0:00:00.000,0:00:04.710 On the island of Madagascar, there’s a kind[br]of moth that drinks tears from the eyes of 0:00:04.710,0:00:06.290 sleeping birds. 0:00:06.290,0:00:10.160 When I first heard this, I just sat with that[br]weird idea: there’s a moth that gets most 0:00:10.160,0:00:13.820 of the nutrients it needs to survive by drinking[br]bird tears! 0:00:13.820,0:00:17.760 Welcome to the biosphere -- the sphere of[br]life that extends from the depths of the ocean 0:00:17.760,0:00:19.880 all the way up to 8 kilometers above Earth. 0:00:19.880,0:00:24.050 A lot of incredible things live here, so of[br]course, as geographers, we want to know why 0:00:24.050,0:00:28.640 bananas and bacteria and tear-drinking moths[br]show up in some spaces but not others. 0:00:28.640,0:00:30.860 And to do that, we have to zoom out a little. 0:00:30.860,0:00:34.860 For example, that moth gets its nutrients[br]from birds, while birds rely on seeds and 0:00:34.860,0:00:38.100 berries from the surrounding plants, which[br]grow with the help of the Sun. 0:00:38.100,0:00:42.449 So the moth and the birds and the plants and[br]the Sun are all part of an ecosystem -- a 0:00:42.449,0:00:46.859 community of living organisms in an area interacting[br]with their environment. 0:00:46.859,0:00:50.839 Ecosystems are built on relationships -- even[br]strange ones that involve tear-theft. 0:00:50.839,0:00:53.899 And the relationship between the amount of[br]energy a place receives and the movement of 0:00:53.899,0:00:57.100 nutrients is what makes the incredible diversity[br]of life possible. 0:00:57.100,0:01:00.275 I’m Alizé Carrère and this is Crash Course[br]Geography. 0:01:00.275,0:01:08.229 INTRO 0:01:08.229,0:01:11.689 The biosphere is a complex web of interconnected[br]ecosystems. 0:01:11.689,0:01:16.869 And all ecosystems depend on two key things:[br]the one-way movement of energy and the cyclic 0:01:16.869,0:01:18.550 movement of nutrients. 0:01:18.550,0:01:21.799 Energy flows are the paths energy can take[br]through an ecosystem. 0:01:21.799,0:01:25.810 Energy generally enters ecosystems from the[br]Sun but doesn’t return to the Sun -- so 0:01:25.810,0:01:28.159 energy flows are one-way relationships. 0:01:28.159,0:01:32.859 Plants absorb the Sun's energy during photosynthesis,[br]adding carbon dioxide and water to make carbohydrates 0:01:32.859,0:01:34.049 and grow bigger. 0:01:34.049,0:01:38.060 So the Sun's energy is converted into chemical[br]energy, which is stored in biomass -- any 0:01:38.060,0:01:40.000 plant or other living thing. 0:01:40.000,0:01:44.158 If a bit of biomass is eaten, it passes on[br]its chemical energy to continue the energy flow. 0:01:44.158,0:01:49.229 The rate photosynthesis makes energy across[br]an entire ecosystem, minus the rate that energy 0:01:49.229,0:01:53.679 is used is its net primary production -- or[br]the amount of stored chemical energy in an 0:01:53.679,0:01:55.909 ecosystem over a certain amount of time. 0:01:55.909,0:01:59.700 For example, on a really small scale, think[br]of a fish tank ecosystem that you can hold 0:01:59.700,0:02:00.939 in your hands. 0:02:00.939,0:02:06.879 There's water, a fish, soil, rocks, air, light,[br]food, and one little plant all in a glass bowl. 0:02:06.879,0:02:10.950 In this fish tank ecosystem, the net primary[br]production is pretty low because only that 0:02:10.950,0:02:14.940 one little plant is absorbing energy from[br]the Sun (along with any photosynthetic bacteria 0:02:14.940,0:02:17.590 or algae that grows when I forget to clean[br]the bowl). 0:02:17.590,0:02:21.960 Globally, net primary production on land generally[br]changes with latitude. 0:02:21.960,0:02:25.969 Productivity is highest between the tropics[br]and decreases towards higher latitudes and elevations. 