This video relates to the coral bleaching post made yesterday - Resilience in Acropora Corals
Margaret Wertheim: The beautiful math that links coral, crochet and hyperbolic geometry
Jesus ‘n’ Mo ‘n’ the Zionist agenda
9 hours ago
Showing posts with label Climate. Show all posts
Showing posts with label Climate. Show all posts
Saturday, April 25, 2009
Friday, April 24, 2009
Resilience in Acropora Corals
Great news - local management of water quality and other factors may significantly contribute to the survivability of coral reefs that have been negatively impacted by climate change.
A massive bleaching event took place on the Great Barrier Reef approximately three years ago and devastated a huge number of inshore reefs, but the Acropora corals made an unprecedented comeback – in only a year’s time!
A massive bleaching event took place on the Great Barrier Reef approximately three years ago and devastated a huge number of inshore reefs, but the Acropora corals made an unprecedented comeback – in only a year’s time!
According to Guillermo Diaz-Pulido, three critical factors contributed to this unprecedented turn around, “first was exceptionally high re-growth of fragments of surviving coral tissue. The second was an unusual seasonal dieback in the seaweeds, and the third was the presence of a highly competitive coral species, which was able to outgrow the seaweed. But this also all happened in the context of a well-protected marine area and moderately good water quality.”
Sophie Dove of the Centre for Marine Studies and Australian Research Council Centre of Excellence for Coral Reef Studies points-out that, “The exceptional aspect was that corals recovered by rapidly regrowing from surviving tissue. Recovery of corals is usually thought to depend on sexual reproduction and the settlement and growth of new corals arriving from other reefs. This study demonstrates that for fast-growing coral species asexual reproduction is a vital component of reef resilience.”
Sophie Dove of the Centre for Marine Studies and Australian Research Council Centre of Excellence for Coral Reef Studies points-out that, “The exceptional aspect was that corals recovered by rapidly regrowing from surviving tissue. Recovery of corals is usually thought to depend on sexual reproduction and the settlement and growth of new corals arriving from other reefs. This study demonstrates that for fast-growing coral species asexual reproduction is a vital component of reef resilience.”
Coral recovery following algal overgrowth
(Images from Artcle)
Branches of Acropora corals died after bleaching and were subsequently colonized by a variety of benthic algae. Remnant coral tissue at the base of the coral colonies regrew upward and deposited new skeleton along the old dead coral branch, overgrowing
Branches of Acropora corals died after bleaching and were subsequently colonized by a variety of benthic algae. Remnant coral tissue at the base of the coral colonies regrew upward and deposited new skeleton along the old dead coral branch, overgrowing
A) algal turfs (arrows). B) fleshy seaweed Lobophora variegata.
C) crustose coralline algae. D) Coral tissue has all but completely overgrown the colonizing algae.
E) Thin section of coral showing benthic algae sandwiched between old coral skeleton and a thin layer of new skeleton. Examination using a compound microscope showed that coral tissue overgrew a range of algal types.
Ove Hoegh-Guldberg of CoECRS and The University of Queensland suggests, “...that managing local stresses that affect reefs such as overfishing and declining water quality can have a big influence on the trajectory of reefs under rapid global change.”
Read the Article from PLoS One - HERE
Diaz-Pulido, G., McCook, L., Dove, S., Berkelmans, R., Roff, G., Kline, D., Weeks, S., Evans, R., Williamson, D., & Hoegh-Guldberg, O. (2009). Doom and Boom on a Resilient Reef: Climate Change, Algal Overgrowth and Coral Recovery PLoS ONE, 4 (4) DOI: 10.1371/journal.pone.0005239
Sunday, April 19, 2009
The Fire Gene Described
A lengthy introduction during the initial post on this topic (available Here) contrasted a harmonious view of nature with the perspective of nature as a series of oppositional organisms struggling to gain a competitive edge over rivals. As a model of this outlook, the ecotone boundaries between various sets of differing plant communities were offered as a case study. More specifically, the prairie, savanna and hardwood hammock ecosystems of the Big Cypress Preserve were forwarded along with the proposition that members of these communities actively challenged each other for limited resources. In staging this proposition the question was asked, “Why don’t trees invade - and take over – the prairie communities currently occupied by grasses?” After eliminating the likelihood that densely growing stands of grass crowded-out young saplings by denying them access to sunlight, cyclic wildfire were explained and presented as an alternative explanation. Moving forward with this production, a profile of one of the previously introduced characters is in order – the conifer tree Pinus elliotti.
Slash Pine Growing from a Log
Slash Pine is a species of the genus Pinus (pine tree) which branched from genus Picea (spruce tree) during the Cretaceous Period, somewhere between 87 and 193 million years ago. There are two distinct varieties of slash pine, variety elliotti and variety densa, although there are several important distinctions, for purposes here both varieties can be considered one and the same. Pine and spruce trees are grouped together with cycads, gnetophytes and ginkgo as gymnosperms, which had a start back in the Pennsylvanian Period of the Carboniferous more than 300 million years ago. The long history of the pine trees, and the slash pine in particular, is significant because these trees have one of the largest and most complex genomes of any organism on the planet today – a result of varied evolutionary forces. Of specific interest in regards to evolutionary history is that gymnosperms arose from the Carboniferous swamps during a period of rapid plant adaptation. In addition to the advent of the bark fiber “lignin,” plants during that period underwent a multitude of morphological changes - many of these changes were adaptations to wildfire. Unlike the 21% atmospheric oxygen present today, the carboniferous boasted 35% oxygen content, this in conjunction with an abundance of herbaceous material (remember Carboniferous = “coal age”) resulted in frequent – and intense – wildfires.
Wildfires…
So, do wildfires prevent trees, such as slash pine, from invading prairie strongholds held by grasses? Not really, some especially intense (“intensity” being a measure of a fire’s maximum temperature and duration) wildfires may destroy slash pine, but fires capable of doing so are relatively rare. The typical “fire seasons,” as described in the first post, may have sufficient intensity to kill some young saplings, but remember - slash pines also have “initial rapid growth genes” which provide a solid head start in defending themselves. Essentially, any sapling greater than two years old has a good chance of getting through the “average” wildfire. As for the periodic “non-average” wildfire, one that is of an unusually high intensity, slash pines may need to rely on evolutionary adaptations other than “initial rapid growth genes” – they may need to lean on morphological phenotypes resulting from a “fire gene.”
A fire gene is a genetic compliment possessed by an organism that is expressed in such a manner that the presence of fire improves the likelihood of that genotype being passed on to future generations. In other words, if a population of trees exists in which some members have a genotype that provides phenotypical resistance to fire, and that population is then exposed to fire, killing a certain percentage of the population, those trees with fire gene advantage will have higher survivability and greater measures of fitness than will those not possessing a fire gene. Through this process of “selection by fire,” the fire gene would become more prevalent in the population, eventually becoming so common as to be called characteristic.
This is precisely what has occurred with the pine trees of the Big Cypress. Through millennia of “trial by fire,” only those trees expressing the most fire tolerant phenotypes have survived. Morphological features such as thickly armored plates of bark shield the trunk from heat, scale plated meristems guard against flames and the pine’s reproductive strategies take into account spring fires by germinating in the fall and producing periodic mast crops. However, these products of natural selection are merely defenses, what is truly remarkable is that another aspect of the fire gene contributes to offensive maneuvers.
