18 posts · 12,557 views

Sci/tech/creative writer from DC area living in Atlanta. Blogs about ecology, environment, biogeography and paleoecology.

Voltage Gate
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August 25, 2010
12:00 PM
471 views

The history of the Joshua tree, threats new and old

by Jeremy in Voltage Gate

And the LORD said unto Joshua, Stretch out the spear that is in thy hand toward Ai; for I will give it into thine hand. And Joshua stretched out the spear that he had in his hand toward the city. And the ambush arose quickly out of their place, and they ran as soon as [...]... Read more »

Cole, K., Ironside, K., Eischeid, J., Garfin, G., Duffy, P., & Toney, C. (2010) Past and ongoing shifts in Joshua tree support future modeled range contraction. Ecological Applications, 2147483647. DOI: 10.1890/09-1800.1

August 3, 2010
11:55 AM
301 views

Communicating environmental realities: framing and fiction

by Jeremy in Voltage Gate

I finally found the time yesterday evening to read through a few of the papers from the latest Frontiers in Ecology and the Environment, which is focused on science/environmental communication this time around. The majority of the articles are driven by Nisbet’s ideas about framing in general, but I don’t really want to dive back [...]... Read more »

Groffman, P., Stylinski, C., Nisbet, M., Duarte, C., Jordan, R., Burgin, A., Previtali, M., & Coloso, J. (2010) Restarting the conversation: challenges at the interface between ecology and society. Frontiers in Ecology and the Environment, 8(6), 284-291. DOI: 10.1890/090160

Nisbet, M., Hixon, M., Moore, K., & Nelson, M. (2010) Four cultures: new synergies for engaging society on climate change. Frontiers in Ecology and the Environment, 8(6), 329-331. DOI: 10.1890/1540-9295-8.6.329

McKnight, D. (2010) Overcoming “ecophobia”: fostering environmental empathy through narrative in children's science literature. Frontiers in Ecology and the Environment, 8(6). DOI: 10.1890/100041

June 15, 2010
04:29 PM
956 views

A hobbit's contemporaries: Biogeography and insular evolution on Flores

by Jeremy in Voltage Gate

Painters create networks. The subject of the piece, even if it’s a simple splotch of color, garners the most attention, but without a descriptive background or other kinds of supporting elements to contextualize the portion of the painting where the artist wants you to look, the intended focus is...

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Meijer, H., Van Den Hoek Ostende, L., Van Den Bergh, G., & De Vos, J. (2010) The fellowship of the hobbit: the fauna surrounding Homo floresiensis. Journal of Biogeography, 37(6), 995-1006. DOI: 10.1111/j.1365-2699.2010.02308.x

June 9, 2010
05:03 PM
1,028 views

Southeast Asia in the Pleistocene, from grassland to rain forest

by Jeremy in Voltage Gate

I’ve been trying to keep up with the Gulf situation, so most of my reading of late has been dominated by those details, and the unread numbers in my RSS folders were a little intimidating, but I finally found some time to read some of the papers I’ve earmarked in the past month or so.

This study...

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Louys, J., & Meijaard, E. (2010) Palaeoecology of Southeast Asian megafauna-bearing sites from the Pleistocene and a review of environmental changes in the region. Journal of Biogeography. DOI: 10.1111/j.1365-2699.2010.02297.x

Marwick, B. (2009) Biogeography of Middle Pleistocene hominins in mainland Southeast Asia: A review of current evidence. Quaternary International, 202(1-2), 51-58. DOI: 10.1016/j.quaint.2008.01.012

April 30, 2010
03:30 PM
591 views

Defining edge effects by resource and sensitivity

by Jeremy in Voltage Gate

Considering the number of studies published describing habitat fragmentation and edge effects, why has the pattern and framework of these effects on ecosystems not been described? Ries and Sisk proposed a conceptual model in that paper that can account and predict, to some extent, the variability of an organism’s responses to different edges, usually indicated through an increase or decrease abundance at the edge, or no change at all.... Read more »

Ries, L., & Sisk, T. (2010) What is an edge species? The implications of sensitivity to habitat edges. Oikos. DOI: 10.1111/j.1600-0706.2010.18414.x

Ries, L., & Sisk, T. (2004) A PREDICTIVE MODEL OF EDGE EFFECTS. Ecology, 85(11), 2917-2926. DOI: 10.1890/03-8021

