Monday, November 30, 2009

A Darkiling Beetle, a Wasp, a Fritillary and an Egret

Random photos from the field; taken last week just south of Tampa, Florida.

Possibly Isomira pulla ???

A species of the Sceliphron genus ???

A couple of Gulf Fritillaries; Agraulis vanillae

Great Egret; Casmerodius albus

Sunday, November 29, 2009

Wetland Plant of the Week #34

Limonium carolinianum

Sea Lavender

Despite its common name ‘sea lavender’ is a member of the Plumbaginaceae Family, which means that it isn’t really a ‘lavender’ at all, as lavenders belong to the Lamiaceae Family. One of the plant’s unique characteristics is that it’s one of only a handful of the Limonium genera’s 120 species with a range limited to North America; the majority of the genera’s members show a much more global distribution. Here in Florida, the Obligate can be found near saltwater or brackish marshes, or as with the one in the above photo, in mangrove swamps.

Limonium carolinianum is an herbaceous perennial with a woody rhizome and alternating leaves. The leaves themselves are basal, generally elliptic in shape and have a leathery feel when touched. The flowers display five stamens, and a five-lobed, whitish colored calyx with a corolla that ranges from blue to lavender. The fruits of the sea lavender bear a single maroon colored seed, which as with the plant’s range mentioned above, represent another unique characteristic. More specifically, the seeds’ morphology and structure have undergone adaptation as to tell-the-tale of plant’s favored mode of geographic conquest.

The brownish-red seeds of the sea lavender are relatively large and display a sheen that likely attracts birds. The plant’s habitat preference for saltwater proximal real-estate when combined with the sheen displayed by its seeds may work cohesively to facilitate dispersal of its genome. As Charles Darwin pointed out on page 361 of the Origin of Species,

“Living birds can hardly fail to be highly effective agents in the transportation of seeds.”

This is likely true of Limonium carolinianum, a plant species that has adapted to near-sea environments that are frequented by shore birds.

Biologically assisted seed dispersal mechanisms can be thought of as primarily working along one of two primary lines. One method of dispersal, called epizoochory, relays on seeds being externally attached to the hair, fur or feathers of animals. Once attached, the seeds are carried with the animal as it moves across the landscape. The second mode of animal derived seed transport is called endozoochory; in this instance the seeds are eaten by an herbivore or frugivore and then deposited elsewhere with the animal’s feces.

Although the possibility of water facilitated seed dispersal is not ruled-out, the seed morphology of Limonium carolinianum increases the plausibility for endozoochory.

FIGUEROLA, J., & GREEN, A. (2002). Dispersal of aquatic organisms by waterbirds: a review of past research and priorities for future studies Freshwater Biology, 47 (3), 483-494 DOI: 10.1046/j.1365-2427.2002.00829.x

Saturday, November 28, 2009

Hints of a Catastrophic Paleoclimatic Event from Manny the Mammoth

In an effort to gain insight into the challenges posed by climate change, I just spent the last couple of hours watching the animated feature film “Ice Age 2 – The Meltdown.” The plot of the cartoon centers on a group of anthropomorphized prehistoric mammals (a mammoth, saber-toothed tiger, sloth and a halfwit saber-toothed squirrel) as they flee an impending flood and their certain extinction. Interestingly enough, the floodwaters in the movie purportedly result from a period of global warming and the associated thawing of their fictional ice-aged world. Initially, the characters in the film celebrate the rising temperatures with lakeside antics, but their clowning around comes to an abrupt end when they realize that their short-term fun-in-the-sun will inevitably end with substantial losses in lakeside real-estate, an ecosystem on which they’ve come to depend.

All considered I enjoyed the cartoon; mostly because of its paleoclimatological accuracy. Well, maybe it wasn’t all that accurate, but the underlying theme wasn’t too far-off…

Parallels between the feature and the real paleontological past can be glimpsed when consideration is given to the thermal fluctuations and water linked extinctions portrayed in the film. To explain, the impending floodwaters in the movie were precariously dammed by a mile-high glacial wall. It was the gradual disintegration of this frozen barrier that established the dramatic timeline for the lead mammals escape from danger. The waters bound by the glacial front had accumulated through the receding of the glacier itself, and should the wall be breached the waters would be freed to reap havoc. Although such a physical setting may seem a bit far fetched, it just so happens that between 12,900–11,500 years ago similar lakeside conditions may have contributed to the extinctions of numerous North American mammal species.

Characters from the ‘Ice Age 2’ ; glacier and glacial lake (Lake Agassiz?) in background.

During the Wisconsin glaciations about 12,000 years before the present, a massive continental ice sheet covered most of what is today the United States and Canada. As the Wisconsin came to a close, rising temperatures instigated its receding glaciers to form a colossal lake; roughly centered on modern day Manitoba. The lake was uniquely positioned in such a way that a combination of topography and its inclusive glacial blockades trapped the discharge of meltwater. The glacial melt, being unable to drain, resultantly accumulated in a water body that covered nearly half of a million square kilometers – Lake Agassiz. As in the animated movie, once sufficient hydrology was achieved to overcome its restricting geography and ice, the water was released in a catastrophic flooding event of incomprehensible immensity. However, unlike the cartoon’s scripted drama, the direst impact to fauna 12,000 years ago wasn’t the risk of drowning; the biggest consequence of the flood was its affects to global climate.

The enormous quantity of water released from the rupture of Lake Agassiz’s glacial banks, as opposed to flowing directly southward, chose to exit by way of the Saint Lawrence River. Following the St. Lawrence, the freshwaters moved eastward and into the North Atlantic. Once in the North Atlantic, the vast icy water cooled the warmer North Atlantic Current, and rapidly diluted the saline gradients that help drive its heat-conveying waters. Known as thermohaline circulation, variations in ocean water density create flow patterns that convey heat from regions proximal to the equator to those areas located more pole-ward; the constituent variations in density are brought about by surficial heat and saline content. The rupture of Lake Agassiz impacted the thermohaline circulation of the North Atlantic Current, altered heat transfer to the northern hemisphere, and drastically changed the Pleistocene climate of the North American Continent. The rapid climate change associated with the Lake Agassiz event is known as the Younger Dryas stadial (a ‘stadial’ is the name assigned to a period of cooling temperatures).

During the Younger Dryas stadial, mean annual temperatures throughout large portions of the Northern Hemisphere plummeted by as much as five-degrees Celsius. The drop in temperature caused some regions to re-glaciate, despite what had until recently been a warming trend. Climate change forced ecosystems into flux, and likely contributed to the extinction of several genera of mammals – The End Pleistocene Extinction Event.

The End Pleistocene Extinction Event marked the end of the road for some of the characters portrayed in the Ice Age movie, saber-toothed cats, giant sloths, mastodons and similar mammals. As a matter of fact, a recent article in Science collaborated the extinction chronology for more than 30 genera of Pleistocene fauna; the study used data from FAUNMAP to determine that the extinctions occurred nearly simultaneously.

Although much is known about the Younger Dryas stadial, its exact contribution to the End Pleistocene Extinction is still largely a matter for debate. Complicating the issue is the immigration of Clovis people into North America at about the same time that the Younger Dryas was putting a strangle-hold on the climate. The Clovis may have participated in the mammals’ disappearance through hunting – the Overkill Hypothesis.

