Ecology – Rules for Living on Earth: Crash Course Biology #40

By | August 21, 2019


For the last 38 episodes
of Crash Course Biology, we’ve talked about how
to make an organism. And you know what I’ve
learned in those 38 weeks? Putting a living
thing together is hard! There are molecules that make
up organelles that run cells, which come together
to form tissues, which make up organs
that make up systems. And knowing this stuff
is incredibly important, because it shows us the ground
rules for being a living thing, on this particular planet anyway. But still, there’s so much
more to biology than that! I mean, understanding how an
organism goes about its internal business is great,
but it doesn’t tell us much about its place in our world. For that, we need ecology, the study of the rules of engagement
for all of us Earthlings. Ecology seeks to explain why the
world looks and acts the way it does. Why the South Pole looks
different from the Congo, and why there are mosquitos
all over the place while black rhinos are
practically extinct. The short answer to
this question is: because the world is crammed
with things, both animate and not, that have been interacting with
each other all the time, every day, since life on this planet began. The even shorter answer is that
all life and all of these things interacting with each other
depend on just two things. Try to guess what they are. In the meantime, get ready, because
Crash Course Biology is taking its final voyage outside the
body and into the entire world! In a way, you can think of all
living things, great white sharks, pond scum, potato plants, as
molecules that react with each other. Each one of us organisms is pretty
piddling in the scheme of things, just like a single oxygen molecule,
which we need to make ATP to fuel our bodies. But it can’t get
much done by itself. But if you get a million
oxygen molecules together with some other types of molecules,
suddenly they’re unleashing a googlejillion
megawatts of ATP power to animate the bag
of meat that is you. This same principle
applies to organisms: As you put individual
organisms together, they can interact with each
other and their environments, to create something larger
than the sum of its parts. And just as every organism has
a hierarchy of biological systems, from molecules to organelles,
cells, tissues and organs, so too does Earth have
tiers of ecological order. Like, when a bunch of members of
a species are together in a certain area, and they interact pretty
often, you’ve got a population. Population ecologists study why
populations grow or shrink over time, depending on where they are. When two or more populations of
different species live together, we call that a community. Think of an ecological community
as Mr. Roger’s Neighborhood, but with the people
in the neighborhood eating each other sometimes. Because that’s what
species do when they live together, they interact. Sometimes that means predation,
sometimes cooperation, and sometimes competition for resources like
food, water and living space. So, a community ecologist studies
how the interactions between community members and their
environment affect how many of each species there are within a community. One level up from
communities are ecosytems, which are made up of groups
of organisms in a specific area and the nonliving parts
of their environment, like soil, water, and air. If you take a bunch of living things
and plop them down in one place that has a specific mix of climate,
soil chemistry, and topography, that’s going to make up
one kind of ecosystem. But if you put them down in
a completely different place, they’re going to work in
completely different ways to form a completely
different ecosystem. Ecosystem ecology specifically
explores how energy and materials flow through an ecosystem,
and how the physical environment impacts the stuff living there. Now, a lot of people
get ecosystems confused with the next step
up: which is biomes. A biome, however, is where
organisms have evolved similar techniques to adapt to a
general set of conditions. For example, a grassland is
a kind of biome, there are scores of different grassland
ecosystems all over the globe, but the organisms in each one
have made similar evolutionary concessions to all the
conditions that grasslands share, like hot summers, cold winters,
and not too much rain but more rain than you’d
find in a desert biome. Other biomes include
tropical rainforest, tundra, deserts, and oceans. The only level above the
biome is the biosphere, which includes the atmosphere,
the whole earth and everything that gets used by
anything that’s alive. So, why do all of these many
levels of ecological activity look the way that they do? Like, why do some organisms like to
live in one place but not another? And what makes Earth’s
various populations, communities, ecosystems and biomes
different from each other? Well, factors that determine
what a place is gonna look like fall into two different
categories: biotic, or living, and abiotic, not living. Biotic factors include
stuff like predators, as well as animals or plants
that provide either competition or some benefit,
like food or shelter. Abiotic factors, on the
other hand, include temperature, moisture, sunlight, elevation, elements that have nothing to
do with organisms in the ecosystem, but which influence them just as
much as other living things do. Now, from these two categories,
the most influential factors are the ones that living
things are most particular about. That is, the things they need
most, but only at certain levels. And these preferences all
come down to chemistry. For example, almost all chemical
reactions that happen inside living things are
governed by enzymes. They’re the catalysts
for pretty much all the action
going on inside you. And these enzymes are most effective
within a set of temperatures: Chemical reactions within the body
slow way down when it’s really cold, and very high temperatures
change the shape of enzymes, making them less effective. So temperature is one of the
major factors that determines why animals live in certain places. And if you look at the places
