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the study of populations and interactions with their environment
groups of organisms of the same species occupying a defined area at a specific time
Characteristics of populations (5)
- Birth Rate
- Death Rate
- Age Structure
- Sex Ratios
# of births/individuals born/unit time
- # deaths/ #individuals/year
- Mortality rate is the number of individuals in a population dying during any given time interval divided by the number alive at the beggining of the time interval
distribution of numbers of individuals of various ages
ratio of number of males to number of females
# individuals/unit area
Birth Rate and immigration often,..
Mortality and emigration often...
Hos is birth rate often expressed?
number of offspring/female/year or per 100 females/year
What is the denisty dependent factor
factor that takes a varying % of the population depending on the density of the population (competition, predation, crowding, parasites, disease)
What is the density independent factor?
factor that takes a constant % of the population independent of pupulation density (climate and weather, shortage of resources-nest sites, den sites, etc, non infections diseases, pollution)
What is exponential population growth?
growth under no environmental resistance or limiting factors
competition and its effects of food, cover, space and water resources, predation (interspecific competition), disease, starvation, etc
What do we have to assume with exponential growth?
that there are no limits such as predation, diseases, etc
Characteristics of exponential growth
- population grows at increasing rates
- "j curve" depicts population growth at increasing rates
Does exponential growth last?
- usually no, environment is not constant and resources are limited
- birth rates will decline, death rates will increase, or both to even out once K is reached
Logistic population growth
- biotic potential of the population is held in check or limited by environmental resistance
- biotic potential is synonymous with reproductive potential, maimum rate of population increase under ideal conditions
In Logistic pop growth
- environmental resistance dictates the carrying capacity of the area or habitat
- there is an S curve graph
What is Carrying Capacity?
the number of animasl an area can support over a period of time without damage to that habitat
What are reproductive strategies
- the more energy spent on reproduction, the less energy it can distribute for growth and maintenence
- investment includes not only the production of offspring but also care and nourishment
- species in different environments will differ in life history traits such as size, productivity, age at first reporduction, # of reproductive events during lifetime, and total life span
- r and k selection
What is r seleciton?
- selection under low population densities
- many offspring
- favors high reproductive rates under conditions of low competition
- fish, bugs, etc
What classifies an r strategist?
- variable climate
- density independent mortality
- variable pop size
- short life span
- rapid development
- high rate of increase
- early reproduction
What is K selection?
selection under carrying capacity conditions and a high level of competition
What classifies a k strategist?
- stable climate
- density dependent
- constant pop size
- long life span (>1year)
- little offspring
- reproduce less often
- slow development
- low rate of increase
- larger offspring
- clumped together populations
- most common type of dispersion
- ex: packs of wolves, elephants, etc
evenly spread out, very specific
- random spacing and distribution
- ex: flower pollen, tree seeds, etc
Population growth equation
- N- number of individuals
- ri- max growth rate, intrinsic growth rate
- t- time
- d- rate of change
- b- birth rate
- m-mortality rate
What are survivorship curves? what different kinds?
- survivorship curves are graphs showing the survival and reproduction of populations
- Types 1,2, and 3
Type 1 survivorship curve?
- like k selection
- few offspring, but live long time
- high mortality rate towards post reproduction years
- ex: humans
Type 2 survivorship curve?
- constant mortality rate throughout life
- ex: Hydra
Type 3 survivorship curve?
- like r selection
- many offspring, but many die close to birth
- few lucky ones survive a longer time
- high mortality rate at pre reproduction years
- Reproduces once before death
- k selected
- ex: bears
- reproduce ofthen througought life
- r selected
how do limited resources and trade offs affect life histories?
limited resources can cause the pop to decrease and the fit survive and trade offs have organisms with low survival rate produce many offspring for a chance and organisms with a higher survival rate produce fewer organisms
Exponental growth equation
Logistic Growth equation
dN/dt=rN x (k-n)/k