The concept of feedback in evolutionary ecology and ecosystem science has a rich theoretical history that underpins our current understanding of the intricate interplay between organisms and their environments. This paper explores feedback across scales and hierarchies of biological organization, reviewing its historical context in evolutionary ecology and advocating for interdisciplinary approaches to uncover novel mechanisms. We present a conceptual framework that emphasizes the hierarchical structure of organisms embedded in multispecies communities and can help elucidate feedback mechanisms that underlie biodiversity change. Our approach simplifies the organismal complexity of individuals using a set of traits with explicit genetic architecture and environment-dependent phenotypic expression, and lifespan dynamics that are spatially-explicit and embedded in a multispecies context. Incorporating these ideas into a comprehensive simulation platform would enable researchers to unravel the intricacies of ecological and evolutionary dynamics underlying population dynamics, species interactions, and ecosystem resilience in response to environmental change.

The adaptation of marine fish to freshwater environments is a prodigious example of rapid evolution, and yet the underlying ecological causes of genomic and phenotypic differentiation are poorly understood for traits associated with lipid content and composition. Threespine stickleback (Gasterosteus aculeatus) have repeatedly colonized, and adapted to, freshwater habitats across the northern hemisphere. These freshwater populations often show elevated copy number of the fatty acid desaturase 2 gene (FADS2), which increases the biosynthetic capacity of ω-3 long-chain polyunsaturated fatty acids (LC-PUFA). The starkly lower content of LC-PUFA in freshwater compared to marine prey, especially docosahexaenoic acid (DHA), likely imposes strong positive selection on freshwater fish for either increased biosynthesis or greater dietary acquisition of LC-PUFA. The threespine stickleback populations in postglacial coastal lakes of Southern Greenland offer an exceptional opportunity to study how variation in the copy number of FADS2 is related to abiotic and biotic conditions of lakes and their morphometry. As expected, we found strong sexual dimorphism in FADS2 copy number in all populations (19 freshwater, 1 marine, and 1 brackish), and an increased dimorphism in some freshwater populations. We also found that FADS2 copy number was negatively correlated, for both males and females, with the abundance of copepods, which are a DHA-rich food source in the zooplankton community. Overall, our results suggest that the prey community context of lakes might influence the process of metabolic adaptation of marine fish colonizing freshwater ecosystems.

A document by Shyamolina Ghosh. Click on the document to view its contents.

Global change alters the stability of biological communities by affecting species richness and how species covary through time (i.e., synchrony). There are few large-scale empirical tests of stability-diversity-synchrony relationships and those mostly focus on the terrestrial realm. Moreover, the effect of synchrony is largely unknown when species only covary at either high or low extremes of abundance (i.e., tail-dependent synchrony), a common phenomenon in ecological communities. Here, we synthesized long-term community time-series data (20+ years of species’ abundances/biomass for 2,668 communities across 7 taxonomic groups) from both terrestrial and freshwater realms and explored how the relationships among richness, synchrony, and stability vary across realms. We also investigated the effect of tail-dependent synchrony on stability across 714 freshwater and 1,954 terrestrial communities. For terrestrial communities, we found a positive diversity-stability relationship and that the tail-dependent synchrony was a more important determinant of stability than the traditional measure of overall synchrony (i.e., based on the covariation of all species). For freshwater communities, only overall synchrony explained some variation in stability. Assessing tail-dependent synchrony can improve our ability to understand why stability varies across different ecosystems and thereby our inferences about the causes of human-mediated biodiversity loss.

In communities structured by body size, coexistence can occur through combinations of ontogenetic changes in competitive ability and dietary niche. Using stable isotopes, we examined ontogenetic niche shifts in Trinidadian guppies (Poecilia reticulata) and killifish (Rivulus hartii) in three types of natural communities (both species with predators, KGP; both without predators, KG; killifish only, KO) and four experimental KG communities, initiated with KGP guppies and KO killifish between 13 and 45 years ago. In all communities, killifish occupied higher trophic positions and changed their diet (δ^13 C) with body size. Only KGP guppies displayed an ontogenetic niche shift. The KG guppies displayed a significant difference in trophic niche from KGP guppies, a character displacement that can facilitate coexistence with killifish. In the experimental communities, the guppy trophic niche was intermediate between those in KGP and KG communities, indicating that evolution has driven the niche shift in KG guppies.

The nutritional diversity of resources can affect the adaptive evolution of consumer metabolism and consumer diversification. Omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA) have a high potential to affect consumer fitness, through their widespread effects on reproduction, growth, and survival. However, few studies consider the evolution of fatty acid metabolism within an ecological context. In this review, we first document the extensive diversity in both primary producer and consumer n-3 LC-PUFA distributions among major ecosystems, between habitats, and among species within habitats. We highlight some of the key nutritional contrasts that can shape behavioral and/or metabolic adaptation in consumers, discussing how consumers can evolve in response to the spatial, seasonal, and community-level variation of resource quality. We propose a hierarchical trait-based approach for studying the evolution of consumers’ metabolic networks, and review the evolutionary genetic mechanisms underpinning consumer adaptation to n-3 LC-PUFA distributions. In doing so, we consider how the metabolic traits of consumers are hierarchically structured, from cell membrane function to maternal investment, and have strongly environment-dependent expression. Finally, we conclude with an outlook on how studying the metabolic adaptation of consumers within the context of nutritional landscapes can open up new opportunities for understanding evolutionary diversification.

Nutrient perturbations are a threat to aquatic ecosystems worldwide. Interactions among important species can influence the recovery of aquatic ecosystems from nutrient perturbations, and the persistence in a clear water state for a given regime of nutrient loading. In a factorial manipulation of two foundation species (macrophytes and mussels), we measured 16 large (15000L) ponds at high resolution (15 min interval) over two years with two periods of nutrient perturbation. We found that each foundation species had strong individual effects on multiple ecosystem properties (e.g. phytoplankton densities and metabolism), largely in line with our expectations (i.e. reduction of algal biomass relative to control). However, when both species were present, we saw dramatic increases in algal biomass and other ecosystem parameters, indicating strong non-additive antagonistic effects. Overall, our results demonstrate how interactions between foundation species can cause surprisingly strong deviations from the expected responses of aquatic ecosystems to nutrient additions.