Faith, J., & Surovell, T. (2009). Synchronous extinction of North America's Pleistocene mammals Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0908153106

Friday, November 27, 2009

Evolutionary and Developmental Biology - The Making of the Fittest

Sean Carroll lecturing on evolutionary and developmental biology. The talk is largely drawn form his book "The Making of the Fittest," which if you haven't read I'd highly recommend.

You'll want to fast forward to about 18:30 due to a lengthy wait before Sean's start and the removal of a copyrighted video used as an introduction.

Thursday, November 26, 2009

From Promiscuous to Palatable, the Making of a Thanksgiving Day Entree

For the truth the turkey is in comparison a much more respectable bird and withal a true original native of America... he is besides, though a little vain & silly, a bird of courage, and would not hesitate to attack a grenadier of the British guards who should presume to invade his farm yard with a red coat on.” (Benjamin Franklin, 1784)

As demonstrated by the above quote, Benjamin Franklin admired the turkey for its courage, and although the bird may have been somewhat “vain and silly,” in his evaluation it would have served as a better emblem for the newly constituted United States than does the bald eagle, which Franklin would describe in the same transcript as “a bird of bad moral character” and as one that “does not get his living honestly.”

In reflecting on Franklin’s impeachment of the eagle’s morality, it becomes blatantly apparent that his basis for turkey endorsement was not derived from the appraising of the two birds’ sexual fidelity or familial loyalty. If Franklin would have objectively weighed the family values displayed by the bald eagle against those shown by the turkey, he would have undoubtedly praised the eagle for its habit of committing to more-or-less monogamous relationships, and he would have scorned the turkey’s shameless and promiscuous lifestyle.

Despite Franklin’s misinformed backing, the mate-choosing habits of the wild turkey (Meleagris gallopavo) have long been known to diverge from those standards held by the majority of human cultures. Turkeys are sexually dimorphic with the seemingly arrogant males of the species being substantially larger than the females and displaying a showy, red-colored head and neck. Vulgarly hanging from the head of the beastly male are fleshy folds of skin called ‘wattles’ that are composed of erectile tissue that can be engulfed by blood to signal agitation or arousal. Changes in the size and color of wattles can be paraded in combination with raised feathers and loud boisterous calls (i.e. gobble, gobble) to signal potential mates or to intimidate rivals.

Furthermore, in contrast to the typically monogamous bald eagle, turkeys commonly practice polygyny; this means that a single dominant and territorial male will guard a harem of hens. However in some cases, particularly when local populations become over-crowded, small licentious groups of roving males may share a territory – though, of course, they’ll still scrap for female access.

Through mating with multiple females, and guarding those females from rivals, male turkeys, being insensitive to the reproductive aspirations of others, selfishly increase the number of offspring in the population that bear their genes - said differently, their genes experience greater frequency in the gene pool. Genes are also important to the self-indulgent female turkey.

The male’s propensity to mate with multiple females means that he has little time to contribute towards the proper rearing of young, or to providing any type of direct benefit to the female. Not foreseeing any direct benefits herself, the female turkey grants sexual access to those males with the best and brightest displays. In addition to wattles and the red-colored face and neck mentioned above, male turkeys flaunt feathers with red, green, gold and iridescent coloration. The overall brilliance of the male’s colors provides the female with clues as to his health and genetic makeup.

Despite the dominant male’s watch, the female turkey - far from being chaste herself - also strives to maximize the occurrence of her genes in the population. Like the male turkey, she’ll mate with multiple partners. To illustrate the female’s wanton ways even more, consider that in a study conducted by Berkeley’s Alan Krakauer about 45% of turkey nests sampled during a study of the turkey’s genetic reach were found to contain eggs derived from multiple parentages. The genetically sampled broods contained not only eggs from multiple males, they also were found to contain the eggs from multiple females!

Even beyond the female turkey’s flagrant granting of sexual access to multiple males, the California study revealed that females practiced a quasi nest-parasitism during which they would mate with the father of a neighbor hen’s clutch, and then lay the eggs from that clandestine joining in the nest of the neighbor – leaving the ‘cheated spouse’ to care for the young born of her rouge and mischievous mate’s digressions.

In light of Benjamin Franklin’s personification of the turkey as a “respectable bird,” it becomes difficult to comprehend the process that he undertook in achieving his conclusions of 1784… Unless of course in addition to his many other famous accolades, Franklin also happened to be a knowledgeable naturalist. Perhaps he wasn’t making a statement about the turkey’s morals and ethics; maybe he was making a statement about the bird’s fecundity…

Or, as yet another possibility, perhaps the vain, silly and promiscuous turkey holds more commonality with the citizenship than we care to admit…

KRAKAUER, A. (2008). SEXUAL SELECTION AND THE GENETIC MATING SYSTEM OF WILD TURKEYS The Condor, 110 (1), 1-12 DOI: 10.1525/cond.2008.110.1.1

Wednesday, November 25, 2009

Sex was a Costly Affair for Ceratopsian Dinosaurs

In a recent article published in The Anatomical Record several scientists, including Florida State University’s resident dino-osteologist Gregory Erickson, constructed a life table for a population of 80 bird-hipped dinosaurs.

Note, a ‘life table’ is a common tool used by population ecologists/biologists to interpret the birth-to-death maturation cycle of an organism. Essentially, a life table can be thought of as a listing of a population’s members with a corresponding age identified for each individual. Through examination of how the table’s age-ranges are distributed scientists can make inferences regarding the population’s ecology.

Drawing reliable conclusions on the subject of population-level processes can be difficult, particularly when that population happens to be extinct and is only known from the fossil record. Without numerous, quantitatively significant, representatives from a population, discussions of maturation rates, reproductive cycles and mortality rates are all but impossible. However, a mass kill event documented in the Lujiatun Bed of the Lower Cretaceous (Yixian Formation, Liaoning Province of China) provided the Erickson led team with the rare opportunity to do just that, study the demography of an extinct population of dinosaurs – specifically the species Psittacosaurus lujiatunensis.

Compared to the ‘lizard-hipped’ dinosaurs (saurischians) relatively little research has been undertaken in understanding the life history and population dynamics of the Ornithischia (bird-hipped), this makes the case of P. lujiatunensis all the more significant. Through histological analysis of the growth rings found within the fossil bones of the ceratopsians, – analogous to counting the growth rings in a tree – Erickson was able to estimate the age of each population member; the frequency of the age-ranges were then correlated to body size estimates. The result was that, like modern birds and mammals of comparable size, the life history of Psittacosaurus lujiatunensis reflected a pattern in which

“[h]igh attrition in young individuals gives way to lower stabilized values once a threshold size is obtained; however, later in ontogeny mortality rates increase (typically from the effects of senescence) leading to the extinction of the cohort.”

In other words, risk of death was found to be at its greatest when the dinosaurs were young and small – possibly because of vulnerability to predation. Once achieving a certain size and becoming less vulnerable, mortality rates decreased. Mortality risks would then increase again as the dinosaurs got old; through the natural ageing process the senior members of the population would once again become vulnerable to predators, disease, and etcetera.

