Download Sect 04.1

Section 04.1
Population Dynamics
Objectives
• Describe the characteristics of populations.
• Understand the concepts of carrying capacity and limiting factors.
• Describe the ways in which populations are distributed.
Main Idea
• Population of species are described by
– density
– spatial distribution
– growth rate
Population Characteristics
• Population
◦ =group of organisms that
• belong to the same species
• live in a particular place at the same time
• Characteristics of populations
◦ used to classify populations of organisms
◦ types
• density
• spatial distribution
• growth rate
• Population density
– = the number of organisms per unit area
• or how crowded a population is
–
expressed as
• number of individuals per unit area
• example:
– Japan has a density of 330 people/Km2
– USA has 30 people/Km2
–
• Spatial distribution
– aka dispersion
– = the pattern of spacing of a population within its area
–
there are 3 main types
• uniform dispersion
• clumped dispersion
• random dispersion
–
Uniform dispersion
– individuals are separated by a fairly even distance
– usu result from social interaction
• individuals keeping their distance from one another
• Clumped dispersion
– individuals are clustered together
– usu occurs
• when resources are clumped
– ex: food, shelter, etc.
• because of species’ social behavior
– ex: herds, flocks, etc.
• Random dispersion
– no definite pattern is noted
– usu results from seed dispersal by
• wind
• birds
• Population ranges
– no population occupies all habitats
• in the biosphere
–
organisms adapt to their habitat’s environmental factors
• abiotic
• biotic
–
organisms may not be able to adapt to an environment’s abiotic factors
Population Limiting Factors
• Density-dependent factors
– = any environmental that depends on the number of members in a population per unit
area
– are often biotic
– examples
• predation
• disease
• parasites
• competition
• Density-dependent factors
– predation
• often controls populations in nature
• this regulation takes place within a predator-prey relationship
– one of the best-known mechanisms of population control
• Density-dependent factors
–
disease
• outbreaks tend to occur when
– population size has increased
– population density is high
• disease is easily transmitted between individuals due to
– frequent contact between individuals
• Density-dependent factors
– competition
• inc when density increases
• if density increases to point where resources become insufficient
– population will become smaller
• can occur
– within a single species
– between different species
• Density-dependent factors
– parasites
• action of parasites similar to disease
• as population inc
– parasites will increase
–
increase will cause decrease in population
• Population growth rate (PGR)
– = how fast a population grows
– 2 factors
• natality
– = birth rate of a population
• mortality
– = death rate of a population
• PGR
–
–
also effected by individuals movements
emigration
• = number of individuals leaving a popul
–
immigration
• = number of individuals entering a popul
–
PGR = (natality + immigration) –
• (mortality + emigration)
• There are two mathematical models for PGR
– exponential growth model
• “J”-shaped growth curve
–
logistic growth model
• “S”-shaped growth curve
• Exponential growth model
– growth pattern of population that has no limits
–
after a “lag phase”
• which is a slow growth period
–
growth occurs “exponentially”
• growth increases rapidly
• Logistic growth model
– occurs when the population’s growth is limited
• carrying capacity (K)
– = maximum number of individuals in a species that an environment can
support
– when a population reaches K of its environment
» its growth levels off
» average growth rate is zero
–
–
limited by available resources
Reproductive patterns
– also play a part in PGR
– some species
– vary in the number of births per cycle
– vary in the age of onset of reproduction
– vary in the life span of the individual
–
–
all organisms are placed into groups based on their reproductive factors
two examples
– R-strategists
– K-strategists
• R-strategists
– aka rate strategists
– an adaptation for living in an environment where
• fluctuation in biotic or abiotic factors occur
–
usually are small organisms have
• short life spans
• large numbers of offspring
• ex: fruit fly, locusts
• R-strategists
– produce as many offspring as possible
• in order to take advantage of the environment
–
usually
• are controlled by density-independent factors
• do not maintain a population near K
• K-strategists
– an adaptation for living in stable environments
– experience a K that changes little
• from year-to-year
–
generally a large animal
• with a long life-span
• produces few offspring
• K-strategists
– adapted for living in environments
• that fluctuate in predictable ways
–
experience a K that changes little
• from year-to-year
–
generally a large animal
• with a long life-span
• produces few offspring