Can competitive asymmetries maintain offspring size variation? A manipulative field test

Area of Science:

• Ecology
• Evolutionary Biology
• Marine Biology

Background:

• Offspring size variation within populations is common but poorly understood.
• Game theory predicts offspring size variation is maintained by asymmetric competition (large offspring as competitors, small offspring as colonizers).
• Empirical evidence for these predictions is limited, especially within species.

Purpose of the Study:

• To investigate the role of offspring size in competitive asymmetries within a species.
• To test whether large offspring are superior competitors in the sessile marine invertebrate Bugula neritina.

Main Methods:

• A field study was conducted on the sessile marine invertebrate Bugula neritina.
• Examined the interactions between offspring of different sizes.

Main Results:

• Offspring size determined whether interactions were competitive or facilitative.
• Large neighbors facilitated small offspring but competed with large offspring.
• Contrary to theory, large offspring were not superior competitors; smaller offspring benefited from larger ones.

Conclusions:

• Asymmetric facilitation, not competition, appears to operate in this system.
• Facilitation of smaller offspring may be a widespread mechanism maintaining offspring size variation.
• Ecological theory should incorporate positive interactions (facilitation) when exploring offspring size variation.