Chapter: Ecology and the Biosphere

Ecology is the study of organisms and their environment. And ecology is studied at several different levels, from individuals and population to biomes and even the entire biosphere.

 Fields of ecology

Organismal Ecology

Organismal ecology is the study how individual organisms interact with their environment. Specifically it is the study of the morphological, physiological, and behavioral adaptations of individuals. Organismal ecologists look at how morphological differences among individuals in a population affect their fitness. In this way, it can be said that Charles Darwin was an organismal ecologist. Organismal ecologists also include the study of behavior within populations. Behavioral ecology is the study of the ecological and evolutionary basis for animal behavior, and the roles of behavior in enabling an animal to adapt to its environment. For example, If an organism has a trait which provides them with a selective advantage (i.e. has an adaptive significance) in a new environment natural selection will likely favor it. Adaptive significance therefore refers to the beneficial qualities, in terms of increased survival and reproduction, a trait conveys.

Population ecology

Population ecology is the study of how numbers of individuals in a population change over time. Population ecology is a sub-field of ecology that deals with the dynamics of species populations and how these populations interact with the environment. It is the study of how the population sizes of species living together in groups change over time and space.

Community ecology

In ecology, a community is an assemblage of two or more populations of different species occupying the same geographical area. Community ecology is the study of the interactions among different species in communities within a given area.

Ecosystem ecology

Ecosystem ecology moves beyond species, and looks at how nutrient and energy moves through different areas.  Ecosystem ecology examines the physical and biological structures and exams how these ecosystem characteristics interact with each other.

Abiotic and biotic factors

What determines where a particular species can live? Why don’t species live in many different biomes? Why can’t I grow this cactus in New York? The range of  a species is what the geographical area of distribution that a particular species has. And it is largely determined by physical factors such as temperature and precipitation. These are known as abiotic factors. So why can’t you grow that cactus in New York. Well, the reason is that all organisms are adapted to certain environments. Because of fitness trade-offs, organisms are adapted to a limited set of abiotic factors. Imagine humans before we began to make our own clothing. We were perfectly adapted to the hot climates of Africa. However, as we began to expand our ranges North, we had to cover our skin. Naked humans would never exist in the North, but having a bunch of hair for fleas to attach to doesn’t make any sense in Ethiopia.

Biotic factors to play a role in a species distribution. However, it is not nearly as important as the abiotic factors in most organisms. Competition is a driving ecological force that can severely deterimine a species distribution. If a new species comes into an ecosystem that is more competitive than another species, over time the new species will reduce the range of that species. Similar results can happen with parasitism and disease.  

Temperature variations

Nearly all of the biomes on Earth are dictated by two factors: how much sun light they receive and how much water they receive. And the amount of water they receive is related to how much sunlight they receive. At the equator, the sun is directly overhead. So it has the most amount of sunlight per unit area of any other latitude. At the middle latitudes there is a moderate angle of incoming light, creating moderate temperature. And a low latitudes, there is the lowest angle of incoming light, giving the smallest amount of sunlight per unit area.

Global Light Intensity

This is a map of global light intensity. In case you didn’t know, the earth is round. So the sun, hits the Earth with greater intensities based on latitude. At the equator, the light intensity is far greater than the poles. And this is the major determinate determining the positioning of earth’s biomes.

Temperature variations

Seasons are caused by Earth’s natural tilt on its axis, known as its angle of incidence. In the northern lattitudes, the Earth is tilted closer toward the sun in the summer months and further away from the sun in the winter months. This determines our seasons. That is why up north it is cold in the winter and warm in the summer. The opposite is true in the summer lattitudes. Their summer is our winter and their winter is our summer.

Hadley Cells

The Hadley cell is a tropical atmospheric circulation, which is caused by the intense nature of the sun at the equator. The sun is most intense directly at the equator. Since the light is most intense at the equator, the air there expands and rises. In addition, warm air has a greater ability to hold moisture. So directly at the equator, hot, wet air rises. And as it rises it cools and the gaseous water condenses into a liquid. This is why the tropical forests of the world are so lush. They have the most sunlight and the most water of any other place on Earth. But that is only ½ of the story of the Hadley cell. As the warm, wet air masses rise they leave a vacuum behind them. As the warm air reaches the upper limits of the atmosphere the air masses move equally in a northerly and southerly direction raining along the way.

