Two of the most important things to remember when designing an ecological survey are that the methods chosen need to be replicable and that the data collected should be representative of the area and the species being studied. In practice, these things are often difficult to achieve and need careful thought and design. As part of the SAFE Project, we wanted to quantify the impacts of logging and conversion of rainforest to oil palm plantation on the arthropod community. By carrying out the survey before logging had started and throughout the conversion to plantation, we aimed to catalogue specific changes in the insect community that occur as plantations become established.
The first thing was to choose the type of trap to use. There are dozens of different ways to survey for arthropods: everything from searching an area by hand to setting pheromone traps that attract the males of a specific species. We wanted a method that would collect a wide range of species, thereby representing the whole arthropod community, and that could be used equally effectively in both forest and plantations. Another consideration was to ensure that each trap collected enough individuals to be representative of the area, but not too many, as this would reduce the number of traps that could be set and processed.
During previous research in Malaysia, I’ve often used insecticide fogging to collect arthropods living in the rainforest canopy. This involves a large bazooka-like machine which pumps a cloud of biodegradable insecticide up into the rainforest canopy. The insecticide surrounds the leaves and branches of the tree like a fog, causing canopy-dwelling insects to drop to the ground where they are collected in fabric trays. Not very environmentally-friendly you might say, but this is one of the only ways of collecting high-canopy arthropods – not an easy task as the largest rainforest trees can be up to eighty metres tall! One problem with this method is that carrying the fogging machine out into the forest can be difficult and dangerous on steep and slippery tracks. Fogging machines are also extremely temperamental, and a sweaty walk often ends with a frustrating half-hour of failing to coax the machine into life before carrying all the equipment back, unused. More importantly, the tree canopy is destroyed during logging and we needed a method that could be used equally well in forested and plantation areas. Another method I had used before was to collect leaf litter from a set area of the forest floor, from which insects could then be collected. Although this would work well in forest and plantations, it wouldn’t collect arthropods actually living on the trees. Clearly what we needed was a method that would collect insects from both the forest floor and above.
In the end we decided to design a trap that would catch insects as they walked or flew close to the ground. As a base to the trap, we chose a plastic funnel that would be sunk into the soil with a collecting bottle at its base. Any insects running along the ground would fall into the funnel and be collected in the bottle. Fitting inside the lip of the funnel, we attached two pieces of interlocking transparent perspex sheets, which would act as a barrier for any flying insects and cause then to fall into the funnel and so the collecting bottle. A problem with this is that lots of insects tend to crawl or fly upwards when they encounter a barrier* and these would escape. We therefore added a gazebo-like star of fabric at the top of the sheets with an upturned funnel enclosing this, to which we attached another collecting bottle. Any insect encountering the perspex and travelling upwards would therefore be corralled into the funnel and collected in the bottle at the top of the trap.
Having designed our trap, we then had to test how well it worked in the field. We had several prototypes made and, with the help of the SAFE research assistants, set them out in the forest and oil palm plantations. In the labs at Maliau, we cleaned, identified and counted the insects we had caught. After some tweaking, we found that our traps worked well to collect a wide range of different arthropods. More active insects like flies and wasps were more common in the upper part of the trap, while slower more clumsy insects like beetles were caught in the lower part. Catching this range of groups is essential, as it ensures that the traps are sampling a broad cross-section of the community, and that changes as a result of deforestation can be assessed for the whole arthropod community.
We have now set out and collected the traps across the SAFE sites three times. Samples were taken from nearly 600 individual trapping locations across the primary forest, logged forest and oil palm plantation habitats. This represents one of the most extensive inventories of arthropod communities across a range of habitat disturbances ever collected in the tropics. Sampling on this scale would never be possible without the help of our large team of SAFE Research Assistants who carry out the sweaty work of carrying the traps into the forest, setting, collecting, and bringing them back. We are now beginning the process of sorting and identifying the samples, which consist of hundreds of thousands of individual arthropods. It is clear that loss of forest and conversion to oil palm plantation have severe impacts on biodiversity. This project will help us to understand exactly how and why these changes occur, so that management can be altered to reduce as many of these negative changes as possible.
*Pick up a slow moving insect like a stick insect and you can prove this for yourself – if you hold your hand upwards they will tend to walk onto it, hold it down and the insect will crawl up your arm!
If you would like to find out more about how science works, how to design your own research projects, conservation and natural history we have lots of courses coming up at Madingley:
Conservation: from theory to practice - 7 September 2012
H is for holly, hornbeam and hawthorn - 2 November 2012
Birds: their hidden world - 9 November 2012
Marine biology and conservation: exploring planet ocean -25 January 2013
Cambridge collections - 18 February 2013
How science works - 19 February 2013