Untitled Notes

Disturbance: An event that alters the biodiversity of a community by removing organisms or changing resource availability.
Disturbances can be either positive or negative in their impact.

Ecosystem Resiliency: Some ecosystems demonstrate the ability to recover from disturbances within relatively short periods.
Positive Disturbances:
- Forest fires can lead to beneficial ecological outcomes through processes such as secondary succession.

Certain ecosystems require extended periods to recover and may never be restored to their original state.
Species extinction can occur due to habitat degradation, leading to reduced biodiversity.
Example: Water pollution resulting in mortality for aquatic species such as fish.

The balance in a salmon-forest ecosystem is represented in a Partial Food Web:   - Key Species:
    - Salmon
    - Bears
    - Berries/Plants
    - Eagles
    - Trout
    - Decomposers
Nutrient Flow:
- Carnivores (e.g., bears) feed on salmon, transferring nutrients to the forest, which are absorbed by trees. - Trees create shaded ponds vital for juvenile trout's growth, demonstrating matter and low-entropy energy flow.

Removal of decomposers leads to nutrient deficiency, hampers tree growth, and results in loss of shade for ponds.
The disturbance causes cascading effects:
- Decline in bear, trout, and eagle populations due to reduced salmon availability.

Disturbances in one part of an ecosystem can induce effects throughout the ecosystem, likened to dominoes falling.
Human-Induced Disturbances:
  - Hunting
  - Deforestation (removal of trees)
  - Unsustainable fishing practices
  - Pollution

Impact: Historically, seen as a pest and hunted excessively, leading to population decline and endangered status.
Resulting Issue:
- Disappearance of alligators correlating with plummeting game fish populations.
- Alligators predominantly prey on large fish (e.g., Gar), which increased in number without alligator predation, harming game fish.

Habitat: Sea otters inhabit kelp forests; giant kelp is crucial in producing oxygen and providing habitat.
Historical Overhunting: In the 18th century, sea otters were hunted to near extinction for their fur and perceived competition by fishermen.
Resulting Ecosystem Changes:
- Increased sea urchin populations due to the absence of sea otters led to kelp forest degradation, disrupting fish spawning habitats.

Keystone Species: Species that have a disproportionately large impact on their ecosystem.
- Example: Sea otters maintain kelp forests; without them, urchin populations explode, destroying kelp and affecting fish.
Trophic Cascade: Removing a keystone species leads to population changes across trophic levels, disrupting ecosystem balance.
- Example: Jaguars as keystone species in Central and South America, controlling prey populations, maintaining ecological balance.

Parrotfish: Cleans corals on the Great Barrier Reef, essential for coral health and ecosystem resilience.
Sharks: Highest order predator in Atlantic Ocean food webs; their decline affects populations of tuna, mackerel, and others, creating imbalance in marine ecosystems.

Through the removal of keystone species (e.g., sharks), food web balance is upset — affecting producers like phytoplankton due to increased shrimp-like creatures that overconsume them.

Commercial Practices: 95% of US commercial salmon fishing occurs off the coast of Alaska employing methods like: - Gillnets: Net openings designed to entrap fish; fatal for fish as they become gilled. - Purse Seines: Nets that encircle fish schools, preventing escape as they are collected.

Bycatch: Unintentional capture of non-target species, including:   - Other fish species
  - Sea turtles
  - Marine mammals (dolphins, whales)
Community Disruptions from Bycatch:
  - High mortality rates in returned bycatch.
  - Juvenile fish populations suffering leads to reduced reproductive capacity.
  - Endangered and keystone species included in bycatch.

Strategies:
- Use of acoustic devices to deter marine mammals from nets. - Designing nets with smaller mesh to reduce entrapment of larger species. - Incorporating weak links in gill nets to allow large animals to escape. - Providing awareness to fishermen about high-risk areas for bycatch and safe return methods.

Examples of human-induced disturbances:
  - Overhunting and overfishing
  - Deforestation
  - Unsustainable farming practices
  - Industrialization and urban development
  - Pollution (water and air)
  - Introduction of invasive species that disrupt native populations.
Impact: Human activities have globally affected every ecosystem, both directly and indirectly.

The possibility of recovery depends on the nature of the disturbance: - Temporary disturbances allow ecosystems to recover.
- Persistent disturbances (e.g., invasive species) lead to potential ecosystem collapse.
Example: Fishing with lines and hooks may be sustainable, while daily net fishing may lead to severe ecosystem damage.

Biodiversity: Increased diversity enhances an ecosystem's resilience and recovery capability.
Scenario Comparison:
- Ecosystem A, with higher biodiversity, better withstands losses (e.g., clams due to parasites) due to multiple food chains supporting top predators.

Human population has risen exponentially over the past centuries.
Carrying Capacity:
- The maximum population sustainable by available resources, determining when growth levels off. - Ongoing debate among experts about whether it nears 6 billion or 16 billion.
Limitations: Potential limiting factors include:   - Fresh water
  - Food supply
  - Diseases
Humans' capability to adapt and modify environments often allows them to exceed anticipated carrying capacities.