In addition to the vulnerable young and old members of the Psittacosaurus lujiatunensis population, incidences of increased mortality were also found for those ceratopsians around the age-range associated with reaching sexual maturity. In this case, energy and resources devoted to the pursuit and winning of mates, as well as the rearing of young once a mate was found, likely conspired to cause escalated mortality levels during the reproductive years.

Erickson, G., Makovicky, P., Inouye, B., Zhou, C., & Gao, K (2009). Initial Insights Into Ornithischian Dinosaur Population Biology
The Anatomical Record, 292 (9), 1514-1521

Tuesday, November 24, 2009

Beetles and Darwin's On the Origin of Species

Good video to watch on the 150th Anniversary of the Origin's publication.

The story starts with beetles and then moves to Darwin's acclaimed work.

QUEST on KQED Public Media.

Monday, November 23, 2009

Supporting Math and Science Education

President Obama speech regarding the math and science initiative.

-Good move!

Visit for Breaking News, World News, and News about the Economy

The Mythical Adaptationist and the Pretend Pluralist’s Aimless Plea

Wow… I generally tend to stick to narrative posts discussing natural history, but in light of a short commentary that I just read from The Society for the Study of Evolution’s journal, I feel obligated to throw a couple of reckless comments onto the web…

The article in point, ADAPTIONISM—30 YEARS AFTER GOULD AND LEWONTIN, was written by Rasmus Nielsen of the University of Copenhagen and to the best of my interpretative ability seems to be making a plea to so called ‘adaptationists’ to reconsider their errant ways..?

Apparently, the author is under the impression that the world’s evolutionary biologists can be dichotomously classified as either ‘adaptationists’ or ‘pluarlists.’ And further, that those classified in the former category should seek reincarnation as enlightened members of the latter.

The commentary’s argument begins (predictably) with Stephen J. Gould and Richard C. Lewontin’s ‘The Spandrels of San Marco,’ an article originally published by the Royal Society in 1979. The broad point of the original Gould piece was to encourage scientists to look beyond natural selection as the sole process of change and to instead consider organisms as complex entities influenced by a myriad of evolutionary forces. In short, to think of the organism’s evolutionary history as being an emergent property derived from its whole, not one measured through the summing of its individual traits. This cautionary imperative is certainly as valid today as it was back in ’79 and it should be heeded; however, it isn’t by any means novel, nor does it say anything in regards to the reality of research – it is simply a warning to be cautious of personal and professional bias.

The Nielsen article moves from The Spandrels to contemporary times in order to assess what valuable lessons have been gleaned from that momentous (?) work of 30-years past. Unfortunately for the field, in conducting this assessment it becomes blatantly apparent that the Gouldian forewarning has fallen on deaf ears…

“…although Gould and Lewontin’s paper did not spell the end to adaptationist storytelling, it radically increased the awareness among evolutionary biologists about the pitfalls of adaptationism.”

Whew... What a relief; but what does that mean exactly?

“Evolutionary biologists are today, arguably, much more reluctant to invent adaptive stories without direct evidence for natural selection acting on the traits in question. We still regularly encounter very naive adaptive stories, particularly about human behavior, but rarely in journals such as Evolution or other related journals with high standards…”

‘Rare’ in this case is good – I think? I’m so glad we have The Society for the Study of Evolution’s journal to guide our path!

What should we do to remain of wholesome purity; what should we do to keep the path?

“…we must rely on inferences regarding past events by observing scant fossil evidence and the current pattern of genetic and phenotypic variation. We may be able to detect selection, but we may never be able to directly determine which traits selection acted on.”

So, we can see selection, but our ignorance blinds us to the characteristics driving that selection…

“Although the presence of selection acting on genes underlying a phenotypic trait of interest does help support adaptive stories, it does not establish that selection acted directly on the specific trait of interest.”


“[m]ost genes have pleiotropic effects and establishing the direct cause of selection in an organism such as humans might in most cases be difficult or impossible.”

That’s a reasonable statement, but couldn’t the before-mentioned inferences guide the ‘adaptationist’s’ filthy lust for storytelling? What prophylactics are available in the event that an adaptationist fails to maintain self-control?

“…speculation… must be done acknowledging that no simple experiment or functional data can falsify or “validate” historical adaptive hypotheses.”

Geee, thanks for the heads-up, I’m going to spread the good-word!

“And in communicating with our peers, and with the popular press in particular, we may individually, and as a scientific field, benefit from understanding the societal impact of the statements we make.”

Or, on the other hand, maybe not…

In closing, I have difficulty believing that radical adaptationists are running rampant in evolutionary biology. I can’t think of a single practicing biologist, in academia or otherwise, that doesn’t consider the impact of drifting allelic frequencies and other possible influences outside the scope of natural selection. As far as the relative importance, or weight, granted to such alternative processes in determining an organism’s evolutionary path, that isn’t a question of individual preference. Rather it’s something that is assessed quantitatively through experimentation and study.

I can’t help but wonder if the entire “adaptationist Vs pluralist” debate is an artificial construct intentionally designed for generating publicity. Judging by this post and similar arguments had at Sandwalk it seems to work…

Nielsen, R. (2009). ADAPTIONISM-30 YEARS AFTER GOULD AND LEWONTIN Evolution, 63 (10), 2487-2490 DOI: 10.1111/j.1558-5646.2009.00799.x

Sunday, November 22, 2009

The Magnificent Urticating Slug Caterpillar

Found this little guy resting on my patio last night….

Euclea delphinii belongs to the Limacodidae Family of moths; it’s called the ‘slug caterpillar’ because of the sluggish way that it moves and its overall rounded appearance.

It also has stinging hairs (i.e. urticating).

Saturday, November 21, 2009

Wetland Plant of the Week #33

Hypericum fasciculatum “Peelbark St. Johnswort”

Peelbark St. Johnswort, also known as ‘marsh St. Johnswort,’ is a Florida native and widely distributed member of the Hypericaceae Family that can commonly be found in swamps, marshes and just about any locality having sufficient water to satisfy its Obligate lifestyle. The multi-branched growth pattern of this upright shrub gives it a very bushy appearance, and provides ample structure for numerous arthropods species to nest and hide (including ticks, take caution).

Though typically about four feet tall, the woody stems of Hypericum fasciculatum can push the plant upwards to reach heights of over two meters (6ft). In an effort to increase available surface area for oxygen absorption, the reddish-bark of the stems is exfoliated giving it a soft and crumbly look and feel.

The needle-like leaves of the plant grow in bundles and average about 2.6cm in length with slightly longer leaves at the top of the stem. The flowers, although not pictured here, display five petals arranged in a whorled pattern and can be found spring-through-summer at the terminal ends of the branches.

The abundance of Hypericum fasciculatum, when combined with its multi-branched physiognomy and its habitat preference for plentiful water, make the plant an integral component of aquatic ecosystems here in Florida. As mentioned previously, the structure provided by the plant’s branches, branchlets and leaves attract a myriad of arthropod species. Once attracted by the ‘peelbark,’ these same arthropods will, in turn, move to occupy niches in proximity to the plant. There they’ll take on roles as pollinators, predators and prey for other organisms. Through such species interactions, the trophic effects of seemingly unconnected organisms become intertwined and bound.

