Study of changes (size&composition) occurring in a population and what causes these changes
2 important characteristics
Density- number per unit area, too many can cause problems; too few can't find mate
Dispersion- pattern of spacing, often determined by mico climate or interaction with other organisms.
Study of stats relating to changes in a population
age specific summary of survival pattern of a population
way to track a cohort (a group of indiv. of the same age) over time
low death rate early in life associated with high amounts of potential care. (large Mammals)
Intermediate, constant death rate throughout life. example rodents and annual plants.
High death rates when young but those individuals who survive this may live a long time example plants and fish.
Population under ideal conditions will increase exponentially. Geometric growth. Characterized by J-shaped curve.
Even if growth rate is constant population will increase since progeny of each generation are added to the base. Generally cannot occur unchecked increases change environment, growth slows, and declines may follow.
the limit an environment can support. Maximum stable population size that a particular environment can support over time. Logistic growth
Grow rates will cary depending upon density.
fewer resources per indiv. thus growth rate slows. toxins can increase. Favors those who can compete, and are efficient
resources abundant growth rates high, favors organisms capable of rapid reproduction and early sexual maturity.
Some factors are density independent
Fire, Hurricanes, Human Activities, Natural or human causes
collective traits that affect an organisms schedule of reproduction and death. Results of evolution (natural selection). Vary among organisms. Will be trade offs associated with each characteristics individual basis. (who should get to eat)
Short generation time/young
energy goes into reproduction. less available for self. less able to reproduce. increase population numbers quickly
Longer generation time/older
Energy available for self. delay "costs" of reproduction. May die before reproducing.
Number of reproductive events
Semeiparity- single, large reproduction event. then dies. Semi=once Parity= to beget
benefits- avoids costs of long term survival of parent, large number progeny increases odds some will survive. Negatives- only one chance for off spring to survive. example insects, annual plants, aquatic, invertebrates, some fish
repeated reproduction throughout life. Benefits- often smaller number progeny and greater parental care. increases the odds the environment conditions will be favorable for some offspring. Neg,- takes more time to increase population energy needed for parental surveil until reproduction may die genes are lost.
K-selection (carrying capacity)
Density Dependent selection. Occurs when population at/near carrying capacity. High levels of competition. Selects for life history traits that favored at high densities. Typically iteroparous reproduction; large long lived organisms. Type I or II survival patterns. (humans large trees and mammals)
R-selection (growth rate)
density indp. selection. occurs when density or comp. is low. Selects for life history traits that maximize reproduction success. Periods of exponential growth. Typically semelparous reproduction. small short lived org. Type III survival ship patterns ( insects, recently devastated areas, dandelions.)
Overall world population is increasing not yet at k. rate of population growth has declined over past 30 yrs. current pop= 7billion. Growth rate very rapid since industrial rev. mostly due to death rates. demographic transition.