0:02:25.969,0:02:30.020 Biogeographers and ecologists who study how[br]life is distributed on Earth probably figured 0:02:30.020,0:02:34.940 that calling regions of the world "very productive[br]ecosystem" or "extremely not productive ecosystem" 0:02:34.940,0:02:36.410 would be boring. 0:02:36.410,0:02:40.790 Instead, we classify ecosystems into biomes,[br]or habitats with similar characteristics, 0:02:40.790,0:02:42.450 including productivity! 0:02:42.450,0:02:44.730 The names are much more descriptive and fun. 0:02:44.730,0:02:48.041 The equator gets the most direct sunlight[br]and a lot of precipitation, so there’s a 0:02:48.041,0:02:50.450 lot of photosynthesis happening here. 0:02:50.450,0:02:54.220 These highly productive ecosystems are all[br]tropical rainforest biomes, which are some 0:02:54.220,0:02:58.570 of the most diverse and complex areas of the[br]planet -- so it's no wonder the tear-drinking 0:02:58.570,0:02:59.660 moth lives here. 0:02:59.660,0:03:02.770 Similar patterns happen on either side of[br]the equator, but we’re going to turn north 0:03:02.770,0:03:04.690 because there’s more land in the northern[br]hemisphere. 0:03:04.690,0:03:08.630 There’s also less and less precipitation[br]as we move out from the equator, and less 0:03:08.630,0:03:12.650 and less productivity because photosynthesis[br]can't happen without water. 0:03:12.650,0:03:17.000 The biomes gradually shift from tropical rainforests[br]to tropical savanna to desert. 0:03:17.000,0:03:21.820 Further north, in temperate and high latitudes,[br]the net primary production varies seasonally. 0:03:21.820,0:03:26.450 Like one biome is the broadleaf deciduous[br]forests with oak, beech, hickory, maple, elm 0:03:26.450,0:03:27.990 and chestnut trees. 0:03:27.990,0:03:31.520 These trees have increased productivity in[br]the sunny spring and summer, and shed their 0:03:31.520,0:03:33.790 leaves in the cooler fall and winter seasons. 0:03:33.790,0:03:37.500 Up here in the middle of continents, there[br]are temperate grassland biomes with rich soils 0:03:37.500,0:03:40.960 that produce the tall grass of prairies and[br]the shortgrass of steppe climates. 0:03:40.960,0:03:45.070 Further north where there are poorer soils[br]and colder climates, we meet the boreal forest 0:03:45.070,0:03:49.030 biomes, which have mainly evergreen pine,[br]spruce, fir and larch trees. 0:03:49.030,0:03:53.720 At even higher latitudes, the decreasing temperatures[br]give us the icy tundra biome with no trees 0:03:53.720,0:03:55.340 and very little productivity. 0:03:55.340,0:03:59.120 So the amount of energy flow through different[br]ecosystems varies wildly, which limits which 0:03:59.120,0:04:00.990 type of plants can thrive there. 0:04:00.990,0:04:05.340 And because plants feed more consumers than[br]any other food source, more plants means more 0:04:05.340,0:04:08.720 biodiversity, or the number of different plants[br]and animals in an ecosystem. 0:04:08.720,0:04:14.365 And we can't talk about biodiversity without[br]the other key component of all ecosystems: nutrients. 0:04:14.365,0:04:19.459 Nutrients are chemical elements like carbon,[br]oxygen, nitrogen, sulfur, and phosphorus -- stored 0:04:19.459,0:04:22.210 in both the living and nonliving parts of[br]an ecosystem. 0:04:22.210,0:04:24.690 And we actually have technical terms for those[br]too. 0:04:24.690,0:04:28.200 The living things like plants and animals[br]and bacteria (or their dead bodies) are the 0:04:28.200,0:04:30.470 biotic parts of an ecosystem. 0:04:30.470,0:04:34.530 And the nonliving things like the soil, atmosphere,[br]and groundwater are the abiotic parts. 0:04:34.530,0:04:38.330 Unlike how energy flows in one direction,[br]the paths that nutrients take through the 0:04:38.330,0:04:43.080 ecosystem are nutrient cycles between the[br]biotic and abiotic parts. 