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RNR 316 Natural Resources Ecology - Chapter 10

RNR 316 Natural Resources Ecology

Chapter 10 Overview

  • Acknowledgment of Indigenous Peoples:

    • The University of Arizona is on the land and territories of Indigenous peoples.

    • Arizona is home to 22 federally recognized tribes, including the O’odham and the Yaqui.

    • The university aims to build sustainable relationships with sovereign Native Nations and Indigenous communities through education, partnerships, and community service.

  • Instructor: Deepak Patel

  • Semester: Fall semester 2025

Housekeeping Notes

  • Module 2: Organisms

    • Chapter 10 content focus.

    • Short Quizzes:

    • Chapters 9 and 10 quizzes due on D2L by Friday.

    • Quizzes open Thursday at 12:15 pm and close Friday at 11:59 pm.

  • Next Week's Schedule:

    • Tuesday (Oct 7): In-class Critical Thinking Exam II.

    • Thursday (Oct 9): Remotely scheduled learning.

    • Thursday - Friday (Oct 9-10): Summative Exam of Module 2 will take place on D2L.

    • Feedback Period: Feedback on phenology project handouts will be provided over the next 2-3 weeks.

Recap from Last Class

  • Reproduction:

    • Can be classified as sexual or asexual.

    • Organisms can evolve as either separate sexes or as hermaphrodites.

    • Typically, sex ratios of offspring are balanced, although they may be altered by natural selection.

    • Mating Systems: Describe the patterns of mating between males and females.

    • Sexual Selection: A process that favors traits that improve reproduction.

Chapter 10 Learning Objectives

  • Social Behaviors

    • Living in groups presents both costs and benefits.

    • Understanding the various types of social interactions is essential.

    • Eusocial species exhibit extreme forms of social interaction.

Benefits of Living in Groups

I. Collective Advantages

  1. Survival:

    • Cooperative behaviors increase the likelihood of survival among group members.

  2. Group Defense:

    • Groups can defend against predators more effectively than solitary individuals.

  3. Dilution Effect:

    • The probability of predation decreases for individuals in a larger group.

II. Feeding Advantages

  • Group living can enhance foraging success and overall access to resources.

III. Mating Advantages

  • Living in groups may facilitate mating opportunities and reproductive success.

Costs of Living in a Group

I. Increased Risk Factors

  1. Predation:

    • High population density can lead to increased disease spread, as parasites and pathogens act as predators.

  2. Competition:

    • Intraspecific competition arises between members of the same species, impacting individual access to resources.

II. Tradeoff Considerations

  • The benefits of group living must be weighed against the costs associated with competition.

Optimal Group Size

  • Tradeoff Analysis:

    • Costs and benefits of living in groups contribute to determining an optimal group size, which may include genetic considerations.

Types of Social Interactions

  • Influences on fitness can be classified into two categories concerning the effects on donors and recipients:

    • Negative (-)

    • Positive (+)

Fitness Effect on Donor

Fitness Effect on Recipient

Interaction Type

Negative

Positive

Cooperation

Positive

Negative

Selfishness

Negative

Negative

Spitefulness

Positive

Positive

Altruism

Direct vs. Indirect Fitness

  1. Direct Fitness:

    • The transmission of genetic material directly to offspring.

  2. Indirect Fitness:

    • Achieved by assisting a relative to enhance its fitness levels.

  3. Inclusive Fitness:

    • The sum of both direct and indirect fitness contributions.

  4. Types of Selection:

    • Direct Selection: Focused on individual reproductive success.

    • Indirect Selection (Kin Selection): Support for relatives enhancing their reproductive success.

Coefficient of Relatedness

  • Definition: The probability that copies of a particular gene are shared between relatives (measured as a value between 0 and 1).

  • Calculation of Indirect Fitness: ext{Indirect fitness} = B imes r Where:

    • B : fitness benefit to a recipient relative

    • r : coefficient of relatedness between donor and recipient

Evolution of Altruism

  • Altruism Condition:
    B imes r > C
    Where:

    • B : fitness benefit to a recipient relative

    • r : coefficient of relatedness

    • C : direct fitness cost to the altruistic donor relative

  • Inequality for Selection:
    rac{C}{B} < r

Kin Selection and Altruism Maintenance

  • Example Calculation:

    1. Given a coefficient of relatedness r = 0.42 (from a mix of full brothers (0.5) and half brothers (0.25)).

    2. Assuming a cost C = 0.9 (average offspring from solo males) and a benefit B = 6.1 (average offspring from a dominant brother).

  • Indirect Fitness Calculation:
    ext{Indirect fitness} = B imes r = 6.1 imes 0.42 = 2.6

  • Inclusive Fitness:
    ext{Inclusive fitness} = ext{direct} + ext{indirect} = 0 + 2.6 = 2.6

  • Condition Check:
    rac{C}{B} < r

    • Here, 0.9/6.1 < 0.42

    • Or simplified 0.15 < 0.42 , indicating that the conditions supporting kin selection hold.

Characteristics of Eusociality

  • Definition of Eusociality:

    • Presence of several adults living together in a group.

    • Overlapping generations of multiple parents and offspring in the same environment.

    • Cooperation in activities such as nest building and brood care.

    • Reproductive dominance is usually exhibited by one or a few individuals while often including sterile individuals.

Leaf Cutter Ants: Ecosystem Examples

Overview

  • Ecological Role:

    • Leaf cutter ants, known as Earth's first gardeners, engage in fungiculture (agriculture) for over 50 million years.

  • Species Information:

    • Comprises 47 ant species (Atta, Acromyrmex), generally found in tropical regions.

  • Fungal Cultivation:

    • Each ant species cultivates a unique strain of fungus from the family Lepiotaceae.

    • This relationship exemplifies obligate mutualism: ants receive food, while the fungus benefits from food and protection.

    • Leaf cutter ants harvest more than 17% of total leaf production in tropical rainforests.

Colony Structure

  • Colony Size:

    • A mature colony can be comparable to the size of an Olympic swimming pool, with approximately 600 m³, containing around 8 million individuals.

  • Roles in Colonies:

    • Sterile castes are responsible for tasks such as defense, foraging, building, care of offspring, and trash removal.

Haplodiploid System and Eusociality

  • Role in Eusociality:

    • In haplodiploid societies, all worker bees are female.

  • Relatedness Index:

    • coefficient of relatedness r = 0.75 among haplodiploid sisters, 0.5 among sisters in diploid systems, and 0.25 between sisters & brothers in haplodiploid systems.

Continuum of Social Behaviors

  • Understanding the diversity and spectrum of social interactions within ecological systems provides insights into the evolutionary advantages and dynamics of cooperation in nature.