50 shades of prey: finding hidden diversity in biodiversity capsules

Occasionally the wife has a hankering for oliebollen, a Dutch sweet doughnut/dumping creation. This is a legacy of her flatting with a Dutch couple when she was at university who would make a batch from time to time. Where do we go to find these oliebollen? There are not a lot of Dutch cafes in Christchurch, only one that I can think of and that seems to move around a bit. There is a reasonable sized population that have moved from Holland in this or the last generation so it seems likely that someone is making this Dutch delicacy. How to find them? We could drive around a lot and survey cafes and restaurants, I guess, and while that might be fun, it would take a long time (and be fairly costly) with no guarantee of success. A better idea would be to go to the Christchurch Farmers’ Market at Dean’s Bush. Every Saturday morning dozens of food-related stalls are found at the site of the first house in Christchurch. There is a cornucopia of food, all delicious. My personal favourite, Posh Porridge, is there. Best of all, there are many stalls from the various cultures that have more recently settled into Christchurch, from Asia to Europe to South America. Sure enough there is a stall selling oliebollen! So the market is a diversity capsule of the Christchurch. By wandering the crowded aisles you can get a feel for the rare or cryptic cultures (and their food) that you would otherwise find hard to locate.

New Zealand Fur seals: our expert diversity collectors.

There is a similar issue when it comes to biodiversity assessment. How do we know that certain species are in an area? Many species are rare or cryptic, or in habitats that are difficult to sample (like the sea or in the soil or in swamps), or just plain difficult to find because their behaviours make it hard for humans (like being nocturnal or dangerous). It would be great if we had access to biodiversity capsules where one sample could provide many species from an area. It turns out that we do have biodiversity capsules. Often they litter the landscape. The most common type is predator faeces. Predators are experts at finding prey, certainly much better adapted than we are to do this. Generalist predators will take many types of prey species at a time and over a year. So a generalist predator will be sampling the local prey diversity of area. For example, a fur seal will consume fish species from the surrounding bays and continental shelf and will access areas, like reefs, which are difficult for us to catch local species from. So predators have a method of collecting local species diversity. We just need to be able to access what they eat. Given that what the eat will often come out again, the faeces of these predators will retain DNA from the species that they have consumed. In theory we should be able to reconstruct biodiversity in an area by identifying DNA in predator poo!

Fur seal biodiversity capsule collected! Many prey within.



Rob Cruickshank and Steve Wratten (Lincoln University), with Stephane Boyer (Unitec) have published in the journal Food Webs about the potential of using next generation sequencing of DNA to assess these biodiversity capsules (mostly faeces but it could be water and soil samples or regurgitation pellets). They point out that technology is now advanced enough that we can take a poo sample and potentially identify multitudes of species within the sample. There is some suggestion that the abundance of the DNA found in the sample may approximate roughly with how often the organism is eaten and possibly how common they might be in the local habitat. There is also the advantage of secondary predation where you detect the prey eaten by the prey. For example, in an ongoing project with fur seals we have detected a number of crustaceans that seems to be too small for fur seals to eat but that would be common in the diet of the fish eaten by the seals. From abiodiversity point of view this is excellent news. Indeed, from just a few samples we have found 50 species of prey.

Using predators to help survey local biodiversity is a promising technique. You are letting experts do a lot of the hard collecting of species for you. It is reasonably low impact to collect the faeces and increasingly straightforward to extract DNA from. Very soon, number twos may be the number one way of assessing local diversity!

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