Genetic analysis of native and introduced populations of the aquatic weed Sagittaria platyphylla – implications for biological control in Australia and South Africa

Sagittaria platyphylla (Engelm.) J.G. Sm. (Alismataceae) is an emergent aquatic plant native to southern USA. Imported into Australia and South Africa as an ornamental and aquarium plant, the species is now a serious invader of shallow freshwater wetlands, slow-flowing rivers, irrigation channels, drains and along the margins of lakes and reservoirs. As a first step towards initiating a classical biological control program, a population genetic study was conducted to determine the prospects of finding compatible biological control agents and to refine the search for natural enemies to source populations with closest genetic match to Australian and South African genotypes. Using AFLP markers we surveyed genetic diversity and population genetic structure in 26 populations from the USA, 19 from Australia and 7 from South Africa. Interestingly, we have established that populations introduced into South Africa and to a lesser extent Australia have maintained substantial molecular genetic diversity comparable with that in the native range. Results from principal coordinates analysis, population graph theory and Bayesian-based clustering analysis all support the notion that introduced populations in Australia and South Africa were founded by multiple sources from the USA. Furthermore, the divergence of some Australian populations from the USA suggests that intraspecific hybridization between genetically distinct lineages from the native range may have occurred. The implications of these findings in relation to biological control are discussed

Continental scale patterns and predictors of fern richness and phylogenetic diversity

Because ferns have a wide range of habitat preferences and are widely distributed, they are an ideal group for understanding how diversity is distributed. Here we examine fern diversity on a broad-scale using standard and corrected richness measures as well as phylogenetic indices; in addition we determine the environmental predictors of each diversity metric. Using the combined records of Australian herbaria, a dataset of over 60,000 records was obtained for 89 genera to infer richness. A molecular phylogeny of all the genera was constructed and combined with the herbarium records to obtain phylogenetic diversity patterns. A hotspot of both taxic and phylogenetic diversity occurs in the Wet Tropics of northeastern Australia. Although considerable diversity is distributed along the eastern coast, some important regions of diversity are identified only after sample-standardization of richness and through the phylogenetic metric. Of all of the metrics, annual precipitation was identified as the most explanatory variable, in part, in agreement with global and regional fern studies. However, precipitation was combined with a different variable for each different metric. For corrected richness, precipitation was combined with temperature seasonality, while correlation of phylogenetic diversity to precipitation plus radiation indicated support for the species-energy hypothesis. Significantly high and significantly low phylogenetic diversity were found in geographically separate areas. These separate areas correlated with different climatic conditions such as seasonality in precipitation. The phylogenetic metrics identified additional areas of significant diversity, some of which have not been revealed using traditional taxonomic analyses, suggesting that different ecological and evolutionary processes have operated over the continent. Our study demonstrates that it is possible and vital to incorporate evolutionary metrics when inferring biodiversity hotspots from large compilations of data

Implications of the 2019–2020 megafires for the biogeography and conservation of Australian vegetation

Australia's 2019–2020 'Black Summer' bushfires burnt more than 8 million hectares of vegetation across the south-east of the continent, an event unprecedented in the last 200 years. Here we report the impacts of these fires on vascular plant species and communities. Using a map of the fires generated from remotely sensed hotspot data we show that, across 11 Australian bioregions, 17 major native vegetation groups were severely burnt, and up to 67–83% of globally significant rainforests and eucalypt forests and woodlands. Based on geocoded species occurrence data we estimate that >50% of known populations or ranges of 816 native vascular plant species were burnt during the fires, including more than 100 species with geographic ranges more than 500 km across. Habitat and fire response data show that most affected species are resilient to fire. However, the massive biogeographic, demographic and taxonomic breadth of impacts of the 2019–2020 fires may leave some ecosystems, particularly relictual Gondwanan rainforests, susceptible to regeneration failure and landscape-scale decline

Land availability may be more important than genetic diversity in the range shift response of a widely distributed eucalypt, Eucalyptus melliodora

