184
the substratum or by vertical, arborescent growth.
Moreover, some modules may lose their reproductive capabilities and become specialised entirely
for feeding or defence without violating the laws
of individual, as opposed to group selection. This
is because all modules are genetically identical.
10.3 Dispersal
The advantages of dispersal generally increase
with the spatial discontinuity or temporal unpredictability of habitat patches. Dispersal via
planktonic larvae is rare in FW. Lakes lack the
strong currents which are required for long
distance dispersal by passive transportation.
Moreover, similar kinds of habitat vary much less
in quality from place to place in lakes than in the
sea. The unidirectional fl ow of rivers makes
planktonic dispersal disadvantageous. However,
ponds are too small for planktonic dispersal to be
advantageous and are isolated by dry land which
can only be crossed by impervious spores, cysts
or eggs blown by wind or carried by attachment
to larger animals.
10.4 Parental Investment per
Offspring
It has been reported that the amount of energy
invested per offspring by the parent decreases in
the order of brooders, oviparity with direct
development, oviparity with lecithotrophic
planktonic larvae, oviparity with planktotrophic
larvae and so on.
Summary
1. Survival is an inherent feature of living beings.
2. Many attributes of organisms, e.g. body form,
diet and breeding methods, are of selective
importance.
3. The common theme of life history strategies is
the trade-off between investment of time and
energy on contracting needs.
4. The biota of land and water differ in two
main features. Biota of land may be fixed
or mobile, while biota of water is generally
not fixed.
5. Further, asexually formed offspring generally
remain attached to the parent body and form a
colony of modular construction.
6. Advantages of dispersal generally increase
with the spatial discontinuity of temporal
unpredictability.
Suggested Readings
Harpes JL (1978) Population biology of plants. Academic,
London
Krebs J, Davies NB (1978) Behavioural ecology: an evolutionary approach. Blackwell Scientifi c Publication,
Oxford
Maynard Smith J (1978) The evolution of sex. Cambridge
University Press, Cambridge
Pianka ER (1978) Evolutionary ecology, 2nd edn. Harper
& Row, New York
10 Strategies for Survival of Aquatic Organisms
the substratum or by vertical, arborescent growth.
Moreover, some modules may lose their reproductive capabilities and become specialised entirely
for feeding or defence without violating the laws
of individual, as opposed to group selection. This
is because all modules are genetically identical.
10.3 Dispersal
The advantages of dispersal generally increase
with the spatial discontinuity or temporal unpredictability of habitat patches. Dispersal via
planktonic larvae is rare in FW. Lakes lack the
strong currents which are required for long
distance dispersal by passive transportation.
Moreover, similar kinds of habitat vary much less
in quality from place to place in lakes than in the
sea. The unidirectional fl ow of rivers makes
planktonic dispersal disadvantageous. However,
ponds are too small for planktonic dispersal to be
advantageous and are isolated by dry land which
can only be crossed by impervious spores, cysts
or eggs blown by wind or carried by attachment
to larger animals.
10.4 Parental Investment per
Offspring
It has been reported that the amount of energy
invested per offspring by the parent decreases in
the order of brooders, oviparity with direct
development, oviparity with lecithotrophic
planktonic larvae, oviparity with planktotrophic
larvae and so on.
Summary
1. Survival is an inherent feature of living beings.
2. Many attributes of organisms, e.g. body form,
diet and breeding methods, are of selective
importance.
3. The common theme of life history strategies is
the trade-off between investment of time and
energy on contracting needs.
4. The biota of land and water differ in two
main features. Biota of land may be fixed
or mobile, while biota of water is generally
not fixed.
5. Further, asexually formed offspring generally
remain attached to the parent body and form a
colony of modular construction.
6. Advantages of dispersal generally increase
with the spatial discontinuity of temporal
unpredictability.
Suggested Readings
Harpes JL (1978) Population biology of plants. Academic,
London
Krebs J, Davies NB (1978) Behavioural ecology: an evolutionary approach. Blackwell Scientifi c Publication,
Oxford
Maynard Smith J (1978) The evolution of sex. Cambridge
University Press, Cambridge
Pianka ER (1978) Evolutionary ecology, 2nd edn. Harper
& Row, New York
10 Strategies for Survival of Aquatic Organisms