As a thought experiment only, image being a tree with the cognitive function of a human and the knowledge that you have an inherit resistance to fire; a resistance that many of your competitors do not posses. If locked in a battle for survival, and you had a match in hand, (or rather, a match in “branch”) would you start a fire?
Of course, matches are of little use to trees outside of thought experiments, but what if there was an adaptation that would provide not only defense, but also allow trees to harness naturally occurring fires to their advantage? Genes don’t exist in isolation; frequently they form partnerships to gain mutual advantage. Epistasis, the interaction between genes, has occurred in pine trees to accomplish the same goal. Not only do the trees have defensive morphologies, they have also adapted the chemistry of their leaves (i.e. pine needles) such that while on the tree the leaves produce flame resistant chemicals, but when wildfires are absent for extended periods of time leaf chemistry changes. In the absence of wildfires leaves are randomly shed, accumulate in the area around the tree and - as opposed to being flame retardant - they become easily ignited at low temperatures and burn at an intensity that, well… An intensity that only a slash pine would love…
Some fires do adversely affect slash pine, but the presence of a “fire gene” provides both defensive and offensive adaptations that can –and have been – utilized to survive. So, why don’t trees such as slash pines invade prairies? It’s a “one-two punch.” Through heat stressing the trees, fires slow down advancing slash pines; however it is what happens after the fire season that stops them cold in their tracks – flooding. Summer rains pile on additional stress to what has already accumulated due to fire defense investment. Grasses are in the same boat, but due to a better water tolerance they can bounce back more readily. The slash pine can survive fires or flood, but taken together these two modes of environmental disturbance overwhelm the trees and limit their prairie-ward charge. This is, however, a function of seasonality, climate and cyclic wildfires; with climate change and alteration of these natural processes all bets are off. (But that’s a topic for another time…)
Beckage, B., Gross, L., & Platt, W. (2006). Modelling responses of pine savannas to climate change and large-scale disturbance Applied Vegetation Science, 9 (1) DOI: 10.1658/1402-2001(2006)9[75:MROPST]2.0.CO;2
Nordlund, D., & Lewis, W. (1976). Terminology of chemical releasing stimuli in intraspecific and interspecific interactions Journal of Chemical Ecology, 2 (2), 211-220 DOI: 10.1007/BF00987744
Morse, A., Peterson, D., Islam-Faridi, M., Smith, K., Magbanua, Z., Garcia, S., Kubisiak, T., Amerson, H., Carlson, J., Nelson, C., & Davis, J. (2009). Evolution of Genome Size and Complexity in Pinus PLoS ONE, 4 (2) DOI: 10.1371/journal.pone.0004332
Platt, W. J., J. M. Huffman, M. G. Slocum, and B. Beckage. In press. Fire regimes and trees in Florida dry prairie landscapes. In: Noss, R. & Singh, S. (eds.) Land of fire and water: The Florida dry prairie ecosystem. Avon Park Air Force Range and Department of Defense, Avon Park, FL,
US.Kabrick, John M.; Dey, Daniel C.; Gwaze, David, eds. Shortleaf pine restoration and ecology in the Ozarks: proceedings of a symposium; 2006 November 7-9; Springfield, MO. Gen. Tech. Rep. NRS-P-15. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station: 28-32.
Slash Pine Growing from a Log
Slash Pine is a species of the genus Pinus (pine tree) which branched from genus Picea (spruce tree) during the Cretaceous Period, somewhere between 87 and 193 million years ago. There are two distinct varieties of slash pine, variety elliotti and variety densa, although there are several important distinctions, for purposes here both varieties can be considered one and the same. Pine and spruce trees are grouped together with cycads, gnetophytes and ginkgo as gymnosperms, which had a start back in the Pennsylvanian Period of the Carboniferous more than 300 million years ago. The long history of the pine trees, and the slash pine in particular, is significant because these trees have one of the largest and most complex genomes of any organism on the planet today – a result of varied evolutionary forces. Of specific interest in regards to evolutionary history is that gymnosperms arose from the Carboniferous swamps during a period of rapid plant adaptation. In addition to the advent of the bark fiber “lignin,” plants during that period underwent a multitude of morphological changes - many of these changes were adaptations to wildfire. Unlike the 21% atmospheric oxygen present today, the carboniferous boasted 35% oxygen content, this in conjunction with an abundance of herbaceous material (remember Carboniferous = “coal age”) resulted in frequent – and intense – wildfires.
Wildfires…
So, do wildfires prevent trees, such as slash pine, from invading prairie strongholds held by grasses? Not really, some especially intense (“intensity” being a measure of a fire’s maximum temperature and duration) wildfires may destroy slash pine, but fires capable of doing so are relatively rare. The typical “fire seasons,” as described in the first post, may have sufficient intensity to kill some young saplings, but remember - slash pines also have “initial rapid growth genes” which provide a solid head start in defending themselves. Essentially, any sapling greater than two years old has a good chance of getting through the “average” wildfire. As for the periodic “non-average” wildfire, one that is of an unusually high intensity, slash pines may need to rely on evolutionary adaptations other than “initial rapid growth genes” – they may need to lean on morphological phenotypes resulting from a “fire gene.”
A fire gene is a genetic compliment possessed by an organism that is expressed in such a manner that the presence of fire improves the likelihood of that genotype being passed on to future generations. In other words, if a population of trees exists in which some members have a genotype that provides phenotypical resistance to fire, and that population is then exposed to fire, killing a certain percentage of the population, those trees with fire gene advantage will have higher survivability and greater measures of fitness than will those not possessing a fire gene. Through this process of “selection by fire,” the fire gene would become more prevalent in the population, eventually becoming so common as to be called characteristic.
This is precisely what has occurred with the pine trees of the Big Cypress. Through millennia of “trial by fire,” only those trees expressing the most fire tolerant phenotypes have survived. Morphological features such as thickly armored plates of bark shield the trunk from heat, scale plated meristems guard against flames and the pine’s reproductive strategies take into account spring fires by germinating in the fall and producing periodic mast crops. However, these products of natural selection are merely defenses, what is truly remarkable is that another aspect of the fire gene contributes to offensive maneuvers.
As a thought experiment only, image being a tree with the cognitive function of a human and the knowledge that you have an inherit resistance to fire; a resistance that many of your competitors do not posses. If locked in a battle for survival, and you had a match in hand, (or rather, a match in “branch”) would you start a fire?
