3.5 Population and Ecosystem

Biotic

A part of the environment of an organism that is living

Birth rate

The reproductive capaticty of a population: the number of new individuals derived from reproduction per unit time.

Carrying Capacity

The maximum number around which a population fluctuates in a given environment.

Community

Interacting populations of two or more species in the same habitat at the same time

Climax Community

a stable end point where there are no further successional stages

Equilibrium Species

Species that control their population by competition rather than by reproduction and dispersal

Fugitive species

Poor at competition and rely on a large capacity for reproduction and dispersal to increase their numbers

generation time

when cell numbers double at discrete time intervals

Ecology

The branch of biology that deals with the relations of organisms to one another and to their physicak surroundings

Ecosystem

A characteristic community of independent species interacting with the abiotic components of their habitat

Environmental Resistance

Refers to the environmental factors that sow down population growth

Immigration

The movement of individuals into a population of the same species

Limiting Factor

A factor that limits the rate of a physical process by being in short supply. An increase in a limiting factor increases the rate of the process

Niche

The role and position of a species in its habitat

Population

An interbreeding group of organisms of the same species and occupying a particular habitat.

Community

Interacting populations of two or more species in the same habitat at the same time

Habitat

The place in which an organism lives

Abiotic

A part of the environment of an organism that is non living

Describe lag phase

Slow growth due to physiological adaption of cells to culture conditions. They are synthesising enzymes and replicating DNA

Describe log phase

As the nutrient availability is high

Describe stationary phase

Growth and death of cells counterbalance each other resulting in no net increase in cell numbers.

Population has reached its carrying capacity for that environment

What causes a reduced growth rate in a population

depletion of nutrients

build up of toxic waste

Describe death phase

Death rate exceeds growth rate resulting in a net loss of viable cells

Examples of environmental resistance - biotic

Available food
Overcrowding
Competition
Accumulation of toxic waste
Predation
Disease

Examples of abiotic environmental resistance

Water
Temperature
Light intensity

Intraspecific competition

competition within a species

Interspecific competition

competition between species

Define density-dependent factor

These factors affect a greater proportion of the population if the population is denser. They are biotic factors

Examples of density dependent factors

disease

Define density-independent factor

The effect is the same regardless of the size of the population and is usually a sudden change in a abiotic factor

Example of density independent factor

Flood or fire

Describe how a population size is regulated by negative feedback

If the population rises above the set point

Define abundance

The number of individuals in a species in a given area or volume

How can animal abundance be measured

capture-mark-recapture experiments

Kick sampling in a stream

How can the abundance of a plant species be measured

Using a quadrant to calculate the mean number of individuals in several quadrants of known area

Estimating percentage cover

Estimating percentage frequency

Define distribution

The area or volume in which the organisms of a species are found

State two sources of error in collecting data for pyramids of biomass

Roots not collected
Water is included in the measurement of biomass

What is the source of energy in food chains

sunlight

How do some animals occupy more than one trophic level

They feed in different levels at different times of the year

Describe the role of detritivores

Feed on small fragments of organic debris which is called detritus

Describe the role of decomposers

Obtain nutrients from dead organisms and animal waste

Define trophic level

Feeding level

The number of times that energy has been transferred between the sun and successive organisms along a food chain

Define biomass

The mass of biological material in living

Summarise a detritus food chain

detritus -> detritivore -> decomposer

State the factors that affect the factors of the food chain

-The more energy fixed in photosynthesis

• If energy is transferred more efficiently
• Larger ecosystems can support longer food chains
• Three dimensional environments have longer food chains than two dimensional habitats

State what a transect is

A useful technique that displays the variation in organisms and its correlation with a changing abiotic factor

What is a belt transect

Shows abundance data for a given area at measured distances along a transect. A quadrant is placed at each co-ordinate along the transect.

State how energy lost limits the number of steps in a food chain

The amount of remaining energy in the food chain may not be great enough to support viable populations at higher trophic levels

Why can not all light energy hitting the leaf be used in photosynthesis

Some energy is reflected by the waxy cuticle

Some energy is the wrong wavelength

Some energy is transmitted through the leaf as it does not strike a chloroplast

How is energy lost in a food chain

as heat in respiration

energy in molecules are egested and excretion

How is biomass lost in a food chain

some of its food will not be digestible and will be egested as faeces

Excess amino acids will be converted to nitrogenous waste and will be excreted as uric acid

Some of it will be used in respiration and will be lost as heat

Gross primary productivity

The rate of production of organic molecules by photosynthesis in a given area per unit time

Units of GPP

kJ m-2 y-1

Define net primary productivity

The organic molecules assimilated

Primary productivity

The rate at which energy is converted by producers into biomass

Secondary productivity

The rate at which consumers convert the chemical energy of their food into biomass

Trophic efficiency

The percentage of energy at one trophic level which is passed on to the next trophic level

How do farmers increase productivity of their livestock

Keeping animals in barns during winter will reduce the heat loss by respiration. The energy saved can be used to increase biomass instead.

