Energy Flow Energy flows INTO an ecosystem as sunlight This is converted into chemical energy by autotrophs It is then passed to heterotrophs in the organic compounds as food It will eventually leave the ecosystem as heat

Energy flow Chemical elements are cycled between the biotic and abiotic environment BUT Energy cannot be recycled so an ecosystem must be powered by a continuous influx of new energy from an external source Therefore energy flows THROUGH an ecosystem whilst matter CYCLES

Trophic structure In biological ecosystems there exists a hierarchy of organisms defined by the way in which they obtain energy from their surroundings This is the ecosystems TROPHIC STRUCTURE The trophic structure of the ecosystem determines the route of energy flow and chemical cycling This can be shown in a FOOD CHAIN which shows the individual populations from each trophic level

Producers Ultimately support all the other organisms Are the Primary producer Manufacture their own organic molecules (energy containing nutrients) Mostly are photosynthetic creating organic molecules from energy from sunlight Mainly plants but also algae and some protocists Terrestrial:plants Oceanic:Phytoplankton (algae/bacteria) Shores:multi-cellular algae and aquatic plants

Consumers These are heterotrophic Directly or indirectly depend on photosynthetic output by primary producers Obtain their energy containing nutrients by consuming other organisms Includes all animals and fungi as well as some bacteria and protocists

Primary Consumers Herbivores Consuming primary producers (plants and algae and other photosynthetic organisms) Many also consume dead matter also Terrestrial:mostly insects, snails, plant parasites and some vertebrates (grazing mammals, birds) Aquatic:zooplankton (including heterotrophic protocists), small invertebrates and some fish Sea-shores:multi-cellular algae and aquatic plants

Secondary and Tertiary Consumers Secondary Consumers: Carnivores that eat herbivores (primary consumers) Tertiary Consumers: Carnivores that feed on other carnivores (secondary consumers)

Decomposers Detrivores Animals that eat detritus. digest much of the material, but unable to digest cellulose/lignin in plant cell walls but do break them down Saprophytes Mircobes (fungi and bacteria) that live on detritus. Digest it by extracellular digestion, and then absorb the soluble nutrients. Can completely break down any organic matter (including cellulose and lignin) to inorganic matter such as carbon dioxide, water and mineral ions.

Producers Primary consumers Secondary Consumers Tertiary consumers Top consumers Decomposers Heat Energy Heat Energy Light Death

Energy Loss As energy flows through each trophic level much is lost before it is consumed by organisms at the next level Herbivores only eat a small fraction of plant material produced and cannot digest all of it, some will be passed unprocessed in the faeces. Of the energy they do take up, only a small percentage would be used for growth and available for the next trophic level.

Energy Loss The rest is used in cellular respiration which degrades food molecules to inorganic waste products and heat Carnivores are slightly more efficient at converting food into biomass (because meat is more easily digested than vegetation) But often secondary consumers use more energy for cellular respiration., decreasing the amount available for the next trophic level

Ecological Efficiency This is the percentage of energy transferred from one trophic level to the next Efficiencies vary greatly among organisms from 5% to 20% Therefore 80 to 95% of available energy is not transferred to the next trophic level This is often represented in pyramids of biomass

Ecological Efficiency Some animals are more efficient at converting energy into organic matter than others. Why? Large or small Homeothermic or Poikilothermic Carnivore or herbivore Young or old

Producers Primary consumers Secondary Consumers Tertiary consumers Top consumers Decomposers Heat Energy Heat Energy Light Death 10 % 2 % 98 %

Pyramids of Energy In general as you go up a food chain the size of the individuals increases and the number of individuals decreases. Pyramids of energy are always pyramidal (energy cannot be created), and always very shallow, since the transfer of energy from one trophic level to the next is very inefficient The "missing" energy, which is not passed on to the next level, is lost eventually as heat.

Pyramid of Energy Producer Primary Consumer Secondary Consumer Tertiary Consumer

Pyramid of Numbers The simplest way to compare different triophic levels. These show the numbers of organisms at each trophic level within a food chain The width of the bars represent the numbers, or the bars may be purely qualitative Pyramids of numbers are most often triangular (pyramid shaped- hence the name) shaped, but can be almost any shape. Advantage: Allows us to overcome trying to compare the numbers of organisms of varying sizes

Typical carnivore pyramid of numbers Grass Snails Mice Owls

Single large producer Tree Caterpillars Blue tits Owls

Parasitic pyramid of numbers Rose bush Aphids Parasites Nettle plant Butterfly larvae Parasitic wasp

Pyramid of Biomass These convey more information, since they consider the total mass of living material (i.e. the biomass) at each trophic level When measured the biomass is dry mass (since water stores no energy) measured in kg m -2 This can be found by drying and weighing the organisms at each trophic level, or by counting them and multiplying by an average individual mass. Pyramids of biomass are always pyramid shaped, since if a trophic level gains all its mass from the level below, then it cannot have more mass than that level (you cannot weigh more than you eat). Except for ONE exception! The "missing" mass, which is not eaten by consumers, becomes detritus and is decomposed

Numbers vs Biomass Rose bush Aphids Ladybirds Birds Pyramid of numbers Pyramid of biomass