Science Man and His Environment/Ecology

Review

 * Environment : Everything that affects a living organism


 * Ecology : The branch of biology studying the relationships between living organisms and their environment

Abiotic/Biotic
We can divide the components of the environment into abiotic and biotic


 * Abiotic : non-living components


 * Biotic : living components

Definitions

 * Organism : Any form of life


 * Species : Groups of organisms which can reproduce and produce fertile offspring


 * Population : group of organisms of the same species interacting within a geographical area


 * Community : All populations of different species within an area


 * Ecosystem : A community and their non-living environment


 * Biosphere : All of the Earth's ecosystems put together



Taxonomy

 * Genus (pl. genera) : Group of closely related species

Species names are given as Genus species. Both words are in italic, the first is always capitalized, the second is never capitalized.

Examples,
 * Felis catus - Domestic cat
 * Homo sapiens - Human

Higher groups with less closely related species (in order of most closely related to least related):
 * Family
 * Order
 * Class
 * Phylum

Example: Felis catus
 * Family: Felidae (all cats - including tigers, lions)
 * Order: Carnivores (carnivores)
 * Class: Mammalia (mammals)
 * Phylum: Chordata (chordates - includes all vertebrates)

Outline of Ecology
 * Energy flow
 * Abiotic factors
 * Population ecology (habitat, niche)
 * Community ecology (food chains/webs)
 * Cycling of matter

Energy flow in ecosystems
This section has its own page: Energy Flow in Ecosystems

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)

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


 * Omnivores : Animals which are both herbivores and carnivores


 * Decomposers : Organisms which get their energy from dead organic matter

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.