Populations in ecosystems Flashcards
Define ecology
- the study of interrelationships between organisms and their environment
Define abiotic
- non living components of the environment
Define biotic
- living components of the environment
Define species
- a group of organisms that are similar in terms of shape, physiology, genetics and behaviour which can interbreed to produce fertile offspring
Define ecosystem
- dynamic systems/units made up of a community and all the interacting biotic and abiotic features in that specific area. Energy flows and there is cycling of elements within the system. These systems can rage from very small to fairly large
Define population
- group of interbreeding organisms of one species that occupy the same habitat at the same time
Define community
- populations of different species living and interacting in a particular place at the same time
Define habitat
- place where an organism normally lives, characterised by physical conditions and the other types of organisms present
Define microhabitat
- smaller units within a habitat with their own microclimate
Define niche
- term used to describe how an organism fits into its environment (where it lives and what it does there) this includes all the abiotic and biotic conditions to which the organism is adapted and how the organism responds/behaves to them
Define natural ecosystem
- an ecosystem not managed or altered by human activity
Define artificial ecosystem
- an ecosystem that is managed or altered by human activity
Define intraspecific competition
- individuals of the same species compete with one another for resources (eg. Water, food, breeding sites). Availability of these resources determines population size
Define interspecific competition
- Individuals of different species compete for resources (eg. Food, light, water)
Which factors are biotic?
- food availability
- predators
- competition from other organisms
- infection from pathogens
Which factors are abiotic?
- sunlight
- temperature
- pH
- water
- minerals
- salinity (salt levels)
Bird species occupying different niches in the same habitat - The question is, how?
- These different species occupy different niches in the same ecosystem to reduce interspecific competition. They feed on different species (biotic condition) and at different water depths (abiotic condition) .
What affects the size of a population?
- Limiting factor
- Carrying capacity
What is a limiting factor?
- the limiting factor is the one whose magnitude limits the rate of the whole process – often it is the factor in shortest supply.
What is carrying capacity?
- the maximum population size that can be maintained over a period of time in a particular habitat
What can be classed as a limiting factor for a population?
- pH
- Water
- light
- carbon dioxide
- predators
- disease
- space
- mates
- food
- oxygen
What affects the size of a population?
- food supply
- predation
- disease
- climate change
How does food supply affect the size of a population?
- Large amount of food = organisms can breed more successfully.
- Food shortage = higher death rate which results in a slow or negative population growth.
How does predation affect the size of a population?
- Organisms which have lots of predators will have a slower rate of population growth as more will be killed by predators
How does disease affect the size of a population?
- Reduces the population by killing organisms. In densely populated areas, disease can spread quickly = may wipe out large population
How does climate change affect the size of a population?
- Organisms that cannot adapt to changes in climate are less likely to survive, reproduce and pass on advantageous alleles
Draw and label the standard growth curve
- organisms acclimatising to new conditions- very few individuals
- Reproduction rate is low as is the growth of the
population - lag phase
- Rapid increase in population– growing conditions are favourable with plentiful resources. Rate of reproduction is greater than
mortality rate - Log/exponential phase
- stationary phase
- rate of growth equal to rate of death
- Stable population; minor fluctuations from changing environment
- Carrying capacity of the environment
- decline/death phase
- Death rate is greater than rate of generation
What are the abiotic factors affecting the size of a population?
- light
- temperature
- pH
- water and humidity
How does light affect the size of a population?
- More light = greater rate of photosynthesis: greater rate of plant growth + seed production. Carrying capacity for plants increased (+ animals that feed on them)
How does water and humidity affect the size of a population?
- Humidity affects transpiration rate, and so limited populations found where water is scarce. Only species able to adapt to dry conditions thrive
How does pH affect the size of a population?
- Populations of organisms thrive where pH is close to their optimum. As pH affects enzyme action, only certain species adapt to regions with particular pH values
How does temperature affect the size of a population?
- Carrying capacity reduced in plants + cold blooded animals if temperature not close to optimum: enzymes work slowly & metabolic activity reduced – high temps could lead to denaturation.
- Carrying capacity also reduced in warm blooded animals if conditions far from optimum: more energy expended in maintaining body temp – therefore less energy used for growth and reproduction
What is Gause’s competitive exclusion principle?
- Where populations of two species occupy the
same niche, one will normally have an advantage over the other. If conditions remain the same this will lead to interspecific competition and the
removal of one species
Why is it difficult to prove that competition could be the reason for variations in population?
- There are many other factors that influence population size e.g. abiotic factors.
- A causal link has to be established to show that
competition is the cause of an observed correlation. - There is a time lag in many cases of competition.
- Data on population sizes are not always reliable
Give examples of characteristics of predators
- Camouflage (hide in surroundings)
- Biological ‘traps’ nets, webs
- Enhanced sound detection + a little patience
- Echolocation
- Speed (short bursts) , & sheer power
- High intelligence
- Enhanced sense of smell
- Poisons such as venom
- Ability to sense body heat
- Sharp teeth & claws
Give examples of characteristics of prey
- Camouflage (hide in surroundings)
- Disguise & distraction
- Protective ‘armor’ for defense
- Poisons + aposematic colour
- The ‘playing dead’ tactic
- Strength in numbers
- Incredible speed to escape
- Mimicry (may be toxic or non-toxic)
Why is there a lag of 1-2 years between the lynx
and the hare?
