Threats to biodiversity

• Threats to biodiversity


  • Direct exploitation
  • Eradication of predators and competitors
  • Changes in abiotic factors
  • Changes in biotic factors
  • Habitat destruction
• Direct exploitation


  • Populations of many species have declined as they been exploited for a wide range of products, or they are considered to be harmful. Some of these species now have legal protection although, in many cases, an illegal trade continues
• Products from direct exploitation

  • Food
  • Furniture and ornaments
  • Traditional medicines
  • Other products
• Some species have become extinct, including the Dodo, Great Auk, and Passenger Pigeon
• Furniture and ornaments


  • Timber from tropical rainforest trees such as mahogany, teak, and ramin
  • Black piano keys made with tropical ebony wood
  • White keys made with elephant ivory
  • Jewellery made with shark's teeth, turtle shell, and mollusc shells
  • Coral and sea shells collected and sold as tourist souvenirs
• Traditional medicines


  The demand for traditional medicines, especially in Asia, has led to large numbers of selected species being collected. There is little scientific evidence that they are effective as medicines. Even they were, they may become unavailable in the future as populations decline
• Traditional medicines


  • Tigers: different parts used to cure a range of problems
  • Rhinoceros: horn used as a supposed cure for many medical problems
  • Seahorses: used to make medicines to treat infertility, baldness, asthma, and arthritis
• Other products


  • Fine oil extracted from whale blubber and spermaceti from the heads of Sperm Whales, used until the 1970s in the manufacture of products such as lamp oil, candles, soap, lubricating oil, cosmetics, and perfume
• Eradication of predators and competitors


  Many species have been killed because they threaten humans or interfere with human activities
• Reasons for eradication of predators and competitors

  • Animals which threaten humans
  • Pathogen vectors
  • Predators of livestock
  • Agricultural pests
  • Wild herbivores that eat crops or compete with livestock
  • Forestry pests
• Changes in abiotic factors

  Human activities may alter a habitat so that it becomes unsuitable for species that are not adapted to the new conditions. The species that are most likely to be affected are those with very specialised habitat requirements
• Changes in abiotic factors

  • Water availability
  • Dissolved oxygen
  • Temperature
  • pH
  • Water turbidity
  • Physical damage
• Water availability


  Land drainage has affected large areas of wetland as land has been reclaimed and farmland has expanded. Over-exploitation of groundwater resources can lower the water table, causing surface wetland habitats to dry out. Hydroelectric power schemes may cause sudden changes in water levels that flood nests, killing the eggs
• Dissolved oxygen


  Dissolved oxygen levels in water can be reduced by hot water discharges from power stations, or by discharging organic wastes, such as sewage, which deoxygenates the water as it decomposes. A drop in dissolved oxygen levels can reduce the survival of aerobic organisms such as fish and insect larvae
• Temperature


  A change in temperature can affect wildlife species in many ways. The growth or survival of some species will increase but others may not be adapted to survive the change
• Temperature changes


  • Global climate change causing changes in species distribution
  • Hot effluent water increasing growth rates of aquatic vegetation or increasing decomposition and deoxygenation
• pH


  Mine drainage water and pollutant gases can produce acidic conditions, which can denature the cell proteins of exposed tissues. Some organisms or tissues are particularly vulnerable to acidic conditions
• Water turbidity


  Activities such as ploughing, mining or dredging may increase water turbidity, reducing light penetration and preventing submerged aquatic plants from photosynthesising. It can also kill filter-feeding organisms such as many bivalve molluscs whose gills become blocked
• Physical damage


  A wide range of human actions can cause physical damage such as discarding litter or old fishing gear
• Changes in biotic factors

  The survival of a species may be affected by changes in the presence and abundance of other species in its habitat
• Changes in biotic factors

  • Loss of pollinators
  • Loss of seed dispersal species
  • Food chain impacts
  • Introduced species
• Pollinators


  Many plants rely on pollen being transported between their flowers by insects. If the insects were to die out, then the plants would not be able to reproduce. The use of pesticides and loss of wild flowering plants has reduced populations of many insect species, including many species of bee
• Seed dispersal species


  Animals that eat seeds and fruit can be vital in the successful dispersal of seeds and therefore future plant survival. Many large herbivore species are endangered, and their conservation would help to protect the plant species that rely on them
• Seed dispersal species


  • Elephants disperse the seeds of most of the tree species where they are found
• Food chain impacts


  The decline in the populations of some species has been caused by the over-exploitation of their food by humans. Over-exploitation of one species may also cause the increase of another species
• Food chain impacts


  • Over-collection of turtle eggs has caused a decline in turtle numbers and therefore an increase in their food species, including jellyfish
  • Decline in sea otters on the west coast of the USA caused an increase in sea urchins that they eat, leading to over-grazing of kelp seaweeds
• Introduced species


  If a species is introduced, it may have adaptations that give it a greater chance of survival than the indigenous species, which may then decline or die out. Populations in isolated areas, such as islands, have been very seriously affected
• Introduced species


  • Grey squirrel out-competing the indigenous red squirrel in the UK
  • Rhododendrons introduced to the UK from Asia being very invasive and shading out native vegetation
• Introduced predators


  The introduction of predators has reduced the populations of many wildlife species, especially in areas where the indigenous species are not adapted to survive in the presence of predators
• Introduced predators


  • American Mink reducing the range of the European Water Vole in UK rivers
  • Cane Toads introduced to Australia becoming serious predators of many other species
  • Cats, rats, pigs, and dogs threatening ground nesting birds on many oceanic islands
• Introduced pathogens


  Humans may introduce pathogens, causing a decline in wildlife populations. The pathogens are often carried by other introduced species
• Introduced pathogens


  • Grey Squirrel introducing squirrel pox virus that kills the indigenous Red Squirrel
  • Signal Crayfish introducing crayfish plague that kills the indigenous White-Clawed Crayfish
  • Tree pathogens like Dutch Elm Disease, Ash Dieback, and Sudden Oak Death being introduced on imported vegetation or in soil
• Species that hybridise


  If an introduced species is very closely related to an indigenous species then cross-breeding may produce fertile hybrids, changing the natural gene-pool
• Species that hybridise


  • Red Deer threatened by hybridisation with introduced Sika Deer
  • Wildcat population in Scotland threatened by hybridisation with domestic cats
• Loss of species that control abiotic factors

  Some species change habitats and produce abiotic features that other species need for survival. If these species are lost then many other species may decline
• Loss of species that control abiotic factors

  • African Forest Elephants creating clearings and water-holes
  • Beavers building dams, creating small lakes
• Habitat destruction


  Human activities may have impacts that cause complete habitat destruction, usually due to a land-use change
• Causes of habitat destruction

  • Deforestation
  • Ploughing of grassland
  • Reservoir creations
  • Mineral extraction, especially open-cast mining
  • Urban expansion
• Setting conservation priorities


  Wildlife conservation involves making choices and decisions that may be subjective and based on partial knowledge
• Questions to consider when setting conservation priorities

  • What is the present day situation - species present, populations, and current changes in abiotic factors?
  • Which species should be conserved? The conservation of one species may be beneficial or harmful to other species
  • What actions need to be taken to conserve the desired species?
  • Can the outcomes be accurately predicted?
  • Can the impacts be monitored accurately to inform further decision making?