1 00:00:00,000 --> 00:00:04,710 On the island of Madagascar, there’s a kind of moth that drinks tears from the eyes of 2 00:00:04,710 --> 00:00:06,290 sleeping birds. 3 00:00:06,290 --> 00:00:10,160 When I first heard this, I just sat with that weird idea: there’s a moth that gets most 4 00:00:10,160 --> 00:00:13,820 of the nutrients it needs to survive by drinking bird tears! 5 00:00:13,820 --> 00:00:17,760 Welcome to the biosphere -- the sphere of life that extends from the depths of the ocean 6 00:00:17,760 --> 00:00:19,880 all the way up to 8 kilometers above Earth. 7 00:00:19,880 --> 00:00:24,050 A lot of incredible things live here, so of course, as geographers, we want to know why 8 00:00:24,050 --> 00:00:28,640 bananas and bacteria and tear-drinking moths show up in some spaces but not others. 9 00:00:28,640 --> 00:00:30,860 And to do that, we have to zoom out a little. 10 00:00:30,860 --> 00:00:34,860 For example, that moth gets its nutrients from birds, while birds rely on seeds and 11 00:00:34,860 --> 00:00:38,100 berries from the surrounding plants, which grow with the help of the Sun. 12 00:00:38,100 --> 00:00:42,449 So the moth and the birds and the plants and the Sun are all part of an ecosystem -- a 13 00:00:42,449 --> 00:00:46,859 community of living organisms in an area interacting with their environment. 14 00:00:46,859 --> 00:00:50,839 Ecosystems are built on relationships -- even strange ones that involve tear-theft. 15 00:00:50,839 --> 00:00:53,899 And the relationship between the amount of energy a place receives and the movement of 16 00:00:53,899 --> 00:00:57,100 nutrients is what makes the incredible diversity of life possible. 17 00:00:57,100 --> 00:01:00,275 I’m Alizé Carrère and this is Crash Course Geography. 18 00:01:00,275 --> 00:01:08,229 INTRO 19 00:01:08,229 --> 00:01:11,689 The biosphere is a complex web of interconnected ecosystems. 20 00:01:11,689 --> 00:01:16,869 And all ecosystems depend on two key things: the one-way movement of energy and the cyclic 21 00:01:16,869 --> 00:01:18,550 movement of nutrients. 22 00:01:18,550 --> 00:01:21,799 Energy flows are the paths energy can take through an ecosystem. 23 00:01:21,799 --> 00:01:25,810 Energy generally enters ecosystems from the Sun but doesn’t return to the Sun -- so 24 00:01:25,810 --> 00:01:28,159 energy flows are one-way relationships. 25 00:01:28,159 --> 00:01:32,859 Plants absorb the Sun's energy during photosynthesis, adding carbon dioxide and water to make carbohydrates 26 00:01:32,859 --> 00:01:34,049 and grow bigger. 27 00:01:34,049 --> 00:01:38,060 So the Sun's energy is converted into chemical energy, which is stored in biomass -- any 28 00:01:38,060 --> 00:01:40,000 plant or other living thing. 29 00:01:40,000 --> 00:01:44,158 If a bit of biomass is eaten, it passes on its chemical energy to continue the energy flow. 30 00:01:44,158 --> 00:01:49,229 The rate photosynthesis makes energy across an entire ecosystem, minus the rate that energy 31 00:01:49,229 --> 00:01:53,679 is used is its net primary production -- or the amount of stored chemical energy in an 32 00:01:53,679 --> 00:01:55,909 ecosystem over a certain amount of time. 33 00:01:55,909 --> 00:01:59,700 For example, on a really small scale, think of a fish tank ecosystem that you can hold 34 00:01:59,700 --> 00:02:00,939 in your hands. 35 00:02:00,939 --> 00:02:06,879 There's water, a fish, soil, rocks, air, light, food, and one little plant all in a glass bowl. 36 00:02:06,879 --> 00:02:10,950 In this fish tank ecosystem, the net primary production is pretty low because only that 37 00:02:10,950 --> 00:02:14,940 one little plant is absorbing energy from the Sun (along with any photosynthetic bacteria 38 00:02:14,940 --> 00:02:17,590 or algae that grows when I forget to clean the bowl). 39 00:02:17,590 --> 00:02:21,960 Globally, net primary production on land generally changes with latitude. 40 00:02:21,960 --> 00:02:25,969 Productivity is highest between the tropics and decreases towards higher latitudes and elevations. 