Personal tools
You are here: Home Biodiversity & Conservation Biology Conservation Biology 5.Threats to biological diversity: Environmental factors

5.Threats to biological diversity: Environmental factors

Document Actions
  • Send this
  • Print this
  • Content View
  • Bookmarks

5.1 What Are The Environmental Factors Causing Loss Of Biodiversity?

Most of the environmental factors affecting biodiversity are all caused by humans. All of the things listed here have huge affects on the natural environment and are all the result of human activity. I want to go through each of these and give some examples from the literature of how these are affecting the environment. (Images from,,,,

5.2 Pesticides

There are hundreds of different pesticides. They are used in intensive farming to increase crop yields by cutting down pests. Many do not just contaminate the area they are used in but travel across the world on air currents and in the water. Some of these chemicals have been seen as agents of evolutionary change in some species. I am now going to talk about some of the pesticides used in the world and how they are affecting the environment. (images from,

5.3 Pesticides: Chlorinated hydrocarbon pesticides (CHs)

There are many problems associated with the chlorinated hydrocarbon (CHs) pesticides. They are all stable so they degrade very slowly in the environment, even when a pesticide is banned it will persist in the environment for years afterwards. The CHs are all easily transported in air or water, some are now world wide and found in mid-ocean water and Antarctic snow. CHs are not very soluble in water but very soluble in lipids. This means that when there is CH contamination in a body of water the organisms living in the water will take up CHs easily as they contain lipids. CHs are toxic to species other than the target species of the pesticide, this is either a lethal effect where the organism dies or a sub-lethal effect where the organism is affected in another way. Probably the most notorious of the CHs is DDT.

5.4 Pesticides: DDT

DDT was created in 1847 but it was only found to kill insects in 1939. It was first used to kill mosquitoes and lice and is probably the reason that most of Europe is malaria free. More recently DDT has been used to kill pests such as the elm bark beetle that causes Dutch elm disease. One of the problems with DDT is that it does not just affect the target species and worryingly it is still used in some developing countries.

5.5 Pesticides: DDT

DDT is known to bioaccumulate in organisms, this means that animals take it from the environment and concentrate it in their bodies. It is also known to biomagnify which means that the concentration of DDT is passed from trophic level to trophic level for example, it will move from phytoplankton to zooplankton when the zooplankton eat the phytoplankton and then onto fish, fish-eating birds and so on. An example of this was studied by Boykins in 1967. Worms were taking DDT up from the soil and then the birds that were eating the worms were absorbing the DDT. The worms kept the DDT for 18 months after the land was sprayed with DDT so the problem persisted in the environment and ultimately it caused bird mortality. This biomagnification is also seen in the artic and sub-artic where DDT is being passed from seals to polar bears and then from the adult polar bears to the cubs through the milk the adult females produce.

5.6 Pesticides: DDT

This is affecting the human population too. In Tanzania DDT has been found in crops of eucalyptus, cashew, plums and casava which are all eaten by humans. In Brazil DDT has been banned and the government has collected all of the stock and placed it in containers in Mato Grosso, here the DDT has leached into the soil and made it to the underground water. In Turkey DDT has been found in 12 edible fish.

5.7 Pesticides: DDT

Looking on the bright side, since the use of DDT has been banned in certain areas, some bird species are recovering from the egg-shell thinning effect. Grey seals are recovering from the gynaecological problems caused by DDT and pregnancies are increasing.

5.8 Pesticides: Carbamates and Organophosphates

Other members of the pesticide family are the carbamates and organophosphates. These do not persist in the environment for as long as the CHs but are very toxic. Herbivorous birds that eat treated plants have died as well as birds that feed on insects that have been treated. The effect of Methocarb on Rainbow trout was studied by Altinok et al. (2006). The fish suffered from lemmellar edima and a separation of the epidermis from the lamellae. Dioxin, another example, was found to cause cancer and birth defects in lab animals. Many of these types of pesticides are now banned.