April 12, 2010
01:45 PM
1,118 views

History of land use determines threat and rarity in mangrove tree species

by Jeremy in Voltage Gate

A new study from PLoS ONE was published last week assessing the threat to mangrove tree species around the world based on IUCN Red List data. At first glance the paper might seem to be just another bleak walk through the anthropogenic dismantling of a fragile biome, but there are some excellent issues presented regarding our relationship between the land and its inhabitants and the interconnectedness of rarity and threat level.... Read more »

Polidoro, B., Carpenter, K., Collins, L., Duke, N., Ellison, A., Ellison, J., Farnsworth, E., Fernando, E., Kathiresan, K., Koedam, N.... (2010) The Loss of Species: Mangrove Extinction Risk and Geographic Areas of Global Concern. PLoS ONE, 5(4). DOI: 10.1371/journal.pone.0010095

April 1, 2010
11:15 AM
854 views

Demonstrating synergy between functional groups: Burrowing mammals and megaherbivores

by Jeremy in Voltage Gate

Davidson et al. published another study a few weeks ago in Ecology further exploring the relationships between black-tailed prairie dogs and their much maligned neighbors, Bos taurus, cattle. Prairie dogs have been generally regarded as a danger to cattle by ranchers and removed through poisoning or other means. Overgrazing can lead to desertification, further threatening these animals. But that's a relatively new trend in a long and complex history of interaction between prairie dogs and megaherbivores like cattle.... Read more »

Davidson, A., Ponce, E., Lightfoot, D., Fredrickson, E., Brown, J., Cruzado, J., Brantley, S., Sierra, R., List, R., Toledo, D.... (2010) RAPID RESPONSE OF A GRASSLAND ECOSYSTEM TO AN EXPERIMENTAL MANIPULATION OF A KEYSTONE RODENT AND DOMESTIC LIVESTOCK. Ecology, 2147483647. DOI: 10.1890/09-1277

