Ecology and Population Biology: Structured Study Notes

Introduction to Ecology

Definition and Scope of Ecology

Ecology is the scientific study of how organisms interact with both living (biotic) and non-living (abiotic) components of their environment. These interactions are shaped by factors from both the present and the past, influencing the distribution and abundance of organisms.

• Biotic Factors: Living components such as plants, animals, bacteria, and fungi.

• Abiotic Factors: Non-living components including weather, water bodies, rocks, and soil.

• Temporal Influence: Both current and historical biotic and abiotic factors affect ecological interactions.

Additional info: The image illustrates how both biotic (organisms like polar bears and mammoths) and abiotic (sea ice, continental drift) factors shape ecological systems over time.

Environment, Habitat, and Niche

Ecologists distinguish between several key concepts:

• Environment: The total sum of all external biotic and abiotic factors surrounding an organism.

• Habitat: The specific part of the environment where an organism lives and reproduces.

• Niche: The ecological role a species performs in its habitat, including resource use and interactions.

Additional info: The diagram visually separates environment, habitat, and niche, emphasizing their hierarchical relationship.

Levels of Ecological Study

Biological Hierarchy in Ecology

Ecology can be studied at multiple levels, each focusing on different aspects of biological organization:

• Organismal Ecology: Examines individual behavior, physiology, and evolutionary adaptations.

• Population Ecology: Studies population dynamics, including birth/death rates and population size.

• Community Ecology: Investigates interactions between different species within a defined area.

• Ecosystem Ecology: Focuses on energy flow and nutrient cycling among biotic and abiotic components.

• Landscape/Seascape Ecology: Explores spatial arrangement and interactions across multiple ecosystems.

• Global Ecology: Examines large-scale interactions and impacts across the biosphere.

Additional info: The images illustrate how ecological questions can be asked at different levels, from individual organisms to the entire biosphere.

Animal Behavior and Behavioral Ecology

Concepts in Animal Behavior

Animal behavior encompasses actions in response to stimuli, including interactions with other organisms and the environment. Behavioral ecology studies how ecological pressures shape these behaviors.

• Proximate Causation: Explains how behaviors occur mechanistically (e.g., genetic, neurological factors).

• Ultimate Causation: Explains why behaviors occur, their function, and evolutionary origins.

• Innate Behavior: Genetically programmed actions, sometimes requiring learning.

• Fixed Action Pattern: Innate behavior with little variation, triggered by a sign stimulus.

Additional info: The image demonstrates how specific stimuli (e.g., red belly) can trigger innate behaviors in animals.

Learning and Communication in Animals

Types of Learning and Communication

Learning involves acquiring or modifying behaviors based on experience. Communication is the transmission and reception of signals between animals.

• Spatial Learning: Establishes spatial memory using cognitive maps.

• Imprinting: Learning during a sensitive period, often early in life.

• Signal: Stimulus transmitted to communicate (e.g., pheromones).

• Stimulus Response Chain: Sequential communication behaviors.

Additional info: The image shows how communication signals are exchanged in a stepwise manner during mating.

Foraging Behavior and Optimal Foraging Theory

Foraging Strategies and Genetic Influence

Foraging is the process of seeking, identifying, capturing, and consuming food. Optimal foraging theory predicts that natural selection favors behaviors maximizing energy gain while minimizing cost and risk.

• Genetic Basis: Genes like for in Drosophila larvae influence foraging behavior (rover vs. sitter).

• Risk-Reward Balance: Animals balance energy expenditure and predation risk.

Additional info: The graphs and diagrams illustrate how foraging strategies are optimized and genetically determined.

Mating Systems and Parental Care

Sexual Selection and Parental Investment

Mating behavior includes mate attraction, competition, and offspring care. Sexual selection involves mate choice and competition, often based on fitness indicators.

• Mating Systems: Monogamy (one mate), polygamy (multiple mates).

• Parental Care: Investment in offspring survival; certainty of paternity affects male care.

