Mother Tigers Pass Down Territory to Their Daughters

Zeff the Amur tiger, photographed at the Bronx Zoo.

Blogging on Peer-Reviewed ResearchImagine walking through a neighbourhood and seeing graffiti, litter, and shopping trolleys strewn about the place. Are these problems to be solved, or petty annoyances that can be ignored in the light of more serious offences? A new study suggests that the former is right - even the most trivial of transgressions can spread and spiral because their very presence stimulates more of the same behaviour. Through a series of stunning real-world experiments, Kees Keizer and colleagues from the University of Groningen have shown that disorder breeds more disorder. The mere presence of graffiti, for example, can double the number of people who litter and steal.

Their study provides strong support for the controversial Broken Windows Theory, which suggests that signs of petty crimes, like broken windows, serve as a trigger for yet more criminal behaviour. It follows that fixing small problems can prevent the build-up of bigger ones and the gradual decay of a neighbourhood. The idea was first proposed in a magazine article published in 1982, but soon became the basis of many a social policy.

It inspired Rudy Guiliani's Quality of Life Campaign in New York, which focused attention on seemingly trivial fixes such as removing graffiti, clearing signs of vandalism and sweeping the streets. The campaign seemed to work, which motivated other cities to try the same tactics.  But despite its popularity, the Broken Windows Theory still divides opinion, for it lacks the backing of hard evidence, it's plagued by woolly definitions of "disorder" and critics have questioned its role in New York's drop in crime. These are fairly hefty shortcomings for a concept that is so central to anti-crime measures and Keiser wanted to address them once and for all.

To do so, he took to the streets of Groningen and watched unknowing passers-by in real-life situations as they reacted to signs of disorder. The recurring question was this: would people exposed to inappropriate behaviour behave in a similar way themselves?

He began in an alleyway in a local shopping district, where bicycles are commonly parked and where a conspicuous red sign warned against graffiti. He attached a flyer from a fictional sportswear shop to the handlebars of parked bicycles and watched what people did as they returned to their rides. Under normal circumstances (picture on the left), most people took the flyer with them and just 33% littered by throwing it on the ground. But that all changed when Keiser covered the wall with graffiti (picture on the right). With this innocuous difference, the proportion of litterers doubled and 69% discarded their flyers on the street.

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Keiser explains this behaviour in terms of "social norms" - the rules that separate appropriate behaviours from inappropriate ones. Problems arise when our view of what is common (in this case, graffiti) fails to mesh with our understanding of what society expects (as epitomised by the "No Graffiti" sign). Graffiti is frowned upon, but the covered walls send a message that it is common and therefore, more acceptable. Keizer calls this the Cialdini effect.

Fence.jpgTo see how far its influence would extend, he set up a temporary fence in front of a car park. He attached two signs to the fence, one banning people from locking their bicycles to it, and another saying that entry was forbidden and asking people to use a detour some distance away. When he placed four bicycles a metre away, just 27% of people disobeyed the detour sign and squeezed through the gap in the fence. But when the bikes were locked to the fence, in blatant disregard of the first sign, 82% of people ignored the detour sign too. With one rule broken, the other followed suit.

A third related study took place in a supermarket car park, where prominent stickers asked shoppers to return their carts to the main building. Keiser plastered various cars with the same flyer from the first study. If the garage was clear of carts, just 30% of shoppers littered with the flyer, but if four unreturned shopping carts were left lying about, 58% did so. Again, when people saw that one rule was broken, they felt less strongly about following another.

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Together, these three experiments show that signs of disregarded rules can spread to affect commonly held behaviours ("don't litter") as well as specific requests from third parties ("don't enter" or "return trolleys").

Signs of disorder don't even need to be seen to have such influences - they can be heard too. In the Netherlands, most people know that setting off fireworks in the weeks before New Year's Eve is illegal and carries a small fine. Keiser found that he could trigger people to litter more frequently by giving them audible evidence that this law had been flouted. Again, he attached a flyer to bicycles parked near a train station. Under normal circumstances, 52% of cyclists littered but if they heard the sound of fireworks let off by Keiser at a nearby location, that figure grew to 80%.

Letterbox.jpgFor his final and most dramatic demonstration, Keiser showed that the mere presence of graffiti can even turn people into thieves. He wedged an envelope into the slot of a mailbox, with a 5 Euro note showing in the transparent window. If the mailbox and the ground around it were clean, just 13% of passers-by stole the envelope. If the mailbox was covered in graffiti, or if the ground around it was covered in litter, the proportion of thieves doubled to 27% and 25% respectively.

