Population genetic structure of a sandstone specialist and a generalist heath species at two levels of sandstone patchiness across the Strait of Gibraltar.

Manuel Jesús Gil-López,José Gabriel Segarra-Moragues,Fernando Ojeda

doi:10.1371/journal.pone.0098602

Abstract

Many habitat specialist species are originally composed of small, discontinuous populations because their habitats are naturally fragmented or patchy. They may have suffered the long-term effects of natural patchiness. Mediterranean heathlands, a representative habitat in the Strait of Gibraltar region, are associated with nutrient-poor, acidic sandstone soils. Sandstone soil patches in the African side of the Strait (Tangier) are, in general, smaller and more scattered than in the European side (Algeciras). In this study, we analyze the effect of this sandstone patchiness on the population genetic diversity and structure of two Erica species from these Mediterranean heathlands that differ in their edaphic specificity, E. australis, sandstone specialist, and E. arborea, generalist. Average levels of within-population genetic diversity and gene flow between populations were significantly lower in Tangier (high sandstone patchiness) than in Algeciras (low patchiness) for the sandstone specialist, whereas no differences between both sides of the Strait were detected in the edaphic generalist. Since most endemic species in Mediterranean heathlands of the Strait of Gibraltar are sandstone specialists, these results highlight an increased vulnerability to loss of genetic diversity and local extinction of the heathland endemic flora in the Tangier side of the Strait of Gibraltar.

Highlights

Plant populations in small habitat fragments have frequently smaller population sizes and experience a higher degree of isolation among populations than those from continuous or less fragmented habitats [1]
Gene flow reduces the risk of extinction of small populations either by avoiding genetic erosion through the input of new alleles mainly via seed dispersal or by recolonization after a local extinction event [10211]
Within the regional context of this study (i.e. Strait of Gibraltar region), E. australis is virtually restricted to highly acidic, aluminium-rich sandstone soil patches whereas E. arborea occurs both within sandstone patches and out in the surrounding matrix on different, non-acid soils [24]

Summary

Introduction

Plant populations in small habitat fragments have frequently smaller population sizes and experience a higher degree of isolation among populations than those from continuous or less fragmented habitats [1]. The smaller and more isolated the populations, the more liable they are to demographic stochasticity, to genetic depletion and, to local extinction [224]. These small, fragmented populations are highly vulnerable to edge effects, habitat degradation or to catastrophic disturbance events, either natural or human-induced [5,6]. Genetic diversity in a plant population is lost mostly by the effect of genetic drift and by reduced genetic communication (i.e. low gene flow and migration) among populations [7]. Gene flow reduces the risk of extinction of small populations either by avoiding genetic erosion through the input of new alleles mainly via seed dispersal or by recolonization after a local extinction event [10211]. Gene flow allows the long-term persistence of small populations and it is a critical process for the management and conservation of threatened species in fragmented or degraded habitats [3,12]

Methods

Results

Conclusion