Sloth update: still symbiotic, still super cute

Sloths popped into the news a while ago, as one of the mysteries of their behaviour – why, once a week, they climb down from the canopy to poo on the ground – was examined in a new paper.

Sloths are known for their leisurely lifestyle in the treetops, but there is more to them than meets the eye. A complex mini-ecosystem involving moths and algae may help keep the sloth both camouflaged and fed, and be the cause of their odd weekly habits. Pieces in the New York Times and National Geographic explain it all.

“The sloth is not so much an animal as a walking ecosystem. This tightly fitting assemblage consists of a) the sloth, b) a species of moth that lives nowhere but in the sloth’s fleece and c) a dedicated species of algae that grows in special channels in the sloth’s grooved hairs. Groom a three-toed sloth and more than a hundred moths may fly out. When the sloth grooms itself, its fingers move so slowly that the moths have no difficulty keeping ahead of them.” Nicholas Wade, New York Time

Sloths popped up again yesterday. Did you know what noise a sloth makes?

Climate change pushing tropical trees upslope ‘exactly as predicted’

This article was first published on You can read the original here.

Tropical tree communities are moving up mountainsides to cooler habitats as temperatures rise, a new study in Global Change Biology has found. By examining the tree species present in ten one-hectare plots at various intervals over a decade, researchers found that the proportion of lowland species increased in the plots at higher elevations. The study, which was undertaken in Volcan Barva, Costa Rica, adds to a growing body of evidence that climate change is having an impact on species range distributions.

As climate change leads to warmer temperatures, species must respond if they are to survive. One way to do this is to migrate to new habitats that become suitable (and away from old ones that become unsuitable); another way is to adapt to hotter temperatures, but the speed of climate change may be too fast for some species to evolve to keep up. In some cases, if their physiology permits it, species may be capable of tolerating increases in temperature, but the likelihood of this is unknown.

The researchers first turned to herbarium records to calculate the preferred temperature of thousands of tree species, by looking at the geographic location of sampling locations and the temperature ranges they encompassed. With the temperature preferences for each species known, it was then possible to calculate a ‘community temperature score’ for each of the ten study plots, by averaging the preferred temperatures of all species present. A high community temperature score indicated an abundance of species found in the hot lowlands, whereas a low community temperature score reflected the presence of high altitude species from cooler habitats.

Looking up at a giant tree in the Costa Rican rainforest Photo credit: Rhett A. Butler /

Looking up at a giant tree in the Costa Rican rainforest Photo credit: Rhett A. Butler /

Plots were monitored over the course of a decade, and in nine of the ten plots the community temperature score increased. This indicates a shift in species composition, with the relative abundance of lowland species increasing over time “exactly as predicted under climate-driven upward species migrations,” Kenneth Feeley, lead author of the study with Florida International University and Fairchild Tropical Botanic Garden, told

These changes corresponded to a mean thermal migration rate of 0.0065°C per year. However, over the past 60 years regional warming has been 0.0167°C per year, so the average migration rate observed across plots is not fast enough to keep up with the rate of warming. Still, encouragingly, when looked at individually, migration in 4 of the 10 plots did keep pace with regional warming.

Changes in species composition can be the result of different processes: species abundance can change without shifts in the overall range distribution, ranges can shift, and ranges can expand or contract. Identifying which of these underlies changes in species composition is important, because “depending on which of these processes is occurring, predictions for the future of ‘migrating species’ will vary from positive (under range expansions), to neutral (under range shifts) to dire (under range contractions),” Feeley explains.

To examine the specific causes of the compositional shifts in the study plots, the researchers measured stem growth, recruitment (the establishment of new trees), and mortality. They found that the main driver behind the increase in the relative abundance of lowland species upslope was in fact the disproportionate death of higher elevation species.

“Our results indicate that dieback is happening much faster than expansion. This means that species’ ranges will shrink. As ranges shrink, species will be more and more prone to extinction,” Feeley said.

