CHAPTER3

Lesson Overview

  • Course Name: EVPP 201 - Environment and You: Issues for the 21st Century

  • Institution: George Mason University, Department of Environmental Science and Policy

  • Lesson Number: 3

  • Key Themes: Evolution, Biodiversity, and Population Ecology

Key Concepts

  1. Natural Selection

  2. Biodiversity

  3. Population Ecology

Classifying Organisms

  • Taxonomy:

    • A nested hierarchical system that classifies organisms according to their evolutionary relationships.

    • Reference: Withgott & Laposata, 2019, Page 55, Figure 3.7

Evolution & Natural Selection

  • Evolution Defined:

    • Change in populations of organisms over time, specifically referring to changes from generation to generation.

  • Natural Selection:

    • Recognized as a primary mechanism driving evolutionary change.

    • Highly supported and regarded as a fundamental concept in biological sciences.

Historical Context of Natural Selection

  • Founders:

    • Proposed by Charles Darwin and Alfred Russel Wallace in the 1850s.

    • Darwin’s observations from the Galapagos Islands led to his conclusions about natural selection as an explanation for biological diversity.

  • Genetic Foundations:

    • Supported by genetic research, prominently that of Gregor Mendel concerning inheritance and trait transmission.

    • This research paved the way for modern evolutionary biology.

Four Tenets of Natural Selection

  1. Variation:

    • Individuals within a population exhibit variability in traits.

  2. Heritability:

    • This variability is heritable; traits are passed down to offspring.

  3. Overproduction:

    • Organisms tend to produce more offspring than what can survive to adulthood.

  4. Survival and Reproduction:

    • Resource limitations result in differing survival and reproductive success; therefore, over generations, populations change with certain traits becoming more common.

Genetic Variation

  • Importance:

    • Selection is influenced by genetic variation among individuals in a species.

  • Sources of Variation:

    • Random Changes in DNA: Mutations that occur accidentally.

    • Sexual Reproduction: Results in novel combinations of parental DNA.

  • Resiliency:

    • Genetic variation increases a population's adaptive capacity to changing environmental conditions.

Evidence of Natural Selection

  • Types of Evidence:

    • Artificial Selection:

    • Observed through selective breeding practices.

    • Examples:

    • Figure illustrating the ancestral wolf (Canis lupus) compared to derived dog breeds and the ancestral Brassica oleracea versus derived crops (Withgott & Laposata, 2019, Page 53).

Types of Evolution

  • Divergent Evolution:

    • Closely related species adapt to differ in traits due to varying environmental conditions and selective pressures.

    • Factors Influencing Divergence:

    • Climate (temperature, precipitation)

    • Availability of different food sources

    • Presence of predators

    • Example: Divergent evolution of Hawaiian honeycreepers (Withgott & Laposata, 2019, Page 52).

  • Convergent Evolution:

    • Unrelated species adapting similar traits due to comparable environmental challenges despite being in separate geographical locales.

Biodiversity

  • Definition:

    • A measure of the richness and complexity of life encompassing diversity at all levels including species diversity, genetic diversity, population diversity, and community diversity.

Habitat and Niche

  • Habitat Definition:

    • The living and non-living elements in an organism's environment (e.g., rock, soil, humidity, plant life).

  • Niche Definition:

    • The functional role of an organism within a community, including its habitat use, resource consumption, energy flow role, and interactions with other organisms.

    • Quote: “Habitat is the organism’s address, and the niche is its profession.”

Population Dynamics

  • 5 Essential Attributes Predicting Population Dynamics:

    1. Population Size

    2. Population Density

    3. Population Distribution

    4. Sex Ratio

    5. Age Structure

Population Growth Rate

  • Growth Rate Formula:

    • ext{Population growth rate ( ext{%})} = 100 imes [( ext{birth rate} - ext{death rate}) + ( ext{immigration rate} - ext{emigration rate})]

  • Related Terms:

    • Natality: Births within a population.

    • Mortality: Deaths within a population.

    • Immigration: Arrival of individuals from outside the population.

    • Emigration: Departure of individuals from the population.

Example Calculation of Population Growth Rate

  • Given Rates:

    • Birth Rate = $20$ per $1000$ individuals per year

    • Death Rate = $12$ per $1000$ individuals per year

    • Immigration Rate = $7$ per $1000$ individuals per year

    • Emigration Rate = $9$ per $1000$ individuals per year

  • Population Growth Rate Calculation:

    • Calculate using the provided formula.

    • An assessment to determine population stability where $0-2 ext{ ext{%}}$ is considered stable.

Unregulated Populations & Exponential Growth

  • Description:

    • Populations grow exponentially under unregulated conditions.

  • Conditions for Growth:

    • Small initial population, minimal competition, and ideal survival and reproduction conditions.

Logistic Growth and Limiting Factors

  • Growth Pattern:

    • Initially sharp population increases, which later level off due to limiting factors.

  • Nature of Limiting Factors:

    • Typically density-dependent, influencing population growth as resources become limited.

    • Eventually stabilizes at what is termed the carrying capacity.

Discussion on Carrying Capacity

  • Global Context:

    • Current global human population has exceeded $7$ billion.

  • Questions for Consideration:

    • How have we increased Earth’s carrying capacity for humans?

    • Is the increase in carrying capacity sustainable? And by what means?

    • What current limiting factors affect human population?

    • Is there potential for a decrease in Earth’s carrying capacity? Why or why not?

Assessment Questions

  • Question 1: What are the four tenets of speciation?

  • Question 2: Identify whether bats and butterflies are examples of A. Convergent Evolution or B. Divergent Evolution.

  • Question 3: What type of population dynamics refer to random, clumped, and uniform distributions? A. Population Distribution, B. Sex Ratio, C. Age Structure, D. Population Size.

  • Question 4: Which type of ecology investigates relationships of organisms and ecosystems geographically? A. Population Ecology, B. Land Ecology, C. Community Ecology, D. Organism Ecology.

  • Question 5: True or False: Genetic variation is caused by sexual reproduction and random mutation.

Upcoming Assignments

  • Due Date: Sunday

  • Tasks:

    • Finish Quiz: Chapters 1 and 2

    • Next Class Focus: Chapter 4 - Ecology of Communities

    • Assignment 2: Assigned based on Chapter 4