Archive for: February, 2007

Know Your Biomes IV: Tropical Savanna

Feb 27 2007 Published by under Basic Concepts, Ecology

A cheetah crouches, shoulders hunched, barely visible through golden stems. The antelope on the edge of the herd has stopped chewing, and scans the horizon with a nervous eye. As it takes a step forward to rejoin the safety of the group, the cheetah makes her move, bounding with impossibly huge leaps towards her prey. The entire herd is on the move with her first step, but the stray is dangerously lagging behind. It flies only for a few seconds before the cheetah leaps one final time, clinging to the young antelope's rump with all her strength, pulling the animal to the ground for the coup de grace.

This should be a familiar scene for anyone with a passing interest in wildlife films; the great African savannas are often filmed to illustrate with detail the great theater of competition and predation in the wild. Visibility plays a large factor in this choice; the savannas have very few trees, and are home to some of the largest groups of the largest mammals in the world, not only in Africa, but also in South America, India and Australia. The same drama could not be effectively captured in a rain forest; animals are much less visible generally.

But that does not mean that the creatures of the savannas are immediately apparent. Most are well camouflaged, especially the predators, matching the golds, browns and sage greens of the flora, or appearing as a distant rock, as in the case of rhinos. Huge herds of ungulates pound the hard earth of the savanna, following the summer rains as they sweep across the enormous stretches of land that savannas occupy. As in all biomes, the climate sets the standard of living.

Like the tropical dry forests, the savanna is doused with rain in the summer seasons (often in just a few weeks depending on the year), and suffers from extreme drought for the rest of the year. What keeps dense plant growth at bay? Well, the answer to that question is threefold:

  • Fire: After the five month long dry season, lightning storms swirl violently over the plains, igniting the parched vegetation. These fires can be prolific, clearing huge tracks of grasses and saplings. The grasses grow back quickly, but millennia of fires like these have selected a small number of fire resistant trees and shrubs that are constantly kept in check by the annual fires.
  • Soil: The soils of the tropical grasslands are relatively impermeable, causing the heavy rains to skim along the surface instead of soaking deeply into the ground.
  • Herbivory: Animals also keep the density of non-poacean plants at a relatively low level. The herbivores of the African savanna, for example, have evolved to fill specific niches* (the specific factors that influence a species existence, in this case feeding) in which they consume plant material at different levels of the ecosystem. Giraffes and elephants browse the upper and middle levels of leafy trees, respectively, while wildebeests and zebras graze on different levels of grasses. The large herds of ungulates roaming the plains are also restrictive to growth.

The number and diversity of trees differ from savanna to savanna around the globe, however. In the Miombo Woodlands, trees of the genus Brachystegia can reach heights of 80 feet (25 meters) or more, assisted by a nutrient fixing fungus in its roots (mycorhizae). There are a few dozen species of this tree in a relatively small area.

Insects, as usual, play a large part in recycling nutrients from dead and dying tissue. Termites are perhaps the most visible of these detritivores (detritus eating) in just about every savanna across the world, living in mounds in excess of two meters high, each home to millions of foraging termites. In the Cerrado Savanna of South America, the giant anteater plays Godzilla, wandering through entire cities of termite mounds and dismantling them with its powerful claws to expose tunnels full of workers and lapping them up with its sticky tongue (links to video of anteater feeding).

Modern humans are believed to have originated in the African savanna before trekking out to inhabit every other biome in one way or another. The savanna is used for supporting non-native livestock in most cases, but there is a movement for domesticating antelope and other ungulates due to the naturally higher feed to meat ratio observed in these animals.

Next we'll move out of the tropics and into the desert.

*We will return to niche theory in a later post; Cheetah image courtesy of schani

This post is part of a series of Basic Concepts: Ecology (Intro, Biomes I, II, III). For the entire list of Basic Concepts in Science, visit Evolving Thoughts.

