Demographic modeling of the endangered subtropical rainforest shrub Graptophyllum reticulatum

Abstract

The subtropical rainforest shrub Graptophyllum reticulatum (Acanthaceae) occurs in only a few populations within a 20-kilometer range in the Sunshine Coast, south-east Queensland, Australia. This endangered plant has been subject to habitat degradation and loss, mostly due to land clearing and urbanization. In the past decades, conservation measures such as land protection and translocation have been put in place to protect the species' wild populations. The aim of the study was to analyze the viability of the species' populations in the long term while assessing the effectiveness of land protection and translocation. Demographic data was collected every decade since 2000; for this study, we resurveyed all known populations including a translocated population and two recently discovered populations. We found that the average number of plants per population has doubled since 2000, except in one population that underwent land clearing. However, after being reduced by 70%, plant abundance in this population has been increasing, giving evidence of natural post-clearing recovery. We developed population growth models for population viability analysis in best, average, and worst-case scenarios to predict the species' viability over the next 100 years. All populations are expected to grow in the next 100 years, except in the worst-case scenario in which removing land protection from the model led to an 80% decline in the total number of plants within 100 years, highlighting the importance of land protection for species' conservation. Overall, if current conservation efforts are maintained, this endangered species is likely to persist for the next 100 years.