336
P. 9. MEADOWS AND J. I. CAMPBELL
stimuli falling into the latter category, but there is little evidence for
this at present. Chemicals emanating from food, hosts, predators or
individuals of the same species in aquatic environments are usually
detected at a distance (Copland, 1918 ; Welsh, 1930 ; Davenport, 1950 ;
Stehouwer, 1954; Lindberg, 1955 ; van Dongen, 1956; Davenport et al.,
1960 ; Frings and Frings, 1965 ; Gore, 1966 ; Bovbjerg, 1968 ; Castilla
and Crisp, 1970; Dahl, Emanuelsson and von Mecklenburg, 1970;
Snyder and Snyder, 1971). On the other hand there are a few well
documented instances of adult invertebrates responding to chemicals
only after contact : certain freshwater snails detect their plant food
onIy on contact (Bovbjerg, 1965, 1968), the marine commensal polynoids Acholoe and Gattyana recognize their respective hosts only after
they have encountered them (Davenport, 1953a), and the swimming sea
anemone Stomphia coccinea has to touch the starfishes to which it
responds before it will swim (Sund, 1958). These examples do not
appear to fall into any set pattern, and there is as yet no clear indication
as to why, under field conditions, some of the chemicals should be
detected at a distance and others only after contact.
Hierarchical relations, peck orders and so on, form an accepted part
of current behavioural thinking, and this has led to similar systems
being proposed for habitat selection. Consider a number of alternatives,
A, B, C, D, where A is preferred to B, B to C, and C t o D. The
alternatives can be offered in pairs or as a group together, and may
differ qualitatively or quantitatively. Few authors have considered
these relationships in detail (Meadows and Campbell, 1972), although
Dawkins (1969a, b) has proposed theoretical models. Dawkins’ reasoning is a little difficult to follow in parts, and we are not entirely
convinced of the ecological significance of his hypotheses although they
were not of course intended as such; however they may well serve as a
basis for experimentation,
The distinction between qualitative and quantitative differences
of preference is a very real one. The mechanisms used by animals to
distinguish between A and B, and B and C, when A, B, and C are
qualitatively different, may well be entirely different, while if A, B,
and C differ only quantitatively the mechanisms are likely to be the
same. An example of qualitatively different alternatives would be the
Kariba weed (Salvinia auriculata Aubl.), line sand, and organic matter,
preferred in that order by larvae of the chironomid Nilodorum brevibucca Freeman when these choices were offered in pairs (McLachlan,
1969). Unfortunately the mechanisms by which the larvae distinguish
between the choices are not known. An example of quantitatively
different alternatives would be the series of grades of sand obtained
P. 9. MEADOWS AND J. I. CAMPBELL
stimuli falling into the latter category, but there is little evidence for
this at present. Chemicals emanating from food, hosts, predators or
individuals of the same species in aquatic environments are usually
detected at a distance (Copland, 1918 ; Welsh, 1930 ; Davenport, 1950 ;
Stehouwer, 1954; Lindberg, 1955 ; van Dongen, 1956; Davenport et al.,
1960 ; Frings and Frings, 1965 ; Gore, 1966 ; Bovbjerg, 1968 ; Castilla
and Crisp, 1970; Dahl, Emanuelsson and von Mecklenburg, 1970;
Snyder and Snyder, 1971). On the other hand there are a few well
documented instances of adult invertebrates responding to chemicals
only after contact : certain freshwater snails detect their plant food
onIy on contact (Bovbjerg, 1965, 1968), the marine commensal polynoids Acholoe and Gattyana recognize their respective hosts only after
they have encountered them (Davenport, 1953a), and the swimming sea
anemone Stomphia coccinea has to touch the starfishes to which it
responds before it will swim (Sund, 1958). These examples do not
appear to fall into any set pattern, and there is as yet no clear indication
as to why, under field conditions, some of the chemicals should be
detected at a distance and others only after contact.
Hierarchical relations, peck orders and so on, form an accepted part
of current behavioural thinking, and this has led to similar systems
being proposed for habitat selection. Consider a number of alternatives,
A, B, C, D, where A is preferred to B, B to C, and C t o D. The
alternatives can be offered in pairs or as a group together, and may
differ qualitatively or quantitatively. Few authors have considered
these relationships in detail (Meadows and Campbell, 1972), although
Dawkins (1969a, b) has proposed theoretical models. Dawkins’ reasoning is a little difficult to follow in parts, and we are not entirely
convinced of the ecological significance of his hypotheses although they
were not of course intended as such; however they may well serve as a
basis for experimentation,
The distinction between qualitative and quantitative differences
of preference is a very real one. The mechanisms used by animals to
distinguish between A and B, and B and C, when A, B, and C are
qualitatively different, may well be entirely different, while if A, B,
and C differ only quantitatively the mechanisms are likely to be the
same. An example of qualitatively different alternatives would be the
Kariba weed (Salvinia auriculata Aubl.), line sand, and organic matter,
preferred in that order by larvae of the chironomid Nilodorum brevibucca Freeman when these choices were offered in pairs (McLachlan,
1969). Unfortunately the mechanisms by which the larvae distinguish
between the choices are not known. An example of quantitatively
different alternatives would be the series of grades of sand obtained