Climate change is challenging many species which are expected to respond through range shifts, in situ adaptation or extinction. Successful plant migration is complex and dependent on many factors including propagule availability, dispersal ability, regeneration sensitivity and habitat suitability. Eucalypts are a common and key component of the Australian flora that have been extensively cleared in south eastern Australia. Under a warming climate eucalypts in this region are predicted to contract and move in a south easterly direction. We used microsatellites to evaluate genetic diversity and population genetic structure in 32 mature stands of Yellow Box (Eucalyptus melliodora) from across the known distribution. We also used niche modelling to explore Yellow Box range shifts from the Last Glacial Maximum (21 Kya) to 2090. We found high genetic diversity, no evidence of genetic bottlenecks and limited population genetic structure suggesting that old Yellow Box trees are remnants of a once large panmictic population. Niche modelling found that habitat suitability in coastal and mountainous areas will become available under a warming climate, especially at higher elevations. While we predict that habitat suitable for Yellow Box colonisation will become available when this was considered in conjunction with land availability opportunities for colonisation will be significantly diminished

Biogeographical regions and phytogeography of the eucalypts

Aim: To map spatial patterns of species richness, species endemism and species turnover of the eucalypts; to propose a biogeographical regionalization of eucalypts based on species turnover; and to identify the environmental correlates of these patterns.\ud \ud Location: Australia and Malesia.\ud \ud Methods: We analysed 798 eucalypt species (Angophora, Corymbia and Eucalyptus) with distributions across Australia and Malesia using square cells with a resolution of 100 × 100 km. Species richness, endemism and species turnover were calculated. Phytogeographical regions were identified using an agglomerative cluster analysis derived from a matrix of pairwise Simpson's beta (βsim) dissimilarity values. Eleven environmental variables were used to analyse the environmental correlates of species turnover. Non-metric multidimensional scaling (NMDS) of the βsim, Getis-Ord Gi* hotspot spatial statistics and an ordination of the βsim -NMDS were used to investigate the environmental drivers at the continental level and for each of the phytogeographical regions.\ud \ud Results: We identified three centres of species richness and fourteen of endemism, of which several are newly identified. The main centres of species richness agree with previous studies. Six major eucalypt phytogeographical regions are proposed based on the species turnover: monsoon, tropical/subtropical, south-east, south-west, Eremaean north and Eremaean south. These findings are supported by significant environmental differences of the NMDS vectors and the Gi* statistics. The environmental drivers of species turnover are broadly consistent with the continental patterns of summer and winter rainfall below and above the Tropic of Capricorn.\ud \ud Main conclusions: The proposed phytogeographical regions are similar to the Australian biomes. Climate is the main driver of the phytogeographical regions, varying from region to region. Comprehensive bioregionalization frameworks and phytogeography updates, as proposed here, are fundamental for enhancing our understanding of the spatial distribution of biodiversity and therefore benefit global biogeography and help planners to identify regions of high conservation relevance

Why non-native grasses pose a critical emerging threat to biodiversity conservation, habitat connectivity and agricultural production in multifunctional rural landscapes

<b>Context</b>\ud \ud Landscape-scale conservation planning is key to the protection of biodiversity globally. Central to this approach is the development of <i>multifunctional rural landscapes</i> (MRLs) that maintain the viability of\ud natural ecosystems and promote animal and plant dispersal alongside agricultural land uses.\ud \ud <b>Objectives</b>\ud \ud We investigate evidence that <i>non-native grasses</i> (NNGs) in rangelands and other low-intensity agricultural systems pose a critical threat to landscape conservation initiatives in MRLs both in Australia and globally. Methods We first establish a simple socio-ecological model that classifies different rural landscape elements within typical MRLs based on their joint conservation and agro-economic value. We then quantify the impacts of eight Australian NNGs(Andropogon gayanus, Cenchrus ciliaris, Eragrostis curvula, Hyparrhenia hirta, Nassella neesiana, Nassella trichotoma, Phalaris aquatica and Urochloa mutica) on different landscape elements and then classify and describe the socio-ecological transformations that result at the MRL scale.\ud \ud <b>Results</b>\ud \ud Our data indicate that two broad classes of NNGs exist. The first reduces both conservation and agro-economic value (‘co-degrading’ species) of invaded landscapes, while the second improves agroeconomic value at the expense of conservation value (‘trade-off’ species). Crucially, however, both classes cause hardening of the landscape matrix, agricultural intensification, reduced habitat connectivity, and the loss of multi-value land use types that are vital for landscape conservation.\ud \ud <b>Conclusions</b>\ud \ud NNGs drive socio-ecological transformations that pose a growing threat to landscape-scale connectivity and conservation initiatives in Australia and globally. There is an urgent need for further research into the impacts of NNGs on habitat connectivity and biodiversity within multifunctional landscapes, and the socio-ecological goals that can be achieved when landscape transformation and degradation by these species is unavoidable