Of course, matches are of little use to trees outside of thought experiments, but what if there was an adaptation that would provide not only defense, but also allow trees to harness naturally occurring fires to their advantage? Genes don’t exist in isolation; frequently they form partnerships to gain mutual advantage. Epistasis, the interaction between genes, has occurred in pine trees to accomplish the same goal. Not only do the trees have defensive morphologies, they have also adapted the chemistry of their leaves (i.e. pine needles) such that while on the tree the leaves produce flame resistant chemicals, but when wildfires are absent for extended periods of time leaf chemistry changes. In the absence of wildfires leaves are randomly shed, accumulate in the area around the tree and - as opposed to being flame retardant - they become easily ignited at low temperatures and burn at an intensity that, well… An intensity that only a slash pine would love…
Some fires do adversely affect slash pine, but the presence of a “fire gene” provides both defensive and offensive adaptations that can –and have been – utilized to survive. So, why don’t trees such as slash pines invade prairies? It’s a “one-two punch.” Through heat stressing the trees, fires slow down advancing slash pines; however it is what happens after the fire season that stops them cold in their tracks – flooding. Summer rains pile on additional stress to what has already accumulated due to fire defense investment. Grasses are in the same boat, but due to a better water tolerance they can bounce back more readily. The slash pine can survive fires or flood, but taken together these two modes of environmental disturbance overwhelm the trees and limit their prairie-ward charge. This is, however, a function of seasonality, climate and cyclic wildfires; with climate change and alteration of these natural processes all bets are off. (But that’s a topic for another time…)
Beckage, B., Gross, L., & Platt, W. (2006). Modelling responses of pine savannas to climate change and large-scale disturbance Applied Vegetation Science, 9 (1) DOI: 10.1658/1402-2001(2006)9[75:MROPST]2.0.CO;2
Nordlund, D., & Lewis, W. (1976). Terminology of chemical releasing stimuli in intraspecific and interspecific interactions Journal of Chemical Ecology, 2 (2), 211-220 DOI: 10.1007/BF00987744
Morse, A., Peterson, D., Islam-Faridi, M., Smith, K., Magbanua, Z., Garcia, S., Kubisiak, T., Amerson, H., Carlson, J., Nelson, C., & Davis, J. (2009). Evolution of Genome Size and Complexity in Pinus PLoS ONE, 4 (2) DOI: 10.1371/journal.pone.0004332
Platt, W. J., J. M. Huffman, M. G. Slocum, and B. Beckage. In press. Fire regimes and trees in Florida dry prairie landscapes. In: Noss, R. & Singh, S. (eds.) Land of fire and water: The Florida dry prairie ecosystem. Avon Park Air Force Range and Department of Defense, Avon Park, FL,
US.Kabrick, John M.; Dey, Daniel C.; Gwaze, David, eds. Shortleaf pine restoration and ecology in the Ozarks: proceedings of a symposium; 2006 November 7-9; Springfield, MO. Gen. Tech. Rep. NRS-P-15. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station: 28-32.
Saturday, April 18, 2009
The Fire Gene: One Organism’s Ability to Exploit Fire
Gazing across the tranquil landscape of the Big Cypress Preserve, nature seems to be in balance, unchanging and at peace - picturesque beyond any poetic description. Here, anthropogenic throngs of sharply angled concrete and glass edifices suspend their battle for roadside dominance and yield themselves to a sea of sparsely treed savanna, rolling prairies of grass, and randomly scattered islands of thickly vegetated hammocks; the perfect environment for a relaxing stroll, a picnic, or even a quick nap. All may appear calm within this enchanting panorama; however, the perceived tranquility is but a chimera. A mere illusion of serenity resulting from shortfalls in the ability of Homo sapiens’ photoreceptors to see beyond the narrow range of the electromagnetic spectrum called visible light, an inability to hear sound outside of 22000 Hertz, and the failure of the human olfactory system to nose its way into the vast chemo-landscape of pheromones and other volatile chemicals in which it is continuously assailed. If the sensory apparatus of Homo sapiens was keener - more finely calibrated – the landscape of the Big Cypress would appear very different.
Very different indeed, imagine the ecological interplay that could be interpreted if humans could see ultraviolet light through the eyes of a bee, smell pheromones from six-miles’ distance like a moth, or interpret chemical stimuli through soil like a plant… Far from serene, if viewed through time, adaptive maneuvers, survival strategies and arms races would be manifest in every action undertaken by the immense diversity of organisms on Earth. If these actions could be viewed more directly, the landscape would appear saturated with war. Even the plant community boundaries which demarcate prairie from savanna from hammock in the above described landscape are maintained by way of fierce battles waged over evolutionary time. These ecosystems, which appear stable and so pleasingly haphazardly scattered, are in fact tightly ordered armies of competing plants struggling for resources and existence. In these recurrent ecotonal conflicts one species has honed a new weapon – it has adapted to exploit the power of fire.
Naturally existing plant communities exist in a continuum of ecosystems which through evolution have adapted to almost every available habitat on the planet; from “box thorns” (Lycium pallidum) in Death Valley to fully aquatic hyacinths (Eichhornia paniculata) floating around the lakes of Brazil, genetic plasticity in plants is the product of natural selection. Although diverse habitats represent a surmountable challenge, a multitude of both biotic and abiotic factors determine the overall abundance (density), composition (diversity) and ultimate success of plant communities at any given location.
For example, looking across the landscape of the Big Cypress, densely concentrated hardwood trees form hammocks which, due to the broad area of their collective canopies, limit the amount of sunlight available to underlying herbaceous groundcover. This is a straight forward relationship - no sun reaching the ground means fewer plants on the ground. Following this rationale, if the tree canopy should be opened (by a storm, hurricane or by the death of older trees) and sunlight is able to temporarily penetrate to the floor, a rapid emergence of both herbaceous plants and new saplings would be predicted. This is precisely what happens; sunlight is the limiting resource, once made available, those plants best able to take advantage of the situation (through rapid growth) will be able to literally overshadow their competitors; plants with genetic compliments favoring a period of “initial rapid growth” are at an advantage and will be positively selected.
Extrapolating this scenario to the prairies of Big Cypress begs the question – why aren’t there any trees in the prairie?
Prairies, typically found on relatively low topographical gradients in Florida, have an abundance of soil nutrients and water; at least enough to support the enormous quantity of grasses and herbaceous plants currently found there. Additionally, from the perspective of a tree, grasses present little competition for sunlight. So, what is it that prevents trees from invading the prairie?
One often suggested possibility is that because prairies are occupied by dense populations of grasses - some of which more than six feet in height - young trees are prevented from taking hold; sort of like a reverse hammock scenario in which the grasses overshadow the young trees thereby starving them of sunlight instead of vice versa… This is plausible, but why wouldn’t trees take hold after wildfires? Wildfires have been historically inevitable in Florida and have the effect of clearing grasses long enough for those trees possessing an “initial rapid growth gene” in their arsenals to stake a claim.
Slash Pine (Pinus elliotti), for example, has just such an initial rapid growth gene. This permits the tree to take advantage of any opportunity to seize real estate, whether it is in a forest or a prairie. Slash Pine is even capable of expressing secondary needles in less than six month’s time – seedlings grow rapidly. Once present, this conifer could easily out-compete grasses for sunlight.
A quick word about wildfires: Florida’s climate cycle is punctuated by alternating dry and wet periods. November to February is the dry season, with relatively little precipitation, and is followed by heavy rains and thunderstorms (particularly near the coasts) during the months of June, July and August. The spring season, February through May, represents a transition from dry to wet, but during this period lightening strikes often cause wildfires due to the parched conditions of plants – parched, having just come out of the dry season. Regularity of climate has resulted in a cyclic “fire season” arriving during the early spring.
Speaking of wildfires… Being a regular occurrence, they are often offered as another explanation for limiting the advance of trees into prairies. Although this suggestion is partially correct, it isn’t the whole story - in some instances trees have even wielded fire as a weapon to destroy its grass competitors.
4-19-09 UPDATE: The Second Half of this Post can be Viewed HERE.
