As teenagers, we probably associate with different people to those whose company we keep as adults. At one point in our lives, we may want subversive influences, while preferring support and stability at other times. The same is true for other partnerships in nature.
Take the whistling-thorn acacia. This African tree forms partnerships with four different species of ants. Some provide a valuable service as bodyguards (even routing elephants), while others have been written off as freeloaders and parasites. But Todd Palmer has found that these labels are too simplistic. In fact, none of the ants is a perfect partner. The tree actually does best by switching its alliances throughout the course of its life. At certain times, partnering with a parasite is actually its best course of action.
Ever wonder if acts of kindness or malice really do ripple outwards? If you give up a seat on a train to a stranger, do they go onto “pay it forward” to others? Likewise, if you steal someone’s seat, does the bad mood you engender topple over to other people like a set of malicious dominoes? We’d all probably assume that the answers to both questions were yes, but James Fowler and Nicholas Christakis think they have found experimental evidence for the contagious nature of cooperation and cheating.
The duo analysed data from an earlier psychological experiment by Ernst Fehr and Simon Gachter, where groups of four volunteers had to decide how much money to put in a public pot. For every unit they chipped in, each member would get 0.4 back. So any donations represent a loss to the donor, but a gain to the group as a whole. The best way for the group to benefit would be for everyone to put in all their money, but each individual player could do even better by putting in nothing and feeding off their peers’ generosity.
This “public goods game” went on for six rounds. At the end of each one, the players were told what their other comrades did, although everyone’s identities were kept secret. The groups were shuffled between rounds so that players never played with each other more than once.
Fowler and Christakis found that the volunteers’ later moves were influenced by the behaviour of their fellow players. Each act of generosity by an individual influenced the other three players to also give more money themselves, and each of them influenced the people they played with later. One act became three, which became nine. Likewise, players who experienced stingy strategies were more likely to be stingy themselves.
Even though the groups swapped every time, the contagious nature of generous or miserly actions carried on for at least three degrees of separation. You can see an example of one such cascade in the diagram below. Eleni contributes some money to the public pot and her fellow player, Lucas, benefits (one degree). In the next round, Lucas himself offers money for the good of the group, which benefits Erika (two degrees), who gives more when paired with Jay in her next game (three degrees). Meanwhile, the effects of Eleni’s initial charity continue to spread throughout the players as Lucas and Erika persist in their cooperation in later rounds.
On Nicobar Island, in the Indian Ocean, a most unusual hunting party is searching for food. Through the branches of the forest, the tiny Nicobar treeshrew scuttles about searching for insects. They’re followed by the racket-tailed drongo, a small bird that picks off juicy morsels flushed out by the foraging treeshrews. So far, this isn’t unusual – many distantly related animals forage together, either because they net more food or because they can watch out for predators.
But this alliance has a third an altogether more surprising member – a sparrowhawk. This bird of prey is five times larger than either of the other two species and can easily kill treeshrews. But it doesn’t – instead, it only deploys its talons on other prey that are disturbed by its partners.
Predator and prey species don’t usually fraternise with each other outside the confines of animated films, but this alliance is unique. The drongos and sparrowhawks will actively seek out the treeshrews and stay with them in consistent formations over long periods of time. If you spot a treeshrew, there’s a 71% chance that there’s also a drongo around, and a 43% chance that a sparrowhawk is too.
Meera Anna Oomen and Kartik Shanker discovered this strange coalition and they suspect that it’s engineered by the drongos. Certainly, sparrowhawks aren’t traditional companions for treeshrews. On their own, these mammals keep their distance from the raptors for their own safety and are extremely vigilant. But with the drongos around, they tolerated the hawks and allowed them to get a couple of metres closer. The hawks, meanwhile, appear to use the drongos as a way of finding treeshrews.
Birds of prey are unusual participants in foraging groups. When they join another species, as is the case with double-toothed kites and capuchin monkeys, it’s usually one relatively big enough that it couldn’t be a possible meal. That clearly doesn’t apply on Nicobar Island.
Nonetheless, the hawks, and certainly the drongos, seem to get a good deal out of their partnership. Oomen and Shanker think that they find more food when they follow treeshrews (although the data on this are still limited). Why a bird of prey should stray from its typical hunting technique is unclear, but it may be that the treeshrews simply aren’t a possible target with the drongos around.
