Saturday, August 31, 2013

Island living

Madagascar is the world’s fourth largest island. It is thought to have reached its present day location in relation to the African continent about 130 million years ago. Today, 400km separate Madagascar from the rest of Africa. Lemuriformes are though to have colonized Madagascar roughly around 65 million years ago, so how did the ancestors of sifakas, ring-tailed lemurs, and others arrive on the island? Are lemurs great endurance swimmers? Not exactly.

Madagascar's hissing cockroaches
What determines whether a species colonizes an island? Is colonization of an island something scientists can predict? The principles of island biogeography lend us a hand in determining whether or not an island will be successfully colonized by new species.

For starters, the closer the island is to the mainland or another large land mass, the more likely that island is to be colonized. The older the island is the more likely the island is to be colonized. The larger the island is the more species are likely to colonize it. All of these fancy rules are pretty simple once you think about them. The older the island is, the more time has passed, allowing species to reach the island. The larger the island is, the more space there is for all of those new species. And the closer the island is to other landmasses, the less distance between the two landmasses makes for an easier crossing for new species.

In terms of the genetics behind island biogeography, the following rules apply. As time passes and the island has been settled by those species that were able to the island and been successfully live there, genes are less likely to be exchanged between the original population from the mainland and the population on the island. As even more time passes, the two populations become genetically different.

Ancestral lemurs likely reached Madagascar by a series of rafts. This would have occurred not over a summer holiday but over an extended period of time in a series of events. As time passed, ancestral lemurs diverged from their original population and became genetically distinct. They thrived on the island of Madagascar and became the species we know today.

Girl power

Sifakas don’t experience a lot of feeding competition, from what I’ve seen so far, which isn’t surprising given their diet. If any feeding competition between a male and a female were to occur though, I bet you’d be surprised at who would come out on top. The female. Sifakas, like almost all of their primate relatives on Madagascar, have a social system in which females are dominant over males. Meaning the females can and do push the males around when it comes to any sort of feeding competition. It’s an unusual system to be sure, and no one is entirely positive as to how female dominance came to evolve.
Ring-tailed lemur sunning in early morning

One of the main theories is that female dominance evolved in response to the unpredictable environment of Madagascar. Females have feeding priority because it is advantageous for them to be healthy so that they can successfully produce offspring. Remember an earlier post about the term “fitness” in the field of biology? If females aren’t eating enough or are eating poorly, and they’re offspring aren’t surviving, no one’s fitness is increasing. It doesn’t matter if you’re a male or a female: the offspring need to survive. 

Like I said, I haven’t seen a lot of aggression in my time here watching sifakas. There seems to be plenty of leaves and flowers to go around. Every now and then, you will hear a rustle in the trees and some squealing, and it’s usually a female kicking a male out of his spot. Otherwise, everyone seems to get along rather peacefully, eating and sleeping all day long. If you’re a fan of girl power, these primates certainly have it. Other species of lemurs, those with choice food items, may experience higher rates of aggression within the troop, but sifakas are pretty laid back.
Lactating mother, Sarah Louise, with infant

Critical thinking: Can you think of a scenario in which female dominance would be beneficial?

Critical thinking: With unlimited funds and resources, how might you test your hypothesis as to what scenario might make female dominance beneficial?

Wednesday, August 28, 2013

Living with others

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.

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.

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.
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?

Sunday, August 18, 2013

Primate diet

Primates can be grouped into categories based on what their diet is primarily composed of. Primates that eat mostly leaves are called folivores. Primates that eat mostly fruit are called frugivores, mostly gums=gumivores, mostly insects=insectivores, and mostly meat=carnivores. There is only one solely carnivorous primate, the tarsier. This small Asian primate eats insects, lizards, and even small mammals. Tarsiers are solitary and nocturnal primates that truly eat nothing but meat.
Crocodile at Berenty  (in enclosure)

