biodiversity and ecosystems

• Areas like tropical rainforests have millions of different species and are very biodiverse. Other areas like the Polar Regions have far fewer species and are less biodiverse.
• Biodiversity is specifically the number of different species. An area with large populations of few species is not biodiverse.
• If the numbers of one species are affected, there are almost always knock-on consequences. A simple food chain is:

  algae → zooplankton → sand eel → puffin → arctic skua

  If the numbers of zooplankton are reduced by pollution, such as plastic waste, then more algae will grow and the population of other consumers will fall.
• Ecosystems with higher biodiversity have fewer species that depend on just one other for food, shelter and maintaining their environment. With the example above, puffins could also eat molluscs and worms. Ecosystems with higher biodiversity are more stable as they can easily adjust to changes.
• We are slowly realising that the future of our species on Earth depends on maintaining high biodiversity. Activities that create air and water pollution, are reducing biodiversity in many ecosystems. Conservation of species and habitats by charities, governments and individuals helps to maintain the range of biodiversity.
• The number of people alive now is at a record level and is increasing. In 2012, the human population exceeded seven billion for the first time. Each year about 75 million more people are born than die. This is known as the net increase.
• There are many reasons why our population increases:

  • better health care so people are living longer
  • new medicines are being developed so people don’t die of previously fatal diseases
  • farmers are able to produce more food using new breeds and equipment
  • some religions do not permit the use of contraception
• Scientists are unsure whether this population increase will continue for ever. Some think that the human population will continue to increase and humans will be able to solve any problems that come their way.
• Others think that humans will run out of food, fresh water or other resources and the earth's population will stop increasing, but remain high. Whereas, other scientists think that the population will reduce significantly, this is called a crash. In the past, plagues have caused a rapid decline in the population (note the dips in the graph at 600 CE and 1200 CE), and this could be a possible explanation for a rapid decline in the population in the future.
• As the population grows, the pollution we produce also increases, which may cause significant issues.
• As the human population increases, the volume of waste and pollution that is produced also increases. Polluting an ecosystem harms or kills the organisms that live within it.
• Modern society is more consumable, which means humans manufacture more products and replace them more often. This consumption is not sustainable. Many natural materials, including fossil fuels, will soon run out and scientists argue that there is already too much waste.
• In some parts of the world, open sewers can lead into water courses, such as streams and rivers, which can cause serious illness in humans that may drink the contaminated water.
• Some farmers use too many fertilisers, which can run off fields during heavy rain. This can pollute nearby streams and rivers leading to eutrophication. Some water pollution even comes from toxic chemicals released illegally by factories.
• Combustion of fossil fuels and other fuels releases carbon dioxide. This contributes to the greenhouse effect and leads to global warming. It also releases sulfur dioxide and nitrogen oxides which can cause acid rain. Air pollution can also be caused by tiny particulates from smoke which can cause smog. Some of the world's major cities like Delhi in India and Karachi in Pakistan have dangerously high levels of air pollution.
• The rubbish we throw out that is not recycled goes into a land fill. These are huge holes in the ground into which our rubbish is dumped. Some things like batteries cannot be put into landfill sites because of the toxic chemicals they contain. They must be recycled. Other land pollution comes when some people dump rubbish in public or other private places, often to avoid paying for it to be disposed of. This is called fly tipping and is illegal.
• The larger the human population gets, the more land we require. More houses must be built, more resources found, more food must be grown and more waste is produced. This often means less space and fewer resources for other animals and plants.
• Often biodiversity is significantly reduced when land is cleared for human uses, such as building, quarrying, farming and waste disposal. Think about the reduction in biodiversity, which occurs when an area of rainforest is cut down to grow crops.
• For thousands of years humans have been deforesting small areas of woodland to build their own houses or grow crops to feed their families. However, in recent years the increase in the human population and development of industrial machinery has meant that much larger areas have been cleared. This is often by large companies who deforest to provide land for cattle, rice fields and growing crops for biofuels.
• In the last 75 years we have cut down over half of the world's rainforests. It is estimated that nearly twenty percent of the Amazon rainforest has been cut down in the last fifty years, and the rate of this deforestation has increased in recent years.
• Deforestation destroys the habitats of the organisms that live there and through this kills individuals of many species. Scientists estimate that several hundred species of plant, animal and insect are lost each day partly as a result of deforestation. This means that deforestation is causing extinctions and dramatically reducing biodiversity.
• Bogs are very wet areas of land without trees in which many types of moss grow. They are acidic and often have very low levels of nutrients. Here decomposition is very slow and peat is formed from partially decayed plants.
• For many years peat was removed from bogs for gardeners to add to their soil or to burn as fuel. This dramatically reduced biodiversity. Because peat takes such a long time to form, it is a non-renewable energy resource like fossil fuels.
• Peat bogs are a very important store of carbon. We call them carbon sinks. If all the peat was removed and burned this would quickly release a huge volume of carbon dioxide into the atmosphere and contribute to the greenhouse effect.
• Without the greenhouse effect the mean temperature on Earth would be -18°C and there would be very little or no life. So the greenhouse effect itself is a good thing. The greenhouse effect traps some of the energy from the Sun, which keeps our planet at a suitable temperature for life.
• The problem is that our increased release of greenhouse gases is causing an increase in the greenhouse effect called the enhanced greenhouse effect. This is leading to global warming.
• Carbon dioxide, water vapour and methane are amongst the most common greenhouse gases. Since the start of the Industrial Revolution in about 1750 the levels of carbon dioxide have increased by 40%.
• Global warming is the increase in the mean temperature of the Earth. The ten hottest years since records began have been in the last 30 years. The mean increase in the last 100 years has been less than 1°C. This might seem small, but is enough to have devastating consequences on many species in different parts of the world.
• As the percentage of carbon dioxide in our atmosphere has increased so has the Earth's mean temperature. Note that the shape of the first graph showing the amount of carbon dioxide in the atmosphere is 'exponential' and is a similar shape to graphs showing human population change over the same time period. When comparing graphs such as changes to carbon dioxide levels and temperature against time, note that the axes are drawn to different scales, and do not start at '0'.
• The consequences of global warming are:

