Professor Jane Memmott, University of Bristol One of the fascinating things about food webs
is you do see the same patterns come up again and again.
So for example, if I had a parasitoid network from my back garden, it wouldn't look that
different to a parasitoid network that we collect from the tops of mountains in Hawaii.
So you do see the same patterns coming out again and again.
In general, you'll find there are a few well-connected species in a network and a lot of species
that are much more kind of peripheral to things.
I'm going to show you how we actually visualise a food web.
Video shows food web visualisation on a computer screen.
So starting at the bottom of a food web we've got all the plants.
So what we've done here is we've counted leaves, or flowers, or seeds, or some part of the
plant.
So we add the caterpillars in this particular case.
So this is the herbivore part of the community.
This is a common caterpillar.
This is a rare caterpillar.
And these are all of the caterpillar species in this particular plot.
So up here we've got the parasitoid community, a common parasitoid and a rare parasitoid.
And the different colour codes in this case tells us something about the biology of the
organisms.
The thing that makes the food webs really useful though is we know who is feeding on
who.
So for example, that particular caterpillar species here is feeding on this particular
plant species.
A parasitoid up here is feeding on that caterpillar species.
And it's feeding on more than one species though as you can see if I fill in the rest
of the community it looks like this.
This parasitoid here is feeding on two species of caterpillar.
This one here, which is the commonest one in the community, is actually feeding on five
different species, one, two, three, four, five.
But it is mostly feeding on these two caterpillars.
So this is the architecture of the network.
You can plot these networks in various ways.
This is the way that I use it because it is the way I am used to reading these things,
but you can plot them in 3D and twizzle them around in space and they look just fantastic.
Studying food webs is really very useful when considering pollination because traditionally
people look at the crop and what visits it.
If you look at that in a network context you need to know if you have a key pollinator
to consider the pollinator you've got to consider what is happening outside of the crops flowering
season.
Video shows bumblebee visiting lavender.
If it's a bumblebee it is going to emerge in March/April, you need food plants around
then so if you look more holistically at the whole picture of the lifespan then you can
see how the pollinator and the crop fits into a much bigger picture.
Then ideally you can manage that network to actually favour the insects you're after for
the pollination services and make sure they are there year after year and you'll get sustainable
pollination that way.
Video shows bumblebee visiting a flower.
It's important to save pollinating insects because an awful lot of the food we depend
on as humans comes from, is the result of pollination.
So while wheat might be wind pollinated, say, all the soft fruits, beans, and a whole variety
of other plants are dependent upon pollination.
We can't, as people, recreate that service any other way, we're dependent on wild and
managed pollinators.
So without pollinators we'd get rather hungry!
We need to know which insect species are pollinating which crop species and which insect species
can pollinate them.
So can we manage these communities better?
Rather than just sitting back and hoping we're doing the right thing, we need to know more
about which environmental schemes really work.
We know that the pollen and nectar mixes can be really rather effective, but there is still
an awful lot we need to know.
So what can we do to make life better for the pollinators?
So we can then actually reap the rewards of this in terms of good pollination services.
Video shows moths, bees and hoverflies collecting nectar from flowers.
It could well be disastrous for UK agricultural loss, major pollinating species.
I mean if things like the bumblebees all disappeared, solitary bees, some of the hoverflies can
be surprisingly important.
If those insects start disappearing, so basically there are no spare parts in the system, we'd
see food productivity potentially drop, potentially fairly catastrophically.
Video shows a 3D model of a food web.
Food webs are an excellent tool for modeling extinctions at the community level because
what you can do is actually, when you've got your food web, when you've spent a long summer
putting together this data, you can load it up onto the computer and then you can actually
model the effect of removing a species.
So you can take out species one by one according to various rules.
So for example, you could remove the rare species as those are the ones most likely
to go extinct.
Or you could take some of the really well-connected species out like the bumblebees in a pollination
network or take out the honey bee and actually ask how many linked extinctions are there?
How many plants, how many crops or native plants are left high and dry with no visits
at all?
And there is good theory to suggest that taking out just a handful of well-connected species
can actually lead to the collapse of a network.
In pollination networks you get patterns whereby plants that actually have a very highly general
light, where lots of things visit them, tend to attract the really rare species in the
community.
So again, in pollination networks, my pollination networks from local farms don't look that
different to pollination networks from urban habitats or from nature reserves.
There are subtle differences and one of the million dollar questions is asking, well you
know, is there a fingerprint of some sort of environmental problem that you can see
on a network?
Is there some subtle pattern that tells you it's about to kind of start having serious
problems?
If you can predict that before it happens then that's really interesting.