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.

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Español.  La especie Corema album se encuentra en el litoral oeste de la Península Ibérica, desde Camariñas (La Coruña) hasta Punta Camarinal (Cádiz), donde ha sufrido un considerable retroceso, como otros muchos taxones de distribución costera. A lo largo del área en la cual aparece se ha usado en ceremonias religiosas, al igual que se aprovechaban sus frutos comestibles, los cuales llegaron a ser un producto más en algunos mercados de ciudades gallegas y portuguesas. En cambio, no estaba constatado el uso de tal especie en la región andaluza, que es el principal objetivo de este trabajo. Por medio de encuestas a los habitantes de Barbate (Cádiz) se demuestra que los frutos de C. album se usaron y comercializaron en este pueblo hasta finales de los años cincuenta, cuando desbroces por parte de los gestores de la zona para favorecer las plantaciones de pino disminuyeron la producción de frutos de este arbusto en los años siguientes. De forma conjunta se produjo en la zona un alzamiento económico, que permitiría la aparición de puestos de trabajo con más beneficios que la venta de frutos de la camarina, lo cual hizo que su el uso de tal especie en la zona desapareciera hasta nuestros días.english. Corema album is an endemic species from the west coastline of the Iberian Peninsula, from Camariñas (La Coruña) to Punta Camarinal (Cádiz). This plant has suffered an intense deterioration in the last few decades. This bush has been used in some religious ceremonies along its natural distribution, and its fruit has been eaten in some towns in Galicia and Portugal. The key objective in this study is analyze whether this fruit was used or not in Andalucía, since this fact is not know yet. By interviewing the inhabitants of Barbate (Cádiz) we have been found that the fruit of Corema album were eaten and sold in this village until the end of the fifties, when consecutive cleanings of the vegetation against bushes joined with a better economic situation caused the end of this activity.

Question Does the number and relative abundance of sandstone specialist woody species in Mediterranean heathland (herriza) communities of the Strait of Gibraltar decrease with increasing sandstone patch isolation? If so, does this reduction suggest deterministic (ecological filtering) or random (ecological drift) effects? Location Strait of Gibraltar region. Methods We recorded the identity and relative abundance of sandstone specialist and generalist woody plant species in 26 herriza samples. We then calculated the degree of sandstone patch isolation of each herriza sample and used generalized linear regression models to examine the effect of sandstone patch isolation on species richness and relative abundance of woody species in the herriza communities, separately for sandstone specialist and generalist species. We finally compared beta‐diversity values among herriza samples from the two sides of the Strait of Gibraltar. Results Increasing sandstone patch isolation determined a loss of sandstone specialist species in herriza communities. This loss of sandstone specialist species is more pronounced in the African side of the Strait, where overall sandstone patch isolation is higher, suggesting that this is a random process (ecological drift) that resulted in higher beta‐diversity between herrizas in Tangier. Conclusions This study highlights the high vulnerability of the highly biodiverse herriza or Mediterranean heathland in the African side of the Strait of Gibraltar as a consequence of its overall higher sandstone patchiness.

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