And at around 30˚ those air masses descend back to the surface of the Earth. While this is happening, the air masses are gaining water hold capacity. This means that if there is any moisture in the environment, it quickly gets locked up into the air mass. This is the fundamental phenomenon that creates the world great deserts, from the Gobi, to the Chihuahua to the Sahara. Some of the driest places on Earth occur at 30˚ N and 30˚S.

 Global circulation patterns

Hadley cells are the circulation patterns that exist from 0˚ and 30˚. There are also two other circulation patterns in both hemispheres. The other notable feature of these circulation patterns occurs around 60˚ N and S. At these lattitudes, there is a similar rise in the air masses. As the air masses rise, they cool and condense, creating a fairly wet pattern at 60˚. This is why areas such as England, New York and Seattle are so wet.

Regional effects

Regional effects can also have a tremendous impact on temperature and moisture. And temperature and moisture are the predominant factors what grows where. There are two major regional effects that determine what grows where. The rain shadow effect occurs when mountains exist. When air masses move toward mountainous regions, the air rises. And as air rises it cools because the higher you go up in the atmosphere, the colder it gets. As the air cools, the gaseous water condenses creating rain.

This effect is dramatic in especially tall mountains like the Cascade Mountains in the Pacific Northwest, or the Sierra Nevada mountains in California. The mountains are so tall that they strip the air mass of nearly all the moisture, except in freakishly big and moist air masses. And the result of this is a tremendous amount of precipitation in mountainous regions. However, this effect also creates high deserts on the opposite sides of the mountain. And we see this on the other side of the Sierra Nevada Mountains. That is where the Mohave desert is.  And it is very, very dry. So the Sahara desert is caused by a global effect from the Hadley cell. It is centered around 30˚ N. Whereas, the Mohave desert is caused by a regional effect.\

Another important regional effect is known as the ocean moderation effect. Water has a tremendous capacity for storing energy. Because of this phenomenon of water, areas near the oceans can absorb a great deal of heat from the atmosphere in the summer when the water temperature is cooler than the air temperature. As a result, the ocean moderates summer temperatures on landmasses very close to the ocean. If that weren’t awesome enough, the ocean also releases heat to the atmosphere in winter, when the water temperature is warmer than the air temperature. AS a result coastal areas have much more moderate climates than inland areas. It is no wonder that everyone wants to live at the beach. You get the best of both worlds.

Terrestrial Biomes

Tropical rain forest

The most important determinant of what biome will exist where is a function of the temperature and rainfall. And these are not just a factor of the averages of temperature and rainfall, but how variable they are. Tropical rainforests all occur very near to the equator. And at the equator, the temperature is always hot. And even more than that, the temperature hardly ever changes. It is hot all the time. What does change is the amount of precipitation. In many tropical rainforests, there are two season in tropical rainforest: the rainy season and the dry season. Tropical rainforests are the biomes that have the most biomass, and have the highest amount of biodiversity. They also are characteristically multilayered, with two, three or even four lays of trees. Light is abundant at the topmost layer, while at the floor, light is all but non existent.

Subtropical deserts

At the other end of the spectrum are subtropical deserts. These deserts are found throughout the world in two distinct latitudes: 30˚N and 30˚S. Most of the world’s great deserts are subtropical deserts: the Sahara, the Gobi, the Sonoran, and the Australian outback. And they are characteristically formed as a consequence of the Hadley cell. They are characterized by having a high average temperature, that varies moderately. They also have very, very low precipitation and very, very low biomass. Most of these plant are space widely apart due to a high level of competition for water.

Temperate grasslands

When I think of temperate grasslands, I am brought back to my homeland. I remember long, warm summers (if you can call 105˚ for 30 days straight warm) and short, bitterly cold winters. Overall, there is low precipitation which is why trees are infrequent. Also another factor controls the growth of woody plants, fire. Fire is very common in grasslands, and without it the grasslands would eventually become shrub lands.