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Know Your Biomes III: Tropical Dry Forest

Feb 20 2007 Published by under Basic Concepts, Ecology

As you move about 10 to 25 degrees north and south of the equator, the unchanging wetness of the rain forest begins to dissipate, giving way to a more seasonal climate. The temperatures are still warm throughout the year, but precipitation in tropical dry forests comes in bursts of only five or six months. The rest of the year is dry and relatively bare; in some areas during the dry season, these forests may resemble savannas or even deserts.

The soils are often relics of the ancient continent Gondwana, especially in directly detached, isolated systems like New Caledonia. The soils are more fertile than that of the rain forests, but erosion is higher, especially in deforested areas.

The dichotomous nature of the climate in the dry forest drives life to cope with the extreme seasonality of precipitation in different ways. The driest areas are dominated by deciduous trees that drop their moisture-exuding leaves once the rains stop, allowing sunlight to pass through the once-thick canopy, to reach the lower levels of the forest. Wetter areas, like Southeastern Indochina, are home to large forests of dipterocarps (pdf) and other evergreens, able to utilize the blessings of the monsoon rain season to keep growing throughout the year. And, unlike the plants of the rain forests, that rely almost entirely on animals to disperse seeds, seeds in the dry forest are swept through open areas by strong winds.

Wildlife is diverse in the dry forests, but necessarily migratory in some areas due to the extreme seasons. During the dry season, many animals will travel to a certain area in the neighboring rain forest to subsist, waiting for the rains to return to their home. This extra level of complexity has given ecologists a new challenge: Tracing the migratory paths of animals reliant on both tropical dry and wet forests. How much do these species rely on each biome for subsistence?

Dry forest systems are not quite as biologically diverse as rain forests, but they are home to many rare species found nowhere else: tigers, leopards and jaguars, sloth bears, a myriad of kingfishers and flycatchers, the Komodo dragon, the maned wolf, the elusive Javan rhino and unique plants like Gouania and Cycas beddomei. The Madagascar dry forests are home to seven species of baobab tree. The whole of Africa can claim only one.

While I'm generally working under the assumption that the reader knows the dangers faced by each biome, the dry forest has been massively altered by human influences. There is a huge difference in human population between tropical wet and dry forests. Murphy and Lugo provided an estimate in 1986: In Central America, only 7 percent of the people lived in wet forest areas, while 79 percent live in dry forest areas. The relatively fertile soil drives deforestation for agricultural purposes, and has whittled dry forests down to just about 2 percent of their former area in places like Central America.

Guanacaste National Park in Costa Rica is usually hailed as the prevailing example of how dry forests can be saved and care of them placed in capable, educated hands of native peoples. Ecologist Dan Janzen began with a simple problem - why does the guanacaste tree produce so much fruit if it just lays around - found a simple answer - it had evolved to rely on herbivores like camel and ground sloths to disperse its seeds; unfortunately, those animals were hunted to extinction 10,000 years ago - and then used this knowledge to set up a system to save the tree - by introducing domesticated herbivores to the park - and encouraging the Costa Rican people to preserve their lands. Janzen called it a "biocultural restoration."

Next in the order of increasing latitude is the savanna, tropical grasslands that actually cross the boundaries with dry forests. More on that later.

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>AAAS Symposium: The Dynamics of Social Extinction

Feb 19 2007 Published by under [Politics], Conference Blogging, Conservation, Links

>Following Collins' presentation on amphibians as model organisms for observing biological extinction, Dr. Charles Redman from the Global Institute of Sustainability at ASU addressed a more sticky area of extinction, one that hits closer to home: social extinction.

"The biological extinction of a society is rare," said Redman, describing social extinction as more of a cultural rollover - certain social orders become antiquated and irrelevant and tend to be replaced.

"At some point, the old ways just die out. In some cases," he said, "the language still exists, but the society may not."

Redman questioned the importance of the collapse of societies in reference to the central theme of the AAAS meeting, sustainable science. The loss of a species is unequivocally deemed morally important, but is the loss of society? What causes societies to fail? Is there such a thing as a truly sustainable society?