As an example of how complex life histories can become tangled, consider for a moment a hypothetical swamp in which a hypothetical fish is swimming around the exfoliated base of a hypothetical Hypericum fasciculatum …

As with many fish, the hypothetical one feeds on aquatic insects like water beetles, mayflies and larval dragonflies. Examining dragonflies in particular, the loss of dragonfly larvae via fish predation ultimately results in the emergence of fewer adult dragonflies than would be predicted in the absence of the fish. Compounding the process further, the presence of fewer adult dragonflies in nearby ecological communities translates to less aerial predation of flying insects. Flying insects, in addition to being food-stuffs for dragonflies, also pollinate plants; from this relationship it can be inferred that with fewer dragonflies, more insect pollinators find the nectar-rich flowers they seek… The end result of this hypothetical situation is that the Hypericum’s proximity to the fish allows the plant to host a greater number of pollinators, and thus to experience a greater level of reproductive success itself.

Image from Cited Article, interaction web showing the pathway by which fish facilitate plant reproduction. Solid arrows ndicate direct interactions; dashed arrows denote indirect interactions. The sign refers to the expected direction of the direct or indirect effect.

As is characteristic of most ecosystem dynamics, the above scenario can also be run in reverse to show that the presence of the common Hypericum fasciculatum could lead to increased fitness in the hypothetical fish species.

Knight, T., McCoy, M., Chase, J., McCoy, K., & Holt, R. (2005). Trophic cascades across ecosystems Nature, 437 (7060), 880-883 DOI: 10.1038/nature03962

Friday, November 20, 2009

A Cool Science Project...

I found this nifty new video on YouTube. The info on the page indicates that it was made for a biology class. The video overviews info on pine flatwoods ecology.

I'd give it an A+

Have a look:

The Tactics of an Egg Tending Lynx

While stomping through a northwest Florida flatwoods community earlier this week, I took pause to admire a couple of swamp sunflowers (Helianthus angustifolius). The sunflowers’ brilliant yellow display glared brightly through the otherwise dark and rainy Tuesday afternoon and beckoned for a closer look. On turning-over one of the composite flower heads to better examine its calyx, I discovered a green lynx spider (Peucetia viridans). The spider was standing guard on top of its egg sac, which it had tethered securely to the optimistic sunflower’s underside with hard-wearing silk.

The green lynx spider is a member of the Oxyopidae Family and accordingly displays several traits characteristic for the group. In terms of identifying morphology, members of the group show a hexagon-like pattern of eye arrangement, and legs that bear large spines. Behaviorally, members of the Oxyopidae are aggressive daytime hunters which, as opposed to constructing webs, stalk their prey over the leaves and stems of the herbaceous groundcover. In regards to Peucetia viridans specifically, the spider’s body is translucent and exhibits a bright green coloration with red spots on the cephalothorax and black spots on its spiny legs.

Considering the presence of an egg sac and the sentinel-like bearing demonstrated by the spider appended to the sunflower, it was very likely a female. As a strategy, females of the species uncompromisingly guard their reproductive investment using a variety of tactics. These protective measures are necessitated by the low-to-the-ground habitat they share with a number of other voracious predators. Here in Florida, some of the most abundant and hostile species encountered by lynx spiders are fire ants (Solenopsis spp.)

The specific tactic used to defend an egg sac from fire ant onslaught is dependent on the intensity of the ant attack. Intensity is here a measure of ant quantity and the frequency of assault. Generally, female lynx spiders will utilize a mode of defensive escalation in which infrequent or isolated attacks from a single ant will be dealt with through deployment of a rapid and violent head-on confrontation. As the ant approaches the female, she’ll pounce forward and use her mass to knock the assailant from the plant, or, if failing to physically remove the ant, she’ll alternatively utilize her fangs to pierce the exoskeleton of her antagonist, ultimately slaying the provoker. The spider will almost always prevail during one-on-one combat with an ant, however if the ant attack is undertaken in number, evasion becomes the best option for the lynx.

If the incidences of attack become too frequent, or if the ants attack in larger quantities, mother Peucetia viridans will attempt to dissuade the egg-seeking aggressors by removing the prize for which they hunger – she’ll move the eggs out of reach. Once again depending on the seriousness and intensity of the ants’ offensive maneuvers, she’ll execute one of two evasive actions. One option is to cut all but a couple of the silk cables holding the egg sac in place, causing it drop from its anchor point and remain suspended in air; the second option to completely untie the sac and relocate to an entirely new host plant. The suspension method removes the eggs from hostility and forces any persistent attackers to travel down individual threads to continue pursuit – where they’ll undoubtedly meet an agitated mother face-to-face. Relocating the egg sac to a new host is a sure-fire way to end the current dispute however it is a risky option, because increased visibility during transport may leave both the mother and her eggs vulnerable to other hungry predators.

Eubanks, M. (2001). Estimates of the Direct and Indirect Effects of Red Imported Fire Ants on Biological Control in Field Crops Biological Control, 21 (1), 35-43 DOI: 10.1006/bcon.2001.0923

Linda S. Fink (1987). Green Lynx Spider Egg Sacs: Sources of Mortality and the Function of Female Guarding (Araneae, Oxyopidae Journal of Arachnology, 15 (2), 231-239

Thursday, November 19, 2009

Adapting to Climate Change, the Uphill Pursuit of the Shifting Niche

This post represents the final in a three part series discussing Joseph Grinnell, climate change and ecological niches. The initial post can be found here: Joseph Grinnell, Climate Change and the Legacy of the California Thrasher, and the second here: Tracking the Niche, a Project of Grinnellian Proportions.

Having adopted Joseph Grinnell’s vision as their own, the current Director of the Museum of Vertebrate Zoology at Berkeley and his colleagues have taken on the challenge of following in Grinnell’s footsteps – quite literally. The group, headed by current Director Craig Moritz, has begun the process of resurveying the 700-plus localities that were originally surveyed by Grinnell in the early 20th Century. Their goal is to compare the newly collected data to that inherited from Grinnell in aspirations of gaining insight into how a century of environmental change has impacted California’s avian, mammalian and herpetological faunas. Through application of carefully recalibrated Grinnellian field-methods, and the employment of modern techniques, the group is expanding biology’s understanding of the ecological niche.

As discussed during the first post on this topic (available HERE), the effects of average changes in global climate can be dramatically amplified at local levels. As a case in point, consider the region of California that was originally surveyed by Grinnell between the years 1914 and 1920. Over the past 100 years an approximate one-degree rise in global temperatures has resulted in a 3.7°C increase in minimum monthly temperature! A four-degree change in temperature has undoubtedly altered the ecology of this region - Yosemite National Park – in substantial and quantifiable ways. Such quantification has been precise goal of Grinnell’s successor.

Pulling data from Grinnell’s field-notes and DNA from his collected specimens, Craig Moritz has used climate models, modern genetics and biodiversity informatics to decipher and compare the demographies of mammals, birds, reptiles and amphibians of past and present. The analysis rendered from this research clearly indicates that the link between environment-and-species has remained true since its inception in Grinnell’s 'The Niche-Relationships of the California Thrasher'. More specifically, as the 3.7°C increase in minimum monthly temperature pushed Yosemite’s available habitats towards new equilibriums its fauna followed suit.