Forested mountains in Costa Rica, where tropical trees communities are changing in response to climate change. Photo credit Kenneth Feeley

Forested mountains in Costa Rica, where tropical trees communities are changing in response to climate change. Photo credit Kenneth Feeley

An earlier study by Feeley and colleagues investigated related questions in the Peruvian Andes and came to similar conclusions, suggesting that their findings may be generally applicable across the tropics.

“The rates of migration that we have documented for the forests of Costa Rica are remarkably similar to what we found in the Peruvian Andes. The rates are also fairly close to the maximum rates of migration recorded for tropical trees during the warming period that followed the last glacial maximum. As such, it appears that what we are observing is trees moving at their fastest,” Feeley said. “In the past, this was fast enough; it is not fast enough now and it certainly won’t be fast enough in the future,”

While range contractions increase the likelihood of extinction for individual species, they also have a broader impact on patterns of biodiversity.

“As species experience dieback at the trailing edges of their distributions due to temperatures becoming intolerably hot, we will get decreases in local diversity through a process that has been termed ‘biotic attrition’,” Feeley said. If species are able to shift their ranges upslope, and not just suffer dieback in the lowlands, “then we may expect an increase in alpha (local) diversity in the mountains over long time periods as large numbers of species move up out of the lowlands and into the highlands. In this case, the real losses of biodiversity are expected in the lowlands where there is no known pool of ‘hot-adapted’ species waiting to fill in the lowlands after the existing species emigrate.”

Migrating to track climate change – either by moving up mountainsides or by moving towards the poles – is not easy: temperature is not the only factor that determines whether a habitat is suitable for a species, it is just the simplest to study in order to predict how species might respond to our warming world.

“Other climatic factors such as precipitation and seasonality can be hugely important for some species as can other non-climatic factors such as soil type and slope. Furthermore, biotic factors such as competition, predation, herbivory, disease, and mutualisms, may also be just as if not more important,” Feeley explains.

“The more realistic you make the models, and the more variables you consider, the number of future options available to species almost invariably decreases.” Even if species are capable of keeping pace with climate change and move upslope, they will still suffer a reduction in available habitat as land area decreases the further up the mountain they go.

“For example, in Costa Rica there is over 6.5 times as much land area between 1800 m and the highest plot at 2800 m as between 2800 m and the highest point in Costa Rica at 3820 m elevation,” the scientists write. Species already adapted to cooler high elevation temperatures will have nowhere to migrate into. And other problems also face tropical species that are a long way from a mountain to begin with.

“Within the tropics there is no latitudinal gradient in temperature. This is very important because it means that species cannot migrate towards higher latitudes to escape the heat but instead must migrate to higher elevations where it does get invariably cooler,” Feeley explains. “For lowland species in the middle of the Amazon basin where it is remarkably flat, this means that they will have to migrate huge, perhaps impossibly huge, distances before they experience any sort of relief.” Add to that the destruction of habitat, and movement becomes more challenging still.

“If species cannot migrate upslope, then their potential responses to climate change are greatly limited. Indeed, the only options left are to adapt or to acclimate. And given the speed at which the world is now changing, I think it is safe to say that adaptation is not a viable option, at least for large long-lived trees with long generation times. So the question becomes, can lowland trees acclimate to climate change?” Feeley posits. “The future of global diversity depends on the answer to this question but right now we are nowhere close to having that answer.”

Species in the lowland tropics inhabit one of the hottest regions on earth, so it is impossible to gauge their heat preferences above present-day temperatures by looking at their range distributions. However, understanding the upper limit of species’ heat tolerance would vastly improve predictions about species survival in a warming world.

Map showing the team's study plots (green squares) stretching from the lowlands up the mountain to a height of 2800 metres. Image credit Kenneth Feeley.

Map showing the team’s study plots (green squares) stretching from the lowlands up the mountain to a height of 2800 metres. Image credit Kenneth Feeley.

