Interdependence of Living Things
The Ecosystem: A Dynamic Network
An ecosystem is a community of interacting organisms and their physical environment. It includes:
- Biotic factors: Living components like plants, animals, and microorganisms.
- Abiotic factors: Nonliving components like sunlight, water, and soil.
Ecosystem: A biological community of interacting organisms and their physical environment.
Diversity and Ecosystem Stability
- Diversity refers to the variety of species within an ecosystem.
- High diversity increases stability by:
- Providing redundancy: If one species is lost, others can fill its role.
- Enhancing resilience: Diverse ecosystems recover more quickly from disturbances.
When analyzing food webs, remember that energy flows in one direction—from producers to consumers to decomposers. Nutrients, however, are recycled within the ecosystem.
Abiotic Factors Shape Ecosystems
Abiotic factors determine which species can survive and thrive in an ecosystem. Key factors include:
- Light intensity: Affects photosynthesis and plant growth.
- Temperature: Influences metabolic rates and species distribution.
- Moisture: Essential for plant growth and animal survival.
- Soil composition: Determines nutrient availability for plants.
- pH levels: Affects enzyme activity and species tolerance.
Abiotic factors often interact with biotic factors. For example, soil composition influences plant growth, which in turn affects herbivore populations.
Biotic Interactions: The Web of Life
Nutritional Relationships
- Food chains: Linear sequences showing energy flow (e.g., grass → grasshopper → frog → raccoon).
- Food webs: Complex networks of interconnected food chains.
A food web in a pond ecosystem might include algae, aquatic insects, fish, and birds, with decomposers recycling nutrients from dead organisms.
Symbiotic Relationships
- Mutualism: Both species benefit (e.g., bees pollinating flowers).
- Commensalism: One species benefits, the other is unaffected (e.g., barnacles on whales).
- Parasitism: One species benefits at the expense of the other (e.g., tapeworms in humans).
Don't confuse mutualism with commensalism. In mutualism, both species benefit, while in commensalism, only one species benefits without affecting the other.
Competition
- Intraspecific competition: Within the same species (e.g., squirrels competing for acorns).
- Interspecific competition: Between different species (e.g., hawks and owls competing for mice).
Goldenrod plants compete for sunlight in open fields but struggle in shaded forests, where light is a limiting factor.
Cyclic Changes and Ecosystem Dynamics
Ecosystems are dynamic and experience cyclic changes, such as:
- Seasonal changes: Affect temperature, moisture, and resource availability.
- Predator-prey cycles: Populations of predators and prey fluctuate in response to each other.
These cycles contribute to ecosystem stability by preventing any one population from overwhelming the system.
Material Cycles: The Foundation of Life
Carbon-Hydrogen-Oxygen Cycle
- Photosynthesis: Plants convert \$CO_2\$ and \$H_2O\$ into glucose and \$O_2\$.
- Respiration: Organisms break down glucose, releasing \$CO_2\$ and \$H_2O\$.
In a balanced ecosystem, plants and animals maintain a cycle where the waste products of one process serve as the raw materials for the other.
Nitrogen Cycle
- Nitrogen-fixing bacteria: Convert atmospheric nitrogen (\$N_2\$) into usable forms for plants.
- Decomposers: Break down organic matter, returning nitrogen to the soil.
Without decomposers, essential nutrients like nitrogen would remain locked in dead organisms, disrupting the nutrient cycle.
Energy Flow: The Pyramid of Life
- Energy enters ecosystems through sunlight, captured by producers.
- Energy is transferred through food chains but decreases at each trophic level.
- Energy pyramids illustrate this loss, with only ~10% of energy passed to the next level.
If producers store 10,000 kJ of energy, primary consumers receive ~1,000 kJ, secondary consumers ~100 kJ, and tertiary consumers ~10 kJ.
Remember, energy flows in one direction and cannot be recycled. This is why ecosystems depend on a continuous input of energy from the Sun.
Carrying Capacity and Limiting Factors
- Carrying capacity: The maximum population size an environment can support.
- Limiting factors: Conditions that restrict population growth, such as:
- Abiotic factors: Water, sunlight, and nutrients.
- Biotic factors: Predation, disease, and competition.
In a grassland, the carrying capacity for buffalo depends on the availability of grass, water, and space.
It's a common misconception that carrying capacity is fixed. In reality, it can change due to environmental factors or human activities.
Ecological Succession: Nature's Recovery Process
- Primary succession: Begins on bare rock or soil after a disturbance (e.g., volcanic eruption).
- Pioneer species: Lichens and mosses break down rock to form soil.
- Later stages: Grasses, shrubs, and eventually trees establish a climax community.
- Secondary succession: Occurs in areas where soil remains intact (e.g., after a fire).
* After Mount St. Helens erupted in 1980, pioneer species like lupines colonized the ash-covered landscape, paving the way for later plant and animal communities.
Climax communities are stable but not permanent. They can change if the environment is altered by natural events or human activities.
The Importance of Biodiversity
- Biodiversity enhances ecosystem stability and resilience.
- It provides:
- Genetic resources: For medicine and agriculture.
- Ecosystem services: Such as pollination, water purification, and climate regulation.
The loss of a single pollinator species can disrupt food production and affect entire ecosystems.
How do we balance the needs of human development with the preservation of biodiversity? What ethical considerations arise when deciding which species or habitats to protect?
Reflection and Application
- How do abiotic and biotic factors interact to shape ecosystems?
- Why is energy flow unidirectional, while nutrients are recycled?
- How does biodiversity contribute to ecosystem stability and human well-being?
