Wednesday, 24 June 2015

Racehorses are reaching the finish line faster

Scientists have just confirmed a pattern that long-time fans of elite horse racing may have noticed over the years: British Horses are getting faster. This is particularly true of equine sprinters—some of whom may be running nearly 13% faster than their predecessors who competed in 1850 (when detailed records were first collected). Over the last 15 years alone, short-distance racers have increased their speed by approximately 0.11% per year, which corresponds to gains of 1.18 seconds, or more than seven horse lengths.

These findings result from analyses of over 616,000 race times run by nearly 70,400 horses in the UK between the years of 1850 and 2012. Researchers from the University of Exeter’s Penryn Campus compiled the massive dataset in the hopes of resolving contradictory patterns reported by previous studies. In particular, they were curious about the suggestion that horses are approaching a speed plateau.

Image courtesy of Froggerlaura

Lead author Patrick Sharman, from the University of Exeter’s Centre for Ecology and Conservation, said: “There has been a general consensus over the last thirty years that horse speeds are stagnating.” However, this seems counterintuitive, given evidence that swiftness is passed down through the generations, and therefore can be selected for—and potentially enhanced—during the breeding process.

Whereas previous studies have predominantly focused on results from middle- and long-distance elite races (8-12 and 14-20 furlongs, respectively), the current dataset also looks at sprint competitions (5-7 furlongs). It also takes into account variations in environmental conditions that can influence horse performance. The full dataset, which focused on races run on flat turf in the UK, included information on race course, ground softness, number of runners, name/age/sex of each horse, race distance, method of timing (automatic or manual), year of race, and, of course, horse speed.

Although the improvements in speed were most noticeable for sprinters, modest increases were also seen amongst middle- and long-distance runners. However, year-on-year changes were not linear, indicating that they have not been consistent over time. Alterations to riding style appear to be responsible for dramatic improvements in performance during the early 1900s and in the final quarter of the 20thcentury. The first period of rapid improvement seems to have resulted from jockeys’ shortening their stirrups and crouching while riding. The second increase in speed has been associated with further shortening of the stirrups—though increased commercialisation of the sport around this same time may have led to an influx of imported horses that may have improved the quality of the gene pool.

Image courtesy of Anthony92931

Despite this tantalizing connection between genetics and speed, the study’s authors are cautious about definitively declaring that decreases in racing time result from human-caused equine evolution. For one thing, there are certain potentially confounding factors—such as horse diet and individual jockeys’ racing techniques—that they were not able to consider in the study. For another, the field does not currently have enough information on equine genetics to fully understand the impact of our horse husbandry techniques on thoroughbred racing performance.

However, the authors suggest that this could be rectified by a detailed analysis of thoroughbred pedigrees. Alastair Wilson, coauthor of the study, said: ”The next step is to find out how much of this improvement is actually down to genetic change. It could be that breeders are effectively targeting the genes that make horses fast - at least over the shorter sprint distances–and we are seeing the result of this. Alternatively, current improvement could be driven entirely by non-genetic factors, for instance improvements in training. At the moment we just don’t know. However, by analysing the performance data in conjunction with knowledge of how horses are related to each other, we should be able to determine just how important genes are for determining speed, and whether the genetic makeup of the thoroughbred population is changing through time”.

In the meantime, don’t expect sprinters to slow down any time soon. Middle- and long-distance runners may be nearing their maximal speeds, but short-distance racers could continue to break records for years to come.
Sharman, Patrick and Alastair Wilson. 2015. Racehorses are getting faster. Biology Letters 11(6).

Monday, 2 February 2015

Behavioral plasticity in pumas may be a boon to smaller predators

In many areas where human activities have resulted in the decline of top predators, smaller carnivores--species such as foxes, raccoons, and rats--benefit from no longer being prey items, as well as from the decreased competition over resources in the habitat. Until recently, this "mesopredator release" was thought to occur only when apex carnivores--things like tigers, wolves, and wild dogs--had been locally extirpated, leaving vacancies in the food web that their smaller brethren could step in to fill. However, a new study on pumas suggests that mesopredator release could happen by another mechanism altogether: changes to the feeding behaviors of top predators.

Scientists from the University of California's Santa Cruz campus discovered this by collaring and tracking 30 pumas between 2008 and 2013. Every four hours, the collars collected information on the location of the cats, and the resulting data points were plotted on a map. Where points were clustered, the researchers suspected a kill site and went to investigate for signs of predation. For logistical reasons, it wasn't possible to visit all potential kill sites, so, to overcome this difficulty, the researchers created computer models into which they could plug variables associated with confirmed kills--factors such as how long the pumas stayed there, whether they were there at night or during the day, and how far the cats strayed from the area. These traits were then used to determine the likelihood that the putative kill sites were, in fact, the location of a puma kill.

Close-up of a puma. Image courtesy of Bas Lammers.