41 00:02:25,969 --> 00:02:30,020 Biogeographers and ecologists who study how life is distributed on Earth probably figured 42 00:02:30,020 --> 00:02:34,940 that calling regions of the world "very productive ecosystem" or "extremely not productive ecosystem" 43 00:02:34,940 --> 00:02:36,410 would be boring. 44 00:02:36,410 --> 00:02:40,790 Instead, we classify ecosystems into biomes, or habitats with similar characteristics, 45 00:02:40,790 --> 00:02:42,450 including productivity! 46 00:02:42,450 --> 00:02:44,730 The names are much more descriptive and fun. 47 00:02:44,730 --> 00:02:48,041 The equator gets the most direct sunlight and a lot of precipitation, so there’s a 48 00:02:48,041 --> 00:02:50,450 lot of photosynthesis happening here. 49 00:02:50,450 --> 00:02:54,220 These highly productive ecosystems are all tropical rainforest biomes, which are some 50 00:02:54,220 --> 00:02:58,570 of the most diverse and complex areas of the planet -- so it's no wonder the tear-drinking 51 00:02:58,570 --> 00:02:59,660 moth lives here. 52 00:02:59,660 --> 00:03:02,770 Similar patterns happen on either side of the equator, but we’re going to turn north 53 00:03:02,770 --> 00:03:04,690 because there’s more land in the northern hemisphere. 54 00:03:04,690 --> 00:03:08,630 There’s also less and less precipitation as we move out from the equator, and less 55 00:03:08,630 --> 00:03:12,650 and less productivity because photosynthesis can't happen without water. 56 00:03:12,650 --> 00:03:17,000 The biomes gradually shift from tropical rainforests to tropical savanna to desert. 57 00:03:17,000 --> 00:03:21,820 Further north, in temperate and high latitudes, the net primary production varies seasonally. 58 00:03:21,820 --> 00:03:26,450 Like one biome is the broadleaf deciduous forests with oak, beech, hickory, maple, elm 59 00:03:26,450 --> 00:03:27,990 and chestnut trees. 60 00:03:27,990 --> 00:03:31,520 These trees have increased productivity in the sunny spring and summer, and shed their 61 00:03:31,520 --> 00:03:33,790 leaves in the cooler fall and winter seasons. 62 00:03:33,790 --> 00:03:37,500 Up here in the middle of continents, there are temperate grassland biomes with rich soils 63 00:03:37,500 --> 00:03:40,960 that produce the tall grass of prairies and the shortgrass of steppe climates. 64 00:03:40,960 --> 00:03:45,070 Further north where there are poorer soils and colder climates, we meet the boreal forest 65 00:03:45,070 --> 00:03:49,030 biomes, which have mainly evergreen pine, spruce, fir and larch trees. 66 00:03:49,030 --> 00:03:53,720 At even higher latitudes, the decreasing temperatures give us the icy tundra biome with no trees 67 00:03:53,720 --> 00:03:55,340 and very little productivity. 68 00:03:55,340 --> 00:03:59,120 So the amount of energy flow through different ecosystems varies wildly, which limits which 69 00:03:59,120 --> 00:04:00,990 type of plants can thrive there. 70 00:04:00,990 --> 00:04:05,340 And because plants feed more consumers than any other food source, more plants means more 71 00:04:05,340 --> 00:04:08,720 biodiversity, or the number of different plants and animals in an ecosystem. 72 00:04:08,720 --> 00:04:14,365 And we can't talk about biodiversity without the other key component of all ecosystems: nutrients. 73 00:04:14,365 --> 00:04:19,459 Nutrients are chemical elements like carbon, oxygen, nitrogen, sulfur, and phosphorus -- stored 74 00:04:19,459 --> 00:04:22,210 in both the living and nonliving parts of an ecosystem. 75 00:04:22,210 --> 00:04:24,690 And we actually have technical terms for those too. 76 00:04:24,690 --> 00:04:28,200 The living things like plants and animals and bacteria (or their dead bodies) are the 77 00:04:28,200 --> 00:04:30,470 biotic parts of an ecosystem. 78 00:04:30,470 --> 00:04:34,530 And the nonliving things like the soil, atmosphere, and groundwater are the abiotic parts. 79 00:04:34,530 --> 00:04:38,330 Unlike how energy flows in one direction, the paths that nutrients take through the 80 00:04:38,330 --> 00:04:43,080 ecosystem are nutrient cycles between the biotic and abiotic parts. 