- 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)