Population Dynamics

Vocab Ecosystem includes biotic and abiotic factors. Population – group of interacting individuals of the same species that inhabit a set geographic area. Community – consists of two or more populations of different species occupying the same geographic area.

Factors Affecting Population Size Birth and immigration increase a population size while death and emigration decrease it. Given unlimited habitat factors, the capacity for reproduction under ideal conditions is called biotic potential. Why don’t organisms meet their biotic potential?

Factors Affecting Rate of Population Increase 1 – age at which species is reproductively mature 2 – number of young produced 3 – frequency of births

Exponential growth results in a j-shaped curve. There are two factors that affect the shape of the curve: the reproductive rate per individual and the initial population. Limited environmental resources limit exponential growth flattening the j-shaped curve into an s-shaped curve fluctuating around the carrying capacity.

Carrying capacity is the number of individuals an environment can support for a prolonged period of time. Carrying capacity changes as the environment changes.

What is the carrying capacity of this species?

Limiting Factors Density – dependent factors are those whose effect increases as the population increases: competition, disease, parasites, and food. Disease will spread more quickly through more dense populations. Density – independent factors are those that affect all populations regardless of their density. Most density – independent factors are abiotic: temperature, flood, drought, storms, and habitat disruption.

Gause's Rule (Competitive Exclusion Principle): Two species cannot live the same way in the same place at the same time (ecologically identical species cannot coexist in the same habitat). This is only possible through evolution of niche differentiation (difference in beak size, root depths, etc.).

Interspecific Competition refers to the competition between two or more species for some limiting resource. This limiting resource can be food, nutrients, space, nesting sites-- anything for which demand is greater than supply. When one species is a better competitor, this competition negatively influences the other species by reducing population sizes or growth rates.

Intraspecific Competition refers to the competition within members of the same species for some limiting resource. The result of intraspecific competition is natural selection.

Homeostasis is one of the fundamental characteristics of living things Homeostasis is one of the fundamental characteristics of living things. It refers to the maintenance of the internal environment within tolerable limits. Environmental factors that must remain balanced include: temperature, salinity, acidity, and the concentrations of nutrients and wastes.

Home Range vs. Territory Home range – area individuals travel during the span of a year Territory – area individuals secure for breeding purposes and will defend. - Territory is smaller than HR - Territory is within HR - As habitat quality increases, HR decreases

Population Biology Ecologists have used the two variables, "r" and "K“, to define end members in the spectrum of animal behavior.

"r"-selected species "r"-selected species rely on a high intrinsic population growth rate in order to succeed. These are "weedy" species which disperse quickly to find newly opened environments, have very many offspring (but small – only a very small portion of the parents reproductive resources are devoted to any single juvenile), and are generally poor competitors.

"K"-selected species "K"-selected species are just the opposite. They are weak dispersers, devote a large amount of their reproductive resources to only one or a few offspring, and are strong competitors.

r & K species r →high potential rate of reproduction → population fluctuates greatly in relation to carrying capacity K → low potential rate of reproduction → population is more stable with less fluctuation

Position in the food chain r K Body size Smaller Larger Life span Shorter Longer Age of first breed Younger Older Parental investment Lower Higher Position in the food chain Population stability Less More Population turnover Number of offspring Juvenile mortality ** These are general trends and there are exceptions in each of these categories

Record Holders: Oldest recorded Quahog (clam): 220 years Oldest recorded Tortoise: 152 years Oldest recorded Human: 120 years Oldest recorded  Giant Salamander: 55 years Oldest recorded Queen Ant: 18 years Oldest recorded Housefly: 29 days