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How Oak Trees Manipulate Squirrels To Abandon Their Acorns - YouTube
Channel: Steve Mould
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- You're probably aware
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of the mutualistic symbiotic relationship
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between oak trees and squirrels,
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but you might not know
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that oak trees do something
incredibly manipulative
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to the squirrels.
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It's all about seed dispersal.
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So, oak trees want to disperse their seeds
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far away from the parent tree,
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in the hope that a new oak tree will grow.
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And it won't be in the shadow
literally of the parent.
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So the oak tree makes acorns.
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An acorn is basically
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a container of nutrients with
a little embryo near the tip.
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Because they're full of nutrients,
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squirrels eat them
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and eat them in their
entirety, including the seed
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which is no good for the oak tree.
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The reason this
relationship is mutualistic
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is because squirrels are caching animals.
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They save resources to use in winter.
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They do this by burying acorns
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in little caches underground.
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The reason this works for the oak tree
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is because occasionally
a squirrel will forget
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about one of its caches
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or will die before getting
around to that cache.
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So, there's potential for a new oak tree
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to grow from that location.
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That much you probably already know
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but oak trees are able to vastly improve
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their chances of getting
acorns into abandoned caches
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by doing something called masting.
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Every approximately five years,
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though it varies a lot.
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An oak tree will produce a
huge overabundance of acorns
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like tens of times more
acorns than on a normal year.
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These years are called masting years.
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This bumper crop of acorns
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is way more than the
local squirrel population
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and other predators could
possibly burry and eat,
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but you know what?
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Those squirrels are
gonna give it a good go.
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You'll forgive me for anthropomorphizing,
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but the squirrel just
looks at these acorns
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and thinks this is incredible,
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I'm just gonna bury as many
of these as I possibly can.
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So they do.
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And loads of those caches end up unused.
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And that's exactly what
the oak tree wants,
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it wants abandoned acorns
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that have the potential to
grow into new oak trees.
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But if an oak tree has this capacity
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to produce an insane number
of acorns on certain years
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why not just spread that
capacity out over all years?
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Well, if oak trees did that,
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then the predator population
including squirrels
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would rise up to meet that capacity.
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Like during mast years
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squirrels get a huge boost in nutrition
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so they make more babies
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and the squirrel population goes up.
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But the following year
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this growth of population
will go back down again
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because we're back down to
a normal level of acorns.
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So doing it this way,
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where you have mostly low yield years
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followed by sudden spikes of yield
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that controls that predator population.
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It keeps it at a low level
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and then you just overwhelm them.
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It's an example of predator satiation.
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It happens with cicadas as well
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for example, cicadas spend
many years underground
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and they all come out at the
same time in a huge swarm
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for the three F's, feeding,
fighting and mating.
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And they overwhelm the predator population
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like the predators are going,
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ah I couldn't possibly another one.
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Actually in the case of cicadas,
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the predator is a wasp.
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So it's the wasp that say
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oh, I couldn't possibly lay another egg
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in the cicada,
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'cause that's what they do.
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By the way,
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there's a potential explanation
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for why certain cicadas live underground
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and then come out in these
prime number cycle of years
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13 and 17 year long cycles.
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I've made a video about
that on number file,
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I'll link in the description to that.
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I actually make the same
three F's joke in that video.
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It's a good joke.
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It's funny 'cause you think I'm gonna say
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feeding, fighting and fu...
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Just like cicadas is
oak trees have to agree
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on when to have a mast year.
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Like if cicadas spend 17
years living underground
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but they're all out of
sync with each other.
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So you've got cicadas
popping up every year,
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then predator satiation wouldn't work.
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It's the same with oak trees.
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If you've got a population of oak trees
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and there's always one
or two having a mast year
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then that wouldn't control
the predator population,
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the squirrel population.
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Instead, like if you go
into your local woods
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and you see one oak tree
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producing an insane number of acorns
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then all the other oak trees
will be doing it as well.
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I think it might be a mast
near where I live actually.
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Don't know it seems like a lot of acorns.
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What do you think?
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Is that a lot of acorns?
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Seems like a lot of acorns.
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Scientists don't know how
this coordination happens.
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It might be that all oak
trees have a mast year
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under very specific weather conditions.
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So it always happens for all oak trees
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or it might be a chemical signaling
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in the roots underground.
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In general seed dispersal
is really interesting,
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like not just the mad thing
that the oak tree does.
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There are loads of examples
of weird seed dispersal
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like tumbleweed, for
example, is seed dispersal,
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coconuts, that's an example
of nautical seed dispersal.
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I actually talk about some
of my favorite examples
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of weird seed dispersal in my new podcast.
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I've got a podcast, it's
actually not just my podcast.
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It's Matt Parker and
Helen Arney's podcasts.
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The three of us talk about
[342]
stuff that we find really interesting.
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It's called A Podcast
of Unnecessary Detail
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because some things
become really interesting
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when you get down into the detail.
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It's only been out for a couple of days.
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It's already doing really
well on the charts.
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I hope you'll have a listen to it
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'cause I'm really excited about it.
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The seed dispersal episode
is out in a couple of weeks.
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So there's three episodes out already
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so you can listen to all those.
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And then they're out on a weekly basis.
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I hope you'll leave review.
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I hope you'll tell your friends about it.
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All the links are in the description.
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It's also on YouTube,
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so I'll put a link to that on the end card
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well it'll be somewhere
on the screen, won't it?
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That's it really.
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This is just one of my
short in betweenie videos
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so there's no sponsor.
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Just wanted to take this opportunity
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to tell you about my podcast.
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I hope you have a listen.
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Thanks a lot.
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See you next time.
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(upbeat music)
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