BSCI161 notes

Originally, wolves were widespread across the United States prior to European colonization.
Current distribution shows significantly diminished wolf populations, typically existing in small patches.

Deer populations are perceived as cute but can have detrimental ecological effects:
- Overabundance of deer leads to significant browsing pressure on flora.
- Understory vegetation predominantly consists of spiny plants that deer do not eat.
Advocacy for reintroduction of top predators like cougars and wolves to manage deer populations for healthier ecosystems.
- Reintroduction could restore natural ecological conditions.

Reintroduction of wolves creates conflict in regions where livestock is raised:
- Farmers concerned about cattle and sheep predation.
- Efforts by conservation organizations to offset losses to livestock.
- Acknowledgment that the situation is complex and multi-faceted.

Historical eradication of wolves in the 1920s elevated elk populations because:
- Park personnel controlled elk numbers which were previously managed by wolves.
- Elk population soared once human control ceased in the 1960s.
Following wolf reintroduction in the mid-1990s, elk populations began to decrease.

Definition: A trophic cascade refers to the chain reaction that follows the removal or addition of top predators and its subsequent impact on lower trophic levels.
Example: Wolves control elk populations, facilitating aspen tree regeneration:
- Pre-1920s, wolves present resulted in healthy aspen growth.
- Post wolf elimination, elk overgrazed aspen, leading to population declines.
- After reintroduction of wolves, aspen started to recover.
Cascading effects extend to broader ecological systems:
- Overgrazing impacts lead to changes in soil erosion and river flow.
- Maintains biodiversity, supports various plant species, and preserves ecological balance.

Misconceptions about ecological simplicity:
- An arrogant human-centered approach has often failed to account for the complexity within ecosystems.
Key Takeaway: Trophic levels are interconnected, and changes at one level can trigger a series of complex reactions throughout the ecosystem.

Definition of Keystone Species: Species that have a disproportionately large effect on their environment relative to their abundance.
- Removing keystone species can lead to dramatic shifts in ecosystem structure and function.
Ecosystem Engineers: Specific category of keystone species that profoundly modify their environment:
- Beavers create wetlands through damming, affecting water flow and habitats.
- Termites promote nutrient cycling and soil aeration that alters habitats.

Research indicates wolves affect beaver foraging behavior:
- Beavers travel farther from water to forage at risk of predation.
- Longer trails correlate with higher mortality due to wolf encounters.
Natural selection favors conservative foraging behavior in beavers where wolves are present.
- Results in selective pressure that affects forest composition around their habitats.

Disturbances: Events that alter conditions in ecological communities:
- Examples include forest fires and floods, which can both destroy and create opportunities for different species.
Frequency and intensity of disturbances can shape community composition:
- Intense and frequent disturbances may reduce species richness due to habitat destruction.
- Low disturbances can lead to competitive exclusion, limiting diversity.
Intermediate Disturbance Hypothesis: Suggests moderate levels of disturbance can promote species richness by allowing less competitive species to survive alongside dominant ones.

Variation in species diversity based on disturbance levels:
- Low disturbance may favor few dominant species while high disturbance excludes many species.
- Intermediate disturbance shows highest diversity as it prevents dominance and allows for numerical stability of varied species.

Ecological succession: Change in species composition over time within a community:
- Predictable patterns in response to disturbances like logging or volcanic eruptions.
- Example: Post-fire forests in Maryland will show a sequential arrival of different plant species over time.

Ecosystem Definition: The sum of all living organisms and their physical environment.
Components of Ecosystems:
- Abiotic Environment: Non-living factors including temperature, sunlight, and water.
- Primary Producers: Organisms (like plants) that capture energy.
- Consumers: Organisms that obtain energy by eating primary producers.
- Decomposers: Breakdown dead organisms and recycle nutrients.

Energy Flow: Energy moves in one direction through ecosystems:
- Loss of energy at each trophic level approximately 90%.
- GPP (Gross Primary Production) and NPP (Net Primary Production) reflect energy capture rates supporting all ecosystems.
- Energy pyramids illustrate the energy loss increasing up trophic levels.

Geographic trends in NPP:
- High NPP in tropical rainforests vs. low NPP in arid regions or polar ecosystems.
- NPP influenced primarily by temperature, precipitation, and nutrient availability.
- Marine ecosystems also reflect nutrient dynamics affected by upwelling currents and river effluents.

Community ecology emphasizes species interactions and influences of disturbances:
- Understanding species diversity dynamics has important conservation implications, especially for managing top predators and recognizing the roles of physical disturbances.
- The complex interplay of factors influencing ecosystems illustrates the need for integrated ecological management strategies.