130 ENVIRONMENTAL SCIENCE
The three major steps in energy flow correspond to:—
(a) Exploitation efficiency,
(b) Assimilation efficiency,
(c) Net production efficiency.
The product of the assimilation net production efficiencies gives gross production
efficiency i.e. by the fraction of the eaten material eventually transformed into consumer
biomass. The whole food web may be taken to be the product of the gross production
efficiency and the exploitation efficiency. The various kinds of energetic efficiencies can be
defined as under:
Exploitation efficiency = Ingestion of food/prey production.
Assimilation efficiency = Assimilation/ingestion;
Net production efficiency = Production/assimilation.
Ecological efficiency = Exploitation efficiency × Assimilation efficiency × Net
production efficiency;
= Consumer production/prey production;
= Production/ingestion.
Gross production = Production/ingestion.
In animals, rate of production appears to depend on body mass. Per unit body mass,
small animals are found more productive than big animals. Again invertebrates are less
productive than mammals. Molluscs, annelids, isopods, and insects are invertebrates of
intermediates size between copepods and echinoids.
Some conclusions regarding energy flow in the ecosystem are as under:
There is no quantitative relationship between the production of a certain trophic level
and the production of the next lower trophic level (both in calorific terms) except for the very
high or very low values of the former. This applies to the “phytoplankton-filter feeders” and
as well as “filtrators-invertebrate predators” trophic links in the plankton food chain.
The utilization of primary production in pelagic zone often depends on the nature of
dominant species of producers and consumers. In a system containing phyto-planktonic
algae-macroconsumers effective utilization occurs mostly via grazing. In the case of larger
algae and smaller consumers, primary production is mainly utilized via bacterial detritus
medium.
The energy transfer efficiency from the filtrator’s trophic level to their invertebrate
predators is often higher than from phytoplankton to filtrators.
ECOLOGICAL SUCCESSION-MEANING AND TYPES
Meaning of Succession
Biotic communities are not static. Instead they change through time. This change can
be understood on several levels. The simplest level is the growth, interaction and death of
individual organisms as they pass through their life cycles, affected by the cycles of seasons
and other natural phenomena. Some other levels of community change act over longer time