Population Ecology

You will explore the field of population ecology and survey factors involved in the decline, expansion, and maintenance of a population. Simulated growth of a population will be modeled, graphed, and analyzed. You will use quantitative data from a cemetery population to study demographics.

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EXPERIMENT

Learning Objectives Upon completion of this laboratory, you will be able to:

● Define species, population, and metapopulation.

● Differentiate between density-dependent and density-independent factors and describe how each can influence population size.

● Outline factors that influence carrying capacity and describe the potential consequences of overpopulation.

● Illustrate graphs of linear and exponential population growth.

● Describe how demography data may be used to calculate probability of mortality.

● Model population growth and determine if the growth was linear, exponential, or had no observable pattern.

● Determine constraints placed on a modeled population and draw conclusions about carrying capacity.

● Use birth and mortality data of a cemetery to investigate demography.

● Determine probability of death within a cohort.

Time Allocation: 3.5 hours

Note: This experiment suggests a field trip to a local cemetery for data collection. Please plan your time accordingly.

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Experiment Population Ecology

Materials Student Supplied Materials

Quantity Item Description 3 Sheets of paper (optional) 1 Pen or pencil 1 Access to a cemetery (optional) 1 Access to a printer (optional)

HOL Supplied Materials

Quantity Item Description 1 Packs of dice, mini (100 pcs) 1 Cup, plastic, 9 oz., short 1 HOL Supplied Cemetery Data Supplemental Document

Note: To fully and accurately complete all lab exercises, you will need access to:

1. A computer to upload digital camera images.

2. Basic photo editing software such as Microsoft Word® or PowerPoint®, to add labels, leader lines, or text to digital photos.

3. Subject-specific textbook or appropriate reference resources from lecture content or other suggested resources.

Note: The packaging and/or materials in this LabPaq kit may differ slightly from that which is listed above. For an exact listing of materials, refer to the Contents List included in your LabPaq kit.

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Experiment Population Ecology

Background Species and Populations

A species is a group of organisms that share many common characteristics and breed among themselves to produce fertile offspring. Individuals of a species that occupy a defined area at the same time are called a population. The habitat area of a population is often naturally enclosed within geographical boundaries, such as rivers or mountains. See Figure 1. In research studies about populations, scientists often define artificial boundaries. For example, scientists may investigate the population within a county or state boundary.

Figure 1. Small population of water lilies (family Nymphaeaceae) inhabiting a pond. © yuriy kulik

When suitable habitat is patchy or fragmented, populations can be

spatially isolated, but members of the population can have some level of interaction

with one another. When this occurs, the interacting populations are referred to as a metapopulation. An example of a species that is often found as a metapopulation is the desert bighorn sheep (Ovis

canadensis). See Figure 2. The bighorn sheep occupies steep slopes of mountains that are separated by flat lowlands. Although the lowlands are an unsuitable long-term habitat for the sheep, individuals and groups of sheep are able to travel through the lowlands to adjacent mountains, resulting in interaction among individuals of different

but connected populations.

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Experiment Population Ecology

Figure 2. Bighorn sheep. © Shane W. Thompson

Population Density

Biologists who study population ecology often investigate population size and factors involved in the decline, expansion, and maintenance of a population. Data about populations include the following:

● Mortality (death) and birth rates

● Movement of members into and out of the population (immigration and emigration)

● Number of individuals in a group, or cohort (for this experiment cohorts are the age classes of deceased individuals)

● Spatial distribution of species

● Population density (the number of individuals per unit area)

Factors related to the density of a population, called density-dependent factors, affect population growth by reducing or increasing the population size. For example, the ability to acquire a mate is a density-dependent factor. When population density is great, competition for mates increases. Members of the population may spend more energy competing for mates than actually mating, and the population size can subsequently decrease due to reduced births. On the other hand, when population density is optimal, competition may be relatively low and mating opportunities may be high, resulting in growth of the population. Other density-dependent factors include resource availability, predation rates, and disease transmission. Density-independent factors influence population growth but are not dependent on population density. Consider how the population density of trees may be affected by weather patterns and wildfires.

Growth rates can follow various patterns, as shown in Figure 3. When resources are unlimited, a population’s growth rate can be exponential. Although the graph of exponential growth illustrates a potentially great increase in population size, no population can grow indefinitely. In nature, members of the population will eventually consume available resources, and the population size will ultimately plateau or decline due to density-dependent factors.