5,4,3,2,1 go… can you talk about food chains and food webs for 60 seconds mentioning as many as the key words as possible? Food web Producer Consumer Decomposer Food chain Primary consumer Omnivore Detritivore Energy loss Quarternary Secondary consumer Trophic level Tertiary consumer Habitat Heat Respiration Carnivore Herbivore

Some Most All Ecological pyramids WAL: About how energy moves and is lost between trophic levels All Most Some What percentage of energy is transferred from one level to the next? What are the relative merits and disadvantages of each? What are the different types of ecological pyramid?

Today we are covering from the specification: Pages 70-72 of your textbook

Pyramids of numbers Food chains and food webs are a useful means of showing what different organisms eat and therefore energy flow. They do not provide quantitative information – ecological pyramids Usually they look like this:

Pyramids of Numbers What can be the problem? They can look odd Ecologists saw that numbers seemed to decline along the food chain, hence pyramid of numbers Of course they can look odd, why? A. 1 tree supports many caterpillars

Pyramids of Numbers No account is taken of size – one tree is given the same value as 1 aphid therefore they can look inverted. The number of individuals s so great that it is impossible to represent them accurately on the same scale as other species in the food chain – one tree and 1 million aphids They can look odd Ecologists saw that numbers seemed to decline along the food chain, hence pyramid of numbers Of course they can look odd, why? A. 1 tree supports many caterpillars

Pyramids of Numbers

Pyramids of biomass More reliable, quantitative description of a food chain is provided when their biomass is measured. Biomass is the total mass of the plants and/or animals in a particular place.

Biomass = dry mass of organisms Pyramids of Biomass Biomass = dry mass of organisms Given as gm-2 for an area Or gm-3 for a volume Biomass – dry mass of organisms in ecosystem

finding the biomass of worms Measuring biomass Problem: finding the biomass of worms Why is this so hard? How would you do it?

Problem the variability due to gut contents: Answer? To eliminate the problem of variability due to moisture content, you can dry your earthworms at 60°C for 24-48 hours to get “dry earthworm biomass”. Problem the variability due to gut contents: Answer? Keep the live earthworms in containers until they empty their guts (24-48 hours, if they don’t die in the process); Dissect the preserved earthworm and flush their opened gut; “ash” dry worms leaving only mineral gut contents.

A statistical relationship between length & dry biomass The answer? A statistical relationship between length & dry biomass Dry worm & weigh “ash” dry @ 500 oC Remove ash Weigh gut contents Subtract gut contents weight from dry weight Q. Why is the graph so useful?

Pyramids of biomass Fresh mass is quite easy to access but varying amounts of water makes it unreliable. Use dry mass but the organisms must be killed, therefore only small sample, which may not be representative.

Anomaly from pyramid of biomass with aquatic food chain Pyramids of Biomass Anomaly from pyramid of biomass with aquatic food chain Q. Why is there less biomass in producers than primary consumers? Even pyramids of biomass can look odd, e.g. marine pyramid where producers are short lived phytoplankton A. Sample is made at a single point in time and plant biomass may vary with season. Phytoplankton may also be reproducing quickly and so large turnover of biomass.

Pyramids of energy Most accurate representation of energy flow through an ecosystem. Collecting data can be difficult and complex. Data are collected in a given area (e.g one square metre) and in a set time (e.g. a year). Results are more reliable than those for biomass as 2 organisms of the same biomass may store different amounts of energy. 1g of fat stores 2x amount of energy of 1g carbohydrate.

Energy stored in each trophic level of a Florida ecosystem Pyramid of Energy Energy KJ m-2 y-1 Energy stored in each trophic level of a Florida ecosystem Q. Why might deriving energy content be difficult? Energy – the energy that flows into a trophic level, useful for chains with rapid turnover at a trophic level e.g. phytoplankton A. Two organisms of the same dry mass may have different energy contents e.g. more or less fat which is high in energy.

Task Do application questions and summary questions

Some Most All Ecological pyramids WAL: About how energy moves and is lost between trophic levels All Most Some What percentage of energy is transferred from one level to the next? What are the relative merits and disadvantages of each? What are the different types of ecological pyramid?