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Honors Biology
Table of Contents
Unit 17 Overview: Ecology
17.1 Levels of Ecological Organization
17.2 Energy Flow in Ecosystems
17.3 Biotic and Abiotic Interactions

Ecology examines life's interconnected levels, from individual organisms to the entire biosphere. These levels form a hierarchy, with each building upon the last, creating increasingly complex systems of interactions between living things and their environment.

Understanding ecological organization helps us grasp how species relate to each other and their surroundings. This knowledge is crucial for addressing environmental issues and maintaining the delicate balance of ecosystems worldwide.

Levels of Ecological Organization

Hierarchy of Ecological Levels

  • Organism: an individual living thing (tree, bird, bacterium)
    • Smallest level of ecological organization
    • Consists of organs, organ systems, and tissues working together to maintain homeostasis
  • Population: a group of organisms of the same species living in the same area at the same time
    • Interact and breed with each other
    • Share a common gene pool
    • Adapt to their environment over time through natural selection
  • Community: an assemblage of populations of different species living in the same area and interacting with each other
    • Includes both biotic (living) and abiotic (non-living) components
    • Involves complex relationships such as competition, predation, and symbiosis

Larger-Scale Ecological Levels

  • Ecosystem: a community of organisms and their abiotic environment interacting as a system
    • Includes the transfer of energy and cycling of nutrients
    • Examples include a forest, a coral reef, or a pond
  • Biome: a large region characterized by a specific type of climate and certain types of plant and animal communities
    • Determined primarily by climate and geography
    • Major biomes include tundra, taiga, temperate deciduous forest, and desert
  • Biosphere: the portion of Earth that supports life, including land, water, and the atmosphere
    • Largest level of ecological organization
    • Encompasses all living organisms and their interactions with the abiotic environment

Ecological Interactions

Habitat and Niche

  • Habitat: the physical place where an organism lives and interacts with the biotic and abiotic factors
    • Provides the necessary resources for survival, such as food, water, and shelter
    • Can be as large as an ocean or as small as a drop of water
  • Niche: the role an organism plays in its environment, including its interactions with other organisms and its use of resources
    • Includes the organism's habitat, as well as its functional role in the ecosystem
    • Helps to reduce competition between species by allowing them to specialize in different resources or roles

Species Interactions

  • Species: a group of organisms that can interbreed and produce fertile offspring
    • Organisms within a species share similar characteristics and occupy similar niches
    • Species interact with each other in various ways, such as:
      • Competition: when two or more species rely on the same limited resources (food, water, space)
      • Predation: when one species (the predator) hunts and consumes another species (the prey)
      • Symbiosis: a close, long-term relationship between two species, which can be:
        • Mutualistic: both species benefit (bees pollinating flowers)
        • Commensalistic: one species benefits while the other is unaffected (remora fish and sharks)
        • Parasitic: one species (the parasite) benefits while the other (the host) is harmed (ticks on a dog)

Key Terms to Review (23)

