Dispersal plasticity, when organisms adjust their dispersal decisions depending on their environment, can play a major role in ecological and evolutionary dynamics, but how it relates to fitness remains scarcely explored. Theory predicts that high dispersal plasticity should evolve when environmental gradients have a strong impact on fitness. Using microcosms, we tested in five species of the genus Tetrahymena whether dispersal plasticity relates to differences in fitness sensitivity along three environmental gradients. Dispersal plasticity was species-and environment-dependent. As expected, dispersal plasticity was generally related to fitness sensitivity, with higher dispersal plasticity when fitness is more affected by environmental gradients. Individuals often preferentially disperse out of low fitness environments, but leaving environments that should yield high fitness was also commonly observed. We provide empirical support for a fundamental, but largely untested, assumption in dispersal theory: the extent of dispersal plasticity correlates with fitness sensitivity to the environment.

Dispersal is a key process mediating ecological and evolutionary dynamics. Its effects on the dynamics of spatially-structured systems, population genetics or species range distribution can depend on phenotypic differences between dispersing and non-dispersing individuals.However, scaling up the importance of resident-disperser differences to communities and ecosystems has rarely been considered, in spite of intraspecific phenotypic variability being an important factor mediating community structure and productivity. Here, we used the ciliate Tetrahymena thermophila, in which phenotypic traits are known to differ between residents and dispersers, to test (i) whether these resident-disperser differences affect biomass and composition in competitive communities composed of four other Tetrahymena species, and (ii) whether these effects are genotype-dependent. We found that dispersers led to a lower community biomass compared to residents. This effect was highly consistent across the twenty T. thermophila genotypes used, despite intraspecific variability in resident-disperser phenotypic differences. We also found a significant genotypic effect on biomass production, showing that intraspecific variability has consequences for communities. Our study suggests that individual dispersal strategy can scale up to community productivity in a predictable way, opening new perspectives to the functioning of spatially structured ecosystems.

Dispersal is a key process mediating ecological and evolutionary dynamics. Its effects on metapopulations dynamics, population genetics or species range distribution can depend on phenotypic differences between dispersing and non-dispersing individuals (i.e., dispersal syndromes). However, scaling up to the importance of dispersal syndromes for meta-ecosystems have rarely been considered, despite intraspecific phenotypic variability is now recognised as an important factor mediating ecosystem functioning. In this study, we characterised the intraspecific variability of dispersal syndromes in twenty isolated genotypes of the ciliate Tetrahymena thermophila to test their consequences for biomass productivity in communities composed of five Tetrahymena species. To do so, dispersers and residents of each genotype were introduced, each separately, in ciliate communities composed of four other competing species of the genus Tetrahymena to investigate the effects of dispersal syndromes. We found that introducing dispersers led to a lower biomass compared to introducing residents. This effect was highly consistent across the twenty T. thermophila genotypes despite their marked differences of dispersal syndromes. Finally, we found a strong genotypic effect on biomass production, confirming that intraspecific variability in general affected ecosystem functions in our system. Our study shows that intraspecific variability and the existence of dispersal syndromes can impact the functioning of spatially structured ecosystems in a consistent and therefore predictable way.

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