on the earth with the most biodiversity, or different
kinds of living things, you’ll find that it’s in the
places where the temperature’s within the ideal range
for enzyme function. What else? Well, everybody’s
got to eat, at least if you’re an animal or a fungus or
some other kind of heterotroph, so you’d think that food
would also be way up on the list. But actually, it’s plants and
other autotrophs like cyanobacteria and protists that are the
base of nearly every food chain, and they have to be fed, too. So again, it comes down to chemistry. The key ingredient plants need
for photosynthesis is water, which is also what
we need to burn ATP, maintain homeostasis in our
bodies, and all that jazz. So the quest for food ultimately
comes down for a need for water. So, yeah: surprise! Water and
temperature are the two things that organisms care about the most. Ergo, they’re what ecologists
focus on when determining why certain organisms hang out
in one place over another. Together, these two factors define
every biome on the planet. For instance, a Saguaro cactus
has evolved to live in the Sonoran Desert of North
America, which is super hot and gets very little precipitation. So, the Sonoran Desert is full
of animals and plants that can, just like the Saguaro, take the
heat and also the extreme, face-crumbling dryness. But if you put these animals
in the Amazon rainforest, even though it’s hot enough
for them, it’s just too wet. So, yeah, the things that
live in a biome are ultimately determined by how much water
is there and the temperature. And in turn, these
inhabitants determine how the biome looks,
called its physiognomy. So now, we are going to take
a look at all the different types of biomes out there. There are places on the planet
that get lots and lots of rain, around 300 centimeters a
year, and are pretty warm, around 25-30 degrees C on average,
which is Speedo-wearin’ weather, as far as I’m concerned. These biomes are the tropical
rainforests, which generally hug the equator and have unbelievably
high biodiversity because everybody’s wanting to get a piece
of that sweet tropical action. And then on the complete
opposite side of that scale, we have the tundra, most of which
is above the Arctic Circle, in Antarctica, or way up at
the top of some mountains. Tundra gets little precipitation
and some well-below-zero temperatures. And what lives there? Not much.
A couple of mosses and liverworts, maybe a few species of grasses,
some birds and a handful of mammals. The same goes for the desert biome,
where there’s very little rainfall and very high temperatures. Like the tundra, without much water,
there can’t be very many large plants. And where there aren’t a lot of
plants, there aren’t a lot of other organisms,
even when temperatures are close to what makes living things happiest. Between these three extremes,
we’ve got biomes that require more or less water, combined with
high-ish or lowish temperatures. These are your moderate
or temperate biomes, and they include temperate
grasslands, like what you find in the North American prairie,
or temperate deciduous forests, found over much of
Europe and North America, and taigas or coniferous
forests, found across Canada, much of northern
Russia, and Scandinavia. So, if all these biomes in the
middle experience pretty moderate temperatures most of the time,
the availability of water must be what makes them
different from each other. Some of these biomes have a
lot of trees, and as we know, trees need a lot of water. So if you find yourself
in a temperate forest, it’s a pretty safe bet that
that particular ecosystem gets a fair amount of precipitation. And if the Carboniferous
forests taught us anything, it’s that having a bunch of trees
around changes the landscape, the climate, and even
the geology of a biome. If you don’t have a lot
of trees in a biome, it means you probably don’t get
enough rainfall for their liking. And without trees, more sunlight
reaches the ground and gets to grasses and other small plants, leading to more of a
temperate grassland ecosystem. And where you get grass, you get
animals like bison and pronghorn and other ungulates whose digestive
systems are big fermentation vats that process
cellulose all day long. And then when you’ve got
ungulates, you also get predators. All these animals are way different than what you’d find
in a temperate forest. So, biomes are different, because
the plants are different, because the rainfall and
temperatures are different. But, of course, there are also
biomes entirely underwater. We can’t forget that the surface of
the planet is three-fourths water. And since water availability
isn’t an issue in the ocean, marine biomes differ in things
like temperature, pressure, oxygen content, how much light
is available, and stuff like that. So, thanks to the science of ecology,
we know that the way the world works can be explained mostly
by temperature and water. But this is just the beginning
my friends. Oh yes! The end of Biology 101, maybe. And we’ll always have that time we
spent learning and loving, won’t we? But there’s so much more
to find out together! How do living things affect the
climate, the chemical makeup of the atmosphere, even the
geology of our planet? How do they affect each other? And maybe more importantly,
how are we humans affecting all of these things, and what can we
do differently to ensure that we all get to keep existing? Join me as we get
to know our planet on a whole new level,
starting next week! Thanks for watching this final
episode of Crash Course Biology and if you’ve been
with us the whole time thank you for participating and
learning with us here at Crash Course. And of course, thank you to all
the people who helped write these episodes, who helped do
these awesome animations, the people who filmed
and edited them. It really is a team effort
here at Crash Course. If you want to review anything
that we talked about in this episode there’s a table
of contents over there. And if you have any questions,
we’re on Facebook, Twitter, and of course, in
the comments below.

