April 30, 2010

Defining edge effects by resource and sensitivity

ResearchBlogging.orgIn 2004 Leslie Ries and Thomas D. Sisk published a study in Ecology asking a simple and surprisingly unaddressed question: 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 of abundance at the edge, or no change at all. The model is based on resources, predicting how organisms will be distributed across the edge between patches by the quality and quantity of resources available in the three zones (patch1 – edge – patch2).

April 27, 2010

Left at the intersection

There's an intersection on the other side of that forest, one that you might miss if you kept the sedan in neutral and let it glide down the slope like water from a flume. It's a canal of tall pines until the sky opens up at the edge of a steep dip in the road, sagging into a four way crossroads of gray, gravely asphalt. No stop sign if you come through the woods on that side, the only side we did; the three millionth time passed was the first time I saw anything stopped there, to the left. It was an old red tractor with an old farmer on its back, squeaking the metal seat, big wad of tobacco in his lip. He waved as we passed at lightning speed. They all wave up there, the phantom residents of the eastern mountains.

April 13, 2010

Standard Application

Tony had walked into the restaurant the day before after smashing a brand new Oldsmobile into the side of the automatic car wash outside of the detailing station at the Good Olds Dealership across town. His manager wanted Tony's paycheck to help pay for the damages and Tony wanted a new job anyway, so he stripped out of his coveralls and walked to his own car in his boxer briefs, which he had also rammed into the automatic carwash earlier in the year. It was a brief sojourn into the world of suits, ties and sales, a multi-tiered social system of puppetry, mealy mouthed businessmen and gruff drones in garages, churning out repairs and eking by on the wage they earned in the dungeon below the suited white men. They made deals.

April 12, 2010

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

This post was chosen as an Editor's Selection for ResearchBlogging.orgA 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.

The major transition of land use to land management (with a cons bio or ecological base) is a shift in public perception driven by the shift in the perceived, publicized and tangible wants and needs of Western culture molded and implemented by government officials, politicians, philosophers and activists. When you juxtapose historical procedure and law regarding resource acquisition with our modern standards, the inescapable constant is Western prerogative, which definitely gives environmentalists a steep rhetorical hill to climb when trying to rationalize proposed protections, especially those that would effectively rope off or reign in particular resources from public access in foreign countries. One of the largest factors in the decline of mangroves worldwide is the proliferation of aquaculture, which is established by local (or not so local) business people to feed the Western-inspired globalized desire for seafood of particular types. It must be delightfully contradictory for locals to simultaneously receive pleas for the environment and orders for product from the same countries.

Portugal found value in the mangroves going as far back as the early 1700’s, when a law was established in Brazil making it illegal to fell a tree without also using the bark. This wasn’t an indicator of some kind of European protoenvironmentalism, however; it protected the tanneries’ interests in the trees, essentially granting exclusive rights to the tanneries for logging. Tannin was big business until more recently, evidenced by chemical evaluations like this:

That passage comes from the second volume on “the tannins”, preceded by historical data on the English interest in mangrove tannin in the early 19th century, so the commercial interest in these areas has been constant even if the primary interests have changed.

There are 70 species of tree that can be classified as “true” mangrove species, though not all of them are closely related. Mangrove trees have two main environmental stressors: an overabundance of salt from the water and a deficiency of oxygen from the soil. These plants have developed root structures like pneumatophores or above-ground, “aerial” roots to absorb oxygen , poking through the largely hypoxic mud. In some mangrove trees, the roots contain high levels of waxy suberin to mitigate the level of salt entering cells; in others, like the white or grey mangrove, the organism is able to secrete excess salts.

But perhaps the most unique adaptation to the high level of salts in the water and soil is the way some mangrove trees nurture and disperse their seeds. Unlike most plants, mangrove trees such as Aegialitis or Rhizophora are viviparous – the seeds germinate while still attached to the tree, forming a buoyant propagule, a protective vessel highly resistant to the desiccating waters encompassing the forest. Blair Niles, Mary Blair Beebe and William Beebe describe these structures in their 1910 book Our Search for Wilderness:

Far out on the tip of a lofty branch a mangrove seed will germinate before it falls assuming the appearance of a loaded club from eight to fifteen inches in length One day it lets go and drops like a plummet into the soft mud where it sticks upright Soon the tide rises and if there is too strong a current the young plant is swept away to perish far out at sea but if it can maintain its hold roots soon spring out and the ideal of the mangrove is realized the purpose for which all this interesting phenomena is intended the forest has gained a few yards and mud and leaves will soon choke out the intervening water.