Yosemite’s geologic and geographic setting entails a range of elevations that extend from about 50 meters to well over 3000 meters above sea level. As is typical for diverging elevations, as altitude increases average temperatures decrease. So, if moving towards the top of a mountain one could anticipate encountering bands of cooler micro-climates. The relationship that exists between a specific temperature range and its corresponding physical components allow for identification of specific ‘life zones’. For example, the hydrology found on a mountain’s glacial peaks will differ in type and quantity to that located near the base of the mountain. In considering this natural phenomenon of elevational transition with specific regard to an overall increase in temperature across the mountainous region as a whole, an upward shift in ‘life zones’ could be predicted. In other words, as a temperature increase reaches a certain threshold, the glaciers capping a mountain will recede as to reduce the total area occupied by ice, and to increase the availability of liquid water. With increased access to water, life zones that had been previously locked in a frozen state will become biologically available to plants formerly bounded to lower glacier-free altitudes.

Moritz’s comparison of the life zones documented by Joseph Grinnell to those surveyed by his research group demonstrated that as Yosemite’s temperature increased over the past century, its life zones moved upwards. Significantly, the research showed that the uphill advance of life zones induced pursuit by those avian and mammalian faunas found below. The general pattern discovered by Moritz was that as temperatures increased in the park, the majority of wildlife populations found at high elevations contacted upwards, abandoning previously occupied portions of their lower habitat range. Correspondingly, those animals occupying lower altitudes shifted their habitats uphill.

The ability of Yosemite’s wildlife to confront ever-shifting environmental attributes with resilience and flexibility is critical to maintaining lineages with the capacity to undergo the morphological and behavioral modifications required for their continued survival. The study of the processes driving this evolution, provides more than just a greater understanding of natural history, it also imparts the tools to ensure species conservation as global climate change accelerates environmental fluctuation. Luckily, field scientists such as Joseph Grinnell have, and will continue, to provide insight into the plasticity of adaptation.

See: The Grinnell Project's website.

Moritz, C., Patton, J., Conroy, C., Parra, J., White, G., & Beissinger, S. (2008). Impact of a Century of Climate Change on Small-Mammal Communities in Yosemite National Park, USA Science, 322 (5899), 261-264 DOI: 10.1126/science.1163428

Tingley, M., Monahan, W., Beissinger, S., & Moritz, C. (2009). Colloquium Papers: Birds track their Grinnellian niche through a century of climate change Proceedings of the National Academy of Sciences, 106 (Supplement_2), 19637-19643 DOI: 10.1073/pnas.0901562106

Joseph Grinnell (1917). The Niche-Relationships of the California Thrasher The Auk, 34 (4), 427-433

Joseph Grinnell (1924). Geography and Evolution Ecology, 5 (3), 225-229

Wednesday, November 18, 2009

Tracking the Niche, A Project of Grinnellian Proportions

This post is the second in a mini-series discussing Joseph Grinnell, climate change and ecological niches. The previous post is available here: Joseph Grinnell, Climate Change and the Legacy of the California Thrasher

Joseph Grinnell was THE quintessential field biologist. From the time of his birth in 1877 (or, roughly thereabouts), until his to death in 1939 he marveled at the natural world. He reveled in nature’s aesthetic splendor, and he contemplated its immense mystery. He dedicated his entire life to the field of biology; birds, reptiles, mammals and amphibians – he studied them all, and he did so with great detail.

Grinnell’s philosophy of scientific inquiry focused intently on the task of accumulating as much raw data as possible. For example, during the biological survey he carried out in Yosemite National Park between the years 1914 and 1920, Grinnell and his field crews collected 817 photographs, nearly 3000 animal specimens and more than 2000 pages of notes! Being organized and detail oriented is one thing, but Grinnell’s drive for thoroughness approached the obsessive.

As testimony to Grinnell’s view on taking accurate field notes, consider the following precept that he was known for continuously repeating as a mantra for meticulousness;

“Put it all down. You might not think it’s important, but somebody else may.” (1)

It may very well have been the sheer bulk of his available data that guided Joseph Grinnell to develop the concept of the ‘ecological niche’ discussed during the last post in this series (Available HERE). After all, he collected information on everything from the individual behavioral characteristics and morphology of observed animals to the daily weather patterns of Yosemite; all of these informational axes have been incorporated into the ecological niche concept. Even if the ‘niche’ wasn’t born of the data directly, the huge quantity of collected information would certainly have been useful during the writing of Grinnell’s numerous research papers and species descriptions, which are more than 500 in number.

Yet greater evidence to Grinnell’s tenacity can be found in the fact that despite his time spent collecting, he still managed to teach and perform administrative duties as the first Director of the Museum of Vertebrate Zoology at Berkeley. An absolutely astonishing scientist!

In considering Grinnell’s knack for field work, another of his now famous quotes comes to mind. This one (from 1910) relates to the long-term value of the data that he and his colleagues were collecting.

“This value will not, however, be realized until the lapse of many years, possibly a century, assuming that our material is safely preserved. And this is that the student of the future will have access to the original record of faunal conditions in California and the West, wherever we now work.”

This quote would turn out to be very prophetic…

What possible value could be reaped in modern times for century-old data collected during Grinnell’s survey of the ‘Yosemite Tract’? What would comprehensive and weather-correlated descriptions of wildlife niches tell us about contemporary linkages of climate-and-niche?

A few steps are required in order to assess the above questions. As an initial step, there would be a need to quantify the climate-to-niche relationships of current systems. Once such modern data was in-hand, comparisons could be made between the ‘old’ and the ‘new’ to identify any patterns or inconsistencies. In other words, to gauge change compare Grinnell’s data with what is exhibited by Yosemite’s ecosystems today.

This is precisely what the present Director of the Museum of Vertebrate Zoology at Berkeley has done. He and his colleagues went to field, and using Grinnell’s notes and methods collected new data for the purpose of comparison. Their resurvey - The Grinnell Project - and findings will be discussed during the next post...

UPDATE: The 3rd and final installment of this series is available HERE.

1-As told to Ward Russell during a field survey; an audio recording of Ward’s 1992 interview can be found at the MVZ @ Berkeley website – HERE

Joseph Grinnell (1917). The Niche-Relationships of the California Thrasher The Auk, 34 (4), 427-433

Joseph Grinnell (1924). Geography and Evolution Ecology, 5 (3), 225-229

Moritz, C., Patton, J., Conroy, C., Parra, J., White, G., & Beissinger, S. (2008). Impact of a Century of Climate Change on Small-Mammal Communities in Yosemite National Park, USA Science, 322 (5899), 261-264 DOI: 10.1126/science.1163428

Tuesday, November 17, 2009

A Gopher Tortoise in my Email...

Below are a couple of pictures emailed to me today by Lisa, a wildlife enthusiast and fellow Floridian. She took them this morning on her farm in central Florida.

I guess her horse had invited a neighbor over for breakfast..?

-Thanks Lisa, great shots!

