Feed aggregator

A herd of elephant hawkmoth caterpillars is trooping across my garden to pupate

Caterpillars are on the march. In the past week I’ve found several elephant hawkmoth caterpillars trooping across my garden. These are arguably the most subtly beautiful of the charismatic hawkmoth grubs. They are deep brown and charcoal grey with four arresting “eyes” of black, brown and silver – part of an armoury of deterrents against voracious birds, which includes the sudden switching into “snake” mode when disturbed, to discombobulate predators.

The adult moth takes its name from the caterpillar’s trunk-like snout, although its bewitching pink hued wings are also the colour of a cartoon elephant.

Continue reading...

Leaf sizes vary according to a complex mix of temperature and water. Peter Wilf/Supplied

Why is a banana leaf a million times bigger than a common heather leaf? Why are leaves generally much larger in tropical jungles than in temperate forests and deserts? The textbooks say it’s a balance between water availability and overheating.

But new research, published today in Science, has found it’s not that simple. Actually, in much of the world the key limiting factor for leaf size is night temperature and the risk of frost damage to leaves.

As a plant ecologist, I try to understand variation in plant traits (the physical, chemical and physiological properties of their tissues) and how this variation affects plant function in different ecosystems.

Read more: How we found out there are three trillion trees on Earth

For this study I worked with 16 colleagues from Australia, the UK, Canada, Argentina, the US, Estonia, Spain and China to analyse leaves from more than 7,600 species. We then teamed the data with new theory to create a model that can predict the maximum viable leaf size anywhere in the world, based on the dual risks of daytime overheating and night-time freezing.

These findings will be used to improve global vegetation models, which are used to predict how vegetation will change under climate change, and also to better understand past climates from leaf fossils.

Conifers, which grow in very cold climates, grow thin needles less vulnerable to frost. Peter Reich From giants to dwarfs

The world’s plant species vary enormously in the typical size of their leaves; from 1 square millimetre in desert species such as common eutaxia (Eutaxia microphylla), or in common heather (Calluna vulgaris) in Europe, to as much as 1 square metre in tropical species like Musa textilis, the Filipino banana tree.

But what is the physiological or ecological significance of all this variation in leaf size? How does it affect the way that plants “do business”, using leaves as protein-rich factories that trade water (transpiration) for carbon (photosynthesis), powered by energy from the sun?

More than a century ago, early plant ecologists such as Eugenius Warming argued that it was the high rainfall in the tropics that allowed large-leaved species to flourish there.

In the 1960s and ‘70s physicists and physiologists tackled the problem, showing that in mid-summer large leaves are more prone to overheating, requiring higher rates of “transpirational cooling” (a process akin to sweating) to avoid damage. This explained why many desert species have small leaves, and why species growing in cool, shaded understoreys (below the tree canopy) can have large leaves.

Rainforest plants under the tree canopy can grow huge, complex leaves. Ian Wright

But still there were missing pieces to this puzzle. For example, the tropics are both wet and hot, and these theories predicted disadvantages for large-leafed species in hot regions. And, in any case, overheating must surely be unlikely for leaves in many cooler parts of the world.

Our research aimed to find these missing pieces. By collecting samples from all continents, climate zones and plant types, our team found simple “rules” that appear to apply to all of the world’s plant species – rules that were not apparent from previous, more limited analyses.

We found the key factors are day and night temperatures, rainfall and solar radiation (largely determined by distance from the Equator and the amount of cloud cover). The interaction of these factors means that in hot and sunny regions that are also very dry, most species have small leaves, but in hot or sunny regions that receive high rainfall, many species have large leaves. Finally, in very cold regions (e.g. at high elevation, or at high northern latitudes), most species have small leaves.

Understanding the mechanisms behind leaf size means leaf fossils – like these examples from the Eocene – can tell us more about climates in the past. Peter Wilf/Supplied

But the most surprising results emerged from teaming the new theory for leaf size, leaf temperature and water use with the global data analyses, to investigate what sets the maximum size of leaves possible at any point on the globe.

This showed that over much of the world it is not summertime overheating that limits leaf sizes, but the risk of frost damage at night during cold months. To understand why, we needed to look at leaf boundary layers.

Every object has a boundary layer of still air (people included). This is why, when you’re cold, the hair on your arms sticks up: your body is trying to increase the insulating boundary of still air.

Larger leaves have thicker boundary layers, which means it is both harder for them to lose heat under hot conditions, and harder to absorb heat from their surroundings. This makes them vulnerable to cold nights, where heat is lost as long-wave radiation to the night-time sky.

So our research confirmed that in very hot and very dry regions the risk of daytime overheating seems to be the dominant control on leaf size. It demonstrated for the first time the broad importance of night-time chilling, a phenomenon previously thought important just in alpine regions.

