Range shifts and species richness changes in the Himilayas due to AGW

The Lachen Valley in the Eastern Himalayas, undergoing dramatic changes in biodiversity due to to human-induced climate change.

The Lachen Valley in the Eastern Himalayas, undergoing dramatic changes in biodiversity due to to human-induced climate change.

A new study published in the last few weeks online in PLoS ONE has revealed significant changes in temperature in two Himalayan Valleys, resulting in range shifts in a large number of endemic plant species and changes in species richness.  Telwala et al used historical and recent data (1849-50, 2007-2010) on temperature and endemic species’ elevational ranges to perform a correlative study.

From the abstract…

We provide first evidence of warmer winters in the region compared to the last two centuries, with mean temperatures of the warmest and the coldest months may have increased by 0.76±0.25°C and 3.65±2°C, respectively. Warming-driven geographical range shifts were recorded in 87% of 124 endemic plant species studied in the region; upper range extensions of species have resulted in increased species richness in the upper alpine zone, compared to the 19th century. We recorded a shift of 23–998 m in species’ upper elevation limit and a mean upward displacement rate of 27.53±22.04 m/decade in the present study.

So, what do these temperature changes look like?

Histyorical and modern temperatures in two alpine valleys in the Himilayas at a range of elevations

Mean historical and modern temperatures of the warmest and coldest months in two alpine valleys in the Himalayas at a range of elevations.

The thing that is immediately apparent is the temperature has increased at each of the elevations in each of the seasons.

The changes in species distribution, the range shifts, took many forms with some species’ range’s expanding, some contracting, some staying unchanged. Similarly there were difference in the direction of range shifts with a small number losing altitude, some not moving, but the vast majority gaining altitude. The concern of course is that these species, under continued warming, will run out of mountain to climb and become extinct.

Ponerorchis chusua, one of the 6 endemic species suffering a range contraction of more than 50%

Ponerorchis chusua, one of the 6 endemic species suffering a range contraction of more than 50%

The most dramatic range contractions occurred in 6 species, that saw reductions of more than 50% of their historical ranges. These are most likely to be among the first coming under the threat of extinction in a continuously warming environment. In contrast, there were a small number of species that expanded their ranges by more than 100%, possibly colonising areas on the higher elevation end of their range, vacated by more temperature sensitive species.
This is a classic case of specialists losing out to generalists that we are starting to see everywhere where climate change induced range shifts in species is taking place as dictated by both niche theory and disturbance theory in ecology. An excellent but unfortunately paywalled paper that discusses this is. The citation is  Joanne Clavel, Romain Julliard, and Vincent Devictor. 2011. Worldwide decline of specialist species: toward a global functional homogenization? Frontiers in Ecology and the Environment 9: 222–228. Click here for the abstract.

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What these two graphs demonstrate is that the greatest range shifts in terms of distance moved occurred at the lower elevations and generally more so at the lower margin of the range than the upper. The vast majority of range shifts have also been up the mountains rather than down which is to be expected with increasing temperatures.

An interesting part of this paper is the authors’ discussion of the effects of these range shifts on levels of species richness.

journal.pone.0057103.g005

The authors report that the elevation at which 50% of the cumulative species counts per hectare occur has moved upwards in altitude by nearly 260 m. Overall species richness declined by 37%. Despite this decline, species richness in the uppermost 200m elevational band increased by an average of 14.7 species. They report that recent surveys in the study area have revealed 15-18 species that are new arrivals. In a nutshell, some species have disappeared, most have undergone range shifts,, and the whole area is being exploited by generalist species and new arrivals who are able to take advantage of the disturbance created by temperature changes and localised extinctions.

This paper hasn’t been out for long and I have already seen one comment in a forum suggesting that the increase in species richness increase in the upper bands of the study area is evidence that climate change is a good thing. For mind, the only time an increase in species richness is a good thing is when an area is recovering from disturbance back to some semblance of what it was prior to the disturbance. That is not what is happening in the pristine areas of the Himalayas. This is human induced climate change ruining ecosystems through the creation of weed habitats and don’t forget that overall decline in species richness.

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