What Are Ecosystems? Crash Course Geography #15 - By CrashCourse
Transcript
00:0-1 | On the island of Madagascar , there's a kind of | |
00:01 | moth that drinks tears from the eyes of sleeping birds | |
00:05 | . When I first heard this , I just sat | |
00:07 | with that weird idea . There's a moth that gets | |
00:09 | most of its nutrients . It needs to survive by | |
00:11 | drinking bird tears . Welcome to the biosphere , the | |
00:14 | sphere of life that extends from the depth of the | |
00:16 | ocean all the way up to eight km above Earth | |
00:19 | . A lot of incredible things live here . So | |
00:21 | of course as geographers , we want to know why | |
00:23 | bananas and bacteria and tear drinking moths show up in | |
00:26 | some spaces , but not others . And to do | |
00:28 | that , we have to zoom out a little . | |
00:30 | For example , that moth gets its nutrients from birds | |
00:33 | , while birds rely on seeds and berries from the | |
00:34 | surrounding plants which grow with the help of the sun | |
00:37 | . So the moth and the birds and the plants | |
00:39 | and the sun are all part of an ecosystem . | |
00:41 | A community of living organisms in an area interacting with | |
00:44 | their environment , ecosystems are built on relationships , even | |
00:48 | strange ones that involved here theft and the relationship between | |
00:51 | the amount of energy a place receives and the movement | |
00:53 | of nutrients is what makes the incredible diversity of life | |
00:56 | possible . I'm al is a career and this is | |
00:58 | crash course geography . The biosphere is a complex web | |
01:09 | of interconnected ecosystems and all ecosystems depend on two key | |
01:13 | things . The one way movement of energy and the | |
01:15 | cyclic movement of nutrients . Energy flows are the paths | |
01:18 | energy can take through an ecosystem . Energy generally enters | |
01:22 | ecosystems from the sun but doesn't return to the sun | |
01:24 | . So energy flows are one way relationships . Plants | |
01:27 | absorb the sun's energy during photosynthesis , adding carbon dioxide | |
01:31 | and water to make carbohydrates and grow bigger . So | |
01:33 | the sun's energy is converted into chemical energy which is | |
01:36 | stored in biomass , any plant or other living thing | |
01:39 | . If a bit of biomass is eaten , it | |
01:40 | passes on its chemical energy to continue the energy flow | |
01:43 | . The rate photosynthesis makes energy across an entire ecosystem | |
01:47 | , minus the rate that energy is used . Is | |
01:49 | its net primary production or the amount of stored chemical | |
01:52 | energy in an ecosystem over a certain amount of time | |
01:55 | . For example , on a really small scale , | |
01:57 | think of a fish tank ecosystem that you can hold | |
01:59 | in your hands , there's water , a fish , | |
02:01 | soil , rocks , air , light food and one | |
02:04 | little plant all in a glass bowl . In this | |
02:06 | fish tank ecosystem , the net primary production is pretty | |
02:09 | low because only that one little plant is absorbing energy | |
02:12 | from the sun , along with any photosynthetic bacteria or | |
02:14 | algae that grows . When I forget to clean the | |
02:16 | bowl globally , net primary production on land generally changes | |
02:19 | with latitude , productivity is highest between the tropics and | |
02:23 | decreases towards higher latitudes and elevations . Bio geographers and | |
02:26 | ecologists who study how life is distributed on earth probably | |
02:29 | figured that calling regions of the world very productive ecosystem | |
02:32 | or extremely not productive ecosystem would be pretty boring . | |
02:35 | Instead , we classify ecosystems into bios or habitats with | |
02:38 | similar characteristics , including productivity . The names are much | |
02:42 | more descriptive and fun . The equator gets the most | |
02:45 | sunlight and a lot of precipitation . So there's a | |
02:47 | lot of photosynthesis happening here . These highly productive ecosystems | |
02:51 | are all tropical rainforest by OEMs , which are some | |
02:53 | of the most diverse and complex areas of the planet | |
02:56 | . So it's no wonder the tear drinking moth lives | |
02:58 | here . Similar patterns happen on either side of the | |
