Component 1.5 - Population growth And Its Factors Flashcards
What is the size of population determined by? (4)
1) Birth rate (Mammals are born, bacteria undergo binary fission, reptiles hatch from eggs and plants develop from seeds)
2) Death rate
3) Immigration
4) Emmigration
What is an equilibrium species and how is their pattern of growth shown on a graph?
Species that control their population by competition rather than by reproduction and dispersal. The graph is a sigmoid shape.
What is the lag phase?
- A period of slow growth
- A period of adaptation or preparation for growth (metabolic activity)
E.g in a population of rabbits it would represent the time for individuals to reach sexual maturity
What is the exponential phase?
- As long as there is no factor limiting growth, more individuals become available for reproduction
- The cell numbers increase logarithmically
State what is meant by environmental resistance and give 3 examples
- The environmental factors that slow down population growth
1) Less food available
2) Concentration of waste products is toxic
3) Not enough space or nesting sites
What is the result of environmental resistance?
The population still increases but more slowly so the gradient of the line decreases
State some biotic and abiotic factors that could affect population size?
Biotic:
1) Predation
2) Parasitism - increased population density allows infection to spread more rapidly
3) Competition from other species for nesting sites and food
Abiotic:
1) Temperature
2) Light intensity
Describe what is meant by the stationary phase and what happens during this period
- It is what occurs when the birth rate is equal to the death rate and therefore the population has reached its maximum size (carrying capacity)
- Population is not absolutely constant and fluctuates around the carrying capacity in response to environmental changes e.g number of predators
How could the carrying capacity be increased ?
It could be increased by there being a larger amount of food available or more nesting sites
What is the death phase?
- The factors that affected population growth at the end of the lag phase become more significant and population size decreases
- When the death rate becomes larger than the birth rate the graph has a negative gradient
What is a predator-prey relationship?
- Where the abundance of prey limits the number of predators and the number of predators controls the number of prey.
- populations oscillate due to negative feedback
What are density-dependent factors and give an example of how it works?
- Factors that affect a higher proportion of the population if the population is denser
- These are biotic factors e.g parasitism, disease, depletion of food supply, predation
- For bacteria: oxygen concentration, waste
What are density independent factors and give an example
- Abiotic factors which have the same effect on the population regardless of the population density
- Usually due to a sudden change in an abiotic factor e.g flood or fire (can cause population crash)
Describe the method of population regulation using negative feedback ?
- Population rises above carrying capacity, a density-dependent factors increase and raised environmental resistance, mortality/reduced breeding meaning population declines
- Population falls below carrying capacity, environmental resistance is temporarily relieved and less effect of density-dependent factors so population increases again
Why are ecosystems described as dynamic?
1) Energy flow varies
2) Biological cycles vary mineral availability
3) Succession changes habitat
4) Species arrive and some species are no longer present
