The (changing) ecology of snow

We are well into winter in the Northern Hemisphere--Thanksgiving holidays are just around the corner in the US--and for much of the area, this is time defined by cold, dark, and snow. So it seemed appropriate to write a post about snow.

Much of the Northern Hemisphere, the Antarctic, and alpine areas are historically snow covered for more than two months of the year. In parts of the Arctic, snow cover may last 9 months of the year.

From Marchand 2014.

Though only a few degrees different from rain, snow alters an ecosystem through its unique physical properties. It is a physical force, an ecological pressure, and an opportunity: snow alters movement, creates and destroys habitat, and places immense pressures on individuals and species. The ecological implications of snow are immense and wide-ranging.

Snow has unique physical properties that make it particularly important, compared to equivalent amounts of precipitation. It stores energy and water. It insulates the soil underneath it, buffering it from cold temperatures and slowing its eventual re-warming. Snow limits light to the plants underneath it, reducing photosynthesis, and drastically cutting primary productivity during its stay. In addition to these physical properties, the sheer weight of snow has to be considered. Plants beneath a pile of snow risk compression, breakage, and deformation. 

A heavy blanket of snow, variable in its depth and consistency, changes the matrix and thus significantly alters movement: snow can ease dispersal, make it much more costly, or even prevent it altogether. Ease of movement in snow is in turn is tied to foraging and predation success. For example, small, lightweight vertebrates such as shrews become active underneath the snow, tunnelling in search of food and constructing nests under deep cover. For them, snow cover may aid winter survival. On top of the snow, some animals (hares, fox, etc.) enjoy ease of movement. If individuals are light enough to travel over the top of the snow, snow can reduce landscape complexity, burying brambles and filling hollows. However, for larger species, snow may come at a cost. Moose or reindeer for example, with their large masses and long, slender legs are at risk when snow depths are too high or a hard crust covers the snow. In these conditions, they may sink, slowing their escape from lighter predators.

Snow is difficult for all life, but plants in particular cannot escape. Places with long winter seasons and late snow melt filter out all but the most adapted vegetation. The plants common to Arctic and alpine areas share many life-history traits. Similar groups of species - mosses, lichens, low-growing shrubs, and grasses - are found in all of these areas. Such species have developed strategies for the conditions, such as seed germination cued by freeze/thaw cycles, small leaf areas to reduce water loss. There are also opportunities. Snow insulates – plants may benefit from burial under drifts, or from collecting snow in dead tissue above ground. Adaptations may permit early growth under thinning snow in the spring, by allowing photosynthesis in cold conditions and low light. 

The type, amount and depth of snow-cover may differentiate plant communities on a fine scale, between wind-exposed ridges where drought tolerance is necessary, and snow-accumulating depressions where tolerance of short growing seasons is required. Early naturalist literature recognized these snow-driven micro-differences, describing them as “schneetälchen” or little snow valleys. The Front Range of Colorado has been used for a number of studies of snow gradients on vegetation, and while many environmental factors vary along snow-melt gradients, the timing of snow melt alone greatly affects species presence and abundance.

Diagram of micro-habitats in alpine areas in Colorado,
where snow affects vegetation dynamics.

Distribution of 2 species in relation to snow depth. Both from Walker et al (2001)

Snow can be a significant source of water, sometimes the majority of water necessary for the year. It is also a sink for nutrients (N, S) from the atmosphere, the canopy, and the soil – leading it to sometimes be called ‘poor man’s fertilizer’. This isn’t always for the best – high concentrations of N and S in snowmelt can damage plant tissues, and snowdrifts can be reservoirs for airborne pollutants. In samples from the Athabasca River (Alberta, Canada), upstream of oil sands facilities, dissolved polycyclic aromatic compound levels averaged between 0.025-0.03 ug/L. However, measures from melting snow around the river had concentrations up to 4.8 ug/L, suggesting that spring snowmelt could have large environmental impacts. 

Snow algae (most common species: Chlamydomonas nivalis)
growth colours snow various shades of pink or red.

These nutrients in snow support unique microbial life. Snow algae, bacteria, yeasts and snow fungi arise. Snow algae are adapted to a life history spent wholly within melting snow – these algae find homes in glaciers, alpine peaks, and the dry valley lakes of Antarctica. These species have various adaptations to a snow-bound life, including enzymes resistant to freezing, and special pigments. These unique populations help replace some of the lost winter primary productivity. Small invertebrates graze on snow microbes, and the energy flows into local food webs.

