Science Man and His Environment/Ecology

Abiotic Factors
Aquatic organism have some additional factors:

Limiting factors

 * Limiting Factor : One factor which is more important than other factors in determining the success of a population

Example 1 If there is enough water, shelter, and space for 20 rabbits, but only food for 10; then the rabbit population will not exceed 10.

Example 2 If there are food for 1000 birds, but nesting sites for 100, the population of birds will be limited.

In Examples 1 and 2, food and nesting sites are the limiting factors, respectively.

Definitions

 * Habitat : the place where a population lives


 * Niche : (pronounced nitch) is the role which a species has within an ecosystem.

Note that the habitat can be considered the address and the niche as the occupation.

Broad versus Narrow
Generalist species - Broad niche


 * lives in many different places, eats a variety of food, or tolerates wide range of environmental conditions


 * examples: cockroach, humans, dogs

Specialist species - Narrow niche


 * lives in only one type of habitat, tolerates narrow range of environmental conditions, or uses only one or a few types of food


 * example: giant panda (eats only bamboo, lives in very specific habitat)

Tolerance
Species have a specific range of tolerance to physical, chemical, and biological conditions and resources.

This range forms the fundamental niche.

However, pressures from other species form a narrower niche, called a realized niche.

Niche Differentiation
The key to understanding the concept of niche is understanding why different niches exist.


 * Competitive Exclusion Principle : Two species competing for the same resource cannot coexist if other ecological factors are constant

In other words, different species cannot exist in the same niche.

How different niches can live in the same area is due to resource partitioning


 * Resource Partitioning : Dividing up resources so that species do not directly compete

Types of resource partitioning:


 * Temporal - species compete for same resources at different times


 * Example: hawks hunt during the day, owls hunt at night


 * Spatial - species occupy different areas


 * Examples:


 * Different species of warblers feed in different parts of the same trees


 * Giraffes feed at the top of trees, while deer and antelope feed near the bottom of the tree

Food Chains
A food chain is a series of organisms each of which is a source of food for the next one




 * Trophic level : each level in a food chain

Major roles

 * Producers : Organisms which use energy to produce their own food


 * Consumers : Organisms which get their food by consuming other organisms


 * Primary consumers or Herbivores : Animal that eat producers


 * Secondary consumers or Carnivores : Animal that eat other consumers


 * Tertiary consumers or Carnivores : Animal that eat aecondary consumers


 * Omnivores : Animals which are both herbivores and carnivores


 * Decomposers : Organisms which get their energy decomposing organic matter


 * Detritivores : Organisms which get their energy by feeding on organic debris (for example, in soil)


 * Scavengers : Organisms which eat meat of animals killed by others

Food Webs
The description of a food chain is too simplistic. Organism eat many other organisms. This leads to a further concept.


 * Food web : A food web is a set of interconnected food chains



Energy Flow
As energy is transferred through the food chain, the concept of energy flow applies.



The efficiency of each trophic level is about 5 - 20%. (10% is typical).

This means that carnivores have about 1% of the energy that plants capture.

The energy can be described in terms of biomass

This energy flow has an effect on the number of organisms at each level.