Population dynamics and population regulation

• • Population dynamics involves the processes that can cause populations to change in size and structure
  • the number of individuals of species that live in an area is controlled by the balance of factors which tend to increase or reduce the population
  • the population will increase if the reproduction rate is high and the death rate is low
• • The population will decline if the reproduction rate is low and death rate is high
  • successful wildlife conservation will maximise the factors that increase the populations while minimising the factors that reduce it
  • the environmental factors that affect the death rate can be controlled by good environmental management
• Birth rate-

  • the maximum birth rate (natality rate) is determined by the natural ability of the species to reproduce
  • evolution has produced birth rates for each species that are appropriate for the death rate
  • species with lower chances of survival have higher birth rates
• Death rate-

  • the death rate is controlled by environmental factors such as disease, drought, predation and shortage of food
• r-selected species-

  • these are species that can respond rapidly to low survival rates
  • they reach sexual maturity quickly, produce many young and an disperse widely
  • may include mice, locusts and greenfly
• k-selected species

  • these are species that recover slowly from a decline in population
  • they usually reach sexual maturity at an older age, produce few young, but often live a long time
  • an increase in the death rate caused by a change in the habitat or by human exploitation may cause a population crash
  • the low reproduction rate of k-selected species may make it impossible to replace the losses
  • include whales, elephants and rhinos
• • an understanding of population dynamics is important in monitoring the survival of a species, its breeding success and to access Maximum Sustainable Yield (MSY)
  • The MSY of a population is an estimate of the greatest exploitation that is possible without causing unsustainable long-term population decline
  • to forecast a change in size of the population these variable are required:
  • current population
  • numbers of births and deaths
  • number of individuals immigrating and emigrating
• Population=starting population +births+ immigrants - deaths - emigrants
• Density independent factors-

  • these include factors where the population density has no effect on the chances of survival of an individual
  • for example, drought, flood or volcanic eruption
• Density dependent factors-

  • include factors where the chances of an individual surviving depend on the population density is low and lower when the population density is high
  • for example:
  • food supply-
  • Intra-species competition for food is greatest where the population density is high
  • disease-
  • diseases spread more easily between individuals when they are close together

  As the population density increases the density dependant factors become more important until the combined mortality rate forms a long term balance with the birth rate
• Carrying capacity-

  • is the greatest population that an area can support indefinitely without damaging or over-exploiting the environment
  • the mortality rate in a population changes if the population size is above or below the carrying capacity so that the population size changes back to the carrying capacity
• Predator-prey population relationships?

  • predator and prey populations are closely related
  • when the prey population rises there is a lot of food for the predators, so their population rises
  • the high predator population causes the prey population to decline
  • the low prey population creates a food shortage for the predators so their population declines
  • the low predator population then allows the prey population to rise again
• Artificial population control-

  • intervention to artificially control the population through culling may be required to enable the species or habitats to survive where natural control mechanisms no longer regulate the population
  • only necessary if:
  • the breeding rate of an endangered species is low so a captive breeding and release programme is needed to maintain or increase the population
• Artificial population control-

  • a non-indigenous species is introduced which reduces the population of indigenous species because it is a predator, competitor or pathogen
  • an indigenous predator has been removed so its prey species becomes over-populated and needs to be culled to avoid the ecological damage it may cause by its impact on other species