Ecosystems

Story hook

In 1991, eight scientists locked themselves inside Biosphere 2 — a 1.27-hectare glass-and-steel terrarium in the Arizona desert that aimed to recreate seven self-contained ecosystems: rainforest, ocean, savannah, mangrove, desert, agricultural area, and human habitat. Built at a cost of $200 million, it was the most ambitious attempt ever to engineer a closed ecological system. The plan was for the team to live there for two years, breathing only the oxygen produced by the plants, eating only what grew inside.

Within months, oxygen levels mysteriously dropped from 20.9 % to 14.5 % — the equivalent of standing at 4,000 m altitude. The team had to be supplied with oxygen from outside. Most pollinators died. The ants and cockroaches exploded into pest populations. The morning glory vines smothered the food crops. By the end of the experiment, 19 of 25 vertebrate species were extinct inside the bubble. Scientists later traced the oxygen mystery to microbes in the soil eating the concrete, which absorbed CO₂ and prevented plants from turning it back to O₂.

Biosphere 2 taught us one humbling lesson: we cannot yet build, from scratch, even a 1-hectare ecosystem that maintains itself. The real Biosphere 1 — Earth — has been doing it for 3.8 billion years, and we are only beginning to understand the rules.

This file is about those rules: how ecosystems are structured, how energy moves through food chains, why pyramids of energy always taper upward, and how matter cycles between living and non-living components.

Why this matters for UPSC

Ecosystems is a foundational topic that anchors the rest of Environment GS-III — biodiversity, climate change, pollution, conservation all rest on ecosystem-thinking. Prelims asks 1-2 factual questions per year (food chain types, trophic levels, energy pyramid percentages). Mains asks analytical questions on ecosystem services, coastal/wetland ecosystems, and human disruption. Interview boards probe applications — restoration ecology, ecosystem-based adaptation to climate change.