Abstract
Elevational gradients provide a unique opportunity to explore species responses to changing environmental conditions. Here, we focus on an elevational gradient in Crete, a climate-vulnerable Mediterranean plant biodiversity hotspot and explore the diversity patterns and underlying mechanisms of different plant life forms. We found that the significant differences in life forms’ elevational and environmental ranges are reflected in α- diversity (species richness at local scale), γ-diversity (species richness at regional scale) and β-diversity (variation in species composition). The α- and γ-diversity decreased with elevation, while β-diversity followed a hump-shaped relationship, with the peak varying between life forms. However, β-deviation (deviation from null expectations) varied significantly with elevation but was life formindependent. This suggests that species composition is shaped by the size of the available species pool which depends on life form, but also by other deterministic or stochastic processes that act in a similar way for different life forms. The strength of these processes varies with elevation, with hotter–drier conditions and increased human activities filtering species composition at lowlands and large-scale processes determining the species pool size overriding local ecological processes at higher elevations.
Highlights
Islands occupy only 5.3% of Earth’s surface but contribute disproportionally to global biodiversity, for example they contribute 17% of plant species [1,2]
Multiple studies have documented that multiple factors affect the species richness of islands, highlighting the role of environmental conditions in driving species diversity patterns within islands [4,5,6]
Given that life form trait is linked to plant responses to environmental conditions, we compare the elevational, environmental, and geographical ranges of species, and we explore how species richness at local (α-diversity) and regional scale (γ-diversity) varies along an elevational gradient
Summary
Islands occupy only 5.3% of Earth’s surface but contribute disproportionally to global biodiversity, for example they contribute 17% of plant species [1,2]. These isolated ecosystems have inspired the classical theory of island biogeography which predicts that islands are in a dynamic equilibrium [3]. Their species richness is determined by the balance between extinction and immigration rates which depend on the size of the island and the distance from mainland, that is, isolation. Species responses are mediated by their traits reflecting behavior, physiology and Diversity 2019, 11, 200; doi:10.3390/d11100200 www.mdpi.com/journal/diversity
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