01 May 2012

Predators in the long grass: spiders in alpine tussocks

Times in my life when I have thought worriedly about my impending mortality have, fortunately been few and far between. Three of these events have been associated with the recent Canterbury earthquakes. The most frightening was the 7.1 event of September 4, 2010 which kicked it all off. Getting thrown out of bed at 4.35am while your house heaves and groans and shudders around you for 45 seconds gives you plenty of time to worry. February 22nd, 2011 and I was in central Christchurch when the 6.34 hit at 12.51pm and devastated the central and eastern parts of the city, the intense shaking for 20 odd seconds allowed little more than a hectic stumble towards the walls of the meeting room I was in. Finally, the 6.4 on June 13th at 2.20pm, although not nearly as shaky, was all the more scary for being at work on the 5th floor of our science building. Your work isn't supposed to make cracking and smashing noises! Prior to these events, however, the most intense and scary time I had was in the field helping a PhD student.
In February 2008, I found myself in Te Papanui Conservation Park on the Lammermoor Range near Dunedin. The park is a beautiful tussock-filled wilderness of rolling hills. I was there to help my PhD student Jagoba Malumbres-Olarte, a Basque from northern Spain. Jagoba was interested in spiders and we had had directed his energies into understanding the diversity of spiders in tussock grasslands at mid-altitudes. Jagoba's fieldwork involved resampling sites several time through the park. In reality, as a found out when I went to help, this meant driving along a small, rutted track for long periods, wading through the tussock sea with tape measure in hand, digging up tussocks to put in sacks for later examination and clearing pitfall traps. All in a pretty, if forbidding, landscape. The weather was not so good and then there was the wind... The Lammermoors are a great place for wind. There are few trees to impede its progress and the rolling landscape allows the wind to reach its full potential. We got back to our campsite in the darkness (GPS is a wonderful thing in a landscape with few landmarks. Luckily we had set a tent up earlier in the day. We parked the 4WD on the windward side of the tent to give some protection as a gale was starting. And how! There was a high wind blowing and the stars were shining bright. As the night progressed the wind continued to pick up until it was deafening. I had never been in anything like it. It eventually blew itself out before dawn and we were met by a brilliant sunrise. Sleep-deprived, Jagoba and I set off for another day of sampling. So was it all worth it? What did Jagoba find? He successfully obtained his PhD last year and now his first paper is being published.

Jagoba has had a paper published in Insect Conservation and Diversity. In this research Jagoba was interested in spider diversity in alpine tussocklands. Spiders are often top predators in many ecosystems, especially in New Zealand but not a great deal was known about this important NZ habitat. Jagoba obtained some study sites in Te Papanui Conservation Park to the east of Dunedin in the Lammermoor range. Jagoba collected spiders in two ways. First, he used pitfall traps (digging small containers flush into the ground where unsuspecting individuals fall in. Second, he removed a whole tussock plant from each sample site to take back to the lab where all of the inhabitants were collected. In addition to simply recording the diversity of the spiders found, Jagoba was interested in finding out about what lead to the variation that he observed. So, many different data were collected from each site. The upside of a sampling approach like this is that you can get thousands of samples. The downside is that you can get thousands of samples! Jagoba spent the best part of a year and a half identifying the many different spiders (14465 individuals from 53 species!) that he had found in his samples.
One of the ideas that Jagoba was keen to test was about whether the diversity of plant species impacted on the diversity of spider species. Although tussock grasslands are dominated by one species, there are other plant species scattered throughout. There was a basic link between diversity of plant and spider species, the more complex the habitat the greater the number of spiders. The structural complexity of each site was also important, the more branches and 3D-ness of the site affected the types of spider species that would live in an area. Environmental factors, like soil moisture also played a role in affecting which species were present for both plants and spiders. One of the best outcomes was discovering that one kind of spiders - wolf spiders from the family Lycosidae, could be used as an indicator species to signal which other spider species would be present in an area. Indicator species are important in that it saves someone like Jagoba having to work through thousands of samples when they can only look a few hundred. So was it worth a night of discomfit to find these results? Of course. And there is more to come from this work.

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