Lab 03 Fall 2007 PopDemogr

Lab 03 Fall 2007 PopDemogr - POPULATION DEMOGRAPHICS Lab 3...

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POPULATION DEMOGRAPHICS Lab 3 3-1 Reminders! Memory stick or floppy disc Appropriate clothing or gear for being outside I. WHAT IS A POPULATION? Over the next few weeks, you will focus on a basic unit for many ecological studies, the population. A population is a group of individuals of one species that simultaneously occupy the same general area; they rely on the same resources and are influenced by similar environmental factors. What actually constitutes a population will vary from species to species and from study to study. In some cases, the boundaries of a population are readily apparent, falling within the geographic limitations of a suitable habitat. In other cases, the boundaries are defined arbitrarily to suit the purposes of the investigator. The Dynamic Population Populations are dynamic, i.e. they are constantly changing over time. The four population parameters that affect the size or density of a population are births, deaths , immigrations , and emigrations (Figure 1). The addition of individuals to a population is due to births and immigration, while loss is due to death and emigration. When the number of births and immigrations is equal to the number of deaths and emigrations, then the population is stable, and will neither increase nor decrease in size. II. AGE STRUCTURE Knowledge of the age structure or age distribution of a population can provide valuable information and insights into future population characteristics. Age structure is defined as the proportion of individuals in each age class of a population. Births, deaths, immigration, and emigration affect age structure. These are in turn affected by environmental conditions, predation, mutualism, and competition. Age Pyramids An age pyramid (Figure 2) is an effective means of visualizing and comparing the age distribution of populations. An age pyramid is a horizontal bar graph of the number (or percent) of individuals in each age class, sometimes separated by gender. The shape of an age pyramid can give a preliminary indication of whether a population is Population Emigration Immigration Deaths Births Figure 1. The size of a population is determined by a balance between births, immigration, deaths and emigration Figure 2. Age pyramid. Notice that it is split into two halves for male and female members of the population.
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Laboratory 3 Population Demographics 3-2 increasing, decreasing, or stable. A very high proportion of reproductive-age (or pre- reproductive age) individuals may indicate that the population is increasing. A pyramid with a very wide base could be the result of very high birth rates or low life expectancies. In human populations, it may also reflect technological improvements in reducing infant mortality. An inverted pyramid with a higher proportion of older individuals may indicate that the population is decreasing. A fairly rectangular shaped pyramid generally reflects a population that is stable in size and age structure. It is important to understand
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Lab 03 Fall 2007 PopDemogr - POPULATION DEMOGRAPHICS Lab 3...

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