A short distance to the last glacial coast best explains a Tasmanian centre of endemism

James B. Kirkpatrick,Joe Atkinson

doi:10.21425/f5fbg47438

Abstract

At the small scales of world, continent and region, centres of local endemism have been hypothesised to be related to refugia and/or distinctive environmental conditions. We consider patterning of local endemics at a large scale to help test the validity of these two hypotheses for centres of local endemism recognised at smaller scales. Our study area was a centre of local endemism on the Tasman and Forestier peninsulas, Tasmania, Australia. We tested the distinctiveness of both the current climatic and edaphic conditions and the potential for refugia during Quaternary climatic fluctuations, using databases, published maps, and direct observation of climate. Inverse rarity analyses at 1 km2 showed a pattern of concentration of local endemics near the east and southeast coasts of the peninsulas. However, the ranges of species at a larger scale were largely non-overlapping. Climate did not differ from other coastal areas in southeastern Tasmania that lacked local endemics. Climatically similar areas to the centre of local endemism on and outside the peninsulas also had treeless vegetation on skeletal soils on dolerite and mudstone that were habitat for many of the species in the peninsulas centre of local endemism. The areas with high concentrations of local endemics on the peninsulas were located close to the coastline of the Last Glacial Maximum, unlike other areas with the same climatic and edaphic environments inside and outside the peninsulas. The conclusion that the centre of local endemism relates to a closely adjacent glacial refugium, rather than being a response to a distinctive environment, was reinforced by the non-overlapping distributions of the most locally endemic species at a large scale, and the variability in the habitat of the most locally endemic species. This study illustrates the value of investigating the causes of centres of local endemism at a range of scales and confirms the tight link between centres of endemism and refugia.

Highlights

It is axiomatic to say that the presence of an organism in an area indicates that the habitat is or has been suitable for its establishment
We describe patterns of local endemism on the Tasman Peninsula and Forestier Peninsula at several scales to test the alternative hypotheses that the centre of local endemism is related to: 1) the proximity of a coastal refugium during colder times; 2) distinctive environmental conditions
Eight out of 532 Tasmanian endemic vascular plant taxa were confined to the peninsulas: Allocasuarina crassa, Bedfordia linearis ssp. oblongifolia var. curvifolia, Boronia pilosa ssp. tasmanensis, Craspedia cynurica, Euphrasia amphisysepala, Euphrasia phragmostoma, Euphrasia semipicta and Euphrasia sp

Summary

Introduction

It is axiomatic to say that the presence of an organism in an area indicates that the habitat is or has been suitable for its establishment. The absence of an organism from an area does not indicate a lack of habitat suitability (Tivy 1993), making it no simple task to unpack the historical and ecological explanations for the distributions of geographically e-ISSN: 1948-6596 https://escholarship.org/uc/fb doi:10.21425/F5FBG47438. Organisms can be endemic at a wide range of spatial scales. Those restricted to a very local distribution are often referred to as ‘local’ (or sometimes ‘range-restricted’) endemics (Kirkpatrick and Brown 1984, Harvey 2002, Bossuyt et al 2004, Garrick et al 2004, Murienne et al 2005, Muñoz et al 2008, Krosch et al 2009, Köhler 2010, Schaefer et al 2011). There is a large literature on local endemism (see Harrison and Noss 2017 for a comprehensive overview)

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