06/10/2015. Lecture 3: Ecological Pyramids and the Transfer of Energy in Ecosystems PYRAMID OF NUMBERS. Pyramid of Numbers. Pyramid of numbers cont.

Transcription

1 Lecture 3: Ecological Pyramids and the Transfer of Energy in Ecosystems ECOLOGICAL PYRAMIDS The trophic levels of an ecosystem can be arranged into in a pyramid and these are called the ecological pyramids An ecological pyramid is a graphical representation designed to show the number of organisms, energy relationships, and biomass of an ecosystem. Succeeding levels in the pyramid represents the dependence of the organisms at a given level on the organisms at lower levels. The first trophic level is placed at the bottom and subsequent trophic level are stacked on top in their feeding sequence There are three types of ecological pyramids and these are the pyramid of numbers, biomass and energy Each of these pyramids illustrate the flow of energy from one trophic level to another PYRAMID OF NUMBERS These display the number of individual organisms at each trophic level Plot of relationships between the number of herbivores (primary consumers), first level carnivore ( consumers), second level carnivore (tertiary consumers) and so forth. Shape varies form ecosystem to ecosystem because the number of organisms at each level is variable. Pyramid of Numbers population of individuals at each trophic level. The typical pyramid of numbers decreases as you This occurs when many small and numerous producers feed a smaller number of primary producers. Total population of tertiary Pyramid of numbers cont. Pyramid of numbers population of individuals at each trophic level. The typical pyramid of numbers decreases as you This occurs when many small and numerous producers feed a smaller number of However, when the producers are large, and are fewer in number than the primary consumers, the pyramid looks like this. Give an example of the kind of producers that would result in this type of pyramid. primary Total population of tertiary Total population of producers. 1

2 Pyramid of numbers However, when the producers are large, and are fewer in number than the primary consumers, the pyramid looks like this. Give an example of the kind of producers that would result in this type of pyramid. The total amount of matter organisms of an ecosystem at each trophic level is biomass. Biomass is preferred to the use of numbers of organisms because individual organisms can vary in size. It is the total mass not the size that is important. Pyramid of biomass records the total dry organic matter of organisms at each trophic level in a given area of an ecosystem. Represents the amount of energy contained in a biomass, at different trophic levels for a particular time. Demonstrates the amount of matter lost between trophic levels. Two types of biomass pyramids: upright and inverted. amount of biomass that is each trophic level, in a given area. Biomass is the amount of dry matter (without water) within organisms. On land, the amount of biomass decreases as levels. Total biomass Total biomass present in primary Total biomass tertiary Total biomass producers. amount of biomass that is each trophic level, in a given area. Biomass is the amount of dry matter (without water) within organisms. On land, the amount of biomass decreases as levels. In the water, the amount of biomass increases as levels, creating an inverted pyramid. This is only possible because the reproductive rate of the organisms increases as you go down trophic levels. Total biomass tertiary Total biomass Total biomass present in primary Total biomass phytoplankton. In the water, the amount of biomass increases as levels, creating an inverted pyramid. This is only possible because the reproductive rate of the organisms increases as you go down trophic levels. 2

3 cont... Pyramid of Biomass cont An unusual biomass pyramid appear with an inverted shape The first trophic level has a lower biomass than the second If the producers are small such as algae they have a high turnover rate, that is a high rate of growth and reproduction balanced by the high rate of consumption or death Upright Inverted PYRAMID OF ENERGY Are often very similar to the pyramid of biomass The energy content at each trophic level is generally comparable to the biomass These take into account the rate of production unlike the numbers and biomass which take the standing states of organisms at a particular moment in time Pyramid of solar energy can be added as an extra rectangle at the base of the pyramid. Allows different ecosystems to be compared. Comparisons using biomass are misleading because two species do not necessarily have the same energy content PYRAMID OF ENERGY Represents the loss of energy with each transfer in a food chain. Pyramids of energy are always upright as the total amount of energy available for utilization in the layers above is less than the energy available in the lower levels. This happens because during energy transfer from lower to higher levels, some energy is always lost. Pyramids of Energy Pyramids of Energy This pyramid indicates the amount of energy that is each trophic level. The amount of energy always decreases as you Total energy Total energy primary Total energy tertiary Total energy producers. 3

4 Pyramids of Energy This pyramid indicates the amount of energy that is each trophic level. The amount of energy always decreases as you In nature, ecological efficiency varies from 5% to 20% energy available between successive trophic levels (95% to 80% loss). About 10% efficiency is a general rule. Energy Pyramid EFFICIENCY OF ENERGY TRANSFER The study of productivity is known as production ecology and it involves the study of energy flow through the ecosystem Primary productivity of an ecosystem is the rate at which energy is stored by producers in form of organic salts which can be used as food materials. Primary productivity determines the total energy flow through the biotic component of the ecosystem, and hence the amount of life which the ecosystem can support. Fig PRIMARY PRODUCTIVITY Primary productivity depends on a number of interrelated factors such as: Light intensity Nutrients Temperature Water Thus its calculation is extremely difficult The primary productivity of oceans is lower than that of terrestrial ecosystems because water reflects or absorbs much of the light before it reaches the and is utilised by producers GROSS PRIMARY PRODUCTIVITY GPP is the total energy fixed by producers in photosynthesis or it is the total organic material produced by plants including that lost to respiration It is expressed as joules or kilojoules per square metre 4

5 NET PRIMARY PRODUCTIVITY This is the amount of energy or biomass that is available to consumers at subsequent trophic levels It is the biomass produced per area per unit time It is obtained by subtracting respiration and photorespiration from the GPP Ecological efficiency This is also known as the efficiency of energy transfer and it is the percentage of energy transferred from one trophic level to another It varies between 5% and 20%. An average figure 10 % is often used This is affected by several factors Not all the energy and materials available in the food is used by the consumer for production. 1.Some energy is lost as heat in respiration. 2. Other losses occur in the organic waste products of metabolism and are excreted 3. Some food materials remain undigested and are lost immediately in the process of egestion. The waste products are used as food sources by decomposers and detrivores BIOGEOCHEMICAL CYCLES This is one other major feature of ecosystems alongside energy flow All matter cycles...it is neither created nor destroyed... Biogeochemical cycles show the movement (or cycling) of matter through a system The biogeochemical cycles of water, nitrogen and carbon are summarised below Rain clouds Precipitation to land Precipitation Infiltration and Percolation The water cycle Condensation Transpiration Evaporation Transpiration from plants Precipitation Evaporation from land Evaporation Surface runoff Runoff from ocean Precipitation (rapid) to ocean Surface runoff (rapid) Groundwater movement (slow) Ocean storage Effects of Human Activities on the Water Cycle We alter the water cycle by: Withdrawing large amounts of freshwater. Clearing vegetation and eroding soils. Polluting surface and underground water. THE CARBON CYCLE Fig. 3-27, pp

6 Effects of Human Activities on the Carbon Cycle We alter the carbon cycle by adding excess CO 2 to the atmosphere through: Burning fossil fuels. Clearing vegetation faster than it is replaced. THE NITROGEN CYCLE Effects of Human Activities on the Nitrogen Cycle Effects of Human Activities on the Nitrogen Cycle We alter the nitrogen cycle by: Adding gases that contribute to acid rain. Adding nitrous oxide to the atmosphere through farming practices which can warm the atmosphere and deplete ozone. Contaminating ground water from nitrate ions in inorganic fertilizers. Human activities such as production of fertilizers now fix more nitrogen than all natural sources combined. 6