Temperate forest

Temperate forest of North America include the Appalachian Mountains from South Carolina to Maine and the Rocky Mountains. These environments have a temperature scheme very similar to grasslands, but with significantly higher precipitation. They also typically have a defined winter, with skiing, snowmobiling, and snow angels. Compared with the world’s other ecosystems they have moderate productivity in terms of biomass, and moderate biodiversity predominanted by deciduous trees. They are the goldilocks biome. And they sure are pretty in the autumn.

Taiga

Just above the temperate rainforest are the Boreal forest (also known as the Taiga). They are really defined by their temperature. They have a very cold, very long winter with short, cool winters. The temperature variation is extreme, and the amount of precipitation is limited. However, there is very little evaporation due to the cold temperatures. As a result, trees can grow. These ecosystems are dominated by the gymnosperms, conifers. These include the pines, spruces and firs. And even though there is a high biomass, there is low productivity. These trees grow very slowly. And there aren’t a lot of species that can tolerate these conditions, so biodiversity is also extremely low.

 Tundra

And if that weren’t inhospitable enough, go to the tundra. These are areas within the Arctic Circle that are not covered by ice 365 days a year. They have very, very low temperature, and very, very low amounts of precipitation. In fact, the growing season of the tundra is limited to about 6 weeks (8 weeks in a freakishly good year). There is cold, and then there is Tundra cold. And only a small part of the soil melts. Underneath that is what is known as permafrost (it is permanently frozen). And to the plants, it might as well be solid rock. This ecosystem is dominated by really short woody shrubs and herbaceous plants. And there is also a whole bunch of lichen. Reindeer live in the tundra, and nearly their entire diet consists of the lichen that grow here.

Aquatic biomes

Lakes and ponds

There are also very distinct aquatic ecosystems. Lakes and ponds are free standing bodies of water that don’t receive any water from an ocean or sea. All their water comes from rain water. And in lakes and ponds there are distinct zones where specific organisms reside. At the edge of a lake is known as the littoral zone. And it is where you would find plants that are rooted into the ground. This is a great place for these plants, because they have the substrate to root into, and they have enough sunlight to effectively go through photosynthesis. The littoral zone is also where alligators will eat you. Be wary at the littoral zone. Free-floating photosynthetic organisms can be found in the limnetic zone or the littoral zone, collectively these are known as the photic zone. The limnetic zone is the zone offshore, but still has enough sunlight that photosynthetic organisms can still make enough sugar to survive. The benthic zone is the bottom of the lake or pond and includes the entire bottom. And this is most likely where you would find detritovores, or organism that are consuming dead matter after it floats down.

Freshwater wetlands

Areas that are relatively shall and really wet typically form freshwater wetlands. And they are differentiated from lakes and ponds in that they have emergent plants, plants that come out of the water. There are three types of freshwater wetlands. Bogs are stagnant (meaning there is no water flowing out of the bog), and they are typically acidic. And they are also usually really stinky. Marshes are a group of freshwater wetlands that are predominated by non-woody plants, typically grasses. Whereas swamps, are predominated by emergent trees and shrubs, like the cypress swamps of Florida.

 Streams and rivers

Streams and rivers are freshwater ecosystems with a flow in a single direction. Estuaries flow in two direction based on tides. The source of river is usually very cold, narrow and fast. However, in terms of organisms there isn’t a lot going on. It is just too cold and too fast. So there aren’t a lot of organisms, and those that are there are mostly animals. At the mouth of a river, the water is warm, the river is wide and it moves really slow. …boring if you ask me. But these conditions allow plants to take root and you also see a lot more animals. 

 Estuaries

Where the river meets the ocean is a special ecosystem that lives in two world, known as an estuary. They are slightly saline due to the incoming tide from the ocean, but they are constantly refreshed with freshwater from the rivers. The salinity that is present at a given area is dependent on a few factors. It is dependent on the strength of the tide. As you know earth’s tides are a factor of the moon’s gravitational pull on the water. However, the effect isn’t the same across the entire globe. The closer the moon is to the surface of the Earth the stronger the tide. And since the earth is a sphere there are very different effects of the moon on the tide. The amount of freshwater coming from the river system also effects the salinity levels. If there is a drought the salinity levels in the estuaries will rise, and when there is heavy rains the salinity levels will fall. Salinity levels in estuaries are also caused by the proximity to oceans. The closer the estuaries are to the oceans, the more salt they will have. The further away the less salt they will have.