Archives for April 2011

Carnivores are most susceptible (image: photolibrary.com)

Death becomes all living things.

But the manner in which they die can tell us a lot about how they lived, and the pressures of life they faced.

It can also help reveal what forces are at work in shaping the ecology and future of different species.

So if I was to ask you what is the single largest killer of animals, what would you answer?

Other animals would be a good guess, as would disease, or maybe old age.

But for the large mammals of North America – the answer is different, and to me, quite shocking.

This week I’ve just learnt a startling statistic – the biggest killer of large and medium sized mammals across North America is…

People.

Humans kill more deer, antelope, raccoons, skunks, porcupines, bobcats and coyotes, among others, than any other cause, including predation, starvation, weather, disease and natural causes including age, accident or developmental defects.

What’s more, humans kill more large mammals in North America than all other causes put together.

It’s obviously impossible to monitor how each mammal on the continent lives and dies.

So how can such significant a claim be made?

The statistics come from a piece of science just completed by Christopher Collins and Roland Kays from the New York State Museum in Albany, New York, US.

Hunt bans lead to a rise in natural causes of animal death

They reviewed data from 69 populations of large and medium sized North American mammal across 27 species.

This produced definite records of 2209 animal deaths, of which the causes of 1874 were known.

Of those animals that died from known causes, 52% died by human hand.

Hunters killed 35% of all the large and medium sized animals that died in the sample, with 30% dying after being legally killed by hunters and another 5% shot or trapped illegally by poachers.

Vehicle collisions accounted for another 9% with other human causes accounting for a further 7%, the researchers reveal in the journal Animal Conservation.

The fact that just over one in two of North America’s largest and perhaps most iconic mammals dies at the hands of humans suggests just how unnatural their natural environment has become.

Or in the words of Mr Collins, a postgraduate student and Dr Kays, curator of mammals at the New York State Museum:

"Our results show the variety and pervasiveness of anthropogenic mortality on many mammal species, suggesting that humans cause most mortalities observed in larger mammals in North America."

Carnivores and omnivores appear more susceptible to being killed by people than herbivores. And larger species are more likely to be killed by people, with smaller species being killed by predators.

Though mortality studies have been conducted for many mammal species, this is the first to examine trends across species.

The data looks solid: all the animals were radio tagged, and where required, autopsies performed, to reveal the cause of their demise. While the researchers acknowledge their sample is not random per se, as it relies on monitoring species of interest to wildlife managers, and can only necessarily follow a small subset of North America's mammals, it ranges over 27 very different species and animals that vary by four orders of magnitude in body size.

Other biases are also removed as many of the studies used weren’t even primarily concerned with mortality – they were more general studies into a species’ movement or behaviour, during which the cause of death was recorded.

Larger mammals face the greatest threat from humans

As to the other causes of death: predation by other animals kills 35% of mammals, while disease kills just 4% and starvation 3%, with other natural causes accounting for 6%.

That raises an interesting question.

By artificially killing so many mammals, via hunting, culling, poaching or driving vehicles into them, are we taking over the role once played by natural selection?

Are we artificially selecting the generations that survive, and in doing so, altering the evolutionary paths of these species?

It’s certainly possible; some studies show that animals, including fish, which are intensively hunted are evolving smaller body sizes, perhaps because they are less attractive to the hunter or are harder to catch.

So we may debate whether we agree with hunting or not. And whether, by taking healthy harvests, or keeping some animal populations in check, it actually helps preserve wildlife and ecosystems.

But do we yet understand the true impact of our actions?

By pre-emptively killing the majority of North America’s large mammals, might we be irreversibly changing the evolution of these species?

Cannibalism is a driving force for locusts (Image: Ingo Arndt / NPL)

Cannibalism – what is it good for?

Food is the obvious answer, but there appear to be significant issues associated with eating your own kind. Eating your offspring is a bit pointless, if you’ve put in the energy to raise them in the first place. Devouring members of the opposite sex limits your ability to find a mate. And gobbling up your neighbours can be self defeating – for these good neighbours can lead you to food and water, warn about predators and provide more sociable creatures with company. And if you start a cannibalism trend, the odds are you may end up a victim.