0:04:43.080,0:04:48.260 And unlike energy from the Sun, all the nutrients[br]we have right now on Earth are all we’ll ever have. 0:04:48.260,0:04:52.240 It's like how nitrogen moves from being a[br]gas in the atmosphere to a solid in the soil. 0:04:52.240,0:04:56.640 [Instead of a one-way system like...aliens[br]dropping gift-wrapped boxes of nitrogen from 0:04:56.640,0:04:58.410 space… or at least not that we know of]. 0:04:58.410,0:05:01.960 The biotic parts of ecosystems really help[br]facilitate these nutrient cycles. 0:05:01.960,0:05:04.940 Like, let's look at our fish tank ecosystem[br]again! 0:05:04.940,0:05:09.080 Producers like our little plant capture nutrients[br]from the abiotic parts, turning carbon dioxide 0:05:09.080,0:05:13.601 into carbohydrates through photosynthesis[br]or absorbing nitrogen compounds through its roots. 0:05:13.601,0:05:17.340 Consumers like the fish take nutrients from[br]other organisms, munching on fish food or 0:05:17.340,0:05:18.340 the plant's leaves. 0:05:18.340,0:05:23.060 And decomposers break down dead plant leaves…[br]or our fish eventually... and return the nutrients, 0:05:23.060,0:05:26.050 like nitrogen gas, to the abiotic parts of[br]the tank. 0:05:26.050,0:05:30.490 Ultimately, nutrients cycling through ecosystems[br]depend on biological, geological, and chemical 0:05:30.490,0:05:35.190 processes operating within the atmosphere,[br]hydrosphere and lithosphere, and make up Earth’s 0:05:35.190,0:05:36.420 biogeochemical cycles. 0:05:36.420,0:05:39.920 We can compare nutrients across the Earth's[br]biosphere just like we compared net primary 0:05:39.920,0:05:42.500 production across different latitudes and[br]biomes. 0:05:42.500,0:05:47.130 Like let's look at three biomes we met before:[br]the tropical rainforest, deciduous forest, 0:05:47.130,0:05:48.600 and boreal forests. 0:05:48.600,0:05:52.050 We know that there's less and less productivity[br]as we move up in latitude, so there's less 0:05:52.050,0:05:54.630 and less biomass, and there's also less and[br]less nutrients. 0:05:54.630,0:05:58.010 Fewer nutrients isn't necessarily a death[br]sentence for the trees, though. 0:05:58.010,0:06:01.050 It just means that the ecosystem is structured[br]differently. 0:06:01.050,0:06:04.650 Like boreal forests have a lot of nutrient[br]filled litter because the cold keeps material 0:06:04.650,0:06:06.110 from decomposing. 0:06:06.110,0:06:09.610 But deciduous forests have a lot of nutrient-rich[br]soil because it’s warm enough for material 0:06:09.610,0:06:12.760 to decompose, but not warm enough for a lot[br]of biomass to grow. 0:06:12.760,0:06:17.220 So a tree that’s adapted to life in a cold[br]boreal forest might not make it in a tropical 0:06:17.220,0:06:20.190 rainforest because of the different energy[br]availability and nutrient stores. 0:06:20.190,0:06:23.690 Let’s consider the tropical rainforests,[br]which are the most diverse biomes with lush 0:06:23.690,0:06:26.280 vegetation and a lot of biodiversity. 0:06:26.280,0:06:31.160 But that decadence hides the fragile balance[br]of all the complex energy flows and nutrient cycles. 0:06:31.160,0:06:32.540 Let's go to the Thought Bubble! 0:06:32.540,0:06:36.389 Within the tropical rainforests, broadleaf[br]evergreen trees form a canopy at different 0:06:36.389,0:06:39.960 heights, and little or no sunlight reaches[br]the shady forest floor. 0:06:39.960,0:06:44.180 These huge trees absorb most of the soil nutrients,[br]which doesn't leave a lot for other organisms. 0:06:44.180,0:06:48.720 And they have a shallow root system to grab[br]as many of the minerals as possible from biogeochemical 0:06:48.720,0:06:50.540 processes near the surface. 0:06:50.540,0:06:54.090 And as the large amounts of rain filter down[br]through the soil, the minerals that dissolve 0:06:54.090,0:06:57.170 in water are leached away to inaccessible[br]deeper levels. 