316
P. 9. MEADOWS AND J. I. CAMPBELL
americana, found in protected fresh waters and sphagnum bogs in
America (Welch, 1914). They construct elaborate tunnel systems,
eventually burrowing lengthwise down the petiole. They then often
leave the leaf and swim on the water surface until they meet ano er
leaf by chance. At this point the larvae must be able to disting r ish
between the leaves of Nymphaea and those of other plants in the same
environment, and laboratory experiments confirm this, for the larvae
will only burrow into the leaves of the white water lily Castalia odorata
= Nymphaea ohrata Aiton if Nymphaea is not available, and consistently refuse Potamgeton and Sagittaria spp. There are a few more
recent studies, but most of them are less comprehensive. The nymphs
of the mayfly Heptagenia juewgrisea (Retz) live associated with the
freshwater plant Batrachium but not with CaZZitriche which is also common in the same environment. When offered a choice they prefer
Batrachium to CaZEitriche, stones, gravel or sand (Madsen, 1968).
Egglishaw (1 964) has conducted some interesting preliminary experiments on the colonization of trays containing different amounts of plant
detritus in a stream riffle. The greatest number of animals colonized
trays containing the most detritus.
The possible complexity of the sequence of behaviour patterns
elicited by plant chemicals can be appreciated if one turns for the sake
of comparison to the terrestrial environment, and to the recent work on
the way in which bark beetles find the particular species of tree into
which they burrow. The situation is analogous to the settlement of
larvae on one particular seaweed, animals aggregating in response to
chemicals produced by their host plant. The only differences are that
in this instance the chemicals act at a distance (the beetles smell
their way to the tree) that both the plant and the beetles produce
chemicals, and that if we are to believe a recent hypothesis (Renwick
and VitB, 1969), a series of chemicals act in sequence, at first to attract
the beetles and then to regulate their sex ratio and population density
(Fig. 3).
We may therefore summarize the associations between invertebrates
and plants and their relation to habitat selection as follows. Associations between sedentary invertebrates and seaweeds appear to be largely
dependent on chemical clues received by larvae as they settle, although
the exact nature of the chemicals involved in these associations is not
known and there is no indication of the relative importance of chemical
and other less specific stimuli at settlement. There is evidence of
inhibitory chemicals in seaweeds, and chemicals of this sort may be more
widespread in aquatic environments than is appreciated ; it is possible,
for example, that they might occur in animals as well as plants, and be
P. 9. MEADOWS AND J. I. CAMPBELL
americana, found in protected fresh waters and sphagnum bogs in
America (Welch, 1914). They construct elaborate tunnel systems,
eventually burrowing lengthwise down the petiole. They then often
leave the leaf and swim on the water surface until they meet ano er
leaf by chance. At this point the larvae must be able to disting r ish
between the leaves of Nymphaea and those of other plants in the same
environment, and laboratory experiments confirm this, for the larvae
will only burrow into the leaves of the white water lily Castalia odorata
= Nymphaea ohrata Aiton if Nymphaea is not available, and consistently refuse Potamgeton and Sagittaria spp. There are a few more
recent studies, but most of them are less comprehensive. The nymphs
of the mayfly Heptagenia juewgrisea (Retz) live associated with the
freshwater plant Batrachium but not with CaZZitriche which is also common in the same environment. When offered a choice they prefer
Batrachium to CaZEitriche, stones, gravel or sand (Madsen, 1968).
Egglishaw (1 964) has conducted some interesting preliminary experiments on the colonization of trays containing different amounts of plant
detritus in a stream riffle. The greatest number of animals colonized
trays containing the most detritus.
The possible complexity of the sequence of behaviour patterns
elicited by plant chemicals can be appreciated if one turns for the sake
of comparison to the terrestrial environment, and to the recent work on
the way in which bark beetles find the particular species of tree into
which they burrow. The situation is analogous to the settlement of
larvae on one particular seaweed, animals aggregating in response to
chemicals produced by their host plant. The only differences are that
in this instance the chemicals act at a distance (the beetles smell
their way to the tree) that both the plant and the beetles produce
chemicals, and that if we are to believe a recent hypothesis (Renwick
and VitB, 1969), a series of chemicals act in sequence, at first to attract
the beetles and then to regulate their sex ratio and population density
(Fig. 3).
We may therefore summarize the associations between invertebrates
and plants and their relation to habitat selection as follows. Associations between sedentary invertebrates and seaweeds appear to be largely
dependent on chemical clues received by larvae as they settle, although
the exact nature of the chemicals involved in these associations is not
known and there is no indication of the relative importance of chemical
and other less specific stimuli at settlement. There is evidence of
inhibitory chemicals in seaweeds, and chemicals of this sort may be more
widespread in aquatic environments than is appreciated ; it is possible,
for example, that they might occur in animals as well as plants, and be