Still, in the warm wet tropics, it seems there are no temperature-related limits to leaf size, provided enough water is available for transpirational cooling. In those cases other explanations need to be considered, such as the structural costs and benefits of displaying a given leaf area as a few large leaves versus many more, smaller leaves.

The view from a canopy crane at the Daintree in Queensland. Peter Wilf

These findings have implications in several fields. Leaf temperature and water use play a key role in photosynthesis, the most fundamental plant physiological function. This knowledge has the potential to enrich “next-generation” vegetation models that are being used to predict regional-global shifts in plant nutrient, water and carbon use under climate change scenarios.

These models will aid the reconstruction of past climates from leaf macrofossils, and improve the ability of land managers and policymakers to predict the impact of a changing climate on the range limits to native plants, weeds and crops.

But our work is not done. Vegetation models still struggle to cope with and explain biodiversity. A key missing factor could be soil fertility, which varies both in space and time. Next, our team will work to incorporate interactions between soil properties and climate in their models.

Ian Wright receives funding from the Australian Research Council.

New research sheds light on why yawns are so contagious.

Scientists are closer to solving one of the big puzzles of the plant world - why leaf size matters.

Experiment in the Bellingshuan Sea reveals temperature rise has more alarming implications for biodiversity in polar waters than previously thought

Marine life on the Antarctic seabed is likely to be far more affected by global warming than previously thought, say scientists who have conducted the most sophisticated study to date of heating impacts in the species-rich environment.

Growth rates of some fauna doubled – including colonising moss animals and undersea worms – following a 1C increase in temperature, making them more dominant, pushing out other species and reducing overall levels of biodiversity, according to the study published on Thursday in Current Biology.

Continue reading...

Rising sea levels pose a serious threat to cites like Boston, New York and Miami Beach. So what are they doing to protect themselves?

Tropical storm Harvey may have bared its teeth at Houston, but other cities in the US have felt the pangs of nervousness. Several cities are vulnerable to the fiercer storms and sea level rise that are being fueled by climate change.

Cities, by their very nature, struggle during flood situations. Water that would have been soaked up by grass and other vegetation washes off the concrete and asphalt of urban areas and, if not properly diverted away, can inundate homes.

Continue reading...

Researchers observe smooth-coated otters watching and learning from each other.

Rescue operations continue to save people across Texas stranded by tropical storm Harvey. Though rainfall is slowing and wind speeds have dropped, officials say the flooding will take longer to subside. Harvey weakened as it moved inland over Louisiana on Thursday, leaving behind record flooding

• Houston flooding: two explosions take place at Texas chemical plant
  

Continue reading...

The reasons why the fourth-largest city in the US has become its flood capital.

More tests next month might mean the pods for the science-fictional transport system hit 500 km/h

This is the largest radio telescope on Earth, 5,000m up in the Atacama Desert. It can see stars and planets being born millions of light-years away.

Protests planned after president suggests Roșia Montană Unesco application could be withdrawn, potentially enabling the return of a controversial mining project

Romania’s prime minister has suggested his government will seek to withdraw an application to have the former gold mining area of Roșia Montană declared a Unesco world heritage site, potentially paving the way for the return of a controversial mining project.

Continue reading...

Tim Flannery speaks about how to help feed, power and clean the world sustainably. 

Conservation charity WWF warns that the species were found in areas at risk from human activity.

A climate “red team” is just a polite way to describe bailing out scientific losers

Climate contrarians, like Trump’s EPA administrator Scott Pruitt and Energy Secretary Rick Perry, don’t understand how scientific research works. They are basically asking for a government handout to scientists to do what scientists are should already be doing. They are also requesting handouts for scientists who have been less successful in research and publications – a move antithetical to the survival of the fitness approach that has formed the scientific community for decades.

The helping handout would be through a proposed exercise called a “red team/blue team” effort. It is a proposal that would reportedly find groups of scientists on both “sides” of the climate issue (whatever that means), and have them try to poke holes in each others’ positions. I will explain why this is a handout but first let’s talk about the plan and how it interferes with the scientific process.

Continue reading...

North Korea has fired a missile over Japan into the Pacific Ocean. How should the international community respond to this provocation? Christopher Hill explains what we can realistically expect from all sides.

Why has the government returned to an industrial strategy abandoned in the 1980s?

Winning and shortlisted images from this year’s competition, from awe-inspiring action shots to charming portraits, featured in a new book celebrating some of the best bird photography of the year

Continue reading...

RN Drive brings you up to speed with news from the wide world of science.

Rescue workers in Mumbai are searching for people feared trapped beneath a collapsed building following two days of torrential rain in India’s commercial hub. At least 1,200 people have died across south-east Asia as a result of flooding caused by heavy monsoon rains, and millions of people are estimated to have been affected

• Mumbai building collapses in monsoon rains as South Asia floods wreak havoc
  

Continue reading...