Population Size and Ecosystems C1 Flashcards
what is a population?
a group of interbreeding organisms of the same species, occupying a particular habitat
what four factors cause ecosystems to be dynamic and population numbers to fluctuate?
birth rate
death rate
immigration
emigration
define birth rate
the reproductive capacity of a population
define death rate
the proportion of individuals dying per unit time
define immigration
the movement of individuals into a population of the same species
define emigration
the movement of individuals out of a population of the same species
when describing population growth of bacteria and yeast, would it be correct to use the term ‘birth rate’? If not, what could be used instead?
No
we can use rate of cell division instead
how is a population of an equilibrium species controlled?
within a stable habitat through competition
what is the pattern of growth if conditions of temperature and nutrients are favourable?
sigmoidal (S-shaped)
give the 4 labels of the phases of the population growth curve and what they mean
1) lag phase - reproduction rate ≥ death rate
2) log phase - reproduction rate > death rate
3) stationary phase - reproduction rate = death rate
4) death phase - reproduction rate < death rate
what are the axis labels of the population growth curve?
number of organisms (x) and time (y)
describe lag phase
slow rate of reproduction
period of intense metabolic activity such as enzyme synthesis
in sexually reproducing organisms this represents the time for individuals to reach sexual maturity
for yeast placed in nutrient broth it represents the time it takes for them to hydrate
describe log phase
rapid increase in population numbers as more individuals available for reproduction
no factors limiting growth
bacterial cells double per unit time
rapid rate of reproduction can’t be maintained indefinitely
environmental resistance occurs at the end of log phase
what environmental resistance will occur for rabbits on a new island?
predation, parasitism and disease and competition for food/habitats
what environmental resistance will occur for bacteria in a flask?
run out of space, lack of oxygen/nutrient availability, competition for nutrients eg glucose and oxygen and toxic waste build up
describe stationary phase
birth rate or cell division is equal to death rate
factors limiting further growth
population reached carrying capacity
actual number of individuals will fluctuate around carrying capacity in response to environmental changes
yeast change from asexual to sexual reproduction as they reach stationary phase and some individuals survive as spores
define carrying capacity
the maximum number of individuals a population can sustain within a particular environment
describe death phase
environmental factors result in death rate greater than birth rate eg glucose running out in a nutrient broth or build up of ethanol when growing yeast
how to calculate population increase from a graph
when increase is very large, the range of numbers is too great to plot a graph on a linear scale
therefore a log10 scale is used so each mark on the population scale is 10x the previous mark
what are two factors that distinguish what will slow down population growth and what might cause a population crash?
density dependent factors and density independent factors
describe density dependent factors and give examples
factors that have a greater effect the larger the population size and more likely to slow down the population growth rate
eg: disease and parasitism, food availability and toxic waste build up
describe density independent factors and give examples
factors that have an effect regardless of the size of the population and is more likely to cause a population crash
eg: floods, fires and sudden temperature changes
describe predator-prey relationships
as the population density of a particular prey increases, more are eaten by the predator
as a result, the prey population decreases
when the prey population increases there is more available food for the predator
as a result, the predator population increases
describe competition and give the two types of competition
it has large impact on the potential breeding success and survival of an organism
intra-specific competition
inter-specific competition
what is the difference between intra and inter specific competition?
intra-specific is competition between members of the same species
inter-specific is competition between members of different species
define the concept of niche
the ecological role and position that an organism takes within an ecosystem, dependant on the resources it uses
only one species can occupy a particular niche within an ecosystem, one species will always outcompete another
how can the concept of niche be demonstrated?
by growing two species of the protozoan ‘Paramecium’ in flasks in a lab
both species can grow well in flasks when grown separately but when grown together ‘P-aurelia’ outcompetes ‘P-caudatum’ for food so the population of ‘P-caudatum’ falls
what is the type of competition demonstrated in the protozoan experiment?
inter-specific
what is the study of abundance and distribution called?
biogeography
what is the sampling technique in an area where abiotic variables are uniform?
1 - set up a 10m x 10m grid and use random numbers to generate coordinates to determine where to place the 1m^2 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
why is percentage cover used instead of counting?
it is quite difficult to count individual plants such as grass or moss
using a gridded quadrat can give a better estimation
a quadrat divided into 10 x 10 squares would mean each square is represented by 1%
what is the sampling technique if you wanted to 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/percentage cover of plant species
review/visit periodically to gain results for comparison
what is the sampling technique in an area where there is a change in an abiotic factor?