“By far the single most important factor is how much warming the species can tolerate. If they can tolerate a significant amount of warming, then our predictions are relatively sanguine. If species are intolerant of warming, then their future will be dependent on migrations and predictions for the tropics become very bleak,” explains Feeley.

To date, the majority of studies examining the potential impact of climate change have focused on North America and Europe.

“In general, there is a dearth of studies looking at the impacts of climate change on the distributions of tropical species. This is despite the fact that the vast majority of species are tropical,” Feeley told “We desperately need to fill the void and have more studies from the tropics. To do these studies we need a better and more systematic system of ecosystem monitoring plots and more importantly, but also harder, a better understanding of the complex abiotic (non-biological) and biotic (biological) factors that regulate species distributions and dynamics.”

Feeley and colleagues continue to monitor their study plots in Costa Rica and Peru, and are expanding their research to better understand the processes that determine species range distributions and movements.

“We are in the initial phase of a large-scale transplant study in which we are moving thousands of seedlings of dozens of tree species up and down the slopes of the Andes under various experimental treatments in order to identify the specific biotic and abiotic factors that limit their distributions,” he says. “Once we have this information we can build it into improved predictions for the fate of these species on a warmer planet.”

The best hope for conserving forests in the face of climate change, and climate-driven migrations, is to anticipate species movements, says Feeley.

“We need to expand the time scale of our thinking and determine not just where species are today but where they will be a hundred years from now. And then we need to protect both of those places and everything in between.”

Paper: Feeley K.J., Hurtado J., Saatchi S., Silman M.R., and Clark D.B. 2013. Compositional shifts in Costa Rican forests due to climate-driven species migrations. Global Change Biology, Available Online. DOI: 10.1111/gcb.12300

The evolution of cooperation: communal nests are best for ruffed lemurs

I wrote this article for where it was first published; you can read it here.

Raising young lemurs in communal crèches benefits both mothers and offspring, a new study has found. Andrea Baden and colleagues, of Yale University, studied a group of black-and-white ruffed lemurs (Varecia variegata) in Ranomafana National Park, Madagascar. This is the first study to examine the consequences of different parenting strategies in the ruffed lemur. By observing how mothers split their time between different activities, they discovered that crèche use – where infant care was shared between mothers – corresponded with an increase in the amount of time a mother spent feeding. For young lemurs, being raised in communal nests actually gave them a higher chance of survival.

Dr Andrea Baden with a black-and-white ruffed lemur.

Black-and-white ruffed lemurs are large-bodied social primates that live in the eastern rainforests of Madagascar, and have an almost entirely fruit-based diet. Reproduction is synchronized, and in this study seven females gave birth during a two week period. Unlike many primate species, young are born undeveloped, even unable to cling to their mothers’ backs, so they must be cared for in nests until they are big enough to travel independently.

The study, published in Behavioral Ecology and Sociobiology, found that females built a number of nests during the gestation period, with some building as many as fifteen. Females gave birth to litters of 2-3 young, and for the first few weeks of life infants were cared for solely by their mothers. Communal nesting, typically involving two litters sharing a nest, began when the young lemurs were six weeks old. Six of the seven mothers nested communally at least once, although the amount of time their young spent in crèches varied. Two of the mothers only rarely or never shared nests. But females who shared nests were able to spend significantly more time feeding than those that did not participate in communal nesting, and time feeding and foraging increased with increasing crèche use. All infants survived until the start of the communal nesting period, but infant mortality was subsequently significantly higher for single nesters than communal ones.

Behavioral observations were combined with genetic data which made it possible to work out whether it was only related lemurs that were assisting each other. The study found that although relatedness and long-term social relationships were positively correlated with the extent of communal nest use, “not all cooperative dyads [two individuals] were related, and not all related dyads cooperated with each other.” The benefits of communal nesting were the same regardless of whether the lemurs were related to each other.