0:06:57.170,0:07:00.400 To survive, the rainforest has to rapidly[br]cycle nutrients. 0:07:00.400,0:07:04.180 The canopy trees are producers, along with[br]understory plants that work together to keep 0:07:04.180,0:07:06.130 vital nutrients moving through the ecosystem. 0:07:06.130,0:07:10.080 Herbivores like gorillas and caterpillars[br]take in those nutrients and move them around 0:07:10.080,0:07:14.270 through their excrement and by being eaten[br]themselves, like by jaguars or geckos. 0:07:14.270,0:07:18.800 And the warmth and humidity helps decomposers[br]and their chemical reactions, so any dead 0:07:18.800,0:07:20.550 plants or animals decay quickly. 0:07:20.550,0:07:24.300 Because nutrients get sucked from the soils[br]so quickly, when those huge trees are cut 0:07:24.300,0:07:27.160 down, the energy flows and nutrient cycles[br]break. 0:07:27.160,0:07:31.730 Those big producers aren't there to sustain[br]consumers or shed leaves to recycle nutrients. 0:07:31.730,0:07:36.050 So deforestation, or removing trees to use[br]the land for something else, can be especially 0:07:36.050,0:07:40.150 destructive in tropical regions if you don't[br]consider the biogeochemical cycles. 0:07:40.150,0:07:41.570 Thanks, Thought Bubble. 0:07:41.570,0:07:45.650 We have negative associations with the word[br]"deforestation" for good reason -- a lot of 0:07:45.650,0:07:48.860 tree removal has caused immense damage to[br]ecosystems. 0:07:48.860,0:07:52.419 But indigenous communities have figured out[br]a type of calculated clearing that allows 0:07:52.419,0:07:56.139 them to work with the rapid nutrient recycling[br]of tropical rainforest biomes. 0:07:56.139,0:08:00.570 In parts of Asia, Africa, and South America[br]with dense tropical forests, many farmers 0:08:00.570,0:08:05.120 have to rely on a kind of subsistence agricultural[br]practice, which means they only grow enough 0:08:05.120,0:08:06.620 food for their families. 0:08:06.620,0:08:11.839 Staples like rice are grown in southeast Asia,[br]maize and cassava in South America, and sorghum in Africa. 0:08:11.839,0:08:16.229 Yams, sugarcane, plantains, and vegetables[br]are also planted to supplement staples and 0:08:16.229,0:08:18.270 to provide fuel and fodder for animals. 0:08:18.270,0:08:23.180 This practice goes by many names, like swidden,[br]shifting cultivation, and slash-and-burn agriculture. 0:08:23.180,0:08:27.710 The farmers begin by cutting small areas of[br]tropical forests into slash, or cut vegetation, 0:08:27.710,0:08:29.610 that’s then dried and burned. 0:08:29.610,0:08:33.449 The ash gets mixed with the poor soil to provide[br]needed minerals and nutrients -- basically 0:08:33.449,0:08:37.469 using all the good stuff stored up in the[br]vegetation biomass to help new crop plants grow. 0:08:37.469,0:08:41.430 Of course, these crop plants use minerals[br]and nutrients from the soil as they grow, 0:08:41.430,0:08:44.189 and we eat them to get those minerals and[br]nutrients in our bodies. 0:08:44.189,0:08:48.010 So after a few years, and before the soil[br]is completely exhausted, the farmers move 0:08:48.010,0:08:51.860 on to another part of land and repeat the[br]clearing, burning, and planting process. 0:08:51.860,0:08:55.959 The previous plot is left unplanted, and eventually[br]the forest will naturally expand to start 0:08:55.959,0:08:59.500 using that soil as part of its carefully balanced[br]nutrient cycling. 0:08:59.500,0:09:02.860 This land rotation is a key part of why humans[br]have been able to keep farming like this for 0:09:02.860,0:09:04.579 thousands of years. 0:09:04.579,0:09:07.930 But when widespread clear-cutting happens,[br]ecosystems can collapse. 0:09:07.930,0:09:11.990 For example, we've seen this destruction in[br]the Amazon when rice, soy, and corn have been 0:09:11.990,0:09:15.649 commercially cultivated and sold in domestic[br]and international markets. 