Those reasons help explain why most animals aren’t cannibals. But it doesn’t elucidate why some do eat their own.

However, a few recent and new bits of research shed a little light on the matter (if you’re squeamish, it may be better not to read on).

Earlier this month, the BBC reported the discovery that male wolf spiders cannibalise older females.

In this unusual case of role reversal (among scorpions, spiders and mantises, cannibalism usually takes the form of females eating smaller males, or babies eating their parents), the ladykilling spiders seem driven to their compulsion by the harsh habitats in which they live, in South America's sand dunes along riverbanks and the Atlantic Ocean coast.

A male wolf spider devours a female (Image: L Watson)

Strong winds and extreme temperatures buffet the dunes, which provide scarce refuges for the wolf spiders and an unpredictable abundance of prey. That means the males often decide to eat low quality females rather than mate with them. A straightforward decision between eating and surviving to mate another day, or mating now and possibly dying.

A more uncomfortable case of cannibalism is reported in the journal Primates.

Uncomfortable because it involves one monkey eating another, even more so because it was a mother eating her baby.

I’ve reported on cannibalism in primates before.

In 2009, I wrote about the cases of two female orangutans seen cannibalising the bodies of their recently deceased babies, the first report of such behaviour in great apes.

Then in 2010, a wild bonobo cannibalised her own recently deceased two and a half-year-old infant – the first record for that species.

But the case of the cannibalistic monkey is especially interesting; the mother moustached tamarin, which lives in the Amazon rainforest in Peru, intentionally killed her young son, by biting and eating its head.

That makes it only the third recorded case of maternal infanticide recorded in wild non-human primates.

Researchers can of course only speculate about her motivation. But the scientists that witnessed the act, and had been following and studying the tamarin troop to which she belonged for years, can make some educated guesses.

They suspect the mother killed her baby because she knew it had a low chance of survival anyway. Tamarins rely on other adults to help raise their young, and there were few of these around when the mother made her fateful decision. So the primatologists think she terminated the investment in her offspring due to the low availability of helpers. The baby was simply born at a bad time, and as tamarins ovulate relatively quickly after giving birth, the mother, in terms of reproductive economics, made a cost effective decision.

That doesn’t explain why she then began to consume her young. In this instance, the mother only ate part of her infant’s corpse; the head, brain and a small part of his shoulder and neck. So she didn’t kill her offspring for its meat. But once dead, she probably gained some nutritional benefit by eating its brain, offsetting some of her costs in producing the baby.

But cannibalism can be about more than just individual survival. The compulsion it seems, can lead to one of the most impressive, complex and difficult to understand phenomenon among all animals.

Eating your own may be the driver behind the mass migration, and swarming, of locusts, researchers have just announced.

Cannibalistic interactions have been shown before to be the driving force behind the collective mass movement of Mormon crickets and Desert locusts.

The basic idea here is that locusts combine into swarms because they are frightened of being eaten by each other.

But researchers have now provided the first evidence that cannibalism has an adaptive benefit for desert locusts, which form “bands” as they migrate en mass.

Australian plague locusts cannibalise other vulnerable locusts to compensate for a lack of protein in their diet. Individuals move forward to find new food, and avoid being eaten by each other, producing an advancing swarm.

But the scientists, led by Matthew Hansen of the University of Sydney, Australia, also show that locusts that are given the opportunity to eat each other on average survive longer and move further.

They call it the “lifeboat mechanism”; locusts actually have a better chance of surviving longer and travelling further if they all jump into a swarm together and become cannibals.

When times are tough, it seems, cannibalism can become a rather attractive option.

Oiled pecilans rescued after the spill in June 2010

It’s a natural disaster without an icon.

A year after the BP / DeepWater Horizon disaster that pumped oil into the Gulf of Mexico, and there is no single image of the disaster that sums up its ecological impact, and makes our green blood boil.

Think about it: can you remember an iconic image of an oil-soaked seal, a big-billed pelican struggling to free its tarred feathers from the brown waves, a sea otter choking on black gold?

Animals did die a plenty, and plenty of pictures of tarred wildlife were captured by photographers documenting the spill. But no one species bore the brunt, and by dying in its thousands acted as a sentinel to the spill's destructive power. No oiled humpback whale washed up ashore to galvanise and focus the eco outrage.

