Community Ecology II: Predators – Crash Course Ecology #5

Community Ecology II: Predators – Crash Course Ecology #5


Of all the ways that species interact on this planet, maybe the one that fascinates us the most is predation, and why not? It’s hard not to be captivated by, say, an Alaska Brown Bear, one of North America’s apex predators, even though they get much of their nutrition
from nuts and bugs and berries. But you can also tell that it’s a pretty big
fan of crushing the bones of other animals because of this amazingly pronounced sagittal
crest, which is where its jaw muscles connect. And maybe part of why we’re so fascinated
by predation is because we are, in many ways, the planet’s top predator, at
least for now. That’s how most of these guys got here, but for hundreds of thousands of years,
we were preyed upon as well, not just by bears and wolves, but by viruses
and bacteria and parasites. Because predation isn’t just animal eats animal. This musk-ox or this big-horned sheep can also be considered predators, even though they only eat plants. But perhaps what’s most important to understand
about predation is the evolutionary pressures that come with hunting and being hunted for
thousands of years. Because of these pressures, predation has driven all sorts of truly amazing adaptations that we see all around us. From the grizzlies enormous claws and teeth,
to the wolves’ habit of hunting in packs, as well as defensive adaptations, like the speed of the pronghorn, the fastest animal in North America. In the end, the effect of predator-prey is
an evolutionary arms race that results in the mind boggling amount of diversity we see
in any ecosystem from the Northern Rockies all the way to the African Savanna. This arms race is known as co-evolution, the
process by which the interactions between two species affect the evolutionary development
of both. It’s been going on since the Cambrian explosion
more than half a billion years ago and it will continue spawning new bursts of diversity long after we humans have eaten ourselves into extinction, and maybe, we’ll end up in a place like this. [Theme Music] We tend to think of predation in terms of
animals — lions hunting zebras, wolves killing sheep,
hawks eating mice — but predation is much more than just carnivores
doing their thing, it applies to any number of interactions where one type of organism kills another for its energy. That’s an important thing to note, because a lot of ecology comes down to the flow of energy through nature, and every living thing needs energy to meet its twin evolutionary goals of staying alive and making lots of babies. Predators kill because they’re hungry, but they’re hungry because they need energy to survive and reproduce. For prey, these interactions are especially
high-stakes, obviously, because nothing quite quashes your reproductive
chances like being dead. But almost all energy on earth starts with
plants, so consider bison eating grass, that’s a type of predation called herbivory, where an organism eats plants or algae to capture their energy. It may not really seem like predation to you,
but bison eating grass, manatees eating seaweed, and sea urchins munching on algae are all
examples of organisms eating other organisms to ingest the energy of the sun. There’s also parasitism, another form of predation
in which organisms derive energy from the host usually harming it and sometimes killing
it in the process. Hair worms, for example, devour the insides of grasshoppers and then brainwash them to make suicidal leaps into water. How exactly the waterborne worm finds its
way to a grasshopper is a mystery, though larva carried by mosquitoes is a likely
route. Once inside the grasshopper, the worm eats
everything non-essential to its host as it grows several times the length of its host’s
body. When only the grasshopper’s head and legs
remain, the hairworm is ready to reproduce, and that’s when the brainwashing begins. See, hair worms breed in water, but grasshoppers
can’t swim, so hair worms pump their hosts full of chemicals that prompt an inescapable urge to leap into a body of water. Once the grasshopper makes the leap, the hairworm is free to burrow out of the host and find a mate. Ew. Yeah, chasing and eating a gazelle is one thing, but turning your prey into, like, a suicidal zombie, that my friends, is predation. So clearly, predator and prey both have millions of years of tricks up their sleeves or stored in their DNA because everyone’s ultimately playing by the
same set of evolutionary rules. Whether lion or zebra, grasshopper or hairworm,
bison or grass, gaining energy while not being eaten is a
prerequisite to reproductive success. So, the need to survive constantly forces
predator and prey to adapt weapons and defense in a never-ending evolutionary arms-race. On the predator side, hunting and feeding
adaptations are obvious and familiar: a wolf’s keen sense of smell and flesh ripping teeth, and an eagle’s sharp eyes and prey-gripping talons. Other creatures like rattlesnakes use heat-sensing
organs to seek out small rodents and toxic venom to strike them dead, but this is where co-evolution takes the stage to give the prey a stake in the evolutionary arms-race, too. Since being caught by a predator is kind of terrible for anything that hopes to spread its genes, species have adapted to all sorts of ways
to avoid getting killed. These can be broken up by what kinds of predatory behavior these adaptations are designed to avoid, namely, detection, capture, and handling. To avoid detection, some prey adapt cryptic
coloration, which we better know as camouflage, to help a species blend into the background. Stick insects that have adapted to look like
sticks, leaf insects that look like leaves, snowshoe hares that turn white in the winter
to blend in with the snow and brown in the summer to blend in with the
grasses are all good examples. Avoiding capture is, at times, pretty straightforward. Antelope, for example, flee predators with