It’s unclear how the treeshrews benefit from this coalition, or whether they simply can’t avoid the pursuit of their partners. Certainly, Oomen and Shanker found that in the drongos’ presence, their foraging rates fell by around two-thirds. Drongos are notorious food thieves, and this was abundantly clear if there were two of them around – in these situations, the treeshrews often turned on them and chased them away.
Ironically enough, the treeshrews may get protection from predators by having the drongos act as intermediaries. These small birds are incredibly vigilant and especially so when hawks are around. Even though a hawk is actively following the treeshrew, the drongo may be able to warn it if the predator partner decides to pull a double-cross, or if another predator flies in from outside the group.
Reference: Biology Letters doi:10.1098/rsbl.2009.0945
Images: Drongo by Nimesh M
More on natural alliances:
When it comes to encouraging people to work together for the greater good, carrots work better than sticks. That’s the message from a new study showing that rewarding people for good behaviour is better at promoting cooperation than punishing them for offences.
David Rand from Harvard University asked teams of volunteers to play “public goods games”, where they could cheat or cooperate with each other for real money. After many rounds of play, the players were more likely to work together if they could reward each other for good behaviour or punish each other for offences. But of these two strategies, the carrot was better for the group than the stick, earning them far greater rewards. .
Public goods games, albeit in a more complex form, are part and parcel of modern life. We play them when we decide to take personal responsibility for reducing carbon emissions, or rely on others to do so. We play them when we choose to do our share of the household chores, or when we rely on our housemates or partners to sort it out.
These sorts of games are useful for understanding our tendency to help unrelated strangers even if we stand to gain nothing in return. The big question is why such selflessness exists when altruists can be easily exploited by cheats and slackers, who reap common benefits without contributing anything of their own. How does selflessness persist in the face of such vulnerabilities?
I live in London. According to Google Analytics, 96% of this blog’s readers make their homes in a different city and 91% live in another country altogether. The fact that most of you are reading this post at all is a symptom of the globalised state of the 21st century.
Through telecommunications, the Internet, free trade, air travel and more, the world’s population is becoming increasingly connected and dependent on one another. And as this happens, the problems that face us as a species are becoming ever more apparent, from our relentless overuse of natural resources to the threat of climate change. But how will globalisation affect our ability to handle these problems? Will it see the cliquey side of human behaviour writ large, or the rise of cooperation on a global scale?
Opinions differ. Some say that globalisation makes the differences between ethnic or geographical groups even starker, strengthening the lines between them. This bleak viewpoint suggests that exposing people to an ever greater variety of world views only reinforces xenophobia. And indeed, recent decades have seen a surge in xenophobic political parties and states seeking independent status.
Others take a more optimistic stance, arguing that in a globalised world, people are more likely to find a sense of common belonging and concepts of ethnicity or nationhood become less relevant. After all, recent decades have also seen an increase in foreign aid to developing countries and human rights campaigns.
Nancy Buchan form the University of South Carolina has used a clever psychological game to show that the latter perspective is stronger. Her group recruited volunteers from six countries across five continents and asked them to play a game where they could cooperate with each other at local or global levels. She found that people who were more connected internationally, or who came from more globalised countries, were more likely to work together at a global level. Globalisation, it seems, breed cosmopolitan attitudes, not insular ones.
Is punishment a destructive force that breaks societies or part of the very glue that holds them together? Last year, I blogged about two studies that tried to answer this question using similar psychological games. In both, volunteers played with tokens that were eventually exchanged for money. They had the option to either cooperate with each other so that the group as a whole reaped the greatest benefits, or cheat and freeload off the efforts of their peers.
In both studies, giving the players the option to punish each other soon put a relative end to cheating. Faced with the threat of retaliation, most players behaved themselves and levels of cooperation kept stable. But this collaboration came at a heavy cost – in both cases, players ended up poorer for it. Indeed, one of the papers was titled “Winners don’t punish“, and its authors concluded, “Winners do not use costly punishment, whereas losers punish and perish.”
But in both these cases, the experiments lasted no more than 10 ’rounds’ in total, and to Simon Gaechter, that was too short. He reasoned that more protracted games would more accurately reveal the legacy of punishment, and more closely reflect the pressures that social species might experience over evolutionary time spans. With a longer version of the games used in previous studies, he ably demonstrated that in the long run, if punishment is an option, both groups and individuals end up better off.
Together with colleagues from the University of Nottingham, Gaechter recruited 207 people and watched as they played a “public goods game” in groups of three. All of them were told that their group would remain the same for the entire game, which could last for either ten rounds or fifty.