bio 30 chap 20

Population Density

Number of individuals in a defined area

Distrubition of populations (patterns)

• Random: no attaction or repulsion among memebers

• Uniform: Competion among individuals for space, nutrients, etc

• Clumped: Grouped around attractant (water)

Population growth

∆N = (birth + immigration) - (death + emmigration)

Growth Rate

gr = ∆N / ∆t

Per capita growth rate

cgr = ∆N/ N

Biotic potential

Regulated by-

• Offspring: max # / birth

• Procreation: # times/year reproduction happens

• Capacity for survival: chance of organism reaching reproductive age

• Maturity: age at which reproduction begins.

• Life span: length of life

Growth curves:

J –curve: Normally is followed by a sharp decline in population numbers, which may rise rapidly again

S –curve: has a point of maximum growth and a carrying capacity (K)

Limiting factors in populations

• Density independent factors: will affect population regardless of its size. (floods, drought, etc)

• Density dependent factors: increase in population size = increase results. (disease, parasites, food, competition)

• Law of the minimum: of all the essential substances required for growth, the one in shortest supply controls population numbers.

• Shelford’s law of tolerance: too little or too much of any factor can be harmful to an organism (ex. Salt, temperature)

r and K population

• r – species: small body size, fast maturing and growing, little parental care, offspring # high

• K – species: large body size, slow growing, require parental care

Symbiotic Relationships

• Predation/consumption: relationship of predator/consumer and prey/plant, leads to coevolution (species adapting due to pressures exerting on each other).

• Parasitism: one species benefits (parasite) while harming theother (host).

• Commensalism: one species benefits with no effect on the other.

• Mutualism: both species benefit.(+/+)

Succession

Gradual changes in organisms from a pioneer community to a climax community (best adapted).

Primary succession: No community existed before event.

Secondary succession:Following a destructive event.

Pioneer: 1st to arrive, hardly able to resist flucuations (weeds)
Seral/intermediate: can tolerate fluctuations (shrubs)
climax: longest lifecycles (hardwood trees) stabilze enviourment