This mangrove forest in eastern Venezuela, the Orinoco delta, is one of the areas of least concern for this biome. The forests are relatively protected in the area, and many of the species are replicated in other areas of the world, as far away as Africa. This is not the case, however, in other places of the world.

Mangrove Distribution

Just north, the mangrove forests along the Pacific and Atlantic narrows of Central America contain the highest proportional number of threatened mangrove tree species in the world, about 25 to 40 percent depending on the area, according to the authors of the new PLoSOne paper I mentioned, Polidoro et al. There are approximately 10 species of trees in the area, a stark contrast to the Indo Malay Philippine Archipelago, which harbors 36 – 46 species out of the 70 known of which less than 15 percent are threatened.

Percent of Mangroves threatened per area

That number can be deceiving however; the habitat has been reduced by 30 percent in the past 30 years due mainly to the establishment of fish and shrimp farms, and the protections on paper are not always translating into enforced policies. Two species in particular are of chief concern due to an 80 percent reduction in their already patchy habitats of late, Sonneratia griffithii and Bruguiera lainesii, of which there are only about 500 and 250 individuals left in the wild respectively.

The authors briefly mention an interesting statistic regarding rarity: Nine out of 11 of the most threatened mangrove trees are considered rare or uncommon, but five out of the rest are also considered uncommon, bringing up an important distinction. There is definitely a tendency for the two factors – rarity and threat level – to be tied for obvious reasons, but it’s not a necessary linkage. In the case of uncommon, least concern organisms, their rarity can be explained by physiological, reproduction or ecological factors like dispersal or certain competitive pressures that are normal for the organism. An uncommon organism might be rarer because of its distribution relative to other, comparable species or it might very well be under certain immediate threats, but is able to reproduce and disperse with greater efficiency than its peers.

This paper was also covered over at Conservation Bytes, where Corey details some of the essential services mangrove forests provide.

Polidoro, B., Carpenter, K., Collins, L., Duke, N., Ellison, A., Ellison, J., Farnsworth, E., Fernando, E., Kathiresan, K., Koedam, N., Livingstone, S., Miyagi, T., Moore, G., Ngoc Nam, V., Ong, J., Primavera, J., Salmo, S., Sanciangco, J., Sukardjo, S., Wang, Y., & Yong, J. (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

Caves, bats, and a newly emerging disease

I've explored caves for practically my entire life. At least a couple times a month for over 25 years, I've ventured into the dark world beneath the earth's surface to explore a world that most people will never see. The reasons I like to explore caves are as complex as the caves I visit. I love the effort required to hike to and locate small cave entrances tucked away on the side of a hill. I enjoy the technical aspects of climbing up tight canyons, crawling through low puddles of mud, and using ropes and harnesses to rappel down to areas otherwise inaccessible. I love finding delicate formations and emerald green pools hidden among cathedrals of solid rock. I have also always loved seeing the strange animals that live in one of the world's most unusual (and totally dark!) environments. My favorite underground animal to observe has long been the bat.

Now, bats across the eastern US are in serious trouble, and over the past two years my love of caving and my love of bats have collided as I've watched in horror as a new, fatal disease has swept through the bat population. In 2006, a cave explorer in New York noticed a few bats with an odd white fungus on their noses, as well as several dead bats on the cave floor. He took some pictures. The next winter, New York biologists found disturbing signs that something was seriously wrong with the bat colonies. Bat were found roosting unusually close to cave entrances, bats were seen flying around outside in the dead of winter when they should have been hibernating, and many of the bats had the strange white fungus on their noses. By the spring of 2007, thousands of dead bats were found in New York caves, and bats that were still alive had white noses. What was going on?

