Since this is another one of the recurring themes on my blog, I decided to republish all of my old posts on the topic together under the fold. Since my move here to the new blog, I have continued to write about this, e.g., in the following posts:
Preserving species diversity – long-term thinking
Hot boiled wine in the middle of the winter is tasty….
Global Warming disrupts the timing of flowers and pollinators
Global Warming Remodelling Ecosystems in Alaska
Clocks, Migration and the Effects of Global Warming (December 23, 2005)
Circadian systems are involved in annual migrations in two ways.
First, the circadian clock is used to measure the gradual changes in daylength (photoperiod), thus giving the animal sufficient time to prepare for the annual migratory event.
Such preparations include molting (change of feathers or hair) and pre-migratory fattening in birds (sometimes to the extent that all other internal organs shrink). Both circadian and circannual (PDF) timers may be involved.
There are also behavioral changes. For instance, migratory animals aggregate into large groups (flocks of birds or herds of wildebeast, for instance). Birds undergo practice flights – you’ve all seen birds flying in circles above your head and practicing their flying formations.
Most migratory birds are normally diurnal (day-active), but tend to do their migratory flights over nights. Changes in hormone levels associated with seasonal preparation for migration induce a splitting in the circadian output into two components: one guiding daytime behavior (foraging, practice flights) and the other controlling nocturnal migratory restlesness which is behavioral preparation for night-time migratory flights.
Photoperiod is not the only environmental cue governing timing of seasonal events. Thermoperiod (relative durations of daily warmth and nightly chills), average temperature, food availabilty and rainfall are secondary (or proximal) cues that fine-tune the timing of seasonal events in animal behavior and physiology.
There is a whole range of responses to photoperiod and other cues. In nature, finches in Australia respond only to rainfall, yet are capable of responding to photoperiod in the laboratory. Tropical/equatorial birds, naturally exposed to minimal yearly changes in daylength are quite capable of (PDF) measuring tiny changes in photoperiod in the lab. On the other end of the spectrum are birds like the famous swallows of San Juan Capistrano, in which photoperiodism is clearly the most dominant seasonal clue.
Photoperiodic response is genetically determined. Variation in the relative importance of photoperiod versus proximal cues exists not just between species but also within species (this has mostly been studied in mammals, see the work of Paul Heideman, for instance).
The second way in which the circadian clock is involved in migration is in orientation and navigation. Animals use a number of clues in the environment to orient to, including landmarks, orientation of the magnetic field of the Earth, sense of smell (“olfactory maps”, specifically in salmon who remember the olfactory stamps of their native streams and rivers), position of the stars and position of the Sun. Position of the Sun changes over the course of the day, thus internal clock is used to correct for the Sun’s movement across the sky (I will write in detail about the mechanism in the future). Likewise, stars move across the sky during the night and the clock controls for such movement. The intensity of the magnetic field is higher during the night, too.
Thus, clocks help animals decide both when to go and where to go. Both the timing and the direction of migration are finely tuned by evolution. Migration is a very energetically expensive, as well as a dangerous endeavor. Thus, it is to be expected that natural selection has resulted in quite optimal solutions for both timing and direction of migration in each species.
Now, this is all starting to fall apart due to global warming. Proximal cues, like temperature and food-availability, are beginning to conflict with photoperiodic information. Species in which photoperiod is dominant continue to migrate at the same time and in the same direction. Other species are shifting their timing to later in fall and earlier in spring. As there is genetic variation within species there is now evidence for change in relative proportions of phenotypes as some strategies are more adaptive than others, namely migrating later, migrating closer, or not migrating at all may be more adaptive than enduring a long dangerous migratory flight.
Some of those changes in bird behavior have already been reported.
For instance, various species of European warblers mainly migrate to Africa for the winter. It has been known for a while now that there is a genetic basis for intra-species variation in migratory direction. There exists a small subgroup that migrates to the South of England instead of Africa. As of very recently, this subpopulation has been doing great and increasing in relative proportion within the species, threatening to completely abolish the trip to Africa from the species’ behavioral repertoire. The genetic basis for the trip to Africa may dissappear, and if the global warming is successfully countered and reversed, this species will be unable to migrate to Africa again, leaving the “England-bound” genotype to freeze and starve in the future. And nobody is asking how will the absence of warblers affect the ecosystems in Africa!
Non-migratory species are also affected. For instance, sparrows in Scotland are not preparing for winter adequately. The falls are mellower and warmer, so they do not prepare for winter in time. At the same time, human activity is limiting their food supply, further diminishing their ability to prepare for cold Scottish winters (and yes, they are still cold, despite global warming, it’s just that they come later, and stopping of Gulf Stream will make them VERY much colder).
A genetic response to global warming in photoperiodic responses in Pitcher-plant mosquitoes and Mexican Jays as well as in many other species have already been documented. Effectively, whole ecosystems are moving North, but some species move faster than the others, thus breaking up old ecosystems and building new ones. A plant predominantly responsive to temperature may move North, but its pollinator-insect may be strongly photoperiodic and lags behind. The plant lacks its pollinator in the North, the insect lacks its plant food in the South. Such times of tumultuous changes often lead to extinctions of species that cannot quickly adapt to such changes.
