The least effective pollinator principle: specialized morphology despite generalized ecology

Area of Science:

• Ecology
• Evolutionary Biology
• Botany

Background:

• Most plant-pollinator adaptation studies focus on single interactions.
• Understanding adaptation in multi-pollinator systems is crucial for evolutionary insights.
• Stebbins' Most Effective Pollinator Principle guides hypotheses on floral trait evolution.

Purpose of the Study:

• To investigate plant adaptation in a multi-pollinator environment.
• To test Stebbins' Most Effective Pollinator Principle using Pelargonium incrassatum.
• To resolve the paradox of trait mismatching in plant-pollinator interactions.

Main Methods:

• Studied pollination biology of Pelargonium incrassatum in Namaqualand, Southern Africa.
• Observed interactions between floral traits (tube length) and pollinator morphology (proboscis length).
• Analyzed pollinator visitation frequency and effectiveness to determine primary pollinators.

Main Results:

• The most effective pollinator of P. incrassatum had a short proboscis, mismatching the long floral tube.
• A rare visitor (Prosoeca peringueyi) possessed a proboscis matching the floral tube length.
• No significant selection on floral tube length was detected at most study sites.

Conclusions:

• Plant adaptation can favor abundant, less effective pollinators when costs of specializing on rare pollinators are high.
• Trait mismatching is resolved by considering trade-offs; adaptation occurs without reduced pollination by abundant species.
• Specialized floral morphology may evolve when ecological specialization does not incur significant costs.