Australian Tropical and Subtropical Rain Forest Community Assembly: Phylogeny, Functional Biogeography, and Environmental Gradients

Abstract

To compare community assemblage patterns in tropical northeastern and subtropical central eastern Australia across selected gradients and scales, we tested the relationship of species traits with phylogenetic structure, and niche breadth. We considered phylogenetic relationships across current-day species in assemblages in relation to rain forest species pool sizes, and trait values along gradients including elevation and latitude. Trait values were quantified across scales for seed size, leaf area, wood density and maximum height at maturity for 1137 species and 596 assemblages using trait gradient analysis (TGA). Local assemblages of subtropical species had narrower trait ranges, and higher niche breadth values than corresponding assemblages of tropical species. Leaf size and seed size increased at low latitudes, and community phylogenetic structure was most strongly correlated with seed traits in the subtropics, reflecting dispersal and recolonization processes. Elevation accounted for little of the variance in community phylogenetic structure or trait variation across local and regional scales. Stable moist forest areas retained many species from ancestral rain forest lineages across a range of temporally conserved habitats; species within assemblages were less related; and rain forest assemblages had higher functional diversity, but lower niche breadth. This suggests that on average, assemblages of species in stable areas had greater trait variation and narrower distributions. Historic and recent rain forest contraction and re-expansion can result in recolonized areas that are dominated by species that are more related (phylogenetically) than by chance, have smaller, widely dispersed seeds, and greater niche breadth (broader distributions).

From ratites to rats: the size of fleshy fruits shapes species' distributions and continental rainforest assembly

“…Volant vertebrates that can ingest fleshy fruits less than or equal to 30 mm are widely distributed across Australian rainforests, while those that can potentially disperse larger fruits and seeds are restricted to more tropical latitudes [9]. In both the tropics and subtropics, richness of large-fruited species tends to track overall richness and high endemism (see electronic supplementary material, figure S1), the latter generally acknowledged as an important indicator of environmentally stable refugia [18,19]. These correlations suggest that these regions maintained high floristic diversity through the climatic extremes of the Quaternary, despite the likelihood that some southern refugia were just too small and/or locally dissected to retain vertebrate dispersers capable of supporting the re-expansion of species with large fruits into newly available habitats [12].…”

“…We expect that if the size of fleshy fruits shapes dispersal potential, small-fruited species dispersed by multiple animals should have larger geographical ranges than large-fruited species. In addition, we expect larger-fruited species to be concentrated within temporally stable refugial areas [18,19] where distribution patterns are regulated by the persistence of a greater variety of vertebrate dispersers or through localized persistence and site-specific dispersal mechanisms [11].…”

Plant functional traits have globally consistent effects on competition

“…The data sets collated fell into two broad categories: (1) national forest inventories (NFI), in which trees above a given diameter were sampled in a network of small plots (often on a regular grid) covering the country (references for NFI data used [39][40][41][42][43][44][45][46][47][48] ); (2) large permanent plots (LPP) ranging in size from 0.5 to 50 ha, in which the x-y coordinates of all trees above a given diameter were recorded (references for LPP data used refs [49][50][51][52][53][54][55][56]. LPP were mostly located in tropical regions.…”

Testing for functional convergence of temperate rainforest tree assemblages in Chile and New Zealand

“…Some of the patterns revealed by our comparisons (Figures 3, 4) are well-documented, in particular the latitudinal trends in leaf and seed sizes in humid forests (Webb 1968;Lord et al 1997;Kooyman et al 2012). Although neither of these trends is well-understood, optimization of water use efficiency provides one possible basis for explaining geographic variation in leaf size (Parkhurst & Loucks 1972).…”