E4BITAT SELEUTION BY AQUATI0 INVERTEBRATES
327
pilings of a pier which extends half a mile out from the shoreline near
Santa Barbara, California. Mytilus, on which it feeds, grows intertidally
in clusters on the pilings, and from time to time clusters of Mytilus fall
beneath the pier helped by predation of the Pisaster on the pilings.
Most of the Pisaster however are found under the pier and here Mytilw
are very patchily distributed. Landenberger, because he was able to
train Pisaster to move down the side of a tank to food with a light
stimulus, suggested that the starfish were kept in the general area of
the pier by learning to associate food with the region of reduced light
intensity under the pier. Perhaps the connection between these
observations is a little tenuous, but the idea is an interesting one.
Under the pier, large aggregations of Pisaster form around the clumps of
Mytilus, only to disperse again when the clump is eaten. Landenberger
(1967) induced the formation of new aggregations by placing clumps of
Mytilus on parts of the bottom where there were few Mytilus and
therefore few Pisaster. Pisaster migrated in from areas nearby but
unexpectedly stayed there for some two or three months after the food
had been eaten, so they may have learned to associate the particular
area of the bottom with food, the association taking some time to
wane. Landenberger (1968) also described in detail the food preferences
of Pisaster. Seven species of intertidal molluscs were offered in pairs,
and Pisaster showed a clear hierarchy of preferences with Mytilus
edulis and M . calij’ornianus Conrad being the most suitable.
If we accept Landenberger’s reasoning about the relationship
between the shade under the pier and training Pisaster to light, his
work demonstrates clearly how the starfish remain in the general area
of their food (the shaded area under the pier) and then within this
area detect and aggregate around clumps of Mytilw-their preferred
food. Landenberger’s detailed analysis shows how a complex example
of habitat selection can be understood by suitable experimentation, and
is likely to lead to further research.
The examples we have quoted illustrate how marine and freshwater
carnivorous invertebrates seek out and aggregate around their prey ;
however, some prey organisms take avoiding action to escape their
predators and this can be considered a form of habitat selection since
their behaviour will influence their distribution. The escape responses
of intertidal gastropods to predatory gastropods and to starfish, of the
sea anemone Stomphia coccinea (Miiller) to starfish, and of bivalves,
gastropods and brittle stars to starfish are examples, and appear to be
based on chemicals detected at a distance from or on contact with the
predator (Bauer, 1913; Weber, 1924; Bullock, 1953; Clark, 1958; Ross,
1965; Gore, 1966; Kohn and Waters, 1966; Mackie, 1970). Mackie loc.
327
pilings of a pier which extends half a mile out from the shoreline near
Santa Barbara, California. Mytilus, on which it feeds, grows intertidally
in clusters on the pilings, and from time to time clusters of Mytilus fall
beneath the pier helped by predation of the Pisaster on the pilings.
Most of the Pisaster however are found under the pier and here Mytilw
are very patchily distributed. Landenberger, because he was able to
train Pisaster to move down the side of a tank to food with a light
stimulus, suggested that the starfish were kept in the general area of
the pier by learning to associate food with the region of reduced light
intensity under the pier. Perhaps the connection between these
observations is a little tenuous, but the idea is an interesting one.
Under the pier, large aggregations of Pisaster form around the clumps of
Mytilus, only to disperse again when the clump is eaten. Landenberger
(1967) induced the formation of new aggregations by placing clumps of
Mytilus on parts of the bottom where there were few Mytilus and
therefore few Pisaster. Pisaster migrated in from areas nearby but
unexpectedly stayed there for some two or three months after the food
had been eaten, so they may have learned to associate the particular
area of the bottom with food, the association taking some time to
wane. Landenberger (1968) also described in detail the food preferences
of Pisaster. Seven species of intertidal molluscs were offered in pairs,
and Pisaster showed a clear hierarchy of preferences with Mytilus
edulis and M . calij’ornianus Conrad being the most suitable.
If we accept Landenberger’s reasoning about the relationship
between the shade under the pier and training Pisaster to light, his
work demonstrates clearly how the starfish remain in the general area
of their food (the shaded area under the pier) and then within this
area detect and aggregate around clumps of Mytilw-their preferred
food. Landenberger’s detailed analysis shows how a complex example
of habitat selection can be understood by suitable experimentation, and
is likely to lead to further research.
The examples we have quoted illustrate how marine and freshwater
carnivorous invertebrates seek out and aggregate around their prey ;
however, some prey organisms take avoiding action to escape their
predators and this can be considered a form of habitat selection since
their behaviour will influence their distribution. The escape responses
of intertidal gastropods to predatory gastropods and to starfish, of the
sea anemone Stomphia coccinea (Miiller) to starfish, and of bivalves,
gastropods and brittle stars to starfish are examples, and appear to be
based on chemicals detected at a distance from or on contact with the
predator (Bauer, 1913; Weber, 1924; Bullock, 1953; Clark, 1958; Ross,
1965; Gore, 1966; Kohn and Waters, 1966; Mackie, 1970). Mackie loc.