Temperature is the key factor explaining interannual variability of Daphnia development in spring: a modelling study.

Area of Science:

• Aquatic Ecology
• Limnology
• Population Dynamics

Background:

• Spring plankton succession in temperate lakes typically involves a phytoplankton bloom followed by zooplankton grazing (Daphnia), leading to a clear-water phase.
• This cycle is often attributed to consumer-resource dynamics, with zooplankton growth dependent on food availability.

Purpose of the Study:

• To investigate the relative importance of temperature versus food availability in driving Daphnia population dynamics and the timing of the spring clear-water phase.
• To model the interannual variability of Daphnia population dynamics during spring in temperate lakes.

Main Methods:

• Utilized a size-structured Daphnia population model.
• Forced the model with seasonal temperature regimes and varied parameters including temperature increase timing, phytoplankton bloom onset, Daphnia mortality rates, phytoplankton carrying capacity, and overwintering abundance.

Main Results:

• Temperature, not food availability, was identified as the dominant factor influencing the timing of Daphnia population peaks.
• A 60-day advancement in spring warming advanced the Daphnia peak by 54 days, whereas a similar shift in the phytoplankton bloom advanced it by only 17 days.
• Peak Daphnia standing stock was primarily controlled by phytoplankton carrying capacity, independent of temperature.

Conclusions:

• Temperature is the key driver for the timing of Daphnia development and the subsequent clear-water phase in spring.
• While food availability dictates the magnitude of the Daphnia spring peak, temperature governs its timing, highlighting a crucial factor in lake ecosystem dynamics.