Effect of salinity on small, ground-dwelling animals in the Western Australian wheatbelt

Abstract

As part of a regional biodiversity survey, in total 304 quadrats, 1 ha each, were positioned to represent the diversity of physical environments across the geographical extent of the Western Australian wheatbelt. Uncleared sites variously affected/unaffected by salinity were chosen, but those showing overt changes caused by other types of disturbance were avoided as far as possible.

Drift fences and pit traps were used to compile lists of the ground-dwelling spiders, scorpions, frogs, reptiles and mammals on the quadrats. For analysis, these data were compiled into a presence–absence matrix of species v. quadrat, and quadrats were assigned to various landform and salinity-'risk' classes.

There was a negative relationship between the richness of small ground-dwelling animals and increasing salinity. Only lycosid spiders showed a positive relationship. A few vertebrates and spiders, particularly lycosids, are centred on saltflats. Another set of species occupies both the saltflats and the surrounding environments (woodlands) of dissection valley floors and lower slopes, while a much more diverse array of vertebrate and arachnid species is associated with these woodlands if they are not salt-affected. Woodland quadrats that are obviously affected by salinity support a subset of the species on their unaffected counterparts or on 'natural' saltflats.

These empirical findings are consistent with predictions that, as soil salinity increases and the valley-floor woodland vegetations die, their faunas also contract. A few saltflat specialists colonise salt-affected sites along with the samphire shrublands.