- Predator numbers take time to establish after an increase in prey
Predator-prey relationships are dynamic. Describe & explain what this means
- Dynamic: ever-fluctuating, with predator/prey
influencing one another’s evolution
What are the three basic principles of population of predator and prey?
- Predation occurs when one organism is consumed by another.
- Predators have evolved and adapted to catching their prey.
- Prey have evolved to avoid predators
explain the shape of the curve at points 1- 5
- Point 1 – increase in prey numbers, few predators and limited intraspecific competition for resource
- Point 2 – increase in predator numbers as more food available; steady increase in reproduction rate
- Point 3 – decline in prey numbers due to hunting from predators, but also competition for the resources available (birth rate < death rate)
- Point 4 – decrease in predator numbers as
prey population has fallen; competition for food, space etc ; some predators will have to migrate from habitat to find food - Point 5 – subsequent increase in prey numbers as there are now fewer predators and with smaller prey numbers, there is less competition for resources
What are the five sampling methods for mobile organisms?
- stick
- sweep net
- pitfall trap
- Tull green funnel
- pooter
Describe how to use a mark, release and recapture method for mobile organisms
- A large sample of animals from a population is caught, counted and marked in an appropriate way. The marked animals are released back into their habitat.
- Make sure that the marking does not harm the animal or affect their survival chances.
- Allow time for the marked animals to randomly distribute.
- After a suitable length of time, collect and count a second sample, and count the number of animals already marked using the Lincoln Index
What is the formula for the Lincoln index?
Estimated population size is:
Total number of individuals in 1st sample x
total number of individuals in 2nd sample/ Number of marked individuals recaptured
What are the assumptions for the mark, release and recapture method?
- The marked individuals released from the first sample distribute themselves evenly within the whole population and have sufficient time to do so.
- The proportion of marked to unmarked individuals in the second sample is the same as the proportion in the population as a whole.
- The population has a definite boundary so that there is no immigration/emigration.
- There are few if any births/deaths within the population.
- The marking method is not toxic to individuals, and it does not make the individuals more conspicuous and hence more liable to predation.
- The mark is not rubbed off during the investigation
Suggest one precaution needed when marking the lemurs to make sure they estimate of the number of lemurs is valid. (1)
- Marking does not affect survival
The mark-release-recapture method can be used to estimate the size of a fish population.
a) Explain how. (4)
-Catch sample of fish, mark + release;
- make sure marking doesn’t harm fish or affect their survival chances, allow time for marked fish to randomly distribute;
- collect and count a 2nd sample and count how many of the individuals are marked.
- Population size is = sample 1 x sample 2 / number of marked in second sample.
The mark-release-recapture method can be used to estimate the size of a fish population.
b) Suggest why this method can produce unreliable results in a very large lake. (1)
- Marked fish less likely to distribute randomly in
the lake OR less likely to catch marked fish in 2nd sample
How could quadrats be used to measure the abundance of daisies?
- Arrange two tape measures at right angles
to each other in the study area - Use a random number generator or table to obtain a series of coordinates
- Place the quadrat at the intersection of each pair of coordinates and count the number of
organisms of interest inside
Why might the sample NOT be representative of the whole population?
- Sampling bias - hence the need for
random sampling - Chance
What could be recorded from a quadrat?
- abundance
- frequency
- percentage cover
- species richness
What is abundance?
- the number of individuals of a species in a given space/area
What is frequency?
- likelihood of a particular species occurring in a quadrat e.g. 15 flowers in 30 quadrat squares = 50% frequency.
What is measuring frequency useful for?
- Useful for hard to count species, and is rapid
What is the disadvantage of measuring frequency?
- but gives no information about density and detailed distribution of a species
What is percentage cover?
- estimate of area within a quadrat that a particular species covers.
Why is measuring percentage cover useful?
- Useful for hard to count species, is rapid and do not need to collect individual data about species
What is a disadvantage of measuring percentage cover?
- less useful if species occur in overlapping layers
What to do if asked to estimate the total number of individuals of a species in an area?
- calculate the mean number per m^2 using the
quadrat sampling, then multiply up by the total m^2 for the area
Describe how you could estimate the size of a population of sundews in a small marsh
- Place tape measures at right angles to set up a
coordinates grid; - Obtain random numbers using a calculator to get coordinates;
- Place quadrat at the position of the coordinates & count number of sundews inside;
- Repeat for at least 10 samples + calculate mean number per quadrat;
- Multiply mean number per quadrat by number of quadrats in the small marsh area.
Suggest and explain how digesting insects helps the sundew to grow on soil with very low concentrations of some nutrients
- digestions of proteins in the insect; provides the plant with amino acids
What factors need to be considered when choosing quadrat?
- size
- number to place
- position
How can size influence quadrat choice?
- Depends on type of species present / if not
evenly distributed, would be better to do many small quadrat samples rather than a few large ones – more representative
How can number to place influence quadrat choice?
