Journal of Experimental Marine Biology and Ecology 250 2000 77–95
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Poor design of behavioural experiments gets poor results: examples from intertidal habitats
M.G. Chapman
Centre for Research on Ecological Impacts of Coastal Cities , Marine Ecology Laboratories A11,
University of Sydney , Sydney, NSW 2006, Australia
Abstract
Many patterns of distribution and abundance of intertidal animals are explained by processes of movements of animals, selecting particular habitats or levels on the shore, or interacting with other
species. Movements of intertidal animals have therefore been studied over many years. During this long history, much intertidal ecology has changed in focus from broad-scale to small-scale patterns
and processes, although there has been recent refocus on a combination of many scales. Simultaneously, there has been an increase in the incidence of field experiments and growing
recognition that behaviour is more flexible than originally thought. This review examines changes in the ways that experiments on movements on intertidal animals have been and are being done,
taking into account these changes in emphasis. Although some progress has been made, there is still a long way to go. The idea is still prevalent that behaviour is simple, rather invariant and that
the animals respond to broad-scale cues that have traditionally been of interest to many investigators. This means that many experiments are still designed to minimise or ignore natural
variation in behaviour rather than to measure it and that any associated disturbances are considered irrelevant and therefore not evaluated. Understanding the role that behaviour has in establishing
and maintaining many of the patterns observed on intertidal shores is crucial to our understanding of the ecology of these habitats. Better experiments, designed logically with appropriate controls
to evaluate realistic processes and to measure how behaviour varies among places and from time to time can only improve this understanding.
2000 Elsevier Science B.V. All rights reserved.
Keywords : Behaviour; Experimental design; Intertidal; Movements; Variability
1. Introduction
Patterns of distribution and abundance of intertidal animals are frequently explained
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2000 Elsevier Science B.V. All rights reserved.
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.G. Chapman J. Exp. Mar. Biol. Ecol. 250 2000 77 –95
by the behaviour of the species under consideration, or of those with which they interact. Although patterns of sessile species may be determined initially by larval behaviour e.g.
Crisp, 1974; Bourget, 1987, these patterns can be altered by mortality caused by mobile animals. Consumers remove species in a patchy manner Fairweather, 1988a, which can
subsequently affect the distribution and abundance of animals which feed on or shelter amongst these prey Underwood et al., 1983. In addition, small animals can be killed
during foraging by larger animals Dayton, 1971; Denley and Underwood, 1979; Hill and Hawkins, 1991. Behaviour of large mobile animals, therefore, has a major influence
on patterns of distribution, abundance and dispersion of many species on intertidal shores.
These effects are patchy because the animals are not distributed evenly across intertidal shores. Animals are generally limited to certain heights on a shore Lewis,
1964, are more abundant in particular habitats Underwood, 1976; Emsen and Faller- Fritsch, 1976; Raffaelli and Hughes, 1978; Byers and Mitton, 1981; Chapman, 1994 or
may aggregate without any obvious correlation with habitat Chapman, 1995. They can select among different patches of habitat and change behaviour and patterns of
movement from time to time or place to place, in response to physical conditions Mackay and Underwood, 1977; Moran, 1985; Jones and Boulding, 1999, growth
Moreno et al., 1993 or the presence of other animals Fairweather, 1988b. For most species, the precise cues that cause variation in behaviour have not yet been identified.
The behaviour of intertidal animals has been studied for a long time, partly because patterns of distribution, abundance and dispersion are easily quantified and because
many species and their habitats are suitable for experimental investigation reviewed by Underwood, 1979, 1985. Many species are easy to see and capture, can be handled,
marked or manipulated to alter densities Menge, 1972; Underwood, 1988, or can be moved among habitats Chapman and Underwood, 1994 or to different heights on the
shore Gendron, 1977; McQuaid, 1981. Their surroundings may also be manipulated to identify cues to which the animals respond Cook, 1969; Menge et al., 1983;
Worthington and Fairweather, 1989; Underwood and Chapman, 1992; Chapman and Underwood, 1994; Crowe, 1996. Thus, the behaviour of intertidal animals on rocky
shores has a long history of direct experimental study, often under natural conditions.
Because the behaviour of mobile intertidal animals is a broad topic, this review will focus on experimental studies of movement, orientation and selection of habitat by
intertidal animals, particularly molluscs. Some species have been studied on different rocky shores using different methodologies, e.g. Patella vulgata L. Lewis and Bowman,
1975; Hartnoll and Wright, 1977; Little et al., 1988; Evans and Williams, 1991; Chelazzi et al., 1994. In other studies, different species have been compared on the same shores
Underwood, 1976; Levings and Garrity, 1983; Fairweather, 1988b; Chapman, 2000. These may allow evaluation of general trends in behaviour, in addition to documenting
how variable they may be.
Over time, there has been a change in emphasis from ideas that the behaviour of invertebrates is rather fixed and invariant Fraenkel, 1927 to the recognition of
flexibility of behaviour in response to local environmental cues Hazlett, 1988, from descriptions of broad-scale patterns of distribution upshore and alongshore zonation;
Lewis, 1964; Stephenson and Stephenson, 1972 to those of multi-scale, hierarchical
M .G. Chapman J. Exp. Mar. Biol. Ecol. 250 2000 77 –95
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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
