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Introduction to Ecology

• Ecology is defined as the comprehensive study of the relationship of organisms to their environment (Ernst Haeckel, 1866).
• Ecology can also be seen as scientific natural history (Charles Elton, 1927)
• Ecology involves studying the structure and function of nature (Eugene Odum, 1963)
• Ecology is the scientific study of the distribution and abundance of organisms (Herbert Andrewartha, 1961; Charles Krebs, 1972).
• Ecology focuses on the interrelationships between organisms and their surroundings, particularly in the natural environment (Robert Ricklefs, 1973).
• Common aspects of ecology include the study of interactions between life and their environment.
• Unique aspects of ecology involve focuses spanning natural history, functional dynamics, and evolutionary perspectives.
• A modern definition of ecology is the scientific study of how life interacts with each other and their environment, influencing distribution and abundance.

Characteristics of a Good Hypothesis

• A good hypothesis provides predictions.
• A good hypothesis is testable and falsifiable.
• A null hypothesis is a statement of no cause-and-effect, for example, stating that light availability has no effect on the number of pine seedlings.
• Falsifiability is essential for scientific inquiry; a hypothesis must be capable of being disproven with counterexamples.

Evolution and Distribution Drivers

• Factors that drive evolution include mutation (creation of new alleles), gene flow (immigration/emigration), and genetic drift.
• Genetic drift involves random changes that are more severe in small populations.
• Evolution can also be driven by nonrandom mating (sexual selection) and natural selection (differential survival and reproduction based on phenotype).

Founder Effect vs. Bottleneck Effect

• The founder effect involves a new population established from a small subset of a larger population, such as polydactyly in Amish populations.
• The bottleneck effect involves a drastic reduction in population size followed by expansion, reducing genetic diversity, such as with Northern elephant seals.
• Both the founder effect and bottleneck effect illustrate genetic drift, where allele frequencies change by chance.

Types of Selection

• Directional selection favors extreme phenotypes at one end, as seen in finches with larger beaks during drought conditions.
• Stabilizing selection favors intermediate traits, such as synchronized hatching in birds.
• Disruptive selection favors extreme traits over intermediate ones, such as stickleback fish with distinct body types.

Biological Species Concept

• The biological species concept defines species as groups capable of interbreeding to produce viable offspring.
• Challenges to this concept include asexual organisms (e.g., bacteria lack interbreeding potential), hybridization (e.g., ligers), and species change over time, as fossil records cannot assess interbreeding potential.

Laws Affecting Distributions

• Liebig's Law of the Minimum states that a biological process is limited by the scarcest resource available relative to its requirements.
• Shelford's Law of Tolerance states that organism distributions are limited by the factor for which they have the narrowest tolerance range.

Types of Dispersal

• Diffusion is a gradual spread across hospitable terrain, like cane toads in Australia.
• Jump dispersal is movement across large inhospitable areas, like island colonization by birds.
• Secular dispersal is slow diffusion over evolutionary time, leading to genetic divergence and speciation.

Ideal Distribution Models

• The ideal free distribution model predicts that organisms distribute themselves proportionally across habitats to maximize resources.
• The ideal despotic distribution model describes more dominant individuals monopolizing the best habitats, forcing subordinates into lower-quality areas.

Population Definitions

• A population is a group of individuals of the same species in a given area.
• Defining populations can be difficult in modular organisms due to clonal reproduction (e.g., coral colonies).
• Unitary organisms consist of distinct individuals (e.g., birds, mammals).

Absolute and Relative Density

• Absolute density is the number of individuals per unit area.
• Relative density is the comparison of population densities without exact numbers.

Methods for Measuring Density

• Quadrat sampling can be used for sunflowers.
• Point counts can be used for songbirds.
• The mark-recapture method can work for Galapagos tortoises.

Mark-Recapture Method

• In a mark-recapture example calculation, if 25 snails are marked in the first capture and 50 snails are captured later with 15 marked, the population estimate (N) is (25 × 50) / 15 = 83.
• Assumptions for accurate mark-recapture estimates include no immigration/emigration, no births/deaths, random mixing of marked individuals, and marks not affecting survival.

Density and Dispersion

• Density is the number of individuals per unit area.
• Dispersion is how individuals are spaced within the area.
• Dispersion patterns can be clumped (e.g., schools of fish), uniform (e.g., territorial birds), or random (e.g., wind-dispersed plants).

Life Tables

• A life table tracks the parameters in a standard life table.
• Parameters include x, nx, number of births, lx, dx, qx, bx, lxbx, and xlxbx.

Limitations on Population Growth

• Density dependence refers to the effect that population density has on birth rates, crude death rates, & overall population growth.
• In the logistic growth model, density dependence is a key factor that limits population growth as the population approaches the carrying capacity (K) of the environment.

