Behavioral Ecology and Parental Investment

Introduction

  • Today's lecture focused solely on bird examples.

  • Recap of previous lecture: Discussed social behavior and cooperation vs. conflict.

Natural Selection and Genes

  • Natural selection operates at the gene level, not individual level.

  • Importance of considering costs and benefits when analyzing behaviors.

  • Core principle: Natural selection aims to increase reproductive success of genes.

Parent-Offspring Conflict

  • Toy Example: Offspring demand more resources than parents are willing to provide.

    • Questions:

    • How much should offspring demand from parents?

    • How much should parents provide?

  • Intuition suggests offspring should demand infinitely; however, reality differs.

  • Provisioning Rates:

    • Let provisioning be denoted as p.

    • Increased resources improve offspring fitness but reduce resources available to parent.

  • Natural Selection's Goal:

    • Maximize the difference between benefit and cost.

Genetic Perspective

  • Offspring's gene controls resource demand, affecting its fitness.

  • The gene's success depends on its presence in sibling offspring, with a relatedness coefficient of 0.5.

  • Parent's gene controls resource provision, also with a relatedness of 0.5 affecting costs and benefits.

  • The result is a formula: 0.5 imes ext{Benefit} - 0.5 imes ext{Cost} for both parent and offspring perspectives.

Graphical Representation

  • Optimal provisioning from offspring perspective is higher than from parents, indicating a conflict.

Case Study: Stitched Bird

  • Species: Threatened bird from New Zealand.

  • Male and female provide resources to a single offspring.

  • Without resource supplementation, unlikely to produce multiple broods.

  • Experimental Setup:

    • Some parents and offspring supplemented with carotenoids.

    • Predictions:

    • Offspring with carotenoid supplementation should receive more food.

    • Parents supplemented should respond less to offspring's increased demand.

    • Result: Higher provisioning correlates with intensified begging signals from offspring.

Parental Investment in Evolutionary Context

  • Examining which parents should provide care in monogamous breeding systems.

  • Biparental Care: About 40 out of 100 studied shorebird species provide care from both parents.

  • Cost vs. Benefit:

    • Benefits of remating vs. costs of current brood quality.

  • Hypothesis: Higher male care predominates due to differing remating opportunities based on sex ratios.

Experiment on Parental Desertion

  • Experimental Design:

    • Observation of survival rates when one parent is deserting.

    • Findings: Male desertion leads to significantly lower brood survival compared to female desertion.

    • Male survival rates lower when left unattended; shows higher associated costs.

Female Parenting Trends Through Breeding Season

  • Graph of Hatching Dates vs. Female Care reveals that females tend to provide more care late in the breeding season.

  • Brood Size Impact: Early in the season, larger broods receive more care; no impact in late season.

    • Cost of deserting increases with larger broods.

  • Late-season females provide more care despite brood size, indicating that benefits of desertion are perceived to be lower at that time.

Conclusion

  • Parent-offspring conflict and the varying ecological contexts can elucidate different behaviors.

  • Conflict resolution relies heavily on understanding relative costs and benefits.

  • Next Lecture Preview: Only one bird image guaranteed and more insights into patterns of behavior in animal systems.