Practical field methods for biodiversity measurement

The web of life within ecosystems is intricate. To gain an understanding of ecosystems, researchers play the role of detective in the natural world. They use manual approaches to take a first look at biodiversity in a designated habitat.

Consider a wooded expanse. Field researchers collect crucial data encompassing the towering overstory, the undergrowth, sightings of wildlife, aspects of soil conditions, and the qualities of the water flowing through the system. In these environments, the manual collection of data remains essential to quantifying biodiversity.

Where to sample

But we rarely have the time or resources to exhaustively sample the entirety of our site. Compromises must be made about the number of locations that we need to visit in the field depending on the available time and resources that we have to monitor them. Thus, we must sample sites and extrapolate from the limited information to estimate and measure biodiversity. But how do we choose the sampling approach and where to sample?

• Random point sampling — where random locations in the target area are preselected and traveled to during the study.
• Regular point sampling — where evenly spaced locations in the target area are preselected and travelled to during the study.
• Transect-based sampling — where the site is traversed (or transected), and samples are taken at regular intervals during the journey.
• Stratified sampling — where an even number of points of each stratum (such as habitat type) are collected and weighted by the relative importance of that stratum in the environment.

Transect samples offer an efficient way of visiting a large area of the site but are at risk of bias if the transect does not cross rate habitats or if a gradient within a site (such as soil moisture towards a river) runs parallel rather than perpendicular to the transect. Regular and random points are more likely to sample evenly across all areas of the site, but can be challenging to plan for: It may be time-consuming to visit all points. Stratified sampling has the same challenges as point sampling, with additional challenges of finding enough independent examples of each strata.

For mobile organisms, it is sometimes best to stay put and see what comes to you. Samples in this case might be periods of time spent sitting in hiding, overlooking a spot that your target organism is likely to congregate at — such as a food source or watering hole. Modern approaches include camera traps and acoustic recorders.

How to sample

At each sampling location a relevant measurement is taken. Methods vary for mobile and non-mobile organisms. Plants, fungi, lichens, and non-mobile animals (e.g. choral, anemones, barnacles) are often sampled using quadrats. Most commonly these are square frames placed on a surface, within which the abundance of different species are recorded using a DARFOR scale. Other types of quadrats, such as circular quadrats, or point quadrats exist for special applications. For larger, non-mobile organisms, such as trees, all organisms over a certain size may be exhaustively sampled within a specified area around the sample point.

Mobile organisms normally, don’t stay still long enough for us to put a quadrat over them. As such we either need to collect them in a standardized way or observe for them for a standardized time.

Collection strategies vary for each organism. Insects can be swept up in nets or sucked up in a pooter and small animals can be caught in non-lethal traps. Animals of the river bed can be disturbed into the water column and swept by the river into a D-framed net during a standard kick sample. Birds and bats may be collected using mist netting, where a wire mesh entangles the animals for recording and fish can be trapped, netted, or hooked. Where animals are caught commercially, a sample of the take can be recorded. This especially useful for tracking fishing and illegal animal poaching.

Sampling and releasing animals can have direct and indirect impacts on the welfare of the sampled organisms, especially if the method might teach behaviors to individuals (such as associating the trap with food or shelter), or may decrease the animal’s fitness (such as marking an animal with an easily identifiable color or object that might reduce its natural camouflage).

Obviously, ecologists must ensure they have training and take extreme care while sampling animals due to animals’ greater capacity to experience pain. Whe3n sampling with traps, ecologists must act quickly to free the animals safely from the trap, record the needed information, and release the animal without causing undue stress. This is why a license is needed to do this work in most cases. Luckily, technology has produced less invasive ways of sampling mobile organisms.

21st century techniques for a 21st century ecologist

Ecologists today look forward to the opportunity to sample in less invasive ways when possible.

Modern approaches can help record mobile organisms without disturbing them by using camera traps or acoustic monitoring. Environmental DNA shed by the organism into their surroundings means that evidence of an organism’s presence can be collected without ever encountering it. Very large animals, such as elephants or herds of herbivores can even be monitored via drone or satellite imagery.

Both traditional and modern sampling techniques have their own advantages and limitations, but used in tandem they can produce very rigorous estimations of species richness. The 20th century saw a reduction in the shooting animals for biological specimen collection and an increase in the less invasive methods of capture-and-release sampling. Modern approaches can reduce the need for physically handling animals to collect the valuable data needed for biodiversity measurement and their conservation. At the same time, these approaches can provide a greater volume of high-quality data than ever before.