EABITAT SELEUTION BY AQUATIC INVERTEBRATES
313
attempt to enter burrows that are already occupied. Hazlett’s (1966)
detailed study on the hermit crab Calcinus tibicen (Herbst) involved
testing a variety of factors in the species’ immediate and past environment that might influence aggressiveness. The aggressive behaviour
of Calcinw was usually limited to exchanges of stereotyped display
movements using the chelipeds and ambulatory legs. In most cases
the presence and movements of one individual caused the other to
retreat. In others, dominance was affected by the following factors:
crabs elevated on a ledge were dominant to a lower crab, and turquoise
green coloured animals dominated the more frequent reddish brown
animals, but there was no sexual dominance. Its past environment
manifested itself as follows : starved animals were dominant to well-fed
animals, and animals that had lost fights for 50 h continued to lose
fights. Finally, isolated animals were more aggressive but not more
dominant than non-isolated ones.
Aggressive behaviour between individuals in which stereotyped
behavioural displays develop after visual or physical contact are
evidently one way of ensuring that crowding in a population does
not reach too high a level. But there are other alternatives which
will produce a spaced out distribution, and one of these is by the
secretion of repellent chemicals which act to ward off other members
of the same species, thus producing a sphere of repulsion around
each individual. The behaviour of the carnivorous marine gastropod,
Fasciolaria tulipa, investigated by Snyder and Snyder (1971) falls into
this category. The behaviour of Fasciolaria, however, is more complicated than might be expected, for the same chemical seems to induce
not only avoidance reactions but also copulatory responses and feeding
behaviour depending on its concentration and on the respective sizes
and sex of the individuals involved in the encounter.
Behaviour which leads to a spaced out distribution has obvious
advantages when predators are common, when a minimum living
space is required, or when food is at a premium, and yet these considerations have rarely been submitted to experimental analysis.
Recently, however, convincing evidence has been provided by Stimson
(1970) that the territorial behaviour displayed by the large owl limpet,
Lottia gigantea Sowerby, is directly responsible for the maintenance of
an uninterrupted suppIy of its food. Individual Lottia occupy a territory
of about 1OOOcm2 on rock surfaces in the intertidal zone on the
Californian and North Mexican coast. Their territories are characterized by a thick algal mat (their food) which is not present on adjacent
areas of rock, and by the absence of other species of mobile and sedentary
invertebrates. Stimson’s field experiments, which included transplants
313
attempt to enter burrows that are already occupied. Hazlett’s (1966)
detailed study on the hermit crab Calcinus tibicen (Herbst) involved
testing a variety of factors in the species’ immediate and past environment that might influence aggressiveness. The aggressive behaviour
of Calcinw was usually limited to exchanges of stereotyped display
movements using the chelipeds and ambulatory legs. In most cases
the presence and movements of one individual caused the other to
retreat. In others, dominance was affected by the following factors:
crabs elevated on a ledge were dominant to a lower crab, and turquoise
green coloured animals dominated the more frequent reddish brown
animals, but there was no sexual dominance. Its past environment
manifested itself as follows : starved animals were dominant to well-fed
animals, and animals that had lost fights for 50 h continued to lose
fights. Finally, isolated animals were more aggressive but not more
dominant than non-isolated ones.
Aggressive behaviour between individuals in which stereotyped
behavioural displays develop after visual or physical contact are
evidently one way of ensuring that crowding in a population does
not reach too high a level. But there are other alternatives which
will produce a spaced out distribution, and one of these is by the
secretion of repellent chemicals which act to ward off other members
of the same species, thus producing a sphere of repulsion around
each individual. The behaviour of the carnivorous marine gastropod,
Fasciolaria tulipa, investigated by Snyder and Snyder (1971) falls into
this category. The behaviour of Fasciolaria, however, is more complicated than might be expected, for the same chemical seems to induce
not only avoidance reactions but also copulatory responses and feeding
behaviour depending on its concentration and on the respective sizes
and sex of the individuals involved in the encounter.
Behaviour which leads to a spaced out distribution has obvious
advantages when predators are common, when a minimum living
space is required, or when food is at a premium, and yet these considerations have rarely been submitted to experimental analysis.
Recently, however, convincing evidence has been provided by Stimson
(1970) that the territorial behaviour displayed by the large owl limpet,
Lottia gigantea Sowerby, is directly responsible for the maintenance of
an uninterrupted suppIy of its food. Individual Lottia occupy a territory
of about 1OOOcm2 on rock surfaces in the intertidal zone on the
Californian and North Mexican coast. Their territories are characterized by a thick algal mat (their food) which is not present on adjacent
areas of rock, and by the absence of other species of mobile and sedentary
invertebrates. Stimson’s field experiments, which included transplants