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By Tim Connell 25 October 2022 5 min read

De Vis’ banded snake (Denisonia devisi) was one of the first species to have their distributions analysed using the BIOCLIM program

Trevor Booth seems aware that his interest in species distribution modelling exceeds most people’s. However, he points out that people in Australia have had a keen interest in plant and animal distributions for more than 60,000 years.

"Aboriginal populations right from the beginning, tracking across this country, developed fantastic appreciation that you had different species in dissimilar places and climates," he says.

Today, Australian researchers’ ability to show the likely impact of climate change on plants and animals, hinges on the quality of climate data they can analyse. Much of this comes from methods honed by CSIRO.

A recent report by Dr Booth on checking bioclimatic variables (or BIOCLIM variables) should help the significance of early CSIRO work to be fully recognized. It also encourages researchers around the world to check some of their most used climatic data.

A new way of seeing and doing things

In the pantheon of Australian inventions, Dr Booth says that “BIOCLIM-related developments are to ecology what wi-fi is to travellers”.

Back in 1984 the creation of BIOCLIM kicked off an area of ecological research called 'species distribution modelling'. Michael Hutchinson at CSIRO developed methods that allowed monthly climatic conditions to be reliably estimated for any location in Australia. Using this information Henry Nix at CSIRO, and John Busby at the Bureau of Flora and Fauna, developed the BIOCLIM program. This took in limited observations – based on longitude, latitude and elevation – of where a particular plant or animal was known to occur. It related these occurrences to climatic conditions and mapped other locations where the species was likely to occur.

For example, Henry Nix used BIOCLIM to analyse the distribution of 73 venomous snake species. Using BIOCLIM, incomplete information about a species distribution (see red stars in map) can be converted into a map of its likely complete distribution.

BIOCLIM map created in 1986 using data for De Vis’ banded snake (Denisonia devisi). Red stars indicate 124 observed occurrence locations. The + symbols indicate core locations and the . symbols indicate marginal locations according to the BIOC IM analysis.

Lessons learned, and a small problem

Researchers still use BIOCLIM for comparative purposes, but there are now improved methods for predicting species distribution. These use the same basic approach that BIOCLIM pioneered but carry out more complex calculations. Each year these improved programs help identify locations of hundreds of plant and animal species. They have, for example, been a rich source of information used by the Intergovernmental Panel on Climate Change (IPCC) to predict the likely impacts of climate change on individual species across the globe.

The climatic interpolation methods used to create BIOCLIM, and a set of 19 variables developed for the program, were adopted by the US-based WorldClim group. This team developed climatic interpolation relationships for six continents (excluding Antarctica) with version one released in 2005 and version two in 2017. The 19 BIOCLIM variables with values from WorldClim are considered the “gold standard” for developing species distribution models.

Dr Booth has used the Atlas of Living Australia to analyse problems with four of those 19 BIOCLIM climatic variables that are available from WorldClim. The variables in question include both temperature and precipitation data, such as precipitation of the coldest three-month period. As gardeners don’t need telling, some plants grow better if rain arrives mainly in winter, while others prefer a rainy summer. So, the interaction between temperature and rainfall matters, when looking at which places are ripe for the natural distribution of species.

And in most of the world, that’s not hard to predict. Precipitation in the coldest three months changes smoothly over most of the world. But in other places, such as the south of the Sahara, it doesn’t. See, for example, the sharp change from blue to orange in the map below.

“You run into problems in locations near the equator where there is little or no variation in temperature across the year,” Dr Booth says.

“For example, moving south near a place called Jos in Nigeria the precipitation of the coldest quarter increases from 3 mm to 764 mm in just a kilometre. This is because very slight monthly temperature changes cause the coldest quarter to flip from November- January which is a very dry period to July-September, a relatively very wet three-month period.”

This is not a biologically meaningful change, says Dr Booth, but an artefact of the sudden change in the coldest three-month period. To solve this problem in the short-term, researchers need to exclude variables which include these odd breaks from their species distribution analyses. Looking further towards the future, Dr Booth sees a solution in developing data using water balance calculations. These would analyse rainfall and evaporation rates to estimate the amount of water in the soil week by week. It’s a method used successfully by the BIOCLIM group for Australia back in 1999.

In the meantime, the Atlas of Living Australia provides a free and ready accessible means to check the WorldClim climatic surfaces for Australia or anywhere in the world.

Striving to be better

The Atlas of Living Australia is the country’s biodiversity bible, and Martin Westgate leads its Science and Decision Support Team. In research, the software we use is sufficiently complex that at some point, we have to stop checking every minor detail of every analysis we do," Dr Westgate says.

“The problem is that sometimes we get that wrong. Something comes to be gospel that really shouldn’t be,” he says.

“Trevor is telling us we better think more critically about what questions we’re trying to answer, and the methods we use to investigate those questions, rather than just ‘this is good, this is bad’. I think that’s a really good lesson. It’s a lesson to us all to be better.

“From research circles to social media, people are starting to note the origins of species distribution mapping. It happened in Australia, because of Australian researchers pushing the limits of what could be done.”

Dr Westgate sees the research growing even more significant as we manage life under climate change.

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