The ecological causes of functional distinctiveness in communities

Abstract

Although how rare species persist in communities is a major ecological question, the critical phenotypic dimension of rarity is broadly overlooked. Recent work has shown that evaluating functional distinctiveness, the average trait distance of a species to other species in a community, offers essential insights into biodiversity dynamics, ecosystem functioning, and biological conservation. However, the ecological mechanisms underlying the persistence of functionally distinct species are poorly understood. Here we propose a heterogeneous fitness landscape framework, whereby functional dimensions encompass peaks representing trait combinations that yield positive intrinsic growth rates in a community. We identify four fundamental causes leading to the persistence of functionally distinct species in a community. First, environmental heterogeneity or alternative phenotypic designs can drive positive population growth of functionally distinct species. Second, sink populations with negative growth can deviate from local fitness peaks and be functionally distinct. Third, species found at the margin of the fitness landscape can persist but be functionally distinct. Fourth, biotic interactions (either positive or negative) can dynamically alter the fitness landscape. We offer examples of these four cases and some guidelines to distinguish among them. In addition to these deterministic processes, we also explore how stochastic dispersal limitation can yield functional distinctiveness.

Trait–environment relationships depend on species life history

“…Definitions of ecological strategies usually assume that one combination of traits corresponds to one environment (a “one‐to‐one mapping” from environment to strategy) (Marks & Lechowicz, 2006; Dias et al., 2020). As a consequence, the possibility that local divergence in trait values results from multiple phenotypic optima is still overlooked in functional ecology (Dias et al., 2020; Munoz et al., 2023). One reason is that a complex environment (here, both stress and disturbance at intermediate levels) can be either considered as a single environment, possibly filtering multiple strategies (van der Maarel & Sykes, 1993; Frenette‐Dussault et al., 2012), or as multiple micro‐environments, each filtering one particular strategy (Barbaro et al., 2004).…”

Beyond trait distances: Functional distinctiveness captures the outcome of plant competition

“…In this study, we argue that functional trait distinctiveness, an emerging facet of trait diversity (Munoz et al, 2023; Violle et al, 2017), can help capture the outcomes of PPI on the performance of both individual plants and groups of coexisting plants. Trait distinctiveness corresponds to the average trait distance between a given species (or genotype) and all the components of a given species pool (Grenié et al, 2018).…”

Bringing traits back into the equation: A roadmap to understand species redistribution

“…Although the consequences of these functional biases on our ability to detect meaningful relationships between range shifts and species traits remain to be formally investigated, to fully understand range shift processes, both functionally common and unique species would benefit from being studied in a shared framework. Functional uniqueness can represent adaptations to specific environmental conditions (e.g., reduced physical capacity for dispersal for flightless birds on islands due to the island syndrome; Wright et al., 2016), distinct alternative phenotypic adaptations to the same environmental challenges (e.g., active dispersal vs. in situ drought resistance forms in aquatic invertebrates; Osakabe et al., 2014) or competition‐driven specialization (e.g., morphological and foraging microhabitat specialization in coral reef fishes; Brandl et al., 2015), and may thus hold key insights to contextualize the functions and evolutionary trajectories of trait syndromes (Munoz et al., 2023), including in the context of species redistribution.…”