great leaping speed. Others find safety in numbers, such as bison forming a giant herds or herring grouping in schools. This kind of grouping certainly doesn’t keep
the prey from being detected, but it greatly reduces chances that any individual
will get picked off by a predator, especially fit members of the group in the
middle of the pack. And finally, some of the coolest and most familiar adaptations are those that prevent handling. Plants are experts at these, think of a rose’s
thorns; or tree sap that traps insects; or the branches of an African acacia tree — they’re most thorny within the range of tree-munching giraffes, but above where the long-necks reach, there
aren’t as many thorns. Other plants also produce chemical weapons,
such as the tobacco plants nicotine and the tannins produced by many plants like
grapevines to fend off foragers. But things get really weird when you see what
animals do with this bag of chemical tricks, because often these critters not only have
wicked toxic cocktails to defend themselves, many have also evolved aposematic, or warning
coloration. The bright contrasting colors such as yellow
and black splotches on the fire salamander or the red, yellow, and black bands of the
coral snake make it clear to predators that eating them
would be a serious mistake. And when you think of it, nature is full of species that are black and yellow in color, or red and black; we tend to avoid them at all costs. We’re
smart that way, and so are most other predators. This, of course, is no coincidence, as German
naturalist Fritz Muller noted in the 1870s, unpalatable species such as Cocobees, Yellowjackets — actually, almost every kind of bee and wasp resemble each other using similar colors and patterns. He figured out that the more unpalatable prey
there are that use the same color patterns, the more likely predators are to avoid all
prey with that appearance in general. This defense technique is today known as Mullerian
mimicry. But it turns out, unsurprisingly, some critters
that look dangerous are getting the last laugh because many of them would actually be quite
tasty to any predator; they just trick everyone by copying the looks
of the truly dangerous species. This technique is called Batesian mimicry, and to explain it to you, I’m going to need to sit down. I’ll give you one guess to figure out who
first described Batesian mimicry. That’s right, it was Bates. More specifically, it was Henry Walter Bates, a 19th century British naturalist and explorer. Bates was born in 1825 to a middle-class family
that paid the bills by making hosiery. He spent most of his spare time reading often
about bugs, and by the young age of 18 he was a budding entomologist with a publication on beetles already to his credit. It was a few years later that he met the famed
entomologist Alfred Russell Wallace. The two hit it off, and Wallace in 1847 proposed to take a trip to South America to collect insects. They would finance their travels by sending collected specimens back to England for sale to museums and private collectors. The pair set sail the following year, and after four years in the field Wallace moved on, but Bates, apparently not wanting to get into
the hosiery business, stayed behind, spending the next eleven years in the jungle. All told, he collected nearly 15,000 species,
about 8,000 of them new to science. Just a few months after Bates arrived home in 1859, Darwin published his On The Origin Of Species. Bates read it and figured he could contribute
evidence to support the new theory of natural selection from his insect collection. Two years later, he presented a paper that
showed how different species of butterfly developed nearly identical color patterns
on their wings. For example, butterflies called Heliconiinae, which were slow-moving and abundant — but toxic — were nearly identical to Pieridae, which were
more rare, but harmless. Bates concluded that natural selection had
driven the harmless butterflies to mimic the patterns on the harmful butterflies for their
individual bids to survive predation by birds. The discovery helped launch Bates’s career
and reputation, and he went on to recount his adventures and other discoveries in a book, The Naturalist on the River Amazon, and later took a job as secretary to the Royal
Geographic Society. Though Bates died in 1892, the concept of Batesian mimicry continues to fascinate scientists today. Why, for example, are so many mimics not perfect
imitations of their dangerous counterparts? Is it because perfect imitation isn’t necessary
to do the job, or because mimics lack the genes necessary
to perfectly resemble their poisonous counterparts. Perhaps budding entomologists armed with 21st-century tools will finally unlock the answers. But don’t think that prey are the only crafty
mimics out there — in the arms-race, some predators have learned
how to win food through imitation as well. You’ve heard me talk about snapping turtles with tongues that resemble wiggling worms to lure fish, and don’t get me started about anglerfish! If predation teaches us anything, it’s that nothing lasts forever, not just for prey, but for every living thing, because the interaction between predator and
prey keeps driving evolutionary change. But the communities themselves that we’ve
been talking about for the last two weeks don’t stay the same either, of course. New tenants are always moving into a habitat and every now and again, a new landlord takes over. That’s part of what makes the living world such a dynamic and beautiful and exciting place — and it’s what we’ll be exploring next week. Thank you for watching this episode of Crash
Course: Ecology. If you want to review anything there’s a table
of contents over there. Thanks to everyone who helped us put this
episode of Crash Course together, and if you have any questions or comments or ideas you can leave them for us on Facebook or Twitter or, of course, down in the comments below.
We’ll see you next time.

