It’s always mind blowing to see how much life and biodiversity a single drop of water from a lake can bear.
There are tons of algae, rotifers, crustaceans, ciliates. All of these microbes are at the bottom of the food chain, starting with algae (phytoplankton) which are primary producers, transforming CO2 and energy from sunlight into sugars by photosynthesis! These algae then get eaten by a lot of small herbivores including all of today’s critters like rotifers, stentors, crustaceans and insect larvae which are all placed in the second level of the food web. Those small organisms then get eaten by bigger carnivorous animals, like fish, frogs, birds and aquatic insects, which are classified in the third level of the food chain. Some organisms can be placed in both the first and the second level of the food web if they’re omnivores or if the way they feed changes over time. For example, when herbivorous tadpoles develop into carnivorous amphibians!