Invasions of ecological communities: Hints of impacts in the invader's growth rate

Abstract

Theory in ecology and evolution often relies on the analysis of invasion processes, and general approaches exist to understand the early stages of an invasion. However, predicting the long‐term transformations of communities following an invasion remains a challenging endeavour. We propose a general analytical method that uses both resident community and invader dynamical features to predict whether an invasion causes large long‐term impacts on the invaded community. This approach reveals a direction in which classic invasion analysis, based on initial invasion growth rate, can be extended. Indeed, we explain how the density dependence of invasion growth, if properly defined, synthetically encodes the long‐term biotic transformations caused by an invasion, and therefore predicts its ultimate outcome. This approach further clarifies how the density dependence of the invasion growth rate is as much a property of the invading population as it is one of the invaded community. Our theory applies to any stable community model, and directs us towards new questions that may enrich the toolset of invasion analysis, and suggests that indirect interactions and dynamical stability are key determinants of invasion outcomes.

On the limits to invasion prediction using coexistence outcomes

“…Linking simultaneous and sequential assembly processes has been a fundamental scientific problem, underpinning our ability to predict the rise and fall of populations forming part of natural ecological communities (Fukami, 2015, Hastings, 2004, Odum, 1969, Vellend, 2016). Recent efforts to integrate these two types of assembly processes have relied on the assumption that it is possible to fully parameterize ecological models (Arnoldi et al, 2022, Hofbauer and Schreiber, 2022), the assumption that environmental conditions remain the same across the entire assembly process (Arnoldi et al, 2022, Hofbauer and Schreiber, 2022, Logofet, 1993, Serván and Allesina, 2021), or the assumption that one has sufficient information about coexistence or invasion outcomes (Friedman et al, 2017, Grainger and Gilbert, 2019, Maynard et al, 2020). While these studies have provided key insights regarding the association of simultaneous and sequential assembly, these assumptions are seldom met in nature (Fukami, 2015, Hubbell, 1997, Miller and Allesina, 2021, Song et al, 2021).…”

“…Thus, our theoretical framework can be applied to communities characterized by competition (where interactions a ij < 0), cooperation ( a ij > 0), or a mix of both types of interactions. The effective growth rate θ = ( θ 1 , …, θ |𝒮| ) T ∈ ℝ |𝒮| consists of the phenomenological joint effect of the internal (e.g., intrinsic growth rate), abiotic (e.g., temperature), and biotic factors (i.e., species not considered explicitly) acting on the per-capita growth rate of each particular species (Arnoldi et al, 2022, Deng et al, 2022). Note that if we multiply θ by any positive scalar, it will not change the qualitative solution of the system.…”

“…To integrate invasion and coexistence theories, it is necessary to link short-term and long-term dynamics (Arnoldi et al, 2022, Hofbauer and Schreiber, 2022). From the invader’s perspective (species i ), a positive invasion growth rate (i.e., g ( i ) > 0, measured as a function of the effect of resident species on the invader species, Eq.…”

“…Therefore, positive invasion growth rates guarantee the successful short-term introduction of an invader species (Barabás et al, 2018). Under these assumptions and under specific model parameterizations, coexistence outcomes can be derived from information about invasion outcomes and vice versa (Arnoldi et al, 2022, Hofbauer and Schreiber, 2022, Logofet, 1993, Serván and Allesina, 2021). While these criteria have provided key insights regarding the translatability between simultaneous and sequential assembly, these results can be difficult to validate in natural communities where outcomes and conditions are rarely the same (Angulo et al, 2021, Hubbell, 1997, Miller and Allesina, 2021, Song et al, 2021, Zhao et al, 2021).…”

Effect of freshwater on plant species diversity and interspecific associations in coastal wetlands invaded by Spartina alterniflora

“…Ecological management practices have shifted the focus from removing the invasive species alone to monitoring and restoring the entire ecosystem (Zavaleta et al, 2001 ; Remm et al, 2019 ). In wetland ecosystem monitoring, plant communities are among the main indicators of invasion in comparative studies before and after restoration (Giljohann et al, 2011 ; Nicol et al, 2017 ; Arnoldi et al, 2022 ). Therefore, it is essential to investigate the characteristics of the coastal wetland plant communities invaded by S. alterniflora before and after restoration.…”