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BIO313: Population Ecology

Unit 3: Population Regulation: Intrinsic Factors and Environmental Pressures That Affect Population Size   In this unit, we will develop an understanding of natural population regulation.  In reality, no habitat can support truly unchecked population growth.  There will always be some limiting factor, whether it be an intrinsic factor imposed by the population itself or an extrinsic factor imposed by the environment (an “environmental pressure”).  In this unit, we will begin to look at the issues that complicate theoretical population dynamics.  We will discuss how intrinsic density-dependent factors, such as food or disease, impose a population ceiling beyond which population growth cannot be sustained.  We will also learn how migration between populations within a metapopulation can sustain smaller, more isolated populations.  Every habitat contains more than one species, and we will see how interactions between species populations will impact growth, carrying capacity, and sustainability of each species.  We will also learn how to quantify the impact of these interspecific interactions on a population’s growth.

Unit 3 Time Advisory
This unit should take you approximately 13 hours to complete.

☐    Subunit 3.1: 1.0 hours

☐    Subunit 3.2: 3.5 hours

☐    Subunit 3.3: 1.0 hours

☐    Subunit 3.4: 4.0 hours

☐    Subunit 3.5: 3.0 hours

☐    Subunit 3.6: 0.5 hours

Unit3 Learning Outcomes
Upon successful completion of this unit, students will be able to: - Explain how intrinsic factors and environmental pressures affect population size.  - Define terms relevant to interspecific interactions and describe the possible outcomes of those interactions. - Use ecological models to predict the effect of interspecific interactions on population sizes. - Discuss factors that threaten the biodiversity of ecosystems. - Explain the intrinsic factors and the environmental pressures that allow invasive species to outcompete native species. - Describe the effects of human activities on habitats and how those activities affect population size.

3.1 Intrinsic Factors: Density-Dependent Factors Affecting Population Regulation   - Lecture: Yale University: Dr. Stephen Stearns: “Population Growth: Density Effects” Link: Yale University: Dr. Stephen Stearns: “Population Growth: Density Effects” (YouTube)
 
Also available in:
Adobe Flash and Quicktime
 
Instructions: Please click the Flash link under “Video” to watch this entire video (approximately 43 minutes).  The transcript for this video is here (HTML).  This lecture discusses density-dependent factors (i.e., factors whose effect on the population increases with population size) and how they affect population growth.  This material also covers subunits 3.1.1 through 3.1.5. 
 
Note: The community interactions we learned about in Unit 1 come into play here.  If there were only one species, with unlimited resources, the population could grow infinitely.  Instead, a natural community will have some constraints.  As a population increases, competition will also increase.  Other organisms may also take advantage of the robust population to fill some of their own resource requirements (for nourishment!); disease, parasite load, and the predator population are also likely to increase.  In this section, we will discuss how each of these can affect mathematical population models.
 
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  • Reading: Tennessee State University: Professor Phil Ganter: “Intraspecific Population Regulation” Link: Tennessee State University: Professor Phil Ganter: “Intraspecific Population Regulation” (HTML)
     
    Instructions: Please read this entire webpage, which discusses factors affecting population growth.  Also, please explore related links on this webpage to learn more about population regulation.
     
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3.1.1 Resource Availability   3.1.2 Disease   3.1.3 Parasitism   3.1.4 Predation   3.1.5 Immigration and Emigration   3.2 Intrinsic Factor: Metapopulation Dynamics   - Reading: National Institute on Aging: Dr. Alexei Sharov: “Metapopulation Models” Link: National Institute on Aging: Dr. Alexei Sharov: “Metapopulation Models” (HTML)
 
Instructions: Please read this entire webpage, which describes how the concept of a metapopulation can be incorporated into models of population growth.
 
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3.2.1 Definition and Models   - Reading: Ramas Ecological and Environmental Software: “A Short Introduction to Metapopulation Models and GIS” Link: Ramas Ecological and Environmental Software: “A Short Introduction to Metapopulation Models and GIS” (HTML)
 
Instructions: Please read this entire webpage, which introduces the concept of a metapopulation: multiple small populations separatedin spacebutconnected via occasional immigration between the populations, such as often occurs between nearby islands.
 