Feed animals more digestible food

Why do herbivores have a lower secondary productivity than carnivores

The protein rich diet of carnivores is more readily and efficiently digested

Why do aquatic food chains tend to be longer than terrestrial ones

The do not use as much energy to move as there is buoyancy from water

Why do cold blooded organisms lose less energy

Cold blooded organisms aren't losing energy to heat from respiration

Why do smaller animals lose more energy

Have a high sa:vol ratio so will lose more heat and will have to respire at a higher rate to keep warm

What do pyramids of biomass measure

The amount of energy converted into living tissue at the different trophic levels

Why might a pyramids of numbers by inverted

A large organism can sustain many smaller organisms

A low biomass of organisms can sustain a larger biomass at the next trophic level because the organisms reproduce rapidly and thus supply continuous nourishment

Why must pyramids of energy by up-right

energy cannot be created or destroyed
During the transfer of energy

Pioneer species

First organism to colonise a new area in an ecological succession

Succession

A change in species composition and communities over time

Primary succession

The change in structure and species composition of a community over time in an area that has not previously been colonised

What are the stages of succession called

seres

Describe an example of primary succession

Lichens arrive on the rock as spores blown in by the wind or carried by animals

Lichens erode the rock and as they decompose a little soil builds up

mosses appear

Soil formed will eventually be deep enough to allow grasses to take root

Does biodiversity increase or decrease because of succession

increase

equation for NPP

NPP = GPP - R

Secondary succession

The changes in a community following the disturbance of damage to a colonised habitat

Where does secondary succession start

Where there is seeds or spores available in the soil

Mutualism

An interaction between organisms of two species from which both derive benefit

Name factors affecting succession

immigration

Competition

Facilitation

Commensalim

An interaction between organisms of two species from which one benefits but the other is not affected.

Describe ammonification

1) Detritivores consume dead organisms and animal waste products and saprophytic bacteria and decomposers secrete enzymes
2) Proteases digest proteins into amino acids
3) Deaminases remove amino groups from amino acids and reduce them to ammonium ions
4) Digestion products are absorbed by decomposers

Describe nitrification

The ammonium ions in decomposition are converted to nitrites and then nitrates

Nitrosomonas

ammonium to nitrite

Nitrobacter

converts nitrite to nitrate

Why do Nitrosomonas and Nitrobacter require aerobic conditions?

The nitrogen atom in the ammonium ion progressively loses hydrogen atoms and gains oxygen atoms and so the reactions are oxidations

What is the energy released in the oxidation reactions in nitrification used for

to synthesise organic compounds in a process called chemosynthesis

Describe denitrification

Anaerobic bacteria converts nitrate ions to nitrogen gas

What do denitrifying bacteria use nitrates for

as a source of oxygen for respiration

What is a common cause for anaerobic conditions in nature

water logging

Name some nitrogen fixing bacteria

Azotobacter and Rhizobium

Describe nitrogen fixation

The conversion of nitrogen gas into ammonium by nitrogen fixing bacteria

What enzyme do nitrogen fixing bacteria have

nitrogenase

Where does nitrogen fixation by Rhizobium occur

in the root nodules of legumes

Describe the mutualistic relationship between rhizobium and legumes

Nitrogen fixation requires much ATP and the Rhizobium gains the sugars for respiration from the plants photosynthetic product.

Plant provides a pigment called leghaemoglobin which binds to oxygen in the root nodule to create anaerobic conditions

Excess ammonium and amino acids are exported to the plant for protein synthesis

Why does nitrogen fixation require anaerobic bacteria

nitrogenase activity is inhibited by high oxygen concentrations

State human activities that can improve the circulation of nitrogen in agricultural soils

Ploughing fields to improve soil aeration

Draining land so it reduces anaerobic conditions

Artificial nitrogen fixation

Large amounts of animal waste

Planting fields of legumes

What will increase atmospheric carbon dioxide lead to

increased greenhouses effect