Populations and Ecosystems Flashcards
What is a population?
group of interbreeding organisms of the same species, occupying a particular habitat
What factors is the fluctuations in populations dependent on?
birth rate
death rate
immigration
emigration
What is the birth rate?
The reproductive capacity of a population
What is the death rate?
the proportion of individuals dying per unit time
What is immigration?
the movement of individuals into a population of the same species
What is emigration?
the movement of individuals out of a population of the same species
What would happen to the population size if birth rate and immigration> death rate and emigration?
It would increase
When describing population growth of bacteria and yeast, would it be correct to use the birth rate? If not, what could be used?
Cell Division
how is the population of an equilibrium species controlled within a stable habitat?
through competition
What happens if conditions of temperature and nutrients are favourable in a population?
the usual pattern of growth is sigmodal (S-shaped)- e.g. bacteria placed into a fresh nutrient solution or rabbits newly introduced to an island
What happens on the lag phase?
-Slow rate of reproduction
-Period of intense metabolic activity such as enzymes synthesis
What does the lag phase represent in sexually reproducing organisms such as rabbits?
the time it takes for individuals to reach sexual maturity
What does the lag phase represent for yeast placed into a nutrient broth?
the time it takes for them to hydrate
What happens in the exponential/log phase?
-rapid increase in population numbers as more individuals are available for reproduction
-no factors limiting growth
-this rapid rate of reproduction cannot be maintained indefinitely
what occurs at the end of log phase?
environmental resistance
what is environmental resistance?
all factors that may limit the growth of a population
what happens in the stationary phase
-birth rate or cell division is equal to death rate
-factors are limiting any further growth
-the population has reached it’s carrying capacity and the actual number of individual will fluctuate around this in response to environmental changes
what is carrying capacity?
the maximum number of individuals a population can sustain within a particular environment
What happens to yeast as they reach stationary phase?
change from asexual reproduction to sexual reproduction and some individuals survive as spores
what environmental resistance will occur for bacteria in a flask?
-glucose availability
-overcrowding
-competition
-toxic waste build up
what environmental resistance will occurs for rabbits in a new island?
predation, parasitism and disease, competition for food
What happens in the death phase?
Environmental factors now result in death rate becoming greater that birth rate e.g. glucose running out of nutrient broth or build up of ethanol (toxic) when growing yeast
How is a population increase calculated from a graph?
A log10 scale
When is a log10 scale used?
used when a population increase is too large (e.g. in a population of bacteria in a test tube, the range of numbers is too great to plot on a linear scale)
What is a log10 scale?
each mark on the population scale is 10x the previous mark
what is the formula for a log scale?
no of…at day… - no of…at day… / …-…
antilog10… - antilog10…/ …-…
How is the size of a population regulated?
-by the balance between the birth and death rate
what are the sizes of populations like?
-populations do not remain constant in size, although the fluctuations are normally small
where do most species in a population lie?
near an equilibrium- the carrying capacity
What are the factors that affect population size?
-Density dependent factors
-Density independent factors
What are density dependent factors?
Factors that have a greater effect the larger the population size (more likely to slow down population growth rate)
What are examples of density dependent factors?
-Disease and parasitism
-Food availability
-Toxic waste build up
What are density independent factors?
Factors that have an effect regardless of the size of the population (more likely to cause a population crash?- e.g. floods, fires, and sudden changes in temp
What happens as the population density of a particular prey (e.g. snowshoehare) increases?
more are eaten by the predator (e.g. lynx), as a result the prey population then decreases
What happens when the prey population increases?
there is more food available for the predator, as a result the predator population increases
What does the two types of competition do?
has a large impact on the potential breeding success and survival of an organism
What are the two types of competition?
intra-specific competition
inter-specific competition
what is intra-specific competition?
competition between members of the same species
what is inter-specific competition?
competition between members of different species
What is the concept of niche?
only one species can occupy a particular niche within an ecosystem, one species will always outcompete the other
How can the concept of niche be demonstrated?
-by growing two different species of the protozoan Paramecium in flasks in a lab
-both grow well in flasks when grown separately, but when grown together P.aurelia P.caudatum for food, so the population of P. C falls
What type of competition is demonstrated in the experiment including the protozoan Paramecium?
Interspecific as only one species can occupy one niche
What is biogeography?
the study of species abundance and distribution
How do you work out biogeography in an area where abiotic variables are uniform?
-set up a 10 m x 10 m grid and use random numbers to generate coordinates to determine where to place the 1m2 quadrat
-count the number of species or percentage cover in each quadrat
-repeat at 10 random coordinates
-evaluate a mean for each species
what must i say when mentioning random sampling in the exam?
say how I would ensure my sampling is random, e.g. through generation of random coordinates
What should you do for consistency when placing down a quadrat?
always place the bottom of the quadrat at the coordinate
How is density calculated?