Beckage, B., Gross, L., & Platt, W. (2006). Modelling responses of pine savannas to climate change and large-scale disturbance Applied Vegetation Science, 9 (1) DOI: 10.1658/1402-2001(2006)9[75:MROPST]2.0.CO;2
Very different indeed, imagine the ecological interplay that could be interpreted if humans could see ultraviolet light through the eyes of a bee, smell pheromones from six-miles’ distance like a moth, or interpret chemical stimuli through soil like a plant… Far from serene, if viewed through time, adaptive maneuvers, survival strategies and arms races would be manifest in every action undertaken by the immense diversity of organisms on Earth. If these actions could be viewed more directly, the landscape would appear saturated with war. Even the plant community boundaries which demarcate prairie from savanna from hammock in the above described landscape are maintained by way of fierce battles waged over evolutionary time. These ecosystems, which appear stable and so pleasingly haphazardly scattered, are in fact tightly ordered armies of competing plants struggling for resources and existence. In these recurrent ecotonal conflicts one species has honed a new weapon – it has adapted to exploit the power of fire.
Naturally existing plant communities exist in a continuum of ecosystems which through evolution have adapted to almost every available habitat on the planet; from “box thorns” (Lycium pallidum) in Death Valley to fully aquatic hyacinths (Eichhornia paniculata) floating around the lakes of Brazil, genetic plasticity in plants is the product of natural selection. Although diverse habitats represent a surmountable challenge, a multitude of both biotic and abiotic factors determine the overall abundance (density), composition (diversity) and ultimate success of plant communities at any given location.
For example, looking across the landscape of the Big Cypress, densely concentrated hardwood trees form hammocks which, due to the broad area of their collective canopies, limit the amount of sunlight available to underlying herbaceous groundcover. This is a straight forward relationship - no sun reaching the ground means fewer plants on the ground. Following this rationale, if the tree canopy should be opened (by a storm, hurricane or by the death of older trees) and sunlight is able to temporarily penetrate to the floor, a rapid emergence of both herbaceous plants and new saplings would be predicted. This is precisely what happens; sunlight is the limiting resource, once made available, those plants best able to take advantage of the situation (through rapid growth) will be able to literally overshadow their competitors; plants with genetic compliments favoring a period of “initial rapid growth” are at an advantage and will be positively selected.
Extrapolating this scenario to the prairies of Big Cypress begs the question – why aren’t there any trees in the prairie?
Prairies, typically found on relatively low topographical gradients in Florida, have an abundance of soil nutrients and water; at least enough to support the enormous quantity of grasses and herbaceous plants currently found there. Additionally, from the perspective of a tree, grasses present little competition for sunlight. So, what is it that prevents trees from invading the prairie?
One often suggested possibility is that because prairies are occupied by dense populations of grasses - some of which more than six feet in height - young trees are prevented from taking hold; sort of like a reverse hammock scenario in which the grasses overshadow the young trees thereby starving them of sunlight instead of vice versa… This is plausible, but why wouldn’t trees take hold after wildfires? Wildfires have been historically inevitable in Florida and have the effect of clearing grasses long enough for those trees possessing an “initial rapid growth gene” in their arsenals to stake a claim.
Slash Pine (Pinus elliotti), for example, has just such an initial rapid growth gene. This permits the tree to take advantage of any opportunity to seize real estate, whether it is in a forest or a prairie. Slash Pine is even capable of expressing secondary needles in less than six month’s time – seedlings grow rapidly. Once present, this conifer could easily out-compete grasses for sunlight.
A quick word about wildfires: Florida’s climate cycle is punctuated by alternating dry and wet periods. November to February is the dry season, with relatively little precipitation, and is followed by heavy rains and thunderstorms (particularly near the coasts) during the months of June, July and August. The spring season, February through May, represents a transition from dry to wet, but during this period lightening strikes often cause wildfires due to the parched conditions of plants – parched, having just come out of the dry season. Regularity of climate has resulted in a cyclic “fire season” arriving during the early spring.
Speaking of wildfires… Being a regular occurrence, they are often offered as another explanation for limiting the advance of trees into prairies. Although this suggestion is partially correct, it isn’t the whole story - in some instances trees have even wielded fire as a weapon to destroy its grass competitors.
4-19-09 UPDATE: The Second Half of this Post can be Viewed HERE.
Beckage, B., Gross, L., & Platt, W. (2006). Modelling responses of pine savannas to climate change and large-scale disturbance Applied Vegetation Science, 9 (1) DOI: 10.1658/1402-2001(2006)9[75:MROPST]2.0.CO;2
Nordlund, D., & Lewis, W. (1976). Terminology of chemical releasing stimuli in intraspecific and interspecific interactions Journal of Chemical Ecology, 2 (2), 211-220 DOI: 10.1007/BF00987744
Morse, A., Peterson, D., Islam-Faridi, M., Smith, K., Magbanua, Z., Garcia, S., Kubisiak, T., Amerson, H., Carlson, J., Nelson, C., & Davis, J. (2009). Evolution of Genome Size and Complexity in Pinus PLoS ONE, 4 (2) DOI: 10.1371/journal.pone.0004332
Platt, W. J., J. M. Huffman, M. G. Slocum, and B. Beckage. In press. Fire regimes and trees in Florida dry prairie landscapes. In: Noss, R. & Singh, S. (eds.) Land of fire and water: The Florida dry prairie ecosystem. Avon Park Air Force Range and Department of Defense, Avon Park, FL,
US.Kabrick, John M.; Dey, Daniel C.; Gwaze, David, eds. Shortleaf pine restoration and ecology in the Ozarks: proceedings of a symposium; 2006 November 7-9; Springfield, MO. Gen. Tech. Rep. NRS-P-15. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station: 28-32.
Wednesday, April 8, 2009
Omnivorous Pleistocene Bears Give Clues to Adaptation
By comparing the morphological features of Pleistocene bear fossils (Arctodus simus and Ursus spelaeus) with that of modern bears, scientists report that analogous cranio-mandibular structures indicate that even the prehistoric hyper carnivores had omnivorous tendencies.
These and other findings provide clues as to the niche plasticity and the ability of mammals to adapt to fluctuating climates.
'Knowing what the extinct bears ate is of utmost relevance to finding out about the evolution of carnivore niches in the Pleistocene when climatic conditions were changing', explains Borja Figueirido, lead author of the study and researcher for the Ecology and Geology Department of the Faculty of Sciences at the University of Málaga.
Figure Above: Landmarks used for describing cranial and mandibular shape. Cranium: (1) most postero-dorsal border of the canine alveolus, (2) most antero-dorsal border of the canine alveolus, (3) most antero-dorsal border of the I3, (4) most anterior edge of the nasal bones, (5) dorsal outline directly superior to post-orbital process, (6) dorsal outline directly superior to the end of the zygomatic arch, (7) most postero-ventral point of the occipital crest, (8) intersection between the occipital condyle and the occiput, (9) intersection between the occipital condyle and the paraoccipital process, (10) ventral tip of postglenoid process, (11) posterior edge of the upper tooth row, (12) point between the upper carnassial and the first upper molar, (13) anterior edge of the upper tooth row, (14) postero-dorsal border of the zygomatic arch, (15) dorsal tip of the frontal process of the zygomatic arch, (16) orbit midheigth, (17) ventral tip of the post-orbital process, (18) ventral intersection between the zygomatic arch and the axilla.Mandible: (1) antero-dorsal border of the incisive alveolus, (2) postero-dorsal border of the canine alveolus, (3) intersection between the trigonid/talonid notch of the lower carnassial and the dorsal border of the alveolus of this tooth, (4) posterior edge of the lower tooth row, (5) posterior edge of the coronoid process, (6) most posterior edge of the articular surface condyle, (7) tip of angular process, (8) ventral outline below the mesial end of the tooth row, (9) ventral outline below the trigonid/talonid notch of the lower carnassial, (10) most ventral point of the symphyseal region. Scale bar equals 5 cm. Deviations of the specimens analyzed from the consensus configuration of landmarks are shown.