But on the anniversary of the largest oil spill in US history we are reminded of an important fact: just because there is no iconic victim of the spill, it doesn’t mean iconic animals weren’t seriously impacted.

Much of the ecological impact has so far been hidden, according to a BBC report today, partly because the spill happened out to sea, and oil was spilt directly onto the sea floor. But as time passes, scientists are slowly getting a better view of how much wildlife was affected.

In February, the BBC reported how video taken by US Navy deep sea submersible ALVIN is showing that the sea bottom around the site of the spill is littered with dead and dying sea fauna - generally invertebrate worms, corals and sea fans.

Yesterday, the BBC also reported how fishermen in Louisiana call the spill “The Monster under the Water” due to the impact it is having on their catch.

But when it comes to more iconic species, a newly published study by an international team of experts is as worrying.

According to this research, the tally of dead cetaceans (whales, dolphins and porpoises) across the northern Gulf of Mexico, which have been linked to the spill, has only just passed 100.

But it’s the dead whales we don’t see that matter more than those we do. The icons that are not, because they died quietly, out in the open ocean, where their bodies would be nibbled away to nothing or be left to fall silently to the sea floor, out of sight and out of mind.

How many humpback whales were affected? (Image: Brandon Cole / NPL)

In the study, the marine scientists estimated how often we come across cetacean carcasses in the Gulf of Mexico for 14 different species, including sperm whales, beaked whales, pilot whales, orcas and other dolphins. They specifically chose species for which we also know their abundance, survival rates and have stranding records.

That allowed the team to calculate the probability that we would even notice a whale or dolphin that had died at sea.

Their preliminary analysis makes stark reading, for those who fear the spill was an environmental catastrophe, and for those that believe it wasn’t.

Carcasses are recovered from, on average, 2% of cetaceans that die at sea, the scientists find.

That means 50 times more whales, dolphins and porpoises may have been killed by the BP / DeepWater Horizon spill than currently assumed.

Or to make it real, the spill may have killed 5000 of these iconic animals. To date.

There are caveats to this estimate, which the researchers spell out in their paper published in Conservation Letters.

For example, it would be hugely helpful if any whales killed did wash ashore, so autopsies could establish if the deaths were due to oiling, or other factors, including natural causes.

A lot of effort was spent by US government agencies searching for dead marine mammals after the spill; that may mean more than the usual 2% of cetacean bodies were recovered after this spill.

However, other evidence suggests that the carcass recovery rate of 2% is itself high.

This is partly because carcasses of some species, such as Cuvier’s beak whales and melon-headed whales, turn up relatively often. But because the deep diving animals are so elusive, scientists acknowledge they make extremely conservative estimates of their abundance.

That means the carcass recovery rate for these species is likely to be inflated, which inflates the overall figure.

Some species naturally fall prey to others (such as orca) so you wouldn’t expect the bodies of oiled whales necessarily to survive long anyway, again suggesting dead whales often disappear before they can be counted.

Finally, cetaceans are social, meaning pods or schools of the mammals may have been killed, and disappeared, en masse. These reasons suggest that the number of cetaceans killed in the Gulf of Mexico is more than 50x the number so far recovered, not less.

The researchers present their results as the starting point for the discussion.

But it’s a discussion that needs to be had: was a natural disaster without an icon a disaster for iconic species?

A rare photo of the rarely seen male midge (Pontomyia natans)

Some animals are so odd you have wonder at their survival.

Take the flightless marine midge Pontomyia. It isn’t new to science, though very little is known about it.

Nor is it unique in any single, stand out way.

Rather it is an animal that has such a bizarre life that it’s hard to imagine it really exists.

But exist it does, I’ve just found out. So please accept this invitation to sit back and wonder with me at some of the fascinating aspects of its life.

Let’s start with some headline facts: the flightless marine midge measures just 1mm long. Despite being a fly, it can’t fly. And male midges live their whole adult life in just one to three hours. Adult females don’t live anywhere near as long. Unlike almost all other insects, it lives in the sea, and no one can yet work out how it has managed to colonise islands thousands of kilometres apart.

