Rocky outcrops conserve genetic diversity and promote regeneration of a threatened relict tree in a critically endangered ecosystem

Abstract

The loss of individuals in disturbed sites may be buffered by the presence of small natural features (SNFs), sites acting as ecological refuges preventing the loss of phenotypic variability and genetic diversity of plants. An important group of SNFs is rocky outcrops, singular geological formations that stand out from the surrounding matrix which could host a greater species diversity. We tested the value of rocky outcrops as SNFs of a Tertiary relict tree, the Chilean lucuma Pouteria splendens (Sapotaceae). We identified vegetation patches with P. splendens and characterized their landscape properties in sites associated with rocky outcrops and clearings (plains). Then, we contrasted the genetic diversity, phenotypic variability and sapling abundance of P. splendens inhabiting rocky outcrops and plains. We observed that rocky outcrops sustained subtle higher genetic diversity compared with plains, but non-significant genetic structuration was detected between habitat types. Independently of the habitat type, P. splendens have a significant role in the sapling recruitment: their number was higher underneath of conspecifics than in open spaces. Besides, plants in the rocky outcrops produced smaller and ovoid-shaped fruits, as a possible result of selective pressures generated by frugivorous. We propose that rocky outcrops are regeneration sites for P. splendens. However, subtle differences in genetic diversity between habitats and the lacking of genetic structuration suggest that conservation strategies should be focused on the protection of all habitat types as a manner of maintaining ecosystem processes in this singular vegetation remnant.