Spidiversity, a personal story

ROBERT WHYTE

As someone with a scientific bent, interested in habitat restoration and engaged in practical activities as a volunteer and professional, I would usually sum up what I was trying to achieve as the “identification, protection and expansion of good-quality remnant habitat, to repair disturbed ecosystems and reconnect habitat corridors”. But why? Are natural areas really more biodiverse? What proof did I have?

In the autumn of 2009 I decided to test this hypothesis with some terrestrial-biodiversity sampling. For a long time I had wanted to remove an infestation of Cape Honeysuckle, Tecoma capensis. It was a dense thicket and possibly providing habitat. It had to go, because it was a threat to ecosystems elsewhere if it spread, but I waited a full five years for nearby scrub to grow and become a refuge, before deciding to give the Cape Honeysuckle the chop.  Before doing so, I decided to sample the Cape Honeysuckle thicket and compare it with an equal area of natural rainforest habitat just next to it.

I took a white plastic tray and a stick and gently whacked the foliage above the tray. This method, called ‘beating’ gives you a pretty reliable indication of comparative spider numbers and diversity when you repeat it across separate areas. As spiders are a generalist, mid-level arthropod they are a good indicator of biodiversity. They need prey and support a wide range of predators.
On average, I found the natural habitat had about three times as many genera as the weedy thicket. In sheer numbers, it had about five times as many specimens. I was relieved. The results suggested, at least for spiders, the weedy thicket had substantially lower biodiversity than the nearby natural rainforest. I could now remove the thicket with a relatively clear conscience.
This got me hooked on doing science. I was keen to try a comparison on a much bigger scale. I chose an average 1,400 square metre, partially bush-friendly garden block with a block the same size of habitat restored by our group at Walton Bridge Reserve, The Gap, Brisbane.

The results? Spider abundance and diversity was much greater in the restoration than in the garden block. More evidence we were doing the right thing.

One of the findings was unexpected and very exciting. Thirty-one specimens of a pretty jewel spider Thwaitesia were found in the dry rainforest remnant, while only one specimen was found in the garden. Could this be the holy grail of ecology – an ‘indicator’ species?

Having a reliable indicator species for good quality habitat would be a great benefit for bush care. Whether this might be Thwaitesia spp. in the Enoggera Creek catchment remains to be seen. Since 2009 I have done a lot more terrestrial biodiversity sampling and I consistently find Thwaitesia in better quality rainforest and adjacent dry woodland. The results are not yet definitive, but very promising.

robert whyte

The author sampling a patch of weeds at Walton Bridge Reserve in the Enoggera catchment to test the theory natural areas really are more biodiverse. Photo: Mark Crocker

thwaitesia

Thwaitesia – Could this pretty little spider, body length about 4 millimetres, be an indicator species of good-quality habitat? Photo: Robert Whyte

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