Population Biology Population Growth JCurve Exponential Growth Unchecked
Population Biology
Population Growth • J-Curve • Exponential Growth – Unchecked growth – As a population gets larger it grows faster
Population Growth • S-Curve • Carrying capacity – Number of organisms the environment can support – Limiting factors • Biotic • abiotic
Patterns • Reproductive pattern = life-history pattern – Variety of patterns – Two extremes
Patterns • Rapid life-history patterns – Changing or unpredictable environment – Small – Mature rapidly – Reproduce early – Short life span
Patterns • Slow life-history pattern – – – Large species Stable environments Reproduce slowly Matures slowly Long life span Stay at or near carrying capacity
Population Density • Dispersal patterns – Random – Clumped – Uniform Random Clumped Uniform
Population Density • Density-dependent factors – – – Disease Competition Predators Parasites food • Density-independent factors – – – Volcanoes Temperature Storms Floods Drought Habitat disruption
Other population factors • Predation • Competition
Human Populations Age Structures and Human Growth
Populations • Populations—large and small—change over time • Meaning, they are DYNAMIC • Humans face similar problems as small or large populations that other organisms do
Factors That Influence Population Size • Population growth rate – Determined by: • Natality or birth rate • Death rate • Also influenced by immigration and emigration. • Expressed mathematically: • r = (b-d) + (i-e)
When Studying Populations… • Straight forward expression of population size is absolute number. • Count up all the individuals in the population. • More frequently used is density. – The number of individuals per unit area.
Labs… Random Sampling • A method of selecting a sample (random sample) from a statistical population in such a way that every possible sample that could be selected has a predetermined probability of being selected • BEST for STATIONARY POP (pic of or plants!!!)
Mark and Recapture • A method of sampling an animal population where animals are caught alive and tagged and then returned (unharmed) to their habitat • over time animals from the pop are trapped and those with marks/tags are counted • a mathematical formula estimates the pop size
• What was the purpose of this lab? • What happened when… • Competition with Osprey • Drought decreases the fish population • Fish spawn and double their population • Pollution decrease the fish population by ¾ • Eagle’s have two offspring • So what does this say about the eagle’s diet? Fish/Eagle
Population Stress • As populations increase in size in environments that cannot support increased numbers, individual animals can exhibit a variety of stress symptoms. • These include aggression, decrease in parental care, decreased fertility, and decreased resistance to disease. • They become limiting factors for growth and keep populations below carrying capacity.
Self Check Characteristics of Population Growth Exponential growth Which of the following would you expect to observe after a population exceeds its carrying capacity? Carrying capacity A. population increases exponentially Population B. births S curve J curve exceed deaths C. deaths exceed births is C. D. population growth. The rateanswer is unaffected by limiting factors Time
Age Structure – A population’s age structure indicates the percentage of individuals at each age. – The right side shows females; the left, males – The x-axis numbers are populations size • Usually in millions – The y-axis is age ranges usually 0 -4, 5 -9, 1014, etc…
US Dynamic Age Structure
me Ya’ll
Population Size • Perils of Small Populations – low genetic diversity – subject to inbreeding – less likely to adapt to environmental changes • Problems being a Large population – Increase food shortages & diseases – Decrease in space, clean water – Live at carrying capacity so can experience huge crash – Adaptable with greater genetic diversity
History of Human Population Growth • The Development of Agriculture – About 10, 000 to 12, 000 years ago, the development of agriculture increased the growth rate of the human population.
What happened in the 1600 s? The Population Explosion – Around 1650, improvements in hygiene, diet, and economic conditions further accelerated population growth. – After World War II, the human population grew at the fastest rate in history, largely because of better sanitation and medical care in poorer countries.
Advances in Human Technology = Growth
Demographic Transition • Human populations have undergone rapid growth, yet in some developed countries, populations have stopped growing. • The demographic transition model shows how these population changes happen.
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