Populations In Ecosystems Flashcards
Ecosystem definition
All the organisms living in a community plus all the non living conditions in the area in which they live
Community definition
A group of interacting populations of different species living in the same place at the same time
Population definition
A group of organisms belonging to the same species found in the same area at the same time and potentially able to interbreed
Habitat definition
The environment in which an organism or population of organisms usually lives
Biotic definition
The living features of an ecosystem, for example, the presence of predators or food
Abiotic definition
The non living features of an ecosystem , such as the temperature and the soil
Niche definition
The role of a species within its habitat, for example what it eats, when and where it feeds
A niche can
Only be occupied by one species
The niche a species occupies includes
Biotic interactions- living interactions, what the organism eats and and what it’s eaten by
Abiotic interactions- non-living interaction, the temperature range an organism can live in or the time of day an organism is active
Competitive exclusion
If 2 species try to occupy the same niche, one will be more successful and out compete the other
Population size is
The total number of organisms of one species in a habitats
Carrying capacity is
The maximum population size that can remain sustainable in an ecosystem
Abiotic effect on population size
When abiotic factors are ideal a population will grow and they can reproduce quicker
I conditions are less favorable, the organism will grow much slower and population may decrease
3 types of biotic effects that influence population size
Inter specific competition
Intra specific competition
Predation
Inter specific competition
Competition that occurs between different species
Competing for the same resources such as food or habitats
Less energy available for growth
One species will out compete and its population will grow
This is known as competitive exclusion principle
This is why two species can’t occupy the same niche
Intra specific competition
Competition between members of the same species
Varies around the carrying capacity
Increases or decreases depending on resources available
Predation
Population sizes of predator and prey are inter linked
Selection pressure , members of the species who are better adapted to escape or hide from predators can survive
This ensures each new population is better adapted to survival
There are often other factors influencing such as food available for prey
Investigating population growth of bacteria
Growing bacteria in a liquid broth
When light is passed through, some is scattered where the bacteria is
Spectrophotometer measures the light passing through and produce an absorbance value
The more bacteria means more absorbance
Graph of absorbance against time is exponential
We use log 10 scale so it is a straight line
Abundance definition
The number of individuals of one species in a particular area
2 ways abundance can be measured
Frequency- the number of samples a species is recorded in
Percentage cover- how much of the area you are investigating is covered by species, can only be used for non mobile or slow moving species
Distribution definition
How a species is spread across a habitat
A species could be evenly spread throughout the whole habitat, they could favour a specific area within an ecosystem or they could be randomly spread
Why use random sampling
If an area is too large, or finding the population size would be too time consuming
Take random samples of an area to give a representation of the population size
Must be taken at random to remove any bias
Larger sample size means more representative
Process of random sampling
- Choose an area to sample
- Devise a method whic will allow for random samples to be taken at a random location, such as a random number generator
- Use an appropriate sampling technique
- Take as many samples as possible(minimum 20)
- Carry out statistical analysis on the data
Frame quadrat
Large square divided into smaller squares
Used to sample organisms on the ground in an area that is relatively uniform
Quadrat can be used to find
Species frequency- likelihood of a particular species occurring within the quadrat, eg if it’s found in 15/30 squares the frequency is 50%
Number of individuals- number of each species in each quadrat
Percentage cover- number of squares covered by a species (square has to be more than half covered)
Transects
Lines through the study area along which samples are taken
Used to help find how organisms are distributed across an area
Useful if there is a change in factor acrosnan area
Two types of transect
Belt transects- quadrat a are placed next to each other along the line of study, this can be used to calculate the species frequency and percentage cover
Interrupted belt transects- place quadrats at regular intervals along the line of study
Mark release recapture
Capturing an individual of species and harmlessly marking them
Marked animals are then released back to the environment
A second sample can then be captured and count the number of individuals that are already marked
Total population size equation
Mark release recapture
Total population size=
No. In first sample x no. In second sample / no. Marked in second sample
Accuracy of mark release recapture (4)
Ethical issues (2)
Relies on assumptions:
- Marked sample has had enough time to mix with unmarked population
- Marking hasn’t affected chance of survival
- Mark is still visible
- There are no changes in population size such as births or deaths
Ethical issues:
- Organisms could be stressed after capture which could lead to reduced chance of survival
- Some organisms may be more likely to enter a trap if they’ve already been caught
