255
D. Kar, Wetlands and Lakes of the World,
DOI 10.1007/978-81-322-1023-8_16, © Springer India 2013
In many ways, the wetland environment is
physiologically harsh. The major stresses are
anoxia and the wide range of salinity and water
fl uctuations which are characteristic of an environment which is neither terrestrial nor aquatic.
Adaptations to this environment have a cost of
energy. It is either because an organism’s cells
operate less effi ciently ( conformer ) or because
the organisation expends energy to protect its
cells from the external stress ( regulator ). It may
be noted here that all organisms have almost similar kind of adaptations at the cellular level .
However, unicellular organisms may display
more novelty. Adaptations of these organisms
include the ability to respire anaerobically, to
detoxify end products of anaerobic metabolism,
to use reduced organic compounds in the sediments as energy sources and to use mineral elements in the sediment as alternative electron
acceptors when oxygen is unavailable. On the
other hand, a wider range of responses are available to multicellular plants and animals. It is
because of the fl exibility afforded by the development of organ systems and division of labour
within the body, mobility and complex life history strategies. It may be noted here that animals
have developed both structural and physiological
adaptations to reduced oxygen availability. These
include specialised tissues or organ systems,
mechanisms to increase the oxygen gradient into
the body, better means of circulation and more
effi cient respiratory pigment systems. Further, in
plants and animals, salt stresses are met with
specialised tissues or organs to regulate the
internal salt concentration or to protect the rest of
the body from the effects of salt (‘osmoregulators’) or with increased metabolic and physiological tolerance to salt at high concentrations
(‘osmoconformers’).
Wetland environments are characterised by
stresses for which most organisms are not always
well equipped to handle. Aquatic organisms
are not well adapted to deal with the periodic
drying which occurs in many wetlands. On the
other hand, terrestrial organisms are stressed by
long periods of fl ooding. Further, temperature
extremes on the wetland surface are greater than
would ordinarily be expected in deeper aquatic
environments. It could be mainly because of shallow water in the wetlands. However, the most
severe stress is, perhaps, the absence of oxygen in
fl ooded wetland soils. This prevents organisms
from respiring through normal aerobic metabolic
pathways. Further, the supply of nutrients available to plants is also modifi ed in the absence of
oxygen. Moreover, the concentrations of certain
elements and organic compounds may reach
toxic levels.
It is not surprising that those plants and animals which are regularly found in wetlands have
mostly evolved functional mechanisms to deal
with these stresses. Adaptations could be broadly
classifi ed into two categories, namely, (a) those
which enable the organisms to tolerate stress
and (b) those which enable it to regulate stress.
‘Tolerators’ (also called ‘resisters’) have functional
16
Biological Adaptations to Wetland
Environment
D. Kar, Wetlands and Lakes of the World,
DOI 10.1007/978-81-322-1023-8_16, © Springer India 2013
In many ways, the wetland environment is
physiologically harsh. The major stresses are
anoxia and the wide range of salinity and water
fl uctuations which are characteristic of an environment which is neither terrestrial nor aquatic.
Adaptations to this environment have a cost of
energy. It is either because an organism’s cells
operate less effi ciently ( conformer ) or because
the organisation expends energy to protect its
cells from the external stress ( regulator ). It may
be noted here that all organisms have almost similar kind of adaptations at the cellular level .
However, unicellular organisms may display
more novelty. Adaptations of these organisms
include the ability to respire anaerobically, to
detoxify end products of anaerobic metabolism,
to use reduced organic compounds in the sediments as energy sources and to use mineral elements in the sediment as alternative electron
acceptors when oxygen is unavailable. On the
other hand, a wider range of responses are available to multicellular plants and animals. It is
because of the fl exibility afforded by the development of organ systems and division of labour
within the body, mobility and complex life history strategies. It may be noted here that animals
have developed both structural and physiological
adaptations to reduced oxygen availability. These
include specialised tissues or organ systems,
mechanisms to increase the oxygen gradient into
the body, better means of circulation and more
effi cient respiratory pigment systems. Further, in
plants and animals, salt stresses are met with
specialised tissues or organs to regulate the
internal salt concentration or to protect the rest of
the body from the effects of salt (‘osmoregulators’) or with increased metabolic and physiological tolerance to salt at high concentrations
(‘osmoconformers’).
Wetland environments are characterised by
stresses for which most organisms are not always
well equipped to handle. Aquatic organisms
are not well adapted to deal with the periodic
drying which occurs in many wetlands. On the
other hand, terrestrial organisms are stressed by
long periods of fl ooding. Further, temperature
extremes on the wetland surface are greater than
would ordinarily be expected in deeper aquatic
environments. It could be mainly because of shallow water in the wetlands. However, the most
severe stress is, perhaps, the absence of oxygen in
fl ooded wetland soils. This prevents organisms
from respiring through normal aerobic metabolic
pathways. Further, the supply of nutrients available to plants is also modifi ed in the absence of
oxygen. Moreover, the concentrations of certain
elements and organic compounds may reach
toxic levels.
It is not surprising that those plants and animals which are regularly found in wetlands have
mostly evolved functional mechanisms to deal
with these stresses. Adaptations could be broadly
classifi ed into two categories, namely, (a) those
which enable the organisms to tolerate stress
and (b) those which enable it to regulate stress.
‘Tolerators’ (also called ‘resisters’) have functional
16
Biological Adaptations to Wetland
Environment