title: Moving beyond presence and absence when examining changes in species distributions.
abstract: Species distributions are often simplified to binary representations of the ranges where they are present and absent. It is then common to look for changes in these ranges as indicators of the effects of climate change, the expansion or control of invasive species or the impact of human land-use changes. We argue that there are inherent problems with this approach, and more emphasis should be placed on species relative abundance rather than just presence. The sampling effort required to be confident of absence is often impractical to achieve, and estimates of species range changes based on survey data are therefore inherently sensitive to sampling intensity. Species niches estimated using presence-absence or presence-only models are broader than those for abundance and may exaggerate the viability of small marginal sink populations. We demonstrate that it is possible to transform models of predicted probability of presence to expected abundance if the sampling intensity is known. Using case studies of Antarctic mosses and temperate rain forest trees, we demonstrate additional insights into biotic change that can be gained using this method. While species becoming locally extinct or colonising new areas are extreme and obviously important impacts of global environmental change, changes in abundance could still signal important changes in biological systems and be an early warning indicator of larger future changes.
authors.affiliation: Centre for Sustainable Ecosystem Solutions, School of Biological Sciences, University of Wollongong, Wollongong, NSW, 2522, Australia.
authors.forename: Michael B
authors.identifier: 0000-0003-2157-5965
authors.initials: MB
authors.lastname: Ashcroft
authors.affiliation: Centre for Sustainable Ecosystem Solutions, School of Biological Sciences, University of Wollongong, Wollongong, NSW, 2522, Australia.
authors.forename: Diana H
authors.initials: DH
authors.lastname: King
authors.affiliation: Australian Antarctic Division, Department of Environment, Kingston, TAS, 7050, Australia.|Antarctic Climate and Ecosystems Cooperative Research Centre, Private Bag 80, Hobart, TAS, 7001, Australia.
authors.forename: Ben
authors.initials: B
authors.lastname: Raymond
authors.affiliation: Centre for Sustainable Ecosystem Solutions, School of Biological Sciences, University of Wollongong, Wollongong, NSW, 2522, Australia.
authors.forename: Johanna D
authors.initials: JD
authors.lastname: Turnbull
authors.affiliation: Centre for Sustainable Ecosystem Solutions, School of Biological Sciences, University of Wollongong, Wollongong, NSW, 2522, Australia.|Australian Antarctic Division, Department of Environment, Kingston, TAS, 7050, Australia.
authors.forename: Jane
authors.initials: J
authors.lastname: Wasley
authors.affiliation: Centre for Sustainable Ecosystem Solutions, School of Biological Sciences, University of Wollongong, Wollongong, NSW, 2522, Australia.
authors.forename: Sharon A
authors.identifier: 0000-0002-7130-9617
authors.initials: SA
authors.lastname: Robinson
mesh_terms: D044002:Bryophyta; D057231:Climate Change; D017753:Ecosystem; D065928:Forests; D006801:Humans; D014197:Trees
keywords: Antarctic mosses; climate change; geographic range; negative binomial distribution; population abundance; presence-absence data; range shifts