Introduction to Ecology Study Notes

Introduction to Ecology

Before You Begin

  • This lecture covers the ecological and evolutionary factors that influence the distribution of organisms.
  • Prior knowledge required: Ability to summarize the scientific process (from Chapter 1).
  • Pre-Lecture Review Question: The most accurate statement regarding the hypothesis-based approach to scientific inquiry is that a hypothesis should lead to a prediction that can be tested.

Learning Objectives

Unit One Objectives

  • Understand the fundamental concepts of ecology.
  • Explain how Earth’s climate and other environmental elements determine the location of major life zones (biomes).

Lecture Objectives

  • Define ecology and describe the hierarchical levels of interaction studied by ecologists.
  • Define key ecological terms.
  • Describe the impact of both abiotic (non-living) and biotic (living) factors on the distribution of species.
  • Describe how Earth’s climate serves as the primary determinant for the location of biomes.

What is Ecology?

  • Ecology is defined as the scientific study of the interactions between organisms and the biotic (living) and abiotic (non-living) components of their environment.

Why Study Ecology?

  • Understanding ecology is crucial for comprehending how changes in one part of an ecosystem can have widespread effects.
  • Example: Yellowstone National Park and Wolves
    • Wolves, once the natural apex (top) predators of Yellowstone, were extirpated (locally extinct) from the park by 1926.
    • Over the next 70 years, significant ecological changes occurred within Yellowstone due to their absence.
    • The Gray Wolf later became an endangered species.
    • In 1996, wolves were successfully reintroduced to Yellowstone, demonstrating an attempt to restore ecological balance.
  • Interactions studied by ecologists can be organized into a hierarchy that spans from individual organisms to the entire planet.

Hierarchy of Ecology

  • Organismal Ecology:
    • Studies how an organism’s anatomical structure, physiological processes, and behavioral adaptations enable it to meet environmental challenges.
  • Population Ecology:
    • Focuses on factors that influence population size over periods of time.
    • Population: Defined as a group of individuals of the same species living within a specific area.
  • Community Ecology:
    • Examines the effects of interspecific interactions (interactions between different species) on the structure and organization of a community.
    • Community: Defined as a group of populations of different species coexisting in a particular area.
  • Ecosystem Ecology:
    • Emphasizes the flow of energy and the cycling of chemical elements (e.g., nutrients like carbon, nitrogen) between organisms and their broader physical environment.
    • Ecosystem: Comprises the community of organisms in an area along with all the physical (abiotic) factors with which they interact.
  • Landscape Ecology:
    • Focuses on the exchanges of energy, various materials, and organisms across multiple ecosystems.
    • Landscape: A mosaic or collection of connected ecosystems.
  • Global Ecology (or Biosphere Ecology):
    • Examines the extensive influence of energy and materials on organisms across the entire biosphere.
    • Biosphere: Represents the global ecosystem, which is the sum total of all the planet’s ecosystems and landscapes.

Hierarchy of Ecology - Practice Questions

  • Question: What is the relationship between resource availability and birthrate?
    • Level: Population Ecology
  • Question: Which factors give rise to the spatial extent and arrangement of the various ecosystems?
    • Level: Landscape Ecology
  • Question: Why do tropical rain forests support a greater diversity of species than temperate forests?
    • Level: Community Ecology or Ecosystem Ecology
  • Question: How does this cone-flower interact with other species of plants and animals in the prairie community?
    • Level: Community Ecology
  • Question: How do yearly variations in rainfall influence the productivity of plants in this prairie grassland ecosystem?
    • Level: Ecosystem Ecology

Key Ecological Terms

  • The ecology of an environment is often characterized by its abiotic and biotic factors.
  • Biotic Factors: These are the living organisms, or things that were once living, within a particular environment.
  • Abiotic Factors: These are the non-living or physical components of the environment (e.g., temperature, light, water, nutrients).
  • Both biotic and abiotic factors are critical components of ecology, as they dictate:
    • Which specific organisms can inhabit certain environments.
    • The distribution patterns of those organisms.
    • The total number of organisms an area can sustainably support.

Habitat and Niche

  • An organism’s habitat:
    • Is the specific environment it lives in.
    • Encompasses both the biotic and abiotic factors of its surroundings.
    • Key factors that can affect an organism’s habitat include energy sources, temperature, water availability, and inorganic nutrient concentrations.
  • An organism’s niche:
    • Represents the unique role the organism plays within its ecosystem; essentially, its “job” or functional position.

