C4.1 Populations and communities Flashcards
What is a population?
A group of individual organisms of same species in a given area
Estimation of population sizes
Based on sampling, (random sampling = everyone has the same likelihood of being selected), can be done by quadrants (plants), capture-mark-release-recapture (animals) ((MxN)/R)
If a population grows too large…
there won’t be enough resources for everyone and some will die
Density-independent factors
Can increase or decrease populations regardless of density, e.g. a volcanic eruption kills everyone equally
Density-dependent factors
Have an increasing effect when population grows, e.g. more prey, more predators –> less prey, less predators
Two population growth curves:
J curve (exponential, unrestricted) and S curve (restricted growth, max capacity)
A community
Groups of populations living together
interspecific relationships (6)
Herbivory, predation, interspecific competition, mutualism, parasitism, pathogenity
Endemic vs invasive species
Endemic (natural), invasive (successful alien species), competing for the same niche
Cyclical oscillations
The cycle of prey numbers affecting predator numbers with four phases
Top down vs bottom up control of food chains
Top down (from up to down, e.g. increase in predator numbers will lead to a decrease in prey), bottom up (from down up, e.g. producers may be limited from amount of minerals in soil)