Redman answered himself simply. "The only thing that is certain is that change is ubiquitous."

He detailed briefly and necessarily the Easter Island paradigm of cultural collapse and the succession of regimes in Mesopotamia as examples, following with a concise definition of societal "resilience," the ability of a society, biologically and culturally, to remain in a desirable state or to be able to change in a desirable way. Redman never exactly defined "desirability," but I think we can assume that state generally involves nonviolent shifts in society.

Redman sees two major threats to a society: environmental changes and the capacity for response in problem solving, either through greater mobility, technology or sweeping social transformations. He pointed out that the simplest and often the most effective response, greater mobility, is no longer feasible. People are generally stuffed into particular nations where travel between is at best, a bureaucratic paper race and at worst, absolutely forbidden. This problem is especially puzzling in this time of globalization, where goods are brought to people across the world. Redman would like to see more people brought to the goods, evening things out a bit more.

I think one of Redman's more poignant statements was "sustainability is not always good" when you're speaking from a societal perspective. The longest lived, strongest governments in human history were not democracies, but totalitarian monarchies and theocracies. Redman questioned the power of democracy to create a lasting, sustainable, resilient society. No answer was implied in the statement; he just wondered if there was potential.

He questioned the value of information to a society, wondering if the availability of information was as much a detriment as a boon, offering too many options, leading to indecision and confusion faced with so many choices. Unlike biological diversity, which is essential in prolonged stabilization in evolved living systems, cultural diversity may lead to gridlock on senate floors, each group holding firm to subcultural principles.

So I'd like to throw a couple of questions that Redman asked out to the blogosphere. Please, spread them around if you would, on your blog, through e-mail, asking friends:

  • When a society is on the verge of extinction, are we morally obligated to save it?
  • Do you agree with Redman about diversity and information in today's society?
  • Is a sustainable, "resilient" society possible? Does in involve greater globalization, as Redman suggests?

I would love to hear your thoughts. It might even be neat to compile a series of responses.

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>AAAS Symposium: Observing Biological Extinction

Feb 17 2007 Published by under Conference Blogging, Conservation, Ecology, Links, Microbiology

>The first symposium I attended was yesterday at 8:30 am entitled "The Dynamics of Extinction," which was organized to be an interdisciplinary approach to examining extinctions in natural, societal and lingual systems, and also the ethics involved in preserving - and perhaps necessarily - intervening in these systems.

Ecologist Jim Collins of the NSF and Arizona State University kicked off the discussion with an analysis of global amphibian decline as an indicator of extinction, and also a type of living experiment. It is usually the job of paleontologists to analyze fossil and climate records, correlating extinctions with major environmental change.

"At this moment, however," said Collins. "Extinction is right in front of us. We actually get to peer through the window this time."

And amphibians are the perfect example, a model class, said Collins. It's easy to see why. Thirty-three percent of amphibians are endangered, with 7.4 percent of those considered critically so, compared with 23/3.8 percent of all mammals and 12/1.8 percent of all birds. It is striking that we're talking about an entire class of animals that are being pushed to the brink, not just a particular family or genus.

Collins listed the different threats that may lead to extinction in these animals, including the "historic" threats,

  • Commercial
  • Introduced species
  • Habitat reduction

as well as some newer, less studied threats, labeled "enigmatic":

  • Climate change
  • Toxins
  • Infectious agents

The enigmatic threats became more prominent as biologists noticed declining amphibians populations even within protected lands. Since the enigmatic threats are not subject to arbitrary human boundaries, they persist even when an area is isolated from the first three historical threats.

But commercial harvesting is still a major threat for amphibians, especially frogs. The frog leg industry is especially destructive, concentrating their harvests on only 11 species of frogs, 95 percent of the time harvested from natural habitats, not farms.

Toxins are hard to label as a concrete cause of because of the stratified and highly variable distribution of contaminants in biological systems, especially those bound to aquatic environments. Collins suggested that the deformities caused by parasites in frogs may be due indirectly to an increase in fertilizers, though that idea has not been confirmed.

