A. J. Underwood

Supply-side ecology and benthic marine assemblages

Many marine invertebrates have a planktonic stage of their life history during which widespread dispersal and much mortality occur. The numbers surviving to recruit into habitats occupied by adults are therefore very variable in time and space. Models for the structure and dynamics of benthic assemblages tend to focus on processes causing death - often assuming consistent arrivals of recruits. Supply-side ecology is a newly fashionable term to describe recent interest in the long-realized consequences of variations in recruitment. Such variations have important influences on theory and empirical research in these assemblages.

Scales of spatial patterns of distribution of intertidal invertebrates

Few comparative studies of spatial patterns at different scales have examined several species in the same habitat or the same species over a range of habitats. Therefore, variability in patterns among species or among habitats has seldom been documented. This study quantifies spatial patterns of a suite of intertidal snails and a species of barnacle using a range of statistical techniques. Variability in densities was quantified from the scale of adjacent quadrats (over a distance of centimeters) to tens of kilometers. Significant differences in abundances occurred primarily at two spatial scales. Small-scale differences were found at the scales of centimeters or 1–2 m and, for many species on many shores, these accounted for most of the variability in abundances from place to place. These are likely to be determined by behavioural responses to small-scale patches of microhabitat. Large-scale differences in abundance were also found in most species at the scale of hundreds of meters alongshore. These are likely to be due to variation in recruitment (and/or mortality) because of limited dispersal by adults of these species. There was little or no additional variation among shores, separated by tens of kilometers, than was shown among patches of shore separated by hundreds of meters. Identification of the scale(s) at which significant differences in abundance are found focus attention on the processes (and the scales at which these processes operate) that influence patterns of distribution and abundance. Some of the advantages and disadvantages of various procedures are discussed.

Observations in ecology : you can't make progress on processes without understanding the patterns

Coastal marine ecology is, quite properly, increasingly focussed on experimental tests of hypotheses about processes. These are, however, done to explain observations and patterns. It is therefore appropriate to be able to publish quantitative observations to provide the context and basis for studying mechanisms and processes. Ecologists are concerned about very different types of observations. Some areas of study are still totally dependent on observational, descriptive evidence; some depend on mensurative tests of hypotheses about patterns. Tests of hypotheses about patterns are also needed to validate casual or qualitative observations. Guide-lines for what constitutes appropriate or publishable ecological descriptions are discussed here. These recognize the experimental, hypothesis-testing nature of many descriptive studies and consider the relevance of sound logic and experimental design in the planning, collection and interpretation of observations.

The Ecology of Intertidal Gastropods

Publisher Summary The structure and dynamics of biological communities cannot be understood without considerable background information about the ecology of the component species. Experimental manipulations of natural populations in field situations are often the most profitable method of determining the factors that affect the distribution and abundance of species. Intertidal organisms have proved to be suitable for such direct experimentation because of the ease of access to intertidal areas, the relatively sessile nature, and due to the great abundance of many of the organisms. The chapter elaborates the key observations made on the ecology of intertidal gastropods such as the factors affecting their establishment of distributional patterns and the maintenance of distributional patterns caused through their behavioral adaptations and physiological stress. It dwells on the competition and predation due to the distribution and abundance of population of intertidal gastropods, its reproductive biology, and the geographical distribution and influences of gastropods on the structure of intertidal communities. The chapter also lists the observations based on general hypotheses and highlights the gap in the knowledge on ecology and behavior of intertidal gastropods, thus, paving a foundation for future research and investigations.

Temporal variation in soft-sediment benthos

Abstract The existence of small-scale temporal variation in the distribution of the fauna of marine soft sediments has long been recognised. The implications of this variation have rarely been adequately addressed in studies of changes in the fauna over longer time-scales. Without knowledge of the presence or absence of variation at smaller scales, comparisons across longer time-scales must be confounded. Temporal variation in the distribution of the macrofauna of sediments in Botany Bay, New South Wales, Australia, is described using a nested, hierarchical sampling design. Significant variation was found at temporal scales from days to months. Implications of short-term variation for environmental sampling and monitoring, and the means of overcoming associated problems, are discussed. The conclusions of the present study are applicable to studies of other variables, such as pollutants.