random placement of quadrats is unsuitable if there is an environmental gradient such as altitude or light intensity
a line transect is used
describe a line transect
it would be used to describe the difference in plants as you enter a wood etc
record the species touching the transect at each point
describe a belt transect
provides more data than a line transect
place a quadrat at regular intervals along the transect
estimate the density/percentage cover of plant species in each quadrat
since an environmental gradient is involved, it is useful to measure the varying abiotic factor
describe how to set up a transect
1 - run a 20m tape measure along the area to sample
2 - for a line transect, identify the species touching the transect every half metre along the tape measure
3 - for a belt transect, place a quadrat down every half metre along the tape measure and calculate percentage cover
4 - repeat multiple times within an area to ensure a representative sample and for a belt transect, calculate a mean
describe kite diagrams
they can be drawn when looking at percentage cover
usually presented in a table and end diagram looks similar to a ‘kite’
give examples of abiotic factors
light intensity, amount of water and nutrients, temperature and altitude
give examples of biotic factors
living bacteria, competition for resources, the amount of predators and disease
define ecosystem
a characteristic community of interdependent species interacting with abiotic components in their habitat
can be large or small
what is the source of all energy for an ecosystem?
the sun - light energy trapped by photosynthesis
define habitat
the place in which an organism lives
often contains a community of organisms
define community
it is populations of different species living within the same habitat
define trophic levels
feeding levels within an ecosystem
which organisms are in the first trophic level?
producers
where does energy flow through?
the sun, producers and consumers
what happens to energy on the death of organisms?
some remains locked up as organic material
what is detritus?
dead particulate organic matter
why are decomposers not classed as a trophic level?
they feed from every level
draw out a trophic level diagram
https://www.khanacademy.org/science/ap-biology/ecology-ap/energy-flow-through-ecosystems/a/food-chains-food-webs
why does an ecosystem rarely support more than 5 trophic levels?
a lot of energy is lost at each level eg heat from respiration, excretion/indigestion and inedible parts
what is photosynthetic efficiency?
a measure of the ability of a plant to absorb light energy
give the formula of 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?
wrong wavelength reflected
hits non-photosynthetic parts of plant
transmitted straight through the leaf
what is gross primary productivity (GPP)?
it is the rate of production of chemical energy in organic chemicals by photosynthesis (KJ m-2 year-1)
what is net primary productivity (NPP)?
it is the gross primary productivity minus the energy used up by the producers in respiration in a year
therefore the energy in the plants’ biomass/rate at which producers convert energy into biomass
what does NPP represent?
the potential food energy available to heterotrophs in ecosystems
why don’t consumers take all of this potential energy?
some parts of the plant are inedible eg roots and bark
some parts are indigestible eg cellulose
some lost as heat by respiration
what is primary productivity only for?
producers!
define biological productivity
the rate at which biomass accumulates in an ecosystem
define biomass
the dry weight of organic matter comprising a group of organisms in a particular habitat
what do ecologists do to find the dry mass of plants?
dry samples in an oven at 65°C
describe how the ecologists would be confident that all the water had been removed but none of the organic matter had been lost?
repeat until constant mass recorded and ensure there is no combustion
what is secondary productivity?
the rate at which consumers accumulate energy from assimilated food in biomass in their cells/tissues
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 a herbivore
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 (meat)
what is gross ecological efficiency?
a measure of how much energy is transferred from one trophic level to the next
give the formula of gross ecological efficiency
energy in trophic level ÷ energy in previous trophic level x 100
how do values for gross ecological efficiency differ in different ecosystems?
they are often around 10%
oceanic food chains can have high values of around 40%
food chains involving birds and mammals may be as low as 1%
why is there a difference between aquatic GEE and birds/mammals GEE?
many aquatic organisms don’t regulate their body temperature and so save a lot of energy
birds and mammals maintain a high body temperature and this uses up a lot of energy and is therefore less efficient
describe pyramids of energy
can be used to give a quantitative account of the feeding relationships in a community
shows the quantity of energy transferred from one trophic level to another per unit area or volume per unit time
(eg; KJ m2 in one year)
why can a pyramid of energy never be inverted?
energy is always lost from one trophic level to the next
it cannot be produced
what aspect of a pyramid of energy overcomes problems associated with pyramids of numbers and biomass?
it can never be inverted
what causes ecosystems to be dynamic and subject to change?
interactions of the organisms and their environment
what is succession?
the change in structure and species composition of a community over time
what is primary succession? and give an example
the introduction of plants/animals into areas that have not previously supported a community e.g bare rock
what is a sere?
each stage during succession when particular communities dominate
what are pioneer species?
the first organisms to colonise the rock e.g lichens
describe the process of primary succession
pioneer species arrive
these organisms slowly erode the rock, and the accumulation of dead and decomposing organic material leads to the formation of primitive soil
as the soil develops, grasses become established
as the soil builds up and nutrient levels increase, deep-rooted shrubs appear
over a very long period, trees and woodlands become established
this results in a stable, long-lived community known as the climax community
what is secondary succession?
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 4 things is succession affected by?
migration
competition
facilitation
commensalism
describe migration
the arrival of spores, seeds and animals is vital for succession to progress
immigrating non-native species may spread themselves widely, altering communites
describe facilitation
positive interactions between species that become increasingly significant as succession progresses
describe mutualism/commensalism
an interaction between two species that is beneficial to both e.g flowering plants and their pollinators
give two factors that 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 which improves nitrate levels in the soil
give six ways human interference can affect the natural development of the climax community during succession and how?
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 and this can cause erosion of the soil
industry - e.g coal mining and quarrying of stone
urban development - building of new roads and buildings
