Learning Objectives State key terms and definitions State that ecosystems are dynamic Describe how energy is transferred through ecosystems

Starter: Card sort

 Ecosystem –All the living organisms and non living components in a specific habitat, and their interactions  Habitat – the place where an organism or population of organisms lives eg a woodland, rocky shore.  Microhabitat – an area within a habitat with specific conditions eg a rotting log.  Niche – The ‘role’ an organisms has in it’s environment – where it lives, what it eats, where and when it feeds, when it is active. Every species has its own unique niche. Key definitions

 Community – All the populations of different species that live in the same place at the same time, and who can interact with each other.  Population - all of the organisms of one species, who live in the same place at the same time, and can breed together  Environment – The conditions surrounding an organism, including both abiotic factors and biotic factors Key definitions

 Abiotic factor – the effects of the non-living components of an ecosystem eg temperature  Biotic factor – the effects of the living parts of the ecosystem eg competition, predation  Autotrophs – organisms that can make their own food.  Heterotrophs - organisms that can’t make their own food.  Trophic level – the level at which an organisms feeds in a food chain

 Producers - autotrophic organisms that convert light energy to chemical energy, which they then supply to consumers  Consumers – living organisms that feed on other living organisms  Decomposer – An organism that breaks down complex organic molecules into simple inorganic molecules that can be recycled. Also know as a saprophyte.  Detritivore – An organism that feed on dead organic matter. Key definitions

Dynamic ecosystems Matter is constantly recycled within an ecosystem eg carbon and nitrogen cycles Energy is not recycled it flows through ecosystems Light energyHeat energy Biotic component Abiotic component PhotosynthesisRespiration Nutrients

Simple Food Chain Producer First Consumer Second Consumer The arrows in a food chain show the transfer of food energy from organism to organism Food chains always begin with a PRODUCER. This is a green plant which is able to make food using the energy of sunlight in photosynthesis Each stem in the food chain is known as a TROPHIC LEVEL In this case the TOP CARNIVORE is the fox. Top Carnivores are not eaten by anything else except decomposers (bacteria and fungi) after they die.

Food Web Simple food chains are not very realistic. In practice very few animals eat just one thing. Most of them can eat several other animals or plants. A more realistic picture is given by a FOOD WEB which is made up of interconnected food chains. Falcon Fox Barn Owl Thrush Rabbit Pigeon Dormouse Cabbage Grain Snail

Energy transfer in the food chain

Pyramids of numbers only give an accurate impression of the flow of energy in a food chain if the organisms are of similar size. Measuring the biomass at each trophic level can give a more accurate picture. Pyramids of numbers are a quantitative way of representing food chains. What are the problems of representing food chains in pyramids of numbers? They record the number of organisms at each trophic level in a specified area. What are pyramids of numbers?

Numbers or biomass?

In a pyramid of numbers, the length of each bar represents the number of organisms at each trophic level in a specified area. As a single tree can support many organisms, this food chain produces an unbalanced pyramid. Understanding pyramids of numbers

Task Draw a pyramid of numbers for the following food chains 1. Grass (10,000) – rabbits (20) – foxes (5) – fleas (15,000) 2. Blackbirds (10) – ladybird (1,000) – aphids (5,000) – rosebush (1) Grass Rabbit Fox Flea Rosebush Aphids Ladybirds Blackbird

Understanding pyramids of biomass In a pyramid of biomass, the length of each bar represents the amount of organic matter – biomass – at each trophic level in a specified area. At each trophic level, the amount of biomass available is reduced, giving a pyramid shape.

Drawbacks of pyramids of biomass Fresh mass is quite easy to assess, but the presence of varying amounts of water makes it unreliable. The use of dry mass measurement overcomes this problem but, because the organisms must be killed, it is usually only made on a small sample and this sample may not be representative. Different species can release different amounts of energy per gram

Pyramids of energy Measures the amount of energy in the organism in kilojoules per square metre per year (kJm -2 yr -1 ). These pyramids are very difficult to measure but are always true pyramids

Drawbacks of pyramids of biomass It’s a ‘snapshot in time’ - Biomass can vary with the seasons. Also, when the producer is a small organism which multiplies very rapidly, the total biomass of the producers present at any one time may be less than the total biomass of the primary consumers. Over the course of a whole year, the mass of phytoplankton (plants) must exceed that of zooplankton (animals), but at certain times of the year this is not seen. e.g. In early spring around the British Isles, zooplankton consume phytoplankton so rapidly that the biomass of zooplankton is greater than that of phytoplankton.

Measuring Energy Transfer Pyramid of Biomass Bars represent dry mass Dry mass: evaporate all water at 80 o C Scientists often measure wet mass and calculate using prior data Pyramid of Energy Different species produce different amounts of energy Use calorimeter to calculate heat released per gram Too destructive for most scientists

Plenary: Summary questions 1. State 2 advantages of using a pyramid of biomass rather than a pyramid of numbers when representing quantitative information on a food chain (2 marks). 2. Explain how a pyramid of biomass for a marine ecosystem may sometimes show producers (phytoplankton) with a smaller biomass than primary consumers (zoo plankton) (1 mark). 3. Name suitable units for the measurement of biomass (2 marks). In a pyramid of numbers: no account is taken of size (1 mark) The pyramid of individuals of one species may be so great that it is impossible to represent them on the same scale as other species in the food chain (1 mark). At certain times of year (e.g. Spring) zooplankton consume phytoplankton so rapidly that their biomass temporarily exceeds that of phytoplankton (1 mark). Grams per square metre (gm -2 ) (1 mark) Grams per cubic metre (gm -3 ) (1 mark)