Hitching a ride – SRE invertebrate dispersal in the 21st century

Apatochernes vastus, NZ, dorsal

Mark Harvey (2002), from the Western Australian Museum, published an article on short range endemism in Australian fauna and provided some examples from non-marine invertebrates. Short range endemic (SRE) fauna are typically those that have naturally small distributions of less than 10,000km2, and within this distribution their area of occupancy may be quite small, discontinuous and / or fragmented. Harvey (2002) noted that SRE taxa typically display characteristic ecological and life-history traits, including:

  • poor dispersal powers;
  • confinement to discontinuous habitats;
  • usually having highly seasonal activity patterns, with many only being active during cooler, wetter periods; and
  • low levels of fecundity.

Post 2002, SRE invertebrate fauna were more extensively investigated in EIAs, with a focus on pseudoscorpions, isopods, millipedes, land snails, trap-door spiders and scorpions. SRE invertebrates can be found in a variety of habitats including vine thickets, boulder piles, isolated hills, vegetated gullies or freshwater habitats even in arid environments and they are typically found in micro-habitats that remain cool and moist (i.e. under bark, rocks or holes in the ground).

Even though there was a large amount of field work being conducted to find SRE invertebrates in WA in the last 15 years, many were new to science and little was known about their life-history or adaptations to survival or dispersal.

Dr Graeme Finlayson and colleagues (2015) reported on the first observation of phoresy of a pseudoscorpion (Apatochernes vastus) on an endemic New Zealand bat (Mystacina tuberculata). Phoresy is the act of ‘hitching a lift’ on another organism but is not a parasite. As invertebrates are typically small and not all have wings, many travel comparatively long distances by using other, more mobile organisms. For example, flower mites are wingless and use foraging bees to travel to new flowers.

Pseudoscorpions are small arachnids with four pairs of legs and a pair of pedipalps (Finlayson et al. 2015) and look like a scorpion without a tail. Due to their small size, lack of wings and micro-habitat niche they generally have a limited ability for dispersal over a large area.

Although phoresy has also been reported in bats in Australia and Africa, it is not something that is often considered during an EIA investigation in WA. This article raises questions about how broadly we should be investigating such specialist creatures and not just assuming that they typically have poor mechanisms for dispersal.

I wonder how many other Australian fauna are using unique or unthought-of techniques for dispersal.

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References

Finlayson, G. R., G. Madani, G. Dennis, and M. S. Harvey. 2015. First reported observation of phoresy of pseudoscorpions on an endemic New Zealand mammal, the lesser short-tailed bat, Mystacina tuberculata. New Zealand Journal of Zoology 42:298-301. (DOI)

Harvey, M. S. 2002. Short-range endemism among the Australian fauna: some examples from non-marine environments. Invertebrate Systematics 16:555-570.

Image credits: (top) Mark Harvey – Apatochernes vastus; (bottom) George Madani – Pseudoscoprion being removed from a bat 

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