Keiser thinks that it's unlikely that people inferred a reduced police presence by the presence of litter or graffiti - certainly, litter is generally tolerated by the police in Groningen. Instead, he thinks that one transgression was actually fostering another. This isn't a simple case of imitation - littering doesn't just beget littering. Keiser's idea is that seeing the breakdown of one social norm makes it easier to ignore others, by weakening our general resolve to act appropriately and strengthening our temptations to act in our own self-interest.

All in all, the suite of experiments, all in a realistic setting, provide powerful evidence that the Broken Windows Theory is valid and all of Keiser's results were statistically significant. Small, petty signs of disorder can indeed turn people away from the straight and narrow. His message to police and policy-makers is stark - it is worth spending time on small and seemingly trivial interventions, to prevent disorder from spreading and escalating. 

Reference: Science doi: 10.1126/science.1161405

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For female Amur tigers, defending your territory is not just about acquiring enough food to survive; it’s also about passing down real estate to your daughter.

As described by a team of scientists led by the Wildlife Conservation Society’s John Goodrich in the latest issue of the Journal of Mammalogy, a 14-year study of Amur tigers in eastern Russia’s Sikhote-Alin Biosphere Zapovednik has shown that male and female tigers establish home ranges of different sizes for different reasons. After capturing and radio-collaring 32 individual tigers (adults and cubs), the team of Russian and American scientists was able to determine that male tigers maintained very large territories (about 1,385 square kilometers) which encompassed the home ranges of several females (about 390 square kilometers).

A map of Amur tiger home ranges between 1992-1997. Solid areas marked "F" designate females and dashed lines marked "M" designate males. From Goodrich et al, 2010.

Blogging on Peer-Reviewed ResearchMany naturalists become so familiar with the animals they study that they can recognise individuals within a population using just their shapes and patterns. If that's too difficult, animals can be ringed or tagged. These tricks give scientists the invaluable ability to track the fates of individuals, but try using them on octopuses.

Wonderpus.jpgRecognising shape and pattern is impossible when your subject has the ability to change the texture and colour of its already pliant body on a whim. Injured individuals are distinctive enough, but only for a short while before their remarkable healing abilities close wounds and regenerate arms. Tags, which work well for closely related animals like squid, are useless for octopuses, which have eight long and dextrous arms for pulling markers off.  And other techniques are simply either too impractical, expensive, or harmful to the creature.

This inability to track individuals in the wild has severely limited our knowledge of octopus populations, including how far their ranges extend, how many individuals live in a certain area and how long the live for. But that may change. Christine Huffard from the Monterey Bay Aquarium Institute has found a way to identify one species of octopus - the grandiosely named wonderpus - just by using the markings on its skin. 

It's a surprising discovery for animals that are so known for their colour-changing abilities but the wonderpus has a relatively static uniform of white markings on a brown background. Huffard was studying photos of this beautiful creature (it's scientific name is actually Wunderpus photogenicus) when she noticed that the white Rorschach-blot patterns on the back of its head differed between individuals.

To see if others agreed, Huffard canvassed several underwater photographers for their best wonderpus shots and eventually collected 30 photos of 15 different individuals, all depicting their head from above. She showed these shots to 33 volunteers, some of whom scoured the full set for matches, while others just had to say if specific pairs were matches. Either way, the observers were remarkably accurate - almost all of them scored more than 90% and just over a third scored more than 95%.

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Based on these results, Huffard thinks that human observers can use these white marks like the equivalent of a wonderpus name tag. It's unlikely that they simply reflect patterns worn by different genders, for there were many more than just two different layouts. Nor is it likely that the patterns change over time - the volunteers managed to match photos of the same octopus taken up to 10 weeks apart.

There are a few caveats. The distinctive white marks of the wonderpus remain even when it camouflages itself, although it can make the boundaries blurrier than usual. It can also push out small nipple-like studs on its skin called papillae to slightly change the shape of the markings. Huffard deliberately left out any shots of octopuses with erected papillae or activated camouflage, so it's not clear if these tricks would make them less recognisable.

