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Chapter 5. Limiting and Regulatory Factors. The Liebig Law of the Minimum. Complex conditions are necessary for the success of individuals, groups of individuals, or biotic communities Think nutrients, competition, predation, etc.

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Chapter 5

Chapter 5

Limiting and Regulatory Factors

The liebig law of the minimum
The Liebig Law of the Minimum

  • Complex conditions are necessary for the success of individuals, groups of individuals, or biotic communities

    • Think nutrients, competition, predation, etc.

  • The one factor that that approaches or exceeds the tolerance level is usually the limiting factor.

  • If that factor changes to become more favorable, then another factor may become limiting.

    • A chain is as strong as its weakest link

Co 2 in an oligotrophic lake
CO2 in an Oligotrophic Lake

  • Lack of CO2 may limit photosynthesis, thus primary production, even if all other nutrients are in excess

  • If CO2 is increased, then primary production should increase.

  • However, primary production will only increase as much as the new level CO2 of allows or some other nutrient becomes limiting.

Shelford s law of tolerance

Lower limit

of tolerance

Upper limit

of tolerance









Abundance of organisms

Population size

Optimum range

Zone of


Zone of

physiological stress

Zone of

physiological stress

Zone of





Shelford’s Law of Tolerance

  • Each individual has a range of tolerance for every physical variable.

Also: Salinity, precipitation, wind, insolation, nutrients, current

Shelford’s Law of Tolerance:

  • The distribution of a species will be controlled by that environmental factor for which the organism has the narrowest range of tolerance.

  • Organisms may have a wide range of tolerance for one factor and a narrow range for another.

    • It only takes one physical or chemical variable to limit a species distribution

  • Organisms that have a wide range of tolerance for limiting factors are likely to be widely distributed

Shelford s law of tolerance1
Shelford’s Law of Tolerance:

  • If conditions are not optimal for one factor, tolerance limits for other factors may be reduced.

    • Low nitrogen may mean less resistance to drought

  • If organisms are not found in their ‘optimum’ range, other factors may be important.

    • Spartina alterniflora grows best in freshwater, but is only found in salt marsh

      • It can extrude salt from its leaves better than other plants, so it is the best competitor in the salt marsh

Shelford s law of tolerance2
Shelford’s Law of Tolerance:

  • Environmental factors are usually most critical during reproduction.

    • Reproductive individuals, seeds, eggs, embryos, seedlings, and larvae usually have a narrower range than adults

      • Adult cypress trees can survive in standing water, but need dry ground for seedling development.

      • Adult blue crabs can survive in freshwater (with high chloride content), but larvae require full strength seawater

Degree of tolerance
Degree of Tolerance

  • Steno narrow; Eury  wide

    • Stenothermal – eurythermal  temperature range

    • Stenohydric – euryhydric  water range

    • Stenohaline – euryhaline  salinity range

    • Stenophagic – euryphagic  food range

    • Stenoecious – euryecious  habitat range

Too much of a good thing
Too Much of a Good Thing

  • Great South Bay, Long Island, New York

    • Oysters

  • Large duck farms resulted in increased fertilization  increased primary production

  • Phytoplankton community shifted from diatoms, green flagellates, and dinoflagellates to very small green flagellates

    • oysters basically starved to death

  • A change in the nutrient composition changed the phytoplankton community (normal community adapted to low nutrients)

Factor compensation
Factor Compensation

  • Some organisms can adapt to reduce the limiting effects of physical conditions.

  • Ecotype – Genetically differentiated subspecies that are well adapted to a particular set of environmental conditions

    • May be locally adapted to light, nutrients, temperature, salinity, etc.


Same species of jellyfish is locally adapted to different temperature regimes.

Reciprocal transplant common garden experiments
Reciprocal Transplant – Common Garden Experiments

  • A common garden experiment can be used to separate the phenotypic (environmental) from the genotypic (genotype) components of variation.

  • Plants of the same species but growing in a diversity of habitats are grown in the same environment.

    • Any differences in phenotype can then be attributed to genotype differences

  • Common garden experiments are also used for animal studies.

    • Temp tolerance, salinity tolerance, reproductive differences etc.

Plantago maritima
Plantago maritima

  • Marsh normal height: 30 – 40 cm

  • Cliff normal height: 5 – 10 cm

  • Each grown in a common garden:

Morphological and physiological differences
Morphological and Physiological Differences

  • Diverse phenotypes can be explained three ways:

    • All differences are phenotypic, and seeds transplanted from one situation to the other will respond exactly as the resident species

    • All differences are genotypic, the mature plants will retain the form and physiology typical of their original habitat

    • Some combination of phenotypic and genotypic determination produces an intermediate result

Circadian rhythm and photoperiod as biological clocks
Circadian Rhythm and Photoperiod as Biological Clocks

  • Physiological mechanism for measuring time

  • Circadian rhythm  24 hr period

    • Tidal marsh fiddler crabs kept in the dark in a lab become active during the time of ebb tides.