As researchers continued to monitor caves in the northeast, they found more and more caves with white-nosed bats. So far, over a million bats have died, and there are no signs that the syndome is getting better or going away. Unfortunately, each winter, the fungus spread to more caves farther away from the epicenter in New York. Each winter got worse. Mortality rates are often 100% in affected caves. Some reports say that the northeast now has almost no bats left. Last winter, WNS spread from the northeast to the Virginias. This winter, it spread to Tennessee. The last reported case of WNS in Dunbar Cave, TN is 100 miles from my house. Only 150 miles from Dunbar, in northeast Alabama, is the largest gray bat hibernaculum in the country. Researchers names this affliction White Nose Syndome, or WNS.

To understand why this syndrome is spreading throughout the country, it might help to understand a bit about bat ecology and migration. Several different species of bats are currently affected by this syndrome, and they all have different habitats as far as where they live during the summer and winter. Many bats live in the forest during the warm summer months or in warmer caves where they can give birth and raise their young. In the winter, most bats migrate at least a short distance to cold caves that are ideal for dropping their body temperature to near freezing, allowing them to enter a torpor for winter hibernation. As a result, bats fly all over wide ranges, come into contact with other species of bats, and probably encounter a variety of habitats during the year.

So what do we know so far about WNS? Researchers succeeded in identifying the fungus, appropriately naming it Geomyces destructans. The researchers found that WNS is "characterized by the presence of profuse yet delicate hyphae and conidia on bat muzzles, wing membranes, and/or pinnae, although these surface signs are readily removed. Histological examination of infected bats shows that fungal hyphae pervade the bat tissue filling hair follicles and sebaceous glands, yet the fungus does not typically lead to inflammation or immune response in the tissue of hibernating bats (Meteyer et al. 2009)." The species thrives in cold conditions. Gene sequencing showed that the fungus is in the genus Geomyces, but the asymmetrically curved conidia are unlike any described species. Interestingly, the new, deadly fungus is closely related to Geomyces pannorum, which causes skin infections in humans. The fungus is new to science.

Even though researchers were able to identify and name the new fungus, there are many more questions than answers. Bats seem to be affected only during hibernation when they roost in cold locations and their bodies go into torpor. It's currently unknown if the fungus itself is what's killing the bats or if the fungus is just a symptom of an underlying and yet unidentified condition (although some researchers now say they believe the fungus is to blame). Affected bats are emaciated and seem to arouse during hibernation to look for food, but we don't know if bats enter hibernation in an emaciated state or become emaciated during the winter. Nobody knows if there is any way to help bats fight off this fungus, remove the fungus from the environment, or generally help stop the bat deaths. Many studies are looking at these kinds of questions, but the real question is will answer arrive in time? Research has shown that bats can be exposed to WNS both through the environment (soil in affected caves) or by contact with other bats. Research has also discovered that soil in caves where numerous bats have died from WNS contains spores of the fungus responsible for WNS. The big fear now is that as WNS moves farther south, it will start to impact huge bat colonies with more than a million individuals in a single cave. One sick bat could potentially spread this illness to an entire colony, wiping out huge numbers of bats. A cave I've worked with for many years in north Alabama has an estimated 1.5 million hibernating bats in the winter. If and when WNS impacts the cave, I don't know how I'll deal with the loss of such a huge number of bats I've come to love.

Many theories have surfaced to explain the sudden appearance of such a deadly affliction. Some suggested an association with pesticides or environmental contaminants, others suggested an invasive species. Many have noted the similarities to bee colony collapse disorder. Although nobody has an answer to why WNS suddenly appeared, one interesting study has shown a link to a fungus in France. When researchers first learned of this new fungus, scientists in Europe started to look around to see if any bats there had unusual fungal growth. French researchers found a bat with white fungal growth on its nose, sequenced the fungus, and it's a genetic match to Geomyces destructans. But, the bats since found in Europe with this fungus appear to be healthy and are experiencing no ill-effects from exposure to the fungus. The mystery deepens.

As researchers in the US spent more time studying affected bats, they also noted that not only does the fungus show up on bat noses, it also affects their wings. The damage isn't simply fungus growing on wings, rather infected bats have holes in their wing membranes, flaking skin, and even necrotic tissue. This means that even if a bat manages to survive a season after being exposed to WNS, the bat may have serious problems flying and hunting.

