Environmental Systems Ecostructure Topic 2.1.4-2.1.5, 5.3.3 Ecological Pyramids

What are Ecological Pyramids A pyramid is a kind of graph/model that can be used to quantitatively represent differences in the trophic levels in a single ecosystem. Three types: Pyramids of productivity Pyramids of biomass Pyramids of numbers Why do most pyramids get smaller as you go up?

Pyramid of Numbers The pyramid of numbers is an ecological pyramid based on the number of organisms at each trophic level Not all pyramids of numbers look like this. How could one look different?

Example of Exception Many insects can be found feeding on a single plant, so there would be a lower number of producers than the primary consumers.

Pyramids of Numbers usually depend upon the size of organisms This pyramid shows that forests have a smaller number of producers than grasslands

Pyramids of Biomass What is biomass? The pyramid of biomass is an ecological pyramid based on the mass of dry tissue of organisms at each trophic level in an area. the standing stock of each trophic level measured in grams (or kg) of biomass/square meter (g m-2 or kg m-2) … can also be measured in units of energy (J m-2 or kJ m-2) Example of when this pyramid could be inverted?

Pyramids of biomass can also be inverted. Example: algae and zooplankton

Pyramid of Productivity The flow in the total available energy at each higher trophic level is called the pyramid of productivity. These show the amount of energy that is passed from one trophic level to the next. Measured in (g m-2 yr-1 or kg m-2 yr-1) or (J m-2 yr-1 or kJ m-2 yr-1), which are units of flow over time instead of the momentary standing stock. Can these pyramids be inverted? Why?

2.1.5 Implications of Pyramids Why are food chain lengths limited? The total amount of energy stored in the bodies of a given population is dependent on which trophic level it occupies. Top Carnivores are very vulnerable if there is a disturbance anywhere in the food chain. Why?

Increasing Toxins Some non-biodegradable toxins that are ingested do not get broken down by the body and released back into the environment. Instead they slowly accumulate in the organism as it consumes through its lifetime (Bioaccumulation). This accumulated toxin is then passed on from one trophic level to the next, so that the concentration in living tissue increases (or magnifies) at each trophic level. This is called biomagification. Therefore, what trophic level is the most vulnerable?

Example: DDT DDT is a highly successful pesticide once used in great abundance throughout the U.S. and world. DDT (a non-biodegradable toxin) is metabolized and excreted much more slowly than nutrients. Due to this, what happened? The hazard of DDT was to “non-target animals” Who were the “target animal”? Who were the “non-target animals”? Why were they so affected? How were they affected?

“There is abundant evidence that some carnivores at the ends of longer food chains (e.g. ospreys, pelicans, falcons, and eagles) suffered serious declines in fecundity and hence in population size because of this phenomenon in the years before use of DDT was banned (1972) in the United States.”