The merits of plasticity
Whether a species thrives or flags can have resounding consequences. When we think of our changing world, we imagine an ecosystem occupied by organisms which are interlinked.
Photosynthesizers like plants and phytoplankton which harvest energy from the Sun occupy the lowest trophic level, while the herbivores that eat them are on the second trophic level, supporting higher level carnivores. When something goes wrong in one part of this pyramid / web / food chain, disconnects can happen that negatively impact linked organisms. Scientists in Alaska studying migratory birds ask questions like: what happens when plants bloom early in response to early snow melt, but insects have not yet emerged? How does that impact birds and their chicks?
Snow and birds
Matthew Sturm, professor of geophysics, University of Alaska Geophysical Institute, is a man who studies snow. Alaska is a great place for such research because snow is a heavily influential part of ecosystems in the far north.
“When my science and avian science meet, all of a sudden that’s an exciting area – we are going to create new knowledge.” “Recently I got hooked up with a group that looks at shorebirds in Barrow. Migrating birds really need areas clear of snow before they do what they need to do which is nest and breed and feed. So the snow is a major control of what birds do.” ~Matthew Sturm
Sturm speaks of avian studies at Barrow, Alaska, on the far northern shore of the state. There, Dr. Richard Lanctot, Region 7 Shorebird Coordinator with the U.S. Fish and Wildlife Service, researches shorebird reproductive ecology. His team locates and monitors nests within six 36-hectar plots at Barrow, Alaska. They also tag birds. The data they collect establishes knowledge about shorebird demographics, the timing of lifetime events, and the implications of weather, food availability, and predators to bird populations.
The warming climate and the constant unpredictability of Arctic weather are factors bound to impact both snow and avian life in Alaska.
“Where my science and someone else’s science meet, that’s where the exciting sciences are. Let’s face it, it is unlikely I’m going to discover a new snowflake or something radically new about snow. People have been watching snow for tens of thousands of years. What is the likelihood I’m going to go out and say ‘No one has ever seen this snow before!’? So what I’m going to discover is how snow plays and interacts, not something brand new.” ~Matthew Sturm
Migratory birds which overwinter in places like Central America, South America or Southern Asia can’t know what weather conditions are like in Alaska. Yet every year they head north to Alaska to breed. Their cue to begin migration is governed from photoperiod: their daily exposure to light.
Dr. Simone Meddle, behavior endocrinologist and associate professor at the University of Edinburgh, explains the role of photoreceptors which spark migration and breeding behavior in migratory songbirds.
”There are only 1000 neurons that control seasonal breeding in birds and they are spread out in a region called the pre-optic area. We’re talking about a single neuron, a cell body with its axion that projects down to an area of the brain called the pituitary which then secrets a hormone into circulation when you get an increase in day length.”
”These birds are seasonal, their breeding is driven by day length. As days get longer they perceive the change in day length and via this endogenous clock and these photoreceptors they have – birds have deep brain photoreceptors, they don’t use their eyes to see the change in day length, they actually use photoreceptors deep within the brain – and using these opsins, deep brain photoreceptors, vertebrate ancient opsin, melanopsin, these types of opsins, they are able to time breeding and activate these GnRH neurons that control breeding and cause the secretion of luteinizing hormone to the pituitary gland.” ~Simone Meddle
Unlike migratory birds, the insect larvae the birds will depend on to feed and strengthen their young do not respond to photoperiod. Arthropod larvae, like plants, respond to local conditions.
The Arctic is vulnerable. Alaska has warmed twice as fast as the rest of the United States has over the last six decades. The speed and extent of climate change influences local life.
Vegetation emerges when snow melts – green-up closely follows the date when local snow cover disappears. And though weather will always be unpredictable, the timing of Arctic snow melt is changing, influenced by global warming. In northern Alaska the melt date – the day when the last of winter's snow melts – has advanced by about 8 days since the mid-1960s. That means insect larvae are emerging sooner in the year.
“The weather up here based on the snow melt determines when the insect larvae come out and when the food becomes available. There’s an hypothesis that this can come out of whack. If birds show up late and the insects have already come and gone, the birds will have a tough time. And this is what they mean by a trophic mismatch.” ~Matthew Sturm
The timing shift represents a disconnect between predator and prey; to flourish the birds need to arrive at the height of insect abundance, but the avian clock is set to photoperiod (governed by the tilt of the Earth) while the insect clock is set to local environmental conditions. This disconnect is called trophic mismatch. It describes a state in which interacting species’ life cycle events fail to line up optimally, and it can cause consequences which echo through food chains and ecosystems.
Adaptation in place
That doesn’t mean that organisms can’t change where and how they live.
Some species make physical shifts to places where climate change stressors are lessened. Between 1966 and 2004, the Audubon Christmas Bird count documented that for 300 bird species in Alaska, the center of abundance (mean annual latitudinal center) shifted north by about 40 miles (64.4 km). A National Park System report notes that there is significant correlation between temperature trends and those new centers of abundance. Many Northern Hemisphere birds, butterflies and alpine herbs are shifting because they thrive best in a certain temperature range, and the location of that range has drifted north.
