No abstract

The limited seed dispersal range of cycads, longevity of individuals, including a long juvenile phase, coupled with dioecy, suggest that the impacts of habitat fragmentation are not straightforward. Cycas megacarpa K.D. Hill. is an endangered cycad that occurs in a highly fragmented landscape derived from past agricultural land clearing. Current threats continue to be land clearing for both urban and rural developments and major infrastructure development for coal seam gas. This study investigated the effect fragmentation has had on C. megacarpa populations across its entire range. Twelve microsatellite loci were developed with next generation sequencing and used to analyse 992 samples from 33 populations. Geographic information system (GIS) analysis of the total reduction in suitable regional ecosystem (RE) habitat in Queensland revealed a 69% loss between 1960s pre-clearing records and 2009 with only 29% of remaining habitat occurring in protected areas. Populations are highly variable with many small populations, and there is evidence of possible declining recruitment of seedlings. The relatively low proportion of adult sized plants that reproduce synchronously promotes outcrossing; however, there is some evidence that reduced population sizes may lead to inbreeding. Genetic diversity is not correlated with population size but it is weakly correlated with isolation. There is evidence of considerable historic gene flow among populations and little genetic differentiation among broad geographic regions. The results show genetic clustering and are consistent with hypotheses that C. megacarpa existed as a set of metapopulations historically linked by gene flow. This has maintained diversity in small populations but suggests that fragmentation that increases population isolation has and will continue to reduce the species viability. The persistence of adult cycads through multiple generations may allow rare alleles to remain within populations over a longer period of time.

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Madagascar is home to 208 indigenous palm species, almost all of them endemic and >80% of which are endangered. We undertook complete population census and sampling for genetic analysis of a relatively recently discovered giant fan palm, the Critically Endangered Tahina spectablis in 2008 and 2016. Our 2016 study included newly discovered populations and added to our genetic study. We incorporated these new populations into species distribution niche model (SDM) and projected these onto maps of the region. We developed population matrix models based on observed demographic data to model population change and predict the species vulnerability to extinction by undertaking population viability analysis (PVA). We investigated the potential conservation value of reintroduced planted populations within the species potential suitable habitat. We found that the population studied in 2008 had grown in size due to seedling regeneration but had declined in the number of reproductively mature plants, and we were able to estimate that the species reproduces and dies after approximately 70 years. Our models suggest that if the habitat where it resides continues to be protected the species is unlikely to go extinct due to inherent population decline and that it will likely experience significant population growth after approximately 80 years due to the reproductive and life cycle attributes of the species. The newly discovered populations contain more genetic diversity than the first discovered southern population which is genetically depauperate. The species appears to demonstrate a pattern of dispersal leading to isolated founder plants which may eventually lead to population development depending on local establishment opportunities. The conservation efforts currently put in place including the reintroduction of plants within the species potential suitable habitat if maintained are thought likely to enable the species to sustain itself but it remains vulnerable to anthropogenic impacts.

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Little remains of the Brigalow (Acacia harpophylla F.Muell. ex Benth.) woodlands of Australia, primarily due to land clearing for grazing and agriculture. Many threatened species in this region are poorly studied, and the life history traits of some herbaceous species such as ephemeral shoot systems, mean that conservation assessments are difficult. Recent gas pipeline developments have led to an increased need to understand the ecology and genetics of such taxa, in order to advise offset and translocation activities. Xerothamnella herbacea R.Baker is an endangered ephemeral herbaceous species from the Brigalow Belt region, which dies back during prolonged dry conditions. The aim of this study was to map the extent of potentially suitable habitat of this species, including determination of population extent within existing protected area estate. The species population sizes, reproductive activity and evidence of clonal spread, as well as the levels of genetic diversity and inbreeding, across the species range were also assessed to provide guidance for potential translocation and offsetting programs. The genetic results were related to the species suitable habitat distribution to test whether historic or recent habitat fragmentation most explains genetic patterns in this species. Most of the populations of this species were found to be small with less than 100 plants. The species appears not to be limited by its reproductive output, suggesting other factors may limit its abundance. The species populations have moderate to low genetic diversity suggesting the species is genetically viable in the medium term but are inbred which may be partially due to vegetative spread. Geographic proximity does not predict genetic similarity of populations and diversity is not correlated with population size. The results indicate potential translocation or offsetting programs need to account for genetic relationships in their planning. Resprouting ability has potentially assisted the species to slow the pace of genetic diversity loss due to anthropogenic fragmentation.

No abstract