“Kinship may have helped the evolution of cooperative breeding in primates but the mutual benefits may outweigh the costs of helping, irrespective of any family relationships” says Baden, who believes that the current research sheds light on understanding just how communal breeding evolved. “Our results contribute to a growing body of evidence suggesting that kin selection alone cannot explain the extensive cooperation observed in many animal taxa.”

In six years of study, only one reproductive event was observed. Such rare and unpredictable reproduction makes research a challenge. The scientists point out that, despite a relatively small sample size, their study “nonetheless represents reproductive output over 48 lemur-years”. The timing of reproduction is not fully understood, but it is likely that the lemurs respond to environmental cues.

“In 2008, Cyclone Ivan hit. More than 2,000 [millimeters] of rain fell over the course of three days. It’s possible that this somehow signaled the likelihood of a highly productive fruiting year”, Baden told

Black-and-white ruffed lemurs are classified as Critically Endangered by the IUCN, having suffered a decline of 80% over the last 27 years. Baden fears that their fruit-dependent diet and sporadic reproduction will make them even more at risk in the future. Ruffed lemurs are “among the first animals to disappear when habitats become disturbed or degraded, as large fruiting trees are typically targeted during selective logging” Baden explains. “My concern is that climate change and the erratic climatic variations that come with it might have severe and significant repercussions for ruffed lemur life histories.”

Female black-and-white ruffed lemur feeding.  Photo by Andrea Baden.

Female black-and-white ruffed lemur feeding. Photo by Andrea Baden.

One of the most surprising aspects of the results for Baden was the extent to which female behavior changed during the breeding period. “It really seems like infants are driving sociality in this species. In non-reproductive years, females were almost asocial.”

“It’s fascinating” Baden added, “by having a litter of three infants and then communally rearing those babies, females can essentially make up for two lost years of reproduction. These animals have really perfected their parenting system to adapt to these reproductive lags.”

Baden feels that lemurs are frequently overlooked in discussions of primate social evolution. “Ruffed lemurs are really interesting because they actually share several traits – things like fission-fusion social dynamics and cooperative infant care – with higher primate species that many would consider to be quite socially complex” Baden said. “I think we’re starting to learn that, while lemurs perhaps differ from higher primates in several of their ‘solutions’ to evolutionary problems, they have come up with some really interesting and unusual adaptations that can still inform our broader understanding of primate evolution.”

Data collection in the field. Photo by Andrea Baden.

Data collection in the field. Photo by Andrea Baden.

Infant black-and-white ruffed lemur. Photo by Andrea Baden.

Infant black-and-white ruffed lemur. Photo by Andrea Baden.

Reference: Baden A.L., Wright, P.C., Louis E.L., Bradley B.J. (2013). Communal nesting, kinship, and maternal success in a social primate, Behavioral Ecology and Sociobiology. DOI 10.1007/s00265-013-1601-y

Introducing Dinner Table Science, and my guest post

I’m excited to be featured on the super cool blog Dinner Table Science! Dinner Table Science has a mission: to get people talking about fascinating facts and exciting discoveries. In their own words, they “want dinner table small talk to be filled up with little amazing things someone learned on the internet that day”. Here’s my post, on the mysterious life of the Brazil nut tree, but I recommend that you also take a look at some of the many other absorbing posts on all aspects of science.

Dinner Table Science

I have some very exciting news for all of my readers – this week my very first guest blogger, Claire Salisbury, comes to Dinner Table Science to talk about some 4-way mutualism in the rain forest!  Claire is a biologist with a particular interest in and love of the rain forest.  Her first taste of the jungle was in Belize, on an expedition she joined while she was still just in high school, and after that she couldn’t wait to find her way to the ultimate jungle: the Amazon!  She’s spent many months in Peru since then, chasing leaf cutter ants and birds, and carrying out research both as an undergraduate student and as a PhD candidate.  Now she is a postdoc, and she hopes to study biodiveristy in tropical rain forests, and work to conserve these amazing areas of our planet.   To read or subscribe to Claire’s…

