Population
A population interbreeding group of the same species living in the same general area:
populations may be distinguished by natural boundaries ( ex island population) or arbitrary boundaries ( California population)
Population Density
The density of a population is the number of individuals per unit area of volume
( number of humans per square mile or number of bacteria per millimeter)
Population Dispersion
refers to pattern of distribution of individuals within the boundaries of the population
( uniform, clumped, or random dispersion )
territoriality leads to uniform dispersion
Uniform Dispersion
territoriality is main reason
Clumped Dispersion
most common
due to an uneven distribution of nutrients or other resources in the environment
Random Dispersion
For immobile species, they dont have ability to live anywhere except their given habitat . they are limited to growing wherever they are first set root
Population Dynamics
Populations are dynamic, not static, and change in density, dispersion and total numbers due to :
- Births
- Deaths
-Immigration
-Emigration
Demographics
the study of vital statistics in a population, primarily birth & death rates, and how they change over time
Life table is a useful way of summarizing vital statistics
Semelparity
Some species reproduce once in their lifetime,typically leaving large number of offspring, most which die
ex. salman, offspring are on their own
Iteroparity
Other species reproduce repeatedly in their lifetime, typically leaving small numbers of offspring, most of which survive
ex, humans and elephants, offspring are cared for
Survivorship Curves
Plot of the number of individuals vs age of life span and reflect reproductive strategies
I. fewer offspring and low mortality until old age due to parental care
II. Death rate is relatively constant throughout the life span
III. Many offspring & high mor
Reproductive Rates
Demographers generally focus on females when studying reproductive rates since only females produce offspring
- reproductive tables summarize reproductive rates in relation to age
Population Growth Rate
the change in population size over time is :
Births (B) - Deaths (D) = change in population size per unit time
Per capita birth and death rate
ex, if 50 births per 1000 people per year, annual per capita birth rate= 50/ 1000 or 0.05
Growth Rates
rN= bN-mN= change in N/ change in T
Exponential (J Curve) Growth
If r is steady and positive, a population will grow exponentially
- under ideal conditions the growth rate will be maximal and growth will also be exponential
- is also called J curve growth bc of shape
- occurs when populations are small and resources pl
Logistic ( S Curve) Growth
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Logistic Model & Real Populations
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Environmental Resistance
Factors in an environment such as predators, competition, climate, and food availability, that keep its various populations from reaching their maximum growth potential.
Density- dependent factors
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Density - independent factors
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Human Population Explosion
Decreased environmental resistance due to:
- protection from disease ( loss of predators)
- better nutrition, hygiene
- improved food protection
has little to do with changes in fertility rates
( avg. # of children per woman is ~ the same)
Demographic Transition
The populations of developed countries have all undergone a transition from:
- high birth and death rates
- high birth, low death rates (population expansion)
- low birth, death rates
developing countries are predicted to follow a similar demographic tran
Age Structures
Useful for predicting future population growth :
it's a summary of the number of individuals of each age in the population
-If most of the individuals in the population are below the age of first reproduction, then you can predict that in the near future,
Ecological Footprint
Surface area required to sustain each person
( at current levels of consumption)