3.7.4 Populations in Ecosystems Flashcards
define community
All the different species that live in one area and interact with each other.
define ecosystem.
All the living organisms found in one area, combined with non-living aspects of their environment. Can vary from very large to very small
Describe biotic and abiotic factors, giving examples.
Biotic = living features of an ecosystem e.g. predators, disease.
Abiotic = non-living features of an ecosystem e.g. light, temperature
Define habitat.
The place where an organism lives within an ecosystem
Define a niche.
The role of a species within its habitat, consisting of both its biotic interactions e.g. what it eats, and abiotic interactions e.g. time of day it is active
What is meant by carrying capacity?
The maximum size of population an ecosystem can support
Name four abiotic factors that affect population growth.
- Temperature
- Light
- pH
- Water/humidity
What is meant by intraspecific and interspecific competition?
Intraspecific = competition between organisms of the same species
Interspecific = competition between organisms of different species
What resources might organisms compete for?
Food, water, shelter, minerals, light, mates (intraspecific only)
Describe the pattern of a typical predator-prey relationship in terms of population change.
- Prey is eaten by predator, resulting in predator population increasing and prey population decreasing
- Fewer prey means increased competition for food, so predator population decreases.
- Fewer predators means more prey survives, and the cycle begins again.
How are quadrats used for estimating population size?
Can be placed on grid coordinates, or at intervals along transects. Results reported as either percentage cover or frequency. For slow-moving or non-mobile organisms.
How is mark-release-recapture used for estimating population size?
- A sample of a species is captured, marked, then released back into the same area they were caught.
- After a certain period of time another sample of the area is captured, and the number of marked organisms are counted.
For mobile organisms
What is the equation for mark-release-recapture?
Estimated population size =
total number of individuals in the first sample X total number of individuals in the second sample
/ number of marked individuals recaptured
What assumptions does the mark-release-recapture method make?
- marked individuals distribute evenly.
- no migration in or out of the population
- few births or deaths
- method of marking does not affect survival
- mark does not come off
Why are ecosystems described as being dynamic?
- populations constantly rise and fall
- any small change can have a large effect
- biotic and abiotic factors may alter the conditions of the ecosystem