Presentation on theme: "Populations have many Characteristics"— Presentation transcript:
1Populations have many Characteristics Populations go through 3 StagesScientists study how populations or organisms change as they interact with each other & the environmentPOPULATION DYNAMICS = study of why populations change & what causes them to change.4 Characteristics define a Population:Population size; population density; population spacing & age structureScientists can predict a Population Change
2Growth, Stability & Decline All populations go through growth, stability & decline.CARRYING CAPACITY = maximum number of individuals an ecosystem can support(with its available resources); if a habitat has enough resources, the population grows fast, then it stabilizes and population stays about the same for a while. This stability stage is usually the longest time period. Often, it is followed by a sharp decrease in population size.During growth phase it can occur very quickly (as in bacteria reproducing, or gradually as in a population of seals).
3Darwin’s Observations of Population Growth Charles Darwin was a naturalist scientist who wrote On the Origin of Species based on his observations in the Galapagos Islands. He noted the following about population growth:All populations are able to grow rapidlyPopulations tend to remain constant in sizeThere are limits to natural resourcesWithin a given population there is genetic variationHe knew that if there were no limitations to growth, populations would grow rapidly. But also realized, there are natural limits to growth in the real world. If birth rate doesn’t match the death rate, a population can decline until it becomes extinct.
4Population SizePopulation size= number of individuals in a population at a given time. (varies from habitat to habitat, & even within a habitat). In our area, mosquito population size changes during different times of the year.Many deserts experience blooming & growing during our spring, but by summer (with less water & higher temperatures) there is a rapid decline in plant population size.
5Population DensityPopulation density= measure of the number of individuals in a certain space at a particular time. Related to population size; if size increases and they all stay in same area, density increases too. Some species live in high density (bees) while others live in low density populations (blue herons).RANGE = the distribution of a population across a large geographic area. The population density within that range may vary (more grasshoppers in middle of prairie than its edge). Habitats located in the middle of a population range usually have a greater density than its edges (more resources)
6Population SpacingPopulation spacing= the pattern in which the individuals of a population are found. 3 main types: clumped, uniform and random.Clumped spacing: individuals form small groups within a habitat (elephants do this due to social nature, salamanders due to habitat-moist rotten logs found in 1 area)Uniformly spaced: individuals living at an equal distance from each other; plants often due this due to competing resources (if too close, some die out)Random spacing: dandelions/weeds grow where ever.
7Age StructureScientists divide a population into 3 groups based on age:Postreproductive: organisms can no longer reproduceReproductive: organisms capable of reproductionPrereproductive: organisms not yet able to reproduceThe age structure of a population affects how much it can grow. On graph below, postreproductive age range is over 45, while prereproductive range is 0-14
8Predicting Population Change Scientists use size, density, spacing & age structure to describe a population & predict how it may change over time.A population may change due to its surroundings(frogs living in pond that gets saltier will probably experience a population decrease).Scientists can also predict change by looking at the distribution of a population. (New York City released a population of 60 starlings in 1890; they now number over 200 million spread across the U.S., Canada & Mexico. The population rose as they moved into new habitats with available resources.