Unit 2 - Ecosysrems and Ecology

Ecosystems

Ecosystems

Made up of the organisms and physical environment and the interactions between the living and non-living components within them.

Community

All the populations living in the same area at the same time.

Species

A group of organisms sharing common characteristics that interbreed and produce fertile offspring.

Binomial name

A scientific name composed of two parts; the genus and the species. E.g. Homo sapiens (human), Giraffa camelopardalis (giraffe).

Population

A group of organisms of the same species living in the same area at the same time, and which are capable of interbreeding.

Population density

The average number of individuals in a stated area e.g. gazelles km^-2.

Factors affecting population

• Natality (birth rate)

• Mortality (death rate)

• Migration; immigration (moving in) and emigration (moving out)

Habitat

The environment in which a species normally lives.

Niche

The particular set of biotic and abiotic conditions and resources to which an organism or population responds.

Abiotic factors

The non-living, physical factors that influence the organisms and ecosystem, e.g. temp, sunlight, water, pH, salinity and pollutants.

Biotic factors

The living components of an ecosystem - organisms, their interactions or their waster - that directly or indirectly affect another organism. E.g. relationships, habitat, resources.

Fundamental niche

The full range of conditions and resources in which a species could survive and reproduce. E.g. a fishes fundamental niche could be

Realised niche

The actual conditions and resources in which a species exists due to biotic interaction.

Why is a populations realised niche smaller than its fundamental niche?

You need to take into account biotic factors e.g. competition, resources, mates.

Why can't two populations with the same niche co-exist?

One will always be better adapted and out compete the other. If many species live together they always have slightly different needs/responses and aren't in the same niche.

Limiting factors

Factors that prevent or slow down the growth of a population/community/organism as it reaches it carrying capacity.

Carrying capacity

The max. number of a species or 'load' that can be sustainably supported by a given area.

The butterfly effect

A term from chaos theory and refers to small changes that happen in a complex system that lead to seemingly unrelated results that are impossible to predict,

Population dynamics

The study of the factors that cause changes to population sizes. E.g. migration, natural disasters, interactions.

Types of interactions between organisms

Competition, predation, mutualism, parasitism, herbivory

Competition

Organisms in an ecosystem have some effect on every other organism in that ecosystem. Also any resources in any ecosystem exists only in a limited supply.

Intraspecific competition

Competition for resources between organisms in the same species. E.g. male red squirrels compete for mates. This tends to stabilise population numbers and produces the S-curve.

Interspecific competition

Competition for resources between organisms belonging to different species e.g. red squirrels vs grey squirrels for food.

Results of interspecific competition

• A balance, when both species share the resources

• Or, one species totally outcompetes the other - "competitive exclusion"

Predation

When one animal, the predator, eats another animal, the prey. E.g. lions eating zebras.

Mutualism

Relationship between two or more species in which all benefit and none suffer. E.g. Oxpeckers eat tickers of rhinos.

Parasitism

A relationship between two species in which one species (the parasite) lives on the other (the host) and causes it harm. E.g. vampire bats and intestinal worms.

Herbivory

An animal (herbivore) eating a green plant. However some plants have defence mechanisms against this such as spines (some cacti) or thorns.

Exponential geometric growth

When the numbers within a population change. For example, when bacteria reproduce asexually by splitting in two (binary fission) so if you start with one bacterium, there will be 2, 4. 8, 16 etc, if there is no limiting factors slowing growth.

S and J population curves

A generalised response of populations to a particular set of conditions (abiotic and biotic factors).

S-curves

Start with exponential growth with no limiting factor at first. But, above a certain population size (or carrying capacity), the growth rate gradually slow down, resulting in a population of a constant size.

Environmental resistance

The area between the exponential growth curve and the S-curve.

J-curves

Show a 'boom and bust' pattern. The population grows exponentially at first then suddenly collapses (dieback). Often the population exceeds the carrying capacity on a long-term or continuing basis before the collapse occurs (overshoot). It does not show the gradual slowdown of population growth with increasing population size.

Similarities between predation and competition

• Both can be species interaction

• In both two individuals are involved

• Can both lead to stable equilibrium in populations

Differences between predation and competition

• Predation negatively affects one species but competition negatively affects both

• Predation only involves animals but competition can involve animals and plants

• In predation one species (predator) depends on the other but in competition neither are dependent on the other

Respiration

The conversion of organic matter (food) into carbon dioxide and water in all living organisms, releasing energy.

