population size and ecosystems Flashcards
define ecology
the study of living organisms within a habitat and their interactions with both biotic and abiotic factors
define ecosystems
a characteristic community of interdependent species interacting with the abiotic components of their habitat
define habitat
the place in which an organism lives
define population
a group of interbreeding organisms of the same species occupying a particular habitat
define community
interacting population of two or more species within a particular habitat
define environmental resistance
environmental factors that slow down population growth
define biotic factors
living factors within the environment e.g pathogens and predators
define abiotic factors
non-living environmental factors
e.g air temperature, oxygen availability
define niche
the specific role and position a species plays within a particular ecosystem
define carrying capacity
the maximum number of individuals a population can sustain within a particular environment
define intraspecific
competition between members of the same species
define interspecific
competition between members of different species
define random sampling
method of sampling when abiotic factors are uniform
define systematic sampling
method of sampling when there is a change in abiotic factors
define photosynthetic efficiency
a measure of the ability of a plant to absorb light energy
define GPP
rate of production of chemical energy in organic chemicals by photosynthesis
define NPP
gross primary productivity minus the energy used up by the producers in respiration in a year
define biological productivity
the rate at which biomass accumulates in an ecosystem
define secondary productivity
the rate at which consumers accumulate energy from assimilated food in biomass in their cells of tissues
define biomass
the dry mass of organic matter of a group of organisms in a particular habitat
name some factors which population numbers are dependant upon?
describe them
- birth rate - the reproductive capacity of a population
- death rate - mortality rate
- immigration - movement of individuals into a population of the same species
- emigration - movement of individuals out of a population of the same species
what would happen to the population size if the birth rate and immigration > death rate and emigration?
population would increases
how many phases of population growth are there?
what are they?
4 STAGES:
1. lag phase
2. exponential phase or log phase
3. stationary phase
4. death phase
outline the lag phase
SLOW RATE OF REPRODUCTION
- periods of intense metabolic activity such as enzyme synthesis.
- in sexually reproducing organisms, this phase represents the time for individuals to reach sexual maturity
- for year in a nutrient broth, it represents the time taken for them to hydrate
outline the exponential/log phase
RAPID INCREASE as more individuals are available for reproduction
- no factors limiting growth
- bacterial cells double per unit time
- rapid rate of reproduction cannot be maintained indefinitely
- environmental resistance occurs at the end of log phase
what environmental resistance will occur for bacteria in a flask?
- glucose availability
- overcrowding
- competition
- toxic waste build up
what environmental resistance will occur for rabbits on a new island?
- predation
- parasitism and disease
- overcrowding
- competition for food
outline stationary phase
BIRTH RATE (or cell division) IS EQUAL TO DEATH RATE
- factors are limiting growth
- population has reached carrying capacity
- actual number of individuals will fluctuate around carrying capacity in response to environmental changes
- yeast change from asexual reproduction to sexual reproduction as they reach stationary phase and some individuals survive as spores
outline death phase
environmental factors now result in death rate becoming greater than birth rate.
for example, glucose running out in a nutrient broth or build-up of ethanol when growing yeast
define density dependant factors
factors that have a greater effect the larger the population size (more likely to slow down population growth size)
give 3 examples of density dependant factors
- disease and parasitism
- food availability
- toxic waste build up
define density independant factors
factors that have an effect regardless of the size of the population (more likely to cause population crash)
give 3 examples of density independant factors
- flood
- fires
- sudden temperature changes
describe predator-prey relationship as a factor affecting population size
- as population density of a particular prey increases, more are eaten by the predator
- as a result, the prey population decreases
- when prey population increases there is more available food for the predator
- as a result the predator population increases
what does competition have an impact on?
- potential breeding success
- survival of an organism
what are the two types of competition and describe them
- intra-specific = competition between members of the same species
- inter-specific = competition between members of different species
state the concept of Niche
only one species can occupy a particular niche within an ecosystem
how would you increase consistency when random sampling?