Equilibrium in Ecosystems

• The equilibrium model assumes that populations and ecosystems reach a stable state over time where birth and death rates (or resource inputs and outputs) are balanced.
• In this model, populations stabilize around a carrying capacity (K) due to density-dependent regulation, and the system remains relatively constant unless disrupted.
• Dynamic equilibrium refers to a system that fluctuates around an equilibrium point due to ongoing births, deaths, immigration, and emigration.
• In real-world ecosystems, true equilibrium is difficult to achieve due to environmental variability, species interactions, human impact, and stochasticity (random events).

Theta Logistic Model

• The theta logistic model is a modification of the simple logistic growth model that introduces a shape parameter θ to adjust how population growth rate responds to population size relative to carrying capacity (K).
• The simple logistic model has issues with density dependence affecting population growth in a linear way.
• Density dependence in the theta model affects population growth in exponential ways.
• The theta model can account for delayed feedbacks & behavioral adjustments
• The theta logistic model provides a more flexible, realistic framework to predict population dynamics.
• Concave 0<θ<1 means: Density dependence is strong even at low population sizes, Growth rate slows earlier than predicted by the simple logistic model & recovery from disturbances is slower because low population sizes experience strong regulation.

Tinbergen's 4 Questions

• Mechanism (Proximate Cause): How is a behavior produced? (e.g., neurological control)
• Development - How does a behavior develop? (e.g., learned or innate)
• Function (Ultimate Cause) - What is the adaptive value? (e.g., fitness consequences)
• Evolution - What is the evolutionary history?

Fixed Action Patterns

• Male sticklebacks exhibit aggressive territorial behavior when they see another male entering their nesting territory.
• This response is automatic and consistent.

Life History Strategies

• Age of Maturity: When an organism first reproduces. Population-level metric: Average age of first reproduction across individuals in a species.
• Individual-level counterpart: The specific age when a particular organism reproduces for the first time.
• Population-level metric: Average time/energy spent per offspring across individuals in a species.
• Individual-level counterpart: The actual care provided by a single parent to its offspring.

Experimental Design

• Mensurative studies are observational with no direct manipulation.
• Manipulative studies directly alter variables to measure responses.
• The independent variable is manipulated or changed by the researcher while the dependent variable is the measure to determin the effect.

Types of Controls

• An experimental control is used in a manipulative experiment to provide a baseline comparison for evaluating the effects of the independent variable
• A group that does not receive the experimental treatment.
• Example: If testing the effect of fertilizer on plant growth, a negative control would be a set of plants that receive no fertilizer to compare against treated plants.

Key Terms

• Null hypothesis: A statement of no cause-and-effect that is statistically testable and could be rejected in favor of an alternative hypothesis.
• Alternative hypothesis: A tentative explanation for observed patterns formatted as a cause-and-effect statement.
• Falsifiability: Information that can be used to reject hypotheses.
• Fitness: Relative ability to survive and reproduce viable offspring.
• Adaptation: Trait(s) of an individual that increases fitness.
• Phenotype vs. genotype: Expressed characteristics vs. genetic makeup.
• Natural selection: Differential survival and reproduction of individuals due to differences in phenotype.
• Founder effect: Establishment of a new population from a small subset of a larger population.
• Bottleneck effect: Large reduction in population size followed by expansion leading to a reduction in genetic diversity; allele frequencies are altered.
• Allopatric speciation: Geographic isolation from a parent population leads to divergence and speciation.
• Sympatric speciation: Speciation in the absence of geographic separation.
• Genetic drift: Change in allele frequency of a population by chance; small populations are affected the mos
• Carrying capacity: The maximum number of individuals that can be sustainably supported in a habitat.
• Emigration: The act of leaving a habitat or region with the intent of living elsewhere.
• Ideal free distribution: Population density increases in 'best' habitat; resources decline until habitat quality becomes equal to 'lesser' habitat.
• Ideal despotic distribution: Territorial, aggressive individuals occupy the best habitats, with subordinates forced into lesser habitats and lower fitness.
• Jump vs. secular dispersal: Movement across large distances vs. diffusion over significant time, where evolutionary change occurs during the process.
• Ethology: The study of animal behavior.
• Fixed action pattern: Behaviors performed by all members of one sex of a species in a stereotypical pattern.
• Sign stimulus: An essential part of a stimulus that elicits a response.
• Imprinting: A limited phase during development that is the only time when certain behaviors can be learned.
• Habituation: Response to stimuli decreases with exposure.
• Latent learning vs. insight: Improvement through repetition vs. natural problem-solving.
• Semelparity: Species that reproduce once, then die, leading to discrete growth.
• Iteroparity: Species that reproduce multiple times, leading to overlapping generations
• Negative control: A group that does not receive any treatment; no response is expected.
• Procedural control: A control group that tests if the method for imposing a treatment causes a response itself, regardless of whether you manipulate the independent variable.
• Independent variable: The "cause" in the hypothesis; this variable changes and is the variable that is manipulated.
• Dependent variable: The "effect" response to the independent variable and is what would be measured.