More or Less? The Effect of Symbiont Density in Protective Mutualisms
Georgia Drew, Kayla C. King
Abstract
AbstractSymbionts can provide hosts with effective protection from natural enemies, but it can sometimes come at a cost. It is unclear to what extent the density of symbionts modulates the cost and benefits of conferred protection. Here, we use a meta-analysis of 103 effect sizes from a broad taxonomic range of protective symbioses to show that the degree of both protection and cost afforded to hosts is a positive function of symbiont density. We found that the effects of symbiont density on protection and cost are robust across ecological contexts. Density-function relationships did not vary with host type, symbiont localization, or transmission mode, nor did they vary with the method of density manipulation. Taken together, our results suggest that symbiont density can be a key variable determining the costs and benefits of a protective interaction.