Primate diets

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So far, we've talked about all
the different groups of primates

and where they live.

So now we're going
to talk about food!

I love food, and so does
pretty much every other primate

out there.

Here we have a variety of
primates and what they eat.

Take a moment.

Do you know what groups
of primates these are?

So we have a couple different
diets displayed here.

We have meat eating, fruit
eating, leaf eating, and also

gum eating.

So this little pygmy marmoset,
they bite into the tree

and they eat the
sap that comes out.

Well, let's start with the
most common diet, frugivory.

This is just a fancy word
that means you eat fruit.

Fruit are interesting
because they are patchy

in both time and space.

So fruit are not
available year round.

So you need to be able to find
the fruit when they're available

and do something else
when they're not.

They're also patchy in
space because not all trees

make fruit that is edible.

The good thing, though, is
they are easy to digest.

And pretty much all primates
do show a preference for fruit

when it is available.

And in fruit, we have high
carbs but low protein.

So if you eat a
lot of fruit, you

will need to supplement your
diet with something else

to make sure you
get enough protein.

So that's why if you're a human
and you're a vegetarian who only

wants to eat fruit,
you're going to need

to add a little something else.

So here we can see our
bonobo eating some fruit.

We also have a red colobus high
up in the tree, grabbing some.

And here we have an orangutan
who really loves his bananas.

This is an adult male.

You can tell because
of the developed cheek

flanges on his face.

Next up we have gramnivory
or eating seeds.

Here we have a capuchin
using a big old rock

to see if he can
crack open that nut.

They are tougher to process,
so they are a little bit harder

and more work intensive.

But in contrast
to our fruit, they

are available most of the year.

And that is a decided benefit.

Next, we have nectivory.

So this means you
eat flowers and/or

the nectar of the fruit,
nectar of the plant.

Again, like fruit,
they are patchy

in both time and space
for similar reasons.

And frequently,
flowers are shorter

lived than the fruit themselves.

We also have folivory or eating
the leaves and stems of plants.

These actually have a
fair amount of protein,

but they don't have many carbs.

They are abundant.

They're available year
round, though some primates

do have a preference for
specific types of leaves,

and those will not be
as abundant equally

throughout the year.

They are very hard to digest.

So many dedicated leaf eaters
have specialized adaptations

to make sure that they
can eat these leaves.

So here we have a black
and white colobus.

Here we have a cute little
gorilla eating a leaf.

Next up we have our gumnivory.

So these are eating exudates,
the gum and sap of trees.

So they are
available year round.

But you do need to have
specialized feeding adaptations.

So here is a pygmy marmoset.

The two little lumps are their
babies, which is really cute.

So what they do is they
bite onto these trees.

And they actually create these
essentially gaping wounds

on the trees, so they
expel some of that sap.

These guys are really
interesting because they

find a tree and they
make it their territory

and they defend it.

So other pygmy marmoset family
groups cannot access that tree.

They will fight each other off.

Next, we have faunivory
or eating other animals.

So this could be
invertebrates or vertebrates.

They are a really good source
of energy, especially protein.

But you have to
catch them first.

So here we have a
picture of a tarsier,

actually right next to an owl.

So you can see that they are
convergent with owls there

on the top.

They're eating a grasshopper.

But you will also
occasionally see

tarsiers eating lizards
or even small birds.

On the bottom there, you see a
chimpanzee eating a red colobus.

That is one of their
favorite snacks.

There's a couple other things
that you'll see primates eating.

So like tubers,
roots, and bulbs.

They do require
some work, though.

These you're going
to need to dig up.

A lot of them are hard to
digest, and a few of them

will eat grass.

Our geladas eat grass.

And orangutans will eat bark
when fruit are not available.

So thinking about
all these diets,

we can actually
classify primates

into different dietary types.

So what we'll do is we'll
try to figure out what's

the most prominent food source.

And that's how we will
categorize a population.

There is a lot of variation.

It will vary across different
populations, vary within a year.

And folivores commonly
do supplement with fruit.

So what we're trying
to do is figure out

what is the most
common across all

of these different variables.

The reason we do this
is it's very helpful

for understanding
evolutionary trend

and to see if there
is any uniting

factor within a particular
group of primates.

So let's look at an example.

Here we have a bushbaby,
spider monkey, langur,

and rhesus macaque.

These are colored to show the
approximate percentages of what

they eat.

So you can see with
our spider monkey.

They eat a lot of fruit.

And they are more frugivorous
than any of the others here.

So we would call this
spider monkey a frugivore.

The first one is our bushbaby.

The biggest one
there is insects,

and they eat a fair
amount of insects.

We would call them an
insectivore or a carnivore.

Our langur, now they
eat a bunch of leaves.

So we would call
them a folivore.

And a rhesus macaque
primarily eats herbs.

That would also be a folivore.

The reason why we care
about this is diet

influences pretty much
everything about a species.

It's the size of your
group, the social dynamics

within that group, the arranging
patterns, body size, activity,

the morphology of your gut
and teeth, how you move,

your life history brain size.

Really, everything boils down
to the effect of the food

that you eat.