Read the research article published in the Journal of Zoology - HERE.
Figueirido, B., Palmqvist, P., & Pérez-Claros, J. (2009). Ecomorphological correlates of craniodental variation in bears and paleobiological implications for extinct taxa: an approach based on geometric morphometrics Journal of Zoology, 277 (1), 70-80 DOI: 10.1111/j.1469-7998.2008.00511.x
These and other findings provide clues as to the niche plasticity and the ability of mammals to adapt to fluctuating climates.
'Knowing what the extinct bears ate is of utmost relevance to finding out about the evolution of carnivore niches in the Pleistocene when climatic conditions were changing', explains Borja Figueirido, lead author of the study and researcher for the Ecology and Geology Department of the Faculty of Sciences at the University of Málaga.
Figure Above: Landmarks used for describing cranial and mandibular shape. Cranium: (1) most postero-dorsal border of the canine alveolus, (2) most antero-dorsal border of the canine alveolus, (3) most antero-dorsal border of the I3, (4) most anterior edge of the nasal bones, (5) dorsal outline directly superior to post-orbital process, (6) dorsal outline directly superior to the end of the zygomatic arch, (7) most postero-ventral point of the occipital crest, (8) intersection between the occipital condyle and the occiput, (9) intersection between the occipital condyle and the paraoccipital process, (10) ventral tip of postglenoid process, (11) posterior edge of the upper tooth row, (12) point between the upper carnassial and the first upper molar, (13) anterior edge of the upper tooth row, (14) postero-dorsal border of the zygomatic arch, (15) dorsal tip of the frontal process of the zygomatic arch, (16) orbit midheigth, (17) ventral tip of the post-orbital process, (18) ventral intersection between the zygomatic arch and the axilla.Mandible: (1) antero-dorsal border of the incisive alveolus, (2) postero-dorsal border of the canine alveolus, (3) intersection between the trigonid/talonid notch of the lower carnassial and the dorsal border of the alveolus of this tooth, (4) posterior edge of the lower tooth row, (5) posterior edge of the coronoid process, (6) most posterior edge of the articular surface condyle, (7) tip of angular process, (8) ventral outline below the mesial end of the tooth row, (9) ventral outline below the trigonid/talonid notch of the lower carnassial, (10) most ventral point of the symphyseal region. Scale bar equals 5 cm. Deviations of the specimens analyzed from the consensus configuration of landmarks are shown.
Read the research article published in the Journal of Zoology - HERE.
Figueirido, B., Palmqvist, P., & Pérez-Claros, J. (2009). Ecomorphological correlates of craniodental variation in bears and paleobiological implications for extinct taxa: an approach based on geometric morphometrics Journal of Zoology, 277 (1), 70-80 DOI: 10.1111/j.1469-7998.2008.00511.x
Friday, March 6, 2009
Isotopes Used in Tracking Migration and Dispersal of Birds
During last week’s post discussing vertebrates as indicators of climate fluctuation (linked here) isotopes were described as a significant tool in reconstructing the evolutionary and ecological histories of organisms. Today, Megan J. Sellick, et al, published an article in PLoS One discussing the value of using hydrogen and strontium isotopes, taken from the feathers of tree swallows, to track migratory dispersion.
Tree Swallow (Tachycineta bicolor)
The research (linked here) revealed that stable hydrogen isotopes were indicative of the latitude of molting sites and strontium was linked to the longitude of geological features found in proximity to the area where feathers were grown. Taken together, modeling revealed that, “these isotopes have the potential to provide predictable and complementary markers for estimating long-distance animal movements.”
GRAPHIC: Geographic variation of (a) dD and (b) 87Sr/86Sr values in Tree Swallow feathers. Contour maps were produced by ordinary kriging and are based on mean values in primary flight feathers at 18 breeding sites (denoted by black circles).
Megan J. Sellick, T. Kurt Kyser, Michael B. Wunder, Don Chipley, D. Ryan Norris (2009). Geographic Variation of Strontium and Hydrogen Isotopes in Avian Tissue: Implications for Tracking Migration and Dispersal PLoS ONE, 4 (3) DOI: 10.1371/journal.pone.0004735
Tree Swallow (Tachycineta bicolor)
The research (linked here) revealed that stable hydrogen isotopes were indicative of the latitude of molting sites and strontium was linked to the longitude of geological features found in proximity to the area where feathers were grown. Taken together, modeling revealed that, “these isotopes have the potential to provide predictable and complementary markers for estimating long-distance animal movements.”
GRAPHIC: Geographic variation of (a) dD and (b) 87Sr/86Sr values in Tree Swallow feathers. Contour maps were produced by ordinary kriging and are based on mean values in primary flight feathers at 18 breeding sites (denoted by black circles).
Megan J. Sellick, T. Kurt Kyser, Michael B. Wunder, Don Chipley, D. Ryan Norris (2009). Geographic Variation of Strontium and Hydrogen Isotopes in Avian Tissue: Implications for Tracking Migration and Dispersal PLoS ONE, 4 (3) DOI: 10.1371/journal.pone.0004735
Sunday, March 1, 2009
Vertebrate Proxies of Climate Change
Haphazardly racing around the net while pumped-up on Peet’s Sumatra coffee (so good!), I noticed that Jessica Blois and Elizabeth Hadley have an article being published in the Annual Review of Earth and Planetary Sciences this upcoming May. This is great news for me, because I have an interest in Cenozoic climate change and these folks are experts in the subject area; however, unfortunately for any readers of this blog lacking sufficient caffeine-ation, this post may seem a bit rambling… Consider it a refresher on vertebrate proxies of climate change.
"Organisms change through time. " - At first read this simple four-word sentence may seem rather barren of substance but within its basic grammar there exists a world of profound scientific insight and understanding. Evolution lies at the center of our biological universe, its principles are essential to science, and by grasping these principles we are able to efficiently navigate the worlds of ecology, paleontology and other life-linked sciences. Paleontologists and paleobiologists often utilize the ideas and tenants of organismal change as tools to decipher the remnants and records of past life in aspirations of better understanding not only biology and life, but also as a means of interpreting the physical history of our beloved planet Earth - the fundamental constants of chemistry and climate.
Numerous factors or mechanisms may signal biological change; natural selection, genetic drift and other gene flow can all introduce variation into a population, but these are merely the effects, or end products of change, what physically lies at the source of the process - what environmental factor triggered or was driving the selection, drift and flow?
What if, for example, some physical barrier was removed from a geographic region, thereby permitting the migration of a herd into previously unchartered lands, or the founding of a new population? Would the organisms – and their fossil remnants - be disrupted in such a way as to leave clues behind explaining the reason for increased rate of change or distribution? Less temporally dramatic, what if the seasonality of a region changed in such a way as to lengthen the mating season, or change the territoriality of a species? Would these events, be recorded in the fossil record? Undoubtedly yes!
