When Rabbits took over Australia (Basic Ecology)

Did you know that rabbits were a big problem in Australia? That in 1887 the New South Wales Government offered £25,000 for an effective way to kill rabbits? Louis Pasteur (who the milk sterilization process is named after) suggest that they inject rabbits with a chicken bacteria. Ok, before we get into all that lets get an introduction into ecology because the reason they did all has to do mainly with ecology.

The word Ecology means:

Study of house. Ecology is greek word. The house is the environment. It also includes interactions between organisms. So it is the Science of the environment and interactions of organisms.

I look at ecology in two ways: how life competes, and how life adapt to its environments. These two parts to ecology change all life on earth.

A broad term of ecology is a niche. A niche is a specialized position an organism fills. Let’s look at a rabbit. A rabbit is a medium-sized herbivore that lives in the ground. There are no other animals that are the same size, eats the same things, and lives in the same place as the rabbit. Rabbits have that niche down. If aliens dropped an animal that occupied the same niche as the rabbit one of three things would happen, eventually; the rabbit would win and out compete for the alien rabbits, the alien rabbit would win and outcompete the rabbits, or one of them would adjust to fill a different niche.

Now imagine that humans are the aliens. That we move rabbits into a new area, Australia. The rabbits breed and occupy a niche in Australia. They then breed like rabbits. The rabbits became such a problem that the Australian government built several fences to contain the rabbits. The fences ran the length of the continent. There are several reasons why the rabbits were able to breed so quickly in Australia and most of them have to do with population dynamics.

Populations follow a set of simple rules:

1. Populations will continue to increase until another rule stops it (Sounds like laws of motion to me)
2. Limited by resources puts a cap on the size of a population
3. Predators decrease a population
4. Prey can decrease a population of predators by being a limiting resource

Rabbits didn’t have any major predators in Australia so they could continue to reproduce. The warm weather allowed them to breed all year long. The rabbits show you what happens when rule one is not stopped.

Rabbits in Australia

Lots of rabbits in Australia. The photo is from the public domain. From National Archives of Australia

So now let’s look at how the other rules would come in. The rabbit population increases Yum Yum Yum the rabbits eat all the grass in the area and some rabbits die off or produce less offspring because of the lack of food. The rabbit population would be limited based on the amount of grass that can be produced every year.

Along came a fox. Let us say the Aussies were successful at bringing in foxes to the continent. Foxes eat rabbits. Yum Yum Yum foxes eat a lot of rabbits. But like the grass for the rabbit the fox is limited by the population of rabbits. The fox population goes down because there isn’t enough tasty rabbits.The next year there isn’t a lot of foxes to eat the rabbits so more rabbits have more babies. The population of rabbits increases. The year after foxes increases because of all the yummy rabbits to eat.

Predator and Prey model graph, Ecology

Photo from Wikipedia. Users: Quadell and Cutler

The cycle continues. Above is the Predator and Prey Model. The population of the predators lags behind the prey population numbers.

The rabbits have a sad happy ending. Now the rabbit population is being controlled by the introduction of diseases. Diseases in their way are predators. There is still a lot of rabbits in Australia, but it less of a problem today.

 The Rabbits Strategy, R and K type

The rabbits are following a strategy. Their strategy is to increase their number as quickly as possible to prevent extinction. They have a high rate of reproduction. This strategy is called R type. R is for rate, but how I remember it is that R is for rabbits and rabbits breed like, well rabbits. R types are found in disturbed or unstable environments. They follow the philosophy of live fast dies young. The parents want to produce as many offspring as possible. The consequence of a lot of offspring is that the parents can’t put a lot of resources into any individual offspring. R types are playing the odds, taking the gamble that some of their offspring will live.

Baby Kangaroo

The photo is in the public domain. Found on Wikipedia

This is the opposite of the other strategy, the K type. K is obviously for Kangaroo. K types know about the carrying capacity (what other people think that the K stands for, but carrying starts with a C, not a K. Who are they trying to fool?). The carrying capacity is the limit of a population. This has to do with rule two; the maximum number of a population is limited by resources. K types invest a lot of resources into each offspring while having fewer kids. K types are also in stable environments and they know that the number of offspring they should have.

The reason why K is for Kangaroos is because Kangaroos have a pouch and normally give birth to only one baby. An even better reason is because female Kangaroos can suspend development of an embryo if the environment isn’t right; drought, or lack of food. Those factors would affect the carrying capacity and decrease the babies chance at survival. K types or I should say Kangaroo types put a lot of time and resources into a single individual to make sure that each one has a high chance of surviving. They don’t like to gamble, they play it safe.

Now you know that…Populations out of control are dangerous. There are four rules that determine if a population will grow. These rules were seen in rabbits taking over Australia. The rabbit is fast and kangaroos are clever, both win with different strategies to survive.


Also See:

Wikipedia: Rabbits in Australia

Wikipedia: Kangaroo Reproduction and life cycle