PARENT SESSION
Oral Session #53: Co-evolved species interactions: Mutualisms and parasitism. Presiding: A. Krist.
Wednesday, August 8, 2001. 1:00 PM to 4:45 PM. Hall of Ideas F.
Population dynamics and mutualism: Functional responses of benefits and costs.
HOLLAND, J.1, DEANGELIS, DONALD2, BRONSTEIN, JUDITH3, 1 2 3
ABSTRACT- We develop an approach for studying population dynamics resulting from mutualism by employing functional responses based on density-dependent benefits and costs. These functional responses express how the population growth rate of a mutualist is modified by the density of its partner. We present several possible dependencies of gross benefits and costs, and hence net effects, to a mutualist as functions of the density of its partner. Net effects to a mutualist are likely either a monotonically saturating or unimodal function of the density of its partner. We show that fundamental differences in the growth, limitation, and dynamics of a mutualistic population can occur when the net effects to that population are either linear, saturating, or unimodal with the density of its partner. We use the obligate mutualism between senita cactus and its pollinating seed-eater moth as an example to show the influence of different benefit and cost functional responses on the population dynamics and stability of the mutualism. Two mechanisms that may alter these benefit and cost functional responses are investigated: non-random distribution of moth eggs among flowers and fruit abortion by cacti. We show that differences in benefit and cost functional responses alter the stability of this mutualism. In particular, fruit abortion may allow for a stable equilibrium point, where none could otherwise exist, when active pollination is behaviorally associated with oviposition, and eggs are laid evenly among flowers.
KEY WORDS: mutualism, functional response, population dynamics, benefits and costs