Characterising Intraspecific Resource Use in a Rotifer Grazer Using High‐Throughput Phenotyping

ABSTRACT 1. Understanding how adaptation to fluctuating resource availability drives life‐history trade‐offs, and in turn promotes niche differentiation among species, is central to ecology. The gleaner–opportunist framework, in which gleaners are better adapted to low resource levels and opportunists to high levels, represents one way in which divergent resource‐use strategies can partition ecological niches across taxa. However, whether such strategies exist within species remains unclear. Here, I tested for intraspecific variation in resource‐use strategies in a clonal rotifer grazer. 2. Using an image‐based high‐throughput phenotyping system, I analyzed population growth rates of 98 genotypes across a resource gradient. 3. I showed that clones exhibited a gleaner‐opportunist trade‐off, as demonstrated by a positive correlation between maximum growth rate ( μ max ) and resource threshold parameters ( k and R *), coupled with divergent fitness optima at low versus high resource levels. Specifically, clones that excelled under low‐resource conditions (gleaners) exhibited lower k and R * values, whereas those performing better at high‐resource levels (opportunists) showed higher μ max . 4. I also identified a few “superclones,” which had superior performance across all environments, challenging the notion of a singular adaptive axis and suggesting that additional ecological and evolutionary mechanisms maintain phenotypic diversity. 5. These results demonstrate that intraspecific variation in resource use strategies mirrors patterns previously observed between species, yet the coexistence of superclones highlights additional complexity in adaptive landscapes. These findings underscore the importance of genetic diversity in buffering populations against environmental variability and provide a framework for linking individual‐level traits to broader eco‐evolutionary dynamics.