DYNAMICS OF TRANSITIONS BETWEEN POPULATION INTERACTIONS - A NONLINEAR-INTERACTION ALPHA-FUNCTION DEFINED

In nature, two populations may interact in different ways during their lifetime, and even undergo transitions from one type of interaction t o another. A model for the dynamics of these transitions has been deve loped in this study. The interaction coefficients alpha(ij) in the Lot ka-Volterra equations are re-interpreted as nonlinear functions of pop ulation densities N-i, N-j, modulated by environmental parameters, whi ch offers the possibility of a change in sign. Transitions can take pl ace owing to variations in population density (endogenous effect), or in the environmental parameters (exogenous effect). Models for both fa cultative and obligate associations are examined. Graphical stability analyses show that multiple density equilibria are possible, accountin g for the occurrence of the transitions.