Stoichiometry, herbivory and competition for nutrients: simple models based on planktonic ecosystems

Area of Science:

• Ecological modeling
• Nutrient cycling
• Food web dynamics

Background:

• Competition and predation are key drivers of community structure.
• Nutrient availability and recycling influence species interactions and ecosystem function.
• Predator stoichiometry, the nutrient requirements of predators, can mediate nutrient competition among prey.

Purpose of the Study:

• To model the effects of nutrient recycling by a predator on competitive outcomes between two prey species.
• To determine how external nutrient supply ratios and predator stoichiometry influence competitive dynamics.
• To investigate the criteria for invasion of a second prey species into an established food chain.

Main Methods:

• Development of mathematical models simulating nutrient competition and predation.
• Analysis of factors controlling nutrient supply and recycling within the ecosystem.
• Parameterization of models using a planktonic ecosystem with algae, cyanobacteria, and Daphnia.

Main Results:

• Predator nutrient recycling, driven by predator stoichiometry, alters effective nutrient supply and competitive outcomes.
• Increased supply of a limiting nutrient enhances predator population and its associated nutrient concentration.
• Predator presence can eliminate or restrict prey coexistence, favoring species that benefit from altered nutrient ratios (e.g., green algae in the presence of Daphnia).

Conclusions:

• Predator-mediated nutrient recycling is a critical factor in structuring ecological communities.
• The interplay between external nutrient supply and predator stoichiometry dictates species coexistence and dominance.
• Understanding nutrient dynamics is essential for predicting ecosystem responses to environmental change.