What Are Ecosystems? Crash Course Geography #15 - Free Educational videos for Students in K-12

What Are Ecosystems? Crash Course Geography #15 - By CrashCourse

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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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