So snow is unique, with wide-ranging implications for ecology and evolution where it occurs. But now snow is changing. Warming temperatures are having widespread and disastrous effects on snow ecosystems around the world. Arctic and alpine systems are among the most vulnerable regions to climate change, and the effects are already showing. Changes in the snow cover, depth and the timing of snowmelt are altering plant phenology and fitness, and restructuring local communities. The effects of changes in snow may be incredibly complex, may interact or be independent from changes in temperatures, and thus are difficult to predict. Some effects of changes in snow (and ice) are already obvious – for example, Glacier National Park in the US is likely to be glacier-less in 30 years. Polar bears, so reliant on their frozen habitat, face a very difficult future. But other effects are very subtle, and may take years to be fully recognized. For example, changes in snow conditions may decrease dispersal and gene flow between Canada lynx (Lynx Canadensis) populations which occur at different ends of a winter climate gradient. With declines in gene flow, the lynx may separate into two increasingly (ecologically?) distinct groups. Shrub encroachment in the low Arctic is a prime example of the complexity of changes in snow. Data shows that shrubs are increasing in abundance in the Arctic over the last 50 years. The snow-shrub hypothesis suggests that this is - indirectly - an outcome of increased snowfall in these regions (though note that warming temperatures are also causing this snow to melt earlier). Shrubs in the region accumulate larger amounts of snow in their branches, resulting in greater insulation and warmer soil temperatures. These warming temperatures encourage greater microbial activity, and perhaps enhance mineralization. The species most able to take advantage of these altered soils are, in fact, more shrubs. All of these examples are reminders that snow - and the organisms adapted to places full of snow - is changing.

References:

Ernakovich, J. G., Hopping, K. A., Berdanier, A. B., Simpson, R. T., Kachergis, E. J., Steltzer, H. and Wallenstein, M. D. (2014). Predicted responses of arctic and alpine ecosystems to altered seasonality under climate change. Global Change Biology, 20: 3256–3269. doi: 10.1111/gcb.12568

Jones, H.G. and Pomeroy, J.W. The ecology of snow-covered systems: summary and relevance to Wolf Creek, Yukon. In Wolf Creek Research Basin: Hydrology, Ecology, Environment (1999), pp. 1-15.

Kelly, E.N. , et al. (2009) Oil sands development contributes polycyclic aromatic compounds to the Athabasca River and its tributaries. PNAS, 106 (52) 22346-2235.

Larose, C., Aurélien Dommergue, and Timothy M. Vogel. (2013). The Dynamic Arctic Snow Pack: An Unexplored Environment for Microbial Diversity and Activity. Biology, 2(1), 317-330.

Marchand, P.J. (2014). Life in the Cold: An Introduction to Winter Ecology, fourth edition. University Press of New England.

Parmesan, C. (2006) Ecological and Evolutionary Responses to Recent Climate Change. Annual Review of Ecology, Evolution, and Systematics, Vol. 37, pp. 637-669

Pomeroy, J. W., and Eric Brun. "Physical properties of snow." Snow ecology(2001): 45-126.

Row, J.R., et al. (2014). The subtle role of climate change on population genetic structure in Canada lynx. Global Change Biology, doi: 10.1111/gcb.12526.

Sturm, Matthew, et al. "Snow-shrub interactions in Arctic tundra: a hypothesis with climatic implications." Journal of Climate 14.3 (2001): 336-34

Walker, D. A., W. D. Billings, and J. G. De Molenaar. (2001) "Snow–vegetation interactions in tundra environments." Snow ecology: an interdisciplinary examination of snow-covered ecosystems  266-324.

http://www.nytimes.com/2014/11/23/us/climate-change-threatens-to-strip-the-identity-of-glacier-national-park.html

Northern White Rhinoceros – On the Brink of Extinction

*Guest post by Monica Choy -one of several posts selected from the graduate EES3001 Scientific Literacy course at University of Toronto-Scarborough.

Photo credit: Elodie A. Sampere, Getty Images

Suni, a 34 year old male northern white rhinoceros, died on October 17, 2014 of natural causes. His death reduced the total number of known northern white rhinos to an alarming six individuals, which has brought his species one step closer to extinction.¹

Suni was born in a zoo in the Czech Republic and was the first of his kind to be born in captivity. Unfortunately, northern rhinos are a finicky species when it comes to breeding and with increasing pressures from poaching, it became critical to provide the animals with a natural, comfortable space.

As a result in 2009, Suni and three others were transported to the Ol Pejeta Conservancy in East Africa.  It was believed this change in scenery would most accurately imitate their natural environment.² Rhino conservationists anticipated that the rhinos would then breed naturally and provide a healthy calf that would bring new hope for the waning species.

Even before these desperate attempts to keep the species going however, the history of the northern rhino has been a sad one. At the time of Suni’s birth, his species was on a very slow rebound. Northern white rhinos had been excessively poached for their horns, and their initial population of over 2,000 animals declined to a shocking 15 rhinos by the late ’80s. Conservation efforts were ramped up in the ’90s and it looked as though the animals were making a gradual comeback. Unbelievably, poachers also increased their efforts and knocked the numbers back down to below 10 individuals by the mid-2000s.³

Northern white rhinos were declared extinct in the wild by 2008.

