- You're probably aware of the mutualistic symbiotic relationship between oak trees and squirrels, but you might not know that oak trees do something
incredibly manipulative to the squirrels. It's all about seed dispersal. So, oak trees want to disperse their seeds far away from the parent tree, in the hope that a new oak tree will grow. And it won't be in the shadow
literally of the parent. So the oak tree makes acorns. An acorn is basically a container of nutrients with
a little embryo near the tip. Because they're full of nutrients, squirrels eat them and eat them in their
entirety, including the seed which is no good for the oak tree. The reason this
relationship is mutualistic is because squirrels are caching animals. They save resources to use in winter. They do this by burying acorns in little caches underground. The reason this works for the oak tree is because occasionally
a squirrel will forget about one of its caches or will die before getting
around to that cache. So, there's potential for a new oak tree to grow from that location. That much you probably already know but oak trees are able to vastly improve their chances of getting
acorns into abandoned caches by doing something called masting. Every approximately five years, though it varies a lot. An oak tree will produce a
huge overabundance of acorns like tens of times more
acorns than on a normal year. These years are called masting years. This bumper crop of acorns is way more than the
local squirrel population and other predators could
possibly burry and eat, but you know what? Those squirrels are
gonna give it a good go. You'll forgive me for anthropomorphizing, but the squirrel just
looks at these acorns and thinks this is incredible, I'm just gonna bury as many
of these as I possibly can. So they do. And loads of those caches end up unused. And that's exactly what
the oak tree wants, it wants abandoned acorns that have the potential to
grow into new oak trees. But if an oak tree has this capacity to produce an insane number
of acorns on certain years why not just spread that
capacity out over all years? Well, if oak trees did that, then the predator population
including squirrels would rise up to meet that capacity. Like during mast years squirrels get a huge boost in nutrition so they make more babies and the squirrel population goes up. But the following year this growth of population
will go back down again because we're back down to
a normal level of acorns. So doing it this way, where you have mostly low yield years followed by sudden spikes of yield that controls that predator population. It keeps it at a low level and then you just overwhelm them. It's an example of predator satiation. It happens with cicadas as well for example, cicadas spend
many years underground and they all come out at the
same time in a huge swarm for the three F's, feeding,
fighting and mating. And they overwhelm the predator population like the predators are going, ah I couldn't possibly another one. Actually in the case of cicadas, the predator is a wasp. So it's the wasp that say oh, I couldn't possibly lay another egg in the cicada, 'cause that's what they do. By the way, there's a potential explanation for why certain cicadas live underground and then come out in these
prime number cycle of years 13 and 17 year long cycles. I've made a video about
that on number file, I'll link in the description to that. I actually make the same
three F's joke in that video. It's a good joke. It's funny 'cause you think I'm gonna say feeding, fighting and fu... Just like cicadas is
oak trees have to agree on when to have a mast year. Like if cicadas spend 17
years living underground but they're all out of
sync with each other. So you've got cicadas
popping up every year, then predator satiation wouldn't work. It's the same with oak trees. If you've got a population of oak trees and there's always one
or two having a mast year then that wouldn't control
the predator population, the squirrel population. Instead, like if you go
into your local woods and you see one oak tree producing an insane number of acorns then all the other oak trees
will be doing it as well. I think it might be a mast
near where I live actually. Don't know it seems like a lot of acorns. What do you think? Is that a lot of acorns? Seems like a lot of acorns. Scientists don't know how
this coordination happens. It might be that all oak
trees have a mast year under very specific weather conditions. So it always happens for all oak trees or it might be a chemical signaling in the roots underground. In general seed dispersal
is really interesting, like not just the mad thing
that the oak tree does. There are loads of examples
of weird seed dispersal like tumbleweed, for
example, is seed dispersal, coconuts, that's an example
of nautical seed dispersal. I actually talk about some
of my favorite examples of weird seed dispersal in my new podcast. I've got a podcast, it's
actually not just my podcast. It's Matt Parker and
Helen Arney's podcasts. The three of us talk about stuff that we find really interesting. It's called A Podcast
of Unnecessary Detail because some things
become really interesting when you get down into the detail. It's only been out for a couple of days. It's already doing really
well on the charts. I hope you'll have a listen to it 'cause I'm really excited about it. The seed dispersal episode
is out in a couple of weeks. So there's three episodes out already so you can listen to all those. And then they're out on a weekly basis. I hope you'll leave review. I hope you'll tell your friends about it. All the links are in the description. It's also on YouTube, so I'll put a link to that on the end card well it'll be somewhere
on the screen, won't it? That's it really. This is just one of my
short in betweenie videos so there's no sponsor. Just wanted to take this opportunity to tell you about my podcast. I hope you have a listen. Thanks a lot. See you next time. (upbeat music)
They’ll bury a shitload of acorns and then get hit by a car. Boom, new forest.
I had to use a leaf blower to push literally thousands of acorns off my lawn this year.
Super cool
Can vouch for this. Last year we had a crazy amount of acorns from the oaks in the neighborhood. Across the street there are oaks overhanging a steel building. Damn near constant noise all fall from acorns hitting the steel.
And then follows a glut of squirrels. You can’t drive a mile without 5 or 6 darting across the road.
IIRC their brains also expand during this time - when they shrink back they forget where they put them.
I have so many oak leaves in my yard that I haven't even started on the acorns. I don't think the squirrels are burying many, as they are stuffing themselves on birdseeds and suet.
Hickory trees do this as well but in three year cycles.
Oak trees can somehow communicate through an unknown means and synchronize acorn production to control the population of squirrels. What a world we live in.