Ecological Energetics and Nutrient Cycles Flashcards
What is the first law of thermodynamics and what implications does this have for ecological energetics?
- Energy can’t be created or destroyed, but can be changed from one form into another
- Energy flows through an ecosystem, and so for an ecosystem to exist it must have an external source of energy
- This is most often provided through sunlight - plants trap light energy using chlorophyll and convert it into chemical energy by producing organic molecules from inorganic.
define photoautotroph
producers that make their own food from inorganic molecules, water and carbon dioxide using sunlight as an energy source
define chemoautotroph
producers that use chemical energy to make their own food
give some examples of chemoautotrophs
- Some species of bacteria living in deep caves with no available light make organic substances using the mineral in the rock as a source of chemical energy
- Nitrifying bacteria are chemoautotrophs
define heterotroph
can’t make their own food, therefore rly on other living organisms to provide them with organic molecules
what do food chains indicate?
- Feeding relationships in an ecosystem
- Energy flow through an ecosystem (direction of arrows) from one trophic level to another
- Each feeding level is known as a trophic level. Producers are always the first trophic level, primary consumers the second, etc.
how many levels are there in a food chain?
Most food chains have 3 or 4 trophic levels but in aquatic ecosystems there may be as many as 6
what are detritus food chains?
food chains that start with dead organic matter - eg decomposers (eg fungi) or detritivores (eg woodlice)
why do food chains only have a small amount of levels?
- Energy is lost at each level so there is less available to transfer to the next
- on a long food chain the small amount of energy gained at the end of the chain wouldn’t be energetically favourable
what are food webs?
a complex linked combination of many food chains. This is because most organisms feed on more than one type of organism
what should be considered when drawing a pyramid of numbers, biomass or energy?
- Producers (trophic level 1) are always at the base of the pyramid
- Drawn symmetrical about the centre
- Bar width must be in proportion to the numbers/biomass of organisms in each trophic level
- Bars must all the same depth
Define pyramid of numbers
a bar diagram indicating the relative numbers of organisms in a food chain, or total numbers of all organisms at each of the trophic levels in a food web
how is the data for a pyramid of numbers collected?
To obtain the data all organisms are counted in theory, but in practice a small area is randomly sampled and multiplied up to give an estimate of the total population size (eg quadrats, nets, humane trapping).
describe the general shape of a pyramid of numbers
Predators are normally larger and smaller in number than their prey, so the pyramid sometimes works, but in the instance of eg oak trees and insects, it can be inverted
name the problems with pyramids of numbers
When very large numbers are involved at any trophic level, it is nearly impossible to scale the bars accurately
Gives quantitative information but doesn’t give indication of the relative mass of organisms at each trophic level - results in inverted pyramids
Only shows numbers of organisms at any one given time
define pyramids of biomass
shows the mass of all living organisms, at a particular trophic level, per unit area or volume, at a particular time
how is the data for a pyramid of biomass collected?
- Random quadrats have all organisms harvested and weighted (wet/fresh mass) and average mass is calculated for each trophic level and multiplied by the number of organisms
- Some scientists prefer dry mass - drying organisms to constant mass - more accurate but more time consuming and means organisms are killed in the process
what are the problems with a pyramid of biomass?
- only show the number of organisms present at any one time (standing crop) - can cause inverted pyramid as it doesn’t take into account changes in biomass over a period of time (eg zooplankton and phytoplankton)
- Difficult to obtain the wet or dry mass of eg an oak tree - should the mass be the entire mass of the tree, or just the edible leaves?
what is the benefit of using a pyramid of biomass rather than numbers?
Overcomes problem of the size of organisms, therefore less likely to be inverted
define pyramid of energy (productivity)
measures productivity (how much new material is produced) for each level in an ecosystem, during a fixed period of time
what are the units for pyramids of energy?
kJm^-2y^-1
what is the benefits of using a pyramid of energy?
- Energy content of tissues varies, and so these pyramids give more accurate info than biomass
- Are never inverted - particularly useful in comparing ecosystems
- often takes into account annual changes
what are the problems with a pyramid of energy?
values are hard to obtain
how much incipient energy do primary producers utilise from sunlight?
0.5-1%
name reasons why energy might be unavailable for primary producers
- Some wavelengths can’t be absorbed by chlorophyll
- Some energy is transmitted through the leaf and misses the chloroplasts
- Some light is reflected from the leaf surface/atmosphere
- Some is lost in photosynthetic reactions (these are quite inefficient) in the form of heat
- Some energy is lost in the evaporation of water (eg from leaf surface)
give the equation for calculating photosynthetic efficiency
Photosynthetic efficiency = (Amount of energy incorporated into carbohydrate)/(amount of energy falling on the plant)
define gross primary production
the energy in organic compounds produced by plants in photosynthesis
* This energy is not all available to the next trophic level
what are the units for GPP?
kJm^-2y-1
why do nutrients cycle through an ecosystem, rather than flow like energy?
here is a finite amount of matter available on earth for organisms to use and build their bodies