Communities and Ecosystem Dynamics

A habitat encompasses the physical and biological environmental factors influencing organisms.
Species possess a tolerance range, defining conditions for survival and reproduction.
A species' niche includes the range of conditions for its survival and reproduction.
Competition shapes community composition and species niches.
Predator-prey and herbivore-plant interactions influence population dynamics.
The competitive exclusion principle: No two species can occupy the same niche in the same habitat at the same time.
Symbiosis: Interdependent relationships between species.
- Commensalism: One benefits, the other is neutral (e.g., Sharks and Remora Fish).
- Mutualism: Both benefit (e.g., Bee and flower).
- Parasitism: One benefits, the other is harmed (e.g., Fleas on dogs).
Keystone species exert significant influence on ecosystem structure, stability, and diversity.

Ecological succession: Predictable community changes over time.
Primary succession: Occurs on bare rock without remnants of an older community (e.g., after volcanic eruptions).
- Pioneer species colonize barren areas first.
Secondary succession: Occurs when some members of the older community remain (e.g., after wildfires).
New communities replace older ones in both types of succession.
Natural disturbances can lead to the original climax community or different communities.
Climax community: Final succession stage, stable until major disturbance.

Biodiversity: Total genetic variation within all organisms in the biosphere.
- Ecosystem diversity: Variety of habitats, communities, and ecological processes.
- Species diversity: Number and abundance of species.
- Genetic diversity: Sum of genetic information in organisms.
Biodiversity is a key resource, contributing to medicine, agriculture, and adaptation to change.
Higher biodiversity increases ecosystem resilience to disturbances.
Ecosystem services: Benefits humans derive from ecosystems.
- Examples: Food production, nutrient cycling, water purification.