Birds optimize fruit size consumed near their geographic range limits

Area of Science:

• Ecology
• Animal Behavior
• Evolutionary Biology

Background:

• Animals adjust diets for optimal nutrient and energy intake.
• Dietary optimization, like matching fruit size to beak size in birds, enhances consumption efficiency.
• Environmental stress may intensify the need for dietary optimization.

Purpose of the Study:

• To test if dietary optimization, measured by fruit-beak size matching, intensifies under stressful conditions at species' range edges.
• To investigate how environmental stress influences frugivore-fruit interactions and trait matching predictability.

Main Methods:

• Utilized fruit consumption and trait data from 97 frugivorous bird species and 831 plant species globally.
• Analyzed the relationship between fruit size and bird beak size across different geographic locations.
• Compared dietary matching patterns between species at their range limits versus core areas.

Main Results:

• Birds exhibited stronger fruit-beak size matching at their geographic range limits, indicating increased dietary optimization under stress.
• This pattern was more pronounced in highly frugivorous bird species compared to opportunistic frugivores.
• Opportunistic frugivores did not show a significant tendency for closer size matching at range edges.

Conclusions:

• Dietary trait matching is context-dependent and influenced by environmental stress, particularly at species' range edges.
• Frugivore-fruit interactions are shaped by stress, leading to intensified selection for optimal resource use in specialists.
• Trait matching alone may not consistently predict resource use in ecological interactions, especially for generalist species.