5.9 Oil Pollution

There is an enormous amount of oil that enters the environment every year, this is not just through accidents and oil spills but through every day use of oil and oil products. The estimate of 3.2 million tons per year is very rough as the lower and upper limits of this estimate are 1.7 to 8.8 million tons respectively. Most of this waste is from every day use of oil in towns and cities and from industry. The rest is from the combustion of oil and its release into the air. However, the large oil spills tend to receive all the media attention. (Image from

5.10 Oil Pollution

The worst oil spill so far has been seen in the Persian gulf during the war to liberate Kuwait in 1991. 1,700,000 tons of oil was released into the sea. Almost as bad was the spill from the Mexican oil platform Ixtoc I, in 1979, over 500,000 tons of oil was spilt into the sea. The more well known spills are often from tanker accidents. (Image from

5.11 Oil Pollution Case Study: The Exxon Valdez

The Exxon Valdez hit a reef off the coast of Alaska in 1989 spilling 41,000 tons of oil into the sea. About half of the oil ended up on the shore, the rest would have evaporated, dissolved or moved into the open ocean. The figures for the numbers of particular animals that were killed are given here but the full extent of the damage cannot be summed up with these numbers, the effects are more extensive than the higher animals that were counted, no one could begin to estimate the number of invertebrates that were killed. (Image from

5.12 Oil Pollution Case Study: The Exxon Valdez

Unfortunately the clean up operation was not well thought out. It took four years and in that time the shores were washed with hot water and the oil and tar was collected. The hot water used to wash the shore killed invertebrates and moved the oil onto unaffected beaches. Often the coast that had been cleaned was worse off than the parts that were left alone. (Images from,

5.13 Oil Pollution Case Study: The Exxon Valdez

The affects of the spill are still being seen. The offspring of the pink salmon breeding in the polluted water were found to be sterile and the sockeye salmon increased in numbers due to not being fished. This resulted in the fry of the sockeye salmon starving to death. The muscles and clams found in the area are still poisoned. The sea otters are slowly recovering their numbers but even 15 years on they are only at half the number that they were when the accident happened. The coastline where the tanker crashed was populated with people who relied on the local fish and seals for food, they had to move away from the area as their was no food left. (,,,,)

5.14 Oil Pollution: Impacts on the wildlife

The impact of oil pollution differs from habitat to habitat. Open ocean oil slicks kill plankton and fish and effect sea mammals and birds. The coastline is affected in different ways depending on what it is made up of. Sandy beaches may retain oil for weeks to months, the oil may be buried by the sand and then uncovered at a later date. Rocky shores suffer worse as the oil can impact for months to years. When the oil reaches the shore it kills most of the organisms and then makes it hard for them to re-colonise by coating all of the rocks with a thick tar. The effect of oil pollution in salt marshes and estuaries can be seen for years to decades. This is because the sediment is quite anoxic and if the oil becomes buried it will not degrade chemically and may be exposed again months or years later.

5.15 Oil Pollution: Impacts on the wildlife

Sea birds suffer greatly when oil is split into the sea. The birds that dive into the sea to catch food will have to cross the oil slick every time they go for food. The oil on their feathers makes flying and buoyancy hard and does not keep the bird warm. When the bird tries to wash the oil off its feathers it ingests the oil which causes trouble in the liver, kidneys and pancreas.

5.16 Polychlorinated biphenyls

Polychlorinated biphenyls are used as insulators and fire retardants. They persist in the environment for a long time with a high solubility in lipids and food chain magnification. These have been seen to cause trouble in bird, seal and polar bear reproduction.

5.17 Polynuclear aromatic hydrocarbons

Polynuclear or polycyclic aromatic hydrocarbons are produced after combustion of fossil fuels and are found in cigarette smoke. The PAHs pollute the aquatic environment. They damage or mutate DNA, RNA or proteins and some bond with DNA, RNA and proteins causing cancer.

