Initial Ecosystem Construction (Day 1)
💧 The sealed jar ecosystem was created using only river rocks, sand, and river water to maintain natural conditions.
🌿 Components included sand/gravel for bacterial growth and hiding spots, algae-covered stones for structure, and loose algae for food and oxygen production ($\text{O}_2$).
🐌 Immediately after assembly, tiny creatures like the bladder snail were visible, with the water clearing by the next day, revealing larger insects like the Dytiscus diving beetle.
🐜 Early inhabitants included diving beetles (predators), back swimmers, bladder snails (which began laying eggs rapidly), scuds (freshwater shrimp look-alikes), and ostracods (tiny creatures filtering water).

Six-Month Ecosystem Evolution (Day 190)
💀 After 190 days, the ecosystem showed signs of change, with some algae weakening, but others showing fresh new growth.
📉 Biodiversity decreased significantly, as is normal for reaching ecological balance; the large diving beetle perished, leaving only its shell.
👑 Scuds emerged as the dominant species due to their hardiness and fast reproductive cycle, self-regulating via cannibalism when food was scarce.
🦠 New species emerged or became visible, including worms gathering on the surface, smaller, darker ostracods, copepods (smallest crustaceans filmed), and a surprisingly large flatworm (over 1 cm long).

Key Points & Insights
➡️ The jar evolved into a self-sustaining ecosystem that achieved perfect self-regulation over six months using only natural components.
🌱 The decomposition of dead organisms (like scud shells) released calcium ($\text{Ca}$), contributing nutrients back into the environment.
🔄 Population control was evident: large predators died out, while dominant species like scuds regulated their numbers through cannibalism when resources were low.
🔬 Initial observation can miss smaller organisms; species like copepods and certain worms only became noticeable or appeared later when larger competitors were gone.

📸 Video summarized with SummaryTube.com on Dec 23, 2025, 18:21 UTC