J. Machnicki, T. A. Carlo, D. C. Haak, A. L. C. Penaloza, & D. J. Levey. (2008) Evolutionary ecology of pungency in wild chilies. PNAS, 105(33), 11808-11. DOI: 10.1073/pnas.0802691105
- August 14, 2008
- 03:11 PM
- 1,214 views
Michael Phelps is fast, but what's his z-score?
by Jeremy Yoder in Denim and Tweed
Even without following the Olympics in any detail, it's hard not to hear about the success of U.S. swimmer Michael Phelps: a new record for career gold medals won by an athlete in any sport, and new time records for just about every race he swims.
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Chatterjee, S, & Yilmaz, MR. (1999) The NBA as an Evolving Multivariate System. The American Statistician, 257-262. http://www.jstor.org/stable/2686106
- October 17, 2008
- 01:05 PM
- 1,208 views
Sympatric skepticism
by Jeremy Yoder in Denim and Tweed
The new issue of The Journal of Evolutionary Biology has a great article on a question that dates back to Darwin: sympatric speciation[$-a].
Sympatric speciation is simply speciation that occurs when a species splits into two reproductively isolated groups without any physical barrier arising between those groups. It's often treated as the opposite of allopatric speciation, in which a species is... Read more »
B.M. Fitzpatrick, J.A. Fordyce, & S. Gavrilets. (2008) What, if anything, is sympatric speciation?. Journal of Evolutionary Biology, 1452-9. DOI: 10.1111/j.1420-9101.2008.01611.x
- October 2, 2008
- 04:28 PM
- 1,192 views
Joshua tree genetics suggest coevolutionary divergence
by Jeremy Yoder in Denim and Tweed
The latest results from the Pellmyr Lab's ongoing study of Joshua tree and its pollinators are online as part of the new October issue of Evolution. It's the cover article, no less. The study, whose lead author is Chris Smith (now on the faculty at Willamette University) compares patterns in the population genetics of Joshua trees and the moths that pollinate them, and shows that although the... Read more »
W. Godsoe, J.B. Yoder, C.I. Smith, & O. Pellmyr. (2008) Coevolution and Divergence in the Joshua Tree/Yucca Moth Mutualism. The American Naturalist, 171(6), 816-23. DOI: 10.1086/587757
C.I. Smith, W.K.W. Godsoe, S. Tank, J.B. Yoder, & O. Pellmyr. (2008) Distinguishing coevolution from covicariance in an obligate pollination mutualism: asynchronous divergence in Joshua tree and its pollinators. Evolution, 62(10), 2676-87. DOI: 10.1111/j.1558-5646.2008.00500.x
- July 27, 2010
- 09:05 AM
- 1,171 views
Before they were yucca moths
by Jeremy Yoder in Denim and Tweed
Yuccas and yucca moths have one of the most peculiar pollination relationships known to science. The moths are the only pollinators of yuccas, carrying pollen from flower to flower in specialized mouthparts and actively tamping it into the tip of the pistil. Before she pollinates, though, each moth lays eggs in the flower—the developing yucca seeds will be the only thing her offspring eat. How does such a specialized, co-adapted interaction evolve in the first place? My coauthors and I attempted to answer this question in a paper just published in the Biological Journal of the Linnean Society, by reconstructing the ecology of yucca moths before they were yucca moths [PDF].
Using the present to reconstruct the past
Before I describe our study's results, let me explain a little about how biologists can reconstruct the characteristics of extinct species using what we know about living ones. First, we use DNA data to reconstruct evolutionary relationships between our favorite living species—this gives us an evolutionary tree, or phylogeny, like the ones in the illustration below. A phylogeny diagrams the branching evolutionary history that led to the living species at the tips of the tree. If we map the different states of some character that all those species have—say, the color of their feathers, onto the tips, we can infer what the ancestors at each of the inner branch points might have been like.
