Vinka Anic and Lohengrin Cavieres, University of Concepción in Chile, discuss their article: Functional and phylogenetic similarity between native and non-native plant species along an elevational gradient in the central Chilean Andes: No evidence for the preadaptation hypothesis
The establishment of non-native species is expected to be constrained in regions affected by harsh environmental conditions such as alpine habitats above the natural treeline. These habitats are mainly characterised by low temperatures and short growing seasons. However, non-native plant species have been recorded in high-elevation habitats around the world, especially along roadsides. Some of these species have become invasive by forming self-sustaining populations with detrimental impacts on other plants. But how do non-native plants succeed in habitats affected by strong environmental filters? Successful non-native species would be phylogenetically close to natives in the introduced area as stated by the preadaptation hypothesis, particularly in harsh habitats, where the two species groups may have similar traits. Habitats subject to drought or cold temperatures have been linked to functional traits (i.e. morpho-physio-phenological traits that impact reproduction and survival) related to a conservative resource-use strategy (e.g. slow growth) such as low leaf area and specific leaf area (SLA, the ratio of leaf area to leaf dry mass).
In the Andes of central Chile, a mountain region influenced by a Mediterranean-type climate (i.e. dry summers), low-elevation drought and high-elevation cold temperatures may promote a conservative growth strategy in coexisting native and non-native plant species. Therefore, non-native plant species are expected to be functionally and phylogenetically similar to native species in harsh Andean environments. We tested this hypothesis by determining the functional and phylogenetic distances between the two species groups along a wide elevational gradient in the central Chilean Andes. We also analysed the variation in individual leaf traits in native and non-native species along the elevational gradient.
Let’s unveil the similarity between native and non-native plants along an elevational gradient
We measured six leaf functional traits in native (N = 91) and non-native (N = 26) plant species from roadside habitats at six elevations (from 1200 to 3600 m a.s.l.) in central Chile. The traits comprised leaf area, SLA, leaf dry matter content, leaf thickness, and leaf nitrogen and chlorophyll contents. We also built a phylogenetic tree of the study species. Subsequently, functional and phylogenetic distance matrices were constructed. Based on these matrices, for each elevation, we calculated the mean functional and phylogenetic distances of each non-native species relative to the native species (focal-species approach).
Surprising findings
- Contrary to our assumptions, we found no significant effect of elevation on the functional and phylogenetic distances between native and non-native plant species. Thus, these distances were unaffected by harsh environmental conditions in the central Chilean Andes.
- Native species exhibited some conservative functional traits in harsh environments including smaller leaves in high-Andean habitats (above the treeline) and low SLA in low-elevation habitats subject to drought. In contrast, non-native species showed leaf traits related to faster resource acquisition such as high SLA in habitats under drought conditions and high leaf area along the entire elevational gradient. Non-native plants occurring in high-elevation habitats were also characterised by high leaf nitrogen contents.
Takeaway message
Non-native plant species less phylogenetically related to resident species can establish in abiotic stressful environments of the central Chilean Andes.
Functional differentiation between native and non-native plant species was found in environmentally severe habitats in the Andes of central Chile. In these environments, the growth strategy of non-native plant species showing leaf attributes linked to high resource acquisition could be influenced by the amelioration of extreme abiotic conditions by nurse plants (i.e. plant facilitation) and/or a high degree of disturbance. Nonetheless, additional research is required to elucidate the mechanisms behind the trait composition we determined for non-native plant species in harsh Andean habitats.
