Could tropical species be intensively vulnerable to global warming?

On 12 January 2002, Cambridge University doctoral student Justin Welbergen was studying the behavior of a large colony of flying foxes in subtropical eastern Australia.  What he witnessed that day shocked him.

Doesn't like the heat... a grey-headed flying fox.

Doesn't like the heat... a grey-headed flying fox.

It was a hot afternoon, and as the thermostat climbed above 40 degrees Centigrade, the giant bats became obviously distressed.  They began fighting over shady spots in the canopy.  Then they began licking their wrists and flapping their wings in a desperate effort to cool themselves.  

Finally, as the temperature hit 42 degrees C, they began to die -- in the thousands.  On that day at least 3,500 bats died, in nine different nearby colonies.  Females and juveniles were especially vulnerable.

What Welbergen observed was a phenomenon that has now been seen elsewhere -- from mass disappearances of lizards in Mexico to the dramatic population collapse of the white lemuroid possum in north Queensland rainforests.

Possum in peril... the white lemuroid ringtail  (photo (c) Michael Trenerry)

Possum in peril... the white lemuroid ringtail (photo (c) Michael Trenerry)

There are two striking conclusions from these observations.  First, to the surprise of many, tropical species may be the most vulnerable of all organisms on the planet to global warming.  Second, it isn't a steadily rising thermostat that endangers most species, but short, intense pulses of unusually warm conditions -- heat waves.

Why are tropical species so vulnerable?  In short, many are thermal specialists.  Think, for instance, about a polar bear -- our traditional icon for global warming.  It has to deal with temperatures ranging from, say, minus 50 degrees C in winter to plus 35 degrees C in summer -- a huge range of temperatures.

But tropical species are different.  Lowland tropical species, for instance, might see temperatures ranging from just 25 to 35 degrees during the course of a normal year -- a far narrower range.  As a result, they can become much more thermally specialized.

Where temperatures vary the most in the tropics is as a function of elevation.  On average, for every thousand meters that one goes up in elevation, the temperature drops by 6 degrees C.  

What that means is that tropical species are not just thermal specialists, they also tend to be elevational specialists.  Species tend to be adapted for the very warm lowlands, or for the cooler mid-elevations, or for the wet, cloudy high elevations, where conditions are almost chilly.

And it's the high-elevation specialists -- such as the white lemuroid possum -- that a lot of scientists are really worried about.   

Many tend to be locally endemic species, because their populations are genetically isolated from other populations on different mountaintops.  Hence, they have small geographic ranges and, often, small population sizes.

And they may be intensely vulnerable to global warming.  As temperatures rise, the geographic ranges of many high-elevation species in the tropics are predicted to shrink and fragment -- potentially disappearing altogether.  For instance, in the Australian wet tropics, most upland-endemic species of mammals, birds, reptiles, and amphibians are predicted to disappear entirely if temperatures should rise by more than 4-6 degrees C.

It's a frightening prospect, and it suggests that global warming could have far wider-reaching impacts than many might suspect -- especially in the tropics, the world's biologically richest real estate.

ALERT member Pierre-Michel Forget has just given a wonderful 30-minute interview on this topic.  Forget is a highly authoritative scientist -- a former president of the Association for Tropical Biology and Conservation and now Vice-President of the Society for Tropical Ecology.  He asks, what would just a 1 degree C increase in temperature do to tropical forests and their species?

It's definitely worth a half-hour to hear this enlightening lecture -- and to share it with your colleagues and students. 

The bottom line is this: Given that tropical ecosystems are so rich in species and thermal specialists, the best icon for global warming might not be a polar bear -- but a tropical white possum or flying fox.

 

Study: Global urban footprint will triple by 2030

If you think cities are big and numerous now, just wait another 15 years.

Our new normal?  (photo by William Laurance)

Our new normal? (photo by William Laurance)

By 2030, some 5 billion people will be living in cities -- many of them mega-cities that each sustain over 10 million residents.  And the total area affected globally by urban sprawl will triple, compared to that in the year 2000.

Those are just a few of the alarming predictions of a recent study by Karen Seto and colleagues, published in the leading journal Proceedings of the National Academy of Sciences USA.

Seto and her team also estimate that, by 2030, an additional 120 million hectares of land will be engulfed by cities -- an area the size of South Africa. 

Notably, some of the most dramatic urban expansion will occur in certain biodiversity hotspots -- regions with high biodiversity and large concentrations of locally endemic species that have already suffered severe habitat loss.

In fact, the most explosive urban expansion will occur in hotspots that have been relatively undisturbed so far by urban development.  These include the Eastern Afromontane hotspot, the Guinean Forests of West Africa hotspot, and the Western Ghats and Sri Lanka hotspot.

In each of these biodiversity hotspots, the expansion in urban lands from 2000 to 2030 is expected to range from 900 to 1900 percent, according to the study.

Such changes reflect the dramatic growth in human populations still occurring in Sub-Saharan Africa and South Asia, as well as increasing urbanization trends globally.

Other places slated for sharp increases in urban area include eastern China, Turkey, the Himalayas, and parts of Mexico.

The world that Seto and colleagues project is not a distant, dystopian future.  This is our near-term tomorrow. 

This will be our reality if we fail to address unbridled population growth in those regions of the Earth most at risk.

As Seto and colleagues show, our new reality will be a planet increasingly dominated by sprawling cities.  Whether those will be polluted, stressful cities or innovative, well-designed cities remains to be seen.

 

Good news: Deforestation slowing in some countries

While there are plenty of environmental concerns to fret about, it's also important to recognize good news.  And some of the best news recently is this: A number of nations have had real success in slowing rampant deforestation.

Conservation strategies really are helping  (photo by William Laurance)

Conservation strategies really are helping (photo by William Laurance)

At the Bonn Climate Conference, the Union of Concerned Scientists has just released a report detailing how some nations are winning the battle to slow forest loss or encourage reforestation. 

Some of the key strategies include:

- Carbon trading, with REDD+ financing benefiting forests in Guyana, Brazil, Kenya, Madagascar, and Costa Rica

- Payments for ecosystem services, which have been successful in various countries, including Costa Rica, Mexico, and Vietnam

- Improving governance and law enforcement, which has aided forest protection in central Africa and Brazil

- Temporary moratoria on forest clearing, which have benefited forests imperiled by the massive beef and soy industries in Brazil

- Notably, most success stories include examples of empowering local communities and decentralizing forest-management decisions

Globally, the rate of forest loss fell by a fifth between the 1990s and 2000s.  Perhaps the most remarkable story of all is the Brazilian Amazon, where the deforestation rate has plummeted by nearly 80% over the last decade.

What these examples reveal is that actions to conserve forests really can produce meaningful results.  The message for conservationists: take note and take heart.