Ecosystem: An ecosystem is a community of living organisms, along with their physical environment, interacting as a system. This term encompasses both biotic factors, like plants and animals, and abiotic factors, such as climate and soil. Ecosystems vary greatly in size and complexity, from small ponds to vast forests, and they highlight the intricate relationships between organisms and their surroundings, showing how life sustains itself within various levels of organization.
Symbiosis: Symbiosis is a biological term that describes the interaction between two different organisms living in close physical proximity, often for an extended period. This relationship can be mutualistic, commensalistic, or parasitic, and it plays a critical role in shaping ecosystems, influencing everything from nutrient cycling to population dynamics.
Field Study: A field study is a research method involving the collection of data in a natural environment rather than in a laboratory setting. This approach allows scientists to observe and interact with subjects in their own habitats, leading to more authentic and ecologically valid results. Field studies are essential for understanding complex interactions within ecosystems and for communicating findings in a way that reflects real-world conditions.
Modeling: Modeling refers to the process of creating a simplified representation of a complex system or phenomenon to better understand and analyze its components and interactions. In ecology, modeling plays a crucial role in predicting ecological outcomes, exploring relationships between different levels of organization, and simulating changes within ecosystems over time.
Population density: Population density is the measurement of the number of individuals living in a defined area, often expressed as individuals per unit area (e.g., people per square kilometer). This concept is crucial for understanding how organisms interact with their environment and how resources are distributed within a habitat. It influences various ecological and biological processes, including competition for resources, mating behaviors, and the overall health of ecosystems.
Taiga: The taiga, also known as the boreal forest, is a biome characterized by coniferous forests, cold temperatures, and long winters. It spans across northern regions of North America, Europe, and Asia, serving as a vital ecological zone that supports diverse plant and animal species while playing a key role in global carbon cycling and climate regulation.
Consumers: Consumers are organisms that rely on other organisms for their energy and nutrient needs. They play a vital role in the flow of energy within an ecosystem by feeding on producers or other consumers, thus forming a crucial part of the food web and contributing to ecological balance.
Tundra: The tundra is a unique biome characterized by its cold temperatures, minimal precipitation, and a short growing season. Found primarily in the Arctic and Antarctic regions, it supports a specific range of vegetation, such as mosses, lichens, and low shrubs, adapted to survive harsh conditions. The tundra plays a vital role in global ecology, influencing carbon cycles and hosting various organisms that are specially adapted to extreme environments.
Biome: A biome is a large ecological area characterized by distinct plant and animal groups, which are adapted to the environment and climate of that region. Biomes are defined by factors such as temperature, precipitation, and soil type, leading to the formation of various ecosystems within each biome. These vast regions play a significant role in the Earth's biodiversity and ecological interactions.
Biogeochemical cycles: Biogeochemical cycles are natural processes that recycle essential nutrients in various chemical forms from the environment to organisms and back again. These cycles are crucial for maintaining ecosystem balance and involve multiple levels of ecological organization, from individual organisms to entire ecosystems. They encompass the movement of elements like carbon, nitrogen, and phosphorus through the biosphere, atmosphere, hydrosphere, and lithosphere, highlighting the interconnectedness of living organisms and their environments.
Producers: Producers are organisms that can make their own food through processes like photosynthesis or chemosynthesis, forming the foundation of the food web in ecosystems. They convert sunlight or chemical energy into organic compounds, which serve as the primary energy source for all other organisms in an ecosystem, linking together levels of ecological organization, nutrient cycles, and energy flow.
Decomposers: Decomposers are organisms, primarily fungi and bacteria, that break down dead organic matter and recycle nutrients back into the ecosystem. They play a vital role in maintaining the health of ecosystems by breaking down waste materials and dead organisms, which helps to release essential nutrients like carbon, nitrogen, and phosphorus back into the soil, making them available for use by plants and other organisms.
Food chain: A food chain is a linear sequence of organisms where each organism serves as food for the next in the chain, illustrating how energy and nutrients flow through an ecosystem. This concept helps to highlight the relationships between producers, consumers, and decomposers, demonstrating how energy from the sun is converted into food and then passed along through various trophic levels.
Niche: A niche refers to the specific role or function of an organism within its environment, including how it obtains resources, interacts with other organisms, and contributes to the ecosystem. It encompasses both the physical habitat an organism occupies and its position in the food web. The concept of a niche highlights the unique adaptations and behaviors that allow different species to coexist and thrive in various ecological contexts.
Carrying Capacity: Carrying capacity refers to the maximum number of individuals of a particular species that an environment can sustainably support over time. It is influenced by various factors such as food availability, habitat space, water supply, and the presence of predators or diseases. This concept is crucial for understanding how populations grow, stabilize, and interact within ecosystems, as it determines the limits to population growth and the dynamic balance between species and their environment.
Predation: Predation is the biological interaction where one organism, the predator, hunts and consumes another organism, the prey, for nourishment. This relationship is crucial for regulating populations within ecosystems, influencing the structure of communities, and driving evolutionary adaptations among species.
Habitat: A habitat is the natural environment in which a particular species or community of organisms lives and thrives. It encompasses all the living and non-living factors that affect the organisms within it, such as food, water, shelter, and mates for reproduction. Understanding habitats is crucial for studying the interactions between organisms and their environment, as well as the biodiversity that exists within ecosystems.
Competition: Competition is the interaction between organisms or species that vie for limited resources such as food, space, and mates. This rivalry can drive natural selection and influence population dynamics, ultimately shaping community structures and ecological interactions.
Community: A community is a group of interacting populations of different species that live in the same geographic area and share resources. It is characterized by the relationships among various organisms, including competition, predation, and symbiosis, which all play a role in the dynamics of the ecosystem. The diversity and interactions within a community can significantly affect its overall health and stability.
Trophic levels: Trophic levels refer to the hierarchical positions in an ecosystem that categorize organisms based on their primary source of energy. Each level represents a different stage in the flow of energy and nutrients, starting from producers at the base, followed by various levels of consumers. Understanding these levels helps clarify the roles of different organisms in food webs and their impact on biodiversity and ecological balance.
Population: A population refers to a group of individuals of the same species that live in a specific area and interact with each other. This concept is fundamental to understanding how organisms thrive and evolve, as it encompasses the dynamics of reproduction, survival, and interactions within their environment. Analyzing populations helps in comprehending larger biological principles like ecosystem balance, speciation processes, and overall biodiversity.
Biosphere: The biosphere refers to the global sum of all ecosystems, representing the zone of life on Earth. It encompasses all living organisms, as well as the environments in which they live, from the deepest ocean floors to the highest mountain peaks. This interconnected system is vital for supporting life and maintaining ecological balance, influencing everything from climate to nutrient cycling.
Organism: An organism is any living entity that can carry out life processes independently, including growth, reproduction, and response to stimuli. Organisms can be unicellular or multicellular, and they display various characteristics that define life, such as metabolism and homeostasis. Understanding organisms helps in studying the organization of life at different levels, from individual cells to complex ecosystems.