  • melting of the polar ice caps
  • the rise in sea level may one day threaten many cities such as London, New York and Amsterdam
  • weather patterns will change with more unusual weather
  • animals will migrate towards the poles to find habitats with suitable temperatures
  • tropical diseases may become more common in other regions, such as the Europe
  • many species will become extinct
• For many years the evidence that linked increased carbon dioxide levels to the greenhouse effect and global warming was not enough to convince everyone. In recent years more and more evidence has been collected and many scientists believe that this is the case. The evidence used by scientists is 'peer reviewed' by other scientists, which is the method used by the science community to ensure that research findings are valid. Peer review ensures that the science community are confident in the accuracy of data and any conclusions made.
• The National Oceanic and Atmospheric Administration (NOAA) in the USA have recorded the top ten hottest years since records begin in 1880. 
• The increase in the human population and waste it produces, deforestation, peat bog destruction and global warming are all reducing biodiversity. Conservation helps reverse this. Conservation is the preservation of ecosystems and the organisms that live within them.
• Scientists and concerned members of the public help maintain biodiversity by:

  • breeding programs to help preserve endangered species, like the panda
  • protection and development of new endangered habitats, often by making National Parks
  • replanting hedgerows because there is higher biodiversity in them than the fields they surround
  • reducing deforestation and the release of greenhouse gases
  • recycling rather than dumping waste in landfill sites
• As you climb up a mountain the temperature reduces. This reduction, together with other abiotic and biotic factors, determines what species of plant are found at different elevations.
• All other food chains in an ecosystem can be added together to make a food web. These stages in a food chain or web are called trophic levels. The arrows show the transfer of biomass from one trophic level to another.
• At the bottom of all food chains is a producer. This is almost always a plant or alga which can photosynthesise to convert carbon dioxide and water into glucose. This provides all the biomass for the food chain. Algae are the producers in the food chain above.
• The second trophic level in all food chains is an herbivore or omnivore called a primary consumer. Mosquito larvae are the primary consumers in the above food chain. The third stage is a carnivore or omnivore which eats the primary consumer. This is called the secondary consumer and is dragonfly larvae in the above food chain. 
• . There may be additional carnivorous consumers here which would be called tertiary and quaternary. The final level is perch, also a carnivore and is often called the top or apex predator. Organisms at the tops of food chains have no predators.
• Decomposers are bacteria and fungi which breakdown dead plant and animal matter. They secrete enzymes on the surface of the dead organisms to break the down and then absorb the digested, smaller food molecules.