Sifakas are folivores. Think about the last time you ate a salad with only lettuce and other leaves. If you’ve ever attempted such a bland meal, was it filling? Probably not. Leaves aren’t exactly the most high-energy food item, so a lot of leaves need to be ingested if that’s going to be your diet. Leaves can also be hard to digest because they contain cellulose (it’s part of the plant cell wall and is what humans call “dietary fiber” in our diets). Some leaves may even harbor toxins that protect the leaves. Sifakas and other folivores have adaptations to handle these difficulties. They have a longer digestive tract than we do and they likely have behavioral adaptations as well. Leaves are low energy, and sifakas are low energy primates. Like many folivores, they do not spend a lot of time engaged in social activities. Rather, sifakas spend significant portions of their day just resting, conserving energy, and digesting their food. (They’re not the most interesting primates to do behavioral observations on, but they’ll suffice for my research questions.)
Sifakas feeding on flower buds

Now, just because we may call a sifaka a folivore does not mean that this species only eats leaves. Many species of primates consume a variety of food items dependant on availability. Gorillas are often classified as folivores for example, but they certainly feast on fruit when it is available. Diet composition can vary within a species too, if the species inhabits multiple habitats with differing food availability.

Critical thinking: Howmight a carnivore’s activity pattern differ from a folivore’s activity pattern? What other variables need to be considered?

Critical thinking: How might introduced plant species or other food sources introduced through humans affect a primate? Think about group size, aggression, infant mortality rates: would these increase or decrease?

Survival of the fittest

Baobab tree
“Survival of the fittest” is a phrase most people have heard of. Some people may even attribute it to Charles Darwin, although he actually adopted it from someone else. Many people don’t understand what the fittest means in terms of biology. An individual’s fitness is their ability to successfully produce offspring that survive to adulthood. I have a fitness of zero because I have no children. My sister has a fitness of two because she has two children. A primate mother who gives birth to twins, but only one infant survives to adulthood would have a fitness of one. An individual’s fitness is related to its adaptations, or traits that make an individual or a species better suited to the environment.

Introduced Brown Lemur on Trail
I am attempting to adapt by changing my project. I originally proposed to study four troops of sifakas. I wanted two troops in the spiny forest and two groups in the gallery forest. However, upon my arrival, I learned from my Malagasy assistant that there are only three groups total in the spiny forest, and each had one lactating female. We were able to locate two groups in our first few days but only one still had a lactating female. Given the scarcity of lactating females in the spiny forest, I have adapted to my environment and am only studying three troops in the gallery forest. I have five lactating mothers total, which is less than I wanted but this is the reality of the situation. We all have to adapt to our surroundings. A species may be perfectly well-adapted to it’s environment, but if a large change comes about, say humans start hunting that species, well then that species better adapt. Those most able to adapt to change are usually the ones most able to survive. Humans aren't exempt from change. 

Brown lemurs were introduced to Berenty, meaning they are not native to this area. The only diurnal primates at Berenty should be ring-tailed lemurs (Lemur catta) and Verreaux's sifakas. However, brown lemurs were introduced in 1975 and I have seen far more of them than sifakas. Clearly they have adapted to their new environment. They seem to be thriving as far as I can tell! The species of brown lemur at Berenty is actually a hybrid of two, genetically distinct species that bred together. They range wherever there is food, although they are a bit more timid than ring-tailed lemurs, the species of lemur Berenty is well-known for. The ring-tailed lemurs often steal food from the tourists and show up to breakfast for any table scraps left behind. Certain troops of ring-tailed lemurs have creatively adapted to the tourists here.

Critical thinking: Can you think of other examples of animals adapting due to their close relationship with humans?

