F. Ojeda et al., BIODIVERSITY COMPONENTS AND CONSERVATION OF MEDITERRANEAN HEATHLANDS IN SOUTHERN SPAIN, Biological Conservation, 72(1), 1995, pp. 61-72
Biodiversity is a complex issue which has frequently been extremely si
mplified both by equating it with species richness, and by addressing
it at the level of regional floras or faunas. In this paper we carry o
ut a detailed assessment of biodiversity for conservation of Mediterra
nean heathlands and related woodland understoreys on acidic 'islands'
in the Gibraltar Strait region which are remarkable for their high spe
cies richness, high endemism and low ratio of species per genus. The r
elationship between the cover of woody plant species and environmental
variables was studied by multivariate (DCCA) analysis of 30 samples.
Species richness shows a unimodal relationship along the main environm
ental gradient primarily determined by physiological tolerance to low
pH and ecological competition. Quercus suber woodland understoreys und
er intermediate environmental conditions are highest in species richne
ss. Woody plant species are assigned to one of seven types of geograph
ic ranges, and distributional spectra of community samples are represe
nted. Open heathlands on nutrient-poor soils on mountain ridges are hi
ghest in endemism. Species distinctness was estimated as the inverse o
f the average number of species per genus ('taxonomic singularity') wi
thin the Mediterranean Basin, Ibero-North African and Southwestern Spa
in ranges. Quercus canariensis woodland understoreys on more fertile s
oils on valley bottoms present the highest taxonomic singularity. The
analysis at the community level of the three proposed biodiversity com
ponents (species richness, endemism richness and taxonomic singularity
) is interpreted with the aim of formulating sound conservation strate
gies of the communities examined. Although we use communities in the G
ibraltar Strait area as a particular case study, we suggest that this
methodology would help conservation efforts in other areas.