What made this information so interesting was that the hunting data could be plotted on maps showing human housing densities. The study area, the Santa Cruz Mountains of California's Central Coast region, encompassed a range of anthropogenic sites, from rural areas with fewer than 1 house per hectare, to suburban locations with nearly 10. Along this disturbance gradient, the hunting behavior of pumas--specifically, female pumas--varied. As housing density increased, these huntresses spent up to 42% less time consuming prey. Their site fidelity was 36% lower, and the farthest distance traveled from the kill site was up to 31% higher.

To make sense of these numbers, it is necessary to understand a bit about the feeding strategies of apex predators like pumas. They can expend quite a lot of energy while stalking, chasing, and taking down prey. These calories can be replaced by eating whatever has just been caught, but big carnivores don't have large enough stomachs to accommodate many of their prey items--things like deer, for example--in a single sitting; instead, the hunters have to drag the body somewhere safe and revisit it until they've had their fill.

Mountain lion eating. Image courtesy of
Mountain lion eating. Image courtesy of Benjamint444

The current results suggest that this is a much trickier prospect for female pumas living in anthropogenically disturbed areas. These cats weren't able to spend as much time eating, and seemed to roam much farther from where they had stashed their kills; the low site fidelity values suggest that many of the animals left the area altogether. Given these figures, it is, perhaps, unsurprising that some of the hunters in these areas were estimated to kill as many as 20 more deer per year than pumas living in the most rural areas. These data suggest that predators in high-human-density areas are having to target more prey because they are starting over after being interrupted while feeding on their previous kills.

Males seem to get off easy because they already spend less time at kills; they are adapted to eat quickly and head back out to patrol the borders of the large territories they defend. The size of their home ranges (up to 170 square km) also means that if humans become disruptive in one area, the cats can withdraw to more natural spots for a bit of privacy. Given that male territories only have approximately 16 houses per square km, this isn't too hard to do. Female pumas, however, don't have as much flexibility; their territories are smaller (as small as 51 square km), and may comprise only exurban or suburban land; their home ranges sometimes contain as many as 27 houses per square km.

Mountain lion kitten about to be outfitted with a tracking device. Image courtesy of the NPS.

Female pumas must also take care of kittens, a responsibility that requires them to bring down even more prey. To adequately feed their young, mothers may need to make more than a dozen additional kills per year. For females living in high-human-density areas, where disruptions to feeding sessions are already inflating hunting rates, this could be untenable; these mothers could begin to lose weight, suffer poor health, or even be driven to abandon their young. Indeed, the researchers provided anecdotal evidence of the last of these possibilities, suggesting that puma populations in human-disturbed sites may only be viable so long as they are replenished by young pumas migrating in from more rural areas.

While this is bad news for pumas, it is potentially great news for mesopredators. Female pumas are leaving a larger number of kills for longer periods of time, giving scavengers more of an opportunity to swoop in and have a free meal. This increased source of nutrition could allow the ecosystem to sustain larger populations of middle predators and give individual animals the energy boost they need to live longer and/or procreate more successfully. Beneficiaries could include a range of species, from raccoons and foxes all the way up to coyotes. Additional work would need to be conducted to explore whether these species are commoner or more successful in more human-dense areas, and, if so, whether those patterns can be directly attributed to puma behavior rather than other characteristics of anthropogenic environments.

Image courtesy of Tony Hisgett.

As the authors point out, "behavioral responses are often overlooked as ecosystem drivers in modified systems, overshadowed by population declines and extirpations." Their current study, however, shows that behavioral flexibility can allow species to persist in modified environments--but that this persistence may come at a cost, and have widespread implications for the habitat.
Source material: Smith, Justine A., Yiwei Wang, and Christopher C. Wilmers. 2015. Top carnivores increase their kill rates on prey as a response to human-induced fear. Proceedings B. 282: 20142711.

Saturday, 24 January 2015

Pink birds in the red: conservation of flamingos

Flamingos have been described as both the most charismatic of all bird species and one of the most recognizable. While some might argue with the former claim, few would challenge the latter. Thanks to their bright, cheerful plumage, hefty, crooked bill, and spindly legs—one often held aloft in that iconic balanced position—flamingos can easily be identified by people around the world.

Though the birds are often referred to generically as ‘pink flamingos’, there are actually six different species: American (also called Caribbean, Cuban, or rosy; Phoenicopterus ruber); greater (Phoenicopterus roseus); Chilean (previously also known as red-kneed; Phoenicopterus chilensus); lesser (Phoeniconaias minor); Andean (Phoenicoparrus andinus); and puna, or James (Phoenicoparrus jamesi). Evidence of ancient flamingo ancestors has been unearthed in both Australia and Antarctica. Today, however, free-living flamingos are only found in North America (American), South America (Andean, Chilean, and puna), Europe (greater), Africa (lesser and greater), and Asia (lesser and greater).

All extant flamingos require habitats linked by a single common feature: shallow saline pools. These can be fed by underwater springs, ocean waves, rivers, and—perhaps most importantly—rain. Water in flamingo habitats is often saltier than the sea and may contain compounds that are toxic to many species if consumed in large doses. This seemingly inhospitable habitat is perfect for brine shrimp, small molluscs, diatoms, and cyanobacteria—all potential prey items for flamingos. Because so few animals can tolerate extremely salty environments or figure out how to collect the tiny particles of food available there, flamingos have been able to exploit this niche virtually uncontested.

