Biology 2B Ecosystems

Populations and relationships

Features of populationsDistribution and abundance

• Abundance or size – how many in a population

• Density – the number of organisms per unit area

• Distribution – the location of individuals within an area

Population composition• Sex ratios – number of

organisms of each sex• Age structure – number of

organisms of different ages• Population fertility – the

reproductive capacity of the females

Factors affecting populations

Density independentPhysical (abiotic) factors• Rainfall• Humidity• Temperature• Acidity• SalinityCatastrophic events• Flood• Fire• Drought• Volcanic eruptions• Earthquakes • Tsunamis

Density dependent (biotic factors)• Food supply (abundance or

distribution of prey species) - this becomes more critical as population size and density increases

• Disease - this is easier to spread as population size and density increases

• Parasites - these spread more easily as population size and density increases

• Competition - this becomes more critical as population size and density increases

• Predation (abundance or distribution of predator species) - this becomes more critical as population size and density decreases

Anything that affects health, survival or reproductive success will affect populations

Abiotic factors – both aquatic and terrestrialFactor Effect on survival Measurement

Temperature Temperature affects cell activity – especially enzymes and reactions in the cell.At low temperatures, cellular reactions slow. As the temperature increases the rate of reactions increases.At extremely high temperatures, enzymes and structures can be damaged and the cell can die. If the cell freezes, ice crystals can burst the cell

Thermometer

Light Light is necessary for photosynthesis.It is affected by water depth and shade (eg trees).

Light meter

pH (soil or water) pH affects cell survival by altering proteins. This can damage cell membranes and enzymes in the cell.

pH meterindicators

Salinity (soil or water) Salinity affects water and ion movement into and out of cells. High salt conditions dehydrate cells, low salt conditions can cause cells to swell and burst

Salinity meterConductivity meters

Wind Wind affects wave action in aquatic environments and humidity and water loss in terrestrial environment.

Wind meterAnemometer

Abiotic factors – mainly aquaticFactor Effect on survival Measurement

Wave action Wave action affects the amount of gases (oxygen and carbon dioxide) that can dissolve in the water. The greater the action, the more gases dissolve.

Height in metre (swell)

Water currents These affect the temperature of water at different levels. They can carry nutrients from estuaries and coasts to deeper water.

Radar and infrared satellites

Buoyancy This is a measure of how easy it is to float. It is affected by salinity – the greater the salt content, the more buoyancy there is.

Viscosity This affects movement. The more viscous a material, the more effort is needed to move through it.

Turbidity This is a measure of small particles in the water (eg silt). High turbidity can reduce light penetration and interfere with gill function making it harder to survive.

Secchi disc

Depth The deeper the water, the less light penetrates. The wavelength of light also varies – red penetrates the least far & violet the most.

SonarPlumb line

Gases Oxygen is needed for respiration, carbon dioxide is needed for photosynthesis

Dissolved oxygen meterChemical tests

Abiotic factors – mainly terrestrialFactor Effect on survival Measurement

Amount of water All organisms need water to survive Rain gauge

Humidity This affects water loss from leaves and the effectiveness of sweating and panting (evaporative cooling) in animals

Humidity meterHygrometer

Mineral salts (in soil)

Plants need minerals to grow. Mineral salts affect salinity Salinity meterChemical tests

Soil type This is mainly determined by particle size, mineral salts and organic matter present. These affect water retention, fertility and the type of plants that will grow.

Soil tests

Topography Features such as slope, hills, valleys affect water movement, soil formation or erosion, shade and altitude. All of these affect the growth of plants and the animals they can support.

InclinometersMapping instruments

Altitude Height above sea levels affects oxygen and carbon dioxide levels. Soil quality is also generally less at higher altitudes.

Mapping instruments

Biotic factors – role in ecosystem

• Autotroph – makes its own food

• Producer – provides energy to a food chain by photosynthesis (using light to convert carbon dioxide and water into sugars) or chemosynthesis (using chemical reactions to make energy or organic compounds)

• Heterotroph can not make its own food, so must eat other organisms

• Consumer – gains its energy by eating other organisms

• Decomposer – gains its energy by feeding on dead or decaying living matter

Biotic factors – feeding relationships

• Herbivore – eats plants • Carnivore – eats animals • Detrivore – eats dead or

decaying matter• Saprophyte – eats dead or

decaying matter • Predator – animal that eats

another • Prey – animal species eaten by

predator • Parasite – lives or feeds in or on

a host without killing it• Host – organism that a parasite

feeds on

Associations and relationships

Relationship Is beneficial to Has no effect on Causes harm to

Predator-prey Predator Prey

Competition Both

Inhibition One One

Symbiosis One or both

Mutualism Both

Commensualism One One

Parasitism Parasite Host

Amensualism One One

Collaboration Both

Disease Pathogen Host

Associations and relationships 2

Predator – prey – predators feed on prey• Numbers of predators depend on number of

prey• There are usually more prey than predators• A rise in prey numbers leads to a rise in

predator numbers• A fall in prey numbers leads to a fall in

predator numbers• The change in predator numbers follows the

change in prey numbers• The lag times in rise and fall depend on the

speed of reproduction of both species

Parasite – host and Disease – hostrelationships show the same patternUsually parasites and disease organisms (pathogens) are smaller than their hosts, so host numbers may be smaller than numbers of the parasite or disease organisms

Associations and relationships 3• Competition – rivalry between two

organisms/species for the same resources – both are harmed

• Inhibition or antibiosis – one organism directly hinders the growth of another

Amensalism – one organism is harmed, but the other is not benefited or harmed itself

Biotic factors – associations

• Symbiosis – one or both species benefito Mutualism – both species benefit and both need

each other eg lichen, pollinationo Commensalism – one species benefits and the other

is unaffected eg epiphytic ferns

o Parasitism – one organism benefits and the other is harmed

• Collaboration - working together so both benefit but they can work without each other eg herbivores herding together so it is easier to avoid predators, seed dispersal