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Population Dynamics. HOMEWORK (write question and answer!) Chapter 4 in txtbk – pgs 55-75 Study Questions #1-11 pg 75 Chapter 8 in cmpn bk – pgs 160-183 Test yourself #1-10 pg 164 Due 1/20. Population Dynamics. The study of how a population changes over time and space.
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Population Dynamics HOMEWORK (write question and answer!) Chapter 4 in txtbk – pgs 55-75 Study Questions #1-11 pg 75 Chapter 8 in cmpnbk – pgs 160-183 Test yourself #1-10 pg 164 Due 1/20
Population Dynamics The study of how a population changes over time and space. Review population from our ecosystem unit. Population – a group of individuals from one species that may interbreed and produce offspring. 5 key properties of populations : 1. Abundance – size of a population at present time, past and future. 2. Birth rates – how many individuals born within a specific time period. (b = B/N) 3. Death rates – how many individuals die within a specific time period. (d = D/N) 4. Growth rates – birth rate – death rate = net number of individuals 5. Age Structure – the proportion of individuals at each age level with a population. • b= birth rate • d = death rate • B= Total # births per time period • D = Total # deaths per time period • N = Population
Age structure A closer look: • Age structure takes into account the affects many different values. • birth/death rates of present and future • impact on the environment • current and future social and economic conditions • Usually modeled as a graph: 4 basic types Pyramid, column, inverted pyramid, and column w/bulge.
Pyramid Structure Population at each stage of life • Short life span • High death rate at each end • High birth rate • Ex: Kenya Older Younger
Column Structure • declining birth rate • Low death rate • Stable population or decreasing population • Ex: US • A bulge in the column occurs if there was in increase in birth or death rates at a certain age group. • ie. war, baby boom, etc.
Inverted Pyramid • More older people than younger. • Low death rate • Low birth rate • Longer life expectancy with good care Ex: Many parts of Europe
Research – Due 1/24 You will research your ancestry’s origins. Pick one country from your family’s past (can not be US, unless Native American, then use your Tribe) Research the population from that time period and the current population. • Draw/graph two pyramids. • 1st one showing the population – age structure from your family’s past • 2nd showing the age structure of the country now. • Write a ½ page paper explaining the difference in graphs and what has accounted for the difference, using your knowledge on population dynamics.
Growth Rates A closer look: • Determined by the change in population over a specific time period. • Populations will increase as long as there is nothing stopping them (ie – limiting factors) • Most populations will double within a specific time, or generation (ie – exponential growth)
Limiting Factors • Population growth will go unheeded if there is an ample supply of space, food and water to sustain the increase in population numbers. (That is, a utopian world with unlimited supplies of all our needs.) • But of course we live on earth, so there are limiting factors that play a role in our population size. • 2 types: density-dependent and density-independent.
Density-Dependent • All biotic factors are density-dependent. • The increase in population size will increase the effect they have on the ecosystem. (negative feedback) • Leads to population stability and/or regulation of the population • Internal factors: • Factors that effect an individual species. • Ex: limited food, availability of habitat area or territory, fertility. • External factors: • Factors between two different species. • Ex: predation and disease.
Density-Independent • Most abiotic factors are density-independent • Populations do not effect density-independent factors within an ecosystem, but these factors play a role in regulating the existing populations. (not a feedback mechanism) • ex: weather and climate, natural catastrophes • Gives rise to two population growth patterns: • S-curves and J-Curves
S-Curves • Shows a pattern where the population will increase exponentially until the available resources are starting to max out. • At the time the resources or density-dependent factors become limited, the population growth rate will start to slow down until it reaches a constant state. (Seen as an S shape on a graph.) • Carrying capacity – the maximum population size in regard to what the environment can support.
J-Curve • Shows a growth and setback type of pattern • Seen in populations that have grown exponentially then collapsed (dieback) • Usually seen in populations that have exceed their carrying capacity (overshoot) • Seen in populations that have had a series of growths, but then a natural catastrophe, or war has decreased their population size drastically. • Typical in microbes, invertebrates, small mammals (ie gerbils), and fish.