For instance, consider the possible scenarios for species A, B, C, and D in the illustration below. In the first case, if A and B are both red, then their common ancestor was probably red, too. However, C is blue—what does that mean for the common ancestor of C, A, and B? Because D is blue, we infer that the common ancestor of C, A, and B was also blue, as was the common ancestor of all four species. This is the most parsimonious reconstruction—it minimizes the number of times that color changes in the evolutionary history of the four species.
.flickr-photo { }.flickr-framewide { float: right; text-align: left; margin-left: 15px; margin-bottom: 15px; width:100%;}.flickr-caption { font-size: 0.8em; margin-top: 0px; } Knowing evolutionary relationships between living species helps us estimate the characteristics of their ancestors. Image by jby.In the second scenario, species D is red, so the same logic infers that the common ancestor of A, B, and C was red. In the third scenario, adding another red species (E) to the tree might also alter the most likely character states for the ancestral species on the tree—but this depends on where the DNA suggests that the new species fits on the tree. Most modern reconstructions of ancestral character states are more statistically complex than what I've just described, but the underlying logic is the same.
What did the ancestors of yucca moths do for a living?
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A small sample of Prodoxid diversity: Greya politella (above) and Tegeticula synthetica (below). Photos by jby.So in order to reconstruct what yucca moths were like before they became yucca moths, we need to know the evolutionary relationships between yucca moths and their close relatives, the other members of the moth family Prodoxidae. This is a diverse group, including The yucca-pollinating genera Tegeticula and Parategeticula;
The genus Prodoxus, moths that lay eggs on various parts of yuccas (and other related plants) without pollinating them;
The genus Mesepiola, which lay eggs on the flowers of plants similar to yuccas—woody desert monocots;
The genus Greya, which lay eggs in the flowers of a number of different plants, and pollinates some in the process [PDF]; and
The genus Lampronia, which lay eggs in another wide assortment of plants.
This diversity offers some intriguing possibilities—depending on how these genera are related to each other, the moths that would colonize yuccas and evolve obligate pollination mutualism might have lived on anything from roses to saxifrages, and their larvae might have eaten leaf tissue, woody twigs, fruit, or flowers. However, the last study to reconstruct the evolutionary relationships among these groups included only one species of Lampronia, leaving a number of current host plant associations and larval feeding habits unrepresented.
So we collected new DNA sequences from another dozen species in the genus Lampronia, reconstructed their relationships to the rest of the Prodoxidae, and used the resulting phylogeny to estimate the host plant association and larval feeding habit of the ancestral species that gave rise to the yucca moths. The results are presented in the large, color-coded figure below. Interpretation of this figure is similar to the example I gave above, except that the reconstruction method we used allows us to estimate the relative probability of each character state at the ancestral nodes, which we present in color-coded pie charts.
This gives us a better picture of the evolutionary changes in the lineage that would become yucca moths. The ancestral moths probably fed inside floral ovaries all the way back to the origin of the Prodoxidae. Before colonizing woody monocots (the Agavaceae, the family including yuccas, and possibly the Ruscaceae, the family fed on by Mesepiola), they most likely fed on plants in the rose family.
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A simplified phylogeny of the Prodoxidae, with reconstructions of ancestral host plant associations (by family) and larval feeding habits. Image from Yoder et al., Figure 2.This reconstruction gives us the best picture we've had to date of the conditions under which yucca moths evolved obligate mutualism—before they were active pollinators, the moths were already feeding inside developing flowers. This suggests that active pollination evolved to help ensure a larval food supply. We might imagine, then, that plants used by these pollinating seed parasites would evolve greater dependence on their highly efficient pollen delivery, moving toward the yucca-yucca moth mutualism we see today.
