Advances in

ECOLOGICAL RESEARCH

Edited by

A. MACFADYEN School of Biological and Environmental Studies, New University of Ulster,

Coleraine, County Londonderry, Northern Ireland

E. D. FORD Centerfor Quantitative Science, University of Washington, 373715th A venue

Seattle, Washington 981 95, USA

VOLUME 16

1987

ACADEMIC PRESS Harcourt Brace Jovanovich, Publishers

London Orlando San Diego New York Austin Boston

Sydney Tokyo Toronto