03:00 | equator , but we're going to turn north because there's | |
03:02 | more land in the northern Hemisphere , there's also less | |
03:05 | and less precipitation as we move out from the equator | |
03:07 | and less and less productivity . Because photosynthesis can't happen | |
03:10 | without water , the bios gradually shift from tropical rainforests | |
03:14 | to tropical savanna to desert . Further north , in | |
03:17 | temperate and high latitudes , the net primary production varies | |
03:20 | seasonally . Like one by OEM is the broadleaf deciduous | |
03:23 | forest with oak , beech , hickory , maple , | |
03:25 | elm and chestnut trees . These trees have increased productivity | |
03:29 | in the sunny spring and summer and shed their leaves | |
03:31 | in the cooler fall and winter seasons . Up here | |
03:33 | in the middle of continents , there are temperate grassland | |
03:35 | biomass with rich soils that produce the tall grass of | |
03:38 | prairies and the short grass of step climates . Further | |
03:40 | north , where there are poorer soils and colder climates | |
03:43 | , we meet the boreal forest by OEMs , which | |
03:45 | have mainly evergreen pine , spruce fir , and large | |
03:48 | trees at even higher latitudes . The decreasing temperatures give | |
03:51 | us the icy tundra bio , with no trees and | |
03:53 | very little productivity , so the amount of energy flow | |
03:55 | through different ecosystems varies wildly , which limits which type | |
03:58 | of plants can thrive here . And because plants feed | |
04:01 | more consumers than any other food source , more plants | |
04:04 | means more biodiversity or the number of different plants and | |
04:06 | animals in an ecosystem . And we can't talk about | |
04:09 | biodiversity without the other key component of all ecosystems nutrients | |
04:13 | , nutrients are chemical elements like carbon , oxygen , | |
04:16 | nitrogen , sulfur and phosphorus stored both in the living | |
04:19 | and non living parts of an ecosystem . And we | |
04:21 | actually have technical terms for those two . The living | |
04:24 | things like plants and animals and bacteria or their dead | |
04:26 | bodies are the biotic parts of an ecosystem and the | |
04:30 | non living things like the soil atmosphere and groundwater are | |
04:32 | the a biotic parts . Unlike how energy flows in | |
04:35 | one direction , the past that nutrients take through the | |
04:37 | ecosystem are nutrient cycles between the biotic and a biotic | |
04:41 | parts . And unlike energy from the sun , all | |
04:44 | the nutrients we have right now on earth are all | |
04:46 | will ever have . It's like how nitrogen moves from | |
04:49 | being a gas in the atmosphere to a solid in | |
04:51 | the soil instead of a one way system . Like | |
04:53 | aliens dropping gift wrapped boxes of nitrogen from space , | |
04:56 | or at least not that we know of the biotic | |
04:58 | parts of an ecosystem really help facilitate these nutrient cycles | |
05:01 | . Like let's look at our fish tank ecosystem . | |
05:03 | Again , producers like our little plant capture nutrients from | |
05:06 | the a biotic parts , turning carbon dioxide into carbohydrates | |
05:09 | through photosynthesis or absorbing nitrogen compounds through its roots , | |
05:12 | consumers like the fish , take nutrients from other organisms | |
05:15 | munching on fish food or the plant's leaves and decomposes | |
05:18 | , break down dead plant leaves or our fish eventually | |
05:21 | and return the nutrients like nitrogen gas to the a | |
05:23 | biotic parts of the tank . Ultimately nutrient cycling through | |
05:26 | ecosystems depend on biological , geological and chemical processes operating | |
05:31 | within the atmosphere . Hydro sphere and with a sphere | |
05:33 | and make up earth's bio geochemical cycles . We can | |
05:36 | compare nutrients across the earth's biosphere just like we compared | |
05:38 | net primary production across different latitudes and by OEMs , | |
05:41 | like let's look at three by OEMs we met before | |
05:44 | the tropical rain forest , deciduous forest and boreal forests | |
05:47 | . We know that there's less and less productivity as | |
05:49 | we move up in latitude , so there's less and | |