Lesser flamingo
Lesser flamingo

It can be difficult to census flamingos because they tend to live in such remote, impenetrable wetlands. To make matters worse, the birds have a habit of relocating frequently and unexpectedly, which means that researchers may show up to known flamingo haunts only to discover they have just been vacated in favour of grounds that are tens or even hundreds of kilometres away. Available data indicate that global population sizes vary widely from one species to the next; the least abundant species is the Andean, with only 34,000 individuals, while the most common is the lesser, with as many 3.2 million birds.

These numbers, however, belie the complexity of flamingos’ conservation situations. All three South American species are threatened by anthropogenic disturbance and habitat destruction; while Andeans are considered ‘vulnerable’, punas (100,000 individuals) and Chileans (200,000 individuals) are listed as ‘near threatened’. This is also the status of lesser flamingos, 90% of which breed at a single site that is threatened by industrial developers. Only the American (330,000) and greater (680,000) flamingos are listed as being of ‘least conservation concern’.

American flamingo. Image courtesy of Martin Pettitt

It’s not entirely surprising that so many flamingo species should be under threat; the pink birds have a long history of unpleasant interactions with humans. Phoenician traders are reported to have transported flamingos to Cornwall, where the birds were passed off as phoenixes and traded for tin. Flamingos were kept in captivity by the Egyptians and some groups of Native Americans, and flamingo meat was enjoyed people of several cultures—though perhaps most of all by the Romans, who have recorded for posterity recipes for properly preparing flamingo tongues for delectation. Even today, the birds are sport-hunted or poached across their range. The illegal slaughter of dozens of adult birds caused an uproar in India in early 2012 because it occurred when hundreds of preeminent ornithologists and birdwatchers were visiting the Gujarat for the Global Bird Watcher’s Conference.

Flamingos are also known to be negatively impacted by nearly all forms of human traffic, including planes, boats, and all-terrain vehicles. Both the noise and visual disturbance caused by these vehicles disrupts feeding and breeding efforts and may even lead to habitat abandonment. Ironically, much of this traffic is associated with ecotourism activities that are supposed to generate funds for protecting the birds over the long term.

Greater flamingo. Image courtesy of Yathin S Krishnappa

Even more worrying is the fact that flamingo habitat is under nearly constant threat from human activities such as mining, farming, and urban expansion. These activities can reduce the quality of feeding and breeding sites by altering water pH, introducing invasive species that out-compete flamingos for food, removing water (for use in irrigation or to facilitate easier access to minerals), and introducing dangerous structures such as power lines, with which flamingos can become entangled while flying. In the Mediterranean, where native greater flamingos often come into contact with escaped lesser, Chilean, and American flamingos, researchers worry about the potential detrimental genetic and behavioural effects of mixed-species breeding attempts.

One of the most contentious issues is the proposed construction of roads through irreplaceable flamingo habitat. This has been one of the biggest threats to lesser flamingos at Tanzania’s Lake Natron—the single most important breeding ground in the world for lesser flamingos. As detrimental as the road itself could be, even worse is the accompanying plan to open a soda extraction plant that could alter water levels at the lake, thereby potentially reducing the quality and quantity of food available to the birds. Over the years, several proposed developments have also threatened to degrade habitat near the ‘flamingo city’ in India’s Rann of Kutch. Biologists fear that construction in this area will alter water flow and reduce the accessibility of vital flamingo food resources.

Andean flamingos. Image courtesy of Wikimedia

Another worry is climate change, which could render favourite habitats unsuitable for feeding or breeding by either drying them up or flooding them to the point that they no longer have the pH required to sustain flamingos’ primary prey. Changing water conditions might also encourage blooms of toxic algal species or the spread of harmful bacteria—issues that have already been implicated in the deaths of large numbers of water birds in Africa. Flamingos are incredibly sensitive to subtle variations in their microhabitat and may decide to forego breeding if they decide that environmental conditions are not optimal for nesting. While some flamingo populations have readily adapted to anthropogenic environments, this is not generally true. This suggests that the birds would not be likely to utilize man-made alternatives introduced as replacements for degraded natural areas.

Worldwide, conservationists have already initiated several efforts to get the threatened birds out of harm’s way. Important habitats for the South American species have been given official protected status, and activists are hard at work to achieve a similar goal at Lake Natron and other African lesser flamingo haunts. Anti-poaching laws have been introduced in some regions and guards have been hired to protect flamingo colonies throughout the breeding season. Perhaps most importantly, researchers have been working on surveying more flamingo habitats—particularly in South America. These intensive efforts are vital for finding out how many birds remain, whether populations are stable or fluctuating, and which flamingo habitats most need to be protected.

