Variation in Lakes

• what happens to lakes in winter?

  the densest water sinks to the bottom and the surface gets even colder and less dense, leading to winter stratification
• what happens to lakes in spring?

  the top layer warms and the wind is able to fully mix the water, leading to spring circulation
• what happens to lakes in summer?

  the surface becomes so warm and less dense that the wind cannot fully mix the water, leading to summer stratification
• what happens to lakes in autumn?

  the surface layer cools down, the difference in water density between layers decreases and the wind can fully mix the lake, leading to autumn stratification
• what is a dimictic lake?

  a lake which sees negligible difference between surface and bottom layer temperature, allowing it to mix vertically twice a year
• what is ecological succession?

  the process by which a community of organisms changes over time
• what causes changes in algae and zooplankton quantity?

  predator prey cycles
• what causes changes in algae and zooplankton quality?

  succession
• what process can be carried out in order to avoid predation in lakes?

  diurnal vertical migration
• what is diurnal vertical migration?

  Movement of organisms in the ocean from deep waters (hypolimnion) during the day to surface waters (epilimnion) at night.
• who practices diurnal vertical migration?

  cladocerans, copepods, rotifers, macroinvertebrates and even some algae
• what does diurnal vertical migration behaviour depend on however?

  predator presence
• do zooplankton migrate vertically in lakes with fish present?

  yes
• do zooplankton migrate vertically in lakes with no fish?

  no
• what is diurnal vertical migration driven by?

  chemical cues of predator presence
• what are the chemical cues of predator presence called?

  kairomones