05:51 | less biomass and there's also less nutrients , fewer nutrients | |
05:54 | isn't necessarily a death sentence for the trees though , | |
05:57 | it just means that an ecosystem is structured differently . | |
06:00 | Like boreal forests have a lot of nutrient filled litter | |
06:02 | because the cold keeps material from decomposing . But deciduous | |
06:06 | forests have a lot of nutrient rich soil because it's | |
06:08 | warm enough for material to decompose , but not warm | |
06:10 | enough for a lot of biomass to grow . So | |
06:12 | a tree that's adapted to life in a cold boreal | |
06:14 | forest might not make it in a tropical rainforest because | |
06:17 | of the different energy availability and nutrient stores . Let's | |
06:19 | consider the tropical rain forests , which are the most | |
06:22 | diverse by OEMs with lush vegetation and a lot of | |
06:24 | biodiversity . But that decadence hides the fragile balance of | |
06:27 | all the complex energy flows and nutrient cycles . Let's | |
06:30 | go to the thought bubble . Within the tropical rainforests | |
06:33 | . Broadleaf evergreen trees form a canopy at different heights | |
06:36 | and little or no sunlight reaches the shady forest floor | |
06:39 | . These huge trees absorb most of the soil nutrients | |
06:42 | , which doesn't leave a lot for other organisms , | |
06:44 | and they have a shallow root system to grab as | |
06:45 | many of the minerals as possible from bio geochemical processes | |
06:48 | near the surface , and as the large amounts of | |
06:51 | rain filter down through the soil , the minerals that | |
06:53 | dissolve in water are leached away too inaccessible deeper levels | |
06:56 | . To survive , the rainforest has to rapidly cycle | |
06:59 | nutrients . The canopy trees are producers along with understory | |
07:02 | plants that work together to keep vital nutrients moving through | |
07:04 | the ecosystem . Herbivores like gorillas and caterpillars take in | |
07:08 | those nutrients and move them around through their excrement and | |
07:10 | by being eaten themselves like by jaguars or gecko's . | |
07:13 | And the warmth and humidity helps de composers and their | |
07:16 | chemical reactions . So any dead plants or animals decay | |
07:19 | quickly because nutrients get sucked from the soil so quickly | |
07:22 | . When those huge trees are cut down , the | |
07:24 | energy flows and nutrient cycles break those big producers aren't | |
07:27 | there to sustain consumers or shed leaves to recycle nutrients | |
07:30 | . So deforestation or removing trees to use the land | |
07:33 | for something else can be especially destructive in tropical regions | |
07:37 | . If you don't consider the bio geochemical cycles , | |
07:39 | thanks that bubble , we have negative associations with the | |
07:42 | word deforestation . For good reason . A lot of | |
07:45 | tree removal has caused immense damage to ecosystems , but | |
07:48 | indigenous communities have figured out a type of calculated clearing | |
07:51 | that allows them to work with the rapid nutrient recycling | |
07:53 | of tropical rainforest by OEMs in parts of Asia africa | |
07:57 | and south America . With dense tropical forests , many | |
07:59 | farmers have to rely on a kind of subsistence agricultural | |
08:02 | practice , which means they only grow enough food for | |
08:04 | their families . Staples like rice are grown in southeast | |
08:07 | Asia maize and cassava in south America and sorghum in | |
08:10 | africa , yams , sugarcane , plantains and vegetables are | |
08:14 | also planted to supplement staples and to provide fuel and | |
08:16 | fodder for animals . This practice goes by many names | |
08:19 | like Sweden shifting cultivation and slash and burn agriculture . | |
08:22 | The farmers begin by cutting small areas of tropical forest | |
08:25 | into slash or cut vegetation that's then dried and burned | |
08:29 | . The ash gets mixed with the poor soil to | |
08:30 | provide needed minerals and nutrients , basically using all the | |
08:33 | good stuff stored up in the vegetation biomass to help | |
08:35 | new crop plants grow . Of course these crop plants | |
08:38 | use minerals and nutrients from the soil as they grow | |
08:40 | and we eat them to get those minerals and nutrients | |
