Described as “an icon of conservation success”, the only Asiatic lion population in the world, found in the Gir Forests of Gujarat, India, has recovered from only 50 of the animals to just over 500. Yet to maintain conservation success, reliable estimates of their abundance are necessary. Researchers at the Wildlife Institute of India have suggested a new approach involving the identification of individual lions from whisker and body patterns to help map lion density in the area.
“Wildlife population estimation science has reached heights of sophistication,” Dr Yadvendradev Jhala, the corresponding author of the study, published in PLOS ONE, who has studied lions for over two decades, told Research Matters. “Yet, the estimation of the only population of endangered Asiatic lions uses a 50-year-old technique known as total counts.”
Total count methods, which can involve just tallying up sightings of animals, are rarely possible for free-ranging populations in areas larger than 10 square kilometers (3.86 square miles), let alone in the habitat of the Asiatic lions that traditionally spans an area of around 1,883 square kilometers (727 square miles). Using this technique means that some animals are overlooked, while others can be counted more than once.
In their new approach, Jhala and colleagues first set out to accurately identify the individual lions. Using a computer program called “Lion”, whisker patterns, ear notch positions, and other permanent body marks were studied from images of the animals. A statistical model called “spatially explicit capture-recapture” (SERC) was then applied in order to estimate lion density.
“This approach uses information on spatial data on individually identified lions to determine their spatial density after accounting for detection probability, thus providing an unbiased estimate,” Jhala told Research Matters.
Out of 368 sightings made by the team over a 725 square kilometer area (280 square miles), 67 individual lions were identified. The estimated overall density given by the study was 8.53 lions (older than one year) per 100 square kilometers (38.6 square miles). To provide more context to their findings, the team also mapped the density of the lions' prey, such as Sambal and Chital deer. However, this information didn’t correlate with lion density, as expected.
“We expected that prey density would determine lion density as more natural food would mean more lions,” Jhala said. “Contrary to our expectations, lion density was highest near tourist hotspots.”
Food is placed in what is referred to as “baiting spots”, to attract lions for tourists to see them. Not only does this perturb natural lion densities, but it also disrupts the lions' behavior and social dynamics, argue the authors. Other unexpected areas of high lion density included flat valley habitats.
In Kenya, a team have been applying similar density models to estimate the number of African lions in the Masai Mara. Dr Arjun Gopalaswamy, science advisor at the Wildlife Conservation Society who helped develop the approach, is skeptical of the findings in Gir.
“In search-encounter based spatial capture-recapture surveys, such as the one used here, it is absolutely essential to consider how much effort you invest in each grid cell on each day,” he told Research Matters. “Because the more effort you invest in a grid cell the more likely you are to detect a lion if present.” This may have been the case for this study in India, Gopalaswamy indicated, therefore a closer look should be given to the unexpected patterns.
However, the authors of the Asiatic lions research still believe their improved technique is of great importance. “Conserving this sub-species with the use of best science and management is a global priority and responsibility,” they said in a statement. “Our research paper addresses this priority by developing a robust approach to their population assessment and monitoring which can be used for all lion populations across the world."
[H/T: Research Matters]