Puna flamingos. Image courtesy of Christian Mehlfuhrer

However, flamingo conservation efforts do not just involve wild birds and field researchers, but also captive birds and aviculturists. Over the years, observations of flamingos at zoos and parks have provided a wealth of information on the birds’ natural histories—particularly for the three South American species, which are difficult to locate and study in the wild. Another benefit of captive flamingo populations is that they are a huge draw to visitors whose admission fees are often funnelled directly into conservation efforts. Outside of zoos, the majority of visitors are unlikely to have an opportunity to see flamingos in the wild. As a result, captive facilities are a vital tool in the campaign to raise awareness of, and support for, these threatened birds.

Although it has taken many years, aviculturists have finally worked out how to keep flamingos happy and healthy enough to breed in captivity. This has been a boon to conservation efforts for two main reasons. First, sustainable captive populations reduce, or even remove, the need to import wild-caught birds—a process that is always associated with the risk of injury and death to the birds, during both trapping and shipping. Second, maintenance of a large and healthy global population of captive birds acts as an insurance policy against any catastrophes that happen in the wild. Captive flamingos may some day be an important source of genetic diversity required for re-invigorating wild stocks, or, if captive breeding programs reach their full potential, they could even be used to produce birds that can be released into natural flamingo habitats.

Chilean flamingos. Image courtesy of Claudio Dias Timm

Recently, there has been increasing interest in keeping captive flamingos happy as well as healthy. Perhaps unsurprisingly given the fact that where there is one flamingo, there is usually another, an integral part of happiness is a satisfactory social life. Observations of ‘friendships’ and ‘coalitions’ within flocks can help managers decide, among other things, what the optimal flock size is, how much space birds need before they start getting on each other’s nerves, and which sex ratios are optimal for promoting breeding behaviour. By being aware of which birds prefer to flock together, aviculturists can also avoid separating ‘friends’ when moving birds between enclosures or giving animals away to other facilities. Studies of sociality in flamingos could also provide insights into group dynamics of other species—including humans.

Typical flamingo habitat (Lake Nakuru, Kenya)
Typical flamingo habitat (Lake Nakuru, Kenya)

Regardless of whether we’re watching flamingos in order to learn something about ourselves or just to admire their beauty, it is hard not to be impressed. Although they may look delicate and slight, these deceptively hearty birds manage to survive in some of the harshest habitats on earth, and have been doing so for millions of years. We can only hope that efforts to protect flamingos and their habitats will keep these living fossils around to brighten many more days over the generations to come.

Sunday, 18 January 2015

Yards as important habitat for urban birds

We often think of the term land management as describing large-scale activities that are carried out by groups such as government bodies and NGOs--the creation of dams, for example, or the restoration of forests and the reintroduction of species. However, studies are increasingly making it clear that individual landowners--even those whose land only comprises a few square meters of lawn stretching out to the sidewalk--can have significant impacts on local wildlife. This is particularly true when those individuals live in proximity to each other, so that their many small patches of land add up to a larger mosaic of potential habitat.

This has been highlighted by a recent study conducted in residential neighborhoods in Chicago, Illinois--one of the biggest cities in the United States. Focusing on homes located near some of the city's nearly 70,000 acres of forest preserves, a research team from the University of Illinois explored whether the richness of local bird communities might be impacted by characteristics of yards located within one kilometer of the forest edge. They also investigated which yard features were most influential, and whether the impacts of these traits depended on the birds' natural history characteristics.

Some of Chicago's many suburbs. Image courtesy of
Some of Chicago's many suburbs. Image courtesy of Charles Tilford.

The research team visited 25 different sites around the city; all study areas were adjacent to preserves found along the Chicago River, the DesPlaines River, and their tributaries. In each study site, an observer conducted two bird surveys during the breeding season--the time of year when richness tends to be highest because both migrants and non-migrants are utilizing the habitat. A total of 36 species were recorded during the study; the mean number per site was 16, though some areas had as few as 11 and others had as many as 21. Twenty of the observed species were migratory, 12 were permanent residents, and 4 were non-natives--including the house sparrow, which was one of the four most common species (the others being American robins, American goldfinches, and northern cardinals).

Across all the neighborhoods, over 900 residents responded to a questionnaire designed to assess whether their yards contained wildlife resources (including features such as plants with berries, bird feeders, and brush piles); the survey also collected data on backyard activities. Of the 11 wildlife resources listed in the questionnaire, the average yard had about six. Over half of respondents (55%) reported having vegetation with fruit or berries, and 34% had a bird feeder; of this latter group, 81% indicated that the feeders were filled for at least a few days each month.

American goldfinches, enjoying seeds at one of the 11 wildlife resources considered in this study--a bird feeder. Image courtesy of Wikimedia.

Six yard characteristics seemed to be particularly important for birds. The one with the biggest impact was trees--both the presence of trees in general and a high ratio of evergreen to deciduous species. These two features probably had such a positive effect on bird richness because a tall canopy and increased structural complexity offer more places in the habitat for roosting, nesting, hiding, and foraging. The other important vegetative features were plants that provide fruits and berries--both of which offer a natural source of high-energy food to foraging birds. Features with negative impacts included, unsurprisingly, the presence of insecticides, dogs, and outdoor cats--the last of which can reduce richness both by acting as a deterrent and through direct predation. The effect of outdoor pets was particularly noticeable on migratory birds, which were found on the transects with the lowest numbers of both cats and dogs; these birds also clearly preferred areas with more trees (especially evergreens), fruits and berries, and an overall higher number of wildlife resources.