place the bottom of the quadrat at the co-ordinate
outline the method of sampling in an area where abiotic variables are uniform
- set up a 10m x 10m grid and use random numbers to generate coordinates to determine where to place the 1m^2 quadrat
- count the number of species or percentage cover in each quadrat
- repeat at 10 random coordinates
- calculate a mean for each species
describe how you would 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 or percentage cover of plant species
- this grid would be visited periodically (e.g every year for 10 years) to gain results for comparison
describe the sampling technique used in an area where there is a change in an abiotic factor
- quadrat is unsuitable
- a line along the gradient is used : called a transect
describe a line transect
used to describe the difference in plants as you enter a wood
- record species touching 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 density or percentage cover of plant species in each quadrat
- as there is an environmental gradient, measure varying abiotic factor
outline how to set up a transect
- run a 20m tape measure along the area to sample
- for a line transect, identify the species touching the transect every half metre along the tape measure
- for a belt transect, place a quadrat down every half metre along the transect and calculate percentage cover
- repeat multiple times within the area to ensure a representative sample. for a belt transect, calculate mean
write a method for a practical to investigate biodiversity in an open meadow
- choose a 10m x10m area and use random generator to generate coordinates to determine where to place the quadrat
- in these areas, measure pH, light intensity and soil moisture to ensure they are constant
- use two tape measures to create a set of axis of which coordinates can be read
- record percentage cover for the chosen species. this can be done by recording how many of the quadrats 100 squares contain the chosen species. a square should only be counted if half or more is covered
- at each coordinate, a measure of the independent variable should be taken. For example, if investigating light intensity, a photometer can be used to take a reading for the light intensity at each coordinate
- repeat sampling every month for a year
what is the source of all energy for an ecosystem?
light energy from the sun trapped by photosynthesis provides the energy for almost all ecosystems
what is detritus?
dead particulate organic matter
describe trophic levels
feeding levels within an ecosystem
- producers are the first trophic level
- energy flows between the sun, producers and consumers
- on the death of the organisms some energy remains locked up as organic material
- decomposers are not classed as a trophic level
why are decomposers not classed as a trophic level?
they feed from every level
why does an ecosystem rarely support more than 5 trophic levels?`
a lot of energy is lost at each level
- heat from respiration
- excretion
- inedible parts`
state the formula for photosynthetic efficiency
(energy incorporated into photosynthetic products / total light energy falling onto plant) x 100
why is not all light energy that falls on a plant absorbed by photosynthetic pigments?
- some light is reflected (green)
- some light passes through the leaf (transmitted)
- some light missed the photosynthetic parts (chloroplast)
- about 50 units that are absorbed are the ‘wrong wavelength’
what is the formula for NPP?
NPP = GPP - respiration
why do not consumers take all potential energy?
- herbivores cannot eat all of the vegetation available to them
- some vegetation is eaten by other herbivores
- cows feed on plant material
To find the dry mass of plants ecologists dry samples in an oven at 65C.
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 there is no burning or combustion
as energy is passed along the food chain why is energy lost from one trophic level to the next?
- energy in egested molecules - mostly cellulose
- energy lost as heat generated in respiration
- energy remains in inedible parts of animals (e.g bones, horns, fur)
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
to reduce the amount of energy lost as heat during respiration so more energy is available to produce biomass
what is the equation for gross ecological efficiency?
(energy in trophic level / energy in previous trophic level ) x 100
why do values for gross ecological efficiency differ in different ecosystems?
many aquatic organisms do not 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.
formula for photosynthetic efficiency?
(energy incorporated into photosynthetic products / total light energy falling onto a plant) x 100
what it net primary productivity?
gross primary productivity minus the energy used up by the producers in respiration in a year. it is therefore the energy in the plants biomass
how is net primary productivity calculated?
GPP - respiration
what is gross ecological efficiency?
a measure of how much energy is transferred from one trophic level to the next
how is gross ecological efficiency calculated?
(energy in trophic / energy in previous ) x 100
how is energy lost at each trophic level?
heat, through respiration, excretion, egestion
why can a pyramid of energy never be inverted?
energy is always lost from one trophic level to the next and it cannot be produced
what aspect of a pyramid of energy overcomes problems associated with pyramids of numbers and biomass?
never inverted, averaged over time
define succession
the change in structure and species composition of a community over time
what is primary succession?
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 is known as a sere
describe the process of succession
- pioneer species are the first organisms to colonise the rock e.g lichens
- 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 are established
- as the soil builds up and nutrient levels increase, deep rooted shrubs appear
- over a very long period of time trees ad 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 many have been damaged by fire or tree felling
- soil is already present
- can produce different climax communities
what is succession affected by?
- migration
- competition
- facilitation
as succession occurs, what happens to species diversity?
increases
how does migration affect succession?
the arrival of spores, seeds and animals is vital for succession to progress.
immigrating non-native species may spread themselves widely, alternating communities
how does competition affect succession?
interspecific competition
how does facilitation affect succession?
positive interactions between species that become increasingly significant as succession progresses.
- mutualism is an interaction between 2 different species that is beneficial to both e.g. flowering plants and their pollinators
state 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. this improves nitrate levels in the soil
how can human interference affect natural development of the climax community during succession?
- grazing : livestock eat the grasses and other plants (die so no succession)
- 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 soil
- industry : coal mining and quarrying of stone
- urban development : building of new roads and buildings