Responsiveness of Vertebrates to Environment
Many studies of vertebrates have suggested that climate is the single best indicator of modern species richness. Over the past decade several different theories have been suggested in hopes of establishing a clear and precise relationship between organismal change and the environment. Some of these hypotheses are relatively familiar, such as Van Valen’s “Red Queen model,” and Vrba’s “Turnover-pulse model,” but others less so… Regardless, the majority of these models work to resolve one key question; how synchronous are climate and biotic change?
Responsiveness of Vertebrates to Environment
Many studies of vertebrates have suggested that climate is the single best indicator of modern species richness. Over the past decade several different theories have been suggested in hopes of establishing a clear and precise relationship between organismal change and the environment. Some of these hypotheses are relatively familiar, such as Van Valen’s “Red Queen model,” and Vrba’s “Turnover-pulse model,” but others less so… Regardless, the majority of these models work to resolve one key question; how synchronous are climate and biotic change?
Vertebrates, and in particular mammals, are highly responsive to changes in the environment. Climate fluctuation can lead to an incredible amount of variation in the diet choice, distribution and even morphology of vertebrates. Even within Humans, biological anthropologists have identified trends associated with body size and appendage length based on climate; they refer to this correlation as Bermand and Allan’s Rule. It suggests that human populations occupying regions closer to the equator statistically contain individuals with larger body size and longer limbs relative to those who inhabit more pole-ward regions. This variation has arisen primarily to promote more efficient thermoregulation as to reduce body heat loss in cooler regions, and to promote cooling in warmer climates. Some vertebrates posses even finer genetic plasticity changing morphologically with what could be termed “hair triggers.”
One of the most highly variable vertebrates is the Pocket gopher (Thomomys spp). These gophers have been intensively studied as indicators of environmental change. Their populations, and individual morphology, have been shown to vary with in a period of less than ten years. The most easily recognized change in morphology is their body size - which fluctuates with everything from altitude to diet. Body size, in turn, has a noticeable effect on territory, fertility of females and distribution of the population (Hadly, 1996). These physiological changes, and the fossils they have left behind, have been intensely studied in relation to Late-Holocene Climatic changes.
Thomomys spp
One site in particular, Lamar Cave, located with in the boundaries of Yellowstone National Park, has been used by Elizabeth Hadley to make correlations to such historic climate changes as the Medieval Warm Period (MWP). Through comparison of fossil dental plates with those of modern descendants, Hadley has been able to demonstrate that during the MWP pocket gophers of this region had the smallest body size than at any other point in the paleontological record. Using similar comparisons she was also able to identify trends in morphology that correlated with the Little Ice Age (LIA) and other events including neoglaciation (Hadly, 1996). The response of vertebrates is not limited to the highly plastic morphology of pocket gophers. Many other vertebrates respond equally as readily to climate change. However, morphological change is not necessarily required of a species in order for it to serve as a climate proxy. During their lifespan, all organisms make detailed records of their environment. Through the fundamental life processes of cellular growth and repair vertebrates have the potential to generate detailed records of their environment. Just as the old cliché exemplifies, “you are what you eat.” This record can later be resurrected and deciphered from their fossil remains to help clarify the picture of the climate and chemistry they endured while alive.
Isotopes
Examinations of isotopic records are commonplace for many paleontologists. Uncountable volumes have been written on Foram 18-O isotopes and their relationship to periods of increased glaciation, or similar correlations of speleothems and 13-C, but accurate isotopic records of both of these elements can be obtained from other sources as well - including vertebrates.
Carbonate apatite is a primary constituent of both skeletal bones and dentition in the vertebrates. It is incorporated into the organism through diet and water uptake. The process is riddled with various “vital effects” but has nonetheless been found to be very accurate. In fact, many conservationist use this isotopic signature in vertebrates to better decipher the life histories of contemporary vertebrates in hopes of aiding in their preservation. For example, remains from the world’s largest cavefish (Milyeringa veritas) have been used by Australian conservationists to better examine and comprehend the environment and ecosystem which the fish inhabits. The cavefish lives in deep columns of water that are rich in dissolved limestone. The depths of the water column posses various corresponding incremental concentrations of dissolved materials and by examining the isotopic signatures of the fish’s skeletal apatite, conservationists were able to discover the exact depth the fish occupies.
Milyeringa veritas
Uptake of elements within vertebrates (O, C, Sr & others) generates a highly detailed record of environmentally available isotopes, and as one might guess, availability is indicative of climate.
As another example, Thure Cerling and others at the University of Utah have refined the technique of laser ablation to such quality and precision that they can use it to vaporize the apatite found in vertebrate teeth, and then analyze the gas to determine its isotopic components. They can examine the teeth to such resolution as to be able to report the dietary preferences of mammals between C3 and C4 plants. Previously, samples of fossil teeth or skeletal structures were far to rare to permit them to be thrown into a TIMS for examination, but now that laser ablation has reached such a high level of efficiency isotopic analysis can be made in the smallest and rarest of specimens with minimum impact on the fossil itself. Laser ablation can be used to examine the minute layer of enamel on the smallest of rodents and the most voluble of fossils on display at museums with little difficulty.
As a side note - many scientists have recently discovered that skeletal tissues, which possess apatite, are very susceptible to diagenic processes that can cause recrystalization and alter results, but dental samples seem to be far more reliable when it comes to maintaining their original isotopic signatures. This coupled with the knowledge acquired in the past few decades in regards to the incorporation of specific 18-O and 13-C isotopes into biological entities has brought to light a highly detailed and accurate record of climate change.
Similar techniques have been used to examine bone fragments from marine vertebrates. Some alteration of samples occurs during fossil formation in paleo-seawater environments which forces users of this technique to integrate other proxies of isotopic variation in their final estimates as a “check,” but as the technique begins to advance some of this error is likely to be eliminated. Others have also verified the validity of the use of dental enamel as an isotopic record. Schmitz and his colleagues examined fossil shark teeth from two different locations in Mississippi (one strata being mixed marine, the other brackish-water). Both samples demonstrated nearly identical isotopic signatures, even though they had been deposited in different strata, one with a high salinity concentration - previously shown to accelerate diagenesis. They also examined skeletal remains from marine vertebrates, but there seemed to be a significant error associated with those found in the marine strata.
Isotopic signatures can be very useful in the interpretation of paleoclimate, but in certain cases the mere presence of an organism at a given location - biogeography - can report volumes of information in regards to past climate.
Biogeography
The vertebrate fossil record can be extrapolated in terms of the diversity, divergence and variation of distinct animal groups over a geographic region to display, with accuracy, the impact of environmental change. Similarly, known vertebrate biogeographic patterns can be used to demonstrate specific climatic fluctuation both locally and on the global scale.
The Cenozoic has been marked by tremendous variation of climate. During the early portions of the Cenozoic high temperatures were the standard with the highest to be found in the Early to Middle Eocene, since then a falling temperature trend has been the rule. It was during the Eocene-Oligocene transition that Antarctica became isolated and sea levels dropped dramatically with the accumulation of ice caps, this had the effect of changing terrestrial habitats significantly. Throughout the Cenozoic, similar patterns of fluctuating glacioeustatic sea level events would continue to occur. Evidence of this can be found across the globe.