References
Brown, J., Leebens-Mack, J., Thompson, J., Pellmyr, O., & Harrison, R. (1997). Phylogeography and host association in a poll... Read more »
Brown, J., Leebens-Mack, J., Thompson, J., Pellmyr, O., & Harrison, R. (1997) Phylogeography and host association in a pollinating seed parasite Greya politella (Lepidoptera: Prodoxidae). Molecular Ecology, 6(3), 215-24. DOI: 10.1046/j.1365-294X.1997.t01-1-00171.x
Pellmyr, O. (1999) Forty million years of mutualism: Evidence for Eocene origin of the yucca-yucca moth association. Proc. Nat. Acad. Sci. USA, 96(16), 9178-83. DOI: 10.1073/pnas.96.16.9178
Yoder, J.B., Smith, C.I., & Pellmyr, O. (2010) How to become a yucca moth: minimal trait evolution needed to establish the obligate pollination mutualism. Biol. J. Linnean Soc., 100(4), 847-55. DOI: 10.1111/j.1095-8312.2010.01478.x
- July 29, 2008
- 11:41 PM
- 1,135 views
Against specialist herbivores, plants give up
by Jeremy Yoder in Denim and Tweed
Plants put up with a lot - everyone wants to eat them! And, basically, there are two ways a plant might respond to being eaten. They can put energy into regrowing bits that get eaten, or they can put energy into making a lot of some nasty chemical, like the milky sap in milkweed. The trouble with the first option is obvious - it doesn't do anything to stop the damage. But the trouble with the... Read more »
A. A. Agrawal, & M. Fishbein. (2008) Phylogenetic escalation and decline of plant defense strategies. PNAS, 105(29), 10057-10060. http://www.pnas.org/cgi/doi/10.1073/pnas.0802368105
P.R. Ehrlich, & P.H. Raven. (1964) Butterflies and plants: A study in coevolution. Evolution, 18(4), 586-608. http://www.jstor.org/pss/2406212
- March 15, 2009
- 02:55 PM
- 1,128 views
The environmental impacts of war
by Jeremy Yoder in Denim and Tweed
Last year Bioscience published a review article proposing a new discipline in conservation ecology: warfare ecology [PDF]. It's now making the rounds in the science blogosphere, with good coverage at Conservation Blog and Deep Sea News, where I first happened upon it - and it deserves all the attention it can get.
In the U.S., at any rate, war and preparation for war tend to get priority over everything - especially tree-hugging environmental concerns. Exhibit A is last year's Supreme Court decision that the Navy's need to practice with sonar trumps the damage sonar can do to whale populations, to the extent that the Navy could not be required to do an environmental impact assessment before beginning the exercise. War is treated as an emergency, and who worries about environmental impacts during emergencies?
Yet environmental damage caused in the course of war has direct impact on the human aftermath of conflict. Refugees provided with nowhere else to go will often set up camp in protected lands. Materials used in warfare - Agent Orange defoliant used in Southeast Asia, depleted uranium in Iraq - can continue to kill people long after the fighting ends. On the other hand, the review's authors, Machlis and Hanson, point out that demilitarized zones and military training grounds often serve as (perhaps overly-well protected) accidental preserves.
This is a subject I've thought about quite a bit before - way back in my undergraduate days, I won a Mennonite Central Committee oratorical contest with a speech that connected peace theology to environmental concerns. That speech now looks to me like slightly embarrassing juvenalia, but the central idea still holds, and it's great to see that working ecologists are thinking along similar lines. By laying out a framework for thinking about the environmental impacts of war, Machlis and Hanson's paper can hopefully help push governments to consider the longer-term environmental, economic, and social consequences of ecological decisions made in the course of preparing for and prosecuting war.
Reference
G. Machlis, & T. Hanson (2008). Warfare ecology BioScience, 58 (8), 729-36 DOI: 10.1641/B580809... Read more »
G. Machlis, & T. Hanson. (2008) Warfare ecology. BioScience, 58(8), 729-36. DOI: 10.1641/B580809
- September 14, 2008
- 06:12 PM
- 1,125 views
DNA barcoding: a glitch in the system?
by Jeremy Yoder in Denim and Tweed
Following up on last week's post about uncovering hidden species using DNA diversity (or "DNA barcoding"), an open-access paper in this week's issue of PNAS demonstrates a potentially significant glitch in the system: mitochondrial pseudogenes.
