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patterns of patchiness Underwood and Denley, 1984; Thompson et al., 1996 and from studies of behaviour done in the laboratory e.g. Fraenkel, 1927 to experimental field
studies Underwood, 1993. These changes have influenced the way in which experi- ments on the behaviour of intertidal animals were done, are still being done and the way
that results are interpreted. Although these trends will be examined separately, it is important to remember that they occurred simultaneously.
This review will evaluate changes in the ways that movements and habitat-selection of intertidal animals has been studied while these broad changes in focus have evolved. It is
attempted in the spirit of learning from mistakes of the past in order to progress into the future with a more rigorous and logical approach to understanding behavioural ecology
of intertidal animals. Unfortunately, it has therefore been necessary to criticise what has been wrong with the ways in which many studies have been done, rather than spending
too much time on what had been found out in such studies. The references cited are a few chosen from a very large set of papers on these topics, simply to illustrate the points
being made. Most are not particularly better or worse than many others that could have been discussed. Most of the errors illustrated are not limited to these papers, but are
widespread in the literature, including many of my own published studies. We can all learn from critical evaluation of past practices. Better behavioural experiments will give
better ecological understanding. It is hoped that this review will help in the design and interpretation of such experiments.
2. Change in focus from fixed to variable behaviour
For many years during the early studies of animal behaviour, it was believed that behaviour of animals, invertebrates in particular, was rather invariable — any variation
shown was simply ‘noise’ and of little interest reviewed by Foster and Endler, 1999. This was followed by increasing recognition of variability in behaviour, particularly at a
geographic scale, which was thought to represent adaptational changes of populations to local conditions. Most of the focus of this work has been terrestrial vertebrates Foster
and Endler, 1999. The reproductive strategy of many marine invertebrates, i.e. broadcast fertilization and long-lived planktonic larvae suggests considerable genetic
interchange among populations Scheltema, 1971 and little genetic connection between adults and recruiting larvae on local shores Berger, 1973; Snyder and Gooch, 1973.
These traits would tend to counteract many local adaptations.
It is important to remember that behaviour and other traits in a population can show considerable variability without a genetic basis. Gotthard and Nylin 1995 emphasise
the importance of distinguishing between two types of traits. ‘Adaptive’ are behavioural or other phenotypic characteristics that confer advantage on organisms under certain
environmental conditions. These are distinguished from the presence of traits in a population as evidence of ‘adaptation’ i.e. the outcomes of natural selection killing
particular genotypes in local habitats. ‘Adaptive’ traits do not need genetic isolation in order to develop because genotypes can have a wide range of possible behavioural or
other forms of phenotypes that will be expressed under different environmental conditions.
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.G. Chapman J. Exp. Mar. Biol. Ecol. 250 2000 77 –95
There are many examples of differences in behaviour among populations of intertidal invertebrates, for some of which there is a genetic basis. For example, Scapini et al.
1999 showed in laboratory experiments that the amphipod Talitrus saltator Montagu orientated seawards, towards the sun or randomly, depending on their shore of origin.
Breeding experiments suggested that orientation was partly genetic, but was also influenced by experiences of juveniles. McKillup 1983 showed that populations of
Nassarius pauperatus Lamarck varied in their behavioural responses to conspecifics differently among shores. There were two distinct forms of behaviour — twisting and
non-twisting. Twisters showed specific rotations of their shells when in contact with conspecifics. Non-twisters did not. The prevalence of each within a population depended
on whether the population had been feeding on a point or diffuse source of food. The behaviour was fixed within individuals and the relative abundance of different morphs
from population to population determined the predominant behaviour in the population. Interchange among populations via planktonic larvae maintained each morph in each
population.
Some forms of polymorphic behaviour can show differences at very small spatial scales, despite considerable genetic interchange among populations. Thus, populations of
the small limpet, Patelloida mufria Hedley living on intertidal rock-platforms, are epizoic on the shells of other gastropods Mapstone et al., 1984. The shells of the
limpets grow to fit the curvature of their host shells and they cannot attach firmly to the rocky substratum. The same species is found under intertidal and shallow subtidal
boulders unpublished data and on subtidal rocky reefs Fletcher, 1988, where they co-exist with a suite of other limpets on the rock surface. Intertidal and subtidal
populations may only be separated by a few metres and are not geographically isolated. Many species show very marked differences in behaviour among different shores, or
among different patches of habitat on the same shore, e.g. in response to tidal amplitude or exposure Cook and Cook, 1978, to different amounts of food Mackay and
Underwood, 1977, or to availability of microhabitat Chapman and Underwood, 1994.
Some species show marked ontogenetic changes in behaviour. The limpet Acmaea incessa Hinds change from feeding on micro-algae on the feeding scars of adults to
developing their own feeding scars on the kelp Egregia laevigata Setchell as they get older Black, 1976. Similarly, young Patella longicosta Lamarck settle and feed on the
shells of adults until large enough to defend their own feeding territories on the rock surface Branch, 1971. These changes in behaviour are well documented, but for many
species, it is not known whether behaviour changes markedly as the animals get older and, for many species, it is not easy to equate size with age or maturity. Therefore,
how much of the variability in behaviour among populations may be governed by the age-structure of the populations is seldom known.
Other species change behaviour rapidly in response to variable environmental conditions. Mackay and Underwood 1977 showed that homing in the limpet Cellana
tramoserica Sowerby varied within and among populations. In any population at a particular time, some individuals homed to fixed sites, whereas others moved randomly.
Individuals changed their behaviour from time to time, apparently in response to the availability of food. Aggregation in intertidal whelks Moran, 1985; Gosselin and
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Bourget, 1989 and littorinds Chapman and Underwood, 1996 was influenced by local environmental heterogeneity, time of emersion and the weather. The decision to forage
by the whelk Thais lapillus L. was influenced by local environmental conditions and the state of hunger of the animals Burrows and Hughes, 1989, 1991.
Much evidence now suggests that behaviour of intertidal invertebrates is very flexible. It changes in response to broad-scale and localized environmental and physiological cues
and, therefore, would be expected to vary spatially and temporally. Nevertheless, many studies of behaviour are done once in one area and the results presented as if they
demonstrate fixed patterns of behaviour.
3. The change in focus from broad to small scales of spatial patterns