Collins instead concentrated on his own work with Central American frog populations and the potential for a type of fungus, Chytrid to extinguish about 100 species of frogs in the area. Chytrid attacks the kerotin-rich skin of the frog, and since these animals respirate through their skin, advanced cases cause cardiac arrest and death. Chytrid has also been known to disrupt normal behaviors in frogs.

The idea of a pathogen driving its host to extinction seems contradictory; where's the benefit for the pathogen?

There are a few species of Chytrid resistant frogs in these communities that act as a reservoir species for the fungus. In other words, these frogs show no symptoms of infection, but still maintain the ability to spread the disease (a kind of Typhoid Mary). It's easy to see how this might cause a large extinction of frogs from the constant exchange of Chytrid between susceptible and resistant species.

And the whole bit might be caused by climate change, at least on the local level. As the microclimate shifts, certain pathogens seem to spread more effectively (as in the case of avian malaria in Hawaiian birds).

Collins and company were also able to predict the spread of the fungus to the next location south, more or less confirming the climatic/pathogenic threat of extinction. He has shipped over 100 different species of the most endangered frogs to a zoo in New York (not sure if it was Brooklyn or not) to try to protect and preserve them.

The question is, does this count? If the animal only exists in a zoo, are we truly preserving diversity? More questions were raised in the ethical implications of extinction: When should we intervene? How do we know when the cause of endangerment is natural or artificial? How to define was is natural or artificial?

Collins urged the philosophers of science to step up and engage questions like these, weighing the importance of value systems in ecology, intrinsic value vs. utilitarian value. He feels that we need a more clear philosophy of what should be preserved and how, all the while keeping in mind what exactly our role is in this process.

Back later with more tidbits from this symposium.

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Know Your Biomes II: Tropical Rain Forest

Feb 11 2007 Published by under Basic Concepts, Ecology

As we begin to take a general sweep through the Earth's biomes, the ever-changing hubs of natural history, the idea of biodiversity should be preeminent. In recent years, biodiversity has become an increasingly important term for ecologists, describing not only the entirety of organisms themselves, but also their behaviors, interactions and genetics. Think about each of these levels as we progress, coupled with the different lenses of ecology we discussed earlier. Hopefully, by the end, we will have a more satisfactory perspective on biodiversity and will be able to better define the term.

As with many systems of classification in science, there are different classifications of biomes; you may run across lists shorter or in excess of the one described in this series of posts. I will detail the most expansive terrestrial biomes here, though later we may delve into some of the more obscure classifications.

The tropical rain forest (tropical wet forest, tropical moist broadleaf forest) is probably the most well-known biome to the non-biologist, immediately recognizable for its garish displays of color, shape and texture. Evolution has produced a nearly unlimited array of plants, animals, fungi and microbes, all interwoven in an intricate organic tapestry.

The source of the density and richness of the tropical rain forest is two fold: temperatures are relatively constant throughout the year and these areas are drenched by rain almost daily. Rainfall can exceed 400 cm in a single year in these forests (temperate forests rarely exceed 100 cm of rain), draining the soil of nutrients and leaving it acidic.

Not all rain forests have soils that are poor in nutrients; those along rivers are consistently rejuvenated by flooding, while those rooted in the soil of young volcanoes have yet to be leached by steady rains.

Nutrients are rapidly recycled in a rain forest system. With as many as 300 tree species inhabiting a single hectare and as many as 1,000 species of insects on a single tree, not to mention the high density of other organisms, it is easy to see how the nutrient budget in the forest would be tight, and how organisms rely on one another to perpetuate. Bacteria, mites and other soil creatures quickly break down organic matter from dead organisms which is absorbed by other animals or by the shallow, twisted roots systems of trees and plants. Mutualistic fungi called mycorrhizae often assist these root systems in acquiring elusive elements like nitrogen and phosphorous. Termites break down tough cellulose with the help of microbes in their guts. Leaf cutting ants slice up plant material and cultivate a nutritious fungi for the colony that aids in decomposition. And, since the density of plant life within the forest almost negates the effects of wind, plants are almost completely reliant on insects for fertilization and frugivorous (fruit-eating) animals for the dispersal of seeds.

