Fragmented but not isolated: Contribution of single trees, small patches and long-distance pollen flow to genetic connectivity for Gomortega keule, an endangered Chilean tree

Abstract

Habitat fragmentation is a major threat to species survival worldwide due to genetic isolation, inbreeding depression, genetic drift and loss of adaptive potential. However the data on how gene-flow changes following habitat fragmentation is contradictory. If there is significant gene-flow between spatially isolated populations then limited conservation resources could be directed away from projects to ‘establish genetic connectivity’ and used to address other consequences of habitat fragmentation. This research focused on an endangered tree species Gomortega keule (Gomortegaceae) in a fragmented landscape in the Central Chile Biodiversity Hotspot and addressed three questions: (1) How far does pollen move between pollen donors and seed trees and what is the shape of the dispersal curve? (2) Do insect pollinators travel outside of forest patches? (3) Do small populations and single trees contribute to genetic connectivity across the landscape? Paternity analysis results show that G. keule’s insect pollinators travel outside of forest patches, over distances of 6 km, beyond the scale of population fragmentation or genetic structure. Pollen moved from small sites and single trees into large sites, as well as in the other direction, indicating these sites play a key role as functioning elements of the wider population and as stepping stones between sites. Fragmentation at the scale investigated has not led to genetic isolation, thus genetic connectivity per se is not a conservation priority. Other consequences of land-use change, specifically continuing habitat loss and population reduction, still threaten the survival of the species.