PT  - JOURNAL ARTICLE
AU  - Christopher M. Moore
AU  - Samantha A. Catella
AU  - Karen C. Abbott
TI  - Population dynamics of mutualism and intraspecific density dependence: how <em>θ</em>-logistic-like density dependence affects mutualistic positive feedback
AID  - 10.1101/108175
DP  - 2017 Jan 01
TA  - bioRxiv
PG  - 108175
4099  - http://biorxiv.org/content/early/2017/04/21/108175.short
4100  - http://biorxiv.org/content/early/2017/04/21/108175.full
AB  - Mutualism describes the biological phenomenon where two or more species are reciprocally beneficial, regardless of their ecological intimacy or evolutionary history. Classic theory shows that mutualistic benefit must be relatively weak, or else it overpowers the stabilizing influence of intraspecific competition and leads to unrealistic, unbounded population growth. Interestingly, the conclusion that strong positive interactions lead to runaway population growth is strongly grounded in the behavior of a single model. This model—the Lotka-Volterra competition model with a sign change to generate mutualism rather than competition between species—assumes logistic growth of each species plus a linear interaction term to represent the mutualism. While it is commonly held that the linear interaction term is to blame for the model’s unrealistic behavior, we show here that a linear mutualism added to many other models of population growth will not lead to unbounded growth. We find that when density dependence is decelerative, the benefit of mutualism at equilibrium is greater than when density dependence is accelerative. Although there is a greater benefit, however, decelerative density dependence tends to desta-bilize populations whereas accelerative density dependence is always stable. Incidentally, even when we model density dependence in birth and death rates separately, as long as one of the rates shows accelerative density dependence, populations will always be stable. We interpret these findings tentatively, but with promise for the understanding of the population ecology of mutualism by generating several predictions relating growth rates of mutualist populations and the strength of mutualistic interaction.HighlightsA Lotka-Volterra model relaxing intraspecific density dependence with mutualism is developedAccelerative density dependence—density dependence that occurs at high densities—is always stabilizingA tradeoff between model stability and benefit from mutualism is revealed