environmental science

• Range of tolerance


  The upper and lower limits of an abiotic factor which permit survival of a species. The young usually have a narrower range of tolerance than the adults.
• Abiotic factors


  The survival and distribution of species is largely controlled by abiotic factors. Being able to survive extreme conditions to which few species are adapted may avoid competition with other species that won't be able to live there, but it may also limit the areas that will be suitable for that species and make it vulnerable to environmental change.
• Temperature


  • No organisms can survive where low temperatures cause the cells to freeze or high temperatures denature their proteins
  • Within this range a species will be able to survive if their proteins, including enzymes, are functional. Even within this range of temperatures that is generally suitable for life, each enzyme will function within a particular temperature range
  • This is a problem for organisms that live where temperatures fluctuate a lot, but the problem can be overcome if the body's internal temperature can be kept constant
  • Bacteria around volcanic vents have evolved to survive at temperatures over 110°C
• Light


  • Light that is absorbed during photosynthesis is the source of energy for most food chains
  • Plants have evolved pigments to absorb light in particular habitats. Many woodland floor plants have red or blue pigments to make use of the green light that passes through the canopy vegetation. These plants often cannot survive continual bright sunlight
  • UV light damages living cells and is particularly dangerous to animals with thin skins, such as amphibians
• pH


  • Organisms with exposed living tissues are particularly susceptible to enzyme damage caused by high or low pH
  • Many plants can only survive if the soil is within a certain pH range. Outside the range their root cell enzymes may not function or they will be unable to absorb nutrients. For example, most lichens cannot survive in acidic conditions
  • Animals with exoskeletons cannot survive very acidic conditions because it dissolves the skeleton. For example freshwater crustaceans such as crayfish cannot survive in acidic water
• Water


  • All organisms require water, but some species have particular requirements, often for breeding or because they do not have the ability to reduce water loss. For instance, frogs have thin skin that must remain moist. If it dries out then the living skin cells die and absorption of oxygen is reduced. Although they spend most of their lives out of water, they live in moist areas and must return to water to lay their eggs. Toads have a thicker skin that reduces water loss so they can live in drier habitats.
• Mineral nutrients


  • Animals get their mineral nutrients in their food or water, but most plants can only absorb them from their surroundings via their roots.
• Turbulence and physical damage

  • Some species are well adapted to surviving conditions of turbulence without being seriously damaged. For example, brown seaweeds on rocky shores are very flexible and coated with mucus that reduces wear against rocks.
• Species interdependence and control of abiotic factors

  • The abiotic factors that affect a species may be controlled or modified by other species living in the same habitat, so the survival of one organism may indirectly depend upon the presence of another species.
• Altered abiotic factors in a woodland

  • Light levels on the woodland floor may be lowered because of shading
  • Humidity will be higher because of transpiration by the canopy vegetation
  • Wind velocities will be reduced because trees act as windbreaks
  • There will be an increase in nutrient availability because of the decomposition of dead leaves and branches
• Biotic factors


  Other species, especially obtaining food and avoiding becoming food. Other biotic factors include disease, nutrient supply, and interrelationships for breeding such as pollination and seed dispersal.
• If a species is not adapted to the abiotic factors then it cannot survive. It must also be adapted to biotic factors
• Feeding adaptations


  • Catching food
  • Eating food
  • Digesting food
• Feeding in harsh environments

  • Eating a wide variety of foods
• Feeding in tropical rainforests

  • Abiotic conditions ideal for plant growth, so productivity is high and food supplies are very abundant and reliable
  • Allows many animals to survive, with enough food for different species to exist with specialised feeding mechanisms to avoid competition
  • Birds' bills vary in shape to allow them to eat different types of food
• Feeding mechanism of woodpeckers

  • Finding insect larvae by pecking into rotten wood
  • Habitat management must include enough old rotting trees
• Avoiding predators in rainforests

  • Having defence mechanisms such as a bad taste, toxins or thorns
  • Using camouflage to avoid being found
  • Tree-living animals may be more prone to predation if they come down to the ground
• Symbiotic nutrition


  Different species have evolved to assist each other with nutrition
• Symbiotic nutrition example


  • The algae that live inside coral polyps on coral reefs are provided with a safe habitat and supplies of nutrients, while the polyps are provided with carbohydrates
• Disease


  • Naturally control populations, when the population density is high
  • While individuals may become ill or die, the overall population may benefit by ensuring the weaker individuals do not survive, but if a population is already threatened then losses due to disease may cause it to decline
• Pollination


  • Plants with a low population density where individuals are spaced well apart need a pollen delivery system, so they have evolved flowers that attract animals, such as bees, beetles, moths or bats that transfer pollen from flower to flower
  • Particular plants have evolved to attract specific animal groups using scent, colour, shape or time of opening
• Seed dispersal


  • Wind dispersal of seeds only works for small seeds and plants in windy areas
  • Larger seeds cannot be carried by the wind and neither can those produced in sheltered areas such as beneath the forest canopy
  • Plants often produce seeds that are intended to attract animals
  • Some seeds may be carried away and eaten, but some may be dropped and can then grow into plants
  • Seeds may be enclosed in edible fruit that attracts the animals, which then disperse the seeds in their faeces
• Nutrient supply


  • Nutrients from dead organic matter are released during the break-up by detritivores and subsequent breakdown by decomposers
  • Plants can then utilise the nutrients again, which ensures future food supplies for the detritivores and decomposers
• Species


  A group of similar organisms which resemble one another and can breed together to produce fertile offspring
• Population


  All the individuals of a species living in a particular area at a particular time
• Taxon


  A taxonomic group of any rank, such as a species, family, or class
• Community


  The populations of all the species living in a particular area at a particular time
• Ecosystem


  The community of organisms, their inter-relationships with each other and interactions with their abiotic environment
• Habitat


  The place where a particular organism lives, which provides a particular set of environmental conditions
• Niche


  That part of a habitat which is inhabited by an organism and the role which it plays within the ecosystem, e.g. what it feeds on, the temperature range it can tolerate
• Biome


  A large geographical region, with a characteristic climate, in which certain types of plants and animals (a community of species) live, usually named from the dominant vegetation
• Biosphere


  The part of the planet which provides conditions suitable for life and is inhabited by living organisms (i.e. the soils of the lithosphere, liquid water and the troposphere)
• Lithosere Succession


  1. No soil, extremes of temperature and water availability, first colonisers are simple autotrophs like algae and lichens

  2. Mosses colonise, thin layer of soil builds up

  3. Grasses and ferns colonise

  4. Soil builds up, abiotic factors become less extreme, seedlings of less hardy plants can survive

  5. Flowering plants colonise once insects that pollinate them are established

  6. Trees colonise when soil is deep enough and edaphic factors are suitable
• Areas with water available all year round usually become woodland, temperature controls the type of woodland
• Areas with seasonal rain usually become grassland: tropical savanna or temperate grassland
• Secondary succession


  Changes that occur in an area that has already reached the climax state
• Secondary succession


  1. Natural events or human activities interrupt the sequence of events in succession and remove the climax community

  2. Succession starts again but happens more quickly than primary succession because there is already organic matter e.g. soil, present
• Plagiochimaxes


  If the human activity that produced a plagioclimax stops, then secondary succession will eventually re-establish the climax community
• Plagioclimaxes in the UK

  • Hay meadows, maintained by mowing
  • Hedgerows, maintained by cutting
• Succession

  A series of changes in a plant community, leading to a climax community