5.18 Heavy Metals

Pollution of the environment with heavy metals has occurred for years. The first examples have been seen from about 8000 years ago. Archaeologists have found evidence of copper extraction and smelting in Jordan and it is estimated that the Athenian civilisation put about 2300 tons of copper into the air every year. The deposits from this were found in the ice sheets in Greenland. This coincides with the advent of a copper based coin system. Other heavy metals that pollute the environment are mercury, lead and nickel. Many of these metals show food chain magnification and affect fish and marine birds. An example of the use of heavy metals is seen in gold mining. Mercury is used to separate the gold and the waste products and the waste from this process is poured into local water. Another example is found in the paint used to paint the hull of ships. This is toxic to marine organisms and has been banned in some countries.

5.19 Selenium

Selenium is needed by most vertebrates in small amounts but in large quantities it is toxic. It occurs naturally in soils and is found in larger quantities in desert soils. This can leach into the water supply and cause problems. In the Kesterson National Wildlife Reserve reproductive failure and embryo deformation was seen in the bird population after selenium poisoning.(Image from

5.20 Radioisotopes

Examples of radioisotopes that pollute the environment are caesium, strontium and phosphorous all of these show bioaccumulation and biomagnification. A well known example of radioactive pollution was seen in the disaster at Chernobyl

5.21 Radioisotopes - Chernobyl

The disaster in Chernobyl occurred in 1986 in the Ukraine. The site had been producing nuclear power since 1977 and had 4 reactors by 1986. The reactor that exploded was undergoing a safety test. After the explosion the core became exposed and radioactive fission products and other debris and smoke polluted the air. This was taken north-west on the wind resulting in contamination occurring in nearly every country in the northern hemisphere. The graphite fire at the centre of the disaster lasted nine days. (Image from

5.22 Radioisotopes - Chernobyl

The government at the time did not raise the alarm when the rector exploded. Only when workers at a Swedish reactor spotted the plume did they admit there was a problem. To try and stop the radioactivity leaching into the soil a tunnel was dug under the core and a concrete slab and cooling system were installed. Ultimately a steel and concrete box was placed around the core to stop anymore radioactivity from getting into the environment. By the time the box was installed a lot of damage had already been done. Six tonnes of uranium dioxide and fission products had been released in to the atmosphere along with xenon, krypton, iodine, tellurium, and caesium. (Image from

5.23 Radioisotopes - Chernobyl

The effects of the disaster has been widespread but understudied. One of the chemicals that was released into the atmosphere was caesium which has a long half life and is absorbed into the body like potassium and so it quickly made its way into the food chain. The ground water in the area also became polluted which allowed the radiation to travel further in the water. There was an increase in cases of thyroid cancer in humans especially children. So far few studies have been carried out but at least 20 species in the area show genetic damage. A study by Moller and Mousseau (2006) looked at Chernobyl 20 years on. The radiation reduced antioxidants. Barn swallows from the area had reduced levels of caratenoids, vitamin A and E in their blood and liver. Barn Swallows were also found to have lower levels of leukocytes and immunoglobulin and a reduced spleen mass. An unusual side effect has been an increase in partial albinism. The Barn Swallows that were studied had 23% of females not breeding, this is unheard of in passerine birds. When the birds do lay eggs their clutch size is reduced with increased levels of radiation and hatching failure is also increased. The survival rate of adult birds is reduced in areas with increased radiation.

5.24 Radioisotopes - Chernobyl

Twenty years on the problem is still here. The concrete and steel box that was placed around the reactor’s core is breaking down and action is being taken to repair cracks and shore up walls. A large arch is under construction to cover the core and the concrete and steel box. It will not be ready until at least 2008 and until then a small earthquake could break up the box and expose the core and all the radiation. The arch is going to cost 840 million euros and will only contain the core for 100 years by which time is it hoped that another answer will have been thought up. The three reactors that were undamaged in the disaster still need to be decommissioned and the waste needs to be disposed of correctly and finally the waste that was dug underground as an emergency measure in 1986 needs to be dug up and disposed of properly. 

