Cheatography
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grade 12 biology - chapter 12.2
Introduction
Populations are dynamic - they change hourly, daily, seasonally, or annually - and depends on the species and environmental conditions |
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Demography
- predicts the growth of a population
- can protect endangered species |
- can be determined by natality, morality, immigration, and emigration |
retrieving data
- done by routine sampling |
analyzing:
- through life tables and survivorship curves |
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definitions
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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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Changes in Population Size
- environmental conditions can increase or decrease population
- biotic and abiotic factors affect the rates of natality, mortality, immigration, and emigration |
calculations:
population change = (births + immigration) - (deaths + emigration) |
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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Life Tables
- a group of individuals born around the same time are marked
- monitored until they all die |
- the lifespans of the individuals are divided into age intervals |
how?
- short life-span: labelled by days, weeks, or months
- long life-span: by years or ranges of years |
morality and survivorship
- the mortality rate is the number of deaths in a population per unit of time |
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 |
survival probability
- the proportion of the cohort that survived at a specific age summarizes the survival probability of a newborn at that age |
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 |
Fecundity
fecundity varies from species to species |
- can increase or decrease depending on:
- environmental conditions
- age structure
- generation time
- sex ratio |
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 |
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 |
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 |
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 |
High Vs. Low Fecundity
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 |
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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Survivorship Curves
they are like life tables; but a graphical representation
- displays the survival of individuals over the lifespan of the species |
types:
- type I
- type II
- type III |
TYPE I CURVE
- flat at the start
- low death rate in the early and middle years
- death rate increases in older age groups
- has a long gestation period
- common in large animals
- produce few offspring and provide their offspring
with a lot of care for a long period of time
TYPE II CURVE
- constant rate of mortality in all age groups
- steady declining survival rate
- preyed by type I organisms
- feed on type III organisms
- has a short gestation period
TYPE III CURVE
- drops rapidly right at the beginning
- in early life, the death rate is really high and then flattens out later on in the life of the organism IF the organism survives
- organisms that produce a large number of offspring
- like plants, insects, and fish.
Survivorship Curve Examples
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 |
Type II example
- lizard; they constantly face a number of diseases, predation, and starvation not matter their age |
Type III example
- fish; has a high juvenile mortality (when they are babies - constantly surrounded by predators) |
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