To assess larger-scale habitat patterns within each neighborhood and across the landscape as a whole, the team put together a second dataset using remote sensing techniques. Within neighborhoods, they looked at percent canopy cover and vegetation within 50 m of the transect; across the landscape, they measured amount of open space, percent canopy cover, and distance to nearest river. These variables were important for assessing the relative impacts of yards, neighborhoods, and landscapes on avian richness. The researchers accomplished this by building seven different mathematical models--one each describing yard, neighborhood, and landscape values; three with the different pairs of those terms; and then a final model with all three terms combined. They then looked to see which model best explained the number of native birds found in the habitat.

Evergreen trees, and the presence of trees in general, had a positive effect on avian richness. Image courtesy of Overlook Circle.

The best model was the one that incorporated only the data on yards--values that had been calculated by collecting survey responses, extrapolating to fill in the blanks that were left by non-responders, and then creating aggregate scores representing, cumulatively, all the private landowner space within the neighborhood. Overall, yard characteristics explained 42.3% of all variance in bird richness--a remarkably high value for an ecological study, given the vast number of other environmental features (e.g., soil characteristics, local fluctuations in humidity and rainfall, disturbance events, windspeed, temperature, and so on...) that have to go un-measured for logistical reasons.

Taken together, these findings clearly show that the design and management of individual yards can have noticeable impacts on native birds in residential areas--probably not just in Chicago, but likely in other urban environments as well. In addition to suggesting that landscape managers and conservationists should remember to include yard habitat when drawing up wildlife preservation plans, the study also reveals that even minor decisions by individual landowners can have significant implications for local birds.

There are lots of easy ways to make a yard more appealing to wildlife. Many bird-friendly features are low-maintenance and aesthetically pleasing. Image courtesy of Pittsburgher in UK.

This should not be seen as intimidating, but, rather, empowering. Working individually or together--via homeowners' associations, conservation initiatives, or municipal schemes, for example--individuals can turn their plots into wildlife refuges. Results from the current study suggest that planting evergreens and fruiting species might be particularly useful, though specific avian needs will likely vary from one ecosystem to the next. The authors do, however, have one word of warning to those who decide to make their yards more bird-friendly: There are many documented side effects of increased exposure to wildlife, including better health, an improved quality of life, an increasing awareness of biodiversity, and a continuing enthusiasm for conservation efforts.
Belaire, J. Amy et al. 2014. Having our yards and sharing them too: the collective effects of yards on native bird species in an urban landscapeEcological Applications 24(8):2132-2143.

Sunday, 11 January 2015

A little disturbance could be a good thing

When you want to maximize biodiversity in a habitat, you should aim to minimize human disturbance there--right? That's certainly the concept at the heart of many conservation initiatives, and is a tenet espoused by the majority of wildlife preservationists. There is, however, a growing literature documenting the ways in which anthropogenic influences may currently give, or have previously have given, certain communities a biodiversity boost.

This has prompted a number of researchers to seek out systems where human disturbances have occurred in a repetitive way over thousands of years. In these places, wildlife would have had the chance not only to adapt to anthropogenic influences, but actually thrive under human disturbance regimes. Exactly this scenario is described by M. Kat Anderson in her 2005 book Tending the Wild, which focuses on the ways that Native Americans interacted with the California wilderness prior to the arrival of the Europeans. A similar discussion can be found in a new review paper by the University of Montana's Stephen Siebert and Jill Belsky, who describe the ecological impacts of swidden in Bhutan.

Bhutan's Haa Valley. Image via Wikimedia Commons, courtesy of Greenmnm69.

Swidden is a slash-and-burn technique used to open up forested areas for agricultural activity. Although swidden had disappeared from Bhutan by 1997, it was previously widespread throughout the country; as many as 200 million swidden farmers are thought to continue the practice throughout the remainder of the eastern Himalayas. Two types of swidden were common: tseri, in which crops were grown for 1-2 years before the field was left to grow over with trees and shrubs for 2-8 years; and pangshing, in which crops were grown for 2-3 years before the field was left to grow over with grass for 6-20 years. Tseri was typically used to produce maize, millet, rice, and vegetables, and could be found at lower altitudes; pangshing was better for wheat, buckwheat, barley, and greens, and was used at higher altitudes. Another major difference between the two techniques is the amount of disturbance required to prepare and tend fields. During tseri, disturbance was minimal because plowing was infrequent and crop maintenance was performed by hand; during pangshing, the top 6 cm of soil were removed, dried, and burned.