08:42 | in our bodies . So after a few years and | |
08:44 | before the soil is completely exhausted , the farmers move | |
08:47 | on to another part of the land and repeat the | |
08:49 | clearing , burning and planting process . The previous plot | |
08:52 | is left unplanted and eventually the forest will naturally expand | |
08:55 | to start using that soil as part of its carefully | |
08:57 | balanced nutrient cycling . This land rotation is a key | |
09:00 | part of why humans have been able to keep farming | |
09:02 | like this for thousands of years . But when widespread | |
09:04 | clear cutting happens , ecosystems can collapse . For example | |
09:08 | , we've seen this destruction in the amazon . When | |
09:10 | rice , soy and corn have been commercially cultivated and | |
09:12 | sold in domestic and international markets . The soil is | |
09:15 | exhausted after 3-5 years , so crops can't really grow | |
09:18 | anymore . And then large cattle operations movin as cattle | |
09:21 | feed and trample the ground . The soils are exposed | |
09:23 | to plenty of UV radiation from sunlight , As well | |
09:26 | as cycles of wetting and drying from precipitation . The | |
09:29 | soils become a brick like substance called lottery , which | |
09:31 | isn't great for growing . So the once lively rainforest | |
09:34 | basically becomes hard , barren and lifeless , tropical rainforest | |
09:38 | covers 6% of Earth's landmass but contained 50% of the | |
09:41 | world's species , many of which haven't been described by | |
09:43 | science and are critical to the world's biodiversity . But | |
09:46 | since the 19 eighties , 1/5 of the amazon has | |
09:48 | been deforested as we build more towns , roads , | |
09:51 | dams , farms and minds across the atlantic deforestation in | |
09:55 | Ituri , in the congo Basin , the world's second | |
09:57 | largest expanse of equatorial rainforest is endangering the mountain gorilla | |
10:01 | and in southeast asia . Clear cutting for palm oil | |
10:03 | plantations , endangered orangutans , sumatran tigers and sumatran elephants | |
10:07 | . When humans disturb the biosphere , we alter how | |
10:10 | energy flows and how nutrient cycle , which can throw | |
10:12 | off entire ecosystems in unexpected ways . And if we're | |
10:15 | not careful , that moth that drinks the tears of | |
10:17 | sleeping birds or plenty of other remarkable living organisms may | |
10:21 | no longer exist . But just like we can be | |
10:23 | good stewards of our little fish tank , we can | |
10:25 | take care of the world around us , and the | |
10:27 | much bigger ecosystems were a part of learning where our | |
10:30 | food comes from and how it's produced is a good | |
10:32 | first step like by supporting farmers who try to grow | |
10:35 | food sustainably . And we'll keep talking about our role | |
10:37 | in ecosystems , energy and food and how geography and | |
10:40 | spatial thinking can help address some of the critical issues | |
10:43 | we're facing , like how we can have enough food | |
10:45 | and water to sustain ourselves and our environment . Many | |
10:49 | maps and borders represent modern geopolitical divisions that have often | |
10:52 | been decided without the consultation , permission or recognition of | |
10:55 | the land's original inhabitants . Many geographical place names also | |
10:59 | don't reflect the indigenous or aboriginal peoples languages . So | |
11:02 | we at Crash course want to acknowledge these people's traditional | |
11:05 | and ongoing relationship with that land and all the physical | |
11:07 | and human geographical elements of it . We encourage you | |
11:10 | to learn more about the history of the place you | |
11:11 | call home through resources like native land dot C . | |
11:14 | A . And by engaging with your local indigenous and | |
11:16 | aboriginal nations through the websites and resources they provide thanks | |
11:20 | for watching this episode of Crash Course Geography , which | |
11:23 | is filmed at the Team Sandoval Pierre studio and was | |
11:25 | made with the help of all these nice people . | |
11:27 | If you want to help keep Crash course free for | |
11:29 | everyone forever , you can join our community on Patreon | |
00:0-1 | . |
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