Patterns of rain forest plant endemism in subtropical Australia relate to stable mesic refugia and species dispersal limitations

Abstract

Aim Our aims were to identify centres of endemism and to infer whether these areas have functioned as refugia for subtropical rain forest plants through historical climate fluctuations.Location Subtropical eastern Australia (23-33°S; 145-155°E).Methods We collated 25,000 records of 179 endemic rain forest plants to identify geographical areas with unusually high concentrations of endemic taxa and range-restricted endemics. We then tested whether centres of endemism coincide with other features indicating refugia, including habitat stability over 120,000 years, and we related dispersal patterns to past habitat stability using seed weight as a surrogate for dispersal ability of endemic plant taxa.Results We identified five main centres of endemism. Historical stability and other processes affecting diversity, including current rainfall, rain forest area, and topographic complexity, explained 58% of variation in plant-weighted endemism. Taxa with poor dispersal ability were concentrated in the areas that were most stable historically.Main conclusions Several lines of evidence suggest that centres of endemism have functioned as important refugia for subtropical rain forest taxa through historical climate fluctuations. The highest concentrations of range-restricted endemic species occur in locations that are predicted to have maintained stable rain forest habitat over at least the past 120,000 years. This association was independent from other factors that were expected to promote diversity (i.e. rain forest area and current environmental suitability). These locations have disproportionately high concentrations of species with poor dispersal ability (large-seeded species).

Genome and transcriptome sequencing characterises the gene space of Macadamia integrifolia (Proteaceae)

“…Australian subtropical rainforests in particular, are ancient refugia with high levels of plant species richness, endemism and rainfall [19]. Recent evidence suggests that insects and pathogens are instrumental in the maintenance of plant species diversity in rainforests [40].…”

“…All four Macadamia species are rare and threatened, and the lowland rainforest ecosystems to which they contribute are listed as critically endangered [17, 18]. The subtropical rainforests of eastern Australia are centres of plant endemism, with high rainfall and low fire frequency that acted as stable refugia through Quaternary glaciation and interglacial periods [19]. This habitat is in contrast to the open, fire-prone habitats that support the majority of extant Proteaceae species.…”

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].…”

Australian spiny mountain crayfish and their temnocephalan ectosymbionts: an ancient association on the edge of coextinction?

“…Therefore, these species are likely to represent key hosts for the conservation of temnocephalan biodiversity [52]. This is a region of high biodiversity, the MacPherson-Macleay overlap (MMO) zone, where temperate and tropical Australian biota overlap [55,56]. Many species of Euastacus occur in close proximity here, likely facilitating exchange of temnocephalans and thereby reducing coextinction risk [10].…”