Respiration formula

Glucose + Oxygen -> Carbon dioxide + Water (and Energy)

C6H12O6 + 6O2 -> 6H2O + 6CO2 (and energy)

Aerobic respiration

Respiration with plenty of oxygen.

Aerobic respiration formula

C6H12O6 + 6O2 -> 12H2O + 6CO2 + energy

Anaerobic respiration

Respiration with little or no oxygen.

Anaerobic respiration formula

Glucose -> Lactic acid (+ energy released)

Where does respiration take place?

The mitochondria

Processes that release energy from living organisms

Movement, respiration, sensitivity, growth, reproduction, excretion, nutrition

Photosynthesis

The process by which green plants make their own food from water and carbon dioxide using energy from sunlight. Green plants respire in the dark and photosynthesis/respire in the light. Water reaches leaves from the roots through transpiration.

Carbon dioxide + water --Light--Chlorophyll--> Glucose + Oxygen

6CO2 + 12H2O --Light--Chlorophyll--> C6H12O6 + 6O2

Where does photosynthesis happen?

In the chloroplast; specifically the palisade cells

Why are the photosynthesis and respiration systems important?

• They explain where energy goes from and to

• Explain why it's lost from systems

• Explains where there are interactions between species

• Explain why there is always a producer at the start of food chain

Respiration as a system

• Inputs: Organic matter (glucose) and oxygen

• Process: Oxidation inside cells

• Outputs: Useful energy e.g. heat

• Transformations: Stored chemical energy into kinetic energy

Photosynthesis as a system

• Inputs: Sunlight as energy source, carbon dioxide and water

• Outputs: Glucose from energy and oxygen

• Transformation: Light energy to chemical energy, to organic matter, chlorophyll

Compensation point

When all carbon dioxide that plants produce in respiration is used up in photosynthesis, the rates of the two processes are equal and there is no net release of either oxygen and carbon dioxide. Usually occurs at dawn/dusk with low light intensity.

Food chain

The flow of energy from one organism to the next. It shows the feeding relationships betweens species in an ecosystem.

Example of a food chain

Vegetation->herbivorous insects->carniviorous insects->spiders->toads->foxes

Trophic levels

Feeding levels that organisms are grouped into. Usually start with a primary producer (plant) and end with a carnivore at the top of the chain - top carnivore.

How can organisms that obtain energy be classified?

Producers & consumers.

Producers

a. Autotrophs (green plants) which make their own food from carbon dioxide and water using energy from sunlight.

b. Chemosynthetic organisms which make their own food from their simple compounds e.g. ammonia or methane, do not need sunlight and are bacteria found in deep oceans.

Consumers (or heterotrophs)

Feed on autotrophs or other heterotrophs to obtain energy (herbivores, carnivores, detritrivores etc)

Primary producers (green plants)

1st trophic level. Autotrophs. Functions include being habitats for other organisms and providing the energy requirements of all the other trophic levels.

Primary consumers (herbivores)

2nd trophic level. Heterotrophs. Functions include dispersing seeds.

Secondary consumers (carnivores and omnivores)

3rd trophic level. Heterotrophs. Functions include pollinating flowers and removing old and diseased animals from the population.

Tertiary consumers (carnivores and omnivores)

4th trophic level. Heterotrophs. Functions include pollinating flowers and removing old and diseases animals from the population.

Decomposers (bacteria/fungi)

Obtain their energy from dead organisms by secreting enzymes that break down the organic matter.

Detritivores (snails, slugs, maggots, vultures)

Derive their energy from detritus or decomposing organic matter - dead organisms or faeces or parts of an organism e.g. shed skin from a snake, a crab carapace.

Functions of decomposers and detritivores

Provide crucial service for ecosystem by breaking down dead organisms, releasing nutrients back into the cycle and controlling the spread of disease.

Food web

A complex network of interrelated food chains.

Difference between food chain and food web

Food chains only illustrate a direct feeding relationship between one organism and another in a single hierarchy, whereas, food webs are the reality of how animals feed in an entire ecosystem and involve many more organisms and one may eat several species.

Bioaccumulation

Increase of concentration of a toxin in an organism.

Biomagnification

Increase in concentration of a toxin in food.

Ecological pyramids

Graphic models of the quantitative differences between amounts of living material stored at each trophic level of a food chain.

Benefits of ecological pyramids

• Allow easy examination of energy transfers and losses

• Give an idea of what feeds on what and what organisms exist at the different trophic levels

• Help to demonstrate that ecosystems are systems that are in balance

Pyramid of numbers

Shows the number of organisms at each level in a food chain at one time - the standing crop. The unit are number per unit area.