Nonetheless, neither change significantly alters the white marks and Huffard maintains that they can be used to identify individual octopuses from photos. Certainly, these shouldn't be hard to come by, for the animal's image is a great prize for keen underwater photographers. It has also become an increasingly popular aquarium species, with specimens fetching up to $700 apiece. With this keen attention and these high price-tags, it's worrying that there is no way of monitoring how healthy the wild populations are and very little is known about their natural history. Sometimes, they'll be everywhere and at others, not a single individual will be seen for months on end.

Huffard hopes that the ease with which individuals can be identified through photos will lead to the start of an easy monitoring program, that underwater photographers will be all too happy to participate in. It has already begun - Huffard's group have set up a website called Wunderpix, where photographers can upload their wonderpus snaps. With brief information on the date and site of shots, individuals could conceivably be tracked to give more of an idea about their lifespans and movements. Conservationists could even use the photo database to work out if specimens that go on sale were taken illegally from protected areas.

It's not clear why the wonderpus has such distinctive markings in the first place. Biologists have mostly assumed that octopuses, being solitary animals, have little need for the ability to recognise other individuals and no one has properly tested whether they can do so.  It's not unfeasible - octopuses are intelligent animals with decent memories and excellent eyesight.

Regardless, it seems that the wonderpus can now join species like whale sharks, cheetahs and coelacanths in the small club of animals that can be recognised solely through colour markings. Other octopus species may gain membership eventually. The blue rings from which the lethal blue-ringed octopus are also arranged in distinctive patterns that could allow naturalists to tell one from the other.

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Reference:Christine L. Huffard, Roy L. Caldwell, Ned DeLoach, David Wayne Gentry, Paul Humann, Bill MacDonald, Bruce Moore, Richard Ross, Takako Uno, Stephen Wong (2008). Individually Unique Body Color Patterns in Octopus (Wunderpus photogenicus) Allow for Photoidentification PLoS ONE, 3 (11) DOI: 10.1371/journal.pone.0003732

Images: by Christine Huffard

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The disparity in territory size was not much of a surprise. Among solitary big cats, males often have larger home ranges than females, and the reason for this difference between the sexes has to do with the different life strategies of male and female Amur tigers. Whereas young male tigers typically leave the home territory of their mother in an attempt to find a vacancy and gain access to as many females as possible, females stake out their territories based upon the resources they can provide for them and their cubs (thus their home ranges can be much smaller).

What intrigued the scientists, however, was that the home ranges of female Amur tigers contracted when they had female cubs, with their daughters taking up residence in the vacant areas. This favored the future reproductive success of the young tigresses as they did not have to face the risks usually encountered by individuals which try to establish themselves elsewhere (and often become victims of poachers). As the authors of the paper state, it appears that the adult female tigers in their study defended larger territories than they actually needed to survive, and by passing down a portion of this land to their daughters they enhanced the potential success of their offspring while mitigating competition for the same resources.

Yet, as the scientists saw firsthand, poaching can disrupt the matrilineal inheritance of territory among Amur tigers. During the early years of their study – from 1997 to 2000 – all but two of the radiocollared tigers living within the Sikhote-Alin Biosphere Zapovednik were killed by hunters. The vacancies were filled by a mix of “immigrant” animals from other areas and individuals which were related to those which had been poached, but, even after a new population became established, it took five years before a mother tiger passed down territory to her female offspring.

The spatial patterning of tigers over time detected by Goodrich and colleagues may very well complicate tiger recovery plans. If there is a large area of land in which tigers were nearly eliminated (as was the case in this study), the new tiger population will not quickly rebound to its maximum capacity. Instead female tigers which move into vacancies will defend larger territories than they require until they pass down some of that area to their daughters, and during this time the tiger population might be more susceptible to poaching as a smaller number of animals will be occupying an area which could actually support many more. But this news isn’t all bad. If tigers can be successfully protected long enough for adult animals to become established, the population size and density can potentially double when the next generation of female tigers mark out their own territories within those initially carved out by their mothers. Given enough time, the tattered remnants of a tiger population can begin to recover.

References:

Goodrich, J., Miquelle, D., Smirnov, E., Kerley, L., Quigley, H., & Hornocker, M. (2010). Spatial structure of Amur (Siberian) tigers (Panthera tigris altaica) on Sikhote-Alin Biosphere Zapovednik, Russia Journal of Mammalogy, 91 (3), 737-748 DOI: 10.1644/09-MAMM-A-293.1

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