Section 7 - Populations in ecosystems Flashcards
What is population size?
Number of individuals in a population at a given time
What is exponential population growth?
When resources are unlimited, populations exhibit exponential growth.
(J-shaped curve)
What is logistic population growth?
When resources are limited, populations exhibit logistic growth.
Population expansion decreases as resources become scarce.
Levels when carrying capacity of the environment is reached.
(S-shaped curve)
How does temperature affect population growth?
Lower temperatures lower metabolic rate so enzymes work more slowly.
Higher temperatures could denature enzymes
Low and high temperatures affect carrying capacity of a population
As more energy is being used to maintain bodies optimum temperature, less energy for growth and reproduction so carry capacity is reduced
What is the carrying capacity?
Each population has a certain size that can be sustained over a long period of time and this is determined by limiting factors.
How does light affect population growth?
Source of energy, rate of photosynthesis increases as light intensity increases.
Carry capacity is increases
(plants grow faster, more source for animals)
How does pH affect population growth?
Affects action of enzymes
Higher pH may denature enzymes, lower pH may decrease rate so enzymes work more slowly
Decreases carrying capacity of a population
How does water and humidity affect population growth?
Lower water, populations are small and only species that have adapted to dry conditions will exist
Humidity affects transpiration rates in plants and evaporation rates from animals
What is a habitat?
Place in an ecosystem where a particular population is found
What is ecology?
Study of inter-relationships between organisms and their environment
What is a microhabitat?
Small units within a habitat
mud at bottom of a stream
What is a niche?
Description of how a species functions within a habitat due to its adaptations
What is a biotic factor?
Living factors in an environment
What is an abiotic factor?
Non-living factors in an environment
What is an ecosystem?
How the community interacts with each other and the physical environment including abiotic factors
What is a community?
The sum of all the organisms in an ecosystem
What is a species?
Group of interbreeding organisms that produce viable and fertile offspring
What is intraspecific competition?
Competition between members of the same species
Availability of resources will determine size of population
What is interspecific competition?
Competition between members of a different species
Species will compete, dominant species will increase in population
What is the competitive exclusion principle?
Where 2 species are competing for limited resources, the one that uses the resources most effectively will eliminate the other
No 2 species can occupy the same niche definitively when resources are limited
What is the pattern of a typical predator-prey relationship in terms of population change?
Prey is eaten by predator
Predator population increases, prey decreases
Fewer prey means increases competition for food, so predator population decreases
Fewer predators means more prey survive, cycle begins again
What are reasons against counting every individual?
Time consuming
Damages habitat
What are methods of studying habitats?
Bell transect Frame quadrat Pitfall trap Light trap Pooter Sweep net Drift net
What are the 2 types of quadrat?
Point quadrat- bar with 10 holes where a pin could be dropped
Frame quadrat
What are 3 factors to consider when using quadrats?
The size of the quadrat to use
The number of sample quadrats to record within the study area
The position of each quadrat within the study area
What does mark-release-recapture do?
Generates an estimate of the population size
What is the equation for mark-release-recapture?
Number in 1st sample X number in 2nd second sample
/
Number of marked animals recaptured in 2nd sample
What are the assumptions made for mark-release-recapture?
Only used for animals which are randomly distributed
Enough time must be allowed for the released animals to mingle
Method of capture must not alter the habitat
Marking method doesn’t harm animals, reduce chance of survival or affect behaviour patterns
Must be no migration or immigration
What is the mark-release-recapture method?
- Capture sample of species
- Mark in harmless way
- Release back into habitat
- Wait a week then take second sample
- Count how many are marked
- Use equation to estimate size
Why would an animal be marked on their underneath and not back in mark-release-recapture?
Does not make them less camouflage so their chance of being prey is not reduced
What is an effective method of random sampling?
- Lay 2 tape measures at right angles along study area
- Obtain coordinates by random generator
- Place quadrat at intersection of each pair and record species
How would you use systematic sampling to find population size?
Using bell transect
Place string across ground in straight line
Move frame quadrat alongside line at regular intervals and record species within
What is abundance?
