What is Homeostasis? It’s why you tilt bikes, it’s why populations never grow forever

This is the second post in the “feedback loops” series.

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In the first blog of this series, I started the post by talking about how our body responds to cold and hot conditions. When it gets too cold, we shiver to increase the body temperature. When it gets too hot, we sweat. The sweat evaporates off of our skin and cools our body.

Both these phenomena are the most common examples of a natural process called Homeostasis. Even though temperature regulation in mammals is considered the most common form of homeostasis in the living world, it is not the only one. There are some fascinating examples of homeostasis in our everyday life as well as the ecosystem at large. In this post, we’ll take a look at some of them.

Homeostasis is nature’s way of regulating things. The word is derived from a Greek word which means “steady”. Therefore, it is the phenomena by which a system resists change. The resistance is achieved through negative feedback loops-

The response of the system will be in such a way that it nullifies the forcing that created the response. In the above example, shivering was the response to cold, that negated the forcing by increasing body temperature.

If there was no negative feedback loop, one forcing would have a runaway effect on the entire system and life as we know could never exist.

Even many of our activities in daily life display the phenomena of homeostasis. Anywhere in life where you resist a force, you are undergoing homeostasis. For example, turning on a bike. When you want to turn your bike at a high speed, what do you do? You tilt the bike a little towards the inside of the bend. This is done to oppose the frictional forces acting on the bike, so that you don’t fall off. You balance (or regulate) yourself. Greater the tilt, more is the speed with which you can turn.

Have you ever touched a hot object? How did you respond to that? You immediately pulled away, screamed out in pain and probably wiggled your hands really fast. Everything you just did was a regulating response to the heat you felt from that object. Many studies show that screaming and swearing helps decrease the perception of pain in the brain. By wiggling your fingers really fast, you use the wind to cool that part of the skin. You may even suck your finger to cool it down further.

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Homeostasis can occur in any system, even the ecosystem. At the population level, there is a beautiful mechanism of population regulation that is an example of homeostasis. Let us take the example of a population of rabbits. The rabbit population tends to increase very fast when there is plenty of resources (food and shelter)available. They consume these resources very fast. However, the resources do not increase at the same rate as the population. Consequently, there comes a time when there are simply too many rabbits for nature to support. This results in competition among individual rabbits, and many rabbits that cannot compete die out. This reduces the population and decreases the demand on resources, creating a stabilized population.

This change in number of organisms is observed in communities of different species as well. Consider a simple example of grass, deer and tiger-ecosystem. The deer feeds on the grass and increases in number. This increase in number of deer means more prey for the tigers. Tigers would then grow in large numbers. Too many tigers mean that the deer population in the ecosystem comes down. When this happens, there is less food for the tiger, and the tiger population also falls.

When the deer population decreases, there is less stress on grasses. They get to proliferate and grow. A simultaneous decrease in tiger population and increase in grasses will allow the deer to increase in numbers again.

What is unique about regulation in nature is that it never achieves a stable equilibrium. There is always fluctuation of around the mean level (as in the case of the population example, and the ecosystem example above). This fluctuation is cyclic or oscillatory. Therefore, it is said that nature regulates itself by homeostasis to achieve a “steady state”.

This steady state regulation is even seen in environmental factors in nature. Rivers show a forever yearning for reaching equilibrium condition of erosion rate=deposition rate. However, this rarely happens because of forcing from tectonic and human-forces. When there is an increase in sea level, for example, the river compensates for this by depositing all its load and meandering in the plains. When there is a fall in sea level, the river compensates by increasing erosion rates and incising into the land. Dams also cause this constant fluctuation of steady-state.

Nature survives in the state that it does because of this delicate balance between forcing and response. If there was no negative feedback loop, one forcing would have a runaway effect on the entire system and life as we know could never exist. This is why, the study of negative feedback mechanism and homeostasis is extremely important.

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For more on homeostasis-

1. A Scientific American Article.
2. Role of species and resources in ecosystem stability.
3. Some more on ecosystem homeostasis.