Food is everything.

One of the reasons we like to
think of this is allometry.

Allometry is the
study of changes

in body size and
its consequences.

Basically, size matters.

The reason why we
talk about allometry

here is that how big you
are or how small you are,

influences the size of other
things and your metabolism.

So as an animal gets
larger, they need more food,

but an absolute
number of more food.

But they need
relatively less energy

because the metabolism curve
is a little bit strange.

And it also means they can
actually more easily digest

foods because naturally, their
digestive tract is longer,

so there's more of
a chance to absorb

more nutrients from that food.

Small animals, they need
absolutely less food,

but it needs to be high quality.

These large animals, they
can actually get away

with more low-quality food.

So you can think
of it like this,

a bigger primate has a bigger
gut and a longer retention time

in that gut without
changing anything else.

So they have increased
digestibility

just because they are bigger.

So what we see is when
we're looking at classifying

different types of
diets, folivores,

they're highly abundant, but
the food is pretty low quality.

So you need to be big.

You need to be a big
animal to have this

be a viable solution for you.

Insectivores,
they're high quality,

but they're hard to
find, hard to obtain.

A lot of work.

So they tend to be small because
it needs to be worth the effort.

They only need to
catch so many insects.

Imagine if a gorilla
only ate insects.

It would take them
forever to catch them all.

Frugivores-- this
really depends on

where they get their
protein because frugivores

have to supplement their
diet with something

to get enough protein.

So if they're larger, they will
tend to supplement their diet

with fruit.

If they're smaller, they will
tend to supplement their diet

with insects.

Here's a really nice graph to
show you the size of species,

species on the x-axis, and
then the number of species

with different
diets on the y-axis.

There's an interesting
thing called

KS threshold of about 500 gram.

If you're smaller
than 500 grams,

you basically have
to be an insectivore

because you need to be able
to get high-quality protein.

If you're larger than
500 grams, that's

when we start to see different
types of diets emerge.

So maybe you'll eat
insects and fruit.

What you can see here
on the bottom one

is we have frugivores,
but they're

split between frugivores
that supplement

their diet with insects
versus supplementing

their diet with leaves.

The smaller ones tend
to supplement their diet

with insects.

And the larger ones tend
to supplement their diet

with leaves, following
the predictions

that we already discussed.

As an example, here
are our tarsiers.

They are very small.

They're just 2 to 6 ounces.

And they are the only
entirely carnivorous primate.

Every other primate
that eats insects

also supplements their diets
through something else,

whether it's fruit,
sap, or leaves.

And you can see this guy in the
middle loves his grasshopper.

And there you can see
there's super long legs right

before they land to
catch that grasshopper.

But more than just
eating, we also

need to be able to get our food.

So let's talk about a couple of
different foraging strategies.

One thing to consider
is your activity budget.

How do you allocate your time?

So a howler monkey,
they actually

spend a lot of time resting.

Howler monkeys eat leaves.

So they actually do
need that amount of time

to sit and digest.

And uakari, they have
a very different type

of activity budget.

They spend a lot
of time traveling.

So these guys eat a lot of
nuts, so they need to find them

in the first place.

The howler monkey.

They don't need to spend
that much time traveling

because leaves are already
pretty much everywhere.

You can also think about
different activity patterns.

We have nocturnal, so you're
active during the night;

diurnal, active during
the day; and these two

other specialized ones--
crepuscular and cathemeral.

Nocturnal primates,
it's harder for them

to communicate with each other.

But there aren't as--
there isn't as much food

competition at night.

If you are diurnal,
you can see better,

but there's actually
decreased levels in olfaction.

So there are benefits and
cons to different types

of activity patterns here.

But let's look at some examples.

So here we are comparing a
siamang, a crab-eating macaque,

and a dusky leaf monkey.

So they all do slightly
different things.

So our siamang,
here, you can see,

they spend the morning calling.

Remember, they are
territorial, but they also

spend a lot of time feeding.

On our dusky leaf monkey,
these three examples,

they spend more time
resting than the others

because remember,
they are leaf eaters.

They need that time
to sit and digest.

So when we're foraging, there's
a couple different measures

we use to characterize
different species.

The first is day range.

It's how far does an
individual or a population

move in a single day.

Second, it's the home range.

That's the total area.

So theoretically, what
you do is you just

watch a group of
primates for a while.

And you calculate a lot
of individual day ranges,

and then you just overlay
them on each other.

And now you have the home range
or the sum total of everywhere

they go.

You can also have a core area.

So that's the home range
that you use a lot.

And the territory, that's the
area that you actively defend

if the species is territorial.

So let's put this on a map.

Here is a day range.

So we have watched one
primate for one day.

And it has traveled from
this tree across a river

to this other tree.

Now if we watch this
primate for a long time,

we would get a map that
looks something like this.

And you can see, all of
it is the home range.

But there's this
part in the middle

that they use a lot, outlined
by the dotted line or sorry,

the dots.

And that, we would
call their core area.

So what does your
favorite primate eat?

Do you know their
activity pattern?

How does their diet affect the
rest of their species' traits?

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