Author: Kennedi Daugherty

100 thoughts on “Community Ecology II: Predators – Crash Course Ecology #5

  1. actually in a way they aren't totally they're energy comes from a combo of solar (plant matter) and geothermal (pressure and heat) which together make them a far more useful fuel source than wood or any resource really

  2. What about the venus fly trap . 🙂 And this is to say for those who say that all types of plants are harmless or don't kill. My a** VFT is a good example that not all plants are designed to be good.

  3. Well, if you had hank explain things from start to finish, he would probably assume there was a bang, and would make absolutely no mention of apocalypse or salvation or whatever.

  4. I guess last just has two meanings; it can either mean the opposite of first, or the opposite of next. Usually you should be able to tell which by context. (for example, if you see a next and last button, you can assume that the last button is being used to mean the opposite of next.)

    Honestly, i think most people don't actually understand what the difference between sex and gender is. The average person probably thinks they mean the same thing. The same goes for people who make surveys.

  5. I think he would do what all scientists do, and claim that he assumes there was a bang due to it being the most prevalent and logical theory to date, but he could also talk about some of the new theories making their debut. And could you blame him for not mentioning anything about an apocalypse? All biblical references to such an event are spiritual at heart, most scientists and researchers are looking to find out if 'God' does exist or what caused all this, but again, there are new theories now

  6. Because we have the ultimate weapon, which defeats not just predators but prey, plants and the very planet itself; unchecked consumption

  7. Most scientists are not, in fact, looking into whether or not god exists, because god (at least the one you're probably talking about) is, by design, undisproveable and therefor not worth a scientists time.

  8. I know why animals that mimic the looks of dangerous species aren't perfect mimics; sex and reproduction. If they look exactly like a different species and hide among them for protection, it would be impossible for them to reproduce without having a blatantly obvious sign, such as a peculiar scent, designed to attract the real thing, which could be picked up on by predators, so they stick to more subtle differences like looking a bit different, but not too much.
    Can I has my nobel prize noaw?

  9. I don't argue with "Know it all's" who make up words. Undisprovable? We common folk like to use the term "Cannot be proven nor denied in existence"
    Scientists are, in fact, looking for the answer to why we're here and where we came from, and as a direct relation of such search, they are also looking for the answer as to whether or not we are here by chance or whether we were placed here by higher beings, and the resulting answers will apply to any 'God'.

  10. No, you've done nothing but spit out already known information, and if you're looking for any kind of reprisals, you're in the wrong place.

  11. Okay, this has nothing to do with the episode, but my ad before the video was a song about TFioS. That made my day 😀

  12. we have brains that invented weapons – pointy sticks and rocks to spears and swords to cannons and muskets to AR-15s and concussion grenades. 😉

  13. I propose that Batesian/Muulerian mimicry is imperfect for a simple reason: sympatric species, which share the same habitat with different species that may be of the same genera, need to be able to know who to mate with so that they don't interbreed and cause infertility in their offspring. Slight variations in the mimicry will act as reproductive isolators, allowing individuals to recognize others of their own species.

  14. We were able to make tools to kill things with. Then when we had killed most things we moved on to killing each other. Now we are trying to figure out how to kill space.

  15. My thinking was along the same lines, but you articulated that better than I ever could. I do believe, though, that mimic animals don't need to look exactly like harmful species anyway. With enough harmful species that have a particular trait, like a color combination, that color combination or other common trait is all that's needed to make the association. Most other traits are irrelevant as far as the predators are concerned.

  16. The variations will mainly focus on traits that won't affect the mimicry however, if we are talking about the mimic. They would use chemical receptors to recognise mates, not differences that predators would notice. So if trying to copy another species and both have predators that use smell to detect them, they would use different mechanisms to recognise each other. The mimicked organism (if batesian) will be selected to be different anyway in order to minimise the dilution.

  17. Not entirely true I believe, I mean, Archeas and Bacterias that use Quimiosintesis or similar process from vents in the bottom of the ocean never see any light in there lives, they use the energy from under the Earth's crust and chemilas that are in there

  18. When as a species has the capability to eat anything it wants, including a predator that has been “perfect“ for 200 million years (Great White shark) then you get to call yourself apex. However, if you take Hank`s definition of predation, then the billions of species of undiscovered soil bacteria would really be the apex predators on the planet.