Thailand, in South-East Asia, is one of many regions that accurately record these glacioeustatic events through its vertebrate fossil record. Thailand is especially significant in that it separates two distinct biogeographical regions (Fig 1). The Indochinese region is located to the north of Thailand and the Sundaic region is located to the south. These two regions have significantly different climates and zoological compositions. Up until about 800kyr B.P. fluctuation of sea level was somewhat constant in the region of Thailand, with the average being somewhere around 70m below the modern, and the greatest change being no more than 100m below the modern. However, near the 800kyr B.P. mark level dropped more dramatically, some fluctuations going as low as 170m below modern sea levels. This had the effect of constructing a land bridge between the Indochinese and Sundaic biogeographical regions, thus permitting the migration of a large variety of animals, including mammals. Through careful comparison of the fossils these migrating animals left behind, and the extant species found in both the Indochinese and Sundaic regions, certain conclusions can be established in regards to their phylogenies. The presence of fossil mammals with Indochinese affinity in the Sundaic regions, and the presence of Sundaic mammals in Indochina suggest some mode of migration in the past that is prevented in modern times by the sea acting as a barrier. Through radio dating of remains, an estimated time for the existence of the land bridge can be calculated, thus the fossil mammals provide dates for periods of reduced sea levels, and in turn, periods of increased glaciation.
FIGURE 1--- Land bridge linking distinct biogeographical regions in Thailand
Thailand is not unique in its ability to provide vertebrate proxies of climate change. Similar scenarios have been played out across the globe. Grenada offers another example of vertebrate biogeography acting as an indicator of sea level change due to increased glaciation.Grenada has a rather sparse population of indigenous mammals at present, and bats represent the majority of these species. However, paleontologists have recently uncovered a variety of fossil mammals near the Grenadine coast dating from the Pliocene. These species, such as representative capybaras and sloth, did not arise independently on Grenada and then become extinct. Their lineages suggest that they arrived on Grenada from the South American mainland, where their descendants can still be found today. Grenada is located on the Southern Antilles Arc Platform, an elongate sub ocean structure that extends some 180km. This arc provides a base for several small islands and at its closest point comes to with in 40km of South America. During the Pliocene, a combination of low sea levels and tectonic activity provided a land bridge that may have conjoined Grenada with South America thus allowing for the migration of mammals. Through accurate dating of these fossil remains and of the associated tectonic activity estimates for late Pliocene glaciations can be made.
Through biogeographic research, other evidence can be in found with the target of determining periods of climatic change that are independent of sea level, and glacioeustaic events. Many other factors can have the effect of generating temporary corridors that permit faunal exchange. A “corridor” is simply a narrow tract, or pathway, which allows for the exchange of animals from one side to another. These corridors can be created by various means, including the growth of a forest.
The western Canadian ice-free corridor is a continuous tract of land that extends from Alberta, Northward to the Arctic Ocean (fig 2). This corridor separates Eastern and Central Canada from the Western Coastal portions of the Country. At one point in the past this corridor was closed to faunal exchange do to the advancing Laurentide ice sheet; however, near the close of the Pleistocene the ice retreated significantly enough to open the corridor temporarily, before finally closing again. This second closing of the corridor was not due to advancing ice caps, but rather to the growth of Boreal forests.
FIGURE 2---- Ice-free corridor, shaded region
Interpretation of paleoclimate is a highly important field of study. Not only is it required to better understand the physical and biological history of our planet, but also to endow us with the knowledge needed to prepare for tomorrows’ inevitable changes. The Cenozoic has been marked by extreme change of temperature and climate as a whole, many such changes visible on a short-term scale. This period in geological history has seen everything from periods of hot and dry, to glaciation. To better understand the past and future effects on humans we must discover how it impacted the existence of other animals, in particular, other mammals. To better understand their evolutionary responses to climate, careful analysis of their fossil record must be made. Their physiology, morphology, biochemistry and even behavioral responses record every detail of their natural histories and the climates that they endured. Organisms change through time; the trick to rendering these records lays in the accurate translation of their fossil remains. To accomplish this end, the vertebrate indicators of climate change are an essential and indispensable tool and I very much look forward to reading more about them in May.
RECCOMENDED READING
Alberdi, M. et al. 2001. Vertebrate taphonomy in circum-lake environments: Three cases in the Guadix-Baza Basin (Granada, Spain). Paleogeogrphy, Paleoclimatology, Paleoecology. 165:1-26.
Badgley, C; Behrensmeyer, A. 1995. Preservational, Paleoecological and evolutionary patterns in the Paleogene of Wyoming-Montana and the Neogene of Pakistan. Paleogeography, Paleoclimatology, Paleoecology. 115: 319-340.
Badgley, C; Behrensmeyer, A. 1995. Two long geological records of continental ecosystems. Paleogeography, Paleoclimatology, Paleoecology. 115:1-11.
Barnosky, A. 2001. Distinguishing the effects of the Red Queen and the Court Jester on Pliocene Mammal Evolution in the Northern Rocky Mountains. Journal of Vertebrate Paleontolgy. 21:172-185.
Barrat, J; etal. 2000. Strontium isotopes in biogenic phosphates from a Neogene marine formation: implications for paleoseawater studies. Chemical Geology. 168:325-332.
Bromage, T.; etal. 1995. Paleobiography of the Molawi Rift: Age and vertebrate paleontology of the Chiwando beds, northern Molawi. Journal of Human Evolution. 28:37-57.
Bussuyt, F; Milankovitch, M. 2001. Amphibians as Indicators of Early Territory “ Out- of -India” Dispersal of Vertebrates. Science. 292:93-100.
Cerling, T; Sharp,Z. 1996. Stable carbon and oxygen isotope analysis of fossil tooth enamel using laser ablution. Paleogeography, Paleoclimatology, Paleoecology. 126:173-186.
Coope, G.R. et al. 1997. Climatic and Environmental Reconstructions based on fossil assemblages from Middle Devension (Weichselion) deposits of the river Thames at South Kensington, Central London, UK. Quaternary Science Reviews. 16:1163-1195.
Cruzan, M and Templeton, A. 2000. Paleoecology and Coalescence: phylographic analysis of hypothesis from the fossil record. TREE. 15:491-496.
Dennistan, R. etal. 1999. Integrating stalagmite, vertebrate and pollen sequences to investigate Holocene vegetation and climate change in the southern Midwestern United States. Quaternery Research. 52:381-387.
Flynn, J; Wyss, A. 1998. Recent advances in South American mammalian paleontology. TREE. 11:449-454.
Gao, C. et al. 2000. Last interglacial and Devension deposits of the river Great Ouse at Toolpack Form, Fenstanton, Cambrideshire, UK. Quarternary Science Reviews. 19:787-810.
Kerr, J; Packer, L. 1999. The environmental basis of North American species richness patterns among Epicauta (caleoptera: Meloidae). Biodiversity and Conservation. 8:617-628.
MacDonald, G; McLeod, T. 1996. The Holocene closing of the ‘ice-free’ corrider: A Biographical Perspective. Quarternary International. 32:57-95.
MacPhee, R.; Singer, R.; Diamond, M. 2000. Late Cenozoic land mammals from Grenada, lesser Antilles Island-Arc. American Museum Novitates. 3302:1-20.
Scasso, R.; Castro, L. 1999. Cenozoic phosphatic deposits in North Patagonia, Argentina: Phosphogenesis, sequence-stratigraphy and paleooceanography. Journal of South American Earth Sciences. 12:471-487.
