populations Flashcards
What is a population growth
curve?
The same characteristics sown by
the growth of most natural
populations
What are the phases in a
population growth curve?
Phase 1 • Slow growth • Small numbers of individuals initially present reproduce, increasing total population • Birth rate higher than death rate, so population increases in size Phase 2 • Rapid growth • Number of breeding individuals increase so the total population multiplies exponentially • No constraints act to limit the population explosion Phase 3 • Stable stake • Further population growth is prevented by extreme constraints • Population size fluctuate but overall size remains relatively stable • Birth rates and death rates are approximately equal - fluctuation as due to fluctuations in limiting factors
What is a limiting factor?
The factor whose magnitude slows down the rate of a natural process • e.g. Competition for resources, build-up of toxic by-products of metabolism, disease
How are limiting factors
categorised?
• Abiotic factors: temperature, light, pH, water and oxygen availability, and humidity • Biotic factors: predators, disease, competition
What is carrying capacity?
The maximum population size that
can be maintained over a period in a
particular habitat
What are the two types of
strategist?
r-Strategists and k-Strategists
Describe k-Strategists
Species whose population size is determined by the carrying capacity The limiting factors have a more significant effect as the population size gets closer to the carrying capacity e.g. birds, larger mammals, larger plants
What are the characteristics of
k-Strategists?
- Low reproductive rate
- Slow development
- Later reproductive age
- Long lifespan
- Large body mass
Describe r-Strategists
Species in which the population size increases quickly and can exceed the carrying capacity of the habitat before the limiting factors start to have an effect aka ‘boom and bust’ population growth e.g. mice, insects, spiders, weeds
What are the characteristics of
r-Strategists?
- High reproductive rate
- Quick development
- Young reproductive age
- Short life span
- Small body mass
What are the steps in the
predator prey cycle?
1. As the predator population gets larger, more prey are eaten 2. The prey population decreases, leaving less food for the predators 3. With less food, fewer predators can survive and so their population size decreases 4. With less predators, fewer prey are eaten and so their population size increases 5. With more prey, the predator population increases, and the cycle begins again
When does competition
happen?
When resources e.g. food or water are not adequate to satisfy all of the individuals that depend on the resource • Intraspecific and interspecific competition
What is intraspecific
competition?
Competition between individuals of the same species The individuals best adapted to obtaining the resources survive and reproduce, whilst the others die
What is interspecific
competition?
Competition between individuals of different species The more overlap between two species’ niches results in more intense competition, and if one species is out-competed, it could die out or become extinct in that habitat
What is preservation?
Maintenance of habitats and
ecosystem in their present
condition, minimising human impact