March 22, 2010
11:15 AM
1,053 views

Reconstructing full-glacial Europe

by Jeremy in Voltage Gate

When Charles Lyell first used the term Pleistocene in 1839 to replace the "long and awkward" use of Newer Pliocene (preceded by, of course, the Older Pliocene), it was done in the interest of streamlining the terminology, but the split of Newer and Older Pliocene was based on the fossil evidence of the time. Lyell designated the split of the Pliocene by recognizing a higher percentage of extant snails and other mollusks found in strata from this Newer Pliocene or, now, Pleistocene period. About 70 percent of the mollusks from this period were extant animals, compared with 50 - 70 percent from the Older Pliocene.Today, snails are still used as an important index for reconstructing paleoenvironments. Michal Horsák and researchers from the Czech Republic, Russia, Poland and Slovakia published a study a couple of weeks back in the Journal of Biogeography that attempts to determine the ecology of full-glacial Europe using index species like snails and trees to identify possible refugia - modern environmental/ecological analogs of the coldest periods in Europe tens of thousands of years ago based on fossil evidence and modern assemblages.Recently, evidence has pointed to the Russian Altai and Sayan Mountains as modern analogs. The climate matches, cool and relatively dry. Surface pollen spectra in these areas are very similar to samples from full-glacial central Europe. The ranges are also home to similar and in some cases, identical biota. Mammal assemblages are largely comparable. So-called sibling species of trees from full-glacial Europe have been found in the area, including the Siberian pine, Siberian larch and Round-leaved dwarf birch(related to or subspecies of the Swiss pine, European larch and arctic dwarf birch respectively).Photo by Ondřej ŽváčekThe most important biotic reference is the snails found in the Altai Mountains for several reasons, as the authors note:First, snail shells can be easily identified to species, whereas plant pollen is often identifiable only to genus or family. Second, each shell represents one individual, which enables an accurate estimation of population density. Third, unlike pollen or vertebrate remains, snail fossils are usually deposited in places where they lived, thus enabling a fine spatial resolution of the resulting palaeoenvironmental reconstruction. Fourth, snail fossils are well preserved in conditions that are usually poor in other fossils, especially in dry and calcium-rich sediments.Samples were taken at 118 sites in a 300 km transect in southern Siberia, 10 x 10 m2 plots and the sites were all characterized according to environmental conditions. The researchers used 13 designations, and instead of reinterpreting or just glossing them over, I'd rather just quote in detail since they were able succinctly describe each environment. These categories are not only important in interpreting the results, they give a good impression of what the environment is like in this portion of the Altai Mountains (n signifies the number of sampled sites).Taiga (n = 11): mesic to wet coniferous forest with a species-poor herb layer and a well developed moss layer, usually dominated by Abies sibirica, Larix sibirica, Picea obovata or Pinus sibirica.Hemiboreal forest (n = 22): dry to mesic coniferous or deciduous forest with a species-rich herb layer and a sparse moss layer, usually dominated by Betula pendula, Larix sibirica or Pinus sylvestris.Wooded fen (n = 2): wet woodland with accumulation of base-rich organic sediment, dominated by Picea obovata.Treeless fen (n = 4): open base-rich fen with sedges and mosses.Acidic mire (n = 7): bogs and mineral-poor fens.Alluvial scrub (n = 3): riverine woody vegetation with willows (Salix spp.).Tall-forb vegetation (n = 5): tall herbaceous vegetation in wet places, usually along mountain streams.Alpine grassland (n = 3): short herbaceous vegetation above the timberline.Shrubby tundra (n = 8): low-shrub vegetation above the timberline, dominated mainly by Betula rotundifolia (= B. nana s.l.), in places also by Dryas oxyodonta.Steppe (n = 36): both short-grass steppe and tall-grass (meadow) steppe, in places with low shrubs such as Caragana or Spiraea.Saline grassland (n = 4): grassland on soils with elevated salt concentration, usually in shallow depressions in steppe landscapes.Meadow (n = 8): mesic grassland used for regular or occasional hay-making.Scree (n = 5): treeless talus slopes.As you can see, steppe and Hemiboreal forest tend to dominate the landscape, dry, cold areas very similar to what is thought to have been the conditions of central Europe during Pleistocene glacial periods. The strange thing, generally speaking, is that snails are poikilothermic animals, meaning that their body temperature is susceptible to changes in ambient temperature, placing them under risk during sudden cold snaps. The authors suspect that these relict snails have not colonized warmer areas because of increased predatory pressures, which seems to line up with a particular ecological circumstance: homeothermic predators have higher metabolic requirements and might not be able to live in certain areas where these poikilotherms thrive.Most of the index species of snails in this study were found in wooded or shrubby areas, wet microclimates protected by tree canopy or shrub cover. These wooded areas tended to be dominated by Larix sibirica and Picea obovata, the sibling species of the European L. decidua and P. abies, evidence that the vast steppes of full-glacial Europe may not have been as devoid of trees as previously thought.So the reconstruction proceeds, trying to refine the conditions of ancient ecosystems and biomes under particular climatic or geologic pressures. It's a fascinating process, assembling such seemingly disparate evidences and mechanisms reaching across an interdisciplinary expanse to make relatively small but essential contributions like this one.... Read more »

Horsák, M., Chytrý, M., Pokryszko, B., Danihelka, J., Ermakov, N., Hájek, M., Hájková, P., Kintrová, K., Kočí, M., Kubešová, S.... (2010) Habitats of relict terrestrial snails in southern Siberia: lessons for the reconstruction of palaeoenvironments of full-glacial Europe. Journal of Biogeography. DOI: 10.1111/j.1365-2699.2010.02280.x

March 3, 2010
01:00 PM
286 views

How do taxonomic preferences shape conservation and science?

by Jeremy in Voltage Gate

...an analysis of the frequency and depth of research based on the mammal, reptile, amphibian and bird species in southern Africa. The study questions scientific priorities, highlighting the massive inequality of attention received by differing groups of organisms.... Read more »

TRIMBLE, M., & VAN AARDE, R. (2010) Species Inequality in Scientific Study. Conservation Biology. DOI: 10.1111/j.1523-1739.2010.01453.x

February 24, 2010
05:37 PM
372 views

Ancient caribou DNA suggests replacement triggered by climate change and/or volcano eruption

