Population Size and Ecosystem Flashcards
Define ecology
The study of living organisms within a habitat and their interactions with both biotic and abiotic factors
Define ecosystem
A characteristic community of interdependent species interacting with the abiotic components of their habitat
Define habitat
The place in which an organism lives
Define population
A group of interbreeding organisms of the same species occupying a particular habitat
Define community
Interacting populations of 2 or more species within a particular habitat
Define environmental resistance
Environmental factors that slow down population growth
Define biotic factors
Living factors within the environment eg pathogens and predators
Define abiotic factors
Non-living environmental factors eg air temperature, oxygen availability
Define niche
The specific role and position a species plays within a particular ecosystem
Define carrying capacity
The maximum number of individuals a population can sustain within a particular environment
Define intraspecific
Competition between members of the same species
Define interspecific
Competition between members of a different species
Define random sampling
Method of sampling when abiotic factors are uniform
Define systematic sampling
Method of sampling where there is a change in abiotic factors
Define photosynthetic efficiency
A measure of the ability of a plant to absorb light energy
Define GPP
The rate of production of chemical energy in organic chemicals by photosynthesis
Define NPP
Gross primary productivity minus the energy used up by the producers in respiration in a year
Define biological productivity
The rate at which biomass accumulates in an ecosystem
Define secondary productivity
The rate at which consumers accumulate energy from assimilated food in biomass in their cells of tissues
Define biomass
The dry mass of organic matter of a group of organisms in a particular havitat
What factors does population numbers depend on?
- Birth rate
- Death rate
- Immigration
- Emigration
What are the 4 phases in the population growth curve?
- Lag phase
- Exponential/log phase
- Stationary phase
- Decline/death phase
Describe what happens in the lag phase of population growth
Slow rate of reproduction.
Period of intense metabolic activity such as enzyme synthesis.
In sexually reproducing organisms, this phase represents the time taken for individuals to reach sexual maturity.
For yeast placed into nutrient broth, it represents the time taken for them to hydrate.
Describe what happens in the exponential/log phase of population growth
Rapid increase in population numbers as more individuals are available for reproduction.
No factors limiting growth.
Bacterial cells double per unit time.
Environmental resistance occurs at the end of log phase.
Describe what happens in the stationary phase of population growth
Birth rate/cell division = death rate.
Factors are limiting any further growth.
The population has reached its carrying capacity.
Actual numbers will fluctuate around the carrying capacity in response to environmental changes.
Describe what happens in the death phase of population growth
Environmental factors now result in death rate becoming greater than birth rate. For example, glucose running out in a nutrient broth or build-up of ethanol when growing yeast.
Define and give examples of density dependent factors affecting population size
Factors that have a greater effect the larger the population size (more likely to slow down population growth rate)
- disease and parasitism
- food availability
- toxic waste build up
Define and give examples of density independent factors affecting population size
Factors that have an effect regardless of the size of the population (more likely to cause a population crash)
- floods
- fires
- sudden temperature change
Describe predator-prey relationships
As the population density of a particular prey increases, more are eaten by the predator therefore the prey population decreases. When the prey population increases, there is more food available for the predator so the predator population increases.
Describe how to sample species in a field
In an area where abiotic factors are uniform:
1. Set up a 10mx10m grid and use random number generator to generate coordinates to determine where to place the 1m2 quadrat
2. Count the number of species or percentage cover in each quadrat
3. Repeat at 10 random coordinates
4. Calculate a mean for each species
How would you sample the change in species over time within an area?
Set up a permanent area within the habitat and create a 10m x 10m grid. Generate random coordinates for quadrat placement and record the number or percentage coverof plant species. This grid would be visited periodically (every year for 10 years) to gain results for comparison.
What sampling techhnique would you use in an area where there is a change in an abiotic factor?
Transect
What is the difference between a line transect and a belt transect?
A line transect would be used to describe the difference in plants as you enter a wood. Record the species touching the transect at each point. A belt transect provides more data. Place a quadrat at regular intervals along the transect. Estimate the density or percentage cover of plant species in each quadrat. Also useful to measure the varying abiotic factor.
