330
P. 8. MEADOWS AND J. I. (IAMPBELL
ness in marine invertebrates. The subject is discussed in further detail
by Macan (1963, Oh. 6).
V. PHYSIOLOGY AND V I A B ~ Y
Elton (1927, p. 40) has suggested that “ t h e ultimate limits of
environment are set by an animal’s physiological make-up ; if these
limits are reached an animal will die. It is therefore undesirable that
the animal should run the risk of meeting such dangerous conditions
and it has various psychological (i.e. behavioural) reactions which
enable it to choose, to a large extent, the optimum conditions for
life. The animal is not usually occupying the extreme range of
conditions in which it could survive”. There is good evidence for this,
and in most cases species choose to live well within their lethal limits.
The relationship between preferences and lethal limits has been
investigated for the following variables and species. (a) salinity:
Ligia baudiniana (Barnes, 1934, 1938) ; 8 species of interstitial animals
(Jansson, 1962, 1968) ; Phyllodoce muculata larvae (Lyster, 1965) ;
3 species of fiddler crab (Teal, 1958) ; Corophium volutator (McLusky,
1967, 1970) ; Branchiostoma nigeriense (Webb and Hill, 1968). (b)
humidity: Ligia italicu Fabr. (Perttunen, 1961); 3 species of talitrid
amphipod (Williamson, 1951a). (c) particle size : Corophium volutator
(Meadows, 1964c, 1967) ; Branchiostoma nigeriense (Webb and Hill,
1958). (d) dissolved carbon dioxide : Cambarus species (Powers, 1914).
(e) temperature : Protodrilus symbioticus (Gray, 1965). (f) phytoplanktonic food: Neomysis vulgaris (= N . integer (Leach)) (Lucas, 1936).
At first sight this seems a large body of work, but some of it is preliminary, and in much of it the results of preference and viability experiments are not related t o each other. Exact correlation is also
intrinsically di5icult because most preference experiments are conducted over an hour or so, while viability experiments may last several
days. There are other difficulties. A species may prefer, say 25%, sea
water while being capable of living in 0 to PO%, sea water. And yet,
the result as such might have very little meaning, since some other
variable might impose limits that in any case restrict the species to
20 to 30%, sea water. Elton (1927, p. 41) realizes this: ‘‘ animals are
not completely hemmed in by their environment in any simple sense,
but are nearly always prevented from occupying neighbouring habitats
by one or two limiting factors only ”. With these provisos, some of the
work is detailed enough to lead to meaningful conclusions.
It would seem most probable a priori that the preferred level of a
paxticular variable should be equidistant from the upper and the lower
lethal limits of the same variable, and this is so of the preferred tempera-
P. 8. MEADOWS AND J. I. (IAMPBELL
ness in marine invertebrates. The subject is discussed in further detail
by Macan (1963, Oh. 6).
V. PHYSIOLOGY AND V I A B ~ Y
Elton (1927, p. 40) has suggested that “ t h e ultimate limits of
environment are set by an animal’s physiological make-up ; if these
limits are reached an animal will die. It is therefore undesirable that
the animal should run the risk of meeting such dangerous conditions
and it has various psychological (i.e. behavioural) reactions which
enable it to choose, to a large extent, the optimum conditions for
life. The animal is not usually occupying the extreme range of
conditions in which it could survive”. There is good evidence for this,
and in most cases species choose to live well within their lethal limits.
The relationship between preferences and lethal limits has been
investigated for the following variables and species. (a) salinity:
Ligia baudiniana (Barnes, 1934, 1938) ; 8 species of interstitial animals
(Jansson, 1962, 1968) ; Phyllodoce muculata larvae (Lyster, 1965) ;
3 species of fiddler crab (Teal, 1958) ; Corophium volutator (McLusky,
1967, 1970) ; Branchiostoma nigeriense (Webb and Hill, 1968). (b)
humidity: Ligia italicu Fabr. (Perttunen, 1961); 3 species of talitrid
amphipod (Williamson, 1951a). (c) particle size : Corophium volutator
(Meadows, 1964c, 1967) ; Branchiostoma nigeriense (Webb and Hill,
1958). (d) dissolved carbon dioxide : Cambarus species (Powers, 1914).
(e) temperature : Protodrilus symbioticus (Gray, 1965). (f) phytoplanktonic food: Neomysis vulgaris (= N . integer (Leach)) (Lucas, 1936).
At first sight this seems a large body of work, but some of it is preliminary, and in much of it the results of preference and viability experiments are not related t o each other. Exact correlation is also
intrinsically di5icult because most preference experiments are conducted over an hour or so, while viability experiments may last several
days. There are other difficulties. A species may prefer, say 25%, sea
water while being capable of living in 0 to PO%, sea water. And yet,
the result as such might have very little meaning, since some other
variable might impose limits that in any case restrict the species to
20 to 30%, sea water. Elton (1927, p. 41) realizes this: ‘‘ animals are
not completely hemmed in by their environment in any simple sense,
but are nearly always prevented from occupying neighbouring habitats
by one or two limiting factors only ”. With these provisos, some of the
work is detailed enough to lead to meaningful conclusions.
It would seem most probable a priori that the preferred level of a
paxticular variable should be equidistant from the upper and the lower
lethal limits of the same variable, and this is so of the preferred tempera-