Finding primates

 A question I often get asked is how we find the animals. Well, the short answer is we look. We walk around the forest, using trails if they’re available, with our heads craned up to see the highest branches. (Yes, it eventually hurts your neck a lot to do so much looking up). If we can’t find them using the trails, we start going into the woods. (If you’re lucky, you’ve got a machete to cut your way through-we didn’t.) Spider webs inevitably cling to your face. Thankfully, I have yet to find any large spiders clinging to me. You can also wave a stick in front of where you walk, like a magic wand, so that the spider webs cling to the stick and not your face. I do this often. Anyways, we search, and we search, and we search, and we listen. Sometimes you can hear the primates moving or hear them foraging. They drop leaves or they may break a twig and it falls to the forest floor. If you’re lucky, they vocalize. Primates are not entirely silent creatures.
Sifaka in gallery forest

In the beginning, when you’re new to a troop of primates you’re studying, there can be a lot of searching. You can spend hours of your week walking around, stopping and looking for the slightest movement. But there are some tricks to finding primates. If it’s first thing in the morning, they’re likely eating somewhere. If it’s cold out, they’re probably high up in the branches sunning themselves. If it’s the middle of the day and really hot, they’re probably resting in a shaded spot. Think like a primate! If it’s starting to get dark, they’re probably moving to their sleeping trees. Once you’ve followed the same troop for a few occasions, you start to know the area they cover and they’re habits. Maybe they have a particular sleeping site they often return to. Perhaps there’s one or two species of tree they really enjoy eating, so you search for those trees.

Can you spot the sifaka?

I think someone should do a study where they have radio-collared troops whose locations are always known, and then send a bunch of primatologists into the forest looking for primates. I bet you anything the primatologists walk right by the primates a few times. I think my assistant and I walked by the group we were trying to find at least twice today. Maybe three times. How hard is it to find seven white, sifakas in a green and brown forest? Well, if the sifakas aren’t moving and the bright sun is making everything look even whiter, it’s not a piece of cake.

Thursday, August 1, 2013

Why scientists need cultural relativism

It can be easy to forget, as a scientist, that a great deal of our work does involve working with people. You may have a vision of spending all day in a lab coat or out in the field with your binoculars, but everyone has to interact with people at some stage or another. Any scientist who wants to work abroad is going to require a firm grasp of what anthropologists have termed "cultural relativism."

Just outside capital city of Madagascar, Antananarivo
Cultural relativism is the notion that our beliefs and thoughts on civilization are relative and are "true" only so far as our own culture goes. It's the idea that our culture makes the most sense, is the most civil, and is the least weird, because it is our culture.

How does this relate to traveling as a scientist? Well, it means that when we judge others, whether it's the locals who are hunting primates for food, communication styles that are less direct, or shamanistic practices we don't understand, we need to take a reflective step back. Had we been raised in these cultures, hunting primates for food would seem as "normal" as eating a hamburger. When comparing children to their parents, the phrase "the apple doesn't fall far from the tree" is often used. Cultural relativism is a bit like an expansion of this idea: we need to keep in mind the context of the tree and not expect that tree to be exactly like our own.
Workers in rice paddy

I think cultural relativism gets easier the more you travel or the more you read. Take a few anthropology courses and you'll realize that the word "normal" is hard to apply to all cultural concepts. What may be common in North America may be very strange to Malagasy and vice versa.

Here in Madagascar, which is a developing country, things tend to run a little slower than I'm used to, getting a check for lunch for example. Children beg for money in the street and particularly target wealthy foreigners, who have a lot of money in comparison to many Malagasy people. Traffic is chaotic and seemingly without rules. Recycling is non-existent. Taxi drivers honk at you, assuming all foreigners need a ride everywhere. All of these things seem strange and different, but not when one stops and realizes that this is a different place. One of the best parts of traveling is seeing new things and meeting new people.

Which of the following is an example of cultural relativism?

A.  An American moves to Madagascar and attempts to educate local people about the benefits of modern medicine because shamanism is silly.
B. An American moves to Madagascar and becomes accustomed to the parasites found in local food.
C. An American moves to Madagascar and no longer gets annoyed at taxi drivers honking but sees this as normal.
D. All of the above
E. B and C

The answer: C. Parasites are not cultural and A is the opposite of cultural relativism.

Critical thinking: Does the idea of cultural relativism only apply when traveling abroad? Why or why not?