View original post 642 more words

The invisible moth: a beautiful illustration of natural selection

Moth camouflage Ecuador cloudforest Bellavista

This moth, found in the cloudforest in Ecuador (at Bellavista, which I have written more about here), blends in perfectly with its background, even down to the lichen spot mimics on the tips of its wings. The purpose of colour patterns such as these is to make the outline of the moth hard to detect, thus making it difficult for predatory birds to distinguish it against the bark of the tree. The success of the camouflage is a question of life or death for the moth. A moth that is a poor match is more likely to get eaten, and one that is a good match is more likely to live. Therefore the next generation will be dominated by descendents of moths that were successful at blending in. This is natural selection, famously stated (and often misunderstood) as ‘survival of the fittest’, with the most camouflaged moths in this example being the most fit. The predatory birds provide the ‘selection pressure’ on the moth population, which has evolved in response to this pressure to be so well camouflaged.

However, the process is dynamic: the birds are also responding to the moths. A bird who is better able to pick out a camouflaged moth against the tree will be better fed, and better able to raise a brood. So again those most successful (the fittest) will contribute more to the next generation than those less fit. Greater visual acuity will in turn select for better camouflaged moths, and so on, resulting in an ongoing coevolutionary relationship. In evolutionary biology, the ‘Red Queen hypothesis’ relates to cases such as these. The name refers to Alice in Through the Looking Glass, by Lewis Carroll, where Alice is told by the Red Queen that ‘here, you see, it takes all the running you can do, to keep in the same place’.

Quito to Rio: the cloudforests and hummingbirds of Ecuador

We landed in Quito just before midnight on New Year’s Eve, watching tiny fireworks silently exploding over the city. At that point, the full extent of our plan was to reach Rio in time for a return flight 15 weeks later. After a couple of days wandering in a jet-lag and high-altitude daze around Quito’s busy streets, we escaped to Mindo, two hours away by bus. This journey took us up and out of the valley in which Quito sits between volcanic peaks, and then wound down into the wet and lush cloud forest on the western slopes of the Andes. Mindo is a quiet little place, surrounded by forests and hills which often disappear into the clouds. We arrived in the rain at dusk, and made our way along virtually deserted streets to our accommodation at Cabanas Armonia. This is an orchid garden masquerading as jungle, and we were led to our little cabin, one of a handful tucked away amongst the plants. After the dry, thin air of Quito, the humidity, the smell of the wet vegetation, and the chorus of frogs, were wonderful.
The path to our cabin, Cabanas Armonia, Mindo, EcuadorPrivate ensuite cabin with hammock, Cabanas Armonia, Mindo, Ecuador

Highlights of our stay at Cabanas Armonia included lazy birdwatching from our private hammock, with toucans and hummingbirds among the many species that regularly passed by. Wandering through the garden finding some of the roughly 200 species of orchid that are grown here was fascinating. Orchid cloudforest Mindo Ecuador

Orchid cloudforest Mindo Ecuador Orchid cloudforest Mindo Ecuador Orchid cloudforest Mindo Ecuador Orchid cloudforest Mindo Ecuador Orchid cloudforest Mindo Ecuador Orchid cloudforest Mindo EcuadorAnd having a delicious breakfast, outside, with a frenzy of hummingbirds zipping around so close to us that we could feel the air from their wings, made getting out of bed easy. Breakfast terrace Cabanas Armonia Mindo Ecuador

Breakfast Cabanas Armonia Mindo Ecuador

The family that owns Armonia maintains feeders for the hummingbirds, and these tiny birds drink litres of sugar water between them every day. Watching and listening to them whirr, chirp and squeak is hypnotic. 

And catching them with your camera becomes an endless challenge.

