Toward trait‐based food webs: Universal traits and trait matching in planktonic predator–prey and host–parasite relationships

Abstract

There is a growing consensus that traits offer a powerful way to examine the relationship between the environment, organismal strategies, species interactions, and ecological success. To date, trait‐based research has largely been focusing on individual trophic levels and not on cross‐level interactions. Looking at traits not only within but across trophic levels and identifying traits that together define trophic interactions holds a great potential for understanding the mechanisms of interactions. Here, we outline the conceptual foundation for cross‐trophic trait‐based frameworks, using planktonic food webs as an example. First, we compile a list of traits important within different individual trophic levels and show that there are traits that are common across trophic levels (“universal” traits), as well as trophic level‐specific traits. Next, we focus on traits that characterize interactions across trophic levels, focusing on two types of interaction—grazer–primary producer and host–parasite, identifying the similarities and differences between these interactions. We outline the trait hierarchies that define possible and realized intertrophic interactions and their strengths. We then highlight the importance of trade‐offs among those traits in shaping interactions and explaining general patterns in the structure and function of food webs. Finally, we discuss the environmental influences on traits, their eco‐evolutionary responses to changing conditions and how those responses may alter trophic interactions. The extension of trait‐based approaches from individual trophic levels to food webs and different trophic interactions should stimulate further conceptual development, enrich the field of aquatic sciences, and provide a framework to better predict global change effects on ecosystems.

Understanding and predicting harmful algal blooms in a changing climate: A trait‐based framework

“…Traits that affect fitness are termed functional traits (Violle et al 2007). Traits can be morphological, physiological, life history, behavioral, as well as genomic and metabolic traits (Litchman and Klausmeier 2008;Litchman et al 2021;Walker et al 2022). In microbes, including phytoplankton, genomic and metabolic traits and the trade-offs may be important for inferring ecological strategies (Litchman et al 2015a).…”

“…Major types of functions, the associated traits and trait examples important for HAB taxa and other phytoplankton (not an exhaustive list). Trait classification modified from Litchman and Klausmeier (2008) and Litchman et al (2021). Some representative references for select traits are also provided.…”

“…They include cell size, nutrient‐ and light‐utilization traits, temperature‐response traits (Fig. 1), susceptibility to grazing, with cell/colony size often being the proxy for that, buoyancy/motility, the ability to fix atmospheric nitrogen, toxicity, and others (Table 1) (Litchman and Klausmeier 2008; Litchman et al 2021).…”

“…In addition to traits that determine the responses of different taxa to abiotic environment, traits describing the relationships with other organisms, such as grazers, parasites, or mutualists, affect fitness and need to be compared across taxa (Litchman et al 2021; Lürling 2021). A general trend is that HAB‐forming taxa often have traits that make them resistant to grazing, through large cell size, coloniality, resting stage formation, and toxicity (Pančić and Kiørboe 2018; Lürling 2021).…”

“…Compared to the traits related to abiotic drivers, traits that characterize biotic interactions, such as predation, parasitism or mutualism, are less frequently characterized (Litchman et al 2021), and should be one of the research foci in HAB ecology. For example, little is known about what traits may protect from viral attacks or other parasites, and if there are trade‐offs between the defense and other traits, such as nutrient uptake capabilities (Menge and Weitz 2009; Litchman et al 2021).…”