100 thoughts on “Ecology – Rules for Living on Earth: Crash Course Biology #40

  1. Nicole Castillo Post author

    Why don't you do videos for Earth Science?

    Reply
  2. Matilyn Reynolds Post author

    ha studying for a pre-ap 7th grade science test. please wish me luckkk

    Reply
  3. Samar Saluja Post author

    id like to add something necessary for ecosystems to be made inhabitable. The main source of energy to this world, without which no life would be possible: Sunlight.

    Reply
  4. Slaughter Princess Post author

    Subject Boringgg I Don’t Know How Im Gonna Focus On This Test 😢

    Reply
  5. Farya Arshad Post author

    population: same species
    community: different species living together
    ecosystems: organisms and non-living things.
    biome: organisms evolve, grassland, rainforests
    biosphere; atmosphere,
    key ecological factors abiotic: temperature, water
    physiognomy: how the biome looks

    Reply
  6. Ely Caceres Post author

    UUUGGGGHHHH SCIENCE CLASS WHYYYYYYYY?!?!?!?!?!?!?!

    Reply
  7. Uncle Dave 42 Post author

    Yo everyone! I'm belgian and I need subtitles to follow x)
    But it's very interesting! what would you recommend to learn electricity on youtube? another crash course learning videos alike? 🙂

    Reply
  8. Brooke F Post author

    does anyone know if there anything specific that I should know for the ap biology exam? any videos I should rewatch? any other topics I should look into?

    Reply
  9. Sinistre Schlauböse Post author

    AP Exam tomorrow, hopefully I manage a five.

    Reply
  10. V. Flower. Post author

    Hank does not look like a living thing. He looks like his soul passed long ago. RIP.

    Reply
  11. Kolfinna K Post author

    Bless up now I won't fail my ecology test!

    Reply
  12. Steve Jennette Post author

    Wish I could get a transcript of these for my students to use as they watch.

    Reply
  13. D12 Post author

    Hank + stan = Hankstein

    The next smarter Einstein ‘s

    Reply
  14. Katie Brennan Post author

    7:47 *deciduous, meaning the trees shed their leaves annually, then experiencing a dormant period (usually winter)

    Reply
  15. nene mokonchu Post author

    live love Crash Course, keep it up guys! You're all so awesome, thanks for all of the help you provide to so many!

    Reply
  16. Heeman Ijaz Post author

    Imagine they eat each other… I got a bad image now

    Reply
  17. Alec Lawson Post author

    1st video I've seen from crash course and i think I'm now a lifer. Very educational and obviously a good time..thanks guys keep it up!

    Reply
  18. Гульнара Акпарова Post author

    Добавьте Русский субтитры
    Add Russian subtitles

    Reply
  19. Sergio Rodriguez Post author

    you know what i learned in the last 38 weeks? that you made 40 episodes, but still say you made 38

    Reply
  20. Happiness cafe Post author

    I learned about ecology so many time. But this is the first time I understand. Thanks hanks!

    Reply
  21. k Bowsh Post author

    Im sorry my dude but I had to put the video speed at 0.75 lol

    Reply
  22. Yigyigs Post author

    i love ecology. i study it at uni. during high school i loved biology, but the more i study ecology the further i leave my love for pure bio behind. idk, i feel like biology is 'too zoomed in' for my liking, if that makes sense? ecology all the way

    Reply
  23. Jasyl Rubis Oraa Post author

    Reporting about ECOLOGY OF LIFE. hays these video help me a lot THANKSSSS 💞

    Reply
  24. Sabri Post author

    Here I am currently studying for my biology finals this Friday wish me luck I have a B hoping to get into the nursing program.

    Reply
  25. David Nzekwu Post author

    is it possible if you could do a crash course on proximate and ultimate causes of behavior, as well as fixed action patterns

    Reply
  26. At least 7 Dwarves Post author

    So I go to school to teach myself a subject that I'm paying for… Nice. Shame there's no 'Mega Like' for this channel. Excellent stuff

    Reply
  27. Jenna Melman Post author

    This isn't against this channel personally, just saying that for me at least and a lot of people i know these science videos on youtube it would be so much easier to process and understand without all the jokes. It's just so much being thrown at you for a viewer, all this information you're trying to make sense of and you have to quickly realize what's important information and what's a joke. The jokes are distracting, and for me and i'm sure a lot of people, annoying-even if it was a good joke, because it distracts from the information and you have to try and think about the concept from the beginning all over again. For me i have to replay things multiple times a lot of the time to go back to try and connect the relevant concepts. I get why the jokes are there, cause creators think it would be boring without them, but a lot of people would prefer it that way- i wish there was at least one channel that had the helpful animatics and that was all it was. If i had the time i would love to make a channel where i take science videos and edit out the jokes so it's just the useful explanation and that's it, they don't try to make it 'comedy'.