Additional info: Images show parental care and courtship behaviors, key aspects of mating systems.

Migration and Altruism

Migration Strategies and Evolution of Altruism

Migration is the long-distance movement of populations, often seasonal. Altruism is behavior benefiting others at a cost to the actor, explained by kin selection and inclusive fitness.

• Piloting: Using landmarks for navigation.

• Compass Orientation: Movement in a specific direction.

• True Navigation: Ability to locate a destination using spatial cues.

• Hamilton's Rule: Altruism is favored when $rB > C$ (relatedness × benefit > cost).

Additional info: The map illustrates global migration routes, a key ecological phenomenon.

Population Ecology

Population Size, Density, and Dynamics

Population ecology studies how and why populations change over time. Key metrics include population size (N) and density (number per unit area/volume).

• Population Size (N): Total number of individuals.

• Population Density: Standardized measure for comparison across regions.

• Factors Influencing N: Births, deaths, immigration, emigration.

Population Change Equation:

$N_{final} = N_{initial} + Births + Immigrants - Deaths - Emigrants$

Metapopulations

A metapopulation is a group of spatially separated populations connected by migration. Local populations may go extinct but can be recolonized, making the metapopulation more stable overall.

Life History and Demography

Life History Strategies

Organisms allocate limited resources to survival, growth, and reproduction. Life history traits include survivorship, fecundity, and reproductive strategies (semelparity vs. iteroparity).

• Semelparity: Single, massive reproductive event.

• Iteroparity: Multiple reproductive events over a lifetime.

Life Tables and Survivorship Curves

Life tables summarize survivorship and reproductive rates. Survivorship curves (Type I, II, III) graph the number of individuals surviving at each age.

Population Growth Models

Exponential and Logistic Growth

Population growth can be modeled mathematically:

• Exponential Growth: Occurs in ideal, unlimited environments; produces a J-shaped curve.

• Logistic Growth: Accounts for environmental limits; produces an S-shaped curve and approaches carrying capacity (K).

Exponential Growth Equation:

$N_t = N_0 e^{rt}$

Logistic Growth Equation:

$\frac{dN}{dt} = rN \left(1 - \frac{N}{K}\right)$

r/K Selection Theory

Life History Strategies

• r-Selection: Many offspring, low investment, adapted to unstable environments.

• K-Selection: Few offspring, high investment, adapted to stable environments near carrying capacity.

Community Ecology

Community Structure and Interactions

Community ecology studies interactions among species and the structure of communities.

• Community Structure: Includes species richness, relative abundance, interactions, and physical attributes.

• Types of Interactions: Competition (–/–), Exploitation (+/–), Mutualism (+/+), Commensalism (+/0).

Competition and Niche Theory

Competition occurs when organisms vie for the same resource. Complete niche overlap leads to competitive exclusion; partial overlap leads to resource partitioning and character displacement.

Exploitation: Predation, Herbivory, Parasitism

• Predation: One organism kills and eats another.

• Herbivory: Consumption of plants or algae.

• Parasitism: Parasite lives in/on host, extracting resources.

Mutualism and Commensalism

• Mutualism: Both organisms benefit.

• Commensalism: One benefits, the other is unaffected.

Community Structure and Dynamics

Trophic Structure

Trophic structure describes feeding relationships (food chains/webs) and energy transfer between levels.

Species Impact: Foundation, Keystone, Ecosystem Engineer

• Foundation Species: High biomass, strong community-wide effects.

• Keystone Species: Low biomass, large ecological impact.

• Ecosystem Engineer: Alters physical environment significantly.

Disturbance and Ecological Succession

Disturbances disrupt communities, leading to ecological succession (primary and secondary). Early-arriving species can facilitate, tolerate, or inhibit later species.

Geographic Impact and Island Equilibrium Model

Species diversity is influenced by latitude and area. The island equilibrium model predicts equilibrium based on immigration and extinction rates, affected by island size and distance from mainland.