Maarg Manthan · Topic 1.6

Ecological Principles

Environment & Ecology › Basic Concepts of Ecology · Topic 1.6

Ecological principles are general rules that describe how organisms respond to their environment and how populations, communities and ecosystems work. Liebig's law of the minimum, stated by Justus von Liebig in 1840, says that growth is controlled by the scarcest essential resource, not by the total amount of resources. Blackman's law of limiting factors, of 1905, extends this to all factors, including temperature. Shelford's law of tolerance, of 1913, says that each species has a minimum, an optimum and a maximum for every factor, and success depends on staying within this range. Lindeman's ten percent law, of 1942, says only about ten percent of the energy at one trophic level passes to the next. Gause's principle, Bergmann's rule, Allen's rule and Gloger's rule describe competition and adaptation.

5 min read · UPSC Prelims · Environment & Ecology · Basic Concepts of Ecology

At a Glance

Minimum Liebig, 1840
Limiting factors Blackman, 1905
Tolerance Shelford, 1913
Energy transfer Lindeman, 10 percent
Body size rule Bergmann
Exam link UPSC Prelims, Environment & Ecology: Basic Concepts of Ecology

Where Does It Fit?

This topic follows the account of deep and shallow ecology. It lists the basic laws that govern how organisms and populations behave, which are used in the later topics on communities and energy flow. Previous topic: Deep Ecology vs Shallow Ecology. Next topic: Structure and Characteristics of an Ecological Community.

Which Laws Govern Limits and Tolerance?

Law or rule	Statement
Liebig’s law of the minimum (1840)	Yield or growth is limited by the essential resource that is available in the smallest amount relative to need, like the shortest stave in a barrel. Example: nitrogen or phosphorus limiting crop growth
Blackman’s law of limiting factors (1905)	When a process depends on several factors, its rate is limited by the factor that is nearest to its minimum value. Extended Liebig’s idea to factors such as light and temperature
Shelford’s law of tolerance (1913)	Presence and success of an organism depend on the completeness of a complex of conditions; each species has a range of tolerance with a minimum, optimum and maximum for each factor
Euryhaline and stenohaline	Species with a wide tolerance of salinity versus narrow tolerance. Similarly eurythermal and stenothermal for temperature
Law of toleration	Another name for Shelford’s law
Limiting factor	The factor that restricts the growth, abundance or distribution of a population
Allee effect	Populations of some species do poorly at very low density

Which Rules Describe Energy, Competition and Body Form?

Lindeman’s ten percent law (1942): only about 10 percent of the energy of one trophic level is stored in the next, the rest being lost as heat and in respiration
Gause’s competitive exclusion principle (1934): two species with the same niche cannot coexist indefinitely
Bergmann’s rule: in warm-blooded species, individuals in colder regions are larger, which reduces heat loss
Allen’s rule: animals in cold climates have shorter limbs, ears and tails
Gloger’s rule: animals in warm humid climates are darker in colour, and those in dry climates are paler
Jordan’s rule: fish in cold water have more vertebrae
Hardy-Weinberg principle: allele frequencies stay constant in an ideal population without evolutionary forces
Principle of allocation: an organism has limited energy and spends it on growth, reproduction or survival

What Else Should You Remember?

Resource limitation: light, water, nutrients, space and temperature are common limits
Compensation point: the light level at which photosynthesis equals respiration
Optimum zone: range where growth is best
Zones of stress: ranges between optimum and the extremes where growth declines
Zone of intolerance: outside range where survival is not possible
Acclimatisation: adjustment of an organism to a change in a factor over time
Conformers and regulators: animals whose internal state follows the surroundings versus those that keep it constant
Homeostasis: maintenance of a stable internal state, as in Homeostasis
Migration, hibernation and aestivation: ways to avoid stress
Photoperiodism: response to day length
Law of the minimum in agriculture: fertiliser use aims to remove the limiting nutrient
Monsoon as limiting factor: rainfall decides crop success and forest type in India
Law of the minimum in oceans: iron or nitrogen limit phytoplankton growth in parts of the sea
Ecological indicators: species with narrow tolerance serve as indicators
Climate change: shifts the limits of tolerance of many species
Ecological laws and models: laws are generalisations with exceptions
Link: energy flow rules are in Flow of Energy in an Ecosystem
Sensitivity of species: species with narrow tolerance are quickly lost under pollution, making them useful indicators
Tolerance and distribution: a species can live only where all factors lie inside its range, so maps of tolerance predict distribution
Interaction of factors: the effect of one factor can change the tolerance to another, such as water stress lowering heat tolerance
Liebig in the sea: upwelling of nutrients raises productivity because it removes the limiting nutrient
Use in planning: farmers test soil to find which nutrient is limiting before adding fertiliser

Why Does It Matter for the Exam?