Count the number or individuals in 10 quadrants and calculate a means, data may be represented as a bar graph
why is it useful to estimate percentage cover?
it is difficult to count individual plants such as grass or moss
What would you do 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 x10m grid
-Generate random coordinates for quadrat placement and record the number or percentage cover of plant species
-This grid would be visited periodically (every 10 years) to gain results for comparison
What would you do if you wanted to sample in an area where there is a change in an abiotic factor?
-Random placement of quadrants are unsuitable if there is and environmental gradient such as altitude or light intensity
-A line along the gradient is used instead
-This is called a transect
What does a line transect do?
-Used to describe the difference in plants as you enter a wood.
-Simply record the species touching the transect at each point
What does a belt transect do?
-Provides more data than a line transect
-Place a quadrat at regular intervals along the transect
-Estimate the density or percentage cover of plant species in each quadrat.
-As there is an environmental gradient, it is useful to also measure the varying abiotic factor, e.g. light intensity
How is a transect set up?
-Run a 20m tape measure along the area to sample
-For a line transect, identify the species touching the transect at 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 an area to ensure a representative sample. For a belt transect repeat and calculate a mean
When can kite diagrams be drawn?
when looking at percentage cover
What is the distribution of a species determined by?
A range of different variables which can be grouped into abiotic (non-living) factors and biotic (living) variables.
What are the abiotic factors?
-light intensity
-amount of water and nutrients
-temperature
What are the biotic variables?
-bacteria which are living
-competition for resources
-the amnount of predators and disease
What type of factors are density dependent factors?
biotic
What type of factors are density independent factors?
abiotic
What are the three sampling techniques I must be familiar with?where fit th
-Random quadrat sampling within a given area where the abiotic factors are uniform
-Interrupted belt transects and line transects where you want to estimate the densities across an area where biotic factors my vary
-Mark-Release-Recapture- for animals that move within
What is the equation for mark capture release?
number of first captured x number of captured/ and marked/ number of marked when recaptured
What is an ecosystem?
-A characteristic community of interdependent species interacting with abiotic components in their habitat
-Can be large or small
What is the source of energy for an ecosystem?
Light energy from the sun trapped by photosynthesis provided the energy for almost all ecosystems (other than those based on chemosynthesis)
What is a habitat?
A place where in which an organism lives -often contains a community of organism
What is a community?
populations of different species living in the same habitat
What is photosynthetic autotrophic?
organisms with the ability to make complex organic molecules like glucose from simpler inorganic ones like CO2 and H2O, using energy from sunlight
What are trophic levels?
Feeding levels within an ecosystem
What are the first trophic level?
producers
How does every flow in trophic levels!
between the sun, producers and consumers
What happens on the death of organisms (tropic levels)?
some energy remains locked up as dead organic material
what is detritus?
dead particulate organic matter
Why are decomposers not classed as a trophic level ?
They feed from every level
What are the trophic levels?
-1. producers (plants)
-2. primary consumers (herbivores)
-3. secondary consumers (carnivores)
-4. tertiary consumers (top carnivores)
Why does an ecosystem rarely support 5 levels?
-some energy is released at each trophic level- e.g. during respiration (lost as heat) and excretion (urea with energy will in it or lost in egested material
-because energy is lost between each trophic level, very little energy remains at level 5 (not enough to sustain another trophic level)
what does photosynthetic efficiency depend on?
external factors such as light intensity and temperature
What is photosynthetic efficiency?
a measure of the ability of a plant to absorb light energy and convert this light energy to chemical energy
Why doesn’t all light energy that falls on a plant get absorbed by photosynthetic
pigments?
-Wrong wavelength to be absorbed by pigments light outside the visible spectrum e.g. infrared/UV isn’t used in photosynthesis
-Green light is reflected by chlorophyll pigment (even if it hits the chlorophyll pigment)
-Transmitted straight through the least (does not hit chlorophyll pigment)
What is gross primary production (GPP) ?
the rate of production of chemical energy in organic chemicals by photosynthesis (kJ m-2 year-1).
What is net primary productivity? (NPP)
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.
What does NPP represent?
the potential food energy available to heterotrophs in ecosystems.
l
on average what is gpp and npp?
l GPP is 0.2% of incident global sunlight energy and NPP is 0.1%.
What does NPP also represent?
represents the potential food/chemical energy available to heterotrophs in ecosystems
How is NPP calculated?
Net primary productivity = GPP – Respiration
Why don’t consumers take all of this potential energy? (NPP)
Some parts of a plant are inedible – roots and bark.
Some parts of a plant are indigestible – cellulose
What is primary productivity all about?
producers
What does the gpp in the npp calculation represent?
the rate at which products of photosynthesis are formed (glucose)
what does npp represent in the npp calculation?
energy left over after respiration is used to make make plant dry carbon biomass (stored as starch /lipids or is used to make new cells e.g. phospholipids/ dna/proteins)= energy available to primary consumers
What does respiration represent in the npp equation?