The story of the discovery of the flightless marine midge is also an odd one.
It goes back some 85 years, when it was first found in 1926 by Patrick Alfred Buxton. There are some 5000 species of non-biting midge, but Buxton only came across Pontomyia when he caught some when out fishing.

Dragging his net across a lagoon to collect plankton, in Apia, Upola Island, Samoa, Buxton collected the midge at low or mid tide, shortly after sunset. At other times of the day, the midge seemed to disappear. Males placed in a beaker tried to swim, but Buxton never observed them skating across the water surface, leading him to declare the midge the first submarine insect known to science.

Little more was heard about the midge until the first detailed biological study was published in a rather obscure Japanese journal in 1932. The fly again disappeared until it was rediscovered by biologist Lanna Cheng in Enewetak Atoll of the Marshall Islands in 1975.

Female larva of the midge P. oceana

Lanna tells me another odd anecdote about this odd little fly. In the late 1970s she visited colleague John Collins of James Cook University in Australia, and announced her interest in these very elusive marine insects.

“He showed me what he thought were 'parasites' of his coral culture. It turned out that he had the only live culture of Pontomyia in the world.”

This serendipitous discovery led to establishing some captive cultures of Pontomyia for study.

Up until now I’ve referenced Pontomyia in the singular. There are actually five known species.

One is known only from a handful of adult females and larvae collected from the Carribean and Atlantic. It is yet to be given a formal scientific description.

A study of three of the other four species has just been completed by Lanna and Danwei Huang, both of the Scripps Institution of Oceanography at the University of California in San Diego, US. Both have kindly supplied the images of the fly and its larva, which are extremely hard to come by. Their study is one of the first scientific investigations of this odd little fly for decades. These midges live far away from their relative on the other side of the world, in the Indo Pacific Ocean.

Buxton initially collected Pontomyia natans (pontos for open sea and nyia for fly in Greek; natans for swimming in Latin), but it ranges from Japan in the north Pacific, to Australia and the Republic of the Maldives in the Indian Ocean. The other three species also range from Taiwan to Australia and Japan. All live fascinating lives.

Their larvae feed and live among algae or marine plants underwater, then the pupae float to the surface prior to emerging as adults. Males have more normal fly-like bodies, though they lack mouthparts, probably because there is no time to eat.

Some 20 minutes later, the females emerge. They lack a mouth, wings, antennae and walking legs. Completely immobile, the males have to drag them into the light. The two sexes mate, the females lay their eggs, then die. All within a matter of minutes. Within an hour or two, the males also die.

Considering their exceptionally short adult lives, the flightless midges have become masters at synchronising their appearance, using sunsets and sunrises to coordinate the emergence of the males and females. One species, P. oceana seems to live and die by the new and full moons.

But that can’t explain how a flightless, tiny, almost immobile blob-like fly, which has one of the shortest life spans of any insect, colonised islands thousands of kilometres apart.

One idea, seriously proposed, is that larvae dispersed on the backs of sea turtles.

Another is that they rafted on floatsam or algal mats that drifted across the seas.

However, Danwei Huang and Lanna Cheng’s new study, the first systematic review of the genus published in the Zoological Journal of the Linnean Society, suggests the species may have first split before the formation of Taiwan, and then further diverged between 11 to 26 million years ago, island hopping on rafts as they increased their range.

It’s this study that I have to thank for revealing these fabulous insights into such a weird and wonderful animal.

Danwei tells me that there is yet more to learn about these midges: their study has shown a remarkable range of genetic diversity among two of the species, suggesting that more previously unknown species may be waiting to be discovered.

It is the first such oddity I’ll report in this blog.

But it won’t be the last.

Let me know what your favourite weird creatures are and why. And let’s not forget Nature’s capacity to continually surprise.

This is a nod to the humble mushroom. It is a celebration of fungi.

Mushrooms are one of my least liked foods, and perhaps because of that, I don’t have a keen eye for wild fungi and couldn’t tell a Stinkhorn from a Death Cap, or a Cauliflower Fungus from a Chicken of the Woods.

But to get a quick idea of how glorious fungi can be - watch this clip below of fungi in the tropics, narrated by the BBC's own Sir David Attenborough.

