Population - group of individuals belonging to the same species living together in a particular place at a particular time
Population - studied in Ecology because the individuals making them up use the same resources in a certain area, are affected by the same conditions in the area and interact with other organisms in the same way
Population studies - hold the key to saving endangered species and controlling pest populations and disease epidemics
Population Ecology - study of populations in relation to the environment
Populations have emergent properties that are not present in the lower level of organization, individuals.
Emergent properties of populations
Population size
Population density
Natality rate (birth rate)
Mortality rate
Age distribution
Population growth rate
Population distribution
Population distribution - The values of these properties change from time to time (population dynamics, demography).
Variables affecting population size
Number of births (B)
Number of deaths (D)
Number of immigrants (I)
Number of emigrants (E)
Change in population size (ΔN/ΔT)
Changes in population size
(ΔN/ΔT) = (B + I) - (D +E)
Population size increases when (B + l) > (D + E).
Population density - number of individuals per unit of geographic area
Population density is higher to areas with plentiful resources rather than areas with scarcity of resources
Higher population density will deplete resources and leads to competition
TRUE OR FALSE: Population density is a more useful quantity than population size because it relates the number of individuals and the wastes they produce with the amount of resources available in a unit of area (TRUE)
Natality - ability of a population to increase in size through reproduction whether by giving birth (sexual reproduction), budding or fission (asexual reproduction)
Maximum natality - greatest number of new individuals produced under ideal environmental conditions
Realized natality - number of new individuals produced under actual environmental conditions.
Mortality - number of deaths in a population
TRUE OR FALSE: Mortality rates increase with age (TRUE)
Minimum mortality - theoretical minimum laws under ideal (non-limiting) conditions
Realized mortality - actual death rate observed under existing or actual conditions
Realized mortality - occurs when environmental conditions are ideal, but often, environmental conditions cause organisms to die earlier than their physiological longevity would allow
Birth rate - number of new individuals/births that occur per one thousand people, per year
Survivorship - how many individuals of a species born together (a cohort) are still alive at different age intervals.
Three Kinds of Survivorship
Type I
Type II
Type III
Type I Survivorship
Humans, large mammals
Convex shape; late loss
This is shown by many large mammals with few offspring that are quite large, including humans
survivorship is high (and mortality rate low) when the individuals of the population are still young
Mortality rates increase with age (growing older)
Type II Survivorship
Birds, mouse
Diagonal line; constant loss
Mortality does not depends on its age; chance of dying independent of age
Constant mortality rate throughout its entire life
Type III Survivorship
Observed in oysters, clam, shellfish
Clams vulnerable to predators in larval stage
Surviving through attaching to substrate
many individuals of the population die at the free-swimming larval stage due to predation, but once the larvae have attached to a substratum and secrete the shell, more individuals survive (mortality rate decreases)
Concave in shape; early loss
Type III Survivorship
Most of these organisms die right away
High death rate following birth, they don't have parental care to their offspring
This type of curve is shown by species that do not provide parental care to their offspring.
Kinds of Age Pyramids
Expanding
Stable
Collapsing
Expanding Age Pyramid
much greater number of young individuals in the population
rapid growth of population in the future
Examples: India, Kenya, Afghanistan, and Philippines
Stable Age Pyramid
also a greater number of young individuals but the difference is not that matched
slow growth
Example: United States, Canada, Australia
Collapsing Age Pyramid
population size declining since there is a greater number of older people compared to younger population
young not enough to replace younger population
Examples: Japan, Germany, Italy, and many other European countries
Age distribution
Pre-reproductive
From birth up to the pre-pubescent stage
0- 14 years old
Reproductive
15 - 44 years
Post-reproductive
45 to end of life
No. of births and deaths in a population
Can be expressed as the average number of births and deaths per individual (per capita) during the time period.
Per capita birth rate (b)
The number of offspring produced per unit time by an average member of the population
By convention it is the number of births per 1000 individuals
Birth rate
If there are 34 births per year in a population of 1000 individuals, the annual per capita birth rate is 34/1000 or 0.034.
Death rate
If 16 deaths in 1000 persons, then per capita death rate is 0.016.
Population growth rate in a year
b-d = r
r
Also the per capita rate of increase
The difference between per capita birth and death rate, with emigration and immigration ignored.
also called the population growth rate, expressed on a per capita basis.
If b>d, r is >0 or a positive value, population is increasing