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Endolithic and epilithic lichens proliferate on calcareous cobbles and rock outcrops in the Negev Highlands, Israel. Whereas epilithic lichens predominate in shaded mesohabitats, extensively covering rock outcrops, endolithic lichens proliferate on loose cobbles. Endolithic lichens were thought to predominate in habitats having a poor dew regime.

Dew measurements were carried out at habitats of endolithic and epilithic lichens. The measurements took place on loose and partially embedded cobbles with 90-100% of endolithic lichen cover, and on rock outcrops inhabited by epilithic lichens (75-90% cover). In addition, independent dew measurements were carried out with the Flare Cloth Method (CPM). A rotal of 60 days of measurements was performed.

Average daily dew amount as obtained by the CPM was 0.20 nun, as compared to 0.18 mm obtained on the loose cobbles, 0.09 mm obtained by the partially embedded cobbles and 0.04-0.08 mm obtained on the bedrock surfaces. The dew amounts obtained on the cobbles were significantly higher than those obtained on the bedrock surfaces (paired t-test, p < 0.001). Thus, although exposed to the first sun beams during the early morning hours, cobbles, due to their excessive heat loss and subsequent higher cooling rates, form a mesic microhabitat las far as dew amount is concerned) within an unshaded and hence xeric las far as dew duration is concerned) mesohabitat. The results point out that endolithic lichens are not necessarily adapted to a poor dew regime. The advantage of the endolithic habitat in light of the present findings is discussed.