81 00:04:43,080 --> 00:04:48,260 And unlike energy from the Sun, all the nutrients we have right now on Earth are all we’ll ever have. 82 00:04:48,260 --> 00:04:52,240 It's like how nitrogen moves from being a gas in the atmosphere to a solid in the soil. 83 00:04:52,240 --> 00:04:56,640 [Instead of a one-way system like...aliens dropping gift-wrapped boxes of nitrogen from 84 00:04:56,640 --> 00:04:58,410 space… or at least not that we know of]. 85 00:04:58,410 --> 00:05:01,960 The biotic parts of ecosystems really help facilitate these nutrient cycles. 86 00:05:01,960 --> 00:05:04,940 Like, let's look at our fish tank ecosystem again! 87 00:05:04,940 --> 00:05:09,080 Producers like our little plant capture nutrients from the abiotic parts, turning carbon dioxide 88 00:05:09,080 --> 00:05:13,601 into carbohydrates through photosynthesis or absorbing nitrogen compounds through its roots. 89 00:05:13,601 --> 00:05:17,340 Consumers like the fish take nutrients from other organisms, munching on fish food or 90 00:05:17,340 --> 00:05:18,340 the plant's leaves. 91 00:05:18,340 --> 00:05:23,060 And decomposers break down dead plant leaves… or our fish eventually... and return the nutrients, 92 00:05:23,060 --> 00:05:26,050 like nitrogen gas, to the abiotic parts of the tank. 93 00:05:26,050 --> 00:05:30,490 Ultimately, nutrients cycling through ecosystems depend on biological, geological, and chemical 94 00:05:30,490 --> 00:05:35,190 processes operating within the atmosphere, hydrosphere and lithosphere, and make up Earth’s 95 00:05:35,190 --> 00:05:36,420 biogeochemical cycles. 96 00:05:36,420 --> 00:05:39,920 We can compare nutrients across the Earth's biosphere just like we compared net primary 97 00:05:39,920 --> 00:05:42,500 production across different latitudes and biomes. 98 00:05:42,500 --> 00:05:47,130 Like let's look at three biomes we met before: the tropical rainforest, deciduous forest, 99 00:05:47,130 --> 00:05:48,600 and boreal forests. 100 00:05:48,600 --> 00:05:52,050 We know that there's less and less productivity as we move up in latitude, so there's less 101 00:05:52,050 --> 00:05:54,630 and less biomass, and there's also less and less nutrients. 102 00:05:54,630 --> 00:05:58,010 Fewer nutrients isn't necessarily a death sentence for the trees, though. 103 00:05:58,010 --> 00:06:01,050 It just means that the ecosystem is structured differently. 104 00:06:01,050 --> 00:06:04,650 Like boreal forests have a lot of nutrient filled litter because the cold keeps material 105 00:06:04,650 --> 00:06:06,110 from decomposing. 106 00:06:06,110 --> 00:06:09,610 But deciduous forests have a lot of nutrient-rich soil because it’s warm enough for material 107 00:06:09,610 --> 00:06:12,760 to decompose, but not warm enough for a lot of biomass to grow. 108 00:06:12,760 --> 00:06:17,220 So a tree that’s adapted to life in a cold boreal forest might not make it in a tropical 109 00:06:17,220 --> 00:06:20,190 rainforest because of the different energy availability and nutrient stores. 110 00:06:20,190 --> 00:06:23,690 Let’s consider the tropical rainforests, which are the most diverse biomes with lush 111 00:06:23,690 --> 00:06:26,280 vegetation and a lot of biodiversity. 112 00:06:26,280 --> 00:06:31,160 But that decadence hides the fragile balance of all the complex energy flows and nutrient cycles. 113 00:06:31,160 --> 00:06:32,540 Let's go to the Thought Bubble! 114 00:06:32,540 --> 00:06:36,389 Within the tropical rainforests, broadleaf evergreen trees form a canopy at different 115 00:06:36,389 --> 00:06:39,960 heights, and little or no sunlight reaches the shady forest floor. 116 00:06:39,960 --> 00:06:44,180 These huge trees absorb most of the soil nutrients, which doesn't leave a lot for other organisms. 117 00:06:44,180 --> 00:06:48,720 And they have a shallow root system to grab as many of the minerals as possible from biogeochemical 118 00:06:48,720 --> 00:06:50,540 processes near the surface. 119 00:06:50,540 --> 00:06:54,090 And as the large amounts of rain filter down through the soil, the minerals that dissolve 120 00:06:54,090 --> 00:06:57,170 in water are leached away to inaccessible deeper levels. 