UNIT 2

THE ECOSYSTEM

2.2 PRINCIPLES OF PYRAMIDS

Principle of pyramids

• A pyramid is a graphical representation or model of the quantitative differences between the amounts of living material stored at each trophic level of a food chain.

• They allow us to easily examine energy transfers and losses.

• They give an idea on what feeds on what and what organisms exist at the different trophic levels.

Principle of pyramids

• They also help to demonstrate that ecosystems are unified systems; that they are in balance.

• It is often drawn from the autotrophic level up.

• It can be used to examine how the population of a certain species affects another.

PYRAMID OF NUMBERS

A pyramid of numbers shows the number of organisms at each trophic level in a food chain.

Pyramid of NumbersThe length of each bar gives a measure of the relative numbers. Pyramids have producers at the bottom, usually in the greatest number. Most are broad at the base, but some may have a large single plant as the producer, like a tree, so the base is one individual which supports many consumers.

foxes

rabbits

grass

blue tits

caterpillars

tree

Pyramid of numbers

90 blue tits

2000 caterpillars

1 sparrowhawk

1Oak tree

Pyramid of numbers

• ADVANTAGE: This is a simple easy method of giving an overview and is good for comparing changes in population numbers over different times or seasons.

• DISADVANTAGE: All organisms are included regardless of their size. Numbers can be too great to represent accurately.

PYRAMID OF BIOMASS

• An ecological pyramid of biomass shows the relationship between biomass and trophic level by quantifying the amount of biomass present at each trophic level.

• Biomass = mass of each individual x number of individuals at each trophic level.

• Biomass is the quantity of (dry) organic material in an organisms, a population, a particular trophic level or an ecosystem.

PYRAMID OF BIOMASS

• Biomass represents chemical energy stored in the organic matter of a trophic level.

• The units of a pyramid of biomass are units of mass per unit area, often grams per square meter (g m - ²) or volume of water (g m -3) or as energy content (joules , J)

PYRAMID OF BIOMASS

PYRAMID OF BIOMASS

PYRAMID OF BIOMASS • There are some exceptions to the pyramid of biomass, particularly in oceanic ecosystems where the producers are phytoplankton (unicellular green algae). Phytoplankton reproduce fast bat are present in small amounts at any one time. As a pyramid represents biomass at one time only, e.g. in winter, the phytoplankton bar may be far shorter than that of the zooplankton which are the primary consumers.

Zooplankton

4.0 g m -2 phytoplankton

21.0 g m -2

PYRAMID OF BIOMASS

• ADVANTEGES: Overcomes the problems of pyramids of numbers.

• DISADVANTAGES: – only uses samples from populations, so its

important to measure biomass exactly. – Organisms must be killed to measure dry mass.– The time of the year that biomass is measured

affects the result (the shape of the pyramid would depend an the season)

Pyramids of productivity

• Refer to the flow of energy through a trophic level and invariably show a decrease along the food chain.

• It shows the energy being generated and available as food to the next trophic level during a fixed period of time.

• Show the flow of energy over time.• Measured in J m-2 yr-1 or kJ m-2 yr-1

PYRAMID OF PRODUCTIVITY

A pyramid of productivity has

trophic levels stacked in blocks proportional in size to the energy acquired from the level below. Food chains are usually

bottom heavy since only 10% of energy is

transferred.

Pyramids of productivity

• ADVANTAGES: shows the actual energy transferred and allows for rate of production. Allows comparisons of ecosystems based on relative energy flows.

• DISADVANTAGES: it’s very difficult to collect energy data as the rate of biomass production over time is required. It’s difficult to assign a species to a particular trophic level when they may be omnivorous.

PYRAMID COMPARISONPyramids of numbers and pyramids of biomass represent storages

How do you apply the second law of

thermodynamics to this pyramid?

answer

• The second law of thermodynamics states that the energy in any system decreases. In this pyramid one can see that the amount of energy that is passed from one level to the other decreases.

• The amount of energy that is available from one level to the next is only 10%. This because all organisms use energy to perform their normal processes, and some of the energy is lost during the consumption process (hunting, eating, unprocessed food, etc.)

Class work• Draw and label pyramids from the data in the

table. Comment on these.Number pyramid

Biomass pyramid (kJ m-2)

Productivity pyramid

1000 kJ m-2 yr-1

Primary producers

100 000 2500 500

Primary consumers

10 000 200 50

Secondary consumers

2 000 15 5

Tertiary consumers

500 1 -

KEY CONCEPTS

SPECIES-organisms with similar characteristics that are able to reproduce fertile offspring.POPULATION-organisms of the same specie that live together in a place and interact with each other.COMMUNITY-group of populations living and interacting with each other.

KEY CONCEPTSNICHE – describes the role of an organisms or population in its community or ecosystem. In other words, the function of an organisms in its living environment.

HABITAT - is an ecological or environmental area that is inhabited by a particular species of animal, plant or other type of organism. It is the natural environment in which an organism lives, or the physical environment that surrounds (influences and is utilized by) a species population.

Key Concepts

Ecosystem - Is a community of interdependent organisms and the physical (abiotic) environment which they inhabit.Ecosystems may be of varying sizes from a drop of rainwater to a forest. Human ecosystems may include a household or a school or a nation.Ecosystems interact to make a biosphere.

Key Concepts

Biome – is a collection of ecosystems sharing common climatic conditions, e.g. tundra, desert, tropical rain forest.

Key ConceptsBiosphere - is that part of the Earth inhabited by organisms. It is a thin layer that extends from the upper part of the atmosphere down to the deepest parts of the oceans which support life – 11 km below sea level to 10 km above. From an ecological point of view, the biosphere is the "global ecosystem", comprising the totality of biodiversity on earth and performing all manner of biological functions, including photosynthesis, respiration, decomposition, nitrogen fixation and denitrification.

INTERACTIONS AMONG BIOTIC FACTORS

• Interaction – is how each species influence the population dynamics of another species, and the carrying capacity of their environment.

• The carrying capacity is the number of animals the habitat can support throughout the year without damage to the animals or to the habitat.

INTERACTIONS AMONG BIOTIC

FACTORSCompetition – is the struggle between organisms to survive as they attempt to use the same limiting resources.

Predation – an interaction in which one organism kills another for food.

INTERACTIONS AMONG BIOTIC

FACTORSSymbiosis or Mutualism – an interaction in which both species benefit.

Commensalism – an interaction in which one species benefits and the other does not get hurt.

Parasitism – an interaction in which one species benefits but the other gets hurt.

HOMEWORK

• Find and explain one example of each kind of interaction that takes place in nature:– Competition– Predation– Mutualism– Commensalism– Parasitism