    Reply
  28. Mae Angelie Paradela Post author

    Hi Sir Green, Could you please make Crash Course Oceanography please

    THANKS A MILLION for you videos It really helped me a lot in graduate school

    Reply
  29. Daniel Hain Post author

    I love these videos! I wish I could donate 2.2 million dollars

    Reply
  30. Janette Ruiz Post author

    i didnt get biology in high school 🙁 but got it in college woop? (cus i gotta pay)
    i feel i missed out and somewhat resent my high school
    unsure what to specifically do but ecology is the main focus 😀

    Reply
  31. Shane Potts Post author

    Need to just say there needs to be more herobrine minecraft theorys

    Reply
  32. Ian Reginio Post author

    This video was great and have a great explanation thanks for making this video hope you could make more.

    Reply
  33. Azen Contento Post author

    I'm watching this for my finals as I finish my 1st year in college.

    Reply
  34. Avi Segal Post author

    Any chance you can do a video or a few on microbiology? Bacteria and AntiBiotics and stuff like that

    Reply
  35. rosella jung Post author

    my teacher showed me this and its highly boring sorry dude WATCH HIM READ THIS :0

    Reply
  36. rachel a Post author

    taking my last high school bio test tomorrow! huge thank you to everyone involved in making these videos and essentially teaching me everything lol <3

    Reply
  37. Victor's Classically Modern Channel Post author

    I remember coming here to finish AP Bio in High School years ago. And here I am again, studying for Bio 2 final on college lol Thanks Crash Course, you are always helpful!

    Reply
  38. Lila Brooke Post author

    Yo y tf does it take u so long to get it something/ur point like goddamn!

    Reply
  39. G W D Post author

    Taking an ecology test tomorrow after a month of notes which scares me

    Reply
  40. Spencer K Post author

    Who else here studying for 2019 AP exam??

    Reply
  41. Markas Skorpkis Post author

    tundra and desert are completely opposites and they dont share any factors as of why they are the way they are for example tundra actually has alot of precipitation in form of snow, and in summer it becomes swamlands or huge creeks and rivers valleys. other than that great video.

    Reply
  42. Crystal Monreal Post author

    Anyone else studying for their IB papers?

    Reply
  43. Dewan Protiva Post author

    These videos have helped me ever since I was in 8th grade and now I am a sophomore in college. Thanks Hank!

    Reply
  44. YANIELLY M STIEHL-SOTO Post author

    Thanks to him i got a B+ on my last exam !

    Reply
  45. Vik R Post author

    As a Middle Schooler, I watched all 40 of these episodes to study for a test.

    Reply
  46. Jack Snyder Post author

    Just binged this whole series. Thanks Hank for teaching me Bio when my teacher didnt. Wish me luck on the AP exam!

    Reply
  47. Chløe De Luna Post author

    Thank you for making everything more understandable 🙂

    Reply
  48. Emilie Andersen Post author

    Anyone here not studying for AP exams, but studying for IB exams?

    Reply
  49. pacandpal3 Post author

    i wasn't ready to see the last episode . in fact i kept postponing it because i enjoy watching all the biology videos so much lol but its time to move on…..after i go through every episode again one last time to make sure i understand everything lol.

    Reply
  50. Gio Martinez Post author

    Who else’s here just to pass normal biology.

    Reply
  51. curly_joni Post author

    I'm taking a biology assessment… Thanks for the help Hank and team!

    Reply
  52. 짜장면 먹은 냥냥이 Post author

    "To animate the bag of meat that is you" -Hank Green, Oct. 29, 2019
    LOL never thought of it like that

    Reply
  53. Stephen Caird Post author

    Hey! Thanks for what you do. I'm a field ecologist by trade and thought I would look to see what's out there on YouTube discussing ecological topics. This was video number 1 that came up in my search, and a very good introduction to the ideas on which so many other nuances of theory are based. Do you have any more on Ecology?

    Reply
  54. Kabir Awan Post author

    2:42
    "Living Space"
    Germans – casually starts engine to Panzer

    Reply
  55. Ali Alrubaye Post author

    did he call everyone a meat bag. someone been watching Futurama

    Reply
  56. M̵r̴ A̴n̷o̶n̸y̴m̶o̷u̸s̷ Post author

    5:10
    I think Hank can rap, guys. lol.

    Reply
  57. Riana Momtaz Zaman Post author

    Can you please make a course of zoogeography?

    Reply
  58. Armani Bolam Post author

    Bruh we have to watch this for class pretty helpful tho ngl

    Reply

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