Population Dynamics Is the study of how age structure, population density, distribution, and numbers change in response to changes in environmental conditions. Most populations live together in clumps or patches. Populations can grow, shrink, or remain stable

Population Dynamics Age Structure – proportions of individuals at various ages Population Density – number of individuals in a population found in a particular area or volume. Immigration – arrival of individuals from outside the population. Emigration – leaving of individuals from population. Biotic Potential - capacity for population growth under ideal conditions. Intrinsic Rate of Increase (r) – rate at which a population of a species would grow if it had unlimited resources.

Population Dynamics Populations with high intrinsic rate of increase typically reproduce early in life, have short generation times, reproduce many times, and have many offspring with each reproduction. Research reveals that no population can grow indefinitely because of limitations. Limiting factors include, space, sunlight, water, nutrients, exposure to predators, competitors, or infectious diseases. There are always limits to population growth in nature

Population Dynamics Environmental resistance - combination of all factors that act to limit the growth of a population. Biotic Potential + Environmental Resistance = Carrying Capacity (K) Carrying Capacity – maximum population of a given species that a particular habitat can sustain indefinitely without being degraded.

Population Growth Exponential Growth or Geometric Growth – starts slowly but then accelerates as the population increases. Plotting the number of individuals against time yields a J-shaped growth curve. Logistic Growth – rapid exponential growth followed by steady decrease in population growth until the population levels off. Plotting the number of individuals against time yields a sigmoid, or S-shaped curve

Identify the J-curve and S-curve on this graph?

Population Dynamics r - selected species – have many, usually small, offspring and give them little or no parental care or protection. The high numbers of offspring help the population revive when it suffers massive losses. Opportunist species. (EX. roaches, rabbits, bacteria, algae) K - selected species – reproduce later in life and have a small number of offspring with fairly long life spans. Competitor species. (EX. Large mammals, elephants, birds of prey)

Population Dynamics Genetic Diversity can affect the size of small populations. Founder effect – when a few individuals in a population colonize a new habitat that is geographically isolated from other members of the population (Limited genetic diversity or variability may threaten the survival of the colonizing population) Demographic Bottleneck – occurs when only a few individuals in a population survive a catastrophe such as a fire or hurricane (Population may increase but decreased genetic diversity may increase the frequency of harmful genetic diseases) Genetic Drift – random changes in gene frequencies in a population that can lead to unequal reproductive success (Some individuals may breed more than others do and their genes may eventually dominate the gene pool of the population. Founder effect is one cause for genetic drift.) Inbreeding – when individuals in a small population mate with one another. This can occur when a population passes through a demographic bottle neck. (Can increase the frequency of defective genes within a population)

Population Dynamics Population Density can affect Population Size Density dependent population controls include predation, parasitism, infectious disease, and competition for resources. Density independent controls are mostly abiotic. Things like a severe freeze, flood, hurricane, fire, pollution and habitat destruction, do not depend on the density of the population.

Humans not exempt from nature’s population controls 14th century the bubonic plague killed at least 25 million people in densely populated Europe. Caused by a bacterium that lived in rodents. Fleas that lived on the rodents bit humans and spread the disease. 1800’s Irish potato blight killed approximately 1 million people and another 3 million migrated away. Phytophthora infestans an oomycete decimated the potato crops which led to mass starvation. Currently AIDS is a global epidemic. Between 1981- and 2007 the virus killed more than 25 million people. It claims 2.1 million lives each year. An average of 4 deaths per minute.

The Human Population Population change = (births + immigration) – (deaths + emigration) Birth Rate – number of live births per 1000 people Death Rate – number of deaths per 1000 people Age Structure can be used to make population and economic projections. This graph illustrates that: France shows an almost steady increase India shows rapid increase

Population Pyramids