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Why Seeds Passed Through Bird Guts Have Greater Survival Rates

Update Date: Jun 21, 2013 11:35 AM EDT
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Scientists have now discovered another reason why seeds eaten by birds and spread across the landscape fare better than those that fall near parent plants. 

Researchers have long known that seeds that fall near parent plants are more likely to be eaten by seed-hungry predators and contaminated by pathogens.

However, a new study published in the journal Ecology Letters reveals another reason why seeds gobbled by birds are more likely to grow into plants. Researchers found that seeds from a wild chili pepper plant found in South America emerge with less of the odor that attracts seed-eating ants and carry fewer pathogens able to kill the seed after being eaten and passed through the digestive tract of birds.

The findings reveal that passing though bird guts increased seed survival by 370 percent, regardless of how far the seeds were dispersed from its parent.

"Ecologists have not been considering gut processing as a factor when they find seeds having less predation or infection away from parent plants, but they should," lead author Evan Fricke of the University of Washington said in a news release. "If similar mechanisms are happening with other species, then ecologists have been missing some major benefits of seed dispersal mutualism between plants and animals."

Scientists previously assumed that seeds fared better when they travel greater distances. However, researchers found that not all plants benefit when seeds are far away fro the parent plant, including the chili pepper.  They found that there was little survival difference between gut-passed seeds planted near other wild chili peppers and those planted some distance away. However, researchers said that this does not mean the short-billed Elaenia, the most common consumer of chilies at the study site in southeast Bolivia, is not important for the wild chili pepper. Previous studies found that the main value of a bird carrying seeds is to get them away from predators and pathogens around parent plants.

Researchers in the current study found that the seed-killing fungal load of infected seeds that have passed through birds was reduced by more than 30 percent. The study also found that gut-passed seeds had twice the survival rate of seeds taken directly from peppers when growing under natural conditions.

When it comes to seed-hungry predators, seeds straight from peppers were twice as likely to be carried off as gut-passed seeds, at least for the first two day. Researchers noted that after two days, ants went after both kinds of seeds about equally.

Researchers suspect gut-passed seeds may fare better because they don't emit volatile compounds that attract predators.  

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