Advantages of pyramids of numbers

Simple, easy method of giving an overview and is good at comparing changes in population numbers with time or season.

Disadvantages of pyramids of numbers

• Don't allow for juvenile/immature forms

• Numbers may be too great to represent accurately

Pyramid of biomass

Contains biomass (mass of each individual x no. of individuals) at each trophic level. units normally g m^-2 or kg km^-3.

Biomass

The quantity of (dry) organic material in an organism, a population, a particular trophic level or an ecosystem.

Advantages of pyramids of biomass

Overcome some of the problems of pyramids of numbers.

Disadvantages of pyramids of biomass

• Organisms must be killed to measure dry mass

• Only uses samples from populations, so it is impossible to measure biomass exactly

Pyramid of productivity

Shows the rate of flow of energy or biomass through each trophic level. It shows the energy or biomass being generated and available as food to the next trophic level during a fixed period of time.

Advantages of pyramids of productivity

• Most accurate, show the actual energy transferred and allows for rate of production

• Allows comparison of ecosystems based on relative energy flows

Disadvantages of pyramids of productivity

• Difficult and complex to collect energy data as rate of biomass production over time is needed

• Problem of assigning a species to a particular trophic level when they may be omnivorous

Why are top carnivores in trouble?

Because of the loss of energy from each trophic level. There is only so much energy available and that is why big, fierce animals are rare. It is hard for them to accumulate enough energy to grown to a large size and to maintain their bodies.

Trophic efficiency

Only 10% of the energy in one trophic level is transferred to the next. Lots of the energy is used in respiration or lost in heat to the environment.

The fate of solar radiation reaching the Earth

31% of light is reflected, 17% is absorbed my inorganic materials

Earth's solar constant

Energy leaving the Sun is about 63 million joules per second per square metre (Js^-1 m^-2). The solar energy reaching the top of the atmosphere of Earth is 1,400 J s^-1 m^-2 (or 1,400 watts per second).

Productivity

The conversion of energy into biomass over a given period of time. It is the rate of the growth or biomass increase in plants and animals. It is measured per unit area per unit time, e.g. metre ^2 per year. (m^-2 yr^-1)

Gross

The total amount of something made as a result of activity e.g. profit from a business or salary from a job.

Gross productivity (GP)

The total gain in energy or biomass per unit area per unit time. It is the biomass that could be gained by an organism before any deductions.

Net

The amount left after deductions are made e.g. costs of production or deductions of tax and insurance from a salary. It is what you have left and is always lower than the gross amount.

Net productivity (NP)

The gain in energy or biomass per unit area per unit time that remains after deductions due to respiration. Results from all organisms respiring to stay alive some some energy is used in living than growing.

Primary & secondary

Primary is to to with plants. Secondary is to do with animals.

Primary Productivity

Autotrophs are the base unit of all stored energy in any ecosystems. Light energy is converted into chemical energy by photosynthesis using chlorophyll within the cells of plants.

Gross primary productivity (GPP)

The total gain in energy or biomass per unit area per unit time by green plants. It is the energy fixed (or converted from light to chemical energy) by green plants by photosynthesis. But some of this is used in respiration.

Net primary productivity

The total gain in energy or biomass per unit area per unit time by green plants after allowing for losses to respiration. This is the increase in biomass of the plant - how much it grows - and is the biomass that is potentially available to consumers (animals) that eat the plant.

NPP formula

NPP = GPP - R(respiratory loss)

The fates of the total amount of plant material

• Lost from food chains as it dies and decays

• Eaten by herbivores which means it is removed from primary productivity

Amount of biomass produced varies

a. Spatially - some biomes have higher NPP rates than others - e.g. tropical rainforest vs tundra

b. Temporally - many plants have season patterns of productivity linked to changing availability of basic resources - light, water and warmth

Gross secondary productivity (GSP)

The total energy/biomass assimilated (taken up) by consumers and is calculated by subtracting the mass of fecal loss from the mass of food eaten.

GSP formula

GSP = food eaten - fecal loss

Net secondary productivity (NSP)

The total gain in energy or biomass per unit area per unit time by consumers after allowing for losses to respiration.

NSP formula

NSP = GSP - R(respiratory losses)

Energy in carnivores

Assimilate 80% of energy in food while 20% is egested. They use their energy chasing animals so higher energy intake is offset by increased respiration during hunting.