Wide-ranging consequences of priority effects governed by an overarching factor

Area of Science:

• Ecology
• Microbiology
• Evolutionary Biology

Background:

• Priority effects shape ecological communities, leading to alternative stable states with taxonomic, functional, and evolutionary consequences.
• The unifying factor underlying these diverse impacts of priority effects remains largely unknown.
• Nectar microbial communities and their interactions with plants and pollinators offer a model system to investigate these dynamics.

Purpose of the Study:

• To identify a common underlying factor governing priority effects in ecological communities.
• To investigate the role of pH in mediating priority effects between nectar-colonizing bacteria and yeasts.
• To explore the eco-evolutionary consequences of pH-mediated priority effects on plant-pollinator interactions.

Main Methods:

• Field surveys of nectar microbial communities and pH in *Diplacus aurantiacus*.
• Laboratory experiments assessing priority effects between *Acinetobacter nectaris* and *Metschnikowia reukaufii*.
• Experimental evolution to study yeast adaptation to bacterial-induced pH changes.
• Field experiments on the impact of nectar pH on hummingbird feeding behavior.

Main Results:

• Nectar microbial communities exhibited alternative stable states dominated by either bacteria or yeasts, correlated with nectar pH.
• *Acinetobacter nectaris* reduced nectar pH, exerting a negative priority effect on *Metschnikowia reukaufii*.
• Yeast evolved resistance to pH-mediated priority effects, and low nectar pH reduced hummingbird nectar consumption, impacting plant reproduction.

Conclusions:

• Nectar pH acts as an overarching factor driving priority effects in nectar microbial communities.
• These pH-driven priority effects have significant eco-evolutionary consequences, influencing microbial community structure, evolution, and plant-pollinator interactions.
• The study demonstrates a systematic explanation for the wide-ranging impacts of priority effects across multiple biological levels.