19. POPULATIONS IN ECOSYSTEMS Flashcards
Define what a population is
A group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed
Define a habitat
A place where a community of organisms live
Define an ecosystem
A biological community of interacting organisms and their physical environment
Define a community
All the populations of different species living in a habitat
Name the three stages of a population growth curve
Lag phase, exponential phase, carrying capacity
Compare the birth rate and the death rate in lag phase
Birth rate > death rate
Explain why population growth is slow in the lag phase, even though resources are plentiful
Because the number of individuals is low
Compare the birth rate and the death rate in the exponential phase
Birth rate > death rate
Explain why population growth is fast in the exponential phase
Resources are plentiful and there are no limiting factors
Define carrying capacity
The maximum population size that an environment can support
Compare birth and death rates in carrying capacity
Birth rate = death rate
Explain why the population size is stable in carrying capacity
Because resources are limiting
Recall the 7 limiting factors of population growth rate and carrying capacity
Food, space, water, mates, parasites/pathogens/disease, light intensity/availability, nesting sites
Which extra phase do bacterial populations experience at the end of the their population growth curves?
Death phase
Why do bacterial populations experience a death phase after their carrying capacity?
As O2 is used up they respire anaerobically, producing ethanol. This becomes toxic and kills the bacteria.
Within a habitat, different species occupy different niches. What are niches governed by?
Adaptations to biotic and abiotic factors, e.g. food sources
What is the benefit of species occupying different ecological niches?
There is less competition for resources
What type of competition exists between individuals of the same species?
Intraspecific
What type of competition exists between individuals of different species?
Interspecific
What is the competition exclusion principle?
When two species are competing for limiting resources, the one that uses the resources more effectively will ultimately eliminate the other
How will increasing competition affect population size / population growth rate / carrying capacity?
Increasing competition will decrease population size / population growth rate / carrying capacity
How will decreasing competition affect population size / population growth rate / carrying capacity?
Decreasing competition will increase population size / population growth rate / carrying capacity
Why do population size fluctuate seasonally?
Because resource availability fluctuates seasonally, therefore so does competition, and so does population size
Which type of species show seasonal fluctuations in population size?
Prey, herbivores, primary consumers
Why do predator population sizes show regular, cyclic population sizes?
Because the predator population size will fluctuate after the prey population size. As the pre population decreases, intraspecific competition increases and the predator population decreases
Out of the predator and prey, which population fluctuates first, and which fluctuates after?
The prey population fluctuates first (because it fluctuates with the seasons), and the predator population fluctuates after (because it is dependent on the prey population)
Define succession
Succession is a change in a community over time due to changing abiotic factors
What is a pioneer species?
The first species to colonise a habitat (after a disturbance)
How do pioneer species make the habitat more suitable / less hostile for other species?
They change the abiotic factors
Give two examples of how pioneer species may change the abiotic factors within a habitat to make them more suitable for other species
They may contain nitrogen fixing bacteria, which will increase the nitrogen-containing compounds in the soil. They may be decomposed by saprobiotic bacteria, increasing the nutrient content of the soil.
What happens to the population of the pioneer species as the population of the second species increases?
It decreases
Why does the pioneer species eventually disappear?
Because the second species is better adapted, and so outcompetes the pioneer species
What happens to the biodiversity of an ecosystem as succession proceeds?
It increases
What is a climax community?
The final stable community in succession
Give three features of a climax community
- it is stable
- the abiotic factors are constant
- the populations are stable (at carrying capacity)
Name some factors that may affect the size of the community in a climax community
Nutrient availability, any factor that affects the rate of photosynthesis, disease, predators, space for nests, and competition
Name some natural resources that humans use for their own benefit
Timber, crude oil, salt, metal ores
Because the human population is so large, we are using our natural resources unsustainably. What does unsustainable mean?
We are using resources at a faster rate than they can replenish naturally
What two things do we need to manage the conflict between to maintain sustainability?
Human need and conservation
Define conservation
Conservation is the maintenance of biodiversity by restoring ecosystems
Conservation is an active process. What does this mean?
It requires human participation and intervention
Name four reasons for conservation
Maintaining / increasing biodiversity, protecting endangered species, conserving sources of medicine, reducing erosion and eutrophication
What is the main loss to humans in the process of conservation?
Financial, e.g. cost of outlay or loss of income
Name the process of sustainable timber production
Coppicing
Why is coppicing sustainable?
Trees are kept alive whilst wood is harvested from them
Describe rotational coppicing
Sections of forest are coppiced one at a time, leaving other sections to regrow so they are ready to be harvested again later
Why does managing / halting succession increase global biodiversity?
By managing / halting succession, you will maintain different habitats and different food sources, increasing biodiversity
When would you use a quadrat to sample species?
When estimating the number of species in an area
Which type of sampling is quadrats?
Random sampling
To be representative, why must sample sizes be large?
To minimise the effect of anomalies
To be representative, why must samples be chosen at random?
To avoid bias
What two ways can an area to be quadratted by mapped?
Using coordinates and using numbered areas
If an area to be quadratted is mapped using coordinates, how would you choose your random sample?
Using a random coordinate generator
If an area to be quadratted is mapped using numbers, how would you choose your random sample?
Using a random number generator
Describe how you would calculate the total estimated population in an area using quadrats
- Count the individuals in each quadrat
- Find the sum of the individuals in each quadrat and divide by the numner of quadrats (giving the average individuals per quadrat)
- Multiply by the total area
When would you use a belt transect to sample a species?
When calculating achange in apopulation/community over adistance in response to achanging environmentalfactor.
Which type of sampling are belt transects?
Systematic sampling
Describe a disadvantage of using belt transects
They may not go through all representative areas
What piece of equipment could be used to lay a belt transect?
Tape measure
How do the quadrats have to be laid along the belt transect?
At regular intervals
As well as counting the individuals in each quadrat along the transect, what else must you do?
Measure the abiotic factor using appropriate equipment
Which statistical test would you apply to your data from a belt transect, and why?
Spearman’s Rank, to calculate the correlation coefficient, which will calculate the strength of the correlation between two variables
What is a kite diagram?
A diagram used to represent the abundance of species along a transect
When would you calculate percentage cover when sampling?
When there are too many individuals to count, e.g. grass
Why is using sampling to estimate the number of animals in an ecosystem problematic?
They are motile. So you could count the same organism twice and some not at all.
Name the technique used to estimate animal populations in ecosystems
Mark, release, recapture
What do we have to ensure about the method we use to mark individuals?
It doesn’t come off
It doesn’t harm the individuals
It doesn’t increase their chance of being predated
It doesn’t change their behaviour
Why do we leave a period of time between releasing the marked individuals, and recapturing the second sample?
To allow them to randomly disperse back into the population
Recall the equation used to calculate the estimated population of animals using the mark, release recapture method
Estimated total population = number of organisms initially caught x number of organisms in second sample / number of marked organisms recaptured
Apart from an appropriate marking method and leaving sufficient time to disperse, what other conditions are must be assumed for mark, release recapture to be valid?
No migration
The same sampling method is used each time
No breeding / births or death
The sample size is large enough
