Population dynamics and mutualism: Functional responses of benefits and costs

American Naturalist
By: , and 



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 mutualists are likely a monotonically saturating or unimodal function of the density of their partner. We show that fundamental differences in the growth, limitation, and dynamics of a population can occur when net effects to that population change linearly, unimodally, or in a saturating fashion. We use the mutualism between senita cactus and its pollinating seed‐eating moth as an example to show the influence of different benefit and cost functional responses on population dynamics and stability of mutualisms. We investigated two mechanisms that may alter this mutualism's functional responses: distribution of eggs among flowers and fruit abortion. Differences in how benefits and costs vary with density can alter the stability of this mutualism. In particular, fruit abortion may allow for a stable equilibrium where none could otherwise exist.

Publication type Article
Publication Subtype Journal Article
Title Population dynamics and mutualism: Functional responses of benefits and costs
Series title American Naturalist
DOI 10.1086/338510
Volume 159
Issue 3
Year Published 2002
Language English
Publisher University of Chicago Press
Contributing office(s) Southeast Ecological Science Center
Description 14 p.
First page 231
Last page 244
Online Only (Y/N) N
Additional Online Files (Y/N) N
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