If you think these techniques sound fairly invasive, then you're not alone. The Bhutanese government, wanting to preserve the amazing biodiversity that can be found in its country, passed the Bhutan Forestry Act in 1969. This spelled the beginning of the end for swidden, which many people viewed as antiquated, dangerous, and ecologically unsound. However, it may have provided a service to a variety of wildlife species that needed more sunlight than thick tree canopy allowed into the forest, but also more cover than was provided by completely open meadows. In other words, swidden may have acted as an intermediate disturbance--something more intense than, say, the toppling of a single disease-ridden tree, but less intense than the felling of a whole hillside's worth of trees during a mudslide.

A patchwork habitat resulting from swidden. Here you can see forests in multiple stages of succession, fallow fields, and current growth of rice crops in a swidden landscape in Yunnan Province. Image courtesy of Wikimedia Commons.

Swidden farmers left in their wake a variety of patches of different ages--and, therefore, at different stages of succession. The entire landscape would have been a mosaic of areas with closed canopies, open canopies, and everything in between. These conditions would have provided habitat for shade-lovers, sun-lovers, shy species that prefer to stay hidden in the undergrowth, and bolder ones not afraid to venture out into the open. From a single habitat--forest--the swidden farmers were creating multiple types of new habitat, each with its own niches. This, in turn, would have facilitated biological heterogeneity--probably not just in terms of the number and type of species present, but also the roles of those species in the local food web, and the functions that the entire ecosystem could collectively perform.

It's difficult to know for sure, because swidden vanished in Bhutan over 30 years ago, and wasn't well quantified before that time. As a result, the authors can't make a clear before-and-after comparison that would allow them to see whether biodiversity levels have dropped since the discontinuation of swidden. (With proper permission, however, it would be possible to investigate this experimentally.) In other countries where swidden is still used, researchers have noted that fallow plots provide habitat for different types of species than those found in the adjacent forest; as a result, the swidden-and-forest patchwork is more biodiverse than tracts of uninterrupted forest alone. We also know that fallow-type habitats are used by sambar deer, wild pigs, and gaur--potential prey items for tigers. This suggests that swidden could facilitate the coexistence of predators and humans even in disturbed, densely populated areas.

Ironically, the curtailing of swidden has not led to a uniform decrease in disturbance across Bhutan's forests, some of which are shown above. Some areas are protected from human activities, but other areas have been subjected to intense logging efforts, which may, over the long run, be more ecologically harmful than traditional slash-and-burn practices. Image courtesy of Christopher J. Fynn.

The best way to know this for sure is to explore the possibility using rigorous scientific methods. That's one of the reasons the authors have used Bhutan as a case study. They suggest that the country missed a trick by outlawing swidden without collecting more data and thinking about the situation more critically. Their hope is that conservationists and policy makers will do better elsewhere--not just in places with swidden practitioners, but in any area where humans continue to use traditional land management techniques that have been employed for thousands, if not tens of thousands, of years.

Although we tend to think of humans as separate from nature, we do, in fact, have a long history of interacting with species, communities, ecosystems, and entire landscapes; removing us from the equation may have unintended consequences. The authors advise us to keep that in mind, and to consider the possibility that a little bit of disturbance might actually be a good thing--both for humans and for wildlife.
Stephen F. Siebert and Jill M. Belsky. 2014. Historic livelihoods and land uses as ecological disturbances and their role in enhancing biodiversity: an example from BhutanBiological Conservation 177:82-89.

Sunday, 4 January 2015

Neolithic farming at the northern frontier

The high northern latitudes have been inhabited by humans since the end of the last Ice Age, approximately 12,000 years ago. Conditions that far north, where the Earth's circumference is about half that at the Equator, are extreme. On the 60th parallel north, for example, the sun is visible for just under 19 hours on the summer solstice, but only for about 6 hours during the winter solstice. Although temperatures may soar above 30°C in exceptional years, the average daily mean is closer to a chilly 6°C (depending on your exact location along the parallel), with record lows in the -30's--and, of course, you can expect at least a meter of snow in the winter. In other words, this is not an easy place to live even now, with our modern conveniences; it's hard to imagine what it must have been like for the region's earliest settlers, who eked out a living by hunting, fishing, and gathering.

A sampling of Neolithic tools. Image courtesy of Wikipedia Commons.

At some point, these intrepid northern colonizers began farming, making use of techniques originally developed in the Fertile Crescent 11,000 years ago. Above the 60th parallel, however, farmers were more vulnerable to climatic stochasticity; archaeologists have uncovered settlements that appear to have been abandoned after the environment became too hostile. In northwestern Europe, exposure to the Gulf Stream allowed Early Neolithic people to initiate farming economies that last to this day. Elsewhere on the continent, however--in Finland, for example--the low average temperature, persistent snow cover, and not-infrequent appearance of summertime snow and ice combined to diminish vegetation periods and make farming a more challenging endeavour.

Until recently, it has been difficult to pinpoint exactly when early Finnish settlers achieved domestication, since there is very little evidence from prehistoric times; the region's acidic soils took care of the majority of useful artifacts long ago. However, those same conditions are favorable for the preservation of biomolecules harvested from the few remaining pieces of ancient ceramic cooking vessels. Analysis of these fragments--via techniques such as high-temperature gas chromatography, mass spectrometry, and ion monitoring--allows researchers to determine the composition and structure of the molecules, and to look for pre-identified biomarkers. Cumulatively, these characteristics can be used to determine whether the vessels are saturated with aquatic fats (indicating storage of fish and other seafood), terrestrial fats (from species hunted on land), and dairy fats (from domesticated livestock).