Ecological Niche and Competition

  • An organism’s niche is frequently constrained or limited by competition from other individuals or species.
  • Competitive Exclusion Principle: States that two species occupying the exact same ecological niche for an extended period cannot coexist indefinitely. One species will eventually outcompete and either eliminate or drive out the other due to competition for limited resources.
  • Fundamental Niche: This refers to the entire range of environmental conditions and resource opportunities where a species could potentially survive and reproduce in the absence of interspecific competition.
  • Realized Niche: This is the actual niche a species occupies within a particular community. It is often smaller than the fundamental niche because it is affected by factors such as competition, predation, and other interspecific interactions.

Ecosystems Around the Globe

  • The Earth features diverse biomes, which are large ecological areas characterized by their dominant plant and animal life, primarily determined by climate.
  • Biome Distribution Factors: Biomes like tropical rainforests, temperate rainforests, deserts, savannas, grasslands, woodlands, taiga, and tundra are distributed across the globe based on combinations of:
    • Annual Precipitation: Ranging from very low (e.g., deserts) to very high (e.g., rainforests).
    • Average Temperature: Ranging from hot (>30^ ext{o} ext{C}) to cold (<-10^ ext{o} ext{C}).
  • Climate (driven by variations in Earth's surface heating) is the primary factor affecting the location and characteristics of these biomes.

Ecologically Equivalent Species & Convergent Evolution

  • Ecologically Equivalent Species: These are species that have evolved independently in different geographical regions across the globe but share similar physical environments and occupy the same ecological niche.
  • This phenomenon often leads to convergent evolution.
  • Convergent Evolution: This is the evolutionary process where two species, despite not sharing a recent common ancestor, develop similar characteristics or adaptations due to experiencing similar environmental pressures and occupying similar niches.
    • Examples: The impala (Africa) and pronghorn (North America) share structural and behavioral similarities due to inhabiting similar open grassland environments. Another classic example includes the flying squirrel (North America) and the sugar glider (Australia), both of which have developed gliding membranes for arboreal locomotion.

Adjusting to Variations in Weather

  • The ability of organisms to thrive in Earth’s highly diverse environments underscores the strong interrelationship between the fields of ecology and evolutionary biology.
  • Evolutionary Adaptation: Adaptations occur in populations over generations via natural selection, which results from ongoing interactions between organisms and their specific environments.
  • Abiotic factors within a habitat can exhibit variability:
    • From year to year.
    • Seasonally.
    • Over the course of a single day.

Environmental Variability & Acclimation

  • Responses that occur during the lifetime of an individual organism do not constitute evolution, as evolution is defined as changes in a population's genetic makeup over multiple generations.
  • Acclimation: This is a gradual, reversible, physiological adjustment that an individual organism makes in response to an environmental change.
  • The extent to which a species can acclimate is generally linked to the range of environmental conditions it naturally encounters.
  • Vertebrate Examples:
    • Endotherms (e.g., birds and mammals) can typically tolerate the widest range of temperature extremes because their internal systems regulate body temperature.
    • Ectothermic reptiles (cold-blooded), in contrast, can generally tolerate only a more limited range of temperatures, as their body temperature largely depends on external conditions.
    • Arctic Fox Adaptation: An example of a species with significant acclimation abilities to extreme cold is the arctic fox.

End of Lecture Review Questions

  • Question 1: Which of the following areas of study focuses on the exchange of energy, organisms, and materials between ecosystems?
    • Answer: Landscape ecology
  • Question 2: If the direction of Earth’s rotation reversed, the most predictable effect would be…
    • Answer: Winds blowing from west to east along the equator (due to altered Coriolis effect).
  • Question 3: Which of the following statements is consistent with the principles of competitive exclusion?
    • Answer: If two species have the same fundamental niche, one will exclude the other competing species.
    • Additional insight: Even a slight reproductive advantage will eventually lead to the elimination of the less well-adapted of the two competing species.
  • Question 4 (Salmon Scenario): Salmon eggs hatch in freshwater, migrate up to 1,000 km to the ocean, spend up to 5 years growing (acquiring over 95\% of their biomass), and then return to their home streams to spawn. Females lay up to 8,000 eggs, males fertilize them, and both typically die. The physiological response that allows salmon to survive in freshwater, then in salt water, and then in freshwater again is an example of .
    • Answer: Acclimation