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  • Reading: Environmental Sciences Division of Oak Ridge National Laboratory and Pacific Northwest Laboratory: Strategic Environmental Research and Development Program: “Metapopulation Models” Link: Environmental Sciences Division of Oak Ridge National Laboratory and Pacific Northwest Laboratory: Strategic Environmental Research and Development Program: “Metapopulation Models” (HTML)
     
    Instructions: Please read this entire webpage to expand your knowledge of metapopulation models.
     
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  • Lecture: YouTube: robertandkylie: “Bugger Off with Metapopulation Theory” Link: YouTube: robertandkylie: “Bugger Off with Metapopulation Theory” (YouTube)
     
    Instructions: Please watch this entire video (approximately 3 minutes).  Pay special attention to how the small populations within a metapopulation sustain one another through immigration.  This material also covers subunits 3.2.2 and 3.5.
     
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3.2.2 Rescue Effect in Metapopulation Dynamics   Note: As you have learned, ametapopulation consists of multiple small populations separatedin spacebut occasionallyconnected via immigration.  Immigrants mightsometimes movebetween two of these populations, thussustaining(“rescuing”) population size ina small population that might otherwise go extinct.  Please review the YouTubevideo “Bugger Off withMetapopulation Theory” in subunit 3.2.1.

3.2.2.1 Huffaker’s Experiments   - Reading: Wikipedia: “Metapopulation” Link: Wikipedia: “Metapopulation” (PDF)
 
Instructions: Please read this entire webpage.  Pay special attention to the sections describing Huffaker’s experiments on predator-prey interactions and Levins’s model of metapopulation dynamics.  This material also covers subunit 3.2.3.
 
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3.2.2.2 Island Observations   - Lecture: Yale University: Dr. Stephen Stearns: “Island Biogeography and Invasive Species” Link: Yale University: Dr. Stephen Stearns: “Island Biogeography and Invasive Species” (YouTube)
 
Also available in:
Adobe Flash and Quicktime
 
Instructions: Please click the Flash link under “Video” to watch this entire video (approximately 41 minutes).  The transcript for this video is here (HTML).  This lecture discusses metapopulation dynamics on islands and the introduction of nonnative species (also termed “exotic” and “invasive” species) and their effects on the population growth of native species.  This material also covers subunit 3.5.
 
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3.2.3 Levins’s Model of Metapopulation Dynamics   3.3 Environmental Pressure: Carrying Capacity— The Ricker Model   - Reading: National Institute on Aging: Dr. Alexei Sharov: “Stability Analysis of the Ricker’s Model” Link: National Institute on Aging: Dr. Alexei Sharov: “Stability Analysis of the Ricker’s Model” (HTML)
 
Instructions: Please read this entire webpage and then complete the questions.  The Ricker model predicts when a growing population will approach its carrying capacity and settle into an equilibrium size.
 
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3.4 Environmental Pressures: Interspecific Interactions—Interactions Between Populations   3.4.1 Interspecific Competition   - Reading: University of Michigan: Global Change Program: “Competition and Resource Scarcity”  Link: University of Michigan: Global Change Program: “Competition and Resource Scarcity” (HTML)
 
Instructions: Please read this entire webpage, which discusses the effects on population size of competition between species for limited resources.
 
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3.4.1.1 The Competitive Exclusion Principle   3.4.1.2 Competitive Release   - Reading: The Saylor Foundation: “Competitive Release” Link: The Saylor Foundation: “Competitive Release” (PDF)
 
Instructions: Please read this entire PDF, which discusses the classic study of competitive release, which showed how the size of a population changes when a competitor suddenly disappears.

3.4.1.3 Lotka-Volterra Interspecific Competition Model   The Lotka-Volterra interspecific competition model is used to predict changes in population sizes when interspecific competitive interactions exist.