121 00:06:57,170 --> 00:07:00,400 To survive, the rainforest has to rapidly cycle nutrients. 122 00:07:00,400 --> 00:07:04,180 The canopy trees are producers, along with understory plants that work together to keep 123 00:07:04,180 --> 00:07:06,130 vital nutrients moving through the ecosystem. 124 00:07:06,130 --> 00:07:10,080 Herbivores like gorillas and caterpillars take in those nutrients and move them around 125 00:07:10,080 --> 00:07:14,270 through their excrement and by being eaten themselves, like by jaguars or geckos. 126 00:07:14,270 --> 00:07:18,800 And the warmth and humidity helps decomposers and their chemical reactions, so any dead 127 00:07:18,800 --> 00:07:20,550 plants or animals decay quickly. 128 00:07:20,550 --> 00:07:24,300 Because nutrients get sucked from the soils so quickly, when those huge trees are cut 129 00:07:24,300 --> 00:07:27,160 down, the energy flows and nutrient cycles break. 130 00:07:27,160 --> 00:07:31,730 Those big producers aren't there to sustain consumers or shed leaves to recycle nutrients. 131 00:07:31,730 --> 00:07:36,050 So deforestation, or removing trees to use the land for something else, can be especially 132 00:07:36,050 --> 00:07:40,150 destructive in tropical regions if you don't consider the biogeochemical cycles. 133 00:07:40,150 --> 00:07:41,570 Thanks, Thought Bubble. 134 00:07:41,570 --> 00:07:45,650 We have negative associations with the word "deforestation" for good reason -- a lot of 135 00:07:45,650 --> 00:07:48,860 tree removal has caused immense damage to ecosystems. 136 00:07:48,860 --> 00:07:52,419 But indigenous communities have figured out a type of calculated clearing that allows 137 00:07:52,419 --> 00:07:56,139 them to work with the rapid nutrient recycling of tropical rainforest biomes. 138 00:07:56,139 --> 00:08:00,570 In parts of Asia, Africa, and South America with dense tropical forests, many farmers 139 00:08:00,570 --> 00:08:05,120 have to rely on a kind of subsistence agricultural practice, which means they only grow enough 140 00:08:05,120 --> 00:08:06,620 food for their families. 141 00:08:06,620 --> 00:08:11,839 Staples like rice are grown in southeast Asia, maize and cassava in South America, and sorghum in Africa. 142 00:08:11,839 --> 00:08:16,229 Yams, sugarcane, plantains, and vegetables are also planted to supplement staples and 143 00:08:16,229 --> 00:08:18,270 to provide fuel and fodder for animals. 144 00:08:18,270 --> 00:08:23,180 This practice goes by many names, like swidden, shifting cultivation, and slash-and-burn agriculture. 145 00:08:23,180 --> 00:08:27,710 The farmers begin by cutting small areas of tropical forests into slash, or cut vegetation, 146 00:08:27,710 --> 00:08:29,610 that’s then dried and burned. 147 00:08:29,610 --> 00:08:33,449 The ash gets mixed with the poor soil to provide needed minerals and nutrients -- basically 148 00:08:33,449 --> 00:08:37,469 using all the good stuff stored up in the vegetation biomass to help new crop plants grow. 149 00:08:37,469 --> 00:08:41,430 Of course, these crop plants use minerals and nutrients from the soil as they grow, 150 00:08:41,430 --> 00:08:44,189 and we eat them to get those minerals and nutrients in our bodies. 151 00:08:44,189 --> 00:08:48,010 So after a few years, and before the soil is completely exhausted, the farmers move 152 00:08:48,010 --> 00:08:51,860 on to another part of land and repeat the clearing, burning, and planting process. 153 00:08:51,860 --> 00:08:55,959 The previous plot is left unplanted, and eventually the forest will naturally expand to start 154 00:08:55,959 --> 00:08:59,500 using that soil as part of its carefully balanced nutrient cycling. 155 00:08:59,500 --> 00:09:02,860 This land rotation is a key part of why humans have been able to keep farming like this for 156 00:09:02,860 --> 00:09:04,579 thousands of years. 157 00:09:04,579 --> 00:09:07,930 But when widespread clear-cutting happens, ecosystems can collapse. 158 00:09:07,930 --> 00:09:11,990 For example, we've seen this destruction in the Amazon when rice, soy, and corn have been 159 00:09:11,990 --> 00:09:15,649 commercially cultivated and sold in domestic and international markets. 