So what does all of this mean to us? Well, bats are essential components of our ecology and help control insects across the country. There are over 1,000 species of bats worldwide, and 40 species in the US. One bat eats half its body weight in insects every single night. One little brown bat can catch and eat up to 600 mosquitoes in one hour! A small bat colony will often eat up to a ton of insects nightly. If WNS continues to sweep across the country, not only will that mean we will lose many individual animals that are fascinating and useful, but our ecological balance will change. Without insects to help control insect populations, will another species fill the void?

I'm spending a ridiculous amount of time these days keeping up to date on WNS information and I'm sure I'll share more in future weeks and months. In the meantime, if you see bats acting in an unusual way (flying around during the day, flying during the winter, or on the ground flopping around), don't touch it. Instead, contact your state's wildlife biologist and/or your local animal control and report the bat. Trying to contact a biologist first. Animal control may not necessarily be aware of WNS and just assume the bat has rabies.

For more information, here are some resources:
And I need to include a cave picture so you can get an idea of why I like the underground world so much. My friend JV Van Swearingen IV took this picture many years ago.

Demonstrating synergy between functional groups: Burrowing mammals and megaherbivores

ResearchBlogging.orgThe black-tailed prairie dogs of the Chihuahuan grasslands have been under enormous pressures due to human activity, mostly from poor land management and overgrazing from cattle in the region. I blogged about a paper back in January from Gerardo Ceballos, Ana Davidson and their colleagues describing the level of colony disruption in the Janos region of Mexico and how the absence of the black-tailed prairie dog, this keystone species, was affecting the populations of other organisms and allowing the encroachment of scrubland to progress more rapidly.

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.

Bison used to roam the Janos grasslands living side by side with burrowing mammals like the banner-tailed kangaroo rat and the black-tailed prairie dog, but across North American grasslands, free-roaming herds of bison have been replaced by cattle herds. There has been a recent push to reintroduce bison to Chihuahua, to reinstate their ecological status, but Davidson et al. are taking a more realistic approach in this study given the wide range of cattle distribution and the importance of these animals to local economies. A level of functional equivalence has been demonstrated between bison and cattle, and the authors seek to pin down the specifics of how cattle and prairie dogs affect their neighbors and the environment both in cohabitation and in isolation. This study addresses a much larger issue of demonstrating the synergy of organisms in different functional groups having a combined effect on the ecosystem.

The authors established and studied four types of plots to tease out individual effects from synergistic: Prairie dogs and cattle present (P+C+), prairie dogs present, no cattle (P+C-), no prairie dogs, cattle present (P-C+) and neither present (P-C-). Important environmental variables were analyzed for each of these plots, waypoints to illustrate discrepancies: "vegetation (plant height, cover, and biomass), animal activity (fecal counts of rabbits, and soil disturbance by prairie dogs, kangaroo rats, and gophers), mounds (of prairie dogs, kangaroo rats, and harvester ants) grasshopper abundance and prairie dog abundance."

First and foremost, prairie dog abundance doubled in the presence of cattle due to grazing and their combined efforts had a dramatic effect on the plant cover on the P+C+ plots, reducing vegetation height significantly. There was also two to three fold decline in the grasshopper population between the P-C- plots and the P+C+ plots.

The study demonstrated some interesting individual effects as well. In the absence of prairie dogs (P-C+), banner-tailed kangaroo rats activity increased. According to the authors it has been speculated in the past that these animals, who are also considered ecosystem engineers and a keystone species, actually compete with the black-tailed prairie dog. The results seem to favor that notion as well as demonstrate at least a short term boon for the kangaroo rats - another burrowing mammal - in the presence of a megaherbivore, particularly one that has been "responsible" for perpetrating the overgrazing leading to desertification that threatens the kangaroo rat.

The important concept here is combined effects; the individual effects on the environment and other organisms by prairie dogs and cattle were mostly not significant, but when they were combined and allowed to synergize, they apply broad controls to the ecosystem. From a land management standpoint, this natural inclination can be employed to help maintain biodiversity and protect threatened species in the Chihuahuan grasslands without pushing ranchers out.

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