Section 7 - Genetics, populations, evolution and ecosystems: 19. Populations in ecosystems Flashcards
What is ecology
The study of the inter-relationships between organisms and their environment, including biotic (living) and abiotic (non-living) factors
What is an ecosystem
Dynamic system made up of a community and the abiotic factors of it’s environment
- Elements and nutrients are cycled and reused
- Energy flows through the system (food chains)
What is a population
A group of individuals of one species that live in the same habitat at the same time
What is a community
All the populations of different species living and interacting in a particular place at the same time
What is a Habitat
The place where an organism lives
- Characterised by the physical conditions and types of organisms present
- Made up of smaller units called ‘microhabitats’
What is an Ecological Niche
How an organism fits into it’s environment, referring to where it lives, and what it does
- Links to how the organism is is adapted to survive within an area
- No two species can occupy the same exact niche (competitive exclusion principle)
What is the ‘Carrying capacity’ of an ecosystem
The maximum population size of a species that an ecosystem can support
- Affected by abiotic factors, and interactions between organisms
What are examples of Abiotic factors that can effect population size
- Temperature
- Light
- pH
- Water levels
- Humidity
- etc.
How can temperature effect population size
Each species has an optimum temperature for it to survive, and deviation away from this will reduce the population size
How can light levels effect population size
Light is the ultimate energy source for most ecosystems
∴ Increased Light energy increases the rate of photosynthesis, leading to an increase in Plant/animal population size
How can pH (eg. soil pH) effect population size
pH effects enzyme action, as each enzyme has an optimum working pH
- ∴ Altering the pH will cause the enzymes to be denatured, reducing metabolic activity
- This can lead to a reduction in population size (eg. bacterial population)
How can water levels effect population size
Different species are adapted to live in conditions with varying water levels, so if the water level varies from the optimum, the population size will be reduced
How can humidity effect population size
Varying the humidity will vary the population size
- Effects transpiration rate in plants, effecting the rate of photosynthesis
- Effects the rate of evaporation of water (eg. from the body of animals as sweat)
What is Intraspecific Competition
When individuals of the same species compete for resources
- ∴ Availability of resources will effect the population size
- Results in natural selection as individuals with favourable traits are advantageous, so more likely to survive and breed
What is Interspecific Competition
When individuals of different species compete for resources
- Species with advantageous characteristics will grow in population size, as other species population is gradually reduced
- If conditions remain the same, one population will be completely wiped out (Competitive exclusion principle)
What is the ‘Competitive exclusion principle’
Principle stating that two species which compete for the same limited resource cannot coexist with constant population sizes
- ∴ No two species can occupy the exact same niche
- ∴ Intraspecific competition under constant conditions will eventually lead to one species being wiped out
What is predation and the ‘Predator-prey’ relationship
When one organism is consumed by another, as part of an interspecific relationship that occurs as species evolve alongside each other, with the predator adapted to hunt and the prey adapted to evade
What are the 4 stages of the ‘Predator-Prey cycle’
1) Predators eat prey, reducing the prey population size
2) Fewer available prey results in competition among predators, reducing their population size
3) Fewer predators allows for an increase in the number of prey, as more survive and reproduce
4) More available prey reduces the competition among the predators, allowing more to survive and breed, so predator population increases
- They cycle then repeats, with the peak population sizes varying based on selection pressures
- Variations in the two populations are less dependant on each other if the predator has multiple prey
What is ‘Abundance’
The number of individuals of a particular species in a given space
- Can’t be fully counted (time-consuming, destructive, etc.)
- ∴ Samples are used to represent the whole population
What are the two types of Quadrats that can be used when investigating populations
- Point quadrat
- Horizontal bar supported by two legs
- A vertical pin is placed in holes set at intervals along the horizontal bar
- Each species the pin touches is recorded
- Frame quadrat
- Square frame with equally sized subdivisions
- Placed at different locations, with abundance measured for each, so average for the whole area can be determined
How can random sampling be used to investigate a population
- Lay 2 perpendicular tape measures as axis along the edges of the area being studied
- Obtain coordinates with a random number generator
- Place the quadrat at these coordinates and count the species within it
- Repeat for at least ten locations
- Calculate the abundance for the whole area based on the mean per quadrat
How can systematic sampling be used to investigate a population
- Place a tape measure along the ground in a straight line (belt transect)
- Frame quadrat is placed at set intervals along the transect, and the species within it recorded
- Method used when there is some form of gradual change within a community
- eg. Distribution of organisms along a line of succession (from the sea, through the dunes, into woodlands)
- eg. Through changing abiotic factors (light intensity, water level, etc.)
How do you measure the abundance of a Sessile species (organisms don’t move)
Samples are made using quadrats, and Abundance can be measured in several ways
- Counting the organisms
- Counting the organisms in a quadrat (sample)
- Using this to estimate the total number in the area
- Frequency
- Likelihood of a particular species occurring in a quadrat
- Useful method for species that are difficult to count (eg. grass)
- Does not provide details on species distribution in the area
- Percentage cover
- Estimate of the % area within a quadrat that a plant covers
- Allows species to be compared
- Not as useful for plants that grow in overlapping layers
How do you measure the abundance of a Motile species (organisms can move)
Mark-Release-Recapture
- A known number of organisms are caught, marked and released
- Some time later, a given number of individuals are capture
- The number that were already marked in the second group is counted
- The whole population size can then be estimated, based on the assumption that the proportion marked within the second sample is the same as the proportion of marked individual within the total population
