Populations and Sustainability

• Population size depends on birth and death rates of the organisms
• Population growth:

  • The Lag Phase:
  • few organisms, acclimatising
  • rate of reproduction is low
  • growth in population size is slow
  • The Log Phase:
  • resources are plentiful, conditions are good
  • rate of reproduction is fast and exceeds mortality
  • the population increases rapidly
  • The Stationary Phase:
  • pop. size levels off at carrying capacity
  • habitat cannot support larger population
  • birth rate = death rate
  • size remains constant with a few fluctuations
• Carrying Capacity (K): The maximum number of individuals that can be supported by an environment without causing damage to it or depletion of resources.
• Limiting factors:

  • availability of food, light water etc.
  • competition
  • aka. environmental resistance
• density-dependent factors:

  • effects that are caused by the size of the population
  • the larger the population, the greater the effect
  • tend to be biotic: food, predation, disease
• density-independent factors:

  • have similar effects regardless of population size
  • often abiotic: drop in temp, fire
• Migration:

  • affects pop. size
  • immigration: movement into a particular area
  • emigration: movement out of a particular area
• Predator-prey relationships:

  • when predator pop. increases, more prey are eaten
  • the prey pop. decreases, leaving less food for predators
  • predator pop. decreases and prey pop. increases
  • more prey so predator pop. increases
• Competition: organisms compete when a resource they require is in short supply
• Intraspecific Competition:

  • within the same species
  • limits population growth
  • natural selection and survival of the fittest
• Intraspecific competition:

  • stage 1: plentiful resources, population increases
  • stage 2: more individuals share resources which become limited, population declines
  • stage 3: less competition due to smaller pop., more survive and the pop. increases
• interspecific competition:

  • only occurs when two niches overlap e.g. food webs
  • more niches = more intense competition
  • one may outcompete the weaker organism
• Conservation - maintenance of biodiversity through human actions or management
• Conservation includes:

  • maintaining diversity between species
  • maintaining genetic biodiversity within a species
  • maintenance of habitats
• Conservation:

  • involves sustainable development
  • reclamation where ecosystems that have been damaged/destroyed are restored
  • is dynamic and needs to adapt to constant change
• Preservation - protection of an area by restricting or banning human interference so that the ecosystem is kept in it original state
• Preservation:

  • often used to protect areas of ecological, archaeological and paleontological interest
• Sustainable use of resources:

  • a sustainable resource is renewable and exploited in a way so that it doesn't run out
  • aims of sustainability are:
  • preserve the environment
  • ensure resources are available for future generations
  • allow all societies to live comfortably
  • enable less economically developed countries to develop by exploiting their natural resources
  • create balance in the consumption of these resources between 1st and 3rd world countries
• Sustainable timber production: small scale

  • coppicing/pollarding: trunk is cut close to the ground to allow new shoots to grow. these are cut and can be used for fencing. rotational coppicing allows biodiversity to be maintained by preventing trees from growing too high
• Sustainable timber production: large scale

  • rotational felling
  • replanting trees that are felled to maintain biodiversity
  • remove only the largest trees
  • plant trees optimum distances apart
  • manage pests and disease
• Sustainable fishing:

  • international agreements (e.g. Common Fisheries Policy of the EU) are in place to create quotas and limits on fishing
  • other methods include:
  • nets with different size mesh
  • commercial and recreational fishing at certain times of year to protect breeding
  • fish farming to take the pressure off wild stocks