Ecology and Behavioral Ecology Review

Week 1 Review

Important Ideas

Observational vs. Experimental/Manipulative vs. Theoretical/Modeling Studies

  • Observation:

    • Measuring things the way they are, without interfering.

  • Experiment:

    • Changing one or more variables and measuring the outcomes of those changes.

  • Modeling:

    • After collecting data through measurements, data can be used to fit various models, thus extracting additional information from existing data.

Levels of Ecological Study

Factors Affecting the Ecology of a Location

Sunlight Availability

  • Direct Sunlight at the Equator:

    • Regions near the equator receive significant direct sunlight.

  • Air Movement:

    • Hot moist air rises due to low density and moves poleward (not all the way to the poles).

    • As it ascends and shifts toward the poles, it cools down.

    • Most moisture condenses and results in rainfall, which creates equatorial rainforests, known for high primary productivity.

  • Dry Air Movement:

    • As the air moves farther poleward and reaches approximately 30° N/S latitude, it cools further (increased density) and sinks.

    • This results in warmer but still lower temperatures than at the equator, creating desert conditions.

  • Hadley Cell:

    • Describes the cyclical air circulation pattern close to the equator, but it does NOT cover the entirety of the planet.

Earth's Tilt

  • Seasons:

    • The tilt of the Earth is instrumental in causing seasonal changes throughout the year.

Elevation and Rain Shadow Effect

  • Moist Air and Mountains:

    • Moist air rises over mountains, cools, and causes precipitation on one side: the windward side.

    • The reverse occurs on the leeward side, which receives cooler and drier air leading to less precipitation.

Proximity to Water

  • Temperature Moderation:

    • Being close to large bodies of water helps moderate local temperature conditions.

    • Specific Heat Capacity:

    • Water has a higher specific heat capacity than land.

    • Consequently, air over land heats up and cools down quicker than air over water, leading to temperature fluctuations based on proximity to water bodies.

Ocean Currents

  • Impact on Climate:

    • Oceans can transport warm or cold water/air, affecting local climates, which explains the significant temperature variations experienced in places like Minnesota in winter 2023-24 due to shifting jet streams.

  • Jet Stream Influence:

    • The jet stream, driven by temperature differences between equatorial and polar regions, becomes weakened because the poles are warming faster, leading to unusual temperature changes.

Biomes

  • Definition:

    • Major types of habitat, characterized by distinct plant and animal life.

  • Influence Factors:

    • Predominantly influenced by temperature and precipitation.

  • Types:

    • Biomes can be broadly subdivided into terrestrial (land) and aquatic (water) types.

Week 2 Review: Behavioral Ecology

Important Ideas

Proximate vs. Ultimate Causes of Behaviors

  • Proximate:

    • Addresses HOW a behavior is produced; involves sensory inputs or physiological methods that lead to the behavior.

  • Ultimate:

    • Concerns WHY a behavior exists; explores how it enhances fitness or survival.

Kinesis vs. Taxis

  • Short-range Movements:

    • Both kinesis and taxis refer to movements in response to stimuli.

  • Kinesis:

    • Movement resulting from a stimulus but not directed toward or away from the source of the stimulus.

  • Taxis:

    • Movement directed either toward or away from the stimulus.

Practice Problem: Woodlouse Movement

  1. Scenario A:

    • Increase temperature in a box; woodlouse moves faster as temperature increases.

    • Is it Kinesis or Taxis?

      • Answer: A is Kinesis; movement is unidirectional in response to increased temperature.

    • Proximate Explanation:

      • Woodlice possess specialized sensory receptors enabling them to sense temperature fluctuations in their environment.

    • Ultimate Explanation:

      • Faster movement at increased temperatures likely helps woodlice find more suitable habitats, enhancing survival and fitness.

  2. Scenario B:

    • Wooden shavings placed in a corner of a box with a bright light; woodlouse runs towards the shavings.

    • Is it Kinesis or Taxis?

      • Answer: B is Taxis; movement is directed toward a shaded area, away from light.

Communication in Animals

  • Definition:

    • The use of specific signals or displays to affect the behavior of others in a group.

Types of Communication

  • Chemical (Olfactory):

    • Used for marking territories and attracting mates.

  • Auditory:

    • Utilized mainly for attracting mates.

  • Visual:

    • Involves male competition to convey dominance or fitness potential.

  • Tactile:

    • Helps convey information within groups and can promote social bonding.

  • Quorum Sensing:

    • A chemical signaling method used by bacteria to communicate within populations.

Living in Groups

  • Benefits:

    • Availability of food, assistance with offspring care, greater access to mates, and reduced predation risk.

  • Costs:

    • Higher intraspecific competition and increased disease spread potential.

Long-Range Migration

  • Piloting:

    • Movement from familiar landmarks to others.

  • Orientation:

    • The capability to follow compass directions and travel in a straight line.

  • Navigation:

    • Following compass directions while having the capability to adjust or set course as needed.

Optimality Theory

  • Theory Description:

    • Focuses on maximizing benefits versus costs in behavioral ecology.

Altruism

  • Definition:

    • A behavioral trait that benefits another individual but incurs a cost to the altruist.

  • Types of Altruism:

    • Kin Selection:

    • If an altruistic behavior improves reproductive success of relatives, even at a personal fitness cost, it can evolve.

    • Represented mathematically as: rB > C .

