Less snow from climate change pushes evolution of browner birds

7 09 2017
© Bill Doherty

© Bill Doherty

Climate changes exert selective pressures on the reproduction and survival of species. A study of tawny owls from Finland finds that the proportion of two colour morphs varies in response to the gradual decline of snowfall occurring in the boreal region.

Someone born in the tropics who travels to the Antarctic or the Himalaya can, of course, stand the cold (with a little engineering help from clothing, however). The physiology of our body is flexible enough to tolerate temperatures alien to those of our home. We can acclimate and, if we are healthy, we can virtually reside anywhere in the world.

However, modern climate change is steadily altering the thermal conditions of the native habitats of many species. Like us, some can live up to as much heat or cold as their genetic heritage permits, because each species can express a range of morphological, physiological, and behavioural variation (plasticity). Others can modify their genetic make-up, giving way to novel species-specific features or genotypes (evolution).

When genetic changes are speedy, that is, within a few generations, we are witnessing ‘microevolution’ — in contrast to ‘macroevolution’ across geological time scales as originally reported by Darwin and Wallace (1). To date, the detection of microevolution in response to modern climate change remains elusive, and many studies claiming so seem to lack the appropriate data to differentiate microevolution from phenotypic plasticity (i.e., the capacity of a single genotype to exhibit variable phenotypes in different environments) (2, 3). Read the rest of this entry »

Spring asynchrony in migratory birds

15 05 2017

Brent geese flock in the Limfjorden (Denmark)courtesy of Kevin Clausen. The Brent goose (Branta bernicla) is a migratory goose that breeds in Arctic coasts, as well as in northern Eurasia and the Americas, starting from late May to early June. Adults are about 0.5 m long, weigh some 2 kg and live up to 30 years. Their nests are placed in the ground, where reproductive pairs incubate a single clutch (≤ 5 eggs) for a couple of months. They are herbivores, feeding on algae (mainly Zostera marina in Limfjord) and seagrass in estuaries, fjords, intertidal areas and rocky beaches during fall and winter. During summer they feed on tundra herbs, moss, lichens, as well as aquatic plants in rivers and lakes. The species is ‘Least Concern’ for the IUCN, with a global population at some 600,000 individuals.

Migratory birds synchronise their travel from non-breeding to breeding quarters with the seasonal conditions optimal for reproduction. Above all, they decide when to migrate on the basis of the climate of their wintering areas while they are there. As climate change involves earlier springs in the Arctic but not in the wintering areas, there is a lack of synchronisation that leads to a demographic decline of these birds in the polar regions where they breed.

When I think about how species respond to climate change, the song from the ClashShould I stay or should I go” comes to mind. As climate changes, species eventually have to face an ultimate choice: (i) stay and adapt to novel conditions or become locally extinct if adaptation fails, (ii) or move to other regions where climatic conditions should be more suitable. Migratory species have to face this decision every time they have to move back and forth from non-breeding to breeding grounds.

Migration is a behavioural strategy shared by different animal groups like sea turtles, mammals, amphibians, insects or birds. Species move from one area to another usually to feed and reproduce in the best climatic conditions possible. For birds, migration is a common phenomenon that typically entails large movements between breeding and wintering grounds. These vertebrates boast some of the longest migratory distances known in the animal kingdom, particularly seabirds like Artic terns, which can complete up to a round-world trip in a single migratory event between the UK and the Antarctic (1). There are several theories about the mechanisms triggering bird migration, including improving body condition and fitness through unexploited resources (2), reducing parasite load (3), minimizing predation risk (4), maximizing day-light (5), or reducing competition (6, 7). Whatever the cause, birds have to decide when the best moment to migrate is, counting only with the (usually climatic) clues they have at the departure site. Read the rest of this entry »

To feed or to perish in an iceless world

1 02 2017

Emaciated female polar bear on drift ice in Hinlopen Strait (Svalbard, Norway), in July 2015 – courtesy of Kerstin Langenberger (www.arctic-dreams.com)

Evolution has designed polar bears to move, hunt and reproduce on a frozen and dynamic habitat that wanes and grows in thickness seasonally. But the modification of the annual cycle of Arctic ice due to global warming is triggering a trophic cascade, which already links polar bears to marine birds.

Popular and epicurean gastronomy claims that the best recipes should use seasonal veggies and fruits. Once upon a time, when there were no greenhouses, international trade routes, or as much frozen and canned food, our grandparents enjoyed what was available at the time. So in some years we had plenty of cherries, while during others we might have feasted on plums. Read the rest of this entry »

Rich and stable communities most vulnerable to change

16 08 2016

networkI’ve just read an interesting new study that was sent to me by the lead author, Giovanni Strona. Published the other day in Nature Communications, Strona & Lafferty’s article entitled Environmental change makes robust ecological networks fragile describes how ecological communities (≈ networks) become more susceptible to rapid environmental changes depending on how long they’ve had to evolve and develop under stable conditions.

Using the Avida Digital Evolution Platform (a free, open-source scientific software platform for doing virtual experiments with self-replicating and evolving computer programs), they programmed evolving host-parasite pairs in a virtual community to examine how co-extinction rate (i.e., extinctions arising in dependent species — in this case, parasites living off of hosts) varied as a function of the complexity of the interactions between species.

