Factors Influencing Population Size
Characteristics of a Population
Ecology: study of a population and its interaction with the environment
investigates factors influencing size, distribution and additional properties of natural populations
Demographics: statistical characteristics to describe a population
this data is used to make conclusions about populations as well as how to manage populations
Population Size: total number of members in a population
Population Density: volume of a population; the number of members per unit of area
Population Distribution: describes location of members in relation to each other
Clumped Distribution: members closer together than predicted by chance
Near-Uniform Distribution: members spread more evenly than expected by chance
Random Distribution: occurs when resources are uniformly distributed
Sampling a Population
Plot Sampling: estimation of population based on direct counts in a single area
Mark-Recapture Sampling: estimates populations of mobile animals. Animals are captured, marked with a unique identifier, then released. At a later date, a sample population is captured again and an estimate of the population size is made
Immigration: arrival of new members who were previously part of another population
many members of one population will leave, moving to inhabit another area/location
Emigration: the departure of members who will take permanent residence elsewhere #
increases when resources in an area are limited
Population Growth Rates
Zero Population Growth: the number of births is equivalent to the number of deaths
Per Capita Growth Rate: per capita birth rate, minus per capita death rate
Exponential Growth Rate: population growth at a fixed percentage rate. the size of each population increase is determined by the current size of the population
Biotic Growth Rate: the rate at which a population would grow given optimum conditions
Limits to Population Growth
Density Dependent Limiting Factors: limit population growth; have a greater effect on denser populations
competition for a limited resource
as a result, birth rates will decline and death rates will increase
predation
parasites and disease
Intraspecific Competition: competition for resources between members of the same species
caused by an increase in the population size
members unable to acquire resources are often die out while those who do obtain resources have expended too much energy and will not reproduce
resources: food, water, hiding places
Density Independent Factors: factors limiting populations regardless of population size
natural disasters
human caused events (oil spills)
Life History Patterns: schedule of how resources are allocated throughout the lifetime of an organism
r-selection: natural selection pattern in which producing offspring quickly is beneficial. Occurs when populations are low
offspring have short generation times and small body sizes
selection: natural selection pattern in which adaptive traits allow organisms to outcompete each other. Occurs when the carrying capacity of the environment is at capacity