Also, two bits of news remind me that among these humble life forms exist some of the most important, influential and vulnerable species on Earth; ones that have been ignored for too long.

The first is research published about a group of fungi known as “black yeasts”.

Black yeasts are generalist fungi – they are good at adapting to a variety of environments. Compared to other fungi, black yeasts can live at high temperatures, in acidic and alkaline environments and survive without water. Their cell walls contain high levels of melanin, a dark pigment producing their black appearance. That makes them resistant to antifungal agents. And remarkably, they can switch shape, growing as filaments, or more like conventional yeast, and then can form difficult to shift biofilms that adhere to surfaces.

They also like to come into our homes.

Domestic environments are, almost by definition, unnatural, stressful places for wildlife. Any fungi entering has to contend with unfavourable conditions – temperatures are kept artificially high, we don’t let water run freely around our houses, and we coat them in unusual substrates and chemicals, such as silicone rubber and disinfectants.

Black yeasts appear to have taken on this challenge: black fungi Cladosporium halotolerans and Aurebasidium pullulans have been found in Arctic glacial ice, and on bathroom surfaces, as both habitats are characterised by periods of extremely low water availability.

By living in our houses, these yeasts may be becoming even more stress tolerant, with potentially severe implications for our health. People are already known to have caught infections of black fungi from their bathrooms, while several species of the genus Exophilia cause various diseases including infections of the feet, nails and brain. Exophilia species have been found in domestic steam baths, drinking water and have just been found lurking in dishwashers.

Now scientists have published a warning that, by being in our homes, black fungi may be evolving traits that make them more pathogenic to humans.

For example, say Cene Gostinčar and colleagues in the journal Functional Biology, as black yeasts adapt to grow at higher temperatures they may become more likely to colonise warm-bloodied organisms – meaning us. By cranking up the heat, keeping rooms dry and using more disinfectants, we may be unwittingly selecting for new strains of disease-causing fungi that will be even harder to eliminate.

“We might have turned our homes into microcosms for the experimental evolution of the most resilient of microbial species, the adaptability of which might enable them to find new niches in the human body,” Gostinčar’s team writes.

How significant a problem this may be remains to be seen and the scientists’ warning shouldn’t be immediately turned into a medical scare story.

But it highlights the adaptability of this remarkable group of organisms, and how little we still know about them.

Which brings me to the second piece of news.

Fungi, the world over, are in danger of going extinct. Yet very few people of aware of them, or their plight.

Part of this lack of awareness is that fungi are often thought to be boring, even though the Hat Throwing Fungus is the fastest living thing on the planet (see it for yourself in the embedded video below), while there are more than 3,000 different types of mushrooms and toadstools in the UK alone.

Another key reason is that fungi are not included in the global IUCN Red List of Threatened Species, the most definitive and relied upon guide to species facing extinction.

Many other species groups are badly represented on the IUCN Red List - for example, though it includes over 12,000 plant species, fewer than one thousand are properly documented.

But fungi are all but absent.

Of the 17,291 animal, plant and fungal species that are globally redlisted, only one macrofungus, (the Critically Endangered White Ferula Mushroom) and two fungi that help form lichens (the Endangered Florida Perforate Reindeer Lichen and Critically Endangered Boreal Felt Lichen) are included.

There is no doubt that fungi populations are harder to survey and some mycologists aren’t sure to what extent it can be done.

Yet on a national level, more than 15,000 species of fungi have been evaluated. In those countries where extensive surveys have been conducted, 20-60% of macrofungal species are thought to be threatened.

This disconnect between national and international red lists means that fungi have essentially become missing from the conservation debate, say researchers Anders Dahlberg and Gregory Mueller in the journal Fungal Ecology.

Considering there may be more than 1.5 million species of fungi, 95% of which have yet to be formally described by science, thousands or maybe hundreds of thousands of fungi species may face an uncertain future. 

So here’s to putting humble fungi back on the agenda.

Let’s celebrate their glorious shapes and glorious names; from the Apricot Jelly Mushroom, Fuzzy Foot, and Satan’s Mushroom, to the Artist’s Conk, Scrambled Egg Slime and Chocolate Chip Lichen.

