Wednesday, August 15, 2012

Cooperating For Selfish Reasons

If you were a young adult Ethiopian wolf, you would have a choice to make: Should you be a member of a monogamous breeding pair or a helper to an already established breeding pair (who are probably your parents)? The choice seems obvious, right? I mean, who wants to be a helper? Why should you forgo all the glory and status of being part of the breeding pair to be a babysitter? 

The Governess painted by Rebecca Solomon in 1851 shows a modestly-dressed
Victorian era governess (in black) who diligently cares for the education needs of
her employer's young children, while the well-dressed employer is free to flirt.
Image provided by Wikimedia.
But Ethiopian wolves often do make that choice. These wolves are territorial rodent hunters and their survival and success depends on how many giant mole rats (their favorite food) and Murinae rats (a second-choice food-option) are available in the territory. In territories with fewer rodents, Ethiopian wolf families are likely to consist of a mother, a father, and their pup born that season. However, in territories with lots of rodents available, wolf families also include some of the older siblings from previous years. Why do they stick around?

An Ethiopian Wolf photographed
by Gert Vankrunkelsven.
Image available at Wikimedia.
Jorgelina Marino, Claudio Sillero-Zubiri, Paul Johnson, and David Macdonald from the University of Oxford in the U.K., set out to ask this question. They collected data on 17 wolf packs in the Bale Mountains of southern Ethiopia for 13 years. They did this by following the packs on foot or on horseback and watching them with binoculars. The researchers also mapped the quality of the habitats to estimate the number of giant mole rats and Murinae rats available.

These wolf packs included 13 wolf packs with territories in optimal rodent-hunting areas (high-quality habitat in the Web Valley-Sanetti area) and 4 packs with territories with very few rodents (poor-quality habitat in the Tullu Deemtu area). The packs in the high-quality habitat had from 3-13 wolves, usually including the breeding pair, their pup, their adult sons from previous years and some of their adult daughters from previous years (Adult daughters were more likely to set out on their own than the sons). The packs in the poor-quality habitat only had 2-3 wolves, including the breeding pair and maybe their pup.

The researchers discovered that the small packs generally had large but poor-quality territories. The wolf packs in high-quality habitats had smaller habitats, but the bigger the pack, the bigger their territory and the more high-quality habitat they had on their territory. This may be because for each additional wolf in the pack, the more hunting territory is needed to support it. But the researchers discovered that these large wolf packs had more high-quality territory per wolf than the smaller packs had. So if you were a young adult Ethiopian wolf, you would have more high-quality hunting territory for you if you were to choose to stay home with mom and dad and your other siblings than if you were to seek a mate of your own.


Wolves that lived in the Tullu Deemtu area had small groups and large territories, but the
territories did not have a lot of access to food. Wolves that lived in the Web Valley-Sanetti
area had more access to food and could live in larger groups on smaller territories. The more
wolves in the pack in the Web Valley-Sanetti area, the more territory they could defend
per wolf.  Figure from Marino, Sillero-Zubiri, Johnson, and Macdonald's 2012 Behavioral
Ecology and Sociobiology paper.
The researchers also explored other possible advantages of group living, but didn’t find much. These animals hunt alone, so larger groups do not hunt more effectively than smaller groups. And the helpers were not all that helpful as babysitters either: The breeding pair did not have more pups, and pups were not more likely to survive, in families that had more helpers.

So the main advantage for a young adult Ethiopian wolf to stay home with mom and dad a bit longer seems to be more access to better hunting grounds. Why would this be? Ethiopian wolves patrol the boundaries of their territories and pee on them to mark their territory. More wolves in the pack means more patrols and more pee. In this way, larger packs are more able to defend more and better-quality territory. This benefits each of the young adults that stay with the family, and even mom, dad and pup too… to a point. Once the pack reaches a size of 8 adults, the benefits per wolf decline. Packs larger than 8 are more likely to split into multiple smaller packs, each with its own breeding pair. One more benefit of being in a larger group: When young adults split off from the family pack to establish their own breeding pair, they often get to inherit some of their natal territory.

If you find yourself living with mom and dad later than you may have anticipated, it may just be worth it as long as the refrigerator stays stocked and the diggs are comfortable. And if you find yourself a mom or dad with an adult child living with you later than you may have anticipated, it may just be worth it as long as they help stock the fridge and keep the place clean. But as soon as the arrangement stops being beneficial for everyone, it is time to strike out on your own.

Want to know more? Check this out:

Marino, J., Sillero-Zubiri, C., Johnson, P.J., & Macdonald, D.W. (2012). Ecological bases of philopatry and cooperation in Ethiopian wolves Behavioral Ecology and Sociobiology, 66, 1005-1015 DOI: 10.1007/s00265-012-1348-x

2 comments:

  1. First of all your blog is amazing! I enjoy reading biological researches the way you present them. I'm also (literally) impressed with all these interesting sections of biology you are covering.

    Thanks for all your work and I hope your blog will stay active for a long time, since you are now booked in my rss reader! :-)

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