The gopher tortoise, Gopherus polyphemus, is a large terrestrial turtle having forefeet well adapted for burrowing, and elephantine hind feet. The front legs have scales to protect the tortoise while burrowing. Body length averages approximately 25 cm (10 inches), with the shell ranging in height from 15 – 37 cm (6 – 15 inches). Body mass averages approximately 4 kg (9 pounds). Color is a dark brown to gray-black, with a yellow plastron (bottom shell). A gular projection is evident on the anterior...

You can find additional gopher tortoise info on the August 10th post - The Threatened Gopher Tortoise

Joseph Grinnell, Climate Change and the Legacy of the California Thrasher

Adaptive plasticity is a predictor of future reproductive fitness. The ability of an organism to confront ever-shifting environmental attributes with resilience and flexibility is critical to maintaining lineages with the capacity to undergo the morphological and behavioral modifications required for continued survival. Regardless if such elastic traits are realized through major swings in ontogenic development, or through the advent of novel life-history strategies, the ability of an organism to accommodate ecological variability is essential. This biological tenet is certainly true today as anthropogenically incited climate change is forcing accelerated rates of ecological alteration.

The Intergovernmental Panel on Climate Change has reported that mean global temperatures could increase by more than six-degrees over the course of the next century. Six degrees of global change translates to extremely dramatic transformations of biotic and abiotic conditions at the local level. Even if the ‘worse case scenario’ of six-degrees doesn’t come to pass changes in hydrology, periodic weather, seasonal patterns, emigration, extinction and in the availability of resources at regional and local levels are almost certainly inevitable during the next century. To cope with these changes it will be necessary for organisms to adjust their tolerances to environmental variability, they may need to more-efficiently utilize the resources on-hand, or they may need to physically relocate to habitats for which they are better suited. To better understand how these impending organism-to-environment adjustments will occur, it's important to seek understanding as to how organisms fit into their ecosystem. It is the relative position of an organism in its environment and the way in which it behaviorally responds to its surroundings that is referred to as the organism’s ‘niche’.

With respect to etymology, the word ‘niche’ is derived from the French word ‘nicher’ which literally means ‘to nest,’ as in a bird going to nest. In regards to the word’s use in biology – broadly defined above - this literal translation is very appropriate, because the term was first introduced by an ornithologist in a publication describing the distribution of a bird - the California thrasher (Toxostoma redivivum).

The California thrasher is the largest member of the Mimidae Family and can grow to be uupwards of 30 cm in length and weigh as much as 85 grams. The bird’s coloration is fairly non-descript; its body is brown and it has a tan or buff-colored ventral side. There are however a couple of characteristics that make T. redivivum especially unique. One is the bird's restriction to a very narrow geographic range in California, and another is its habitat preference for densely vegetated brushlands. It was the thrasher’s limited distribution and fondness for the concealment offered by shrubs that first attracted the interest of the celebrated naturalist and scientist Joseph Grinnell.

In the October 1917 issue of The Auk, Joseph Grinnell published his work 'The Niche-Relationships of the California Thrasher'. In that enduring contribution Grinnell explained that the reason for the thrasher’s

“…restricted distribution is probably to be found in the close adjustment of the bird in various physiological and psychological respects to a narrow range of environmental condition.”

In other words, Grinnell clearly recognized that the bird’s morphological and behavioral traits linked it to the specific ecosystem that it inhabited. Furthermore, Grinnell identified that

“[t]hese various circumstances, which emphasize dependence upon cover, and adaptation in physical structure and temperament thereto, go to demonstrate the nature of the ultimate associational niche occupied by the California Thrasher.”

In Grinnell’s mind, the relative position of the thrasher in its environment, as well as its distinctive behaviors, established a general rule that could be extrapolated and used as a tool for detailing and predicting the spatial and temporal relationships held between organisms and their environments. The ‘niche’ would quickly become a tool for not only itemizing individual life-history traits, but also for interpreting the evolutionary and adaptive implications of the organism-to-environment dynamic.

Building on his idea of an ecological niche, in July of 1924 Grinnell went on to publish ‘Geography and Evolution,’ a work in which he fathered what are contemporarily known as the competitive exclusion principle and the concept of ‘vacant niches.’

“Some of us have concluded that we can usefully recognize, as measures of distributional behavior, the realm, the region, the life-zone, the fauna, the subfauna, the association, and the ecologic or environmental niche. The latter, ultimate unit, is occupied by just one species or subspecies; if a new ecologic niche arises, or if a niche is vacated, nature hastens to supply an occupant, from whatever material may be available. Nature abhors a vacuum in the animate world as well as in the inanimate world.”

The competitive exclusion principle is the idea that two species occupying the same habitat and fighting for the same resources will not obtain equilibrium until one species overcomes, or out-competes, the other. These ideas are front-and-center to modern biology and are both credited to Grinnell.

Serving as the founding father of the ‘niche’ was but one of Joseph Grinnell’s numerous contributions to science. Over the next couple of days I hope to post more of Grinnell’s work, as well as that of his modern counterparts that are – literally – following in Grinnell’s footsteps in hopes of gaining insight into how the observations of an early 20th Century scientist can be used to decode the effects of climate change in a 21st Century world.

UPDATE: The second part of this post available HERE.

Joseph Grinnell (1917). The Niche-Relationships of the California Thrasher The Auk, 34 (4), 427-433

Joseph Grinnell (1924). Geography and Evolution Ecology, 5 (3), 225-229

Monday, November 16, 2009

Jack Horner on Dino-Chickens

Another short clip from a Jack Horner interview that appeared on CBS's 60-minutes last night. This one touches on the possibility of reverse-engineering chickens to create a dinosaur (or, dinosaur-like critter).

The Evo-devo clip with Sean Carroll (previous post) is from the same broadcast.

Watch CBS News Videos Online

Sunday, November 15, 2009

Prime Time Evo Devo with Sean Carroll

Sean Carrol Talking Evo Devo on 60-Minutes

Watch CBS News Videos Online

Saturday, November 14, 2009

Dead Zones, Conservation and Commercial Fishing

I’ve just read in the local news that Kevin Craig from the Florida State University’s Coastal and Marine Laboratory will be heading-up a collaborative four-year project funded by NOAA's Northern Gulf of Mexico Ecosystem and Hypoxia Assessment Program. The project’s goal is to assess the impact of the Gulf of Mexico’s ‘dead zone’ on marine ecosystems with a particular focus on shrimp and the shrimping industry.

It has long been known that agricultural run-off carrying excesses of fertilizer from the ‘bread basket’ of the United States are finding their way into the tributaries of the Mississippi River, and in turn, into the Gulf of Mexico. Once in the Gulf they consequently spawn explosions of algae growth resulting in hypoxic conditions and the conception of massive Dead Zones. Surges in the growth of algae and other noxious plants as a product of fertilizer facilitated Nitrogen and Phosphorous loading is called eutrophication. Eutrophication leads to de-oxygenated environments, and the resultant death of those organisms that require oxygen - of which there are many. The loss of oxygen-dependent organisms leaves vacant important positions in long established food-webs, potentially leading to the total breakdown of ecosystem function. To make matters worse, far from being stationary the dead zones move or “creep” from their epicenters corrupting ecosystems both far and wide. For Florida, the Gulf of Mexico Dead Zone may contribute to “Red Tide” and the death of everything from phytoplankton to manatees in the State’s coastal waters.