by Jeremy in Voltage Gate

I’ve become increasingly interested in the practice of paleoecology of late, trying to find and gather bits and pieces when I have time. This study from Molecular Ecology came to me, which, based on the probability that you can assign probabilities to cosmic events, I’m going to carefully and tentatively (and gentlemanly) attribute to Providence, or Wiley Interscience press releases.In the Yukon, there are several distinct caribou herds that inhabit and move within certain, definable regions. The authors wanted to use DNA sampled from living caribou in the different regions and compare it to that of ancient caribou, using well-preserved soft tissues and bones excavated from scattered ice patches, in order to determine the historic ranges of these animals and the level of gene flow between herds. Establishing these genetic/ecological reference points and comparing modern data to them can provide administrators with more accurate data which can be used to create more effective management plans.When Kuhn et al. compared the modern caribou DNA from the Southern Lakes region to that of caribou living in that area over 1,000 years ago, they found that the historic residents were more closely related to herds in the northwest than the existing population of caribou in the region. In other words, the caribou currently living in the Southern Lakes region did not descend from the animals that lived there over a millennium ago.So what happened to the ancient caribou? How were they displaced completely by these genetically dissimilar animals? There are two suspects that might have worked together in purging these animals from the area.The first is climate change (Clade 1 is the clade accounting for the Southern Lakes herds):The appearance of Clade 1 in the Southern Lakes region at ~1000 BP follows a 400 year period during which no remains were preserved within the sample ice patches (1440–1030 BP, Farnell et al. 2004).Coincidently, this was concurrent with the Medieval Warming Period, where temperatures increased globally. This would produce negative ecological circumstances for the caribou like frequent thaws and loss of snow patches that could have cut their numbers.But there was another, much more sudden event that could have affected these animals. Mt. Churchill in the Wrangell Mountains erupted twice between ~1200 and 1900 years ago; the second time created the so called “eastern lobe” of the White River Ash (noted as "2" in the illustration), covering an area of over 300,000 square kilometers with tephra, which has been shown in studies to be deadly to both livestock and caribou.When the dangers began to disappear and the cold temperatures returned, the area was re-colonized, but not by the herds in the surrounding regions. Most likely the modern Southern Lakes caribou are descended from herds farther to the south riding the sweep of the Little Ice Age that returned optimal temperatures to the area.KUHN, T., MCFARLANE, K., GROVES, P., MOOERS, A., & SHAPIRO, B. (2010). Modern and ancient DNA reveal recent partial replacement of caribou in the southwest Yukon Molecular Ecology DOI: 10.1111/j.1365-294X.2010.04565.x

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KUHN, T., MCFARLANE, K., GROVES, P., MOOERS, A., & SHAPIRO, B. (2010) Modern and ancient DNA reveal recent partial replacement of caribou in the southwest Yukon. Molecular Ecology. DOI: 10.1111/j.1365-294X.2010.04565.x