A large amount of glucose is used up in respiration by plant/ energy lost in heat
What is biological productivity?
the rate at which biomass accumulates in an ecosystem
what is biomass?
the dry weight of organic matter comprising a group of organisms in a particular habitat
what is npp (in terms of rate)?
rate at which producers convert energy into biomass.
What is the NSP equation?
NSP = GSP - R
NSP= (ingested- (Egested + excreted))- respiration
What is nsp in the nsp equation?
new biomass in consumer (dry mass of carbon molecules =new cells/tissues)
what is gsp in the nsp equation?
food consumed - fibre/cellulose not digested/absorbed
what is r in the nsp equation?
glucose used up in respiration = energy lost as heat
What do ecologists do to find the dry mass of plants?
dry samples in an oven at 65°C.
how would the ecologists be confident that all the water had been removed but none of the organic matter had been lost? (dry samples in an oven)
Repeat until constant mass recorded and ensure there is no burning or combustion
What is secondary productivity?
the rate at which consumers accumulate energy from assimilated food in biomass in their cells or tissues.
What causes the loss from the food chain at each level as energy is passed along it from one trophic level to another?
Energy in egested molecules – mostly cellulose.
Energy lost as heat generated in respiration.
Energy remains in inedible parts of animals e.g. horns, bones and fur.
why do carnivores have more efficient every conversion that herbivores?
Protein is more rapidly and easily digested than cellulose.
A lot of cellulose is lost in the faeces of a herbivore.
why do 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). (endothermic metabolism)
What is gross ecological efficiency?
a measure of how much energy is transferred from one trophic level to the next.
What is the GEE equation?
GEE= energy in trophic level/energy in previous trophic level x 100
what are fish’s blood like?
ectothermic (cold blooded)- don’t need heat from respiration
What are the values for GEE in different ecosystems?
•They are often around 10%.
•Oceanic food chains can have high values, around 40%.
•Food chains involving birds and mammals may be as low as 1%.
What is the difference in the values for GEE because of?
-many aquatic organisms don’t regulate their body temperature and so save a lot of energy.
-birds and mammals maintain a high body temperature (endothermic) and this uses up a lot of energy and is therefore less efficient
what are the units for npp?
KJ-2 . year-1
What is the equation for photosynthetic energy?
energy incorporated into photosynthetic products/total light energy falling on the plant
What causes ecosystems to change over time?
Interactions of the organisms and their environment
What are nitrate ions needed for?
synthesis of DNA, RNA, amino acids, protein
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
What is the process of primary succession into a climax community?
-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 become established.
-As the soil builds up and nutrient levels increase, deep rooted shrubs appear.
-Over a very long period of time trees and woodlands become established.
-This results in a stable, long-lived community known as the climax community.
What are the features of a climax community?
-doesn’t change further over time (succession has finished)
-community in equilibrium consisting of a stable community of dominant species
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 is succession affected by?
migration
competition
facilitation
What is migration in succession?
- the arrival of spores, seeds and animals is vital for succession to progress. Immigrating non-native species may spread themselves widely, altering communities.
What is facilitation in succession?
- positive interactions between species that become increasingly significant as succession progresses.
-Mutualism is an interaction between two different species that is beneficial to both, e.g. flowering plants and their pollinators.
What is competition in succession?
interspecific competition
As succession occurs, what happens to species diversity?
Increases
How do primary and secondary succession differ?
Secondary succession is much more rapid as soil is already present.
What are 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.
What can human interference affect and what are the examples?
affect natural development of the climax community during succession e.g.
•Grazing
•Moorland
•Farming
•Industry
•Urban Development
What is grazing?
Grazing: livestock such as sheep eat the grasses and other plants.
What is moorland management?
•Moorland management: heather colonisation is controlled by burning.
What does farming do?
ploughing and growth of crops by monoculture stops trees and shrubs from getting established.
What does deforestation do?
trees are cut down and this can cause erosion of soil
What is industry?
coal mining and quarrying of stone.
What is urban development?
building of new roads and buildings
What can pyramids be used to do?
give a quantitative account of the feeding relationships in a community
What does a pyramid of energy show?
quantity of energy transferred from one trophic level to another per unit area/volume per unit time. e.g. kilo joules per square metre of an ecosystem in one year (kJ/m2/yr).
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, cannot be produced
What aspect of a pyramid of energy overcomes problems associated with pyramids of numbers and biomass?
never inverted
What is the definition of ecology ?
The study of living organisms within a habitat and their interactions with both biotic and abiotic factors.
What is the detention of niche?
The specific role and position a species plays within a particular ecosystem.
What is random sampling?
Method of sampling when abiotic factors are uniform