  19. If you take Hank`s definition of predation, that it is simply one organism eating a part of another organism then the billions of species of undiscovered soil bacteria would really be the apex predators on the planet, not humans. They consume anything and everything with a more complex carbon atom than CO2 that they come in contact with.

  20. and then there is the mongoose where they are all like "oh you snakes want to kill me oh im just gonna become immune to your poison and comeback wit my homboys and fuck you all up!"

  21. NO ! fake hope or excessive optimism made me stop the vid at 1.40

    How can you imagine we will become extinct ? I (humble but there) can't imagine a path where this would be possible

  22. Wouldn't perfectly mimicking the poisonous butterfly cause problems for the non poisonous butterfly? As distinguishing between their own species and the one of the poisonous butterflies might become a bit on an issue during mating season as they would both look the same. Though with the aid of scents and other factors the animals could potentially look the same but there would then be the issue that they could be tracked via their scent. Also I would like to say that I love watching your lectures they have helped me allot with my studies over the past couple of years, they are really insightful and are a great builder to help foundation my studies. Thanks to all of you   

  23. Crash Course actually makes me feel passionate about Ecology, which is a feat I once thought impossible. Thank you. 

  24. I am using this series and the Biology one to study for my finals this week 🙂 Enjoying the format and information greatly. Thanks!

  25. When a species mimics another, I wonder if it's a conscience decision that they manage to manifest, or if it's simply the two species breeding with each other. 

  26. hey guys, not sure if that kind of request is common around here, but as i've never seen any i must say your channel is probably the best educational one, and as all videos are pretty well made and the subjects you approach absurdly understandable i was wondering if there is any possibility of making a series of videos over fine arts and/or astronomy. it would be awesome! thank you though for all the videos you've already uploaded, they are great, really 

  27. Did he really talk about predation on early humans and not mention tigers? Even worse, did he use bears instead?

    By the time we saw any bears, we had already become apex predators through direct conflict with lions and tigers (no bears); after that, we only competed with other apex predators, never consistently fed them.

  28. Did he really talk about predation on early humans and not mention tigers? Even worse, did he use bears instead?

    By the time we saw any bears, we had already become apex predators through direct conflict with lions and tigers (no bears); after that, we only competed with other apex predators, never consistently fed them.

  29. Roses don't have thorns. They are classified as prickles. An educational program should vet it's information from better sources than pop culture songs.

  30. i like your video but you didnt really talk about the major ones. you only talked about herbivory and paratisism. there are disease, mutualism, commensalism, and predation.

  31. Can you explain to me directly as to what Mullerian Mimicry and Batsian Mimicry is? I didn't really understand the defenitions.

  32. Why are you mentioning all the time evolution? There is no MAKROevolution. Yes, we can observe variety of spieces but not changing of kinds.

  33. GOD BLESS YOU'RE TEACHING ME EVERYTHING MY AP BIO TEACHER DIDN'T 🙂 i'm not even cramming and i'm really enjoying learning this THANK YOU

  34. Dear Hank, I can't tell you how many times you help me in life and school. THANK YOU!!! PS. John is super awesome as well.

  35. not every human is a predator, because what about people who only eat vegetables that doesn't means they are predating on a living organism

  36. Looks like the title is plural, "The Naturalist on the River Amazons," but thanks for contributing to my to-read list. I love historical science books, especially the era of naturalist explorers.

  37. There's a movie based on the hair worm. I don't know the name of it, but its basically people getting infected by a worm that finds its way into their bodies and makes them go full on zombie. It had a terrible ending, but yeah…

  38. Is there a thing about the angler fish? I have used crash course for several courses over time and in many I have seen a stuffed animal angler fish

  39. Hey, guys. Can I just suggest, completely irrelevantly, that you should not search up "hairworm" into youtube? No prior experience. Just something that I'd like to put out there, for no reason.

  40. I feel like the word mimicry makes it seem like these animals did it on purpose, instead of it just happening via evolution. Wouldn't that be the reason that the animals who "mimic" other species don't get it exactly right? It's not like they sat down one day and thought "Hmm, I should make myself look like that other dangerous snake so predators don't eat me." No, they just happened to be born with a certain pattern or certain colors, which made them look like the other dangerous animal, and therefore allowed them to not get eaten, and therefore pass on their genes.

  41. Can anyone explain to me why is parasitism categorized as predation? My teacher taught me that the term of parasitism and predation are at the same level because they are both categorized as interspecific relationship. Thanks in advance!

  42. The reference link just re-directs me to the main page of something called SM Boost. Any help to find the rederences?

  43. its reallly a high quality education. god bless you dear.god will shower you the entire happiness of the world.

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