The role of landscape composition and heterogeneity on the taxonomical and functional diversity of Mediterranean plant communities in agricultural landscapes.

Joana Cursach,Carmelo Gómez-Martínez,Miquel Capó,Carles Cardona,Amparo Lázaro,Juan Rita,Daehyun Kim

doi:10.1371/journal.pone.0238222

Abstract

The expansion of agriculture is a major driver of biodiversity loss worldwide, through changes generated in the landscape. Despite this, very little is still known about the complex relationships between landscape composition and heterogeneity and plant taxonomical and functional diversity in Mediterranean ecosystems that have been extensively managed during millennia. Although according to the Intermediate Disturbance Hypothesis (IDH) plant richness might peak at intermediate disturbance levels, functional diversity might increase with landscape heterogeneity and decrease with the intensity of disturbance. Here, we evaluated the associations of landscape composition (percentage of crops) and heterogeneity (diversity of land-cover classes) with plant taxonomical diversity (richness, diversity, evenness), local contribution to beta diversity, and functional diversity (functional richness, evenness, divergence and dispersion) in 20 wild Olea europaea communities appearing within agricultural landscapes of Mallorca Island (Western Mediterranean Basin). In accordance with the IDH, we found that overall plant richness peaked at intermediate levels of crops in the landscape, whereas plant evenness showed the opposite pattern, because richness peak was mainly related to an increase in scarce ruderal species. Plant communities surrounded by very heterogeneous landscapes were those contributing the most to beta diversity and showing the highest functional richness and evenness, likely because diverse landscapes favour the colonization of new species and traits into the communities. In addition, landscape heterogeneity decreased functional divergence (i.e., increased trait overlap of dominant species) which may enhance community resilience against disturbances through a higher functional redundancy. However, a large extent of agriculture in the landscape might reduce such resilience, as this disturbance acted as an environmental filter that decreased functional dispersion (i.e, remaining species shared similar traits). Overall, our study highlights the importance of considering several indices of taxonomical and functional diversity to deeply understand the complex relationships between ecosystems functions and landscape context.

Highlights

Maintaining high levels of biodiversity is crucial for the stability of communities against disturbances [1, 2]
When we tested the interaction between the percentage of crops and the ruderal character of species, we found this interaction to be significant (Habitat preference -ruderal vs. non-ruderal-: χ2 = 299.62; df = 1; P-value < 0.0001; Habitat preference × % Crops2: χ2 = 5.099; df = 1; P-value = 0.024), which indicates that the increase in richness at intermediate percentage of crops was mostly due to the increase of ruderal species, the non-ruderal plants peaked at intermediate crop levels (Fig 2B)
Both functional richness and evenness were highest when the communities were surrounded by more heterogeneous landscapes. This positive relationship between functional richness and heterogeneity was expected, because diverse landscapes containing more habitats may increase the probability of different species with varying functional traits to colonize their communities [83, 84]. This may be the case in our study sites, as we have shown a positive relationship between landscape heterogeneity and local contribution to beta diversity

Summary

Introduction

Maintaining high levels of biodiversity is crucial for the stability of communities against disturbances [1, 2]. Land-use changes, and especially the expansion and intensification of agriculture, strongly threaten the biodiversity worldwide [3,4,5]. Land-use changes influence landscape composition, i.e. type and extent of habitats contained within the landscape, as well as landscape heterogeneity, i.e. the diversity of habitats in the landscape, which in turn may directly affect both plant taxonomical and functional diversity. Several studies have shown that changes in landscape composition and, the loss of natural and semi-natural habitats, have a negative effect on plant taxonomical diversity [8,9,10,11]. IDH has been assessed for diverse types of disturbances and in different habitats [14,15,16,17,18,19]. It has been shown that the conformity to IDH may depend on other factors, such as the environmental stress of communities [19]

Methods

Results

Discussion

Conclusion