The likelihood that Suni’s species will become extinct in our lifetime has increased significantly with his death. And although the Ol Pejeta Conservancy will continue trying until the bitter end with the use of techniques such as artificial insemination, the precarious position the northern white rhino is in, as stated in their press release, is “a sorry testament to the greed of the human race.” ¹

The extinction of such a charismatic species is a tragedy and should bring awareness to how heavily humans really affect our environments. Although the northern white rhino may be on the brink of extinction, there are still a countless number of other species out there that need our help. It is up to us to work together in order to keep other species as far from the fate of the northern rhino as possible.

More information

¹Ol Pejeta Conservancy press release  - http://www.olpejetaconservancy.org/about/news/breaking-news-ol-pejeta-conservancy-loses-one-its-northern-white-rhinos

²Northern white rhino conservation project - http://www.olpejetaconservancy.org/sites/default/files/NWR_FAQ_FINAL.pdf

³WWF profile of the northern white rhinoceros - http://wwf.panda.org/what_we_do/endangered_species/rhinoceros/african_rhinos/white_rhinoceros/

Giving Turtles a Head Start

*Guest post by Jethro Valido -one of several posts selected from the graduate EES3001 Scientific Literacy course at University of Toronto-Scarborough.

Photo from  Adopt-a-Pond at Toronto Zoo

When I think about turtles, the first things to come to mind are that they are slow and that they’ve been on Earth for forever. So it came to me as a surprise when I found out that most of Ontario’s turtles are actually endangered and at risk of disappearing in Ontario. In fact, seven out of the eight turtle species found in Ontario are threatened

and are in dire need of help in order to maintain populations. The problem with turtles are that they are extremely long-lived (can live up to 70+ years) and that they have a late sexual maturation (20-25 years). This makes it hard for us to study them and pin-point a cause to their decline, especially when action is required immediately.

So what exactly can we do to help their numbers from declining? One way we can help our turtles is through a head-start program. A head-start program is the process in which juveniles (in this case turtle eggs) are raised in captivity until they reach a certain age, and then they are release back into the wild. This is exactly what I am doing at the Toronto zoo; where we are head-starting the Blanding’s turtle.

The Blanding’s Turtle is one of the threatened species of turtles in Ontario. It can be easily identified and differentiated from other native turtles by its yellow throat and jaw. The biggest threats to this species are associated with humans; ranging from habitat loss due to land development, to being hit by cars when trying to cross roads due to habitat fragmentation, to predation from urban wildlife, such as raccoons, coyotes, skunks, etc. Though once numerous, their numbers have drastically declined, and to help restore their numbers, we are implementing a head-start program for this species at the zoo. This will help encourage the young to grow to maturity, where they have a higher success rate at surviving than when juveniles.

Photo from  Adopt-a-Pond at Toronto Zoo

The head-start program starts off with looking for Blanding’s turtle nests in at-risk locations. These locations are areas such as crop fields, where the eggs they would not have a good chance for survival. These eggs are then transported to the Toronto zoo where they are raised in captivity until they are 2 years old. The reason for this is to prevent predation. At birth, the turtles are very small and are easy prey for animals such as raccoons. By raising them until they are 2 in what could be called a “safe haven” for the turtles, they can grow to a sufficient size to deter predation once released. By deterring predation, their chances for survival is increased.  Once released, the turtles are tracked by radio-tracking devices and monitored.

The really interesting part about this all as a research student working at the Toronto zoo, is that there a lot of questions around the idea and process of head-starting. Although head-starting has been successful for sea turtles, its success is unknown for these freshwater turtles we have in Ontario; including Blanding’s turtle. The Toronto zoo is invested in this project long term, especially since the Blanding’s turtle has a late maturation, thus this project will be heavily research-based to understand the effects head-starting has on these turtles and whether the protocols are well-suited for the turtles. Because of this, there is a huge range of flexibility in adjusting or improving protocols and it is really something that can be applied to other turtle species around the world.

Photo from  Adopt-a-Pond at Toronto Zoo

The Adopt-a-Pond Program at the Toronto zoo is heavily involved with this project and they are quite determined to restore our Blanding’s turtle populations. With the release of these two year old turtles, Adopt-a-Pond is as well restoring their habitat; wetlands. Not only will these turtles receive help but they will act as an umbrella species to protect other threatened wetland species as well. Though we are not 100% certain whether head-starting will restore the Blanding’s turtle populations, this project is just a step in aiding declining turtle populations. From this, hopefully we can gain and discover answers to many of the questions concerning its decline, and eventually manage a long-term solution. Though rare today, hopefully one day, I can walk around the Rouge Park and bump into a yellow-throated turtle.

Here are some additional links:

-       Adopt-a-Pond Blog http://adoptapond.wordpress.com/ - Here, you can follow the Adopt-a-Pond team on their blog. They post up plenty of blogs following the status of their turtles (including Blanding’s turtles) and their releases

-       Earth Rangers Blog http://www.earthrangers.org/blog/ - Here, you can follow the Earth Rangers blog (Earth Rangers are in partnership to head-start the Blanding’s turtle). The website is mostly for children but they have posted up head-starting blogs.