February 19, 2010
05:19 PM
930 views

Island biogeography: State and case of spider diversity in Macaronesia

by Jeremy in Voltage Gate

Some of the first organisms found on a newly risen or recently destroyed island are spiders. On mainlands, spiderlings of smaller species weave a tiny drag chute, perched atop the highest point in their immediate area – the leaf of an herb or the very tip of a blooming meadow grass – and let the breeze, even the slightest one, carry them away. Most only travel short distances, remaining in the ecosystem in which they were born, but some are spun upwards in varying winds, and swept into jet streams carrying millions of aerial plankton that sometimes happen upon bare, isolated earth of an island. Insects, birds and driftwood carry seeds and other organisms and their larvae which chances upon the island. The fertile soil provides a foundation for the burgeoning community of explorers and hitchhikers. The original inhabitants evolve and diversify, adapting to the alien and continually changing young environment. Immigration slows, mitigated by extinction, reaching an equilibrium point. Creative forces converge, proceed and decline on a tiny speck of land beaten by endless currents, forces described by island biogeography.E.O. Wilson and Robert MacArthur first outlined the theory of island biogeography, publishing the dynamic model of equilibrium in 1967, which basically says that immigration, speciation and extinction will determine the number of species present in relation to area (more area, less extinction) and isolation (greater isolation, less immigration). As the number of species present increases, immigration rates decrease and extinction rates increase. There is a “dynamic” theoretical equilibrium point where these rates meet. Wilson and MacArthur’s theory is as influential and essentially applicable as any in ecology. The model is not only used for actual islands, but also in other isolated systems.Ecologists and biogeographers have been trying to build on the theory for some time. A recent study published in the Journal of Biogeography tests a recent synthesis of island biogeography theory based on the equilibrium model, the general dynamic model of oceanic island biogeography (or GDM), along with other factors like area, elevation and distances between islands in the Canary and Azores archipelagos and the mainland in an attempt to find an adequate predictor of spider species diversity and endemism in those chains, diversity that was initiated by ballooning spiders from the mainland millions of years before.Macaronesia* the “islands of the fortunate” is a general term applied to five chains of volcanic islands off the western coasts of Europe and Africa: Azores, Canary Islands, Cape Verde, Madeira and the Savage Islands. The results of the study focused on the Canary Islands and the Azores.The Canary Islands exhibited the greatest richness with the highest numbers on Tenerife: 84 single-island endemics, 145 archipelago endemics and 230 indigenous spider species (Macaronesian total was 255, 370, 584 respectively). The numbers in the Azores were significantly lower (from 0% – 9% of the total); on Corvo, for example, the researchers found no single island endemics, only one archipelago endemic and five indigenous. There are different factors at work in these numbers and the researchers found that this wasn’t a one size fits all situation.From Whittaker et al. 2008 doi: 10.1111/j.1365-2699.2008.01892.xThe GDM seemed to apply to main islands according to the authors, producing the notable hump-shaped curve pictured above. The GDM was proposed by Whittaker et al. in 2008 and incorporates geologic succession and time into determining species diversity on islands. Like Wilson and MacArthur’s model, immigration (I) decreases and extinction (E) rates increase through over the course of island development (time performs the same function as species number here). But notice the extra parameters. As succession proceeds, speciation (S and therefore richness (R) increases as the environment diversifies (niche opportunity/allopatry) and decreases as the island ages and becomes smaller and more homogenous, eventually disappearing into the sea, marking the end of its lifespan. The decreasing curve of richness in the chart is not as steady as its increase; that represents the progression of niche adaptations along the rise of environmental diversification, followed by interactions among and between trophic levels on the decline.One genus in particular displayed this “deceleration” of speciation:Maximum likelihood-based analysis of patterns of diversification in the Dysdera species endemic to Lanzarote and Fuerteventura revealed that diversification in this lineage has decelerated through time, which is consistent with an increase in extinction rates due to ecosystem transformation driven by island ageing.The Dysdera species began this decline between 5 and 2 mya.The Azores have very different environmental circumstances than the Canary Islands. First of all , they’re more isolated, farther west off the coast. Wind and sea currents in the area seem to be a barrier to all but the most mobile species, circulating north and south in the area, which favors deposition in the islands closer to the mainland more or less along that axis. The researchers believe that highly mobile spiders colonized the Azores and spread across the archipelago, which would allow for a high level of gene flow and ultimately low species richness. This contradicts the idea that more isolated archipelagos will always have more endemic species.Habitat loss seems to be a more powerful predictor here. The Azores archipelago has retained only 2% of its natural forests after 400 years of deforestation. Anthropogenic changes have prematurely homogenized the environments, removing mass amounts of vegetation useful to spiders for web building and providing transportation for invasives. It’s been shown that habitat loss tends to more greatly affect organisms at higher trophic levels, and spiders in Macaronesia are historically the main terrestrial predator on those islands. This situation seems to fall in line with that observation. Since spiders exhibit this level of sensitivity, the authors suggest that these animals may be a good indicator species for future study.As a side note, the laurel forests (laurisilva) are exceedingly beautiful. The trees are relicts of the Pliocene era, representational of the forests that once covered a warmer, more humid Mediterranean. I have that scrawled in the notebook in the hopes that I have time to write a series about relict and perhaps even prehistoric ecosystems.*I didn’t know this before researching this article, but Macaronesia is the true spelling of the area, not Macronesia, which is how it’s spelled in the paper.Whittaker, R., Triantis, K., & Ladle, R. (2008). A general dynamic theory of oceanic island biogeography Journal of Biogeography, 35 (6), 977-994 DOI: 10.1111/j.1365-2699.2008.01892.x... Read more »

Whittaker, R., Triantis, K., & Ladle, R. (2008) A general dynamic theory of oceanic island biogeography. Journal of Biogeography, 35(6), 977-994. DOI: 10.1111/j.1365-2699.2008.01892.x

Cardoso, P., Arnedo, M., Triantis, K., & Borges, P. (2010) Drivers of diversity in Macaronesian spiders and the role of species extinctions. Journal of Biogeography. DOI: 10.1111/j.1365-2699.2009.02264.x

