Law of the Limiting Factors, Law of the Minimum, Law of Tolerance

Critical Factors and Limiting Limits

Every living organism has limits to the environmental conditions it can endure

Environmental factors must be within appropriate levels for life to persist


These factors are primarily responsible for determining the growth and/or reproduction of an organism or population. It may be a physical factor such as temperature or light, a chemical factor such as particular nutrient, or a biological factor such as a competing species. The limiting factor may differ at different times and places.

The Law of Limiting factors states that too much or too little of any abiotic factor can limit or prevent growth of a population of a species in an ecosystem

Examples of limiting factors of a population growth
A. Terrestrial Ecosystem
1. Temperature
2. Water
3. Moisture
4. Soil nutrients

B. Marine Ecosystem
1. Salinity
2. Temperature
3. Sunlight
4. Dissolved Oxygen

Law of the Minimum

Proposed by Justus von Liebig in 1840.
It says that the success of organism determined by crucial ingredient that is in short supply.
As abundance of one resource increases another resource may become limiting.
Also known as Liebig's Law of Minimum - a system maybe limited by the absence or minimum amount (in terms of that needed) of any required factor.

What this law states is that the rarest requirement of an organism will be the limiting factor to its performance.

As an example a crop's yield is restricted by the lack of a single element, in this case lets suppose the soil is low in Nitrogen, adding more phosphorus will not improve the crops yield. Once the soil has nitrogen added crop yield will increase until another element becomes the limiting factor. And no further improvement in yield is possible until more of that element is made available.

Law of Tolerance

Proposed by Victor Shelford in 1913.
This is an extension of the Law of the Minimum.
It refers to the upper and lower bounds to physical environment an organism can tolerate.
These boundaries affect the ability to function, grow, and reproduce. These changes can be broad and narrow.
There are seasonal shifts in tolerance ranges, but within physiological limits.
Implication - no organism can live everywhere.

The law of Tolerance states that the existence, abundance, and distribution of a species in an ecosystem are determined by whether the levels of one or more physical or chemical factors fall above or below the levels tolerated by the species.

Carrying Capacity

The maximum population of a given species that an ecosystem can support without being degraded or destroyed in the long run. The carrying capacity maybe exceeded, but not without lessening the system's ability to support life in the long run.

Population Growth and Carrying Capacity
a. An ecosystem can support only a given number of individuals at a given time. When the capacity level exceeded, an imbalance in the ecosytem occurs.
b. Carrying capacity - is the size of the population of users a resource is able to keep in good condition. Or a number of factors in the environment, such as food, oxygen, diseases, predators and space, determine the number of organisms that can survive in a given area.

Four Factors interact to set the Carrying Capacity
1. the availability of space
2. the availability of energy
3. the accumulation of waste products and their means of disposal
4. the interaction and amount of organisms

Community Properties

This section focuses on how fundamental properties of biological communities and ecosystems are affected by factors such as tolerance limits, species interactions, resource partitioning, evolution, and adaptation.

Productivity

Primary productivity: rate of biomass production is an indication of the rate of solar energy conversion to chemical energy.

• The energy left after respiration is the net primary production.

  

• Photosynthetic rates are regulated by many factors.
  • Light levels
  • Temperature
  • Moisture
  • Nutrient availability

Tropical forests, coral reefs, and estuaries have high levels of productivity because they have abundant supplies of all of the above resources.

Other systems do not have sufficient levels of the necessary resources.

• Lack of water in deserts limits photosynthesis.
• Cold temperatures in Arctic tundra or high mountains inhibit plant growth.
• Lack of nutrients in the open ocean reduces the ability of algae to make use of plentiful sunshine and water.

Even in the most photosynthetically active ecosystems, only a small percentage of the available sunlight is captured and used to make energy-rich compounds.

• Much of the light reaching plants is reflected by leaf surfaces
• Most of the light that is absorbed by leaves is converted to heat is either radiated away or dissipated by evaporation and water.

Abundance and Diversity

Abundance: expression of the total number of organisms in a biological community

Diversity: measure of the number of different species, ecological niches, or genetic variation present.

• Abundance of a particular species often is inversely related to total diversity of the community.
• Communities with a very large number of species often have only a few members of any given species in a given area.
• Climate and history are important factors that dictate the abundance and diversity in a biological community.
• Productivity is related to abundance and diversity, both of which are dependent a several factors.
  • Total resource availability in an ecosystem
  • Reliability of resources
  • The adaptations of the member species
  • Interactions between species.

Complexity

Complexity: number of species at each trophic level and the number of trophic levels in a community.

• Diverse community may not be very complex if all species are clustered in only a few trophic levels.
• Diverse community may be complex if it has many interconnected trophic levels that can be compartmentalized into subdivisions.

Resilience and Stability

Three types of stability or resiliency in ecosystems

• Constancy: lack of fluctuations in composition or functions
• Inertia: resistance to perturbations
• Renewal: ability to repair damage after disturbance

The more complex and interconnected a community is, the more stable and resilient it will be in the face of disturbance.

In highly specialized ecosystems, removal of a few keystone species can eliminate many other associated species.