Names and years: Liebig 1840, Blackman 1905, Shelford 1913
Statements: minimum versus tolerance
Rules: Bergmann, Allen, Gloger
Current affairs link: climate limits on species
Common errors: swapping Liebig and Shelford or Allen and Bergmann

As an analytical point, these laws show that organisms are constrained by limits and that the weakest link matters. This idea guides farming, conservation and the prediction of how species will cope with climate change.

Why Is This Topic Important?

Limits Minimum, tolerance
Energy Ten percent
Body form Bergmann, Allen

What Came Next?

The next topic covers the structure and characteristics of an ecological community. Next topic: Structure and Characteristics of an Ecological Community.

Key People and Terms

Limiting factor Factor that restricts growth
Tolerance range Span a species can endure
Eurythermal Wide temperature tolerance
Stenohaline Narrow salinity tolerance
Optimum Best condition
Acclimatisation Gradual adjustment

Exam Corner

Points to Remember

Liebig: minimum; Shelford: tolerance.
Lindeman: 10 percent.
Bergmann: colder, larger body.
Allen: colder, shorter limbs.
Gloger: humid, darker.

Do Not Confuse With

Liebig and Blackman Resource minimum versus all factors
Bergmann and Allen Body size versus extremities
Euryhaline and stenohaline Wide versus narrow salt tolerance

Memory Hook

Liebig’s shortest stave, Shelford’s range, Lindeman’s ten, Bergmann bigger in the cold.

Mains Angle

Questions ask for matching laws with statements. These points help.

Limits Laws
Adaptation Rules
Use Agriculture

A Question You May Face

An original practice question, not a past paper question.

“Explain Liebig’s law of the minimum and Shelford’s law of tolerance and their importance in ecology and agriculture.”

How to Answer

Liebig Minimum.
Shelford Tolerance.
Rules Bergmann etc.
Use Farming, climate.

GS Relevance

Prelims: named laws with scientists and statements. GS Paper 3: ecology.

Frequently Asked Questions

What is Liebig's law of the minimum?

Liebig's law of the minimum, stated by Justus von Liebig in 1840, says that the growth of a plant or population is controlled not by the total resources available but by the single essential resource that is scarcest relative to need, like the shortest stave of a barrel limits how much water it can hold.

What is Shelford's law of tolerance?

Shelford's law of tolerance, put forward by Victor Shelford in 1913, says that the existence and success of a species depend on the range of conditions it can tolerate. For each factor there is a minimum, an optimum and a maximum, and beyond these limits the species cannot survive.

What is the ten percent law?

Raymond Lindeman's ten percent law of 1942 states that on average only about 10 percent of the energy at one trophic level is stored in the next higher level, while the remaining 90 percent is lost mainly as heat in respiration or is not consumed. This is why food chains are short.

What is Bergmann's rule?

Bergmann's rule says that within a widespread warm-blooded species or group, individuals living in colder climates tend to have larger bodies than those in warmer areas, because a larger body has less surface relative to volume and loses heat more slowly. Allen's rule adds that cold-climate animals have shorter limbs and ears.

What is the difference between eurythermal and stenothermal species?

A eurythermal species can tolerate a wide range of temperature, like the common carp, while a stenothermal species can live only within a narrow temperature range, like many coral polyps. Similar terms exist for salinity as euryhaline and stenohaline, and for water as euryhydric and stenohydric.

PYQ Practice — Statement Analysis

1 Liebig's law deals with the minimum resource limiting growth.

True

Stated in 1840.

2 Shelford's law of tolerance was proposed in 1840.

False

In 1913.

3 Gloger's rule links colour with climate.