Examples of pottery from the Corded Ware period; these pieces date to ca. 2500 BC. Image courtesy of Wikipedia.

Out of a collection of 70 prehistoric fragments unearthed at sites across southern Finland, an interdisciplinary team of researchers was recently able to isolate 19 that were suitable for just such an analysis. The pottery was representative of a range of prehistoric eras, from the Comb Ware period (ca. 6000-4300 years ago) through the Corded Ware (ca. 4800-4100 years ago) and Kiukainen Ware (ca. 4400-3500 years ago) periods, all the way to the Early Iron Age (ca. 2500-1600 years ago).

The earliest molecular samples (dated to approximately 3900-3300 BC) were predominantly marine in origin, indicating a heavy reliance on fishing; the ceramic fragments themselves may have come from vessels used for cooking, storage, or even transport. On the other hand, residues from pottery shards dating to approximately 2500 BC were from terrestrial ruminants. Though they could have come from either wild or domesticated stock, there was evidence of milk fat--indicating that the settlers had begun farming and were now heavily dependent on land animals despite their relative proximity to the coastline. Interestingly, the final Neolithic samples, dating to the Kiukainen Ware period, contained a mixture of terrestrial and aquatic compounds, suggesting that local climate changes may have required a diversification in subsistence techniques. By the Early Iron Age (approximately 1200-500 BC), however, agricultural intensification seems to have allowed population growth and a renewed focus on farming; pottery fragments from this time yielded only dairy fats.

Iron Age pottery (in this case, from Orkney). Image courtesy of Rita Roberts.

Although these patterns may initially seem relevant only to the small portion of researchers specializing in ancient Finnish history, they actually offer some interesting insights to the rest of us, too. For one thing, these archaeological results map nicely onto spatial patterns showing the prevalence of the lactase persistence (LP) genotype--which confers the ability to continue digesting dairy products well into adulthood. While this may be a fairly common characteristic throughout much of the developed West, it is either rare or lacking in parts of the world without a strong tradition of dairy farming. This correlation helps validate the molecular results, and also can be used to draw conclusions about gene flow in Europe. There is a SW-NE gradient of LP allele frequency in Finland, suggesting several separate waves of immigration over the past 6000 years. Further, low LP frequencies in some parts of the eastern Baltic indicate that this region may have acted as a "genetic refuge" for populations who continued to lead a hunter-fisher-forager lifestyle rather than pursuing farming. Pretty amazing that all of this ancient history can be inferred from gene patterns analyzed thousands of years after the fact.

Another interesting implication of the findings is related to what they reveal about how early humans dealt with their difficult and variable habitat. The analyses suggest that animal domestication occurred in southern Finland much earlier than previously thought (ca. 2500 BC), but that use of aquatic resources lasted much longer, post-domestication, than it did in other places settled by Neolithic peoples. In fact, Late Corded Ware Finns appear to have responded to their changing environment by vacillating between hunting/gathering, farming, and some mixture of the two as required. This sort of flexibility is probably one of the major reasons why early settlers were able to maintain populations in such marginal habitat.

Miina Äkkijyrkkä is an artist and dairy farming expert who combined her two passions during a project making cow sculptures from recycled car parts. Images courtesy of the artist, via Inhabit.

The authors of the study write that, even today, "conventional" farming in this part of the world is not for the faint-hearted. A changing climate may prompt humans to push their boundaries ever northwards, but conditions above the 60th parallel will likely always be challenging. If we hope to utilize this "frontier zone" in order to increase food production and make use of the available land, we will probably have to follow our predecessors' example and demonstrate a willingness to adapt.
Cramp, Lucy J.E. et al. 2014. Neolithic dairy farming at the extreme of agriculture in northern Europe. Proceedings of the Royal Society B 281:20140819.

Tuesday, 23 December 2014

Tiny hitchhikers: An analysis of stowaway ants

We’ve all seen news coverage of the terrifying and destructive creatures that make their way across our borders by hitchhiking on shipments from around the world—Asian long-horned beetlesvia wood pallets, for example, or Brazilian wandering spiders in boxes of tropical fruit. These are only two of many examples worldwide, and the cumulative cost of these invasions is in the hundreds of billions of dollars as individuals, organizations, and governments race to contain outbreaks that can damage property, reduce ecosystem function, and threaten human health.

While some invaders are easy to spot and identify, others, such as ants, may go unnoticed thanks to their diminutive size and furtive nature. In fact, five different types of ant are listed among the world’s top invaders, and over a hundred other ant species are known to have expanded their ranges thanks to global trade activities. One recent study suggested that 147 varieties of ant have been transported—and transplanted—to date, but this is likely to be an underestimate given than more than 200 species have been intercepted at the borders of the USA alone.

Asian longhorned beetle, which has caused the destruction of tens of thousands of trees across North America. Image courtesy of the CISR.