    • Juvenile flounder kept in a lab will become active during an incoming tide

  • Photoperiod – a measure of light hours versus dark hours in a 24 hour period

    • 12:12, 14:10

    • Change in photoperiod can trigger flowering plants

    • Long day (increasing day length) vs. short day (decreasing day length) plants

Artificially induced spawning
Artificially Induced Spawning

  • By manipulating photoperiod, we can (sometimes) get fish to spawn out of season.

    • Works best when coupled with correct temperature regime


  • Unlike photoperiod, rainfall in the desert is extremely unpredictable

  • Ephemerals – persist as seeds during drought, but sprout, flower, and produce seeds as soon as enough moisture is available

  • Many seeds have a germination inhibitor that must be washed away

    • Ensure 1 – 2 cm of rain will fall to wash away inhibitor (enough rain to produce seeds)

Soil chief organizing center for terrestrial ecosystems
Soil: Chief Organizing Center for Terrestrial Ecosystems

  • Soil is created by

    • Weathering of rock

    • Deposit of sediments by erosion

    • Decomposition of organic matter in dead plants and animals

  • Complex mixture of eroded rock, mineral nutrients, decaying organic matter, water, air, and billions of living organisms (mostly decomposers)

    • Nutrients regenerated and recycled during decomposition

    • Community respiration can be controlled by the rate nutrients are released

Soil horizons
Soil Horizons

  • Distinct layers found within the soil column (A, B, and C)

  • Rhizospheres - metabolic ‘hot spots’ found around roots, fecal pellets, patches of organic matter, and mucus secretions

    • Although may only be 10% of soil volume, make up 90% of total metabolic activity

Soil horizons1
Soil Horizons

  • A horizon (topsoil) – composed mostly of plant and animal bodies that are being reduced by humification

    • A-0 – litter/detritus

      • Bacteria and fungi work in association with microarthropods (shredders)

    • A-1 – Humus

    • A-2 – leached zone

  • B horizon – mineral soil

    • Organic compounds have been converted to inorganic compounds

      • Leached down from the A horizon

  • C horizon – Unmodified parent material

    • Original that is disintegrating

    • Transported by gravity (colluvial deposits), water (alluvial deposits), or wind (eolian deposit).

Topsoil renewable resource
Topsoil – Renewable Resource?

  • Is regenerated by renewable resources, but it takes 200 - 1,000 years to produce about an inch of topsoil in tropical and temperate climates

    • Rate depends on climate and soil type

  • If erosion exceeds regeneration, then the resource is not renewable

Soil erosion – movement of soil components, especially surface litter and top soil, from one place to another.

- Typically caused by flowing water and wind

Any activity that destroys plant cover makes soil vulnerable to erosion (e.g., farming, logging, construction, over-grazing by livestock, off-road vehicles, and deliberate burning of vegetation).

Harmful effects of soil erosion
Harmful Effects of Soil Erosion

  • Loss of soil fertility and its ability to hold water

  • Runoff of sediment that pollutes water, kills fish and shellfish, and clogs irrigation ditches, boat channels, reservoirs, and lakes.

Methods to control erosion
Methods to Control Erosion

  • Silt Fence / hay bales

    • Allows water to pool so that sediment is dropped.

Riparian buffer zone
Riparian Buffer Zone

  • Areas of trees, shrubs and other vegetation, that are adjacent to a body of water, that are managed for several purposes:

    • to maintain the integrity of stream channels and shorelines;

    • to reduce the impact of upland sources of pollution by trapping, filtering, and converting sediments, nutrients and other chemicals;

    • to supply food, cover and thermal protection to fish and other wildlife.

  • The main purpose of a riparian buffer is to help control non-point source pollution.

Fire ecology
Fire Ecology

  • Fire is an important regulatory component to some ecosystems

  • Crown fires – very intense; destroy almost all vegetation and some soil organic matter

  • Surface Fires – have a selective effect, more limiting to some organisms than to others

Light surface fires
Light Surface Fires

  • Longleaf pine – an example of fire resistant seedlings

  • Supplement bacteria in breaking down organic material.

  • Nitrogen fixing legumes often thrive immediately after a fire.

  • Regular surface fires reduce chance of crown fire