I spend my days
alternating between three troops of Verreaux’s sifakas. Two of my troops
contain six individuals and one troop contains seven. Verreaux’s sifaka group
size ranges from one individual to up to ten members. Here in Berenty, I’ve
seen quite a few groups with six or seven individuals. Although, group size is
much smaller in the spiny forest, which is very dry and where food is
potentially limited.
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Resting midday |
Most species of primates
live in social groups. While some members may live on their own for some time
after they disperse from their natal group to seek new mating opportunities,
many primates will spend the majority of their lives living with others. Living
in a group has its advantages and disadvantages. Living in a larger group means
better protection against predators, such as snakes, birds of prey, and cats.
An individual may feed and feel a little safer, knowing that multiple eyes and
ears are on the lookout. Larger groups are also better able to defend
resources, such as a valuable fruiting or flowering tree. Primates have
competition from members of their own species and members of other species, and
a larger group size may mean the difference between abandoning a food source or
remaining and continuing to feed. This is especially true in instances where
the food item is nutritious, such as fruit. Sifakas, consuming mainly leaves,
don’t have a lot of competition from other troops of sifakas or from other
primate species. However, there can still be instances where one sifaka will
displace another sifaka over a valued food item, such as flowers. More members
in the group means greater competition within the group.
This is one of the
disadvantages of group living. Living in a group also means that primates must
get along with each other. Just think of a time when you didn’t get along with
a sibling or a roommate. Energy must be invested in maintaining harmony within
the group. Sifakas usually get along pretty well with each other, from what I
have observed. There isn’t a whole lot of social interaction. I’ve only seen
some sort of aggression a few times, usually a quick squabble over food. I’ve
seen the sub-adults play wrestling with each other twice now, but otherwise
these primates mainly feed, rest, and groom themselves.
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Troop clinging to trees |
Madagascar is a unique
country in that there are no cat species on this island. There are no lions or
leopards to worry about. The closest animal this island has to anything
resembling a lion is the fossa, which is actually not a member of the felid
family at all but a member of the civet family. Fossas are small but they will
hunt and kill lemurs. There are no fossas in this part of Madagascar though, so
the primates in Berenty need not worry. Their main concern comes from aerial
predators. Large group size protects them from predatory birds, as do other
strategies, such as feeding lower in the canopy, which I’ve observed both the
smaller ring-tailed lemurs and brown lemurs doing. Sifakas are relatively
large, which may be part of the reason they feel safe feeding on the tops of
trees.
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Mother with infant on back feeding on leaf buds |
Many variables affect the
size of a primate’s group: food availability, space, predation, etc. If the
local habitat is reduced drastically by human activity, a primate may not be
able to disperse into new territory to find mating opportunities outside of its
natal group, causing tension and aggression within the group.
Critical thinking: Can you
think of other instances in which human activity may affect the group size of a
primate population?
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