Card Set Information
BIOL 1215-18 Population Ecology
Study of populations relative to environment
Group of individuals of single species living in same area.
Number of individuals per unit area or volume.
Result of processes that add or remove inividuals from population.
Pattern of spacing of individuals in boundaries of population.
Influenced by environmental and social factors.
Impractical or impossible to count all individuals in a population.
Sampling techniques estimate density and total population size.
Population size estimated from small samples, index of population size, or mark-recapture method.
Three Methods for Marking:
Bands on Feet (Birds)
Radio Collars (Wolves)
Recognizing Individual Uniqueness (Dorsal fin on Whales)
Assumption for Marking Techniques:
Method will not affect organisms way of life.
Processes that Change a Population Size:
Immigration - Influx of new individuals from other areas
Emigration - Movement of individuals out of a population
Individuals aggregate in patches.
Influenced by resource availability and behavior.
Individuals are evenly distributed.
Influenced by social interactions like territoriality.
Position of each individual is independent of others.
Occurs in absence of strong attractions or repulsions.
Study of vital statistics of a population and change over time.
Death rates and birth rates are important to demographers.
Life tables to study death rates.
Reproductive tables to study birth rates.
Age-specific summary of the survival pattern of population.
Best by following fate of cohorts.
A group of individuals of the same age.
Calculation of Death Rate:
[(Deaths During Year)/(Alive At Start)] = Death Rate
Graphic way of representing data in a life table.
Survivorship Curve Classification:
Type I - low death rates early-mid life, increase in older age.
Type II - constant death rate.
Type III - high death rates early, lower death rate for survivors.
Species with sexual reproduction, concentrate on females.
Also called a Fertility Schedule.
Age-specific summary of reproductive rates in population.
Describes reproductive pattern of population.
Calculation of Average Number of Female Offspring:
[(Females Weaning a Litter)X(Females in Litter)] = Female Offspring
Traits Affecting Reproduction and Survival Schedule:
Age which reproduction begins.
How often organism reproduces.
How many offspring produced during reproductive cycle.
Life History Traits:
Evolutionary development in physiology and behavior of organism.
Reproduce once and die.
Variable or unpredictable environments favor big-bang reproduction.
Produce offspring repeatedly.
Dependable environments favor repeated reproduction.
Survival and Reproduction:
Finite resources lead to trade-offs.
For Finite Resources:
Reduced brood size
has higher survivability because there of lower population of species (
Enlarged brood size
has lower survivability because there of higher population of species (
Parental care of smaller broods facilitate survival of offspring.
Some plants have many small seeds ensuring growth and reproduction.
Other plants have few large seeds giving large energy store to help seedlings.
Modeling Population Growth:
Change in population size = Births + Immigrants - Deaths - Emigrants
Ignoring immigration and emigration, population's growth rate (per capita increase) equals birth rate minus death rate.
Per capita rate of increase(r):
Difference of per capita birth rate(b) and per capita death rate(d)
r = b-d
Increasing if birth rate is higher than death rate (r>0).
Decreasing when birth rate is lower than death rate (r<0).
growth if birth rate equals the death rate (r=0).
Calculating population size (N):
Population growth over many time intervals:
t = rN
Discrete time interval, no immigration or emigration.
Population Growth Instantaneously:
dN / dt = r
is the instantaneous per capita rate of increase.
Exponential Growth Model:
To study population growth in idealized situation.
Ideal situations help us understand capacity and factors of species to grow.
Exponential Population Growth:
Population increase under ideal conditions.
Rate of reproduction is at maximum (intrinsic rate of increase).
dN = r
If r > 0, population increase is rapid.
Result of exponential population growth.
Population growth depends on the value of N and r,.
Thus population increase is greater as time passes.
Characterizes some rebounding populations.
Logistic Growth Model:
Exponential growth cannot be sustained for long in any population.
Realistic population model limits growth by using carrying capacity.
Fit few real populations but useful for potential growth.
Carrying capacity(K) is max population size environment can support.
Per capita rate of increase declines as carrying capacity reached.
_ _____ _
(K-N)/K close to 1, per capita rate of increase approaches maximum rate.
(K-N)/K is close to 0, per capita rate of increase is small.
Result of logistic model of population growth.
Some overshoot K before settling down to stable density.
Some fluctuate greatly and difficult to define K.
Some show an Allee effect.
Difficult time surviving/reproducing if population size is small.
Logistic Model and Life Histories:
Life history traits favored by natural selection vary with population density and environmental conditions.
K-selection and r-selection are oversimplifications but stimulated alternative hypotheses of life history evolution.
Selects life history traits sensitive to population density.
Selects life history traits maximizing reproduction.
Factors Affecting Population Growth:
Environmental factors that stop a population from growing.
Radical Fluctuations in size over time.
Birth rate and death rate do not change with population density.
Birth rates fall and death rates rise with population density.
Negative feedback that regulates population growth.
Affected by competition for resources, territoriality, disease, predation, toxic wastes, and intrinsic factors.
Competition for Resources:
Crowded populations intensifies competition for resources resulting in lower birth rates.
In vertebrates and invertebrates competition for territory limit density.
Cheetahs use chemical communication to warn other cheetahs of their boundaries.
Oceanic birds exhibit territoriality in nesting behavior.
Influences the health and survival of organisms.
Pathogens can spread more rapidly in dense populations.
Population growth attracts predator preferential.
Accumulation contribute to density-dependent regulation of population size.
Physiological factors regulate population size.
Challenged hypothesis that large mammal populations are relatively stable.
Biotic and abiotic factors influence population size.
Some undergo regular booms-and-bursts cycles.
Global Human Population:
No population can grow indefinitely.
Increased slowly until 1650 and began to grow exponentially.
Still growing but began to slow during the 1960s.
Regional Human Population Configurations:
Zero population growth = High birth rate & High death rate
Zero population growth = Low birth rate & Low death rate
Demographic transition goes from first state toward second state.
Associated increase in quality of health education.
Most global population growth concentrated in developing countries.
Relative number of individuals at each age.
Age structure diagrams predict population's growth trends.
Illuminates social conditions and help plan for the future.
Infant mortality and life expectancy at birth vary greatly.
Global Carrying Capacity:
Carrying capacity of humans on Earth uncertain.
Average estimate is 10-15 billion.
Ecological footprint concept summarizes land and water needed to sustain a nation.
Measures proximity to carrying capacity of Earth.
Great footprint size and ecological capacity variation.