Spatial Scaling in Model Plant Communities

We present an analytically tractable variant of the voter model that provides a quantitatively accurate description of beta-diversity (two-point correlation function) in two tropical forests. The model exhibits novel scaling behavior that leads to links between ecological measures such as relative species abundance and the species area relationship.Comment: 10 pages, 3 figure

Non-Neutral Vegetation Dynamics

The neutral theory of biodiversity constitutes a reference null hypothesis for the interpretation of ecosystem dynamics and produces relatively simple analytical descriptions of basic system properties, which can be easily compared to observations. On the contrary, investigations in non-neutral dynamics have in the past been limited by the complexity arising from heterogeneous demographic behaviours and by the relative paucity of detailed observations of the spatial distribution of species diversity (beta-diversity): These circumstances prevented the development and testing of explicit non-neutral mathematical descriptions linking competitive strategies and observable ecosystem properties. Here we introduce an exact non-neutral model of vegetation dynamics, based on cloning and seed dispersal, which yields closed-form characterizations of beta-diversity. The predictions of the non-neutral model are validated using new high-resolution remote-sensing observations of salt-marsh vegetation in the Venice Lagoon (Italy). Model expressions of beta-diversity show a remarkable agreement with observed distributions within the wide observational range of scales explored (5⋅10(−1) m÷10(3) m). We also consider a neutral version of the model and find its predictions to be in agreement with the more limited characterization of beta-diversity typical of the neutral theory (based on the likelihood that two sites be conspecific or heterospecific, irrespective of the species). However, such an agreement proves to be misleading as the recruitment rates by propagules and by seed dispersal assumed by the neutral model do not reflect known species characteristics and correspond to averages of those obtained under the more general non-neutral hypothesis. We conclude that non-neutral beta-diversity characterizations are required to describe ecosystem dynamics in the presence of species-dependent properties and to successfully relate the observed patterns to the underlying processes

Beta-diversity of intertidal vegetation species under the neutral assumption.

<p>The hollow symbols represent observational values, while solid lines are plots of eq. (1) from the neutral model fitted on observations.</p

Vegetation map of the San Felice salt marsh in the Venice Lagoon (geometric resolution is 0.5 m, channels and creeks are in blue).

<p>The inset provides an indication of the high level of detail characterizing the data, which resolve small-scale channel and vegetation structures.</p

Beta-diversity of intertidal vegetation species.

<div><p>The solid symbols represent the probability of occurrence of species <i>i</i> and <i>j</i> at two sites separated by a distance <i>r</i> as computed from the vegetation distributions of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0000078#pone-0000078-g001" target="_blank">Figure 1</a>.</p> <p>The solid lines are plots of eqs. (1) from the model fitted on observations.</p> <p>Panel a) refers to the case in which <i>i = j</i>, (conspecific sites).</p> <p>In panel b), referring to the case <i>i≠j</i>, only one beta-diversity curve involving soil was indicated for clarity, the remaining ones being similar.</p></div

Taking species abundance distributions beyond individuals

The species abundance distribution (SAD) is one of the few universal patterns in ecology. Research on this fundamental distribution has primarily focused on the study of numerical counts, irrespective of the traits of individuals. Here we show that considering a set of Generalized Species Abundance Distributions (GSADs) encompassing several abundance measures, such as numerical abundance, biomass and resource use, can provide novel insights into the structure of ecological communities and the forces that organize them. We use a taxonomically diverse combination of macroecological data sets to investigate the similarities and differences between GSADs. We then use probability theory to explore, under parsimonious assumptions, theoretical linkages among them. Our study suggests that examining different GSADs simultaneously in natural systems may help with assessing determinants of community structure. Broadening SADs to encompass multiple abundance measures opens novel perspectives in biodiversity research and warrants future empirical and theoretical developments.</p