- Depends on how many samples you want to take- more samples, more reliable, more representative
How does position influence quadrat choice?
- Random sampling: use grid coordinates +
random number generator…avoids bias
How could a student compare the population of daisies in 2 areas of the college grounds?
1.Mark out a 10 x 10 metre area using large tape measures in both locations A and B.
2. Use the random number generator function on your calculator to pick coordinates along the tape measures.
3. Place the bottom left corner of the quadrat at that point (or intersection)
4. Count the number of daisies in the quadrat and record it in a suitable table.
5. Repeat steps 2-4 for 9 further readings.
6. Calculate mean no. of daisies per quadrat for each area.
7. To get the total population in the location, multiply the mean by how many square metres there are in the area.
8. By taking other data such as the physical
environmental (abiotic) factors at each location you can hypothesise why the populations are different.
Why does quadrats need to be random?
- to avoid bias
Why is it important to place the bottom left of the quadrat at the coordinate point?
- improves consistency in recording data
How can you measure how a distribution of a species changes across a habitat?
- use a transect - a line (or belt) along a sample area, where there is an environmental gradient (a gradual change in environmental conditions along a distance). Quadrats are placed in succession - at regular intervals - and data recorded. This is systematic sampling (not random)
Measure how the distribution of organisms’ changes across a woodland path
- Lay a tape measure along the environmental gradient e.g., across a woodland path (at right angles to woodland) to see the effects of changes in light intensity on plants.
- Place a quadrat at regular intervals;
- Record what you need from each quadrat;
- Repeat using several parallel transects to
ensure data is representative.
How could you measure how biodiversity changes using a quadrat?
- look at the number of different species in each quadrat
what might you expect to see in the daisy
population as you move your quadrat closer
to the regions in the sunshine?
- Plants need light for photosynthesis, so you’ll find more daisies growing in quadrats exposed to greater sunshine (i.e., closer to the sun in this picture)
Transect B is called an ‘interrupted’ transect,
because we place quadrats at regular intervals along the transect line instead of across the whole length. Can you suggest when this type of transect would be used?
- When the sample area is too large and / or
you are short on time to investigate
What is succession?
- The changes that occur in a community in an
area over time due to changes in abiotic factors
and the species present
What is primary succession?
- The development of an ecosystem in an area where no life previously existed
What is secondary succession?
- Process of re-stabilisation following a disturbance / damage in an area where life had
previously formed an ecosystem
Describe how primary succession occurs
- Area is first colonised by pioneer species;
- Pioneers change the conditions of the habitat;
- Environment is now less hostile to other species;
- New species colonise (plants and animals) once there is this change and these will eventually outcompete the previous species e.g. for light needed for photosynthesis;
- Biodiversity gradually increases;
- Eventually a climax community is achieved
What qualities should pioneer species have?
- Tolerance to extreme conditions
- Ability to fix nitrogen to provide a nutrient supply (when lacking)
- Ability to photosynthesise so not dependent on animal species for food
- Rapid germination of seeds
- Rapid production of wind-dispersed seeds/spores to colonize distant regions
As succession proceeds, the number of species in an area increases. This creates more habitats and niches for wildlife, and a greater variety of food sources for animals. We also see more complex food webs form and an increased biomass (notably during mid succession).
Eventually a mature, stable ‘climax community’ will become established with the ability to reproduce itself. This is the final stage of ecological succession. At this point, there is usually a dominant plant and dominant animal species. Describe and explain why there is a
decline in the level of biodiversity at this point.
- Competitive exclusion – dominant species outcompete others for resources (light, space), leading to their decline or local extinction.
- Reduced disturbances - in climax community, disturbances that provide opportunities for pioneer + intermediate species to establish
are reduced. - Lower availability of new niches - they become occupied by dominant species, limiting the introduction and survival of new species
How do plants get dispersed into new areas?
- Seeds blowing on wind;
- Seeds attached to animals;
- Seeds carried in intestines of animals after feeding on plants (then out in faeces)
What are climax communities?
- the long-term stable community at the end of succession.
What is plagioclimax?
- humans can manipulate the process creating an artificial climax community
What are two ways succession is managed?
- Burning heather and grazing sheep on moorland prevents it reaching its climax
community. This destroys young tree saplings. If this were to be stopped, then the ecosystem develops naturally and succession would resume. - Despite their legal protection, Hen harriers are killed on grouse moors because of their negative impact on grouse-shooting. Grouse-shooting is an important land use in the uplands and benefits conservation because it retains heather
moorland. Shooting also generates income for landowners. The conflict brings into opposition ‘hunters’ who own much of the uplands; and ‘conservationists’ who attach value to birds
What is conservation?
- The method of maintaining ecosystems and the living organisms that occupy them
biodiversity), by human intervention
Why should conservation occur?
- ethics (respect for other living organisms)
- economic reasons (extensive gene pool may prove to harbour valuable resources in future)
- cultural and aesthetic reasons (appreciation for beauty - habitats and organisms enrich our lives)
- personal (to maintain our planet, our life support system)