Starting from a single ancestor digital organism, the authors let evolve several artificial life communities for hundred thousands generation under different, stable environmental settings. Such communities included both free-living digital organisms and ‘parasite’ programs capable of stealing their hosts’ memory. Throughout generations, both hosts and parasites diversified, and their interactions became more complex. Read the rest of this entry »

Give way to the invader

25 01 2012

By weird coincidence, Salvador Herrando-Pérez (student blogger extra-ordinaire – see his previous posts on evolution, pollination, bird losses, taxonomic inflation, niche conservatism, historical biogeography, ecological traps and ocean giants) has produced a post this week expanding on the problem of roads. Also weirdly coincidental is that both Salva and I are in his home country of Spain this week.

Australia’s > 800,000-km road network would go 60 times around the equator of our planet. Confined to the boundaries of any one country, roads are a conspicuous component of the landscape, and shape the dispersion, survival and reproduction of many plants and animals in urban and remote areas.

Those who drive (or are driven by) will be familiar with the image of a crushed kangaroo on the roadside (a hedgehog in Europe), or the sticky mosaic of insects smashed against the windscreen after a high-speed run. Mortality by collision is one of the many effects that roads can have on the demography of organisms – including humans. Those effects encompass

  • physical alteration of terrestrial and aquatic habitats,
  • chemical pollution leakage during road construction and maintenance, and from asphalt compounds during storms,
  • alteration of animal behaviour (e.g., change in home range, or in patterns of flight or vocalisation),
  • access to remote areas by hunters, fishermen and gatherers in general, and
  • intense habitat fragmentation1-3.

However, some species get around those negative impacts by using the roads as pathways to new territories, thereby eluding barriers like seas, mountains, rivers, dense vegetation, or competition for vital resources with other species. Read the rest of this entry »

All that glitters is not gold – ecological traps

27 09 2011

Another corker from Salvador Herrando-Pérez:

Cinema fans know that choosing a movie by the newspaper’s commentary or the promotional poster might be a lottery. In the movie of nature, to confuse ‘the attractive’ with ‘the appropriate’ can compromise the life of an individual and its offspring, even to the extent of anticipating the extinction of an entire population or species.

Animals make daily choices about when, where or with whom to engage in basic activities like eating, hibernating, mating, migrating or resting. Those choices are often strongly tied to highly specific cues – e.g., air temperature, tree density, location of water, or smell of other individuals. And it happens to hair lice jumping from head to head among school kids, or to caribou forming their winter herds prior to the seasonal migration. All species, without exception, persist in nature because those ‘choices’ translate into survival or successful reproduction more often than do not. They are a kind of evolutionary memory imprinted in an organism’s genes and behaviour. However, sometimes the right choice (‘right’ meaning perceiving a cue for the role it actually has in the life cycle) places an individual in the worst of all possible situations. The environment cheats, ‘the attractive’ merely mimics ‘the appropriate’, and the individual fails to reproduce, starves, sickens, or even dies.

Figure 1. Water reservoirs tainted with fuel (see dark contours) in Kuwait following the Gulf War in the early 1990s. Overlaid pictures show the silhouettes of trapped odonates (right), vertebrates (top left) and invertebrates (bottom left) (Photos courtesy of Jochen Zeil).

At the mercy of mirages

During the Gulf War, the destruction of infrastructure for crude exploitation spilled large amounts of fuel in many water reservoirs over the desert landscape of Kuwait. A little later, Horváth and Zeil1 found agglomerations of dead insects (and a range of vertebrates) along the shores of these polluted reservoirs, and observed dragonflies drowning in their kamikaze attempt to spawn on the oily surface (Figure 1). This work stimulated further research whereby Horváth and his team in Budapest showed that odonates are attracted by light polarization at the surface of oiled water2 – hence ‘polarized light pollution’3. Not only that, they recorded insects struggling to spawn on or mate with riveting surfaces such as solar panels, asphalted roads, plastic bags or (creepy enough!) cemetery crypts4. It goes without saying: these insects are victims of a mirage.

Those habitats or features of the habitat that mislead an animal’s choice, often hampering the completion of its life cycle, are known as ‘ecological traps’ – in other words, the environmental cue is decoupled from the quality of the habitat it is meant to signal. Ecological traps were first described in the 1970s by Dwernychuk and Boag5. They found that ducks on the islands of Miquelon lake located their nests among those of seagulls despite the latter happily devoured their ducklings and eggs. When these islands emerged in the middle of last century, they were first colonized by common terns (Sterna hirundo). By defending their own nests ferociously from predators (mainly crows and magpies), the terns inadvertently shielded the nests of their ducky comrades. The Canadians hypothesized that when seagulls subsequently replace terns, the ducks continued to sense their new neighbours as a (now misleading) sign of protection. Read the rest of this entry »

Evolution of biodiversity: the hard evidence

25 09 2009

Just a plug for Richard Dawkins’ new book “The Greatest Show on Earth“. Hard to believe, but there are still billions of people who are blind to how life actually works, mainly from the intellectual blindfold of religion.

For more things Dawkins, visit http://richarddawkins.net/.