160 00:09:15,649 --> 00:09:19,660 The soil is exhausted after 3-5 years, so crops can't really grow anymore, and then 161 00:09:19,660 --> 00:09:21,339 large cattle operations move in. 162 00:09:21,339 --> 00:09:25,569 As cattle feed and trample the ground, the soils are exposed to plenty of UV radiation 163 00:09:25,569 --> 00:09:29,449 from sunlight, as well as cycles of wetting and drying from precipitation. 164 00:09:29,449 --> 00:09:33,430 The soils become a brick-like substance called laterite, which isn’t great for growing… 165 00:09:33,430 --> 00:09:38,110 so the once-lively rainforest basically becomes hard, barren, and lifeless. 166 00:09:38,110 --> 00:09:42,379 Tropical rainforests cover 6 percent of Earth’s landmass, but contain 50 percent of the world’s 167 00:09:42,379 --> 00:09:46,704 species, many of which haven’t been described by science and are critical to the world’s biodiversity. 168 00:09:46,704 --> 00:09:51,790 But since the 1980s, 1/5 of the Amazon has been deforested as we build more towns, roads, 169 00:09:51,790 --> 00:09:54,069 dams, farms, and mines. 170 00:09:54,069 --> 00:09:57,999 Across the Atlantic, deforestation in Ituri in the Congo Basin, the world’s second largest 171 00:09:57,999 --> 00:10:01,740 expanse of equatorial rainforest, is endangering the mountain gorilla. 172 00:10:01,740 --> 00:10:06,410 And in southeast Asia clearcutting for palm oil plantations endanger orangutans, Sumatran 173 00:10:06,410 --> 00:10:08,350 tigers, and Sumatran elephants. 174 00:10:08,350 --> 00:10:12,730 When humans disturb the biosphere, we alter how energy flows and how nutrients cycle, 175 00:10:12,730 --> 00:10:16,019 which can throw off entire ecosystems in unexpected ways. 176 00:10:16,019 --> 00:10:20,140 And if we're not careful, that moth that drinks the tears of sleeping birds -- or plenty of 177 00:10:20,140 --> 00:10:23,449 other remarkable living organisms -- may no longer exist. 178 00:10:23,449 --> 00:10:26,829 But just like we can be good stewards of our little fish tank, we can take care of the 179 00:10:26,829 --> 00:10:29,790 world around us and the much bigger ecosystems we're a part of. 180 00:10:29,790 --> 00:10:33,830 Learning where our food comes from and how it’s produced is a good first step, like 181 00:10:33,830 --> 00:10:37,129 by supporting farmers who try to grow food sustainably. 182 00:10:37,129 --> 00:10:41,069 And we’ll keep talking about our role in ecosystems, energy, and food and how geography 183 00:10:41,069 --> 00:10:45,070 and spatial thinking can help address some of the critical issues we’re facing, like 184 00:10:45,070 --> 00:10:49,459 how we can have enough food and water to sustain ourselves and our environment. 185 00:10:49,459 --> 00:10:53,540 Many maps and borders represent modern geopolitical divisions that have often been decided without 186 00:10:53,540 --> 00:10:58,200 the consultation, permission, or recognition of the land's original inhabitants. 187 00:10:58,200 --> 00:11:02,860 Many geographical place names also don't reflect the Indigenous or Aboriginal peoples languages. 188 00:11:02,860 --> 00:11:06,639 So we at Crash Course want to acknowledge these peoples’ traditional and ongoing relationship 189 00:11:06,639 --> 00:11:10,279 with that land and all the physical and human geographical elements of it. 190 00:11:10,279 --> 00:11:13,800 We encourage you to learn about the history of the place you call home through resources 191 00:11:13,800 --> 00:11:18,399 like native-land.ca and by engaging with your local Indigenous and Aboriginal nations through 192 00:11:18,399 --> 00:11:21,029 the websites and resources they provide. 193 00:11:21,029 --> 00:11:24,339 Thanks for watching this episode of Crash Course Geography which is filmed at the Team 194 00:11:24,339 --> 00:11:28,119 Sandoval Pierce Studio and was made with the help of all these nice people. 195 00:11:28,119 --> 00:11:31,999 If you want to help keep all Crash Course free for everyone, forever, you can join our 196 00:11:31,999 --> 00:11:34,603 community on Patreon.