2.3 Ecosystems and Sustainability Flashcards
What is an ecosystem?
All the living organisms and all the non-living components in a specific habitat, and their interactions
Definition of habitat
The place where an organism lives
Definition of population
A collection of individuals of the same species in a defined area
Definition of community
All of the populations of different species who live in the same place at the same time, and can interact with each other
What are biotic factors?
Living factors that influence organisms
Give 2 examples of biotic factors
Predation, disease, food supply
What are abiotic factors?
Non-living factors that influence organisms
Give 2 examples of abiotic factors
pH, temperature, soil type
What are producers?
Plants and photosynthetic organisms (e.g. algae and bacteria) that supply chemical energy to all other organisms
What are primary consumers?
Organisms such as animals and fungi who feed on plants (herbivores)
What are secondary consumers?
Organisms that eat primary consumers
What are tertiary consumers?
Carnivorous organisms that eat secondary consumers
What are decomposers?
Organisms (such as bacteria, fungi and some animals) that feed on waste material or dead organisms
How do living organisms release energy?
Via respiration
Where does the energy that organisms release come from?
Sunlight - light energy is captured through photosynthesis and converted to chemical energy stored in molecules like glucose
What is a trophic level?
The level at which an organism feeds in a food chain
What do the arrows in a food chain represent?
The transfer of energy
Why is some energy lost from the food chain between trophic levels?
- Living organisms need energy to carry out living processes. Some of this energy is eventually converted to heat
- Energy remains stored in dead organisms and waste material. This energy is only available to decomposers.
What is the result of losing energy from a food chain?
Less energy is available to sustain living tissue at higher levels of the food chain
- This means that less living tissue can be kept alive
- So there are fewer consumers at higher levels
Definition of succession
A directional change in a community of organisms over time
How does a community develop from bare ground?
By primary succession:
- Algae and liches begin to live on the bare rock (pioneer community)
- Erosion of the rock, and a build up of dead and rotting organisms, produces enough soil for larger plants like mosses and ferns to grow. These replace, or succeed, the algae and lichens
- Larger plants can then succeed these smaller plants in a similar way, until a final, stable community is reached. This is called a climax community
What is secondary succession?
Succession that takes place on previously colonised, but disturbed or damaged, habitat
What is the first stage in the succession of sand dunes?
- Pioneer plants such as sea rocket and prickly sandwort colonise the sand just above the high water mark
- These can tolerate salt water spray, lack of fresh water and unstable sand
What is the second stage in the succession of sand dunes?
- Wind-blown sand builds up around the base of these plants, forming a ‘mini’ sand dune
- As plants die and decay, nutrients accumulate in this mini dune
- As the dune gets bigger, plants like sea sandwort and sea couch grass colonise it
- Because sea crouch grass has underground stems, it helps to stabilise the sand
What is the third stage in the succession of sand dunes?
- With more stability and accumulation of more nutrients, plants like sea spurge and marram grass start to grow
- Marram grass is special; its shoots trap wind-blown sand and, as the sand accumulates, the shoots grow taller to stay above the growing dune
- This traps more sand
What is the fourth (and final) stage in the succession of sand dunes?
- As the sand dune and nutrients build up, other plants colonise the sand
- Many, such as hare’s-foot clover and bird’s-foot trefoil, are members of the bean family
- Bacteria in their root nodules convert nitrogen into nitrates
- With nitrates available, more species, like sand fescue and viper’s bugloss, colonise the dunes
- This stabilises them further
- Eventually, a dune’s community may develop into grassland, and then into woodland
Why do ecologists usually study ecosystems?
To find out whether the abundance and distribution of a species is related to that of other species, or to environmental factors
What is a quadrat?
A square frame that defines the sample area, used for sampling ecosystems
What types of data can you collect from a quadrat?
- Distribution: presence or absence of each species
- Abundance: estimate or count the number of individuals
What are the disadvantages to estimating percentage cover?
- Difficult
- Inaccurate
How can you improve the percentage cover method?
By using a point frame
How does a point frame work?
- Stand the point quadrat firmly on the ground
- Lower each needle downwards
- Record the species that the tip touches on the way down
- The number of needles that touch each species is proportional to the percentage cover of that species
Why is it important to decide where to place the quadrats before starting to sample?
- You may bias the sample
- E.g. Sampling from only one corner of the area may not be representative of the whole area due to abiotic or biotic factors
How can you avoid biasing a sample and provide a sample that is representative of the whole habitat?
- Randomly position the quadrats across the habitat (e.g. by using a random number able to create coordinates)
- Take samples at regular distances across the habitat
How can ecologists work out how many quadrats they need?
- Ecologists carry out a pilot study
- They take random samples across the habitat and make a cumulative frequency table
- They then plot cumulative frequency against quadrat number
- The point where the curve levels off tells them the minimum number of quadrats to use
- Ecologists often double this number
How can you work out how big your quadrats should be?
- Count the number of species you find in larger and larger quadrats
- Plot quadrat area on the x-axis, against the number of species you find in each one
- Read the optimal quadrat size at the point where the curve starts to level off
What is a transect?
A line taken across a habitat
How is a line transect taken?
At regular intervals, make a note of which species are touching the tape
How is an interrupted belt transect taken?
At regular intervals, place a quadrat next to the line
How is a continuous belt transect taken?
Place a quadrat next to the line, moving it along the line after looking at each quadrat
When does competition between organisms occur?
When resources are not present in adequate amounts to satisfy the needs of all the individuals who depend on those resources
What happens when the intensity of competition increases?
- The rate of reproduction decreases
- The death rate increases