Disturbed habitats locally reduce the signal of deep evolutionary history in functional traits of plants

Abstract

The functioning of present ecosystems reflects deep evolutionary history of locally cooccurring species if their functional traits show high phylogenetic signal (PS). However, we do not understand what drives local PS. We hypothesize that local PS is high in undisturbed and stressful habitats, either due to ongoing local assembly of species that maintained ancestral traits, or to past evolutionary maintenance of ancestral traits within habitat species-pools, or to both. We quantified PS and diversity of 10 traits within 6704 local plant communities across 38 Dutch habitat types differing in disturbance or stress. Mean local PS varied 50-fold among habitat types, often independently of phylogenetic or trait diversity. Mean local PS decreased with disturbance but showed no consistent relationship to stress. Mean local PS exceeded species-pool PS, reflecting nonrandom subsampling from the pool. Disturbance or stress related more strongly to mean local than to species-pool PS. Disturbed habitats harbour species with evolutionary divergent trait values, probably driven by ongoing, local assembly of species: environmental fluctuations might maintain different trait values within lineages through an evolutionary storage effect. If functional traits do not reflect phylogeny, ecosystem functioning might not be contingent on the presence of particular lineages, and lineages might establish evolutionarily novel interactions.

Keywords: community assembly; disturbance and stress; functional diversity; niche conservatism; phylogenetic diversity; phylogenetic signal; species-pool; trait evolution.

Fig. 1

Habitat conditions drive phylogenetic signal (PS) of functional traits within local communities, and thereby whether or not the phylogenetic past relates to the functioning of species in local communities. In this example, habitat conditions are the presence or absence of disturbances (i.e. flooding). Trait states are different life forms. PS is high when differences in life forms among species reflect ancient rather than recent diversifications. Under low disturbance, access to resources is predictable and is constrained by competitors, enemies or abiotic stress, potentially increasing local PS. This may happen in two ways: first (top graph), such constraints increase the performance of species with specific strategies, often established in specific lineages. Any three such species in a local community are likely to represent the trait states of their respective lineages, that is, local PS is high. Second (bottom graph), past presence or lack of disturbances may, in addition, have influenced trait evolution within lineages, and thereby the present species‐pools. In habitats lacking disturbance, species may have retained the ancestral traits of their respective lineages, that is, species‐pool PS is high. Local communities sampled from these pools may reflect pool PS. Testing these scenarios requires using individual habitat types as data points, each characterized by its disturbance level, mean local PS and species‐pool PS (Fig. 3; Tables 3, 4). Testing for differences among habitat types per se requires using local communities as data points, each characterized by its local PS and its habitat type (Fig. 2; Table 2).

Fig. 2

Habitat types differ in local phylogenetic signal (PS) of reproduction type (top, ANOVA F _{37, 6584} = 86.93, P < 10^–5). Means and 95% confidence intervals are given. Individual habitat types are identified by numbers (named in Supporting Information Notes S1 Table A) and grouped into major groups (x‐axis). Also, the diversity of reproduction type and phylogenetic diversity differ among habitat types (middle and bottom; ANOVA F _{37, 6584} = 74.03 and 60.09, respectively; P < 10^–5). See Table 2 for similar results for all 10 traits. Mean local PS of reproduction type change differently across habitat types than do mean local diversity of reproduction type or mean local phylogenetic diversity. The variation of mean local PS of reproduction type across habitat types can hence only incompletely be explained by a combination of mean local diversity of reproduction type and of mean local phylogenetic diversity (R ² = 0.18; overall similar results for other traits in Notes S11).

Fig. 3

Relationship between disturbance regime (UD, undisturbed vs D, disturbed) or stress regime (US, unstressed vs S, stressed) of habitat types and the phylogenetic signal (PS) of ‘reproduction type’. PS is quantified either within local communities and the mean is calculated within each habitat type (left) or across the entire species‐pool of each habitat type within the study region (right); n = 18 habitat types. Per category of habitat types, means and 95% confidence limits are given. Mean local PS of reproduction type in a habitat type (left) tends to decrease with disturbance (‘D’ vs ‘UD’) and to increase with stress (‘S’ to ‘US’) (P < 0.001, Table 3). At the level of habitat species‐pools (right) these relationships to disturbance and stress tend to disappear (corresponding to significant interaction terms of either disturbance or stress with ‘mean local’ in Table 4). Table 3 shows similar relationships of mean local PS to disturbance and stress, and Table 4 similar scale‐dependency, for most to all other traits. Disturbance and stress regime were ranked based on observations, namely names of habitat types, representing three of the possible combinations of stress and disturbance. See Notes S7 and S9 for analyses using continuous gradients of stress and disturbance inferred from species ranks in disturbance and stress tolerance.

Fig. 4

Phylogenetic signal (PS) of reproduction type within local communities of habitat types is only partly related to PS within the species‐pool of the same habitat types across the region (R ² = 0.22, without outlier: 0.49), suggesting that a major part of the variation among habitat types in local PS is determined by local processes. See Table 5 for overall similar results for PS of other traits.