If you want to find most of the life in a rain forest, it might be best to look up. The canopy is home not only to countless species of birds, monkeys, amphibians and snakes, but also to thick draping vines called lianas. Epiphytes, plants that live on other plants, make homes out of the crooks and crannies of trees that can reach 80 meters in height.

Rain forests make up only about 2% of the Earth's terrestrial surface, but contain about half of the planet's land-loving species. On a macroscopic level, these forests are the taxonomist's last great frontier of discovery, especially in entomology; low estimates predict tens of millions of unclassified insects.

The thick web of life, the behavior guiding (sometimes forcing) interaction and the underlying genetics of it all that constitutes the tropical rain forest system is the quintessential representation of biodiversity. While other biomes on the planet may not by as dense, the biological relationships of each provide a fresh view of the diversity of life on Earth.

Some authors skip the tropical dry forest when listing biomes, but due to its peculiar (and extreme) double life of wet and dry seasons, we'll give it a nod, next time.

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Know Your Biomes I

Feb 07 2007 Published by under Basic Concepts, Ecology

Over the past few billion years, life has persisted through countless geologic, atmospheric and extraterrestrial disturbances through its ability to change with the environment. Ecosystems exist in their present state because they have evolved to be as such. It took trillions of events - biotic and abiotic - for these complex systems to weave their thick web of dependence.

One way for ecologists to define and correlate these varied environments is by categorizing these areas by the types of plants that inhabit them. These categories are called biomes. Categorizing each biome by plant life is not an end in itself; instead, indigenous plant life acts as an indicator of the animal life, soil composition and the climate of an area.

Most of us already know the biomes - desert, rain forest, savannah, tundra, etc. - but how exactly are they defined?

Life within a terrestrial biome is founded by its soil. Soil is created by the weathering of rock (inorganic content) and by the decay of tissue from animal, plant and microbial life (organic content). A mature soil - one that has been undisturbed by geologic or human activity - is characterized by distinct layers called soil horizons that will vary from biome to biome. Deserts have a very different soil stratification than rain forests due to the varying organic and inorganic composition of the biome. The horizons will be immediately apparent and distinct with a deep core sample.

In Western Maryland, there are large swaths of land reclaimed from strip mining operations and repopulated with native or analogous plant life. If you take a core sample in these reclaimed areas, there is no stratification. You will see the same trend in park land that was once used for agriculture. The soil will not become mature again for some centuries, perhaps even millennia.

Soil horizons are typically defined as such:

  • The O horizon, as shown above, is the "organic" layer, a mixed bag of leaf litter and other organic bits found on the biome floor. This layer will vary with particular biomes, obviously, with deserts or tundra having very little litter at all.
  • In the topsoil layer, or A horizon, is usually associated with humus, mostly decayed organics that have been compacted and mixed with fine inorganic particulates such as clay, silt and sand.
  • The B and C horizons are mostly composed of inorganic rock in different sizes; C will have larger "chunks" than B.
  • Below C is the bedrock.

So, plants form the foundation of each biome, and soil provides a suitable anchor and a source of nutrients for the plants (not to mention for the trillions of microbes and fungi feeding and assisting plant growth).

Climate is also an essential factor in understanding the distinctions made between environments. The Earth's "average" climate is determined by an enormous number of factors, but generally speaking, we can zero in on a few.

Heat from the sun is what drives the circulation of air on Earth, and with the circulation of air, the factors of precipitation. Much of the basis of climatic variation seen between biomes is created by uneven heat from the sun due to the Earth's tilt on its axis and its ovoid orbit around the sun. In short, these variations combined with the ever changing geology have created our extant biomes, which lie within more or less predictable latitudes.

