Frozen ground, mosses & lichens, brief blooming summer.
Boreal conifer forest — spruce, fir, pine; the green crown of the north.
Deciduous forests & grasslands; four seasons, oak, beech, prairie.
Year-round warmth & rain; rainforests cradle half of Earth's species.
Less than 25 cm rain a year — life adapts with succulence and silence.
Open ocean, reefs, kelp & deep — the largest biome by far, covering 71% of Earth.
Energy enters ecosystems as sunlight, captured by photosynthesizing producers. From there it travels along trophic levels — and at each transfer, most of it is lost.
Roughly only 10% of the energy at one level is incorporated into the next. The rest is exhaled as heat, spent in respiration, or lies undigested in scat.
This is why apex predators are rare. A pasture supports millions of grass blades, thousands of voles, hundreds of foxes, and perhaps a single eagle nesting overhead.
Unlike energy, which flows through and dissipates, the elements of life are recycled — passed between living tissue, soil, water, and air across geological time.
Photosynthesis pulls CO₂ from the air; respiration & decay return it. Reservoirs in oceans, soils, and rock release on slow rhythms — disturbed now by combustion of fossil seams.
Atmospheric N₂ is fixed by lightning and bacterial root partners (legumes, cyanobacteria) into ammonia & nitrates plants can use; denitrifiers eventually return it to air.
Evaporation, condensation, precipitation, transpiration — the hydrologic loop. Forests sweat the rain that falls downwind; remove the trees and rivers fail.
Slow & sedimentary — has no gaseous phase. Weathered from rock, taken up by plants, returned by decomposition. Often the limiting nutrient in fresh waters.
In 1925–26, Alfred Lotka and Vito Volterra independently described how the populations of a predator and its prey can oscillate — each chasing the other in slow waves.
When hares are plentiful, lynx multiply. Their abundance then thins the hares; without prey the lynx starve, and the hares rebound. Decades of Hudson's Bay Company pelt records (1845–1935) show this rhythm in nature.
The cycle is roughly ten years long, and the predator's peak lags the prey's by a season or more — a fingerprint of coupled lives.
A niche is the role a species plays — its food, its shelter, its hours of activity, its tolerance for cold and damp. Every dimension of life it occupies.
Georgii Gause (1934) put two species of Paramecium in a single tube of broth. They could not coexist: one always drove the other extinct.
In the wild, species solve this by partitioning resources — different prey sizes, different perch heights, different times of day. MacArthur's warblers each forage in a distinct part of the same spruce.
A keystone species exerts disproportionate influence on its community — its absence reorganizes everything beneath it. Robert Paine (1969) coined the term after pulling starfish from a Washington coast and watching mussels overrun all other life.
Otters eat sea urchins. Without otters, urchins explode and graze kelp forests to bare rock — entire submarine cathedrals collapse into “urchin barrens.” Otters returning to the Pacific coast in the 20th c. brought the kelp back.
Reintroduced in 1995 after a 70-year absence. Elk could no longer browse riverbanks unmolested; willows and aspens recovered, beavers returned, river channels themselves shifted shape — a famous “trophic cascade.”
Norman Myers (1988) noticed that biodiversity is wildly uneven — a few small regions hold disproportionate amounts of the world's living variety. Conservation International today recognizes 36 hotspots, defined by extreme endemism and severe loss.
A trophic cascade is the rippling effect of one trophic level on the levels far beneath it. Top-down: predators shape herbivores, herbivores shape vegetation, vegetation shapes soil and rivers themselves.
In the kelp-otter system: more otters → fewer urchins → more kelp → more fish, sea birds, whales.
In Yellowstone: more wolves → wary elk → recovering willow → returning songbirds & beavers → re-meandered streams. The wolf, in this telling, is also a hydrologist.
Cascades reveal that ecosystems are not loose collections but tightly braided wholes; pulling on any single strand redraws the whole pattern.
Five times in Earth's deep history more than three quarters of all species have vanished within a geological eyeblink — at the close of the Ordovician, Devonian, Permian, Triassic, and Cretaceous.
We are now midway through a sixth. The 2019 IPBES Global Assessment estimated that around one million species face extinction in the coming decades — many within decades, not centuries.
The drivers are by now familiar: habitat loss, direct exploitation, climate change, pollution, and invasive species. Each amplifies the others.
There is no single remedy, only a working repertoire — practiced across scales from the gene bank to the continent.
National parks, marine reserves, biosphere reserves. The 30×30 framework asks for 30% of land & sea protected by 2030 — a target adopted in Montreal, 2022.
Returning missing species (wolves, bison, beavers) and restoring ecological processes — letting landscapes reassemble themselves rather than be gardened.
Stitching fragmented habitat with bridges, underpasses, and connecting strips so populations can mix, migrate, and adjust to a shifting climate.
Last-resort insurance for the brink: California condors, Arabian oryx, Mauritius kestrels — pulled from extinction through breeding & reintroduction.