The original DNA barcoding concept is straightforward, if not uncontroversial - use a standard DNA sequence marker to identify ("barcode") species that... Read more »
P.D.N. Hebert, A. Cywinska, S.L. Ball, & J.R. deWaard. (2003) Biological identifications through DNA barcodes. Proc. Royal Society B, 270(1512), 313-21. DOI: 10.1098/rspb.2002.2218
H. Song, J.E. Buhay, M.F. Whiting, & K.A. Crandall. (2008) Many species in one: DNA barcoding overestimates the number of species when nuclear mitochondrial pseudogenes are coamplified. PNAS, 105(36), 13486-91. DOI: 10.1073/pnas.0803076105
- September 11, 2009
- 10:34 PM
- 1,109 views
Bat-eating tits!
by Jeremy Yoder in Denim and Tweed
Like pretty much anyone else writing about this, I'm in it for the headline. Well, maybe 30% for the headline -- this is also just freaky natural history. A paper in Biology Letters reports that great tits (Parus major -- basically big chickadees) will hunt and eat hibernating bats [$-a] if they can't find other food sources.
The paper reports on ten years of recorded bat-eating by a population of great tits in Hungary, capped by two years of systematic observations and a couple simple experiments. Are the tits hunting bats because other food is scarce? The authors put out birdseed and bacon near the bat cave, and observed that the birds killed many fewer bats. Do the tits use audio cues to find their prey? The authors played a tape recording of bats calling, and watched as the birds oriented to the sound and approached the speaker. There are also a number of grisly photos of tit-killed bats.
This is really the kind of work that attracts most field biologists to science in the first place -- a wild, interesting observation that provides an excuse to do some really unusual (and thorough) birdwatching. More complicated science will follow, I hope, like an estimate of the selective advantage this new food source provides to the birds. But it all starts with an incredible story.
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You might want to count your fingers after hand-feeding a great tit. Photo by joyrex.
Reference
Estok, P., Zsebok, S., & Siemers, B. (2009). Great tits search for, capture, kill and eat hibernating bats Biology Letters DOI: 10.1098/rsbl.2009.0611
... Read more »
Estok, P., Zsebok, S., & Siemers, B. (2009) Great tits search for, capture, kill and eat hibernating bats. Biology Letters. DOI: 10.1098/rsbl.2009.0611
- September 17, 2009
- 12:05 PM
- 1,082 views
With or without you? Species interactions and responses to climate change
by Jeremy Yoder in Denim and Tweed
Reading a pair of papers recently published in PLoS ONE, you might be forgiven for thinking that ecologists don't know whether or not interactions between species matter. Both examine the effects of climate change on ecological communities -- but where one assumes that species in a community are as interchangeable as bricks in a wall, the other concludes that the presence of competitors is pretty important.
First, Stralberg et al. attempt to predict what will happen to the birds of California under projected climate change. They constructed individual models of each bird species' environmental requirements, and then figured out where those requirements would be met under a range of possible climate change scenarios. They find, not surprisingly, that this produces a lot of never-before-seen bird communities:Our analysis suggests that, by 2070, individualistic shifts in species' distributions may lead to dramatic changes in the composition of California's avian communities, such that as much as 57% of the state ... may be occupied by novel species assemblages.But do species really move across the landscape as independent agents? It's hard to believe that the do. Every species interacts with others -- competitors, predators, prey, parasites -- and presumably these interactions have some impact on where that species can survive.
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How far can this common crossbill move its range if its favorite food tree doesn't come along? Photo by omarrun.That's certainly what the other paper suggests. Adler et al. tested the effects of altered water availability (as a proxy for climate change: normal, supplemental, or drought conditions) and competition (normal or with competitors removed) on experimental plantings of three different prairie grass species. They found significant effects of both competition and rainfall on the plantings' growth -- although there wasn't a meaningful interaction between the two factors. (That is, competition conditions didn't alter the effect of water availability.)
There are actually a lot of studies suggesting that species interactions will be important in determining how communities cope with changing climates:The prototypic example of this is the case of Great tits and the caterpillars they prefer to feed their chicks -- warming climate means that the period when the caterpillars are most abundant is earlier and earlier each year, disrupting the tits' breeding season [$-a].
