Variations in numbers of animals in time and space

Professor Tony Underwood and Professor Gee Chapman

Rocky shore

All environmental impacts are defined by (and must be measured as) spatial and temporal interaction in biological measurements. What this means is that an impact is some change (a temporal difference) in the affected area that makes it different from what it was before the impact and different from what is happening in areas not experiencing that disturbance. So, an impact also causes a spatial difference. In natural circumstances, numbers of animals and plants change from time to time and are different from place to place. So, an impact is an unnatural amount of temporal change that differs from what naturally happens in undisturbed places. This sort of pattern - a different temporal change in disturbed places and, simultaneously, a different spatial pattern after an impact starts compared with before - is called an interaction.

Understanding environmental impacts that affect populations of coastal animals and plants requires understanding their natural interactions in space and time.


Among many on-going projects on processes influencing the ecology of local populations, this research is an analysis of interactive processes in numbers of animals. We have been collecting data on numerous populations of snails and barnacles (which are quite cheap to sample) on rocky shores on various parts of the coast. Quantitative estimates of their numbers are made over long periods, in order to have reliable data (which must be independently sampled from one time to another to allow statistical analyses). Then, we are developing new quantitative tools to describe and analyse the variation in numbers in space, in time and their interactions.

This is being done at small and large scales (within a metre, a few metres, 10s and 100s of metres apart and from shore to shore) because we already know that the way numbers vary from time to time depends on the size of the area examined.


Two important outcomes of this work relate to our ability to detect and measure environmental impacts. First, by understanding the interactions better, we can design much more efficient sampling programmes to detect the interactions caused by impacts.

Second, in analyses of many types of impacts, it is impossible to get data before the impacts start (particularly where it is an accident). So, it is crucial to understand how much interaction there is naturally so that the amount of interaction after the impact starts can be assessed. This work is contributing to the development of theories about interactions and impacts, to be able to help interpret other measures on other species in different habitats.


Some of the interesting results from this project are given in the publications listed below.

Chapman, M.G. (1999). Improving sampling designs for measuring restoration in aquatic habitats. Journal of Aquatic Ecosystem Stress and Recovery.

Underwood, A.J. (1997). Environmental decision-making and the precautionary principle: what does this principle mean in environmental sampling practice? Landscape and Urban Planning,Vol. 37, pp. 137-146.

Underwood, A.J. (1999). Physical disturbances and their direct effect on an indirect effect: responses of an intertidal assemblage to a severe storm. Journal of Experimental Marine Biology and Ecology, Vol. 232, pp. 125-140.

Underwood, A.J. (2000). Trying to detect impacts in marine habitats: comparisons with suitable reference areas. In: Statistics in Ecotoxicology, edited by T. Sparks, John Wiley and Sons, New York.

Underwood, A.J. (2000) Importance of experimental design in detecting and measuring stresses in marine populations. Journal of Aquatic Ecosystem Stresses and Recovery