Schmitz, B. et al. 1997. Testing 87Sr/86Sr as a paleosalinity indicator on mixed marine, brackish-water and terrestrial vertebrate skeletal apatite in late Paleocene-early Eocene near coastal sediments, Mississippi. Chemical Geology. 140:275-287.
Vigne, Jean-Denis. 1996. Small mammal fossil assemblages as indicators of environmental change in northern Corsica during the last 2500 years. Journal of Archeological Science. 23:199-215.
Wing, S; Alroy, J; Hickey, L. 1995. Plant and mammal diversity in the Paleocene to early Eocene of the Bighorn Basin. Paleogeography, Paleoclimatology, Paleoecology. 115:117-155.
Elizabeth A. Hadly (1997). Evolutionary and ecological response of pocket gophers (Thomomys talpoides) to late-Holocene climatic change Biological Journal of the Linnean Society, 60 (2), 277-296 DOI: 10.1111/j.1095-8312.1997.tb01496.x
William F. Humphreys (2001). Milyeringa veritus (Eleotridae), a remarkably versatile cave fish
from the arid tropics of Northwestern Australia.
Environmental Biology of Fishes, 62 (1/3), 297-313 DOI: 10.1023/A:1011880726946
Wednesday, February 11, 2009
Adaptation and Evolution in a Changing Climate
I haven't had a whole lot of time to blog the last few days, but I came across this quick write-up on Science Daily and liked the quote at the end, “We lose diversity with a rapid change, but always life finds a way. Some kind of life will fill the gap.”
Charles Darwin may have been born 200 years ago come Feb. 12, but his theory of evolution remains an everyday touchstone for modern biologists. And while the Origin of Species author might not have known the term “global warming,” he wouldn’t have been surprised that the environment is changing. He would, however, be astonished by the speed at which it’s happening today, researchers believe.
“Every species is under temporary permanence,” says Bill Saidel, an associate professor of biology at Rutgers University’s Camden Campus, where he teaches Animal Behavior and Behavioral Neurobiology. Darwin would have predicted changes in species’ habits and even changes in the environment, but the planet’s facing changes that are both drastic and unpredictable.
Saidel notes some already observed results of global warming today, like changing avian migration patterns and pH levels in oceans. But how would Darwin begin to determine how every species might respond to climate change? Most likely he’d begin by observing those habitats that are uniquely individual and well-defined.
This approach – researching one specialized habitat for insight into a larger understanding of evolution – is how Saidel conducts his own research at Rutgers–Camden. His interest in the exotic African butterfly fish is precisely because it has evolved two retinas in each eye, but only feeds from information derived from one. The fish’s highly specialized adaptations, from retina to brain, serve as a model for discerning the circuitry of feeding in all vertebrae whose visual traits aren’t as clearly segmented.
“This fish has much to teach us. It has adapted extraordinarily to a single unique environment. Yet, the consequences of a highly adapted species is that any change can be dire,” says Saidel.
Dan Shain, associate professor of biology at Rutgers–Camden, also researches highly specialized creatures: worms that thrive in the world’s most extreme climates. He studies them for insight into their adaptations and their unique cocoon production processes, which have biomaterial applications. Only the intensely frigid environs Shain once explored in destinations like Alaska aren’t as cold anymore.
This summer, the Rutgers–Camden researcher traveled to Denali National Park to observe ice worms, whose glacial habitats make them an ideal indicator species for climate change.
“Ice worms have been around at least a few million years and have been through many ice ages, but the change there now is dramatic,” Shain says. “I’ve been traveling to Alaska for 10 years studying ice worms. The mass of the glaciers is about half of what it was a decade ago.”
Disappointed, Shain didn’t find new specimens allegedly living in Eldridge Glacier. Even the glaciers he previously identified as housing a plethora of ice worms had sadly receded.
“The number of ice worms is radically down. We think ice worms are getting washed off the glaciers and they don’t have the capability to move up the glacier quickly enough,” he reports.
The issue of time is crucial to understanding the implications of global warming. Shain calls it “accelerated evolution” and predicts large-scale extinctions that even Darwin couldn’t comprehend. Species that can best adapt to this abrupt change will go on and multiply, leaving the world with less of a variety.
“We lose diversity with a rapid change, but always life finds a way. Some kind of life will fill the gap.”
Rutgers University (2009, February 10). Big Year For Darwin, But What Would He Make Of The Climate Change Ahead?. ScienceDaily. Retrieved February 11, 2009, from http://www.sciencedaily.com/releases/2009/02/090202113611.htm
Charles Darwin may have been born 200 years ago come Feb. 12, but his theory of evolution remains an everyday touchstone for modern biologists. And while the Origin of Species author might not have known the term “global warming,” he wouldn’t have been surprised that the environment is changing. He would, however, be astonished by the speed at which it’s happening today, researchers believe.
“Every species is under temporary permanence,” says Bill Saidel, an associate professor of biology at Rutgers University’s Camden Campus, where he teaches Animal Behavior and Behavioral Neurobiology. Darwin would have predicted changes in species’ habits and even changes in the environment, but the planet’s facing changes that are both drastic and unpredictable.
Saidel notes some already observed results of global warming today, like changing avian migration patterns and pH levels in oceans. But how would Darwin begin to determine how every species might respond to climate change? Most likely he’d begin by observing those habitats that are uniquely individual and well-defined.
This approach – researching one specialized habitat for insight into a larger understanding of evolution – is how Saidel conducts his own research at Rutgers–Camden. His interest in the exotic African butterfly fish is precisely because it has evolved two retinas in each eye, but only feeds from information derived from one. The fish’s highly specialized adaptations, from retina to brain, serve as a model for discerning the circuitry of feeding in all vertebrae whose visual traits aren’t as clearly segmented.
“This fish has much to teach us. It has adapted extraordinarily to a single unique environment. Yet, the consequences of a highly adapted species is that any change can be dire,” says Saidel.
Dan Shain, associate professor of biology at Rutgers–Camden, also researches highly specialized creatures: worms that thrive in the world’s most extreme climates. He studies them for insight into their adaptations and their unique cocoon production processes, which have biomaterial applications. Only the intensely frigid environs Shain once explored in destinations like Alaska aren’t as cold anymore.
This summer, the Rutgers–Camden researcher traveled to Denali National Park to observe ice worms, whose glacial habitats make them an ideal indicator species for climate change.
“Ice worms have been around at least a few million years and have been through many ice ages, but the change there now is dramatic,” Shain says. “I’ve been traveling to Alaska for 10 years studying ice worms. The mass of the glaciers is about half of what it was a decade ago.”
Disappointed, Shain didn’t find new specimens allegedly living in Eldridge Glacier. Even the glaciers he previously identified as housing a plethora of ice worms had sadly receded.
“The number of ice worms is radically down. We think ice worms are getting washed off the glaciers and they don’t have the capability to move up the glacier quickly enough,” he reports.
The issue of time is crucial to understanding the implications of global warming. Shain calls it “accelerated evolution” and predicts large-scale extinctions that even Darwin couldn’t comprehend. Species that can best adapt to this abrupt change will go on and multiply, leaving the world with less of a variety.
“We lose diversity with a rapid change, but always life finds a way. Some kind of life will fill the gap.”
Rutgers University (2009, February 10). Big Year For Darwin, But What Would He Make Of The Climate Change Ahead?. ScienceDaily. Retrieved February 11, 2009, from http://www.sciencedaily.com/releases/2009/02/090202113611.htm
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