A recently-published experiment transplanted butterflies from populations near the middle of their home range to sites at the northern edge to simulated climate-change driven shifts, and found that the availability of preferred host plants shaped how well the butterflies performed [$-a].
A study of arctic plant communities' response to climate change found that herbivory by large mammals could slow or prevent changes driven by warming temperatures [$-a]. (I've posted about this study in detail before.)
All of which is to say, we may not know how the species interactions within a particular community will shape its response to climate change, but there's good reason to think that they will.
References
Adler, P., Leiker, J., & Levine, J. (2009). Direct and indirect effects of climate change on a prairie plant community PLoS ONE, 4 (9) DOI: 10.1371/journal.pone.0006887
Pelini, S., Dzurisin, J., Prior, K., Williams, C., Marsico, T., Sinclair, B., & Hellmann, J. (2009). Translocation experiments with butterflies reveal limits to enhancement of poleward populations under climate change Proc. Nat. Acad. Sci. USA, 106 (27), 11160-5 DOI: 10.1073/pnas.0900284106
Post, E., & Pedersen, C. (2008). Opposing plant community responses to warming with and without herbivores Proc. Nat. Acad. Sci. USA, 105 (34), 12353-8 DOI: 10.1073/pnas.0802421105
Stralberg, D., Jongsomjit, D., Howell, C., Snyder, M., Alexander, J., Wiens, J., & Root, T. (2009). Re-shuffling of species with climate disruption: A no-analog future for California birds? PLoS ONE, 4 (9) DOI: 10.1371/journal.pone.0006825
Visser, M., Holleman, L., & Gienapp, P. (2005). Shifts in caterpillar biomass phenology due to climate change and its impact on the breeding biology of an insectivorous bird Oecologia, 147 (1), 164-72 DOI: 10.1007/s00442-005-0299-6
... Read more »
Adler, P., Leiker, J., & Levine, J. (2009) Direct and indirect effects of climate change on a prairie plant community. PLoS ONE, 4(9). DOI: 10.1371/journal.pone.0006887
Pelini, S., Dzurisin, J., Prior, K., Williams, C., Marsico, T., Sinclair, B., & Hellmann, J. (2009) Translocation experiments with butterflies reveal limits to enhancement of poleward populations under climate change. Proc. Nat. Acad. Sci. USA, 106(27), 11160-5. DOI: 10.1073/pnas.0900284106
Post, E., & Pedersen, C. (2008) Opposing plant community responses to warming with and without herbivores. Proc. Nat. Acad. Sci. USA, 105(34), 12353-8. DOI: 10.1073/pnas.0802421105
Stralberg, D., Jongsomjit, D., Howell, C., Snyder, M., Alexander, J., Wiens, J., & Root, T. (2009) Re-shuffling of species with climate disruption: A no-analog future for California birds?. PLoS ONE, 4(9). DOI: 10.1371/journal.pone.0006825
Visser, M., Holleman, L., & Gienapp, P. (2005) Shifts in caterpillar biomass phenology due to climate change and its impact on the breeding biology of an insectivorous bird. Oecologia, 147(1), 164-172. DOI: 10.1007/s00442-005-0299-6
- March 31, 2009
- 04:33 PM
- 1,076 views
That "mystery of mysteries": What makes a species?
by Jeremy Yoder in Denim and Tweed
In a special issue of Philosophical Transactions of the Royal Society on speciation, James Mallet argues that the Biological Species Concept is at odds with Charles Darwin's original ideas about what a species is - and that current research supports Darwin [$-a].
When The Origin of Species was first published, biologists mostly thought species were easy to recognize - they looked different from each other, and they couldn't successfully interbreed with each other. This view was a problem for Darwin's ideas about gradual evolution by natural selection, since gradual divergence shouldn't give rise to nice, discrete species. In fact, as Darwin argued, different groups of organisms exhibit a whole spectrum of reproductive isolation, from complete interfertility to total isolation - and the degree of isolation is not easy to predict based on how similar organisms look. In Darwin's description, species are just labels that humans put on clusters of similar-looking organisms.