Number of individuals of a species within a given area
What are 2 ways of finding the abundance of a species that doesn’t move?
Frequency- likelihood in area
Percentage cover- estimate of area that species covers
What is the advantage and limitation of percentage cover?
Useful where a species is hard to count
Data collected rapidly
Less useful where organisms occur in several overlapping layers
What is the advantage and limitation of frequency?
Useful where species is hard to count
Gives quick idea of species present
Doesn’t provide information on density and detailed distribution
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 conditions of ecosystem
What is succession?
A change in a community over time
What is primary succession?
Where an area previously without life is colonised by a community of organisms
What is the pioneer species?
First species to colonise an area
Able to rapidly exploit sudden change in conditions
Grow quickly and usually short-lived
What is the climax community?
Achieved once succession has gone as far as conditions will allow
What is the process of primary succession?
Pioneer species colonise area
Change abiotic factors of environment
Allows more complex organisms to survive
What effect does death and decay of the pioneer species have?
Adds organic matter creating basic soil.
What are harsh abiotic conditions?
Decreased fresh water
Increases salt
Strong winds
No proper soil
Why does plant diversity decrease at the climax?
Climax community organism takes light and stops other species growing
What is a seral stage?
Each stage in succession
What do successful pioneer species have?
Rapid growth
Rapid reproduction
Efficient seed dispersal
Tolerant to harsh conditions
Why would species at earlier conditions at early stages disappear?
Shading by larger plants
Eaten by herbivores
Unable to compete
What is secondary succession?
Succession when soil or vegetation is already present
What common features emerge during succession?
Abiotic environment becomes less hostile
Greater number of habitats
Increased biodiversity
More complex food webs
Increased biomass
What is the general name given to the first organisms to colonise bare land?
Pioneer species
How do changes in the environment lead to increased biodiversity during succession?
Pioneer species die and form a soil with nutrients
Further colonisers can survive in soil
Environment is less hostile
More habitats and food sources available
Other species survive
Increased biodiversity
What is the name of the stable, final stage of any succession?
Climax community
What is an example of a plagioclimax community?
Intensive grazing by sheep can deflect succession from a forest climax community to grassland
How might succession be managed in order to aid conservation?
Succession is prevented in order to preserve ecosystem
What are the main reasons for conservation?
Personal- maintains our planet
Ethical- respect for living things
Economical- animals can make substances which can prove valuable
Cultural & aesthetic- variety adds interest to everyday life
How might succession be managed in order to aid conservation?
Succession is prevented in order to preserve ecosystem
What measures could be taken to prevent succession?
Cut back reeds to prevent them becoming dominant
Remove dead vegetation
What is a niche?
The role and space that an organism fills within its habitat
What is plagioclimax?
The climax community produced when succession is artificially stopped by human intervention
Why would a student measure percentage cover of each species rather than counting individual plants?
To allow comparisons as plant sizes may vary
A student carrier out a belt transect in an identical area at an identical time as another student but results were not the same.
Why?
There is a chance that one transect doesn’t represent the full habitat or community
What are the abiotic factors that affect population growth?
Temperature
Light intensity (for photosynthesis)
pH (impact on enzyme action)
Water and humidity
How should plants be chosen to get a representative sampling site?
Large sample area
What is the role of the pioneer plants?
Make conditions less hostile
Soil development
Increase nitrogen
Provide shelter
Sustainable environment
How could deflected succession be caused?
Grazing
Burning
Exposure to wind
How does biomass change during primary sucession?
Increases
Plants at later stages are large
How is stability maintained in a population with a high reproduction rate?
Limited food
Disease
Competition
What are 2 limitations of the mark-release-recapture method?
Assumes no emigration
Assumes there is no death or birth
Assumes marking doesn’t affect survival
Assumes marked organisms don’t loose their mark
Why is genetic drift more likely to affect an endangered species?
Endangered species so found in lower numbers
Genetic drift due to chance fluctuations in allele frequencies
More likely to affect smaller frequencies
