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?