Many researchers around the world are watching evolution in action right now. Ecosystems break down and new ones get assembled. Migratory patterns change and new predator-prey and pollinator-flower relationships will emerge. Some species will go extinct and others will change so much their entries in ornithology (and entomology, mammalogy, botany, etc) books will have to be substantially re-written.
On one hand, watching evolution in fast action is fascinating (not to mention that it provides plently of new ammunition to counter creaitonists’ claims against what they like to call “macroevolution”). On the other hand, watching species go extinct due to unwillingness of some humans to accept responsibility for global warming and to implement strategies to counter it, is more than frustrating. It makes one ashamed to be a Homo sapiens.
Penguins have to rush sex – ‘quicky’ is the new norm (April 05, 2006)
Apparently, the Southern Hemisphere is not immune to global warming either, though most of the research has been done in the North, probably due to socio-political reasons – that is where the rich countries tend to be located.
However, several recent papers look at the effects of climate change on Antarctica. Just like in the Arctic, where polar bears are drowning when they try to swim between ever more distant pieces of floating ice, the same thing is happening in the Antarctica, negatively affecting the birds that nest there.
First, Warming signs mount up in Antarctica (the paper is: Significant Warming of the Antarctic Winter Troposphere) looks at the ice melting in the Antarctica.
The ice is breaking. This makes it more and more difficult for populations of penguins and other birds to travel between their feeding grounds and their nesting grounds. There are clear evolutionary consequences as the populations are getting more fragmented: Penguin evolution linked to shifting icebergs (Microevolution and mega-icebergs in the Antarctic).
Now, in the latest paper – Mating march of the penguins slows down – (not online on PNAS yet) this change in the ice forces the birds to remain at the feeding grounds longer in order to fulfill their metabolic needs. They need to stock up on all the calories for the long period of fasting while they court, mate, nest, lay and incubate the eggs and raise the hatchlings. So, they are arriving at their breeding sites late and starting the whole reproductive effort later.
In the extremes of polar regions, there is only a very narrow window of opportunity, during the super-short summer, to successfully raise hatchlings. Exact timing is crucial, especially for smaller animals (elephant seals don’t seem to care – they are completely unsynchronized with the planet and breed every 9 months) and for migratory species.
In penguins, the climate change is placing their metabolic needs and the survival needs of their offspring in conflict, similarly to the situation in the Northern Hemisphere. How much longer can this go on until the window of opportunity for reproduction is completely closed?
Global Warming restructures plant (and animal) biogeography (April 24, 2006)
Climate change forces plants to search for better places to live:
Climate change is reshaping the landscape of Britain as rising temperatures allow orchids and ferns to flourish in the north, while other species retreat to cooler conditions on high land and mountainsides.
The conclusion, published today in a comprehensive survey of the nation’s flora, suggests that the changing climate has already brought about a rapid and dramatic shift in the country’s plantlife, a trend researchers say will be exacerbated by future warming.
So, individual species migrate, proliferate or die-out. This also means that entire ecosystems are being remodelled.
Getting out of sync in the real world (May 04, 2006)
Due to climate change, plants and animals are loosing synchronization with each other, resulting in remodelling of entire ecosystems, which inevitably leads to some species suffering, sometimes to the point of extinction. Here is the latest story on this phenomenon:
Earlier Spring Starves Migratory Birds:
Trees are blossoming, plants are flowering, and temperatures are warming up. Spring is finally is here and everyone seems happier. Well, except for the pied flycatcher, a small bird that can’t schedule its breeding time to cope with the earlier spring season caused by climate change.
The pied flycatcher winters in West Africa then migrates to The Netherlands for spring breeding. Offspring feed on caterpillars.
Because spring is arriving sooner than in the past, the caterpillar population peaks earlier than the flycatcher’s arrival, resulting in scarcity of food for the chicks, a new study reports.
This altered timing and resulting food shortage has led to a population decline of 90 percent over the past two decades in areas where the food peaks earlier. However, numbers dropped only about 10 percent in areas where food peaks the latest.
Polar bears and grizzlies require an extended mating ritual to reproduce, Stirling said. Both live by themselves in large, open habitats. To prevent wasting their eggs, females ovulate only after spending several days with a male, Stirling explained. “Then they mate several times over several days.” In other words, the mating between the polar bear and grizzly was more than a chance encounter.
Archy makes a very important point:
Polar bears and grizzlies are essentially different breeds of the same species, so a hybrid isn’t a genetic problem. What mainly separates them is that they have completely different ranges and slightly different breeding seasons. David Paetkau, a geneticist quoted in the article, suggests the hybrid might be a sign that the bears are moving to new, overlapping ranges in response to global warming climate change.
So, this is another example of the break-down and remodelling of entire ecosystems in response to global warming, with different species migrating at different rates to different places, as well as changing the timing of reproduction.
In the case of bears, what is going to happen long term? Is hybridization going to become common and the two sub-species eventually completely fuse into one species? Is that good or bad? Only time will tell, but what do you think?