Species richness and patterns of overdispersion, clustering and randomness shape phylogenetic and functional diversity–area relationships in habitat islands

Abstract

AbstractAimThe aim of this study was to evaluate how the area of habitat islands influences multiple facets of diversity.LocationSouthern Brazil.TaxonBirds.MethodsUsing an Information Theoretic approach, we compared the fit of 20 diversity–area relationship (DARs) models in three habitat island systems. We tested for the best‐fit model, model‐family, shape and the presence/absence of an asymptote. We used species richness (SR), Faith's phylogenetic diversity (PD) and Faith's functional diversity (FD) to assess species–area (SARs), phylogenetic (PDARs) and functional diversity–area relationships (FDARs). We controlled for the effect of SR in PD and FD via null models to assess PDARs and FDARs independently of SR and to explore the influence of phylogenetic and functional randomness, clustering and overdispersion.ResultsPDARs and FDARs built with PD and FD resembled SARs and were all best fitted by convex or sigmoidal, upwards oriented, non‐asymptotic models. Controlling for SR in diversity indices produced flat or downwards oriented, weak PDARs and FDARs, which were best fitted by convex, non‐asymptotic models or the linear model. Taxonomic diversity accumulated faster with area than functional diversity, which accumulated faster than phylogenetic diversity. Randomness and clustering patterns prevailed in shaping PDARs and FDARs relative to overdispersion.Main conclusionsControlling for SR in PD and FD affects DARs patterns and the strength of the relationships. Irrespective of this influence of SR, a few simple models of the power and exponential model‐families best fit DARs. Model parameters reveal differences in the response of each facet of diversity to increases in area, highlighting the complementary nature of DARs. When considered independently of SR, PDAR and FDAR patterns largely reflect the broad variation of phylogenetic and functional diversity in small islands. This suggests that the ecological processes that generate phylogenetic and functional overdispersion and clustering operate at contrasting spatial scales.