Unit 1: Ecological concepts
Table of Contents
Basic Concepts and Definitions
This section covers the fundamental vocabulary of ecology.
- Ecology: The scientific study of the interactions between organisms and their environment (both living/biotic and non-living/abiotic).
- Landscape: A heterogeneous area composed of a cluster of interacting ecosystems (e.g., a mosaic of forests, fields, and ponds).
- Habitat: The natural environment or "address" where an organism or population lives, characterized by its physical and chemical features.
- Ecozones (or Biogeographic Realms): Large areas of the Earth's surface where organisms have evolved in relative isolation over long periods, separated by geographic barriers (e.g., deserts, oceans).
- Biosphere: The global sum of all ecosystems; the zone of life on Earth, including parts of the lithosphere, atmosphere, and hydrosphere.
- Ecosystems: A community of living organisms (biotic) interacting with their non-living (abiotic) physical environment as a single functional unit.
- Autecology: The study of the ecology of a single species, focusing on its interactions with its environment (also called species ecology).
- Synecology: The study of the ecology of a group of species that form a community, focusing on their interactions (also called community ecology).
Major Terrestrial Biomes
Biomes are very large ecological areas on the Earth's surface, defined by the dominant plant life and a shared climate. Climate, particularly temperature and precipitation, is the main factor determining a biome.
| Biome | Climate Characteristics | Dominant Vegetation |
|---|---|---|
| Tropical Rainforest | High temperature, high rainfall (all year) | Broadleaf evergreen trees, dense canopy, lianas, epiphytes. High biodiversity. |
| Savanna (Tropical Grassland) | High temperature, distinct wet and dry seasons | Grasses with scattered drought-resistant trees (e.g., Acacia). |
| Desert | Low rainfall (arid), can be hot or cold | Succulents (e.g., cacti), drought-deciduous shrubs, annual herbs. |
| Temperate Grassland | Moderate rainfall, hot summers, cold winters | Perennial grasses and forbs (e.g., prairies, steppes). |
| Temperate Deciduous Forest | Moderate rainfall, four distinct seasons | Deciduous trees (e.g., oak, maple, beech) that lose leaves in winter. |
| Taiga (Boreal Forest) | Low precipitation (snow), long/cold winters | Coniferous evergreen trees (e.g., pine, spruce, fir). |
| Tundra | Very cold, low precipitation, short growing season | Mosses, lichens, dwarf shrubs, grasses. Permafrost (frozen soil). |
Ecological Amplitude
Ecological Amplitude refers to the range of tolerance an organism or species has for a specific environmental factor (e.g., temperature, pH, salinity).
- Species with a wide ecological amplitude are generalists and can survive in a broad range of conditions. They are often widely distributed. (e.g., a rat).
- Species with a narrow ecological amplitude are specialists and can only survive in very specific conditions. They are often rare or restricted in their distribution. (e.g., a panda).
Laws of Limiting Factors
These two laws explain how environmental factors control the growth and distribution of organisms.
Liebig's Law of the Minimum (1840)
"The growth of a plant is dependent on the amount of foodstuff which is presented to it in minimum quantity."
Concept: Imagine a wooden barrel with staves of different lengths. The barrel can only hold water up to the height of the shortest stave.
Application: An organism's growth is not controlled by the total amount of all nutrients, but by the one nutrient that is scarcest (the "limiting factor"). For example, plant growth in a lake is often limited by phosphorus, even if nitrogen and carbon are abundant. Adding more nitrogen won't help; only adding phosphorus will increase growth.
Shelford's Law of Tolerance (1913)
"An organism's success is determined by a range of environmental conditions, with a minimum, maximum, and optimum value for each factor."
Concept: This law expands on Liebig's Law. It states that it's not just "too little" of a factor that limits an organism, but also "too much".
Application: For any factor (like temperature), an organism has:
- Optimum Range: The ideal level where it thrives.
- Zones of Stress: The levels where it can survive but not reproduce or grow well.
- Zones of Intolerance: The minimum and maximum levels beyond which it cannot survive.
For example, fish can die if the water is too cold (minimum) or too hot (maximum). Their "ecological amplitude" is the range between these two extremes.
Ecological Niche
The ecological niche is one of the most important concepts in ecology. It describes the functional role and position of a species within an ecosystem.
The niche includes all the biotic and abiotic factors a species needs to survive and reproduce, such as:
- What it eats (e.g., insects)
- When it eats (e.g., at night)
- Where it finds food (e.g., on the bark of trees)
- Its tolerance ranges (e.g., temperature, humidity)
Types of Niche
- Fundamental Niche: The full range of environmental conditions and resources an organism could theoretically occupy and use, in the absence of competition and other biotic interactions.
- Realized Niche: The actual range of conditions and resources an organism occupies and uses, as a result of biotic interactions like competition, predation, and disease. The realized niche is always smaller than or equal to the fundamental niche.