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Biology library
Course: Biology library > Unit 28
Lesson 8: BiogeographyClimate
Global, regional, and local factors that influence climate. How climate affects where species are found.
Key points:
- Each species has a unique range, the set of locations where members of that species are found on Earth.
- A species' range depends on the biotic (living) and abiotic (non-living) conditions it needs for survival and on geography.
- The ranges of species and the distribution of biomes (types of ecosystems) are shaped by climate.
- A place's climate depends on global patterns of solar energy input and air flow, as well as features like mountains and bodies of water.
Introduction
Let's start off with a question: Where would you find a polar bear?
Like me, you may forget whether polar bears live near the North or South pole. (I looked it up: the answer is North!) Even so, you probably wouldn't look for one in, say, the rainforest or desert.
Let's think about why that's the case. Polar bears need certain conditions in order to live, thanks to the way their bodies are built and function. These conditions are found only in certain places. For instance, the thick fur coat that helps a polar bear survive in the cold would be useless (and even harmful) on hot day in the desert.
This is a general rule in ecology: each species is found only in a certain set of habitats out of the many on Earth. This occupied region is called the species' range.
Some organisms have broader ranges than others, but no species is found everywhere. That's because different species have different needs, as well as different histories of dispersal, or how they've spread from place to place.
One of the most important factors determining where different species are found is climate, or long-term, typical weather conditions. In this article, we'll take a look at biogeography (the study of why different organisms are found in certain locations, in certain numbers) and how species ranges are affected by climate .
Each species has a range
The range of a species is the set of locations where that species is found on Earth. For instance, the diagram below shows the range of polar bears (looking down on the Earth from above the North pole):
What determines a species' range? Historical chance and geographical barriers can play important roles. For instance, maybe polar bears could survive at the South pole as well as the North pole. But they were never introduced to the South pole, and have had no way to disperse, or spread, across the oceans in between.
Once a species has been introduced to an area, it can only survive in that area if the conditions are right. Some of the conditions that must be "right" are biotic, meaning that they're directly related to living organisms. For instance, a species may not be able to get a foothold in a given area because a competing species, predator, or pathogen is already there, or because no food supply is available.
Many factors that determine whether a species can live an an area are abiotic, or non-living. Examples of important abiotic factors include temperature, sunlight, and moisture level. These factors sometimes determine whether a species can live in a place in a very direct way. For instance, a plant species will only take root and spread in a place where it's getting enough sunlight and water.
However, abiotic factors can also affect where species are found in less direct ways. For instance, climate and soil quality directly affect the type and number of plants that can grow in a particular area. Since energy enters ecosystems via plants and other primary producers, climate and soil quality indirectly determine what other trophic levels, or "food chain links," the ecosystem can support.
Global distribution of biomes
Abiotic factors shape the ranges of individual species, such as our friend the polar bear. At a more zoomed-out level, though, they also determine where different types of biomes are found on Earth.
What exactly is a biome? Basically, it is a type or category of ecosystem. One familiar example is the desert biome. Each desert is in a different place and has its own unique set of plants and animals. Still, Earth's deserts are all distinctively deserts and share common features. They tend to have little rain, high daytime temperatures, and sparse plants adapted to the harsh conditions.
Climate is the key abiotic factor that determines where terrestrial (land) biomes are found. Each biome has a characteristic range of temperatures and level of precipitation (rainfall and/or snowfall). If we know what temperature and precipitation are like in a location, we can often predict what type of biome will be found there.
Certain types of biomes tend to fall in rough bands along Earth's north-south axis. For instance, there is a big band of tropical forest (green in the diagram above) that encircles Earth's midline, or equator, including parts of Central and South America, Africa, and Southeast Asia.
However, Earth's biomes also don't form a strict "stripe" pattern, as you can see from the bumpy shapes on the map.
We can explain both the general pattern of bands and variations from this pattern by looking at different factors that affect climate.
What is climate?
Climate is just the weather, right? Well...sort of. In ecology (unlike in everyday life), these terms have slightly different meanings:
- Climate refers to long-term, typical atmospheric conditions in an area, such as temperature and rainfall. "It's usually hot in Dallas during the summer" is a description of climate.
- Weather refers to the same types of conditions, but on a shorter timescale. For instance, "The high was
Basically, you can think of climate as a place's “average” weather.
How climate changes with latitude
In general, temperatures on Earth’s surface drop as we move from the equator to the poles. That's not a big surprise—we tend to think of the Arctic as chillier than then tropics! But why is it the case?
The basic answer is that the equator gets more insolation, or solar energy per area per time, than the poles do. Rays of sunlight hit the Earth directly near the equator, but at an angle near the poles, so the same amount of energy is spread over more area in the polar regions, as you can see in the diagram below:
Also, at the poles, sunlight travels a longer path through the atmosphere before reaching the surface. That means more light is deflected into space by particles in the atmosphere (and thus never reaches the surface) at the poles than at the equator
The strong sunlight at the equator (and weak sunlight at the poles) makes the tropics warmer than the Arctic. Not only that, but this difference in solar input also generates major global patterns of air circulation. Because air is heated by the sun most strongly at the equator, it has the greatest tendency to rise there. This rising of air at the equator drives large-scale patterns of air flow and rainfall.
What do these large-scale patterns look like? Earth's atmosphere contains six rotating cells of air are found (three north of the equator, three south of the equator). Each of these cells encircles the Earth like a giant "air donut," as shown in the figure below.
