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Saturday, 14 March 2020

Climate change, glacial recession and mammal communities

By now, we are probably all familiar with the alarming fact that the polar ice caps are melting, and we’ve probably all seen the pictures of starving, stranded polar bears on thin pieces of sea ice. Scientists often look to the cryosphere – or the frozen water part of the Earth, such as ice caps, glaciers, areas of snow, and ice shelves – to understand the progression of climate change and predict how things may change in the future.

Changing climates have impacted the cryosphere for millions of years, and massive ice sheets have repeatedly advanced and retreated throughout history. The recession and advancement of these walls of ice has had an enormous impact on landscapes and the distribution of species, and while there have been many studies investigating how historical glacial recession has impacted current species distribution, little is known about how current species distribution is impacted by present day glacial recession.


Example of a tidewater glacier in Glacier Bay National Park. Johns Hopkins Glacier. ©

This is important because glacial recession today is occurring at an unprecedented rate. One reason why we don’t know as much about the impact that present day glacial recession has on species distribution is that rapid glacial recession is a fairly new phenomenon.

But is it?

Enter Glacier Bay National Park in southeast Alaska. Glacier Bay is the product of the Little Ice Age, a period of a few hundred years beginning around the fourteenth century that saw a decrease in average annual temperature of ~0.6 degrees Celsius. This may not seem like much, but during this period, mountain glaciers expanded well beyond their previous extents, covering vast areas of land in sheets of ice. The Little Ice Age reached its maximum ~1750, and what followed in Glacier Bay National Park was the most rapid glacial recession recorded in modern times[1]. The massive glacier that once filled its basin retreated over 100 km in just a few hundred years. Normally, glacial recession takes place thousands or millions of years! This makes Glacier Bay an incredibly unique place to study the impacts of present day glacial recession on present day species distribution.

How do communities of mammals respond to glacial recession?

11 different published temperature reconstructions over the last 2000 years, showing a slight decrease in average temperature during the Little Ice Age. By Robert A. Rohde via Wikipedia Commons.
Because of its unique glacial history, much of what we know about plant succession, or how plant communities change over time, was discovered in Glacier Bay. Over the last 100 years, the chronosequences – or ecologically similar sites of different ages – at Glacier Bay have become the most intensely studied anywhere[2]. But what about animals? And how do mammal communities change over time following glacial recession?

This is what my research in Glacier Bay investigates. We found that one of the main factors driving patterns in mammal community succession is dispersal ability.

Glacial recession fragmented the landscape in Glacier Bay – where there was once a deep, lush valley, there is now a 400-meter-deep water body, which acts as an immense barrier to wildlife movement. Mammals that are unable to travel up and over the bay, or those who aren’t great long-distance swimmers (to cross the bay), have a much harder time recolonising parts of Glacier Bay. We found that dispersal ability has a larger impact on patterns of mammal species distribution than what habitat is available. In other words, even if there is good, quality habitat, mammal species are limited by their ability to access it.

So, what does this mean?

Our research in Glacier Bay highlights an important issue: plants and animals are different. Glacier Bay has helped us understand quite a bit about how plant communities change following disturbances like glacial recession, but we should be very cautious when assuming that changes in wildlife communities following glacial recession simply track changes in vegetation. Animals are complex, mobile creatures that may not follow the same successional paths and patterns as plants. When scientists are trying to predict how future animal communities will respond to a changing cryosphere in the present, dispersal ability will be an important factor to consider.

Glacier Bay from above. The glaciers you see in the top of the photo (the white extending from the mountains) were once one large glacier that extended all the way to the mouth of Glacier Bay in the bottom right of the picture. By Landsat Project Science Office at NASA’s Goddard Space Flight Center via Wikipedia Commons.



Mira Sytsma Author Bio:


Mira Sytsma is a Science Communication Fellow with the Pacific Science Center in Seattle, Washington and a recent MSc graduate from the University of Washington where she studied wildlife ecology. To learn more about her research, follow her on twitter @mirasytsma and visit her website



For more reading about ecosystems and animal movements, check our article on keystone species. Hear more unanswered questions on extinction, or explore biodiversity on ice.


References
why don't all references have links?

[1] Kohls, S. J., Baker, D. D., van Kessel, C., and Dawson, J. O. (2003). An assessment of soil enrichment by actinorhizal N2 fixation using δ 15N values in a chronosequence of deglaciation at Glacier Bay, Alaska. Plant Soil, 254, 11–17.
[2] Bormann, B.T. and Sidle, R. S. (1990). Changes in productivity and distribution of nutrients in a chronosequence at Glacier Bay, Alaska. Journal of Ecology, 78, 561-578.

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