C11-Population_Growth_JRM presentation_blackboard

BIOL 3309 Principles of Ecology

• Course Title: Principles of Ecology

• Instructor: Dr. Joseph McMillan

• University: Texas Tech University

• Semester: Spring 2025

Learning Objectives

• Understand population growth models under different scenarios.

• Identify what factors limit population growth.

• Analyze population growth in humans.

Key Concepts in Population Ecology

Population Distribution and Abundance

• Fundamental question: Where are organisms found and how many are present?

• Represents a snapshot in time, helping to assess population ecology.

Population Dynamics

• Populations can change over time, influencing size, density, and age structure.

• The age distribution of a population reflects its survival history, reproductive success, and potential for future growth.

Types of Population Growth

• Geometric Growth: Population grows in discrete steps.

• Exponential Growth: Continuous growth without resource limitations.

• Logistic Growth: Growth slows as resources become limited.

Growth Dynamics

• In the presence of unlimited resources, populations can grow geometrically or exponentially, leading to similar growth shapes through different mechanisms.

• Main Assumptions for Growth Models:

  • All individuals are identical in characteristics.

  • Populations are closed, without immigration or emigration.

  • Unlimited resources are available.

  • Time is treated as continuous.

Mathematical Models

• Change in population size (∆N) can be expressed with formulas:

  • ∆N/∆T = (B−D) + (I−E)

  • When immigration and emigration are constant, it simplifies to ∆N/∆T = B−D.

• Continuous population growth is represented by the equation: dn/dt = rN, where r is the intrinsic rate of increase.

Case Studies of Population Growth

Whooping Crane (Grus americana)

• Historical context:

  • 1930s: Aransas population = 18 birds.

  • 2015-2016: Population ≈ 329 birds at Aransas National Wildlife Refuge.

  • Current estimates show growth to over 400 birds.

Phlox drummondii

• Initial population: 996 individuals.

• Net reproductive rate (R0): Average of 2.4177 offspring per individual.

• Projected exponential growth over several generations leads to population escalation:

  • Year 0: 996

  • Year 1: 2,408

  • Year 2: 5,822

  • Year 3: 14,076, and so forth, reaching millions by year 10.

Logistic Population Growth

• Defined by limited resources leading to a sigmoidal growth curve:

  • Growth rate slows as the population approaches carrying capacity (K).

• Key assumptions include:

  • All individuals are the same.

  • The population is closed and limited in resources.

  • Continuous time.

Factors Influencing Growth

• Density-dependent factors: Birth and death rates change with population density.

• Density-independent factors: Examples include natural disasters and climate events.

Age Distributions in Humans

• Pyramid-shaped distributions indicate rapid growth potential.

• Constant age distributions suggest stable or slow growth.

• Historical events, such as World War II, significantly affect demographic patterns and distributions over time.

Summary of Concepts

• Population dynamics are influenced by a variety of factors, including environmental conditions and life history strategies.

• Understanding these dynamics is crucial for conserving species and managing ecosystems.