What Is a Community

Attempts are often made to distinguish a community of organisms from a haphazard assemblage of populations of various species that happen to be together at any place and time. These depend on definitions of those organisms to be included in the community and of the appropriate temporal and spatial scales that might demonstrate consistency in coincidence and interdependence of the set of organisms. Some of the problems with such definitions are discussed, and it is concluded that much of the definition of a community is somewhat arbitrary. The historical debate between proponents of integrated communities and those who favor individual populations as the appropriate units for study continues. The argument that communities might have emergent properties not revealed by the more reductionist studies of populations is considered to be without firm foundation and of no relevance to the design of ecological studies. Patterns and processes should be investigated at several spatial and temporal scales, and community-level attributes of assemblages of species only become relevant where less holistic research programs fail.

On Beyond Baci

Publisher Summary This chapter discusses the approach in which multiple Control sites are used to detect impacts in a different way and which can detect a greater variety of impacts.. Lack of time and resources for powerful sampling before many impacts requires research to determine the rates of temporal change and the magnitudes of spatial differences for various populations. This is done for key habitats in which repeated disturbances are planned, like for disturbances of similar sorts in many habitats such as those due to forestry, salmon fishing, agriculture, foreshore developments in mangrove forests, mussel and oyster fanning, building marinas, boat-ramps, outfalls from different types of industries, cooling-water outlets. Choosing some suitable species and monitoring in a range of undisturbed, randomly chosen replicated habitats is useful because these will recur repeatedly. If these are randomly chosen and the times of sampling are randomly assigned, the variance among times, locations and their interactions are objective measures of the variances from a population of such locations and times.Publisher Summary This chapter discusses the approach in which multiple Control sites are used to detect impacts in a different way and which can detect a greater variety of impacts.. Lack of time and resources for powerful sampling before many impacts requires research to determine the rates of temporal change and the magnitudes of spatial differences for various populations. This is done for key habitats in which repeated disturbances are planned, like for disturbances of similar sorts in many habitats such as those due to forestry, salmon fishing, agriculture, foreshore developments in mangrove forests, mussel and oyster fanning, building marinas, boat-ramps, outfalls from different types of industries, cooling-water outlets. Choosing some suitable species and monitoring in a range of undisturbed, randomly chosen replicated habitats is useful because these will recur repeatedly. If these are randomly chosen and the times of sampling are randomly assigned, the variance among times, locations and their interactions are objective measures of the variances from a population of such locations and times.

Populations, frequency distributions and samples

Introduction The preceding account of a logical framework for investigating biological observations is not as easy to use as might be hoped. The major problem is that neither the original observations nor the results of tests are unambiguous. Biological observations (in whatever form the data are collected) are not constant, fixed truths, but vary from place to place and from time to time. So, of course, do measurements in other sciences, such as chemistry and physics. Even where intrinsic variability is small or absent (i.e. the measurement is of some physical or chemical constant), both the machinery used to make measurements and the observers themselves are not constant. Variability in measurements There are intrinsic and extrinsic reasons why biological observations are variable. Intrinsic reasons include, first, fundamental properties of biological systems. For example, the size of an animal, the rate of growth of a plant, the speed of movement of a predator are all subject to genetic variability from one individual to another. Thus, unless the individuals are identical in all genetically determined processes of growth or speed (respectively), there is no possibility that their sizes (or speeds) will be identical. Second, in addition to innate properties of systems, there are intrinsic processes causing variability. For example, the diameters of oocytes in a gonad are influenced by stresses, pressures, rates of cellular division, position in the gonad, etc.

Conclusions: where to from here?

Be logical, be eco-logical The major purpose of the information provided here is to help you to get good professional help. Use the information to help to plan and to consider the relevant parts of the biology so that your discussions with statistical advisers include the biological reasons why the requirements and assumptions of statistical procedures may be problematic. Use available accounts of experiments and reviews of experimental procedures as tools to evaluate designs – not just as methods of identifying ways of doing experiments. Use other accounts (such as the text by Scheiner & Gurevitch (1993), which appeared during the final writing of this one). Constantly probe better ways of doing experiments. Do not be frustrated that this book has not discussed such topics as how to deal with unbalanced sets of data. Apart from the serious recommendation that we try to avoid having unbalanced data in the first place, the issues are complex and beyond this discussion. You will need help, but the help you get will be improved if you are aware of the issues. The preceding sections were chosen to be an introduction to the major themes of modern experimental design as needed by ecologists. The issues discussed are the most general in ecological experimentation. Spatial scales of patterns and processes vary. Intensities of effects and outcomes of processes vary from place to place and time to time.