Take a look at the map below:

The middle dotted line is the equator, while the outer two both lie at 30 degrees. Notice that the dark green areas (tropical rain forest) are pretty much bound to the equator, while the yellow areas (deserts, generally) skirt along the 30 degrees north and south. This is caused by the constant heating and cooling of air at the equator leading to almost daily rainfall.

With the moisture expelled in the form of rain, this now dry air mass rises, moving north and/or south. It sinks into the areas at 30 degrees N & S, reabsorbing moisture, and in the process, robbing the area of rain. The mass continues its journey, eventually dumping moisture into the temperate zones. This is a generalized model, but it proves the point.

So, biomes are categorized by the plants that live within certain areas, but those plants exist in their present state only because of the atmospheric and geologic pressures placed upon ancestral organisms. With recent evidence confirming that human beings are indeed causing the global climate to rise prematurely, ecologists will rely on plants to continue their role in indicating climatic influences.

In the next few posts, we'll briefly review the different types of biomes on Earth, making distinctions in precipitation levels, geography and indigenous life.

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What Is Ecology?

Feb 06 2007 Published by under Basic Concepts, Ecology

Ecology is a study of interactions or relationships between organisms and the environment; the connectedness between living systems and non-living systems on the Earth. Ecology is, in a sense, a historical field, founded upon the Earth's far reaching and ever evolving natural history.

The term ecology comes from the Greek root words oikos logos, literally “the study of household,” first combined by Ernst Haeckel in 1866. Haeckel was referring to the interactions within the house of nature, and we have used the word ecology (translated from the German Oekologie or Ökologie) to describe complex systems of life both extant and extinct.

The shear range of fields that the term "ecology" encompasses is staggering. Why? Think about how many levels of biological interaction can be described by focusing on one animal, a red panda (Ailurus fulgens).

At the individual level, the red panda itself, an ecologist could look at a particular panda's ability to thermoregulate, or absorb and expel heat within its environment. Within a population of red pandas, the next step up, an ecologist could analyze the gene flow within the population and how this particular group of red pandas is distinct in adaptations from a neighboring one.

Communities of organisms are composed of two or more populations. At this level, an ecologist could take a closer look at the cohabitation of red pandas and giant pandas in a certain area, studying how the animals share food and space.

The distinction between a community and an ecosystem is slight, but essential to understand. While a community describes interaction between organisms in an area, an ecosystem describes the entirety of the area, including chemical and physical factors. Research at this level would concentrate on things like nutrient cycling (i.e. the phosphorus or carbon cycle) or the distribution of energy within the slope forests of the Himalayas.

As we expand, things become more generalized. We are not longer talking specifically about the red panda, but about the living/nonliving system of which the red panda is a part. Landscape ecology looks at a certain heterogeneous conglomerate of ecosystems, their composition ("patches" of forests, plains, etc.) and the interaction between these ecosystems. (I will zero in on this level and be a bit more descriptive in a later post.)

A geographic ecologist (who studies regions of interaction) might take a look at the geologic history of an island or lake and try to explain the distribution of organisms in that area due to the large scale geologic activity or other environmental variables. R.H. MacArthur (an associate of E.O. Wilson) thought that geographic ecology could be described as the "search for patterns of plant and animal life that can be put on a map."

Finally, ecologists can look at biological interaction through the widest scope by analyzing the biosphere, or the entirety of life's systems on the globe. Ecology at this level usually involves major atmospheric phenomena like the long term effects of climate change or El Niño on the Earth's living systems.

At each of these levels of organization, there are near infinite examples of questions to ask about interaction. Those are just a few examples. Additionally, we have not even considered narrowing the focus to the levels of physiological, cellular and molecular interaction.

In the next posts in the Basic Concepts: Ecology series will discuss terrestrial biomes, but in order to appreciate the distinction and formation of these regions across the Earth, we'll delve into some basics about climate distribution and soil composition.

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