Diversity and distribution of extra-floral nectaries in the cerrado savanna vegetation of Brazil

John Boudouris,Simon A Queenborough

doi:10.7717/peerj.219

Abstract

Aim. Throughout evolutionary history, plants and animals have evolved alongside one another. This is especially apparent when considering mutualistic relationships such as between plants with extra-floral nectaries (EFNs, glands on leaves or stems that secrete nectar) and the ants that visit them. Ants are attracted by the nectar and then protect the plant against destructive herbivores. The distribution of these plants is of particular interest, because it can provide insights into the evolutionary history of this unique trait and the plants that possess it. In this study, we investigated factors driving the distribution of woody plants with EFNs in the cerrado vegetation of Brazil.Location. BrazilMethods. We used a database detailing the incidence of 849 plant species at 367 cerrado sites throughout Brazil. We determined which species possessed EFNs and mapped their distributions. We tested for correlations between the proportion of EFN species at each site and (i) three environmental variables (mean annual temperature, mean annual precipitation, and the precipitation in the driest quarter of the year), (ii) a broad soil classification, and (iii) the total species diversity of each site.Results. We found a wide range in the proportion of EFN species at any one site (0–57%). However, whilst low diversity sites had wide variation in the number of EFN species, high diversity sites all had few EFN species. The proportion of EFN species was positively correlated with absolute latitude and negatively correlated with longitude. When accounting for total species diversity, the proportion of EFN species per site was negatively correlated with precipitation in the driest quarter of the year and positively correlated with temperature range.Main Conclusions. These results suggest either that herbivore pressure may be lower in drier sites, or that ants are not as dominant in these locations, or that plant lineages at these sites were unable to evolve EFNs.

Highlights

The large-scale distribution patterns of many plant traits, as well as the factors that drive these distributions, are still poorly understood in many ecosystems
We modelled the proportion of Extra-floral nectaries (EFNs) species at each site as a function of annual mean temperature, temperature range, and temperature seasonality (SD of temperature), annual mean precipitation, precipitation in the driest quarter, and precipitation seasonality
There was a greater proportion of species with EFN in the south and east of Brazil (Figs. 3A, 3C and 3D)

Summary

Introduction

The large-scale distribution patterns of many plant traits, as well as the factors that drive these distributions, are still poorly understood in many ecosystems. Various studies have demonstrated a general trend of increasing anti-herbivore defences in plants moving toward the equator (Coley & Barone, 1996; Fiala & Linsenmair, 1995; Oliveira & Oliveira-Filho, 1991; Pemberton, 1998; Schemske, Mittelbach & Cornell, 2009). This trend is generally believed to correlate with the intensity of current herbivory in the region, or the intensity of herbivory with which the flora’s ancestors had to contend. The results of both a recent meta-analysis and a global observational study contradict these findings, suggesting that plants at higher (temperate) latitudes possess greater herbivory resistance traits than plants at lower (tropical) latitudes (Moles et al, 2011a; Moles et al, 2011b)

Methods

Results

Conclusion