Ecology Review
8.1: Introduction to Ecology and Levels of Organization
Ecology: The scientific study of interactions among organisms and between organisms and their environment.
Levels of Ecological Organization:
Organism: An individual living being.
Population: A group of individuals of the same species living in the same area at the same time.
Community: All the different populations of species that live and interact in the same area.
Ecosystem: A community of organisms and their physical environment, including both biotic (living) and abiotic (non-living) components.
Biome: A large regional or global ecosystem characterized by its climate, plant, and animal life (e.g., deserts, rainforests, tundra).
Biosphere: The sum of all the ecosystems on Earth; the global ecological system integrating all living beings and their relationships.
Biotic Factors: Living or once-living components of an ecosystem (e.g., plants, animals, fungi, bacteria).
Abiotic Factors: Non-living physical and chemical parts of an ecosystem (e.g., sunlight, water, temperature, soil, oxygen, salinity).
8.2: Energy Flow Through Ecosystems
Energy transfer within ecosystems occurs through various trophic levels, starting from primary producers to primary consumers, and then to higher-level consumers, highlighting the importance of each level in maintaining ecological balance.
Producers (Autotrophs): Organisms that produce their own food, primarily through photosynthesis (using sunlight) or chemosynthesis (using chemical energy).
Examples: Plants, algae, some bacteria.
Consumers (Heterotrophs): Organisms that obtain energy by consuming other organisms.
Primary Consumers (Herbivores): Eat producers (e.g., deer, rabbits).
Secondary Consumers (Carnivores/Omnivores): Eat primary consumers (e.g., wolves, birds eating insects).
Tertiary Consumers (Carnivores/Omnivores): Eat secondary consumers (e.g., eagles eating snakes).
Decomposers (Detritivores): Break down dead organic matter and return nutrients to the soil (e.g., bacteria, fungi, worms).
Trophic Levels: The position an organism occupies in a food chain.
Energy Transfer Efficiency: Only about 10\% of the energy from one trophic level is transferred to the next; the rest is lost as heat (90\% loss).
This explains why there are fewer organisms at higher trophic levels.
Food Chains: Linear pathways showing how energy is transferred from one organism to another.
Food Webs: Complex networks of interdependent food chains within an ecosystem, showing multiple feeding relationships.
8.3: Biogeochemical Cycles
Water Cycle: The continuous movement of water on, above, and below the surface of the Earth (evaporation, condensation, precipitation, runoff, infiltration).
Carbon Cycle: The biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. Key processes include photosynthesis, respiration, decomposition, and combustion.
Nitrogen Cycle: The process by which nitrogen is converted into various chemical forms as it circulates among the atmosphere, terrestrial, and marine ecosystems (nitrogen fixation, nitrification, assimilation, ammonification, denitrification).
Phosphorus Cycle: The biogeochemical cycle that describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere. Unlike other major cycles, it does not involve a significant atmospheric component.
8.4: Population Ecology
Population: A group of individuals of the same species living in the same geographical area.
Factors Affecting Population Size: Birth rate, death rate, immigration, emigration.
Population Growth Models:
Exponential Growth: Occurs under ideal conditions with unlimited resources, resulting in a J-shaped curve. Represented by \frac{dN}{dt} = rN, where N is population size, t is time, and r is the intrinsic rate of increase.
Logistic Growth: Occurs when population growth slows or stops as it reaches the carrying capacity, resulting in an S-shaped curve. Represented by \frac{dN}{dt} = rN\left(1 - \frac{N}{K}\right), where K is the carrying capacity.
Carrying Capacity (K): The maximum population size that an environment can sustain indefinitely, given the available resources.
Limiting Factors: Environmental factors that restrict population growth.
Density-Dependent Factors: Factors whose effects intensify as the population density increases (e.g., competition for resources, predation, disease).
Density-Independent Factors: Factors whose effects are not related to population density (e.g., natural disasters like floods, wildfires, extreme weather).
8.5: Community Ecology
Community: An assemblage of different populations interacting in the same location.
Interspecific Interactions: Relationships between different species.
Competition: Species vie for the same limited resources (-/- interaction).
Predation: One species ( ext{predator}) kills and eats another species ( ext{prey}) (+/ - interaction).
Symbiosis: Two different species live in close physical association.
Mutualism: Both species benefit (+/+ interaction, e.g., bees and flowers).
Commensalism: One species benefits, the other is unaffected (+/0 interaction, e.g., barnacles on whales).
Parasitism: One species ( ext{parasite}) benefits at the expense of the other ( ext{host}) (+/ - interaction, e.g., ticks on mammals).
Ecological Niche: The role and position a species has in its environment, including all its interactions with the biotic and abiotic factors of its habitat.
Competitive Exclusion Principle: Two species competing for the exact same limited resources cannot coexist indefinitely; one will eventually outcompete the other.
Ecological Succession: The process of change in the species structure of an ecological community over time.
Primary Succession: Occurs in an area devoid of life and soil (e.g., bare rock after volcanic eruption).
Secondary Succession: Occurs in an area where soil remains after a disturbance (e.g., after a forest fire).
8.6: Ecosystem Structure and Dynamics
Ecosystem Services: Benefits that humans receive from ecosystems (e.g., clean air and water, pollination, climate regulation).
Biodiversity: The variety of life in the world or in a particular habitat or ecosystem, often measured at genetic, species, and ecosystem levels.
Keystone Species: A species whose presence is crucial for maintaining the structure and integrity of an ecosystem (e.g., sea otters).
Foundation Species: A species that plays a major role in structuring a community by creating or enhancing a habitat (e.g., coral in coral reefs).
Indicator Species: A species whose health and population size serve as early warnings of environmental changes or degradation.
8.7: Disruption in Ecosystems
Disruptions in ecosystems can arise from natural events and human activities, leading to changes in species composition, loss of biodiversity, and alterations in energy flow within the food web.
Natural Disruptions:
Short-term: Wildfires, floods, droughts, volcanic eruptions, earthquakes.
Long-term: Climate shifts, glaciation cycles.
Impacts: Can lead to species migration, extinction, or new successional pathways, contributing to ecosystem resilience and evolution.
Human Activities (Anthropogenic Disruptions):
Habitat Destruction and Fragmentation: Leading cause of biodiversity loss; results from urbanization, agriculture, deforestation.
Pollution: Introduction of harmful substances into the environment (air, water, soil pollution, plastic pollution, light/noise pollution).
Climate Change: Primarily due to increased greenhouse gas emissions, leading to global warming, ocean acidification, extreme weather events, and sea-level rise.
Overexploitation of Resources: Unsustainable harvesting of resources (e.g., overfishing, deforestation, overhunting).
Invasive Species: Non-native species introduced to an ecosystem, often outcompeting native species and disrupting food webs.
Consequences of Disruptions:
Loss of Biodiversity: Reduction in the variety of life forms, impacting ecosystem stability and function.
Alteration of Biogeochemical Cycles: Changes in the cycling of essential nutrients (e.g., increased carbon in the atmosphere, nitrogen runoff).
Changes in Food Web Dynamics: Loss of keystone species or introduction of new species can dismantle complex feeding relationships.
Ecosystem Degradation/Collapse: Severe and lasting damage to ecosystem health, reducing its ability to provide essential services.