Insularity forcing on plant persistence strategies in edaphic island systems

Abstract

Aim: Trait-based approaches are increasingly implemented in island biogeography, providing key insights into the eco-evolutionary dynamics of insular systems. However, what determines persistence of plant species once they have arrived and established in an island remains largely unexplored. Here, we examined links between non-acquisitive persistence strategies and insularity across three terrestrial edaphic island systems, hypothesising that insularity promotes strategies for local persistence. Location: Europe: Western Carpathians, Moravia, and Cantabrian Range. Time period: Present. Major taxa studied: Vascular plants. Methods: For each system, we used linear models at the island scale to test whether persistence-related plant trait patterns (average trait values and diversity) depend on three insularity metrics (island size, isolation and target effect). We focused on patterns of edaphic island specialists because, in contrast to matrix-derived species, their presence is confined to the edaphic islands. Results: We found that insularity metrics explained large proportions in the variation of the average and diversity of persistence-related traits of edaphic island specialists. Insularity was associated with a decline in the proportion of island specialists that have clonal abilities, yet it affected trait values of specialists towards enhanced abilities to persist locally (e.g. more extensive lateral spread) while reducing trait variability. Higher degrees of insularity within the systems were translated to stronger effects on functional trait patterns. Main conclusions: Insularity affects plant species diversity, distribution and forms in terrestrial island-like systems, similarly as it is assumed for true islands. Insularity, measured using a single (island size, isolation) or combined (target effect) predictors, may operate selecting for enhanced and less diverse persistence strategies. Ultimately, this process, which we call insularity forcing, operates as a selective process to promote species ability to avoid local extinction and to persist on terrestrial islands.

Sticking around: plant persistence strategies on edaphic islands

“…We focused on 13 perennial plant species confined to the discrete outcrop grasslands, constituting ∼45% of the total number of specialist species of this vegetation type (Méndez-Castro et al, 2021). These specialist species should be: 1) adapted to the harsh environment of rocky outcrops (especially concerning the putatively strong edaphic filter), and 2) more affected by insularity than non-specialists (for which the surrounding landscape should not be as inhospitable; Conti et al, 2021; Méndez-Castro et al, 2021). The selected species belong to different plant functional types (9 forb species, 2 chamaephytes, 1 grass, 1 sedge), and life histories (5 clonal, 8 non-clonal species).…”

“…the largest and specialist-richest island) and the square root of its area (Méndez-Castro et al, 2021). Higher values of target effect imply that islands are harder to colonize because of their smaller size or their location far away from the species source (Conti et al, 2021; Méndez-Castro et al, 2021). In the study system, the target effect effectively captures different dimensions of insularity, namely isolation, area, and connectivity ( Fig.…”

“…How these functions play out under specific circumstances can be assessed through trait-based approaches (Klimešová et al, 2019; Ottaviani et al, 2020a; Pérez-Harguindeguy et al, 2013; Weiher et al, 1999). A good example is offered by seasonal and disturbance-prone temperate grasslands hosting many perennial herbaceous species with different persistence strategies (Klimešová et al 2016a, 2021; Ottaviani et al, 2020b). A major group comprises long-lived clonal species, capable of both sexual and vegetative reproduction and investing considerable resources belowground into bud-bearing and carbohydrate storage organs (Janovský & Herben, 2020; Klimešová et al, 2016a).…”

“…All of these plants can cope effectively with seasonally cold climates and recurrent disturbances (e.g. mowing, grazing, fire; Klimešová et al, 2018, 2021; Ottaviani et al, 2020b). Some of them are also able to deal with increasingly drier seasons, nutrient deposition or altered management regimes (Fischer et al, 2020; Qian et al, 2021).…”

“…Another potentially critical example in the analyses of persistence strategies is constituted by insular systems. These are “natural laboratories ” (Warren et al, 2015; Whittaker et al, 2017) and suitable models to examine persistence strategies because plants with limited dispersal on steadily isolated islands tend to exhibit adaptive strategies to successfully survive (Cody & Overton, 1996; Conti et al, 2021; Ottaviani et al, 2020a). At the same time, insular systems are particularly vulnerable to species extinctions linked to environmental changes (Courchamp et al, 2014; Macinnis-Ng et al, 2021; Veron et al, 2019).…”