Reconstructing wildlife declines in Imperial China

Today there are just four surviving gibbon species singing and swinging among Chinese trees, all of which are threatened with extinction. But it wasn’t always like that. Just a few centuries ago, the lesser apes were abundant enough on mainland China to feature in traditional mythology. Their distinctive songs were thought to symbolize homesickness and longing for the familiar, and came to represent travelers who were far from home. Rather than their songs, ecologists are now more concerned with understanding how their populations declined. Effective management strategies can only be created if researchers are armed with accurate information about how a species’ historical range and population contracted in the first place.

That sort of data is hard to come by. Most modern scientific records only extend back a matter of decades (often far less), and historical records are often incomplete, inaccurate, biased, or haphazardly organized in terms of geography or time. There’s a unique dataset in China, though, that just might be useful for researchers to reconstruct the geographic distribution of threatened wildlife over not just decades, but centuries. While the region has quite a rich paleontological and archaeological record in general, primates are poorly represented within it. But there’s 2,000 years worth of written records containing information about wildlife presence there.

Local gazetteers, or difangzhi, according to Zoological Society of London researcher Samuel T. Turvey and colleagues, typically included local environmental records, including information about wild animals, along with information about local economics, politics, and demographic data. While the gazetteers have been used by researchers interested in reconstructing aspects of China’s societal and economic past, they’ve only rarely been used to reconstruct wildlife patterns, and almost never in a formal quantitative manner.

Turvey and his team curated a dataset comprising 525 gibbon records from 420 gazetteers, which combine to provide spatio-temporal natural history data for China across the Ming Dynasty (1368-1644), Qing Dynasty (1644-1912), and the Republican Period (1912-1949). To that they added more recent data for 1950 until the present day. Because the gazetteer records didn’t distinguish the different gibbon species, their analysis covers all Chinese gibbons as a single group.

Today, gibbons only occur in 11 prefectures in a small region of southwestern China, but the historical dataset shows that they occurred in another 149 administrative regions across 19 Chinese provinces. The dates associated with those localities range from 250 CE in Chongqing to 1995 in Hainan province. By the year 1600, gibbons apparently disappeared from 17.5% of regions in which they had once lived. Since then, the number of regions in which gibbons could be found continuously decreased through successive 50-year intervals. Then, between 1850 and 1900, the rate at which they decreased accelerated significantly. Between 1600 and 1800, gibbons had disappeared from 18.1% of provinces. By 1850 that number had increased to 36.6% and by 1900 it was 57.5%. In 1950, gibbons had been wiped out from 84.4% of their historical range.

Black regions represent areas in which gibbons were present at a given time. Grey areas are ones in which they were absent but historically present. White areas contain no historical records of gibbon presence.

Black regions represent areas in which gibbons were present at a given time. Grey areas are ones in which they were absent but historically present. White areas contain no historical records of gibbon presence. (via Turvey et al.)

More interesting than the rate of decline, though, was the pattern in which the decline played out geographically. There are several theoretical models that can describe the way in which a species declines. In the “demographic model,” it’s assumed that the decline was due to a species’ own population structure. The final persistence will be near the center of its historic range where populations are larger and less variable. Alternatively, if a species declines due to external factors that coincide with geography (the “contagion model”) then the species would persist along the edges of its historical range that are impacted last by those threats.

Since the decrease in gibbon populations spread geographically, starting in the eastern and northern parts of their range and spreading toward the southeast, Turvey suspects that their decline was due to external anthropogenic factors, or the contagion model. That’s consistent with historical patterns of human population density, with migration patterns moving from north to south and then towards the west. “Gibbon populations therefore appear to have been highly vulnerable to the wavefront of this internal Chinese human population expansion, which would probably have included combined increases in both forest loss and hunting,” write the researchers.

The researchers also found that groups living at lower elevations were more vulnerable to extirpation than those at higher elevations, perhaps because humans tend to remain at lower elevations, while higher elevations tend to retain more of their natural landscapes. Indeed modern gibbons are overwhelmingly restricted to montane forests.

They hope to reconstruct the population dynamics of other Chinese species, like tigers and Asian elephants, using local gazetteers to see whether their decline follows similar trends. If so, then the contagion model could represent a more general phenomenon that describes the ways in which wildlife responds to human demographic changes. – Jason G. Goldman | 14 August 2015

Turvey ST, Crees JJ, Di Fonzo MMI. 2015 Historical data as a baseline for conservation: reconstructing long-term faunal extinction dynamics in Late Imperial–modern China. Proceedings of the Royal Society B. DOI: 10.1098/rspb.2015.1299.

Header image: Hoolock gibbon via Magale L’Abbe/Flickr.