February 12, 2010
01:49 PM
621 views

For Darwin Day: The Biogeography of Darwin's Gourd

by Jeremy in Voltage Gate

In September of 1835, Charles Darwin was visiting an island of Floreana, one of the smaller islands in the Galapagos archipelago where he came across crawling beds of Sicyos villosus, a fairly typical member of the squashes and cucumbers (Cucurbitaceae). Darwin noted that the cucurbit was "injurious" to the surrounding vegetation, referring to its prolific takeover of the landscape nearby.Darwin sent a sample of S. villosus (pictured above) back to Great Britain along with 209 other plants from the Galapagos, where Joseph Hooker described it and since then, it's been sitting in one receptacle or another for the past century and a half. The desiccated cucurbit was recently pulled out of storage at the University of Cambridge for a bit of molecular analysis. Why this plant in particular? S. villosus hasn't been found in the Galapagos islands or anywhere else since Darwin plucked it from those infectious beds nearly 175 years ago.The analysis of the cucurbit's DNA, extracted from the seed samples taken by Darwin, revealed that S. villosus is closest in relation to cucurbits in North America and Mexico. The species probably diverged roughly 4 mya, when the Galapagos were still geologically young. Dispersal was not human in origin, meaning long distance from the mainland, potentially from its spiny fruits stuck to birds, the authors suggest.As far as why it disappeared and so quickly, there's no way of knowing for sure, but it's likely that the settlement of the island was to blame. Cucurbit-specific viruses could have been carried from the mainland and transferred to the natives, or the plant could have been grazed to extinction. When Darwin was on the island in 1835, there were already 2,000 head of cattle and later in the 19th century, it was reported that agriculture had wrecked much of the ecology.These exact processes - divergence via evolution, dispersal and extinction - were described and linked in The Origin of Species, bolstered by experiments that Darwin himself carried out; they also happen to be the central tenets of modern biogeography.He called it Geographical Distribution in Origin, and there are two chapters toward the end that delve into his thoughts regarding these tenets, particularly dispersal:If the difficulties be not insuperable in admitting that in the long course of time the individuals of the same species, and likewise of allied species, have proceeded from some one source; then I think all the grand leading facts of geographical distribution are explicable on the theory of migration (generally of the more dominant forms of life), together with subsequent modification and the multiplication of new forms. We can thus understand the high importance of barriers, whether of land or water, which separate our several zoological and botanical provinces. We can thus understand the localisation of sub-genera, genera, and families; and how it is that under different latitudes, for instance in South America, the inhabitants of the plains and mountains, of the forests, marshes, and deserts, are in so mysterious a manner linked together by affinity, and are likewise linked to the extinct beings which formerly inhabited the same continent.John C. Briggs wrote a paper last year on Darwin's contribution to biogeography, and how his ideas on dispersal - a cornerstone of biogeography and ecology - were challenged in the 1970's.Darwin was necessarily focused on dispersal in his exploration of species. The ocean, in particular seemed impassable, and yet somehow animals and plants were able to transverse these inhospitable environments and establish themselves and their descendants on far away land masses like islands. He immersed seeds in seawater and found that 14% of them were still viable after 28 days of exposure. He found seeds in bird pellets and on muddy bird feet. In the soil caked to the leg of partridge long dead he found the seeds of 82 different plants. They clung to anything they could, even turning up in the dung of flying insects like locusts. Darwin was curious about how land snails turned up on islands so far away from continental land masses, so he tested how resilient their hibernation techniques would be on an oceanic voyage, surmising that their operculum could be a sufficient barrier to immersion for up to a week. It was clear to him that species originated from central points and found ways to transverse environmental barriers via their own dispersal abilities and subsequently diversify. For the next century or so, this was plainly accepted.Following the development of plate tectonic theory in the late 1960's, there was a push to bring vicariance, the idea that geological boundaries have caused allopatric speciation, to the forefront of biogeography. Some even went so far as to discount dispersal as the main shaper of diversity and distribution:From Croizat et al. in 1974:We reject the Darwinian concept of the center of origin and its corollary, the dispersal of species, as a conceptual model of general applicability in historical biogeography.Now, vicariance was always acknowledged as a potential factor, but it was always considered a relatively minor one. The idea had its proponents and its proponents had - what else - a prioi assumptions. According to Briggs:Thus, vicarianists came to rely on a model that did not permit them to consider all aspects of the distribution puzzle, and their work was therefore handicapped. As time went on and more works indicating dispersal were published, this handicap became more obvious and contributed to a gradual loss of confidence in the method.The ease of molecular analysis in the 1990's vindicated Darwin's initial ideas regarding evolution and dispersal, according to Briggs. S. villosus tells the story of its origins, its journey and its life through its DNA and that story shows us that it ended up on Floreana as a stowaway on an unsuspecting seabird, not as splintered remnant from the remains of supercontinents. So it was a quiet battle for footing, virtually unknown outside of this specific scientific community, but proof again of Darwin's extraordinary problem solving abilities and intuition.Sebastian, P., Schaefer, H., & Renner, S. (2010). Darwin’s Galapagos gourd: providing new insights 175 years after his visit Journal of Biogeography DOI: 10.1111/j.1365-2699.2010.02270.xBriggs, J. (2009). Darwin’s biogeography Journal of Biogeography, 36 (6), 1011-1017 DOI: 10.1111/j.1365-2699.2008.02076.xBriggs, John C. 1987 Biogeography and plate tectonics / J.C. Briggs Elsevier ; Distributors for the U.S. and Canada, Elsevier Science Pub. Co., Amsterdam ; New York : New York, NY, U.S.A.
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Sebastian, P., Schaefer, H., & Renner, S. (2010) Darwin’s Galapagos gourd: providing new insights 175 years after his visit. Journal of Biogeography. DOI: 10.1111/j.1365-2699.2010.02270.x

