Population ecology
is the study of population in relation to their environment including environmental influences on density and distribution, age structure and population size
A population is
a group or individuals of a single species living in the same general area; described by their boundaries and size
Density is
the number of individuals per unit area or volume
Dispersion is
the pattern of spacing among individuals within the boundaries of the population
How to estimate density?
population size can be estimated by either extrapolation from small samples; an index of population size
Mark-recapture method
N=sn/x
Determinants of Population density is
birth and death, immigration and emigration
Clumped pattern of dispersion
resource availability and behavior
Uniform pattern of dispersion
social interactions ex. territoriality
Random pattern of dispersions
the absence of strong attractions of repulsions
Demography is the study of
the vital statistics of a population and how they change over time; death rates and birth rates are of a particular interest to demographers
A life table is
survival by age class
Cohort
a group of individuals of the same age
Survivorship curves are
a graph used to demonstrate the rate of survival of a certain species
Humans survivorship curves
most survive until adulthood then rapidly die of old age
Squirrels survivorship curves
equal probability of dying at any point at time
Oysters survivorship curves
mortality is high when young then the ones that survive live for a long time
A reproductive table or fertility schedule is
an age-specific summary of the reproductive rates in a population
Models of population growth describe
population growth in an idealized, unlimited environment
Change in population size =
birth-deaths
In this equation what does it mean: Delta N/Deta T = B-D
Delta N = the change in population size
B=bn D=mN
b=the annual per capita birth rate m=the per capita death rate N=population size
Zero population growth (ZPG)
occurs when the birth rate equals the death rate (r=0)
Exponential population growth is
population increase under idealized conditions
Exponential growth equation
dN/dt=rmaxN
Carrying capacity (K)
the maximum population size the environment can support; varies with the abundance of limiting resources
Logistic population growth model
the per capita rate of increase declines as carrying capacity is reached
dN/dt=rmaxN(K-N)/K
Life history traits
the traits that affect the schedule of reproduction and survival; the age at which reproduction begins, how often the organism reproduces, how many offspring are produced during each reproductive cycle
Evolutionary outcomes reflected in
development, physiology and behavior
Semelparity, or big-bang reproduction
reproduce once and die
Iteroparity or repeated reproduction
produce offspring repeatedly
Organisms have
finite resources, which may lead to trade-offs between survival and reproduction
K-selection or density-dependent selection
selects for life history traits that are sensitive to population density
r-selection or density-independent selection
selects for life history traits that maximize reproduction
There are two general questions about regulation of population growth
what environmental factors stop a population from growing indefinitely? Why do some populations show radical fluctuations in size over time, while others remain stable?
In density-independent populations
birth rate and death rate do not change population density
In density-dependent populations
birth rates fall and death rates rise with population density
Competition for resources
increasing population density intensifies competition for resources; results in a lower birth rate
Toxic wastes
accumulation of toxic wastes can contribute to density-dependent regulation of population size
Predation
as a prey population builds up, predators may feed preferentially on that species
Intrinsic Factors
for some populations, intrinsic (physiological) factors appear to regulate population size
Territoriality
in many vertebrates and some invertebrates, competition for territory may limit density
Disease
population density can influence the health and survival of organisms; in dense populations, pathogens can spread more rapidly
The study of population dynamics focuses on
the complex interactions between biotic and abiotic factor that cause variation in population size
Stability once considered the norm, long tern data sets
suggest fluctuation
Metapopulations
immigration and emigration are particularly important when a number of local populations are linked forming this
High levels of immigration combined with higher survival can result in
greater stability in populations
States that achieve zero population growth
zero population growth=high birth rate-high death rate
zero population growth= low birth rate-low death rate
The demographic transition is
the move from the first state to the second state
The demographic transition is associated with an
increase in the quality of health care and improved access to education, especially for women
Most of the current global population growth is concentrated in
developing countries
One important demographic factor in present and future growth trends is a country's
age structure
Age structure is the
relative number of individuals at each age
Age structure diagrams
predict a population's growth trends, illuminate social conditions, plan for the future
To determine the density of a rabbit population, you would need to know the number of rabbits and
the size of the area in which they live
In wild populations, individuals most often show a___pattern of dispersion
clumped
What conditions favors "big-bang" reproduction
low rates of offspring survival
Factors that increase K
an abandoned building creates more nesting areas; a main competitor for food is eliminated, increasing food availability
Factors that decease K
a parking lot is built, shrinking the habitat; wetlands are drained, decreasing the about of available water; a species with the same food requirements is introduced
Factors that have no effect on K
offspring live longer
The number of individuals that a particular habitat can support with no degradation of that habitat is called
carrying capacity
Resource competition, territoriality, disease, and toxic wastes are some of the factors that provide___and help regulate population
negative feedback