Short-Range Endemics (SREs)
Short-range Endemic Invertebrates
The term ‘short-range endemic’ (SRE) was first proposed my Harvey (2002) to identify organisms with distributions less than 10,000 square kilometres. These organisms were regarded as having conservation significance owing to their potential vulnerability to large scale land clearing/modification. In application, the term is more usually applied to terrestrial invertebrates, since that was the focus of Harvey (2002) and the significance of these SREs in Western Australia has resulted in them being considered significant environmental values (EPA 2016).
Short-range endemism in invertebrates can result from several processes
- RELICTUAL SRE
- HABITAT SPECIALIST SRE
- Subterranean Fauna
- Salt lake specialists
HABITAT SPECIALIST SREs
Living on the edge
Specialist, or habitat specialist SREs are restricted to specific habitats that are often characterised by extreme environmental conditions. Specialiased evolutionary adaptations to these environments appears to have resulted in these species becoming dependent on these conditions to the extent that they are dependent on them and are unable to survive elsewhere.
Three such habitat are known in Australia:
- subterranean habitats
- troglobite (air filled subterranean void networks)
- stygobite (water filled subterranean void networks)
- salt lakes and surroun ding salt marshes (Samphire)
- exposed rocky hill tops.
Salt Lake SREs
Salt lakes are high stress environments owing to the high levels of salt in these environments: mostly NaCl but also MgCl and MgSO4. The concentration of NaCl is usually so high that it crystalizes in a crust on the mud surface. The thickness of the salt crust can vary spatially on the lake as well as temporally. These lakes are characterized by being dry salt/mud plains (playa) for most years but periodically become partially or completely filled with water after periods of very heavy rainfall. When dry, surface temperatures can exceed 60°C in summer and animals living on the playa live in burrows and are nocturnal. When the lakes are inundated, some species (salt lake scorpions and wolf spiders) appear to seal themselves in their burrows, while others (adult tiger beetles) move to the edges of the lake that remain dry.
Salt lake SREs have physiological and behavioural specialisations allowing them to survive (or evade) the extreme salt concentrations, high summer surface temperatures and periodic flooding for several months. These invertebrates typically have one or more of the following characteristics:
- most have pale body colouration
- all life stages live on the salt lake surface, or on its edges
- all live in permanent or temporary burrows
- most are nocturnal or crepuscular
- most are flightless, if wings are present they are usually ineffective and the adults can’t fly
The diversity of terrestrial salt lake fauna is still very poorly known and most of these species are currently undescribed. Research (López-López, Hudson and Galián, 2016) on the phylogeography and species delimitation of Pseudotetracha (tiger beetles) showed the presence of cryptic species to be present on Australian salt lakes and that their distributions were limited to paleodrainage channels that connect chains of salt lakes. Other salt lake invertebrates are likely to exhibit similar distributions but remain unstudied.
Salt lake SREs are relatively new environmental values and are not specifically considered in the current EPA Guidance recommendations. Salt lake SREs may be impacted by the following activities:
- that excavate into the lake surface,
- deposit hypersaline water onto the lake surface,
- infrastructure that can change water flow on the lake surface, such as causeways
- artificial lights from infrastructure near or on the salt lake
Pseudotetracha sp., Tiger beetle
Lycosa salifodina, Salt lake wolf spider
Lychas ‘jonesae complex LN’, Salt lake scorpion
Apterogryllus sp., Salt lake cricket