By the mid-Twentieth Century, evolutionary biologists favored what is commonly called the Biological Species Concept (BSC), defining species as non-interbreeding populations of living things. Research on speciation has accordingly focused on the ways that evolution creates reproductive isolation between populations. Mallet argues that this amounts to an abandonment of Darwin's insights, and that by focusing on isolating mechanisms, biologists have returned to viewing species as distinct, "real" entities, missing much of the evolutionary process as a result.
I'm not sure I believe the distinction that Mallet makes between Darwin's description of species and the BSC; they seem to me more different in their emphasis than in their fundamentals. Darwin was interested in demonstrating that species arise gradually, as accidents of adaptation to different environments - and, as Mallet says, he was trying to overcome the then-predominant view that species were real, discrete entities instead of the names that humans assign to clusters of similar organisms. Research motivated by the BSC generally takes this view as well, but it's interested in the processes that create such clusters, and can prevent them from merging into nearby clusters by interbreeding.
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Two types of Joshua tree
Photo by jby.Research on the evolution of isolating mechanisms necessarily focuses on cases where isolation is incomplete, somewhere between complete speciation and free interbreeding. A prime example is my lab's research on the two pollinator-associated types of Joshua tree, Yucca brevifolia. It's not clear that the two types are reproductively isolated - preliminary genetic data suggests they're not [PDF] - even though they're pollinated by different moth species, and classified as separate subspecies, the taller Y. brevifolia brevifolia and the short, bushy Y. brevifolia jaegeriana. They may be on the way to becoming different species, but they're not there yet. Two other examples out of the endless forms available: marine snails that choose mates by their slime trails, and wildflowers that would interbreed if only they could survive each other's habitat.
As Mallet concludes in the more empirical part of his review, this is what we see across the diversity of life: a continuum of reproductive isolation between populations, not a granular world of neatly divided, obviously different species. Rather than over-simplifying this reality, the Biological Species Concept gives us a framework through which to understand it.
References
Darwin, C. 1859. On the Origin of Species by Means of Natural Selection. First ed. London: John Murray. Full text on Google Books.
Mallet, J. (2008). Hybridization, ecological races and the nature of species: empirical evidence for the ease of speciation Phil. Trans. R. Soc. B, 363 (1506), 2971-86 DOI: 10.1098/rstb.2008.0081
Smith, C., W. Godsoe, S. Tank, J. Yoder, & O. Pellmyr (2008). Distinguishing coevolution from covicariance in an obligate pollination mutualism: asynchronous divergence in Joshua tree and its pollinators. Evolution, 62 (10), 2676-87 DOI: 10.1111/j.1558-5646.2008.00500.x... Read more »
Mallet, J. (2008) Hybridization, ecological races and the nature of species: empirical evidence for the ease of speciation. Phil. Trans. R. Soc. B, 363(1506), 2971-86. DOI: 10.1098/rstb.2008.0081
Smith, C., W. Godsoe, S. Tank, J. Yoder, & O. Pellmyr. (2008) Distinguishing coevolution from covicariance in an obligate pollination mutualism: asynchronous divergence in Joshua tree and its pollinators. Evolution, 62(10), 2676-87. DOI: 10.1111/j.1558-5646.2008.00500.x
- August 21, 2009
- 12:10 PM
- 1,050 views
That possum you just ran over? It might have saved you from Lyme disease
by Jeremy Yoder in Denim and Tweed
Growing up in suburban Pennsylvania, where the most hazardous wildlife not extirpated from our woods is the occasional crazed whitetail deer, there was really only one danger I associated with the outdoors -- ticks. Specifically, ticks carrying Lyme disease, a not-very-pleasant bacterial infection that attacks the joints, heart, and nervous system if left untreated. According to a paper released online early in Proceedings of the Royal Society B, my risk of picking up Lyme disease on an excursion into the woods behind my parents' house may have depended on the diversity of bird and mammal species in those woods [$-a].
