Ecology Flashcards
What is an ecological pyramid?
Ecological pyramids provide information about the numbers of organisms at each trophic level of a food web.
Why can an inverted pyramid sometimes occur? Examples?
A pyramid of numbers does not take into account the relative sizes of the organisms
For example in a forest ecosystem there may be a small number of large trees and a large number of plant eating insects (primary consumers).
What is biomass? And how is it measured (units)?
The total amount of matter (mass) present in living organisms at each trophic level at a given time in an ecosystem
It generally declines with increasing trophic levels
Biomass is measured in units of mass such as kilograms or tonnes per unit area, and is typically measured after the removal of water
How can biomass be lost at successive stages of the food chain? (5)
Death Cellular respiration Excretion Elimination/egestion Body parts being inedible for the next trophic level.
How is biomass calculated?
It is not the size of the individual organism that matters but the total mass of organisms in a given area that is important.
Biomass in a given area of land or volume of water can be calculated by estimating the total numbers of organisms at each trophic level and multiplying this by an average weight of all organisms.
What does a pyramid of biomass record?
A pyramid of biomass records the total dry organic matter of organisms (biomass) at each trophic level in a given area of an ecosystem.
Give examples on how some organisms build up their biomass at different times.
Long lived herbivorous fish in an ocean ecosystem build up their biomass over a period of several years.
In contrast, short lived algae in the same ecosystem have only a few weeks to build up their biomass before they die.
What does biomass not take into account?
This type of pyramid does not take into account the time during which the biomass of organisms at different trophic levels has been built up.
Therefore if the biomass is sampled over a short period, the pyramid of biomass can be inverted.
What is the pyramid of energy?
Shows the amount of energy input into each trophic level in a given area of an ecosystem over an extended period, often one year.
Pyramids of energy are never inverted.
The flow of energy through all ecosystems is reduced as energy flows from one trophic level to another.
Typically approximately 10 percent of energy from one level is available to the next
How much does the flow of energy reduce from one trophic level to another?
The flow of energy through all ecosystems is reduced as energy flows from one trophic level to another.
Typically approximately 10 percent of energy from one level is available to the next
What does the length of each bar of a pyramid of energy? What is pyramids of energy expressed in (units)?
The length of each bar indicates the chemical energy at each trophic level.
Pyramids of energy are expressed in units of energy per area in a given time.
Kilojoules per square metre pre year.
i.e. kJm-2yr-1 or kJ/m2/y.
What is productivity?
Productivity is the rate at which biomass (amount of organic matter) accumulates. It is the amount of energy fixed in organic compounds.
What is productivity measured in? Units?
Productivity is measured as the increase in biomass over time, that is the rate at which chemical energy is produced per metre square per year.
Units = kilogram/m2/year
How is productivity affected by photosynthesis? (abiotic factors)
As productivity is the rate that biomass accumulates
The rate at which photosynthesis occurs is influenced by abiotic factors, therefore glucose production from photosynthesis will differ in summer and winter and also with changes in latitude and altitude. (due to the amounts of light available).
How do biotic factors affect productivity?
Such as pests and disease, these can reduce the productivity of communities.
