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Populations are dynamic - they change hourly, daily, seasonally, or annually - and depends on the species and environmental conditions
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- predicts the growth of a population
- can protect endangered species |
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- can be determined by natality, morality, immigration, and emigration
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retrieving data
- done by routine sampling |
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analyzing:
- through life tables and survivorship curves |
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Demography
the study of the growth rate, age structure, and other characteristics of populations
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Natality
the birth rate in a population mortality the death rate in a population
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Immigration
the movement of individuals into a population
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Emigration
the movement of individuals out of a population
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Life table
a chart that summarizes the demographic characteristics of a population
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Cohort
a group of individuals of similar ages
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Age-Specific Mortality
the proportion of individuals that were alive at the start of an age interval but died during the age interval
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Age-Specific Survivorship
the proportion of individuals that were alive at the start of an age interval and survived until the start of the next age interval
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Survivorship Curve
a graphic display of the rate of survival of individuals over the lifespan of a species
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Fecundity
the potential for a species to produce offspring in a lifetime
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Generation Time
the average time between the birth of an organism and the birth of its offspring
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Sex Ratio
the relative proportion of males and females in a population
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- environmental conditions can increase or decrease population
- biotic and abiotic factors affect the rates of natality, mortality, immigration, and emigration |
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calculations:
population change = (births + immigration) - (deaths + emigration) |
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analysis:
- if natality and immigration are equal to mortality and emigration → the population’s size will remain stable - when natality and immigration are greater than mortality and emigration → there is population growth - when mortality and emigration are greater than natality and immigration → population will decrease |
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- a group of individuals born around the same time are marked
- monitored until they all die |
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- the lifespans of the individuals are divided into age intervals
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how?
- short life-span: labelled by days, weeks, or months - long life-span: by years or ranges of years |
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morality and survivorship
- the mortality rate is the number of deaths in a population per unit of time |
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morality/survivorship calculations:
age-specific mortality = # that died during the interval / # alive at the start of the interval age-specific survivorship = # still alive at the end of the interval / # alive at the start of the interval |
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survival probability
- the proportion of the cohort that survived at a specific age summarizes the survival probability of a newborn at that age |
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calculations:
probability of being alive at a specific age = # alive at the start of the age interval / # alive at the start of the initial age interval |
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fecundity varies from species to species
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- can increase or decrease depending on:
- environmental conditions - age structure - generation time - sex ratio |
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environmental conditions:
- plenty of food and the climate is optimal = species tend to have higher rates of reproduction - little food and precipitation → reproduction rates drop |
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age structure:
describes the relative number of individuals in each age category - pre-productive: younger than the age of sexual maturity - reproductive: reproducing age - post-reproductive: older than the max. age of reproduction this reflects its recent growth history to predict its future growth |
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generation time:
- i.e. E. coli has a short generation time → they mature very quickly and reproduce quicker - humans have a much longer generation time in comparison to E. coli |
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sex ratio:
# of females have a greater impact because they produce offspring - a male can mate with several females → does not greatly influence reproduction - but; some species have lifelong pairs and the # of males matter as much as females |
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high fecundity
= an animal that has many offspring - but does little care for them - e.x. hawksbill turtle lay as much as 100 eggs, but leave the nest (the offspring fend for themselves at birth |
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low fecundity
= produces fewer offspring per year - has more energy to care for them - can be protective - e.x. bears stay and teach their cubs how to survive |
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they are like life tables; but a graphical representation
- displays the survival of individuals over the lifespan of the species |
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types:
- type I - type II - type III |
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Type I example
- humans; when a baby is born, we take great care of them until their young adult years in which they provide for themselves |
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Type II example
- lizard; they constantly face a number of diseases, predation, and starvation not matter their age |
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Type III example
- fish; has a high juvenile mortality (when they are babies - constantly surrounded by predators) |
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Cheatography n. The art of mapping complex subjects into clear, instantly navigable reference guides.