Hummingbird Mindo EcuadorHummingbird Mindo Ecuador Hummingbird Mindo Ecuador Hummingbird Mindo Ecuador Hummingbird Mindo Ecuador Hummingbird Mindo EcuadorHummingbird Mindo EcuadorHummingbird Mindo Ecuador

Hummingbirds have co-evolved with the flowers that they feed from, sometimes resulting in such close relationships that the length and curve of a beak perfectly matches the dimensions of the host flower. This ensures that the bird has access to nectar and the flower is guaranteed a pollinator. However, in other cases, as in one frequent visitor to a flower next to our cabin, species bypass this reciprocal relationship and simply pierce the base of the flower to access the nectar without any pollination benefit to the plant. Hummingbirds were a frequent sight on our Andean journey south, through Ecuador and Peru, and as ever Attenborough explains it best:

In between poring over our guidebooks and hatching a tentative plan to visit Ecuadorian jungles, volcanoes and colonial cities en route south to Peru, we went for walks in the countryside around Mindo. Strolls along the roads leading out of town led through verdant green valleys, coffee plantations, dripping tropical vegetation, and sightings of gaudy tanagers, toucans and aracaris, and a stunning quetzal. We took a rickety ‘cable car’, more accurately a cage on a wire, across a steep valley to walk along trails that linked a series of waterfalls in the forest. And we tried to reconcile the warmth and tropical surroundings with Twelfth Night celebrations in the church, and the curious nativity scene outside it.

On our way back to Quito a week later we had arranged to visit Bellavista Cloud Forest Reserve, 1000m higher up the mountains than Mindo. We got off the bus at a small village called Nanegalito, and were quickly approached by the driver of a pick-up truck taxi who drove us up the steep and winding single track lane to the lodge. The lodge is an incredible place, within a private reserve that protects 700 hectares of hugely biodiverse cloud forest. There is an extensive trail system, comfortable accommodation, excellent food, and it is renowned for its birding. Such luxury and biodiversity meant that the lodge itself was way beyond our tight backpacker budget – but it is still possible to stay and explore the reserve: a small research station doubles as basic hostel accommodation, but incredibly, very few people make use of this. This is a big shame because the forest around Bellavista is like nothing we had seen before – huge tree ferns, and trees dripping with multiple layers of vegetation, shrouded in ethereal mist and cloud which sometimes broke to reveal the  precipitous view down to the valleys below. The trails were easy to follow, and took us up and down steep ravines to hidden streams. Bellavista cloudforest Ecuador Bellavista cloudforest EcuadorBellavista cloudforest EcuadorBellavista cloudforest Ecuador

Bellavista cloudforest Ecuador

Ecuador (108) Ecuador (102)The research station accommodation was basic, but we had a warm bed and a hot shower, and pots and pans to cook with over a gas stove. Fellow residents included scientists from the States, their Ecuadorian research assistants, a couple of temporarily captive birds that were the focus of their studies, a sink-full of beetles collected for a small project, and a noisy mouse who helped itself to a chunk of banana in the kitchen. The captive birds were, of course, early risers and woke us from their room next to ours with an ear-splitting duet at dawn. Electricity is from a generator that is only run for a few hours a day, and as we were virtually on the equator it got dark about 6. Evenings were spent quietly by the light of candles and headtorches, listening to the myriad noises coming from the forest.  Ecuador (97) Ecuador (96)Ecuador (95) Ecuador (94) Ecuador (93)

It was the duetting of the birds that interested the scientists, as explained by Dr Eric Fortune in this video. The song he plays is the one that woke us each morning. It would wake the dead.

After ten days of cloudforest meanderings we made our way back to Quito, pausing to pose at the equator for a photo, bedraggled in wet and muddy clothes from the last hike along the trails that morning. Everything we had was damp, and had been for days, and just as the humidity had been so welcome after the dryness of Quito, returning to dry land was also a great relief after such a soggy time. Our clothes soon covered every available surface in our hostel room, and were dry by the morning.