Kevin Craig is certainly the person for the job; back in 2005 he wrapped-up a research project that examined the effects of hypoxia on the abundance and distribution of Farfantepenaeus aztecus - the Gulf of Mexico’s ‘brown shrimp’. In that study, Craig, Larry Crowder, and Tyrrell Henwood used shrimp trawl surveys to compare the distributions of shrimp between hypoxic and non-hypoxic areas. What the team found was that the spatial distribution of shrimp in hypoxic regions was substantially different that those associated with non-hypoxic areas. The researchers also concluded that the effects of hypoxia contributed to as much as a 25% loss in F. aztecus’s available habitat.

The new NOAA funded project will undoubtedly have implications for both the science of ecology and in that of conservation. Shrimping is a major industry in the United States, and as such the participating fishermen and other commercial industries hold considerable economic and political clout. I'm eerily reminded of the warnings from biologists that were left unheeded and initially overthrown by rule-makers during the collapse of the Northern Cod Fishery…

Craig, J., Crowder, L., & Henwood, T. (2005). Spatial distribution of brown shrimp (Farfantepenaeus aztecus) on the northwestern Gulf of Mexico shelf: effects of abundance and hypoxia Canadian Journal of Fisheries and Aquatic Sciences, 62 (6), 1295-1308 DOI: 10.1139/f05-036

Friday, November 13, 2009

Wetland Plant of the Week #32

Aster carolinianus

Climbing Aster

Climbing aster, unlike the majority of the other varieties in the genus (which are herbaceous), presents as a many branched shrub with a woody stem base and often even woody branches. The Obligate plant displays numerous leaves that range from elliptic to lanceolate in shape. The flowers are typically about an inch in diameter and generally have a light-blue or light-purple color.

Aster carolinianus is native to the coastal plain of the southeastern United States and is often found residing in marshes, along stream banks and - as pictured above - in freshwater swamps.

As a characteristic trait, the climbing aster has the habit of entangling itself in the branches of surrounding plants, or even tying itself in large tousled masses.

Asterales, the order to which the Asteraceae family belongs, has origins in the Cretaceous period about 100 million years ago and probably experienced diversification during the Oligocene and Miocene. In regards to their evolutionary past, recent research by Tom Viaene (et al) examined the variability of stamen and petal morphologies within the basal asterid families. Through comparisons of the genes that coded for these floral structures, he determined that the early members of the asterid group likely duplicated the petal and stamen genes as a strategy for moving into a wider range of niches.

The above images were taken last week near St. Marks National Wildlife Refuge in northern Florida.

Viaene, T., Vekemans, D., Irish, V., Geeraerts, A., Huysmans, S., Janssens, S., Smets, E., & Geuten, K. (2009). Pistillata--Duplications as a Mode for Floral Diversification in (Basal) Asterids Molecular Biology and Evolution, 26 (11), 2627-2645 DOI: 10.1093/molbev/msp181

Thursday, November 12, 2009

Fire Ecology Marathon; Nature Red in Tooth and Flame Part-4

The savannas of the southeastern United States are inimitable natural communities that have undergone ecological assembly in the presence of seasonal fire cycles and, as discussed during the first three installments on this topic (available here; Part-1, Part-2, Part-3), are rich in organisms capable of manipulating the regularity, movement and intensity of these wildfires. During the preceding post (Part-3) the phenotypes of two such fire-born species, the longleaf and slash pines, were detailed as exemplars of organisms with traits that not only aid in defending against heat and flame, but also as species that exhibit specific physical structures, chemicals and behaviors that could intrinsically promote fire. In closing that previous discussion, consideration was given to the possible motives behind the longleaf and slash pine’s ability to deliberately provoke fire.

Though it may initially seem to be counterproductive or even a hindrance to survival, through promoting fires the savanna pines obtain benefits that directly enhance their inclusive fitness. Because of the processes that drove the organismal evolution of the longleaf and southern slash pines in geological time, and the processes that propelled community assembly in savannas, the presence of wildfires effectively created a duality in the character of potential pine competitors and that of would-be savanna inhabitants - either they can tolerate fire, or they can’t tolerate fire.

In the absence of wildfires over extended periods of time (i.e. fire suppression) several ecological changes can occur in savannas. Most profoundly, without regular wildfires not only would the already present fire-tolerant plant species survive, but in addition, fire-intolerant species would experience greater fecundity. Without the deterrence provided by fire, resource-rich savannas can quickly become the envy of plants from surrounding hammocks and mixed hardwood forests, thus encouraging invasion and recruitment from these neighboring communities. Such movement of new species into the savannas would contribute to substantial ecological alteration of the natural processes that maintain the system’s predictable boundaries, ecotones and makeup.

Recall from Part-1 of this post that the plants found in hammocks have undergone selection for initial rapid growth and direct competition for sunlight. Just as the natural history of the pines has been shaped by fire, the history of dense-canopy species have evolved to fight for radiance. If unobstructed access to the abundant savanna sun is tantalizingly flaunted, these species would quickly invade, rapidly recruit and hurriedly regenerate to overtake all biologically available space. What was initially a patchwork of invasive species would spread to encompass and overcrowd the savanna, in the process reducing the diversity of appropriate groundcover plants, and adversely impacting the reproductive success of the native inhabitants – slash and longleaf fitness would decline.

In addition to increasing interspecific competition in the savannas, invasive species also create positive feedbacks in the wildfire cycle - magnifying fire suppression. The presence of abundant shrubs and woody species in a normally open savanna formulate densely vegetated landscapes that reduce fine fuel loads on the ground and decrease the likelihood of fire propagation. The lack of fire - in turn - facilitates further invasions, which increases vegetative densities even more, which reduces fire even more, which allows for yet greater invasive proliferation, etcetera…

With continued fire suppression, what was once a savanna, characterized by thinly distributed trees, would transition towards a densely canopied hammock with an impenetrable thicket understory. Growing populations of invasive species would amplify competition for resources, thus pushing the fitness experienced by the longleaf and southern slash pines to dangerously low values. This is precisely why the ‘fire gene’ is so critically important to the pine’s genotype. As crowding increases in this scenario, and essential resources dwindle, hormonal stress responses within the pines intensify. The hormones drive physiological changes in the trees causing leaves to drop and internal hydrocarbon chemistry to move toward increased combustibility. The probability for fire is increased. And, when fire does return, the stems, branches, leaves and roots from newly arrived invasives will serve as kindling for augmented wildfire intensity - to such extremes that only the hardiest of the fire-tolerant will be able to survive.

For clarification, conceptual genes (like the ‘fire gene’) aren’t confirmed as actual chromosomal localities for which variable alleles compete. Rather, conceptual genes are offered as thought-tools for understanding the premise that natural selection operates on phenotypical traits that are the products of genotypical coding. In regards to the ‘fire gene’ specifically, it is a hypothetical genetic compliment that is expressed in such a manner that the physical presence of fire improves the likelihood of that genotype being passed on to future generations. In other words, if a population of trees exist in which some members have a genotype that provides increased fitness in the presence of fire, AND that population is then exposed to fire - ultimately killing a certain percentage of the population - those trees with fire gene advantage will experience higher survivability and greater measures of fecundity compared to those not possessing a fire gene.

