How To Study Diversity: A Few Gallons of Water or Thousands of Photos?

One way is cheaper and more efficient.

Grizzly bear caught on camera trap
A grizzly bear caught on a camera trap.

Robin Naidoo\WWF

Studying diversity is a critical part of conservation management. And the most common way of doing it when observing land animals is by setting up camera traps. But a new study finds that a better answer might be in the water.

Research by scientists at the World Wildlife Fund (WWF) finds sampling large amounts of stream water, looking for environmental DNA (called eDNA) can measure the diversity of terrestrial mammals just as effectively as camera trap monitoring.

Researchers say monitoring is necessary, but camera traps aren’t always ideal.

“Good quality biodiversity monitoring over time is vital to make informed conservation management decisions. Comprehensively measuring terrestrial biodiversity, or species of plants and animals that live on land, usually requires costly methods that can rarely be deployed at large spatial scales over multiple time periods,” Arnaud Lyet, senior conservation scientist at the WWF, tells Treehugger.

Traditional methods such as camera traps make it easier to gather high-quality data on wildlife, but there are limitations, Lyet points out.

“Camera trapping works better with abundant species, can target a small range of species effectively, and requires trained and skilled observers,” he says. “In addition, camera trap surveys are still too expensive to be deployed at large scale.”

For the study, which was published in Scientific Reports, scientists investigated using eDNA as a less expensive method to survey an entire area by only taking water samples from a stream network.

“The idea was that a few samples of water collected over a few days from one or two strategically located streams could provide as much information, or more information, than 60 camera traps deployed over the entire area for several months,” Lyet says. “Are a few gallons of water worth as much as thousands of pictures?”

How eDNA Works

WWF researchers get water sample
Researcher gets water sample from stream. WWF

As animals move through the environment, they shed cells with DNA through their skin, hair, and feces. By sampling soil, water, snow, or air, researchers can access that eDNA.

“A few liters of water carries genetic fragments (fragments of the genome) of tens, maybe hundreds, of animals,” Lyet says.

The DNA in a sample is analyzed through a process called metabarcoding which recognizes short sequences of DNA. These sequences are compared to those of known species in order to identify them.

For their work, in 2018 the researchers set up 57 camera traps and took water samples from 42 locations to match the camera grid in Tyaughton Creek and Gun Creek in the South Chilcotin mountains of Gold Bridge, British Columbia. The next year, they kept the same camera, and collected 36 samples from only two large streams that drained the whole study area.

They analyzed the water samples and found traces of grizzly bear, wolverine, red squirrel, and mule deer, among other species. That matched with what was found on the images from the camera traps.

They calculated the cost and result of the surveys and found the eDNA sampling detected the presence of 35 mammal taxa and cost $46,415. The camera trap survey detected 29 mammal taxa and cost $64,195.

“Collecting water samples from large streams that are easier to access, represents an incredible advantage over methods that require to survey physically the entire area,” Lyet says. “It saves time, is more convenient for the staff and also allows data capture without any intrusion, or with limited intrusion in the study area. This could be a game changer to study biodiversity in sensitive areas due to armed conflict, landmines, or strict protection for instance.”

These findings are important, the researchers say, because they can rapidly provide cost-effective information in many situations.

“Our results suggest that the application of optimized eDNA sampling strategies could transform how biodiversity is monitored in large landscapes, providing decision-makers with more comprehensive quantitative biodiversity data and on faster time scales, ultimately improving our ability to safeguard biodiversity,” Lyet says.

“A single sample containing eDNA can be used to potentially detect the presence of any organism from a bacteria to a large elephant, a scope that is no match for any existing method such as camera traps, aerial surveys, acoustic monitoring, etc. eDNA can be used to monitor endangered species, study the impacts of climate change, alert us to invisible threats such as pathogens, and assess the overall health of aquatic and terrestrial ecosystems.”

View Article Sources
  1. Lyet, Arnaud, et al. "Edna Sampled from Stream Networks Correlates with Camera Trap Detection Rates of Terrestrial Mammals." Scientific Reports, vol. 11, no. 1, 2021, doi:10.1038/s41598-021-90598-5

  2. Arnaud Lyet, senior conservation scientist at the WWF