Demography, passive surveillance and potential habitat modelling of an Australian giant trapdoor spider (Idiopidae: Euoplos grandis) from the Queensland Brigalow Belt: half a decade of population monitoring for conservation outcomes

Abstract

‘Slow science’ approaches to generating authoritative longitudinal datasets for long-term monitoring are fundamental to conservation biology. Following reports of significant arthropod declines worldwide, and recent climate-driven disasters such as the devastating ‘Black Summer’ bushfires of 2019–2020, there has been a renewed focus on invertebrate conservation in Australia and further calls for informative baseline datasets with which to understand increasingly rapid biotic change. Trapdoor spiders of the infraorder Mygalomorphae, in particular, have been the subject of decades of research highlighting their sensitivity to environmental change and their special significance to conservation biology. In 2019, the senior author and collaborators introduced within this journal a new long-term monitoring study system for an Australian mygalomorph spider (Euoplos grandis Wilson & Rix, 2019; family Idiopidae), then in its infancy with just 18 months of quantitative demographic data. In the current study, we extend and build upon that work and provide a synthesis of demographic information accumulated over half a decade, resulting in 166 collective years' worth of times-series data from 101 individual spiders. We infer an estimated average cumulative growth curve for the species based on census data from 77 spiders, with evidence for a 7+-year juvenile female growth period and a potential life span for adult females of over 20 years. Passive surveillance using a camera trap deployed at the study site for 8 months resulted in significant advances in our understanding of the biology and behaviour of E. grandis, with a suite of behaviours observed for the first time, including rarely documented interactions with conspecifics, potential predators and prey. We further summarise the results of maximum entropy potential habitat modelling as informed by extensive on-ground surveys and a refined taxonomy, and provide an updated conservation assessment using the International Union for Conservation of Nature (IUCN) criteria. These results reveal that E. grandis is a Vulnerable threatened species endemic to the highly fragmented southern Brigalow Belt bioregion, with population dynamics and life history characteristics that underscore the considerable sensitivity of Australian idiopid trapdoor spiders to a multitude of threatening processes.