Variation in abundances of intertidal populations: consequences of extremities of environment

Spatial and temporal variability in patterns and processes are poorly under stood for most assemblages, including intertidal assemblages on rocky shore s. Such habitats represent gradients of increasing physical harshness towar ds the top of the shore. Influences of environmental harshness on numbers a nd recruitment of animals lead to the hypotheses that there should be great er small-scale spatial variance in more extreme parts of the environment (h igher on the shore) and greater short-term temporal variance in less extrem e (lower) parts of the shore. These predictions were tested using two barna cles (Tesseropora rosea and Chamaesipho tasmanica) and two limpets (Patello ida latistrigata and Notoacmea petterdi) in up to five locations on wave-ex posed rocky shores in New South Wales (Australia). Only T. rosea showed dif ferent spatial variation at higher and lower levels - but greater at lower than higher levels, contradicting the hypothesis. T. rosea and P. latistrig ata had greater temporal variation at lower levels, supporting the hypothes is. C. tasmanica, however, showed the opposite pattern, contradicting the h ypothesis. Despite close associations between T. rosea and P. latistrigata, patterns of relationship of spatial variances were inconsistent. The study demonstrates the need for tests in numerous sites and that ecological patt erns can differ markedly even for closely related species. It also demonstr ates that much more widespread sampling and experimentation are needed to r etain predictive and explanatory understanding of environmental gradients.