Linking the fundamental and realized niches in ahypersaline consumer-resource system

A changing abiotic environment may affect the fitness and performance of an organism directly by challenging its environmental tolerance (related to its fundamental niche), or indirectly by modifying the abundance of other species it interacts with, and/or the strength of their interactions (related to its realized niche). The strength of an interaction may itself depend on how well each of the involved species performs across environments. However, there is a dearth of studies investigating how the intrinsic fitness of each interacting species covaries with the intensity of their interaction across an abiotic environmental gradient. We addressed this question in a hypersaline consumer-resource system: the microalga Dunaliella spp. grazed by the brine shrimp Artemia franciscana. We exposed four Dunaliella strains to a range of salinities, from just below to much above seawater, with or without brine shrimps. We tracked their population sizes over time and the survival of their grazers, to estimate basic parameters of a Lotka-Volterra model. We found that the intrinsic growth rate of algae, the survival rate of grazers, and the per-capita grazing rate, all varied with salinity and algal strain. Significant interactions between strain and salinity further revealed that these ecological responses to salinity are evolvable. Together with correlations between demographic parameters across salinity, this suggests that predation may influence the evolution of salinity tolerance curves, blurring the line between the fundamental and realized niches.