Elevational gradient of vascular plant species richness and endemism in Crete--the effect of post-isolation mountain uplift on a continental island system.

Panayiotis Trigas,Spyros Tsiftsis,Maria Panitsa,Corrie S Moreau

doi:10.1371/journal.pone.0059425

Panayiotis Trigas, Spyros Tsiftsis + Show 2 more

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https://doi.org/10.1371/journal.pone.0059425

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Abstract

Understanding diversity patterns along environmental gradients and their underlying mechanisms is a major topic in current biodiversity research. In this study, we investigate for the first time elevational patterns of vascular plant species richness and endemism on a long-isolated continental island (Crete) that has experienced extensive post-isolation mountain uplift. We used all available data on distribution and elevational ranges of the Cretan plants to interpolate their presence between minimum and maximum elevations in 100-m elevational intervals, along the entire elevational gradient of Crete (0–2400 m). We evaluate the influence of elevation, area, mid-domain effect, elevational Rapoport effect and the post-isolation mountain uplift on plant species richness and endemism elevational patterns. Furthermore, we test the influence of the island condition and the post-isolation mountain uplift to the elevational range sizes of the Cretan plants, using the Peloponnese as a continental control area. Total species richness monotonically decreases with increasing elevation, while endemic species richness has a unimodal response to elevation showing a peak at mid-elevation intervals. Area alone explains a significant amount of variation in species richness along the elevational gradient. Mid-domain effect is not the underlying mechanism of the elevational gradient of plant species richness in Crete, and Rapoport's rule only partly explains the observed patterns. Our results are largely congruent with the post-isolation uplift of the Cretan mountains and their colonization mainly by the available lowland vascular plant species, as high-elevation specialists are almost lacking from the Cretan flora. The increase in the proportion of Cretan endemics with increasing elevation can only be regarded as a result of diversification processes towards Cretan mountains (especially mid-elevation areas), supported by elevation-driven ecological isolation. Cretan plants have experienced elevational range expansion compared to the continental control area, as a result of ecological release triggered by increased species impoverishment with increasing elevation.

Highlights

Elevational gradients are ideally suited for examining biodiversity drivers, as elevation is correlated with several environmental variables while providing more constant ecological conditions and history than can be obtained along continental or global spatial gradients and at the same time they represent reproducible environmental gradients that can be replicated across the globe [1,2]
The impact of the post-isolation mountain uplift to the present elevational species richness and endemism patterns on a continental island has been studied for the first time
We found that total and SUBE vascular plant species richness monotonically decreases with increasing elevation in Crete, while species endemic to Crete (SIE) show a unimodal response to elevational gradient

Summary

Introduction

Elevational gradients are ideally suited for examining biodiversity drivers, as elevation is correlated with several environmental variables while providing more constant ecological conditions and history than can be obtained along continental or global spatial gradients and at the same time they represent reproducible environmental gradients that can be replicated across the globe [1,2]. Two main patterns of species richness-elevation relationships are dominant in the relevant literature, i.e. decreasing and hump-shaped [3]. Growing evidence suggests that the hump-shaped pattern, with diversity peaking at mid-elevations, represents half of all case studies for a wide range of taxa; the other half of the studies includes monotonic decreases or increases as well as roughly constant relations [2,4,5]. The proposed drivers of elevational gradients of biodiversity could be grouped into four main categories: (1) climatic variables like temperature and rainfall that determine energy availability and ecosystem productivity, (2) spatial aspects like area size and geometric constraints, i.e. middomain effect (MDE), (3) evolutionary history like clade age, speciation and extinction rates, and (4) biotic processes like competition, mutualism and ecotone effects [5]. Elevational gradients of diversity are often taxon-specific and they depend on the geographical location of the gradient [4]

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