In this six-celled pattern of air flow, air rises in low-pressure zones: one at the equator (under the influence of the strong equatorial sun) and two more at
Having already dropped its moisture, the air that rose in the low-pressure zones is dry as it flows towards the poles (traveling high up in the atmosphere). When it comes down again in high-pressure zones (which are found at
Mountains, elevation, and climate
Latitude patterns in climate give us broad patterns, such as bands of desert and high rainfall at different latitudes. but as you may have guessed, they're only part of the picture. After all, not all places at the same latitude have the same climate or the same type of biome!
Elevation above sea level is one key factor that shapes climate. To give a real-life example, when I was a kid, I went to a school on top of a big hill. My classmates and I sometimes got a snow day (day off from school) when other kids in the area didn't. Why? It was colder on the top of the hill than it was at sea level, so it sometimes snowed at our school when it was raining in the areas below.
To put that idea more generally, places at high elevations tend to have a colder climate than nearby low-lying areas. In general, for each
Because temperature changes with altitude (along with things like moisture and soil type), a mountain can have different biomes at different altitudes. For instance, a tall mountain may have grassland on its lower slopes, but a zone of alpine tundra, like the arctic tundra biome found near the north pole, at higher elevations
Mountains also affect patterns of rainfall, both on their own slopes and in surrounding areas. Imagine the case where a mountain tends to get hit by winds coming from a certain direction—say, off the ocean. Especially if those winds are damp, the windward (wind-facing) slopes and surrounding areas will tend to get lots of rain.
Why is that the case? The air loses its capacity to hold water as it rises and cools while moving up the slopes, and it drops the extra moisture as rain. The air that makes it over the mountain is dry, so the other side (the leeward side) tends to have a desert-like climate. This dry region on the leeward side is known as a rain shadow.
Lakes, oceans, and climate
As the example above shows, bodies of water (especially big ones like oceans and lakes) can affect the climate of surrounding regions. In fact, bodies of water influence climate in a variety of ways, even when mountains are not in the picture.
At a basic level, lakes, oceans, and streams play a vital role in climate processes by serving as reservoirs for water, which can evaporate from the surface to fall later as rain or snow. You can learn more about this process in the water cycle article.
Bodies of water also minimize changes in temperature of nearby landmasses. That is, they keep high temperatures from getting as high and low temperatures from getting as low as they otherwise would. You can learn more about how water's unique properties make this possible in the video on specific heat capacity of water.
Finally, ocean currents (which carry water from one place to another) can strongly affect the climate of nearby land. The map below shows some of Earth's major currents:
To see how currents affect climate, let's compare two cities at nearly the same latitude: London, England and Calgary, Canada
This difference between London and Calgary can be traced to a current called the Gulf Stream. The Gulf Stream carries water heated at the equator up past the eastern coast of the United States, feeding into another current called the North Atlantic Drift. This current carries warm water past England and the west coast of Europe, making the climate warmer than it otherwise would be
Why does this climate stuff matter?
Climate is a key factor that determines where different species can live. This principle holds true across the many branches of the tree of life, from animals (like our friend the polar bear) to plants to microbes. Each species needs its own specific set of conditions for survival, many of which are directly or indirectly related to climate.
If climate conditions in an area change, the species that can live there may also change. For instance, a drop in rainfall may mean that a region can no longer support the plant species it previously did, becoming more desert-like instead. Such changes can have cascading effects on ecological networks, with shifts in plant communities affecting all the animals that depend on them.
This principle holds true for any change in climate, whether it affects a tiny area or a large one. However, it's especially important in light of the global climate change that is now taking place. As a result of human activities, scientists predict a rise in average temperatures of
To learn more about global climate change and how it can affect species ranges and biodiversity, see the climate change and biodiversity video from the California Academy of Sciences.
Want to join the conversation?
Why some winds are highlighted in blue or red in the picture of Water Circulation Pattern?(5 votes)
Blue currents are cold currents red currents are warm.(0 votes)
How May Pollution and Greenhouse gasses specifically destroy the Climate and atmosphere?(list the things that are harmed by pollution and greenhouse gasses as well as how they destroy that one thing)(5 votes)
Pollution causes greenhouse gases. These trap excess heat close to the earth, heating everything up. They affect everything.(6 votes)
Why does dry air only travel to about 30 degrees north or south, why not any other location?(3 votes)
In other areas the conditions are not right for dry air. In most of these places you have allot of water which moistens the air. If the air is moistened it cannot be dry. This might not be true for all places but is true for most. As for the other places, all I know is that there is a reason, and that reason was carefully thought outt by God when he created the earth and there is a good reason for why this is the way it is. Hope this helps.😊(2 votes)
What are the names of the cells of air flow?(3 votes)- So many animals that need to be in there natural habitat because they will die if they are not in there natural habitat(2 votes)
- Yes, because they are adapted to survive in that type of habitat.(3 votes)
- If an animals natural habitat some how is gone about how long would it take for and animal to adapt to a new habitat?(3 votes)
It depends on how different a new habitat from the last one is.
For example, if you do it artificially by burning forests or transferring desert animals to the meadow, then it wouldn't end up successfully.(1 vote)
The uneven heating of the Earth's surface by the sun.(6 votes)
what does it mean by tropic ?(1 vote)- The tropics are the region of the Earth surrounding the Equator.
There is no special meaning behind it, it is the name.(4 votes)
- How do species differ from the poles to the equator(2 votes)
- See through evolution species have adapted to their habitat. Say polar bears were in the desert 10000 years ago now they would be desert bears. So with every creature there is a different special and remember the main degrees of the earth are:
60*
23.5*
0* (equator)
23.5*
60*(1 vote)
- Why is the Earth rotating on its axis?(1 vote)
Angular momentum of all the mass that formed the Earth, plus all tidal forces that have altered it.(2 votes)