The uncertainty surrounding this issue prompted a team of Spanish and American researchers to undertake a global survey in order to more accurately estimate the number of ant species arriving, and establishing viable populations in, temperate habitats. Further, they wanted to explore whether these patterns were influenced by the geographical origins of the exotic ants—were they, for example, more likely to do well in habitats like those from which they came, or did they thrive in entirely different types of ecosystem?

The research team focused on data from the USA, New Zealand, and Holland—three countries characterized by high levels of shipping activity and excellent records of invasive species sightings. By employing a range of species richness equations, the researchers were able to use invasive ant presence/absence data to estimate the total number of introduced and established species in each of the three countries.

Estimates varied depending on which equations were used; for example, the total number of introduced species worldwide ranged from a low of 366 to all the way up to a high of 2027. The variation is a result of differences in how each equation deals with species that had very low detection levels. To deal with this uncertainty, the researchers calculated a mean across all the estimates—a figure that was often towards the lower to middle portion of the scale, meaning that the resulting analyses would likely be a conservative estimate of ant invasions in the focal regions.

The tawny crazy ant, a species that has invaded the Houston, Texas area of the USA. Image courtesy of Mother Nature Network.

It turned out that many of the invasive species had been spotted only once—a pattern that was particularly obvious in the USA. This suggests that there is a large diversity of exotic ants being transplanted around the world. Further, the richness estimates revealed a surprisingly high rate of introductions. Nearly 900 species are likely to have been transplanted globally, even though we’ve only observed and confirmed about 300. In North America, which is home to approximately 1000 types of ant, the number of invasives could almost equal the number of natives.

Not all of the exotics are likely to become established residents of their new ecosystems; the study estimated that just under 600 species found a way to embed themselves and set up colonies. This number is nearly 5 times higher than what has actually been observed during surveys, and represents nearly two-thirds of all introductions.

Most of the invasive species are Neotropical, with fewer coming from the Palearctic, Indo-Malay, and Australasian regions. The US was particularly hard hit by Neotropical ants, which made up the majority of both introductions (58%) and establishments (51%). The other two countries surveyed were most inundated from species from their own regions: most of Holland’s stowaway ants came from the Palearctic, while most of New Zealand’s came from Australasia. Interestingly, there were no significant biogeographical differences between the introduced and established ants within each study region, indicating that all species were equally likely to thrive once they had reached their new home.

Overall, the analyses suggest that approximately 1/14th (or 7%) of the world’s estimated 13,000 species of ants have been shipped to new habitats at some point. The authors admit that these estimates may be slightly inflated by the high rates of importation into the US, which offers more ant habitat than the other two countries examined here—both because it is physically larger and because it contains a greater variety of ecosystem types. However, results were similar even when additional countries were added to the sample, suggesting that the reported patterns are likely accurate reflections of global ant introductions.

Range of the red imported fire ant, a global pest. Image courtesy of the USDA.

There are probably two main reasons why stowaway ants are most successful within their own biogeographical regions. First, they are more likely to benefit from “climate matching”, or similarities between climatic conditions in their native and adopted countries. Second, there is greater “propagule pressure”—a larger number of migration opportunities thanks to simple physical proximity and repeated exposure.

That’s not exactly a surprising result, but probably a useful one nonetheless if we want to improve our ability to locate, identify, and prevent impending invasions. After all, ants can play a critical role in ecosystem function, and an imbalance in local myrmecofauna could have serious implications for the health of local habitats—or, at the very least, could prove to be an expensive and sometimes painful annoyance, as anyone who has dealt with a red imported fire ant could tell you.

Given the non-random nature of ant introductions, the authors suggest that we should develop targeted strategies for monitoring shipping routes (especially from the Neotropics). Now that we know where the ants end up, it would also be helpful to have a better understanding of where they originate. This will require further studies of introduced and established ant populations in other destination habitats, since the stowaways may hop on board at any number of ports—not just those in their homelands.
Miravete, V., N. Roura-Pascual, R.R. Dunn, and C. Gomez. 2014. How many and which ant species are being accidentally moved around the world?Biology Letters 10: 20140518.

NOTE: Since the publication of this blog post, the paper has been retracted. The authors' public statement is as follows:
Herewith, we retract our paper ‘How many and which ant species are being accidentally moved around the world?’ by Verónica Miravete et al., published online on 23 October 2013 (Biol. Lett. 9, 20130540; doi:10.1098/rsbl.2013.0540). After careful examination of the original data on introduced and established ants on regions worldwide, we realized that we used a wrong list of species and omitted to include a reference (Sarnat E. (2012) North America checklist. Antkey <http://antkey.org>. Extracted 3 June 2014) in the paper. Although the main arguments and conclusions remain the same after correcting these errors, the use of the wrong version of the data affected the magnitude of the analyses conducted at the country level (in the electronic supplementary material) and, to a lesser extent, when all countries were considered together (in the main text). Therefore, we wish to retract the article. We deeply apologize for any inconvenience this publication might have caused to the readers of Biology Letters.