Much sampling to detect and quantify human environmental disturbances is flawed by a lack of appropriate replication. BACI (Before—After—Control—Impact) designs have only a single control location, and any conclusions from them are illogical. Asymmetrical designs using one putatively impacted and several control locations can reliably detect a variety of environmental impacts, including those that do not affect long—run mean abundances, but do alter temporal variance. When abundances of populations in different locations show temporal interaction, the asymmetrical designs allow tests for impact that are not possible in BACI designs. Asymmetrical designs are also extendable to sample at hierarchical spatial and temporal scales. The power of tests using asymmetrical designs is great for non—interactive sets of abundances, but greatest for pulse (short—term) responses to disturbances, large alterations of temporal variance, or combinations of temporal variance, or combinations of sustained, press responses in mean abundance coupled with altered temporal heterogeneity. Power in temporally interactive sets of data is generally poor. Alternatives to pre—disturbance sampling, including generalized assessment of spatial and temporal variances and experimental impacts, may provide better guidance for detection of human disturbances.

On Beyond Baci: Sampling Designs That Might Reliably Detect Environmental Disturbances

Ichnology is the study of traces created in the substrate by living organisms. This is the first book to systematically cover basic concepts and applications in both paleobiology and sedimentology, bridging the gap between the two main facets of the field. It emphasizes the importance of understanding ecologic controls on benthic fauna distribution and the role of burrowing organisms in changing their environments. A detailed analysis of the ichnology of a range of depositional environments is presented using examples from the Precambrian to the recent, and the use of trace fossils in facies analysis and sequence stratigraphy is discussed. The potential for biogenic structures to provide valuable information and solve problems in a wide range of fields is also highlighted. An invaluable resource for researchers and graduate students in paleontology, sedimentology and sequence stratigraphy, this book will also be of interest to industry professionals working in petroleum geoscience.

Ichnology: Organism-Substrate Interactions in Space and Time

Tidal Flat Ecology

V a r ~ a t ~ o n (patchiness) In the d~st r~but ion of organisms and other env~ronmental vanables exists at different spatial scales This patchiness has Important implicat~ons for comparative and d e s c r ~ p t ~ v e studies of d~stnbution and abundance because ~t complicates comparisons of abundance at the largest spa t~a l scales Although the existence of patchiness has been recognised for a long time, it has not been adequately addressed in most studies of manne soft s ed~ment s which are often confounded (or pseudoreplicated') because of a lack of appropriate spatlal replicat~on Spatial vanation In the distnbution of soft-sediment macrofauna In Botany Bay, Australia 1s described using a nested hierarchical sampling design Significant vanatlon was detected at spatial scales from 10 m to 3 5 km Implications of patchiness for environmental sampllng and monitoring and the means of overcoming associated problems are discussed The present study concerns the abundance of macrofauna but the conclusions are general and are relevant to s tud~es of other vanables such as pollutants

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Spatial variation in soft-sediment benthos

Experimental tests of clearly articulated hypotheses are an increasingly widespread feature of modern marine ecology. Increased use of experiments has not, however, been accompanied by increased understanding of the logical structure of falsificationist tests. Most observations can be explained by several different models or theories. To distinguish among these requires demonstration of the falsity of the consequences or predictions of incorrect models. This is best achieved by deriving from each model one or more hypotheses (predictions) about the type, form or nature of observations that should occur in some not-yet-examined set of circumstances. Because of logical constraints on the possibility of proving the correctness of such hypotheses, they must be inverted to form logical null hypotheses which comprise all alternative possibilities to those predicted in the hypotheses. Correctness or not of null hypotheses can then be ascertained by an appropriately designed experiment (or test), leading to unambiguous rejection or retention of the null hypotheses. The former corroborates the hypotheses and provides support for the correctness of the explanatory model for the original observations. In contrast, retention of a null hypothesis identifies an incorrect model. The growth of knowledge is thus the elimination of false models, theories and explanations.

Ecological experiments usually require statistical procedures for determining whether or not null hypotheses should be retained. Construction of statistical null hypotheses (i.e. definitions of parameters of frequency distributions of test statistics) sometimes requires that these be identical to logical hypotheses (and not to the logical nulls). This leads to irrational acceptance of hypotheses and the models or theories from which they were derived. It also poses immense problems for determinations of statistical power of experiments.

Ecological experiments are analysed to reveal the nature of, and linkages between, their components in relation to falsificationism, statistical procedures and the logical properties and interpretations of ecological theories.

Experiments in ecology and management: Their logics, functions and interpretations

In the region of Barnstable Harbor, Massachusetts, 67 species of larger invertebrates were found in 3 faunal associations characteristic of different tide levels. The number of species per sample was highest at the intermediate tide level. Temperatures of sediments and densities of several species were followed for a year at two intertidal levels (60 cm and 90 cm above mean low water). Temperature variation was lower at the 60—cm level than at the 90—cm level at all times of the year, and at both levels was higher in spring than at any other time of the year. In three of the four species studied, spatial variation in density and rate of density change was significantly higher at the 60—cm location than at the 90—cm location. The mortality rate for adult G. gemma was higher at 60 cm (where density was lower) than at 90 cm, while the reverse was true for young—of—year. Release of young began sooner in the spring at 90 cm than at 60 cm. The growth rate of G. gemma at Barnstable Harbor was much lower than that reported at Union Beach, New Jersey, although at both places virtually all growth took place in summer. At Barnstable Harbor the maintenance requirements were 20—30 times higher in summer than in early spring. The Q10 within the temperature range 5—20°C was 4.1. G. gemma at 90 cm had less time to feed than at 60 cm, but had higher requirements for population maintenance because of an older age structure and a higher density. The growth rate of G. gemma was higher at 90 cm than at 60 cm.

Katharine D. Hobson

Papers

Spatial and Temporal Structure in a Temperate Intertidal Community, with Special Emphasis on Gemma Gemma (Pelecypoda: Mollusca)

Factors Determining Spatial and Size-Frequency Distributions of Gemma gemma