19.2 Variation in Population Size Flashcards
What is meant by population size
The number of individuals in a population
What is meant by populations being dynamic
They vary in size and composition over time
When is it possible to plot a graph of numbers in a population against time
When a population grows slowly, when it grows quickly it isn’t as possible
What factors can limit growth (limiting factors)
- Availability of food
- Light
- Water
- Food
- Oxygen
- Disease
- Predators
What is the carrying capacity of a population
The size of a population that can be sustained over a long period
What are the abiotic conditions that influence population size (non-living conditions)
- Temperature
- Light
- pH
- Water and humidity
How does temperature influence population size
Each species has a different optimum temperature which it is best able to survive
The further away from this optimum, the fewer individuals in a population are able to survive
This REDUCES the carrying capacity
How does light influence population size
Light is the ultimate source of energy for most ecosystems. As light intensity increases, so does the rate of photosynthesis
Greater rate of photosynthesis = faster growth rate of plants, therefore the more seeds and spores they produce
This INCREASES the carrying capacity
How does pH influence population size
pH affects the action of enzymes
Each enzyme has an optimum pH at which it operates most effectively
A population of organisms is larger where the appropriate pH exists, or smaller/non-existent if too large/small
How does water/humidity influence population size
Where water is scarce, populations are small and consist only of species that are well adapted to living in dry conditions
Humidity affects transpiration rates in plants and the evaporation of water from animals
What is the impact of an abiotic factor being below the optimum for a population
Fewer individuals are able to survive due to adaptations not being suited to the conditions
What happens if no individuals have adaptations that allow survival
The population becomes extinct