Briggs, J. (2009) Darwin’s biogeography. Journal of Biogeography, 36(6), 1011-1017. DOI: 10.1111/j.1365-2699.2008.02076.x

February 3, 2010
11:55 AM
828 views

Forest fragmentation and the isolation of the giant panda (a goodbye to Tai Shan and Mei Lan)

by Jeremy in Voltage Gate

In recent surveys, researchers have shown that the number of individual pandas has increased due to conservation efforts in the country, but the populations remain disparate. A recent study published in the Journal of Biogeography takes a look at how exactly these pandas are distributed in the forests of Southwest China, in relation to the level of fragmentation.... Read more »

Wang, T., Ye, X., Skidmore, A., & Toxopeus, A. (2010) Characterizing the spatial distribution of giant pandas ( ) in fragmented forest landscapes . Journal of Biogeography. DOI: 10.1111/j.1365-2699.2009.02259.x

January 30, 2010
02:08 PM
472 views

Climate change, invasives and extinction in Thoreau's Woods

by Jeremy in Voltage Gate

The data that Thoreau collected is meticulous enough to be considered a viable, useful data source by modern researchers. Thoreau's records of the area's wildlife have been carried on by others, providing us with over 150 years of data regarding the phenology of Northeast American flora; that is, life cycle events like fruiting or flowering days or migration and how these events are influenced by the seasons and the climate. Simply put, after 150 years of suffering the effects of disturbance and climate change, the natural communities of Concord are not quite the forests and fields of yore.... Read more »

Willis, C., Ruhfel, B., Primack, R., Miller-Rushing, A., Losos, J., & Davis, C. (2010) Favorable Climate Change Response Explains Non-Native Species' Success in Thoreau's Woods. PLoS ONE, 5(1). DOI: 10.1371/journal.pone.0008878

Willis CG, Ruhfel B, Primack RB, Miller-Rushing AJ, & Davis CC. (2008) Phylogenetic patterns of species loss in Thoreau's woods are driven by climate change. Proceedings of the National Academy of Sciences of the United States of America, 105(44), 17029-33. PMID: 18955707

Miller-Rushing AJ, & Primack RB. (2008) Global warming and flowering times in Thoreau's Concord: a community perspective. Ecology, 89(2), 332-41. PMID: 18409423

January 28, 2010
11:00 AM
679 views

Climate change drying up streams, reducing the reproductive success of bats in the Rockies

by Jeremy in Voltage Gate

Bats, as this article in Ecology explains, are particularly sensitive to these changes and, due to their enormous numbers, are integral to food webs as predator and prey. They may be that indicator ecologists are looking for.... Read more »

Adams, R. (2010) BAT REPRODUCTION DECLINES WHEN CONDITIONS MIMIC CLIMATE CHANGE PROJECTIONS FOR WESTERN NORTH AMERICA. Ecology, 2147483647. DOI: 10.1890/09-0091

