Resource limitation in the compensatory response of a plant community to loss of a dominant species
In the face of biodiversity loss, ecosystem processes (i.e. productivity) can be maintained when compensation in function is achieved by shifts in the abundance of species, producing a net stabilizing effect on the community The mass-ratio hypothesis proposes that ecosystem function is overwhelmingly determined by the traits of the dominant species due to their larger contributions to productivity. Thus, loss of the dominant species should have a large impacts on ecosystem function. Also, through competitive release, it can provide opportunity for other species to establish, become abundant, and produce a compensatory response. However, the remaining species in the community not always make use of the available space and resources, making compensation a not so common response in nature Davies and collaborators have proposed three constraints for compensation to occur: 1) presence of functionally redundant species in the community, 2) functional traits that promotes compensation, and 3) resource availability when compensation is resource-dependent. In the tallgrass prairie plant community of the Central US, Andropogon gerardii is the dominant grass. Using a removal experiment, here we examine the third constraint, assessing the effects of water availability on the compensatory response (biomass production) of a tallgrass prairie plant community to the loss of A. geradii during two growing seasons.
The effectiveness of the removal treatment was in average 79.83% reduction in stem density of A. gerardii (range: 50-99%) with a mean of 124.3 tillers/plot (SD. = 52.88) removed in 2013, and 82.77% (range: 11-100%) and a mean of 23.5 tillers/plot (SD=22.34) removed in 2014. During 2013 there was not a significant effect of water addition or removal on the biomass production of the remaining species in the community. However, during 2014 the biomass production was more responsive, with a significant effect of water addition (p-value >0.001) and water * removal interaction (p-value <0.001) on the response of the community, but not enough to produce complete biomass compensation. We also examined the effect on community structure and composition, with a marginal effect of water addition during 2013, but no significant effect on 2014. Our results show that where water is a limiting resource, increased water availability produces a higher biomass response to the removal of A.gerardii than ambient conditions, but the response is not immediate, making a full compensatory response delayed in time, requiring increased resource availability.