Fair enough ecology might not sound like the most interesting topic off the bat, but if we take a closer look it’s vital in knowing so much about the animals and plants around us and the environment in which we live.
Ecology is the study of different organisms and their environment. Before we get started, let’s get some key definitions nailed down:
The interactions between a species and the habitat they live in is an ecosystem.
The area where a species lives is called a habitat. A collection of different species living in an area is called a community.
An environment is all the conditions that surround any living organism – both the other living things and the non-living things or physical surroundings.
Finally, the population of an area is the total number of a certain species that live there. Quadrats are often used to measure the population of a species.
They separate the total area into smaller samples to test. First, the area is gridded, then random co-ordinates are chosen to place the quadrat and take a sample from.
The number of the species within the quadrat is then measured. To get a more reliable estimate of the total population, several quadrat samples are normally taken to work out an average.
And that’s our basic definitions out of the way – so onto some more interesting stuff – the food chain.
The way that organisms feed on each other in a habitat can be shown by a food chain. The organisms are ordered by which other organism they eat (e.g. Wheat Mouse Owl Tick).
Predators catch and eat other organisms for food, and animals which are eaten by them are called prey.
Arrows are used in the food chain to show the flow of energy through the chain. In this example, an arrow would go from the wheat to the mouse, as the energy is going to the mouse after eating the wheat.
However, not all of the energy at one level of a food chain is available at the next. Energy is mainly lost in two ways:
Through respiration, as heat into the surroundings. Respiration is caused by movement and other processes
In waste, such as sweat and faeces
In fact, in most cases only the energy used for growth is available to be eaten by the consumers – this is usually around 10% of the energy originally ingested (or manufactured) by the organism.
For instance, if the wheat plant absorbs 1000kJ of energy from the sun, only about 100kJ of this will be available as digestible plant mass to be eaten by primary consumers. For this reason, food chains rarely contain more than four or five organisms as the energy simply runs out.
Heterotrophs are any organism that gains nutrients by eating other organisms. Autotrophs are organisms that can synthesise their own food, for instance when plants process energy through photosynthesis.
These organisms are usually at the start of a food chain, as they do not eat any other organisms. This means that the original source of energy for most food chains is the sun, as that is what plants use to create food.
Each stage of a food chain is called a trophic level. The first trophic level contains the producer (in this case, the wheat).
Each trophic level after that contains consumers, as they get energy by consuming other organisms. To tell between the consumers, the second trophic level is the ‘primary’ consumers, the third is ‘secondary’ consumers, the fourth is ‘tertiary’ consumers, and so on.
The primary consumers usually eat plants and are herbivores. In this example, the mouse would be the primary consumer, as it eats the wheat. The secondary or tertiary consumers are usually predators which eat animal material and kill for food.
After the predators, there are other organisms which eat animal matter, but don’t hunt and kill for it. They are known as scavengers. Scavengers such as hyenas and vultures feed on dead animals.
Decomposers get nutrients by breaking down and eating dead and decaying matter. They can also feed on animal matter in faeces.
Foodwebs are sometimes used instead of food chains to show the feeding interactions between organisms because they are more realistic, including more organisms from an ecosystem and how they all interact.
A pyramid can also be used to represent the numbers, biomass (mass of living material) and energy at each trophic level of a food chain.
Depending on what the pyramid represents, the bars are different sizes. For example, as the number of ticks feeding on one owl is large, the bar for ticks would be large in a pyramid of number. If it was a pyramid of biomass, the bar for the ticks would be much smaller as the total biomass of all the ticks would be lower than an owl.
Similarly, the total energy of the ticks would be small compared to an owl, so the bar for the ticks would also be small on a pyramid of energy.
The atmosphere of the earth can have also have a major impact on many ecosystems and food chains – as you might expect.
For instance, water vapour, carbon dioxide, nitrous oxide, methane and CFCs (long chain molecules found in aerosol sprays) are all greenhouse gases. These warm up the planet by absorbing and reflecting back into the earth some of the long wave heat radiation from the sun, which would otherwise be reflected back out.
The greenhouse layer is vital to life on earth as the planet would be too cold to inhabit without it, but human activities have added excessive levels of greenhouse gases to the atmosphere.
The thicker the greenhouse layer, the more the reflection and hence the warmer our planet becomes. This is called the greenhouse effect, and leads to polar ice caps melting, rising sea levels, ocean currents carrying warm water redirect to previously cold areas, changing temperatures causing habitats to change and changing rainfall patterns – all of which are very very bad.
Carbon is the most abundant element on earth and is found in almost all the biological molecules that make up organisms. The carbon cycle shows how it is released and recycled.
Carbon dioxide, a greenhouse gas, is taken in by plants during photosynthesis and turned into sugars such as glucose and starch. These are then consumed by animals, and used as energy to respire. Carbon dioxide is released into the atmosphere through many processes.
Furthermore, decaying organisms release carbon dioxide as the microbes that decompose the dead matter respire. Organic dead matter can also fossilise into fossil fuels over millions of years, releasing carbon as carbon dioxide when they are combusted – so basically there is a hell of a lot of carbon dioxide floating around. Too much in fact.
Aside from carbon dioxide, let’s take a look at some of the other gases that are being omitted.
Carbon monoxide, sulphur dioxide and nitrogen dioxide are released by fuel combustion from cars.
Carbon monoxide is a colourless and odourless gas which binds to haemoglobin in red blood cells and prevents oxygen from doing so. This can lead to asphyxiation (being deprived of oxygen which can cause suffocation).
Nitrogen dioxide and sulphur dioxide cause acid rain when released into the atmosphere. They dissolve into the rain forming nitric and sulphuric acid.
Acid raid decreases soil pH which can kill plants. It also makes lakes acidic, which can kill bacteria, algae and fish eggs.
Some fertilisers also contain nitrates. Fertilisers are soluble, so when it rains, they run off into lakes and rivers.
This causes algae to grow very quickly (algal bloom). The algae blocks light from the plants deeper underwater, stopping them from photosynthesising so they die. When the fertiliser is used up, the algae sinks to the bottom.
The effect which these nitrate fertilisers can have on ecosystems is known as eutrophication.