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Sure, it looks like a giant rat, but that opossum is a walking death trap for disease-carrying ticks. Photos by ricmcarthur and jkirkhart35.In a way, the ticks that carry Lyme disease are a threat to humans precisely because they don't rely on us as a regular source for blood. Instead, they feed on a variety of mammals and birds, which allows them to maintain population densities high enough that a human wondering into a woodlot stands a good chance of picking up one or two of the little buggers.
But it turns out that not all of these non-human hosts are equally hospitable for ticks. The new paper's authors, Keesey et al., caught a range of tick hosts -- white-footed mice, eastern chipmunks, gray squirrels, opossums, veeries, and catbirds -- and experimentally infested them with ticks. They found a huge range of tick success across the six host species: almost half of all ticks introduced onto mice were able to feed, while only 3.5% of ticks introduced onto opossums were. Most ticks that failed to feed disappeared -- they were probably eaten when the host groomed itself.
The authors' field surveys of ticks carried by these animals in the wild make the difference even more pronounced. Wild-caught opossums carried an average of almost 200 ticks -- if that's 3.5% of the ticks that try to feed on a opossum, then that means each opossum had attracted, and eaten, up to 5,500 ticks!
But the real impact of this result comes into focus in a mathematical model the authors develop to determine the effects of removing each of the six hosts from a woodland ecosystem. Removing intermediately-useful hosts like veeries or catbirds doesn't have much effect on tick density. On the other hand, if you remove very tick-friendly hosts like the white-footed mice, tick populations plummet. And if you remove opossums, they increase dramatically. This is important because, the authors say, larger mammal species are the first to leave as patches of woodland are reduced to make way for human development -- so an early effect of woodland fragmentation may be to reduce or eliminate opossums in that woodland, and boost the density of disease-bearing ticks.
This result goes a long way to fulfilling a proposal the authors made in a 2006 review article, that the diversity of alternative hosts for disease vectors like mosquitoes and ticks may shape the risk they pose to human populations [$-a]. It shows that, even in the relatively tame landscapes of suburbia, the way we humans manage what wildlife remains may have real consequences for our own well-being.
References
Keesing, F., Holt, R., & Ostfeld, R. (2006). Effects of species diversity on disease risk Ecology Letters, 9 (4), 485-98 DOI: 10.1111/j.1461-0248.2006.00885.x
Keesing, F., Brunner, J., Duerr, S., Killilea, M., LoGiudice, K., Schmidt, K., Vuong, H., & Ostfeld, R. (2009). Hosts as ecological traps for the vector of Lyme disease Proc. R. Soc. B, (online early) DOI: 10.1098/rspb.2009.1159
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Keesing, F., Holt, R., & Ostfeld, R. (2006) Effects of species diversity on disease risk. Ecology Letters, 9(4), 485-98. DOI: 10.1111/j.1461-0248.2006.00885.x
Keesing, F., Brunner, J., Duerr, S., Killilea, M., LoGiudice, K., Schmidt, K., Vuong, H., & Ostfeld, R. (2009) Hosts as ecological traps for the vector of Lyme disease. Proc. R. Soc. B. DOI: 10.1098/rspb.2009.1159
- January 18, 2009
- 11:44 PM
- 1,045 views
Stick insects not so excited about sex, apparently
by Jeremy Yoder in Denim and Tweed
Stick insects in the genus Timema have evolved asexual reproduction on five different occasions in their evolutionary history, according to a new study in this month's Evolution [$-a]. Why? Well, it turns out that from an evolutionary perspective, sex isn't always a good thing.
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M. Dybdahl, & A. Storfer. (2003) Parasite local adaptation: Red Queen versus Suicide King. Trends in Ecology , 18(10), 523-30. DOI: 10.1016/S0169-5347(03)00223-4
P.D. Keightley, & S.P. Otto. (2006) Interference among deleterious mutations favours sex and recombination in finite populations. Nature, 443(7107), 89-92. DOI: 10.1038/nature05049
T. Schwander, & B.J. Crespi. (2009) Multiple direct transitions from sexual reproduction to apomictic parthenogenesis in Timema stick insects. Evolution, 63(1), 84-103. DOI: 10.1111/j.1558-5646.2008.00524.x
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