Species distribution modelling

Species distribution modelling (SDM) is about observing species – such as animals or plants – and locations where they occur, and then linking these observations with environmental conditions such as temperature, rainfall, or vegetation cover. By combining both data sets, statistical environmental models can be made that describe relationships. This helps to determine under which conditions a species is and isn’t likely to occur. 

One of the key applications of SDM is to make those models and then interpolate over an entire area to determine which areas are suitable for a species. 

How is the data gathered?

Data for SDM observations can be gathered in different ways. The traditional way is with scientists going out in the field with binoculars to make recordings. An alternative that is less consuming of time and money is voluntary information. There are many enthusiasts who are interested in birds, butterflies or amphibians. They can record their observations and then upload them to a depository. Scientists can access and use this data. Of course, the fact that the data is often collected by non-experts means there is a risk of misclassification. Moreover, enthusiasts tend to only go to places where they know their favourite species will occur, whereas for SDM it’s important to also have observations of blank spots where species do not occur. 

An excellent means of getting those observations for animal species is with strategically-placed wildlife cameras, but unfortunately they are often considered too expensive to be used for identifying blank spots. 

Another way of data gathering is by capturing animals, putting GPS tags on them, releasing them and then tracking their movements.  

Finally, a new technique, called environmental DNA, involves taking a sample from water and soil and analyzing it for DNA sequences. These samples can tell you something about the presence of a certain species, or at least species groups. 

What is SDM useful for?

SDM can serve multiple purposes. One is conservation. For species with high conservation values, such as panda bears or polar bears, modellers can make maps of areas that are suitable for them. These maps can be used to help make decisions about how to protect a species, e.g. by not invading suitable areas. 

In agriculture, SDM can be used for extermination, by identifying areas that are prone to being infested by pest species. 

SDM maps can also be very practical for planners. If there is a good model available and a relationship with climatic factors and climate change can be found, it is possible to make projections of which areas would be suitable in the future for a certain crop. 

Another possible field of application is Geo Health. Some diseases are carried by vectors, such as mosquitoes or flies, and SDM can help to pinpoint areas where they are most likely to occur. This way, interventions can be organized for eradicating them. Dr. Groen’s current projects in this area include the mapping of tsetse flies, a species that carries trypanosomiasis - also known as sleeping sickness. These flies have very particular requirements in terms of vegetation. They prefer shade to avoid excessive heat. On the other hand, they need to be close to hosts like domestic or wild animals to feed on their blood. By feeding this way, they can transfer the disease. Through the modelling of host animals and flies, trypanosomiasis risk areas can be identified. 

The impact of climate change and land use change

These days, climate change forms an important part of SDM research. The general trend is that suitable areas for species are declining and being driven north by the climate – or, in mountainous areas, up the mountains. Whilst some species of conservation value benefit from this - in the Netherlands, for example, certain rare butterflies are now able to survive today’s less harsh winter conditions - the general picture is that climate change causes most species to suffer from declines in suitable areas. 

Climate change is not the only factor that influences where species may occur. The way land is used has significant impact as well. By building cities, roads and other infrastructures, humans are fragmenting landscapes. The combination of climate change and land use change is often where the real danger is. 

This article is based on an interview with Dr. ir, Groen. To view the original interview, check out the Geo Hero Youtube channel here