The strength and direction of local (mal)adaptation depends on neighbour density and the environment

Abstract

1. Populations are embedded in communities, but despite their potential to affect individual fitness, it is unknown whether and how species interactions evolve in communities. Evolutionary outcomes are likely more complex in natural communities because (a) the evolution of interactions may not be evenly distributed among all community members and (b) coevolution is conditional on the environmental conditions within which interactions are playing out. 2. To test the evolution of interaction strengths in natural communities, we performed two common garden experiments in grassland communities in Northern California. In each garden, we transplanted individuals of four populations (one local, three foreign) of an annual invasive grass Bromus hordeaceus into natural communities, characterized the interaction neighbourhood around each focal individual, and quantified individual fitness. This method allowed us to fit multispecies competition models to fitness data, estimating interaction strengths between focal B. hordeaceus populations and each of seven species that were common in the interaction neighbourhoods, in each garden.3. We found that interaction strengths significantly differed among local and foreign source populations, but the direction and magnitude of evolution differed among common gardens and among neighbour species-in neither garden were interactions experienced more strongly by foreign populations compared to local populations. The fitness of local populations (relative to foreign populations) decreased when neighbours were removed, strongly enough in one garden to cause strong local maladaptation, and the local population did not perform the best in either garden. 4.Synthesis. Together, our results demonstrate how species interactions evolve to determine fitness in ecological communities, providing a richer view of adaptation in natural systems. In our study, this richness included the unique challenges populations face in nature: uneven abundances and a diffuseness of species interactions, nonlinear density effects on fitness, and evidence of (mal)adaptation that is conditional on local conditions. We conclude by hypothesizing the causes and consequences of challenges to adaptation and how they help identify priority areas for the field.

Environmental context, parameter sensitivity, and structural sensitivity impact predictions of annual‐plant coexistence

“…Predictions of species coexistence constitute the building blocks for many ecological studies, such as community assembly (Grainger et al, 2019; HilleRisLambers et al, 2012; Kraft et al, 2015), the evolution of competitive communities (Germain et al, 2022; Letten et al, 2021; Pastore et al, 2021), or the role of species richness in ecosystem functioning (Godoy et al, 2020). Many of these studies rely on mathematical models as the basis of their predictions.…”

Environmental context, parameter sensitivity and structural sensitivity impact predictions of annual-plant coexistence

“…Predictions of species coexistence constitute the building blocks for many ecological studies, such as community assembly (HilleRisLambers et al ., 2012; Kraft et al ., 2015; Grainger et al ., 2019), the evolution of competitive communities (Letten et al ., 2021; Pastore et al .,2021; Germain et al ., 2022), or the role of species richness in ecosystem functioning (Godoy et al ., 2020). Many of these studies rely on mathematical models as the basis of their predictions.…”

Dependency of diversity-productivity relationships on ecotypes of the dominant species across a precipitation gradient

“…Deviations from the HBM null model were likely related to nonlocal ecotypes at nonlocal sites being maladapted and not competitive enough to drive down the diversity of subordinate species, especially at sites at intermediate points along the precipitation gradient, i.e., dry and moist sites. The degree to which community dominants are locally adapted affects the strength of interspecific interactions and thereby local diversity (Germain et al 2022). The lack of agreement between the local ecotype and the HBM at the dry site showed that the home-site advantage effect on the diversity of the surrounding community was not expressed across the precipitation gradient.…”