3.4.2 Predator-Prey Interactions   3.4.2.1 Lotka-Volterra Predator-Prey Model   - Reading: National Institute on Aging: Dr. Alexei Sharov: “Introduction,” “Lotka-Volterra Model,” “Functional and Numerical Responses,” and “Predator-Prey Model with Functional Response ” Links: National Institute on Aging: Dr. Alexei Sharov: “Introduction,” “Lotka-Volterra Model,” “Functional and Numerical Response” and “Predator-Prey Model with Functional and Numerical Responses” (HTML)
 
Instructions: Please read these entire webpages.  The Lotka-Volterra predator-prey model is used to predict predator-prey population size cycles based on the current size of each population.  These materials also cover subunits 3.4.2.1.1 and 3.4.2.1.2. 
 
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3.4.2.1.1 Functional Responses   3.4.2.1.2 Numerical Responses   3.4.3 Mutualism   - Reading: Utah State University: Dr. Michelle Baker: “Mutualism” Link: Utah State University: Dr. Michelle Baker: “Mutualism” (HTML)
           
Instructions: Please read this entire webpage, which discusses how mutualism relationships affect population size.
 
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3.4.3.1 Facultative Mutualism vs. Obligate Mutualism   - Reading: University of Michigan: Global Change Program: “Ecological Communities: Networks of Interacting Species” Link: University of Michigan: Global Change Program: “Ecological Communities:Networks of Interacting Species (HTML)
 
Instructions: Please read this entire webpage.  Pay particular attention to the difference between facultative (optional) mutualism relationships and obligate (required) mutualism relationships.
 
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3.4.3.1.1 Simple Model of Mutualism   - Reading: Tennessee State University: Professor Phil Ganter: “Modeling Mutualism” Link: Tennessee State University: Professor Phil Ganter: “Modeling Mutualism” (HTML)
 
Instructions: Please read this entire section.  Models of mutualism attempt to predict the effect of the mutualism relationship on the population sizes of the species involved in the relationship, but these models have not been useful when employed in real situations in the past.
 
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3.4.4 Host-Parasite Interactions   3.4.4.1 Parasite-Vector Model   3.4.4.2 Host-Parasitoid Model   3.5 Environmental Pressure: Invasive Species—Introduced Environmental Pressure   - Reading: United States Department of Agriculture: National Invasive Species Information Center: “What Is an Evasive Species?” and Global Environmental Governance Project: "Invasive Species" Links: United States Department of Agriculture: National Invasive Species Information Center:“What Is an Invasive Species?” and Global Environmental Governance Project: "Invasive Species

 Instructions: Please read these entire webpages.  Also, please
explore other links on both websites to learn more about the global
problems caused by species being accidentally or intentionally
released into habitats in which they did not evolve.  These related
links also cover subunit 4.4.  
    
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3.5.1 Characteristics of Invasive Species   - Lecture: YouTube: Rob Piggott and Andrew Boncher: “Invasive Species Introduction” and Vimeo: World Wildlife Foundation: “Invasive Species – Introduction to the Issue” Link: YouTube: Rob Piggott and Andrew Boncher: “Invasive Species Introduction” (YouTube) and Vimeo: World Wildlife Foundation: “Invasive Species – Introduction to the Issue” (Adobe Flash)
 
Instructions: Please watch these entire videos (approximately 8 minutes and 2 minutes, respectively).  Pay particular attention to the characteristics that make some introduced species more likely to be successful in new habitats.
 
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3.5.2 Establishment of an Invasive Species in a New Habitat   - Reading: The Saylor Foundation: “Establishment of an Invasive Species in a New Habitat ” Link: The Saylor Foundation: “Establishment of an Invasive Species in a New Habitat” (PDF)
 
Instructions: Please read this entire PDF, which discusses how the initial population size of an introduced species might be small initially but can rapidly reach problematic size.  This material also covers subunits 3.5.2.1 through 3.5.2.3.

3.5.2.1 Propagule Pressure   3.5.2.2 Lag Period   3.5.2.3 Exponential Growth   3.6 Environmental Pressures: Human Activities that Affect Population Size   - Reading: The Saylor Foundation's “Environmental Pressures: Human Activities That Affect Population Size” Link: The Saylor Foundation's “Environmental Pressures: Human Activities That Affect Population Size” (PDF)
 
Instructions: Please read this entire PDF about human activities that dramatically impact and even threaten the survival of wild populations, taking notes where appropriate.