0:09:15.649,0:09:19.660 The soil is exhausted after 3-5 years, so[br]crops can't really grow anymore, and then 0:09:19.660,0:09:21.339 large cattle operations move in. 0:09:21.339,0:09:25.569 As cattle feed and trample the ground, the[br]soils are exposed to plenty of UV radiation 0:09:25.569,0:09:29.449 from sunlight, as well as cycles of wetting[br]and drying from precipitation. 0:09:29.449,0:09:33.430 The soils become a brick-like substance called[br]laterite, which isn’t great for growing… 0:09:33.430,0:09:38.110 so the once-lively rainforest basically becomes[br]hard, barren, and lifeless. 0:09:38.110,0:09:42.379 Tropical rainforests cover 6 percent of Earth’s[br]landmass, but contain 50 percent of the world’s 0:09:42.379,0:09:46.704 species, many of which haven’t been described[br]by science and are critical to the world’s biodiversity. 0:09:46.704,0:09:51.790 But since the 1980s, 1/5 of the Amazon has[br]been deforested as we build more towns, roads, 0:09:51.790,0:09:54.069 dams, farms, and mines. 0:09:54.069,0:09:57.999 Across the Atlantic, deforestation in Ituri[br]in the Congo Basin, the world’s second largest 0:09:57.999,0:10:01.740 expanse of equatorial rainforest, is endangering[br]the mountain gorilla. 0:10:01.740,0:10:06.410 And in southeast Asia clearcutting for palm[br]oil plantations endanger orangutans, Sumatran 0:10:06.410,0:10:08.350 tigers, and Sumatran elephants. 0:10:08.350,0:10:12.730 When humans disturb the biosphere, we alter[br]how energy flows and how nutrients cycle, 0:10:12.730,0:10:16.019 which can throw off entire ecosystems in unexpected[br]ways. 0:10:16.019,0:10:20.140 And if we're not careful, that moth that drinks[br]the tears of sleeping birds -- or plenty of 0:10:20.140,0:10:23.449 other remarkable living organisms -- may no[br]longer exist. 0:10:23.449,0:10:26.829 But just like we can be good stewards of our[br]little fish tank, we can take care of the 0:10:26.829,0:10:29.790 world around us and the much bigger ecosystems[br]we're a part of. 0:10:29.790,0:10:33.830 Learning where our food comes from and how[br]it’s produced is a good first step, like 0:10:33.830,0:10:37.129 by supporting farmers who try to grow food[br]sustainably. 0:10:37.129,0:10:41.069 And we’ll keep talking about our role in[br]ecosystems, energy, and food and how geography 0:10:41.069,0:10:45.070 and spatial thinking can help address some[br]of the critical issues we’re facing, like 0:10:45.070,0:10:49.459 how we can have enough food and water to sustain[br]ourselves and our environment. 0:10:49.459,0:10:53.540 Many maps and borders represent modern geopolitical[br]divisions that have often been decided without 0:10:53.540,0:10:58.200 the consultation, permission, or recognition[br]of the land's original inhabitants. 0:10:58.200,0:11:02.860 Many geographical place names also don't reflect[br]the Indigenous or Aboriginal peoples languages. 0:11:02.860,0:11:06.639 So we at Crash Course want to acknowledge[br]these peoples’ traditional and ongoing relationship 0:11:06.639,0:11:10.279 with that land and all the physical and human[br]geographical elements of it. 0:11:10.279,0:11:13.800 We encourage you to learn about the history[br]of the place you call home through resources 0:11:13.800,0:11:18.399 like native-land.ca and by engaging with your[br]local Indigenous and Aboriginal nations through 0:11:18.399,0:11:21.029 the websites and resources they provide. 0:11:21.029,0:11:24.339 Thanks for watching this episode of Crash[br]Course Geography which is filmed at the Team 0:11:24.339,0:11:28.119 Sandoval Pierce Studio and was made with the[br]help of all these nice people. 0:11:28.119,0:11:31.999 If you want to help keep all Crash Course[br]free for everyone, forever, you can join our 0:11:31.999,0:11:34.603 community on Patreon.