January 22, 2010
05:14 PM
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Coastal dune ecology: Invasive grass driving native herb to extinction through direct and apparent competition

by Jeremy in Voltage Gate

I was reading through this study from Ecology yesterday, which tells the interesting story of how coastal dune ecology in northern California was invaded in the 19th century and subsequently disrupted. In order to stabilize the ever-shifting sand dunes, a grass called Ammophila arenaria, the European beachgrass, was planted along the coastline. A. arenaria grows from a strong, thick network of branching rhizomes, allowing it create a fast hold on loose soil and, as the coastal managers intended, create a framework that slowed erosion.Of course, what was preferable to coastal managers wasn't for the native wildlife. A. arenaria has spread all the way up to British Columbia since then, supplanting the native populations and potentially pushing one particular species of plant to extinction in the near future.Lupinus tidestromii (link to the researchers' project homepage with some great photographs) was flowering on the dunes of northern California long before the European beachgrass arrived. The beachgrass is a direct competitor with L. tidestromii for the basics - sunlight, water and territory - but according to the authors, there are two other ways in which A. arenaria threatens L. tidestromii.First, A. arenaria has limited L. tidestromii's seed scarification and germination. By anchoring the sand dunes, the invasive beachgrass has greatly reduced the chance for strong winds to remove the top layer of soil and vegetation from the dunes, which can expose and disperse dormant seeds. The researchers believe that L. tidestromii probably thrived when this mode of scarification was more prevalent since its seedlings are usually the first to establish after such "blowouts", but are quickly overtaken by A. arenaria.Second, there is not only direct competition between the invasive and the native, but also a type of indirect competition called "apparent" competition that is playing a greater role in L. tidestromii's decline. In general, this type of competition revolves around two producers and a shared predator. One producer's population changes, which leads to a change of the predator population and finally, a change in the second producer's population (this is not exclusive to invasive populations, this mechanism applies to native communities as well). In this case, the invader A. arenaria is providing housing for L. tidestromii's main pre-dispersal seed predator, the deer mouse (Peromyscus maniculatus), which is bolstering their numbers and increasing pre-dispersal predation within 100 meters of these refuges. The beachgrass covers large areas of coastal land, giving these animals plenty of places to hide and plenty of opportunities to snatch up seeds en masse before they can be dispersed.In order to restore L. tidestromii's dwindling population, the beachgrass needs to be removed, which will reduce the area of refuge for the deer mouse, reduce their populations and alleviate some of the pressures on the lupine's seed dispersal. The researchers have already projected an increase in one population of L. tidestromii, from only a marginal reduction in seed predation.(I tried to keep in mind while reading that this is only two species evaluated regarding an introduced species that affects many other organisms in a wider ecosystem; that the effects are so pervasive in so small an interaction is remarkable.)The authors believe that apparent competition may be responsible for homogenization and certain cases of selective extinction dependent on predator preference:When invasive plants compete strongly with native plant communities via apparent competition, native species preferred by consumers are selectively eliminated from the community. As a result, invaded communities will ultimately contain a more homogenous composition plant species that are not preferred by consumers.There are many examples where changes in the abundance of an herbivore or introduction in an exotic herbivore changes plant community composition towards less preferred species. Throughout eastern North America, white-tailed deer have increased in density due to habitat fragmentation, supplemental food sources and the eradication of large carnivores; this in turn causes a reduction in the relative abundance of their preferred plant species (Augustine and McNaughton 1998). In addition, the introduction of exotic cattle to American landscapes similarly shifts plant communities toward those species that are not preferred (Fleischner 1994).Two of the three populations of L. tidestromii that were analyzed are on a projected decline to extinction. Unless measures are taken to reduce the omnipresent influence of European beachgrass, this unique little lupine may disappear for good.Dangremond, E., Pardini, E., & Knight, T. (2010). Apparent competition with an invasive plant hastens the extinction of an endangered lupine Ecology DOI: 10.1890/09-0418

... Read more »

Dangremond, E., Pardini, E., & Knight, T. (2010) Apparent competition with an invasive plant hastens the extinction of an endangered lupine. Ecology, 2147483647. DOI: 10.1890/09-0418

January 14, 2010
12:06 PM
659 views

Irreplaceable natural services: A look at the plight of the Chihuahuan grasslands and the black-tailed prairie dog

by Jeremy in Voltage Gate

This article from PLoS ONE, provides a very clear, apt example of just how delicate this biome can be, and illustrates the services that native animals can provide in an ecosystem that would cost considerable sums to replace.... Read more »

Ceballos, G., Davidson, A., List, R., Pacheco, J., Manzano-Fischer, P., Santos-Barrera, G., & Cruzado, J. (2010) Rapid Decline of a Grassland System and Its Ecological and Conservation Implications. PLoS ONE, 5(1). DOI: 10.1371/journal.pone.0008562

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