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Gause's principle gets one line in most NEET notes: two closely related species competing for the same resources cannot coexist. The man behind it is more interesting than the line, and so is the fine print that NCERT adds. This post covers who Georgy Gause was, what he did in his test tubes, how the maths of competition works, and where the principle breaks down.
Who was Georgy Gause?
His obituary in Nature, by Nikolai Vorontsov and Jakov Gall, gives the outline. Georgyi Frantsevich Gause (1910 to 1986) died on 2 May 1986. He began studying biology at Moscow University in 1927. His mentor, V. V. Alpatov, spent two years in Baltimore working with Raymond Pearl, the scientist who revived the logistic growth curve, and brought back what the obituary calls "the spirit of experimentalism". You can read about that curve in our post on Pierre Verhulst and logistic growth.
The obituary says Gause "belonged to two worlds in biology". The second world was antibiotics. In 1942 he and his wife, Maria Brazhnikova, isolated a strain of *Bacillus brevis* that produced an antibiotic later named gramicidin S, used in military hospitals on infected wounds. From 1960 until his death he directed the antibiotics institute that grew out of their laboratory.
What did Gause do in his test tubes?
In a 1932 paper in the Journal of Experimental Biology Gause studied two species of yeast and measured how each one's reproduction changed when the other was present. The abstract says the problem had recently been treated mathematically by Lotka and by Volterra. In 1934 he reported in Science an experimental analysis of Vito Volterra's mathematical theory of the struggle for existence.
His most famous book, *The Struggle for Existence* (1934), summarised experiments on competition between protist species in controlled systems, test tubes he called microcosms. The obituary says this let him formulate the principle of competitive exclusion: "two species belonging to one ecological niche cannot coexist for any length of time." In 1957 the statistician P. H. Leslie reanalysed Gause's data on the protists *Paramecium aurelia* and *Paramecium caudatum* in Biometrika. The phrase "competitive exclusion principle" became the title of a 1960 essay in Science by Garrett Hardin.
What does NCERT say about it now?
The Class 12 chapter on organisms and populations states Gause's principle and then qualifies it. Gause and other experimental ecologists showed in the laboratory that, when resources are limited, the competitively superior species eventually eliminates the other. Evidence from nature is "not always conclusive". More recent studies suggest that competing species may evolve ways to coexist, such as resource partitioning: feeding at different times or foraging in different ways. NCERT's example is MacArthur's five closely related warbler species, which live on the same tree and coexist because of differences in how they forage.
A worked example: the maths of competition
Gause's work tested the Lotka-Volterra competition model. One common textbook form, extending the logistic equation, is:
dN₁/dt = r₁N₁(K₁ − N₁ − αN₂)/K₁
Here α measures how much one individual of species 2 uses up species 1's resources, counted in species-1 individuals. The values below are invented for practice.
Let r₁ = 0.6 per day, K₁ = 500, N₁ = 150, N₂ = 400 and α = 0.8.
Room left for species 1 = K₁ − N₁ − αN₂ = 500 − 150 − 0.8 × 400 = 500 − 150 − 320 = 30.
dN₁/dt = 0.6 × 150 × 30/500 = 90 × 0.06 = 5.4 per day.
Without species 2: room = 500 − 150 = 350, so dN₁/dt = 0.6 × 150 × 350/500 = 63 per day.
The competitor cuts species 1's growth from 63 to 5.4 a day. Now suppose species 2 grows to N₂ = 650. Then αN₂ = 520, which is more than K₁ = 500. The bracket is negative for every N₁ above zero, so species 1 can only decline. That is competitive exclusion in one line of algebra.
Common mistakes:
Dropping α. One individual of species 2 does not always count as one of species 1. Multiply N₂ by α first.
Stating the principle without the condition. It applies when resources are limiting.
Confusing competition with predation. In competition both species are harmed; in predation one benefits.
What can a student take from his way of working?
Pair a theory with a test. Lotka and Volterra wrote equations; Gause built a system simple enough to check them.
Use simple tools well. The obituary praises "simple technical means, clear thinking, imaginative planning and the right choice of system."
Carry your methods to new problems. He took an ecologist's way of thinking into the search for antibiotics.
When an equation like this one is easier to follow with someone checking each step, Fermi's AI tutor can work out what you already know and build a plan for the session. For the field test of competition on a real shore, read our post on Joseph Connell's barnacles.
Next step: in the example, find the value of N₂ at which species 1 just stops growing when N₁ = 150.