And let’s give them some more attention before it’s too late. If we don’t, you can be sure that some species, such as the black yeasts, may soon demand it.

Asiatic lions are extending their limited range

Conservation stories can be hard to tell. Not so the story of the Asiatic lion - which is a rare beast, in every sense.

New research just published highlights an increase in the numbers of Asiatic lions surviving in the Gir Forest of India.

The numbers aren’t large. From a base of 180 lions left in 1974, the population has risen to 411 by 2010.

But that’s impressive considering just a few dozen survived at the beginning of the 20th Century.

Even more impressive is how it was achieved (more of that later) and how lessons might be learnt that could help ensure the survival of other threatened big cats, such as snow leopards.

It may seem odd to say that conservation stories can be hard to tell. BBC Nature has recently reported on the decline in British oil beetles, and how an oil spill is affecting up to 10,000 rockhopper penguins on Tristan da Cunha island, a UK overseas territory.

But they are hard to report. Not because they don’t matter – they do, hugely so. And not because they are dull – they are not, often focusing on some of the world’s most beautiful, iconic, unique or interesting species.

They are hard to tell because they tend to follow the same narrative: a once populous species suffers an alarming decline in numbers due to habitat loss, poaching, invasive species or disease.

It can become numbing to repeatedly hear this basic plot line. So much so that we struggle to listen to the hugely complex web of ecological factors that can drive a species toward extinction, or help bring it back.

That’s why it’s important to celebrate the good news stories. If you care about wildlife, you’ll want to celebrate them for their own sake. But it’s important to highlight them for another reason: because success breeds success, and successful breeding programmes can help bolster each other.

Take India’s Gir lions.

Asiatic lions are a subspecies of the modern lion, which remains much more abundant in Africa, although its numbers there are dwindling. Being a subspecies doesn’t make the Asiatic lion less worthy – it's the last of a kind that once roamed the Asian subcontinent.

This big cat has a preference for dry deciduous forests, thorny forests and savannah, which have disappeared fast in India. But it's also worth remembering something that seems obvious: big cats have a taste for wild flesh.

The key to the Gir lions' revival appears to have been a dramatic increase in the numbers of wild ungulates. Between 1970 and 2010, numbers of chital, sambar, blue bull and wild boar among others rose 10-fold in total within the Gir forest in the southwest part of the Saurashtra region in the state of Gujarat, scientists report in the journal Biological Conservation.

Even more important, this new abundance of natural food meant the lions no longer relied on hunting livestock, which brought them into direct contact, and conflict, with local herders.

The increase in prey, and lions, has come as the result of decades of hard work and intensive management by conservationists in Gujarat.

The big cats are even tentatively dispersing out into their former range with a quarter of the population (35 males, 35 females, 19 subadults and 16 cubs at the last count) now existing outside the Gir forest. 

Lessons learned here could be vital for bringing other large carnivores back from the brink.

Which brings us to the snow leopard. Fewer than 7000 snow leopards are thought to survive in the mountains of central Asia.

New research has, for the first time, attempted to establish exactly what wild snow leopards in the Himalayan and Karakoram mountain ranges in Baltistan, Pakistan, are eating.

The study, published in the European Journal of Wildlife Research, examined the faeces, or scats, left by these elusive animals.

It revealed that 70% of what snow leopards are eating in the region is domestic livestock, and a range of livestock at that: 23% of the biomass eaten came from sheep, 16% from goat, 10% from cattle and the rest from yak or yak-cattle hybrids.

This heavy predation on domestic livestock appears to be a likely cause of conflict with local inhabitants - and when conflict between humans and wild animals occurs, there tends to be only one winner.

So it’s clear that conservation initiatives need to focus on mitigating this conflict by minimising livestock losses – and one way to do that, the Gir lions recovery tells us, is to boost wild prey numbers once more.

(On a related note, news arrived late last month, sent by the Snow Leopard Network, (SLN) that the Mongolian government has reversed an earlier decision to allow the killing of four snow leopards in the country. The volte face came after pressure from conservationists, including Charudutt ‘Charu’ Mishra, executive director of the SLN and a past winner of the Whitley Gold Award.)

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