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2.2. COMMUNITIES AND ECOSYSTEMS (Ecological pyramids (Pyramid of…
2.2. COMMUNITIES AND ECOSYSTEMS
Knowledge and Understanding
Interactions of species with their environment result in energy and nutrient flow
Photosynthesis and respiration play a significant role in the flow of energy in communities
Feeding relationships in a system can be modeled using foodchains, foodwebs and ecological pyramids
Respiration and photosynthesis
Respiration
- all living things must respire to get energy and stay alive
Involves breaking down food normally in the form of glucose to release energy which is used in living processes - movement, respiration, sensitivity, growth, reproduction, excretion, nutrition
can be aerobic (using oxygen) or anaerobic (no oxygen)
AEROBIC - energy released and used and carbon dioxide and water are waste products - much of energy released during respiration is heat energy and this is dissipated (released) into the environment - increases entropy of system but organism maintains high level of organisation (low entropy)
Photosynthesis
- green plants convert light energy into chemical energy - transformation of energy from one state to another
Food chains and trophic levels
- food chain: flow of energy from one organism to the next - shows feeding relationships between species in an ecosystem - arrows connect the species usually pointing to the direction of transfer of biomass and energy
organisms are grouped into trophic levels
PRODUCER
PRIMARY CONSUMER
SECONDARY CONSUMER
TERTIARY CONSUMER
Usually the top of the food chain is most susceptible to alterations in the environment - top carnivores often have a limited diet so a change in their food prey has a knock on effect - their population numbers are low because of the decrease in efficiency along a food chain - their ability to withstand negative influences is more limited than lower down species with larger populations
Producers can be autotrophs (green plants) which make their own food from sunlight or chemosynthetic organisms make their own food from other simple compounds e.g. ammonia
Consumers aka heterotrophs - feed on autotrophs or other heterotrophs to obtain energy
Trophic efficiency is 10% - only this much transferred to next level - most of the energy is used in respiration to keep organism alive and then is finally lost as heat - 2nd law
Food webs
- presents complex network of interrelated food chains (there are always overlaps e.g. omnivores)
Ecological pyramids
allows easy examination of energy transfers and losses
gives 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 number of organisms at each trophic level in a food chain at one time (the standing crop) units are number per unit area
length of each bar gives a measure of the relative numbers - most pyramids are broad at their base and have many individuals in the producer level - but some may have a large tree as the producer so the base is one individual supporting many consumers e.g. birds
Advantage - simple, easy method of giving an overview and is good at comparing changes in population numbers with time or seasons
Disadvantage - 1) all organisms are included regardless of their size, therefore a pyramid based on an oak tree would be inverted 2) does not allow for juveniles or immature forms 3) numbers can be too great to represent accurately
Pyramid of biomass -
contains biomass (mass of each individual x number of individuals) at each trophic level . Biomass is the quantity of dry organic material in an organism, a population, a particular trophic level or an ecosystem
Units = mass per unit area often grams per sq m
Pyramids of biomass are more likely to be pyramid shaped with exceptions such as oceanic ecosystems where producers are phytoplankton (reproduce fast but only present in small amounts at a time)
Advantage - overcomes some of the problems of pyramids of numbers
Disadvantages - 1) only uses samples from populations - impossible to measure exactly, 2) organisms must be killed to measure dry mass, 3) time of year that biomass is measured may affect the result
Pyramid of productivity
- shows rate of flow of energy or biomass through each trophic level - shows energy or biomass being generated and available as food to the next trophic level during a fixed period of time - show levels over this fixed period of time
Pyramid shaped in healthy ecosystems as they should follow the second law of thermodynamics
Measured in units of energy or mass per unit area per period of time
Productivity values are rates of flow whereas biomass is rhe store existing at one period in time
Advantages - 1) most accurate system, shows actual energy transferred, 2) allows comparison of ecosystems based on relative energy flows 3) pyramids are not inverted 4) energy from solar radiation can be added
Disadvantages - difficult and complex to collect energy data (rate of biomass production overtime is required), problem of assigning species to a particular trophic level when they may be omnivorous