Terrestrial Short Range Endemics

(SREs)

Shield-back Trapdoor spider Idiosoma dandaragan

What are SREs

Short-range endemic invertebrates (SREs) are invertebrate species with small distributions. Harvey 2002, defined SREs as having distributions less than 10,000 km²; however, many species have significantly smaller distributions. Short-range endemism is not restricted to invertebrates and all organisms with restricted distributions can be categorised as SREs; however, in Western Australia, the term SRE is usually applied to invertebrates.

The restricted distributions of SREs makes these species vulnerable to large-scale habitat change or destruction. The Western Australian EPA recognises SREs as important environmental values (EPA 2016). Short-range endemic invertebrates can result from several processes:

  • Relictual SRE’s

  • Habitat specialist SREs

  • Anthropogenic SREs

The ancestors of these SRE species were widespread. During the late-Meiocene (c.a. 11 million years ago) the Australian continent experienced significant aridification, during which widespread mesic environments contracted and became fragmented, a phenomenon often described as post-Meiocene aridification. Species that were unable to adapt to the increasingly drying habitats became restricted to these fragmented refugia. Subsequently, evolutionary processes (principally genetic drift) resulted in each isolated population becoming independent species. Such species often belong to relatively ancient lineages such as velvet-worms (Onychophora), harvestmen (Opiliones) and some pseudoscorpions.

Relictual SREs

(Refugees from historical climate change)

Kumbadjena occidentalis is a velvet-worm (Onychophora) an ancient lineage that contains many SREs.

Habitat specialist SREs

(Species living on the edge)

These SREs are typically found in habitats that exert high physiological stresses on them. Such habitats include subterranean void systems, salt lakes and exposed rocky outcrops. Animals inhabiting these environments often exhibit specialised physiological and or behavioural traits that enable them to exploit these physiologically stressful habitats; however, these traits also restrict them to living in these habitats.

In Western Australia, subterranean SREs are managed under specific legislation targeting subterranean fauna.

The current SRE guidance was developed in 2009. Subsequent to the development of that guidance, terrestrial salt lake invertebrates have been recognised as having the potential to be range restricted, most notably by Alejandro López-López et al. (2016). While the current Guidance does not specifically recognise salt lakes as being significant SRE habitats, the Western Australian EPA is aware of the significance of these habitats and their potential to support SREs at Lake Mackay and Lake Way.

Alacran tartarus is a scorpion restricted to caves of Oaxaca, Mexico. Image provided by Peter Sprause at Zara Environmental LLC.

Salt Lake endemic Wolf Spider from Lake Carey, Western Australia.

Anthropogenic SREs

(Refugees of human activities)

These SREs result from habitat destruction or alteration by human activities. Small fragmented habitats in urban sprawl or in heavily developed agricultural regions, such as the W.A Wheatbelt. These species are often flagged for conservation in WA as “Priority species” and include some trapdoor spiders (some Idiosoma and Kwonkan species), land snails (some Bothriembryon species) and scorpions (some species of Lychas).

Lychas sp. ‘majerorum’ is a scorpion from the Swan Coastal Plain, currently known from only two localities but likely to have been previously more widespread.

Dr Erich S. Volschenk Surveying at Lake Lefroy, 1998

Alacran SRE Surveys

Alacran has been undertaking SRE surveys since 2015 and Dr Volschenk has been undertaking invertebrate surveys for over 20 years in Australia, Africa and the Caribbean. Alacran’s surveys focus on sites representing potential SRE habitats. These are intensively surveyed using multiple sampling methods, with the objective of sampling the majority of, if not all, invertebrate species from SRE target groups.

Alacran spends significantly more time surveying each site than most other consultants. These surveys generate large data sets that are more likely to identify ‘true’ SREs, rather than ‘false’ SREs resulting from under sampling. Surveying sites for short time periods (less than 2 person hours per site) runs the risk if misinterpreting more widespread species as SREs.