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