5.25 Plastic

Plastics are polluting the land and sea. The estimates of the quantity of plastic in the environment are large, for example on the surface of the Sargaso sea there are 290 grams of plastic per square kilometre. Animals are known to ingest these plastics, for example sea turtles eat plastic bags assuming that they are jellyfish and the Laysan albatross has been seen to feed plastic bags to its chicks. In a study by Maser and Lee in 1992 birds were collected from the western North Atlantic. Out of the 38 bird species, 21 species had individuals with plastic in their stomachs. The amount of plastic in the birds stomachs increased from 1975 to 1989. Some of the birds ate a particular colour or shape of plastic which suggests that they are mistaking it for food. (Images from www.ocean.

5.26 The answer

There is no easy answer to the types of pollution mentioned here. Man has polluted for many years and will continue to do so. Some governments are regulating certain pollutants and oil tankers are now being built with a double hull. An international convention has been agreed on that dumping of CHs, PCBs, some heavy metals, plastics, petroleum and radioactive waste must be stopped.

5.27 Light Pollution

Light is now considered a pollutant and it is having a negative effect on many species although we are only just starting to understand the full extent of these. Two thirds of the human population lives in areas where the light pollution is over the accepted levels. Trees are seen to increase their growing season which makes them susceptible to winter frosts, the Hawk moth looses its ability to see in colour in light conditions and in the lab artificial light at night is seen to increase tumour growth and decrease survival in female rats.

5.28 Global Climate Change

Global climate change is a huge topic and discussed extensively in the scientific literature. Estimates suggest that 18% of the species in Central America, Australia, South Africa and Europe will disappear due to climate change. The earth is warmer now than it has been for the past 40 million years. The problems with climate change is that it is occurring so rapidly that the organisms do not have time to adjust. This is made worse by habitat degradation and fragmentation and the new conditions are often more suitable for invasive species. Climate change has already caused species distribution shifts.

5.29 Global Climate Change

Species distributions are moving pole-wards. Predictions show that ranges will move north by 6.1 km per decade and spring will occur 2.3 days earlier. Non-migratory butterfly species were studied by Parmesan et al. (1999) they found that 63% of the 35 species studied had shifted their range north wards by 35-240 km. Species are also adjusting their breeding seasons as is seen in amphibian species in Britain, are moving higher up mountains and are becoming extinct.

5.30 Global Climate Change - Species altering breeding season

In a study by Beebee (1995) the time that amphibians entered a pond to breed was recorded over a 17 year period. Two of the anuran species spawned earlier each year and the three newt species arrived five weeks earlier in 1994 than in 1978. The pond arrival time and the spawning of the frog species gets 9 to 10 days earlier every 1 degree increase in temperature.

5.31 Global Climate Change - Species becoming extinct

In a study by Pounds et al. (1997) it is suggested that the disappearance of the Golden toad is due to the changing climate. The toad relied on the cool wet cloud forest and water bodies to breed and as the climate has altered the wet weather regime in the cloud forest has changed. This has possibly caused a decrease in successful breeding or it has even been suggested that the decrease in suitable climate forced the animals to live in a small area where chytrid fungus, a fungal disease that is known to kill frogs, could spread throughout the population.

5.32 In conclusion

This is a large topic to draw conclusions from. The human population is polluting the environment at an amazing rate and will continue to do so with the population growing the way it is. So far the effects of all this pollution are not fully understood and lets hope that by the time we are getting to grips with it, it wont be too late.

Copyright 2007-2008, by the Contributing Authors. Cite/attribute Resource. nondumiso. (2007, November 16). 5.Threats to biological diversity: Environmental factors. Retrieved April 21, 2014, from UWC Free Courseware Web site: This work is licensed under a Creative Commons License : Attribution-ShareAlike 3.0. Creative Commons License : Attribution-ShareAlike 3.0