Department Fish Ecology and Evolution

All living organisms modify their biotic and abiotic environment. Niche construction theory posits that organism-mediated modifications to the environment can change selection pressures and influence the evolutionary trajectories of natural populations. While there is broad support for this proposition in general, there is considerable uncertainty about how niche construction is related to other similar concepts in ecology and evolution. Comparative studies dealing with certain aspects of niche construction are increasingly common, but there is a troubling lack of experimental tests of the core concepts of niche construction theory. Here, we propose an operational framework to evaluate comparative and experimental evidence of the evolutionary consequences of niche construction, and suggest how such research can improve our understanding of ecological and evolutionary dynamics in ecosystems. We advocate for a shift toward explicit experimental tests of how organism-mediated environmental change can influence the selection pressures underlying evolutionary responses, as well as targeted field-based comparative research to identify the mode of evolution by niche construction and assess its importance in natural populations.

There is increasing evidence that rapid phenotypic evolution can strongly influence population dynamics, but how are such eco-evolutionary dynamics influenced by the source of trait variation (i.e., genetic variation or phenotypic plasticity)? To investigate this, we used rotifer–algae microcosm experiments to test how the phenotypic and genetic composition of prey populations affect predator–prey population dynamics. We chose four genetically distinct strains of the green alga Chlamydomonas reinhardtii that varied in their growth rate, standing levels of defense, and inducible defense. To additionally test for strain specificity of plasticity responses, we quantified protein expression of each strain in the presence and absence of rotifer predators (Brachionus calyciflorus). We then tested how different strain combinations influenced the outcome of pairwise competition trials with and without rotifer predation. We tracked individual strain frequencies using quantitative polymerase chain reaction (qPCR), and compared the observed dynamics to a suite of eco-evolutionary models of varying complexity. We found that variation in trade-offs between growth and defense between algal strains strongly influenced the outcome of competition and the overall predator–prey dynamics. Our purely ecological model of the observed dynamics, which allowed for the presence of phenotypic plasticity but no trait variation between strains, never outperformed any of our eco-evolutionary models in which strains could have different trait values. Our best fitting eco-evolutionary model allowed strains to differ in an inducible defense trait. Overall, our results provide some of the first experimental evidence that variation in phenotypically plastic responses among prey genotypes can be an important component of eco-evolutionary dynamics in a predator–prey system.

Inter and intra-population variation in morphological traits, such as body size and shape, provides important insights into the ecological importance of individual natural populations. The radiation of Diaptomid species (~400 species) has apparently produced little morphological differentiation other than those in secondary sexual characteristics, suggesting sexual, rather than ecological, selection has driven speciation. This evolutionary history suggests that species, and conspecific populations, would be ecologically redundant but recent work found contrasting ecosystem effects among both species and populations. This study provides the first quantification of shape variation among species, populations, and/or sexes (beyond taxonomic illustrations and body size measurements) to gain insight into the ecological differentiation of Diaptomids. Here we quantify the shape of five Diaptomid species (family Diaptomidae) from four populations each, using morphometric landmarks on the prosome, urosome, and antennae. We partition morphological variation among species, populations, and sexes, and test for phenotype-by-environment correlations to reveal possible functional consequences of shape variation. We found that intraspecific variation was 18–35% as large as interspecific variation across all measured traits. Interspecific variation in body size and relative antennae length, the two traits showing significant sexual dimorphism, were correlated with lake size and geographic location suggesting some niche differentiation between species. Observed relationships between intraspecific morphological variation and the environment suggest that divergent selection in contrasting lakes might contribute to shape differences among local populations, but confirming this requires further analyses. Our results show that although Diaptomid species differ in their reproductive traits, they also differ in other morphological traits that might indicate ecological differences among species and populations.

A major challenge in ecology is to understand determinants of ecosystem functioning and stability in the face of disturbance. Some important species can strongly shape community structure and ecosystem functioning, but their impacts and interactions on ecosystem-level responses to disturbance are less well known. Shallow ponds provide a model system in which to study the effects of such species because some taxa mitigate transitions between alternative ecosystem states caused by eutrophication. We performed pond experiments to test how two foundation species (a macrophyte and a mussel) affected the biomass of planktonic primary producers and its stability in response to nutrient additions. Individually, each species reduced phytoplankton biomass and tended to increase rates of recovery from disturbance, but together the species reversed these effects, particularly with larger nutrient additions. This reversal was mediated by high cyanobacterial dominance of the community and a resulting loss of trait evenness. Effects of the foundation species on primary producer biomass were associated with effects on other ecosystem properties, including turbidity and dissolved oxygen. Our work highlights the important role of foundation species and their interactive effects in determining responses of ecosystem functioning to disturbance.