Energy 

Important definitions • Biomass – the mass of biological material in living or recently living organisms • Climax community – a stable, self-perpetuating community that has reached equilibrium with it’s environment and no further change occurs • Commensalism – an interaction between organisms of two species from which one benefits and the other is unaffected • Community – interacting populations of two or more species in the same habitat at the same time • Decomposers – microbes that obtain nutrients from dead organisms and animal waste • Detritivores – organisms which feed on small fragments of organic debris • Ecosystem - a characteristic community of independent species interacting with the abiotic components of their habitat • Habitat – the place in which an organism lives 

Important definitions - continued • Mutualism – an interaction between organisms of two species from which both benefit • Saprobionts – microorganisms that obtain food from dead or decaying remains of plants and animals • Succession – the change in structure and species composition of a community over time • Symbiosis – the association between individuals of two or more species • Trophic level – the number of times energy has been transferred between the sun and successive organisms along a food chain 

Energy flow through ecosystems • Green plants (producers) trap solar energy and manufacture sugars during photosynthesis • The sun’s energy is passed down from one trophic level to the next through the ecosystem • Herbivores feed on plants and then carnivores feed on them • Each of these groups form a feeding or trophic level with energy passing from each level to a higher one as material is eaten • Eventually the energy leaves the system as heat • Energy is lost at each level through heat and excretion of waste products and so the amount of energy available to the next level is reduced 

Types of productivity Gross primary productivity > the rate of production of chemical energy in organic chemicals by photosynthesis (kj m-2 year-1) Net primary productivity > the rate at which organic matter is produced by plants Secondary productivity > the rate at which consumers accumulate energy in body tissue Photosynthetic productivity > the efficiency of a plant to trap light energy GPP – respiration = NPP 

Energy flow through consumers Efficiency of energy transfer = (energy incorporated into biomass after transfer/energy available in biomass before transfer) x 100 • Energy conversion efficiency > 10% primary consumers and 20% secondary consumers • Herbivores do not eat all of the plant matter, many leave roots or woody parts. For every 100g of plant material ingested, only about 10g is incorporated into their biomass • Some energy is lost due to faeces (grass in faeces) and lost in respiration 

Pyramids of energy Pyramids of number > Fail to take size of organisms into account and do not recognise the difference between juvenile and adult forms of organisms Pyramids of biomass > Difficult to measure accurately and do not indicate productivity or amount of energy flowing through the ecosystem Pyramids of energy > Never inverted pyramids as material passes up through the food chain, energy is lost from the ecosystem so the area of the bars decrease accordingly 

Succession Primary succession The sequence of changes following the introduction of species into an area that has not previously supported a community Secondary succession The change in a community following the disturbance or damage to a colonial habitat 

Factors affecting succession Humans > • Grazing cattle or sheep prevent shrub and grass growth • Farming removes all except deliberately introduced species • Deforestation removes a community of trees, small ones may be replanted Intraspecific competition > • Dense populations lead to less surviving as organisms tend to produce more offspring than the habitat can support and so numbers are regulated • Survival of the fittest Interspecific competition > • Species may have the same common needs but different requirements • Each species has it’s own niche that only it can occupy whichever species has the competitive advantage will survive