By combining behavioral and climate data in a statistical modeling framework the researchers found dramatic spatial and environmental variation in social behavior globally. "We discovered 'hot-spots' in places like Australia and Africa where family-living species are overrepresented, as well as 'cold-spots' in places like South and Central America where there are fewer family-living species than we would have expected," said Jetz. This geographic unevenness coincided with the occurrence of specific bird lineages, but also carried a strong signal of environmental and biotic factors. In particular, among year variation, or climatic uncertainty, in rainfall emerged as a key predictor of family-living in birds.
The study demonstrates that even on a global scale, the incidence of complex avian social behavior may be greatly influenced by the consequences of living in unpredictable environments. Variable environments encompass a broad range of climate conditions that pose a greater range of challenges to survival and reproduction than predictable ones. Family-living among birds may therefore be a conservative "'best of a bad job'' strategy to maximize fitness when breeding conditions vary unpredictably from year to year.
"Families act as insurance against environmental uncertainty," said Rubenstein. "Just as predicting a drop in the stock market is difficult, so too is determining when food is going to be scarce." When times are bad and food is difficult to find, joining up to raise young may pay off for both parents and helpers.
This thinking may have implications for an entirely different group of animals: humans. "Think twice," cautions Rubenstein, "before you kick your grown kids out of the house, as you never know when you might need them."
|Contact: Clare Oh|