Lec 07 Ecological Communities

Species Interaction Outcomes
- Competitive Exclusion: When one species is a better competitor (e.g., Species X over Species Y), the weaker species may be excluded from shared environments.
- Coexistence: If species populations are low, both can persist through resource sharing in overlapping areas.
- Character Divergence: Prolonged niche partitioning in overlapping zones may lead to character divergence, assisting in coexistence.
- Predator-Mediated Coexistence: The presence of a predator that prefers the weaker competitor may allow both species to coexist by controlling population sizes.
Definitions and Distinctions
- Trophic Facilitation: Positive interactions where a consumer benefits indirectly from interactions between its prey and another species.
- Trophic Cascades: Changes in species abundance at lower trophic levels due to predation at higher levels, affecting community composition (e.g., loss of apex predators like sharks).
Types of Species
- Keystone Species: Species with a disproportionate effect on the community relative to their abundance (e.g., sea otters).
- Ecosystem Engineers: Species that modify their environment in a way that creates habitat for others (e.g., beavers).
- Dominant Species: Species that are numerically abundant or have the highest biomass in an ecosystem (e.g., deer).
- Foundational Species: Provide structural habitat for other species (e.g., trees, coral).

Definitions
- Genetic Diversity: Variation within and between populations.
- Species Diversity: Total species in an area, including species richness (count of species).
- Ecosystem Diversity: Variation of species and ecosystems in a certain area.

Habitat Heterogeneity: Higher structural complexity can increase species richness.
Climate Stability: Stable climates typically support higher biodiversity compared to fluctuating environments.
Disturbance Frequency: Intermediate disturbance hypothesis suggested that moderate disturbances can enhance biodiversity by allowing coexistence of diverse species.
Historial Events: Areas with stable environments may have higher biodiversity due to fewer large-scale disruptions over time.

Types of Succession
- Primary Succession: Development after a complete disturbance (e.g., glacier retreat).
- Secondary Succession: Recovery following partial disturbance (e.g., after a forest fire).
Pioneer Species: First colonizers in a new habitat; often opportunistic.
Climax Community: Mature ecosystem in equilibrium until a disturbance resets the process.

Species-Area Relationship: Larger islands support more species due to higher colonization rates and lower extinction rates.
Distance to Source of Colonization: Closer islands have higher colonization rates, impacting species richness.

Competitive Exclusion: If species X (like a certain plant) is better at utilizing sunlight compared to species Y, species Y may be excluded from areas where both species compete for light.
Coexistence: In a forest with low population levels, species A (small shrubs) and species B (perennial flowers) might share space by utilizing different soil nutrients, allowing both to thrive.
Character Divergence: In a shared habitat with limited resources, two bird species could evolve different beak shapes over time, allowing them to exploit different food sources while living in the same area.
Predator-Mediated Coexistence: If there are wolves that primarily hunt deer, both a smaller species of deer and a larger species can coexist, as the wolves control the population of the smaller deer species.

Trophic Facilitation: In a grassy ecosystem, rabbits may benefit from plants that grow better due to the presence of certain soil bacteria, allowing them to thrive.
Trophic Cascades: When sea otters (predators of sea urchins) are removed from a kelp forest, the sea urchin population can explode, leading to a decline in kelp and affecting the entire ecosystem.

Keystone Species: The removal of sea otters from a coastal ecosystem can lead to overpopulation of sea urchins, drastically changing the community structure.
Ecosystem Engineers: Beavers building a dam create wetlands, which provide habitat for various other species including fish and birds.
Dominant Species: In a grassland, elephant grass may outcompete other species, representing a dominant species due to its high biomass and coverage.
Foundational Species: Coral reefs provide structural habitat for numerous marine organisms, making them foundational in marine ecosystems.

Genetic Diversity: The variation in flower color within a single species of wildflower reflects genetic diversity which can affect survival rates in changing climates.
Species Diversity: In a tropical rainforest, the number of different tree species contributes significantly to its species diversity.
Ecosystem Diversity: A region with rainforests, deserts, and wetlands exemplifies ecosystem diversity.

Habitat Heterogeneity: A landscape with varied elevations and moisture levels tends to support more species compared to a uniform flatland.
Climate Stability: Tropical areas with minimal seasonal changes often host greater biodiversity than polar regions, where conditions fluctuate dramatically.
Disturbance Frequency: A forest experiencing occasional fires may have more diverse plant species as they adapt and coexist with fire-resistant varieties.
Historical Events: The stability of the Amazon rainforest over millions of years has allowed continuous biodiversity to flourish compared to more disturbed landscapes.

Primary Succession: Following a volcanic eruption, pioneer lichens colonize bare rock, paving the way for subsequent plant species.
Secondary Succession: After a forest fire, grasses and wildflowers often dominate the area first, followed by shrubs and eventually, trees regrowing.
Pioneer Species: Lichens and mosses are often the first organisms to establish in barren terrains, initiating soil development.
Climax Community: A mature oak-hickory forest represents a climax community that will remain stable until a significant disturbance occurs.