      • Where:

      • r = relatedness of the altruist to the recipient,

      • B = benefit to the recipient,

      • C = cost to the altruist.

    • Reciprocity:

    • Altruistic acts performed by individuals for those who have previously helped them; can occur without relatedness but requires a recognition system for altruists.

Week 3 Review: Population Size

Population Definition

  • A population is defined as a group of interbreeding individuals of the same species occupying the same area at the same time.

    • Note: Limitations of this definition, especially regarding species like bacteria, were highlighted.

Methods for Measuring Population Size

  • Counting Organisms:

    • Visually count organisms in small areas with large organisms.

    • Particularly applicable to sessile organisms.

Population Density

  • Population Density:

    • Defined as the number of organisms per unit area or volume.

Methods for Measuring Population Density

  • For Sessile Species:

    • Quadrat Method:

    • A frame, often 1x1 meter, is placed randomly, and the organisms within are counted to give density estimates per square meter.

    • Line Transect Method:

    • A string is laid out and organisms along its length are counted.

  • For Mobile Species:

    • Traps:

    • Various trap types, such as pitfall traps and live traps, are used to estimate population density through capture and recapture.

Dispersion Patterns

  • Types of Dispersion Patterns:

    • (a) Clumped

    • (b) Uniform

    • (c) Random

Clumped Dispersion

  • Description:

    • Most common dispersion pattern.

    • Resources in nature tend to cluster, possibly influenced by social behaviors.

Uniform Dispersion

  • Description:

    • May arise from intraspecific competition or specific social interactions.

Random Dispersion

  • Description:

    • Rarest pattern, as resources are seldom randomly distributed; may occur when resources are abundant.

Reproductive Strategies

  • Semelparity:

    • Refers to a strategy involving a single reproductive event during the organism's lifetime.

  • Iteroparity:

    • Involves repeated reproduction at various intervals throughout the lifecycle, either seasonally or continuously.

Demography

  • Definition:

    • The study of birth rates, death rates, age distributions, and the sizes of populations.

  • Population Pyramid:

  • Representation of age distributions within populations, showing trends related to birth and death rates:

    • Example: High birth and death rates balance, and lower death rates leading to growth.

Survivorship Curves

  • Types of Survivorship Curves:

    • Type I:

    • Most individuals die late in life, with high survival rates until a certain age.

    • Type II:

    • Uniform rate of decline in survivorship across ages; typically reflects constant mortality rates.

    • Type III:

    • Huge declines in young individuals, indicating high infant mortality rates.

Life Tables

  • Definition:

    • A life table summarizes the probabilities of survival and reproduction for individuals at various ages across their lifetimes.

  • Key Components:

    • Age Cohort (x): Number of individuals at age x.

    • Number Surviving (n_x): How many individuals are alive at the beginning of the year.

    • Age-Specific Death Rate (d_x): Number of deaths during the year.

    • Age-Specific Fertility (m_x): Average number of offspring born to females at age x.

    • Proportion Surviving (lx): Fraction of individuals surviving from birth to age x, calculated as lx = \frac{nx}{n0} .

Population Growth Rates

  • Net Reproductive Rate (R_0):

    • Indicates whether a population is growing, stable, or declining:

    • R_0 > 1: Population will grow (births > deaths).

    • R_0 = 1: Population remains stable (births = deaths).

    • R_0 < 1: Population will decline (deaths > births).

Population Growth Over Time

Population Growth Rate Equation

  • Equation:

    • \frac{dN}{dt} = \text{population growth rate} = \text{instantaneous rate of change in the number of individuals in the population}

Factors Influencing Population Growth

  • Per Capita Growth Rate (r):

    • Defined as:

    • The maximum growth rate of a population, calculated as the per capita birth rate minus the per capita death rate:

      • r > 0: Population expands.

      • r = 0: Population remains constant.

      • r < 0: Population decreases.

Population Dynamics: Barnacle Study

  • Population Density Measurement:

    • Example showing barnacle density variations over time, with graphical representations of density (# per cm²) measured over several days.

  • Equations:

    • \frac{dN}{dt} = \frac{N2 - N1}{t2 - t1} representing change in population density over time.

  • Exponential Growth and Logistic Growth:

    • Represent population growth models, illustrating how populations can grow without limits vs. with constraints.

    • Exponential growth model is shown as \frac{dN}{dt} = rN and the logistic growth as \frac{dN}{dt} = rN \left(1 - \frac{N}{K}\right) where K = carrying capacity.

Life History Strategies

  • r-selected Species:

    • Characteristics: Fast development, high reproductive rates, low survival rates, short lifespan, weak competitive ability, often found in disturbed environments.

  • K-selected Species:

    • Characteristics: Slow development, high survival rates, larger body size, high competitive ability, often reside in stable environments.

Exam Preparation Tips

  • Reading:

    • Carefully read questions, ensuring that all components of short-answer questions are answered.

    • Pay attention to keywords in multiple-choice questions; phrases like “NOT correct” or “FALSE” can change the answer.

  • Understanding Problems:

    • Fully comprehend all weekly project problems, not limited to only the ones completed.

  • Short Answer Responses:

    • Provide detail in answers without overcomplicating; balance brevity with completeness.

    • Utilize key terms relevant to the subject, such as fitness, optimality, and specific heat capacity, to enrich answers.