Identifying drivers of Proteaceae declines on Western Australia's islands

Abstract

Western Australia (WA) is home to several high biodiversity regions with unique flora, and preventing the decline and possible extinction of these species is a global and national priority. While there have been multiple studies investigating extinction risk factors for plants on the mainland, there is a lack of literature describing processes that threaten flora on WA’s islands. Focusing on the diverse Proteaceae plant family, this thesis asked three questions: 1) how much flora survey information is available for assessing the status of Proteaceae on WA islands? 2) is there evidence that Proteaceae populations are declining? and 3) what island-specific factors or plant biological traits contribute to declines? I pooled comparable presence-absence data on insular Proteaceae populations from 25 published or otherwise publically available flora surveys. Overall, survey detection of these populations has declined significantly over time. I used generalised linear models (GLMs) to test for the effects of island-specific factors (latitude, longitude, area, distance from the mainland, presence of introduced herbivores, and land clearing) and plant traits (growth form, fire response, and flowering period) on population declines. The best-supported model of population declines considered the interactive effect of herbivore introduction with island latitude. The strong effect of latitude on population declines merits further investigation and may indicate that there are additional, unknown processes that threaten Proteaceae on WA’s northern islands. Biogeographic factors and species’ biological traits were not supported as explanatory variables, showing that population declines of WA’s island Proteaceae are largely driven by factors relating to human-disturbances. Show more