FOOD WEBS AND TROPHIC LEVELS: These are two widely employed conceptual models/maps
used to explain the linkages among species in relation to production in the ecosystem and
transfer of energy. They are used to illustrate pathways of energy flow in an ecological
community, usually starting with solar energy being used by plants during photosynthesis.
Food webs can be more complicated depending on which ecological dimension is being
mapped such as SPECIES COMPOSITION (types), SPECIES RICHNESS (number), BIOMASS (dry
weight of plants and animals), PRODUCTIVITY (rates of conversion of energy and nutrients
into growth) and STABILITY (food webs over time).
TROPHIC DYNAMICS:
When the relative abundance or biomass of each functional feeding group is stacked into
their respective trophic (feeding) levels they naturally sort into a PYRAMID OF NUMBERS .
One of the several patterns that is repeated amongst the planet’s ecosystems is the emergent
pyramidal arrangement or trophic levels with amounts of energy transfer decreasing as
species become further removed from the source of production.
The size of each level in the pyramid generally represents biomass which can be measured as
the dry weight of an organism. Autotrophs may have the highest global proportion of
biomass, closely rivalled or surpassed by microbes.
Functional trophic groups sort out hierarchically into pyramid trophic levels because it
requires adaptations to become a photosynthesizer or a predator, few organisms have the
adaptations needed to combine both abilities. Each trophic level contains unrelated species
that grouped together because they share common ecological functions.
The net effect of direct or indirect relations if called TROPHIC CASCADES.
SOME ELEMENTARY METHODS OF STUDY:
Students are expected to undertake some field practical on the following:
PRACTICAL 1: COLLECTING DATA AND DATA HANDLING
PRACTICAL 2: ESTIMATION OF POLUATION SIZE USING QUADRAT METHOD
PRACTICAL 3: MEASURING ENVIRONMENTAL FACTORS ON LAND
PRACTICAL 4: MEASURING ENVIRONMENTAL FACTORS IN WATER
PRACTICAL 5: MEASUREMENT OF EDAPHIC FACTORS