6.3.2 Populations & Sustainability Flashcards
Define population
A group of organisms of the same species living in the same area at the same time
Name the 4 stages of population growth curves
Lag phase
Log phase
Stationary phase
Death phase
Give key aspects about the lag phase
- organisms acclimatising to the habitat
- birth rate slightly higher than death rate
- overall population growth slow
Give key aspects about the log phase
- rapid growth of population
- resources are plentiful and conditions favourable
- no constraints to growth
- when birth rate>death rate then population increases in size
- number of breeding individuals increases - population multiplies exponentially - doubles in a fixed time
Give key aspects about the stationary phase
- a stable population size levelled to carrying capacity
- habitat can not support a larger population
- birth rate=death rate
- may fluctuate due to limiting factors
Define carrying capacity
The maximum population of a species in a particular environment determined by limiting factors
Give key aspects about death phase
- reproduction almost ceased
- death rate>birth rate
Explain ‘boom or bust’ strategy
- extremely high reproductive rate + high population growth rate before limiting factor take effect
- harsh environments which are subject to change
- small, short lived species
Define limiting factors
Factors that prevent further growth of a population and in some cases cause it to decline
Give examples of abiotic + biotic limiting factors
Abiotic
- temperature
- water availability
- oxygen availability
- inorganic ions
- pH of soil
- light intensity
Biotic
- competition for food (intraspecific + interspecific)
- grazing
- predation
- disease
- behaviour
These are density dependant factors (depend on population size + have greater effect on bigger population)
Define density independent factors
Factors that affect populations of all sizes in the same way. Their effect is independent of population size. Their effect is not related to the population size.
Give examples of density independent factors
- earthquakes
- volcanic eruptions
- fires
- storms
- tsunami
- hurricane
Define immigration + emigration
Immigration - Movement of individual organisms into a particular area
Emigration - Movement of individual organisms out from a particular area
How can introduced species affect other species living in the area?
- may be predators for other animals
- might stop birds breeding - reducing offspring
- fewer breeders for the next year
- death rate>birth rate
How can introduced species to an island dramatically increase in numbers after introduction
- plenty of food + spaces
- few/no predators
- fill a vacant niche + not reached carrying capacity
- cannot leave island so restricted
Define competition
When organisms compete for limited resources e.g. light, mates, food, water, minerals, space
What is the difference between intraspecific and interspecific competition
Intraspecific: Between same species
Interspecific: Between different species in same niche
Give key aspects of interspecific competition
- less food + less energy for growth + reproduction
- two populations will be smaller in size than if only one species is present
- competitive exclusion principle - two species competing for same food sources ultimately eliminate each other
- e.g. red + grey squirrels