Returning to the savanna pines expressly, irregardless or not if there is literally a single gene that provides for all of the phenotypical adaptations to fire described throughout this post, or if these traits are the result of a cooperative epistasis, or if the characters are disparate and independent, it remains likely that their occurrence and continued propagation through evolutionary time has provided a significant advantage.

Through 300 million years of natural selection, wildfires have propelled the savanna defending pines to levels of adaptation in which they are capable of wielding fire. ‘Nature, red in tooth and flame’ has fashioned a true ecosystem engineer, one that is capable of establishing and defending the ecotonal boundaries between natural communities.

Beckage, B., Platt, W., & Gross, L. (2009). Vegetation, Fire, and Feedbacks: A Disturbance‐Mediated Model of Savannas The American Naturalist, 174 (6), 805-818 DOI: 10.1086/648458

Stevens, J., & Beckage, B. (2009). Fire feedbacks facilitate invasion of pine savannas by Brazilian pepper New Phytologist, 184 (2), 365-375 DOI: 10.1111/j.1469-8137.2009.02965.x

Wednesday, November 11, 2009

Ecosytem Engineering and Fire Ecology, Part 3

The closing paragraph of ‘Nature, Red in Tooth and Flame Part-2’ mentioned how extrinsic factors in the environment, such as the presence of increased atmospheric oxygen and an abundance of herbaceous plants to serve as fuel, collectively worked to generate frequent and intense wildfires during the Pennsylvanian Period approximately 300 million years ago. It was the presence of these Carboniferous wildfires that positively selected fire-tolerant gymnosperm species for continued development, and initiated their adaptive radiation towards the representative pine trees that occupy the modern-day savannas in the southeastern United States. It is within contemporary savannas that the longleaf pine (Pinus palustris) and the southern slash pine (Pinus elliottii var. densa) express their fiery ancestry; however, the fire ecology observable in these natural communities isn’t limited to wildfires born of purely extrinsic factors. Through, evolution the longleaf and slash pines have developed the ability to intrinsically influence the movement of fire, and they have learned to use this powerful tool as an instrument for customized ecosystem engineering.

During the description of savanna communities in Part-2, it was detailed that the canopies of these systems exist in an open condition that allows for ample access to sunlight by a diverse range of groundcover plants. Ample sunlight, water and soil nutrients can all be found in savannas. So, considering the occurrence of these botanical prerequisites, compounded with the highly competitive, almost war-like, tendencies of nature (as elaborately described in Part-1), one might wonder why trees from the hammocks don’t advance to occupy the promising and resource-rich savannas… The reason for the limited progress of hammock trees in moving to the savannas is that invasions are tightly controlled by the few trees already inhabiting the systems – the few trees usually being longleaf and slash pine.

An open canopy is a characteristic physiognomy of savannas precisely because the ground gaining charge of closed-canopy trees is impeded by the heirs of the Carboniferous gymnosperms. Said differently, the trials-by-fire endured by the antecedents of the modern-day conifers have shaped the phenotypes of the savanna-defending longleaf and southern slash pines. Furthermore, the phenotypes shown by the longleaf and slash pine reach outward to encompass the savanna as a whole, where these phenotypes serve as catalysts for engineering ecosystem towards one purpose – making more pine trees.

The longleaf and southern slash pine exhibit a host of morphological features that facilitate their continued manipulation of fire. For instance, both of these trees have thickly armored plates of bark on the exterior of their trunks; like fire-retardant shields, the plates guard the tree's interrior tissues against excessive heat and all but the most intense of wildfires. Similarly, the undifferentiated cells (meristematic cells) found within the trees, the ones that make-up the growth tissue found in meristems, are safeguard by a casing of heat resistant scales. And, as opposed to a pattern of wide lateral spreading, the roots of the slash and longleaf trees penetrate perpendicularly downward, where they are sheltered from harsh surficial temperatures. These are but a small number of the morphological – anatomical – traits displayed by the fire-scaping pines; their reproduction and growth habits give additional clues as to their natural history.

The reproductive cycle of the longleaf and southern slash pine include strategies that take into account the recurring spring fires described in Post-2; by germinating in the fall and occasionally producing periodic mast crops, young pines are afforded several months of growth before the first ravages of wildfire arrive. In spite of the head start gained through fall germination, the longleaf and slash pine don’t approach growth from a mere lackadaisical standpoint, quite the contrary, both trees posses the ability to quickly establish themselves. Just as the most successful plants of a closed canopy hammock battling for access to solar radiation (see the ‘competition for sunlight’ example provided in Part-1), the savanna pine trees – in addition to a ‘fire gene’ – also hold in their genetic arsenal a ‘rapid growth gene.’ Slash pine, for instance, has a genetic compliment that permits the tree to take advantage of every opportunity to seize real estate; once germinated, it rapidly shoots upward expressing secondary needles in less than six month’s time, and by the time it is two-years old, it is able to survive a wildfire of ‘average' intensity.

The above characteristics depict but a few of the intrinsic phenotypes that improve the survivability and reproduction of the savanna dwelling pines in the presence of fire; but what is truly remarkable is the trees’ ability to channel fire directly – the trees’ ability to shape their ecosystem through offensive tactics.

In addition to the defensive phenotypes of the savanna pines, the chemistry of their leaves (i.e. pine needles) have undergone adaptation such that while on the tree, the leaves produce flame resistant chemicals, but when the leaves are shed, their chemical consistency changes to achieve an altogether different effect - they become flammable and easily ignited. As the leaves are shed from branches, they fall to the ground where they accumulate around the circumference of the trees. The piled pine needles are composed of cellulose-laden fibers, which unlike the fire-resistant lignin that evolved during the Paleozoic, serve as excellent fuel for fires. So when on the tree, the pine needles are similar to the armored plates found on the trunks, they help defend against tissue damage when exposed to wildfire; but, in the absence of recurrent fire, the leaves are quickly dropped and their chemistry changes to promote fire. Moreover, pine leaves aren’t the only fire stoking property of the savanna pines. The very structure of the pine’s thin and supra-numerous branches can facilitate the spreading of fire (horizontally and vertically) through increasing the surface area of exposed tissues to flame. And, the flammable hydrocarbons produced in the plant’s resins can incite wildfires or encourage lightening strikes to take hold (for example, the terpenes produced by the conifers in question; think ‘turpentine’).

Though it may initially seem to be counterproductive, or a hindrance to survival, through promoting fires the savanna pines obtain benefits that actually enhance inclusive fitness….

[Continue HERE, PART-4.]

Beckage, B., Platt, W., & Gross, L. (2009). Vegetation, Fire, and Feedbacks: A Disturbance‐Mediated Model of Savannas The American Naturalist, 174 (6), 805-818 DOI: 10.1086/648458

Stevens, J., & Beckage, B. (2009). Fire feedbacks facilitate invasion of pine savannas by Brazilian pepper New Phytologist, 184 (2), 365-375 DOI: 10.1111/j.1469-8137.2009.02965.x