Describe how to set up a transect
- Run a 20m tape measure along the area to sample
- For a line transect, identify the species touching the transect every half metre along the tape measure
- For a belt transect, place a quadrat down every half metre along the transect and calculate percentage cover
- Repeat multiple times within the area to ensure a representative sample. For a belt transect, calculate a mean
What is the source of all energy for an ecosystem?
Light energy from the sun trapped by photosynthesis
What is detritus?
Dead particulate organic matter
On the death of organisms, where does some energy remain?
Locked up as organic material
Why are decomposers not classed as a trophic level?
They feed from every level
Why does an ecosystem rarely support more than 5 trophic levels?
A lot of energy is lost between trophic levels. By the 4th or 5th trophic level there is not enough energy left to support another one
State the formula for photosynthetic efficiency
Energy incorporated into photosynthetic products/total light energy falling on the plant x 100
Why isn’t all light energy that falls on a plant absorbed by photosynthetic pigments?
- Reflection 90%
- Not all wavelengths are absorbed for photosynthesis
- Light transmitted straight through the leaf (may not fall on chlorophyll)
What is gross primary productivity (GPP)?
The rate of production of chemical energy in organic chemicals by photosynthesis (kJ m2 year)
What does net primary productivity (NPP) represent?
The potential food energy available to heterotrophs in ecosystems
State the formula for NPP
NPP = GPP - respiration
As energy is passed along the food chain from one trophic level to the next, there is loss from the food chain at each level. What is this due to?
- Energy in egested molecules - mostly cellulose
- Energy lost as heat generated in respiration
- Energy remains in inedible parts of animals eg horns, bones, fur
Explain why carnivores have a more efficient energy conversion than herbivores
Protein is more rapidly and easily digested than cellulose. A lot of cellulose is lost in the faeces of herbivores
Explain why farmers keep animals in barns during the winter
They won’t have to use as much energy maintaining their body temperature, so more energy is available to produce biomass
Define gross ecological efficiency
A measure of how much energy is transferred from one trophic level to the next
What is the equation for gross ecological efficiency?
energy in trophic level/energy in previous trophic level x100
How do the values for gross ecological efficiency differ in different ecosystems?
- They are often around 10%
- Oceanic food chains can have high values, around 40%
- Food chains involving birds and mammals may be as low as 1%
What is the reason for the difference in gross ecological efficiency between aquatic organisms and birds and mammals?
Many aquatic organisms don’t regulate their body temperature and so save a lot of energy. Birds and mammals maintain a high body temperature (endothermic) and this uses up a lot of energy and is therefore less efficient
Why can a pyramid of energy never be inverted?
Energy is always lost from one trophic level to the next, cannot be produced
Define succession
The change in structure and species composition of a community over time
What is the difference between primary and secondary succession?
Primary succession is the introduction of plants/animals into areas that have not previously supported a community eg bare rock
Whereas secondary succession is the reintroduction of organisms into a bare habitat previously occupied by plants and animals that may have been damaged by fire or tree felling
What is succession affected by?
- Migration: arrival of spores, seeds and animals is vital for succession to progress
- Competition: interspecific competition
- Facilitation: positive interactions between species that become increasingly significant as succession progresses
Why is secondary succession more rapid than primary succession?
Soil/roots and seeds are already present
Describe the process of primary succession
- Pioneer species are the first organisms to colonise the rock eg lichens
- These organisms slowly erode the rock and the accumulation of dead and decomposing organic material leads to the formation of primitive soil
- As soil develops, grasses become established
- As the soil builds up and nutrient levels increase, deep rooted shrubs appear
- Over a very long period of time, trees and woodland become established
- This results in a stable, long lived community known as the climax community
Describe 2 factors which assist in the colonisation of a habitat
- The seeds previously dispersed by flowering plants and spores from fungi may remain in the soil and begin to germinate
- Migrating animals produce droppings. This improves nitrate levels in the soil
Name 6 ways that human interference can affect the natural development of the climax community during succession
- Grazing: livestock such as sheep eat the grasses and other plants
- Moorland management: heather colonisation is controlled by burning
- Farming: ploughing and growth of crops by monoculture stops trees and shrubs from getting established
- Deforestation: trees are cut down which can cause erosion of soil
- Industry: eg coal mining and quarrying of stone
- Urban development: building of new roads and buildings
