Populations, Communities,and Species Interaction

Chapter 3

Outline:

• Critical Factors and Tolerance Limits• Adaptation and Natural Selection• Speciation• Ecological Niche• Species Interaction• Population Growth• Community Properties and Structure• Succession

Critical Factors and Tolerance Limits

• Critical Factor - Single factor in shortest supply relative to demand is a critical determinant in species distribution. Tolerance Limits refer to minimum and

maximum levels beyond which a particular species cannot survive or reproduce.

- Many species exhibit tolerance limits that are more critical for young than adults.

Tolerance Limits

Adaptation

• Adaptation - Process where species acquire traits that allow them to survive in their environments. Limited range of physiological modifications

(acclimation) – change not permanent. Inheritance of specific genetic traits allowing

a species to live in a particular environment.- Population-level phenomenon – traits

passed on. Evolution – species change gradually

thru competition for scarce resources

Natural Selection

• Natural Selection - Describes process where better competitors survive and reproduce more successfully. Small, spontaneous, random mutations

occur in every population creating genetic diversity.

Limited resources or environmental conditions may exert selective pressure on a population.

Mutations – may be negative or positive

Factors Exerting Selective Pressure

• Physiological stress due to in-appropriate levels of a critical environmental factor. Moisture, Light, pH

• Predation Including parasitism & disease

• Competition• LUCK

Speciation

• Given enough time, mutations may collectively allow a species to become better suited to new environmental conditions. Divergent evolution - Separation of one

species into new species. Convergent evolution - Unrelated

organisms evolve to look and act alike.

Galapagos Finches

Ecological Niche

• Habitat - Set of environmental conditions in which a particular organism lives.

• Ecological Niche – description of either- The role played by a species in a

biological community, or- Total set of environmental factors that

determines species distribution. Generalists - Broad niche Specialists - Narrow niche

Resource PartitioningLaw of competitive exclusion – no two populations of different species will occupy the same niche and compete for exactly the same resources in the same habitat for very long

So they migrate, or adapt to partition the resources, or die!

Ecological Niche

• Resource Partitioning - Alter behavior or physiology to minimize competition. Allows several species to utilize different

parts of the same resource.

Ecological Niche

Resourceseparation

• spatially or• temporally

Weedy Species

• Opportunistic Species - Quickly appear when opportunities arise. Many weeds are generalists.

• Pioneer Species - Can quickly colonize open, disturbed, or bare ground.