For other species, life cycle events are happening sooner to coincide with warmer temperatures happening earlier in the year. What makes this possible? There are two possibilities for ‘adaptation in place’, when organisms manage to retain healthy survival in their current location despite changing environmental conditions.
One mechanism is adaptive evolution, through which advantageous mutations within genes are promoted via natural selection. A group of birds whose genes prompt them to migrate north slightly earlier in the year may have better reproductive success, and their offspring and their offspring’s offspring will spread that early-flying prompt through the species’ gene pool. However, the fulfillment of microevolutionary processes occurs across generations. The process requires time… very likely, more time than is granted in such a rapidly changing environment.
A second mechanism is phenotypic plasticity, which describes an organism’s ability to flexibly adjust now, without undergoing genetic change.
“I’m not a biologist so I cannot speak with any authority. But having watched a number of melts, and having watched a number of birds interacting with the melt. I have a feeling that they have a resiliency, some ability to adapt to a late snow season. Part of my thinking goes this way: if I’m an Arctic bird or creature, the variability of snow melt in my lifetime is extreme. They have to have some ability to adapt to varying snow conditions because they would never have survived. Because that’s the nature of snow: it’s very different from year to year. The inner-annual variability of snows can be enormous. So almost any biologic system up here must be adaptive to that, is the basic thinking I have.” ~Matthew Sturm
Any given species has a range within which individuals can adjust their behavior or physical characteristics. Phenotypic plasticity may allow migratory birds to change their behavior in order to deal with changing environmental conditions. For migratory birds which come to Alaska, it's important to survival:
These birds go through this really fast transition from arrival to breeding, setting up pairs and bringing up their nestlings in an environment that is quite unpredictable. ~Simone Meddle
Birds may cope with unpredictable conditions by, for example, building nests or initiating breeding earlier after arrival at northerly breeding grounds. During years when weather causes snow to linger late, they might cope by breeding later but meet less success. This flexibility has the potential to help ameliorate climate change-related stressors but is no guarantee; the question becomes whether the range of behavioral adjustment allowed by a species’ phenotypic plasticity is enough to cope with future annual temperature changes. While birds have some ability to adjust once they have arrived at their northerly breeding grounds, the timing of their migrations are likely more hardwired to photoperiod, less plastic.
Marilyn Ramenofsky is an adjunct professor at the University of California Davis in the Department of Neural Biology, Physiology and Behavior. She talks about migratory songbirds surviving a particularly cold and stormy spring in 2013.
“Coming into areas, it was like winter for them, it was still migratory conditions but it wasn’t anywhere near breeding. They just held out. They fed on grass seedlings. They would crawl up these stems, and nibble off dried seeds. They would eat berries that had over-wintered. They are just incredible in terms of surviving and being able to withstand harsh conditions.”
“So when these birds come in to breed, this year conditions were pretty rough, other years they might be more advanced so the resources that the bird needs, the refugia, the food, might be a little advanced or a little slower. So in many ways, it’s great if the populations can keep pace, but it’s hard to keep pace when you are wintering thousands of kilometers south and coming to an area where you don’t know what its conditions are going to be from year to year.” ~Marilyn Ramenofsky
Her team hopes to track the songbirds’ movements as they prepare for migration, and set out on the journey home. To accomplish this they fit captured birds with tiny temporary 2-3 centimeter backpack transmitters.
We have a lot more to learn about birds breeding in extreme environments; continuing efforts like those at Barrow and at Toolik Field Station add to our growing knowledge.
Frontier Scientists: presenting scientific discovery in the Arctic and beyond
- 'Annual Summary Compilation: New or ongoing studies of Alaska shorebirds' Alaska Shorebird Group (Oct 2012)
- ‘Effects of climate change on avian life history and fitness‘ Nicole A. Schneider, essay, Sveriges Lantbruks Universitet (2008)
- ‘Keeping Pace with Fast Climate Change: Can Arctic Life Count on Evolution?’ Dominique Berteaux, Denis Réale, Andrew G. McAdam, Stan Boutin, Integr. Comp. Biol. (2004) 44 (2): 140-151 doi:10.1093/icb/44.2.140
- ‘North Slope birds nesting earlier to keep pace with earlier snowmelt, study says’ Yereth Rosen, Alaska Dispatch (Jun 28 2014)
- ‘Phenological advancement in arctic bird species: relative importance of snow melt and ecological factors’ J. R. Liebezeit, K. E. B. Gurney, M. Budde, S. Zack, D. Ward, Polar Biology (May 2014)
- ‘Region: Alaska’ Third National Climate Assessment (May 2014)
- 'Terrestrial Ecosystem Adaptation' Steven W. Running and L. Scott Mills, RFF Report, An Initiative of the Climate Policy Program (June 2009)
- ‘Travelling through a warming world: climate change and migratory species’ Robert A. Robinson et.al., Endangered Species Research, doi: 10.3354/esr00095 (Jun 17 2008)
- ‘Understanding the Science of Climate Change Talking Points – Impacts to Alaska Boreal and Arctic’ Natural Resource Report NPS/NRPC/NRR—2010/??? National Park Service, U.S. Department of the Interior (July 2010)