Topic 9.10 - Human Impacts on Biodiversity and Feedback Loops

Topic 9.10- Feedback Loops in Environmental Science

Positive Feedback Loops: These represent systems where a change results in "more, then more" of that change, amplifying the original stimulus. Tundra Permafrost Example: 1. Temperatures become warmer. 2. Permafrost begins to thaw. 3. Thawing creates standing water in anoxic (low $O_2$ ) conditions. 4. Anaerobic decomposition occurs. 5. Methane ( $CH_4$ ) is released. 6. $CH_4$ increases global warming, leading to more thawing. Decomposition Example: 1. Higher levels of $CO_2$ lead to higher temperatures. 2. Higher temperatures lead to faster rates of decomposition. 3. Faster decomposition boosts the rate at which $CO_2$ is added to the atmosphere, reinforcing the temperature increase. Atmospheric Water Vapor Example: 1. As atmospheric temperatures increase, more water evaporates. 2. Water vapor concentration in the atmosphere increases. 3. Because water vapor is a greenhouse gas ( $GHG$ ), higher concentrations lead to further increases in atmospheric and water temperatures. Arctic Albedo Example: 1. As Earth warms, arctic regions experience warming and permafrost/ice melts. 2. Standing water reflects less sunlight than ice, which results in less albedo (reflectivity). 3. More sunlight is absorbed by the water/land, further increasing arctic temperatures.
Negative Feedback Loops: These are "self-correcting" systems characterized by "more, then less," where the system responds to a change by returning toward its original state. Plant Growth Example: 1. Increased atmospheric $CO_2$ stimulates plant growth. 2. Plants require $CO_2$ for photosynthesis. 3. More plants result in the increased removal/uptake of $CO_2$ from the atmosphere. 4. The rate of $CO_2$ and temperature increase becomes smaller than it was previously. Cloud Cover Example: 1. As temperatures increase, more water evaporates, forming more clouds. 2. Clouds block incoming sunlight. 3. This reduction in solar radiation reaching the Earth reduces temperatures.

HIPPCO: The Drivers of Biodiversity Loss

Definition: HIPPCO is an acronym used to describe the main factors leading to a decrease in global biodiversity. H: Habitat fragmentation / Habitat destruction. I: Invasive species. P: Population growth (human populations). P: Pollution / Pollutants. C: Climate change. O: Over exploitation.

Habitat Fragmentation and Its Effects

Definition: Habitat fragmentation occurs when large, continuous habitats are broken into smaller, isolated patches.
Primary Causes: Urbanization and urban sprawl. Construction of infrastructure, including roads, bridges, cities, and pipelines. Building of dams. Clearcutting for lumber extraction for construction. Extraction of fossil fuels and other natural resources. Clearing land for agriculture or development.
Scaling of Effects: The adverse effects of fragmentation vary from species to species within a given ecosystem depending on their mobility and habitat requirements.
Metapopulations: A group of geographically separated populations of the same species that interact through dispersal and migration. In fragmented habitats, local populations may face extinction but can be recolonized by individuals from other patches within the metapopulation. Fragmented populations often suffer from disrupted breeding, hunting, and migration patterns. Vulnerable Species: Predators requiring large hunting territories and $k$ -Selected species are typically the most negatively affected by fragmentation.
Edge Effect: This occurs when two adjacent ecosystems meet, creating new environmental conditions different from those in the middle of individual ecosystems. Examples: Forest boundary meeting a grassland; a river meeting the ocean. Positive Impacts: Some species thrive at the edge because of increased access to food, shelter, or different nutrients. Negative Impacts: The edge can expand the range of disruptive or generalist species, reducing the core habitat for specialists.
Mitigation via Wildlife Corridors: Continuous habitats or corridors help connect isolated areas, increasing gene flow and genetic diversity. Banff National Park, Alberta, Canada: Noted for its wildlife crossings. The Netherlands: Famous for an extensive network of "ecoducts." United States: Use of underpasses and overpasses in states like $CA$ , $CO$ , and $FL$ . Christmas Island, Australia: Built crab bridges to facilitate red crab migration.

Invasive Species

Core Impacts: They outcompete native species for resources, decrease overall biodiversity, and are expensive to remove.
Case Studies: Cane Toads: Introduced to Australia, Pacific/Caribbean islands, and Florida to control agricultural pests; they were ineffective and harmful to local ecosystems. Asian Carp: Fast-growing, prolific breeders with no natural North American predators. Imported in the $1970s$ for aquaculture, they escaped into the Mississippi River. They consume vast amounts of plankton and threaten the $7 imes 10^9$ ( $7$ billion) Great Lakes fishing industry. Kudzu Vine: Invasive in the southeastern $U.S.$ (Georgia, Alabama, Mississippi); reported as far as Connecticut, Florida, Texas, North Dakota, and Oregon. Zebra Mussels: Invasive in North America and Europe. In the $U.S.$ , they spread through the Great Lakes to Lake Mead and the Hudson River. In Canada, they have spread into the Mississippi and St. Croix Rivers. Other Examples: Bamboo, Spotted Lanternflies.

Human Population Growth and Pollution

Population Growth Pressures: Rising human populations drive habitat loss (due to the need for homes) and habitat fragmentation (due to the need for food/agriculture).
Pollution and Specific Pollutants: Pollutants negatively affect the health of humans, plants, and animals. The 6 Criteria Air Pollutants: $NO_x$ , $VOCs$ , $SO_x$ , $O_3$ (Tropospheric Ozone), $PM$ (Particulate Matter), $CO$ , and Lead. Other Key Pollutants: Asbestos, Radon, Mercury, $DDT$ , Atrazine, and $CFCs$ .

Climate Change and Over Exploitation

Climate Change Factors: Terrestrial Impacts: Shifting biomes and decreased habitat ranges. If temperature and precipitation changes occur too rapidly for species to adapt or migrate, extinction follows. Aquatic Impacts: Warmer water holds less dissolved $O_2$ , causing respiratory stress or migration. Coral reef bleaching leads to massive declines in habitat and biodiversity. Sea Level Rise: Floods risk submerging coastal estuary habitats like salt marshes and mangroves.
Over Exploitation: Taking too many resources for human use, often governed by the "Tragedy of the Commons." Examples: Bluefin tuna, Sharks, Orangutans, Rhinos, Elephants, and over-harvesting of trees/plants.

Domestication and Biodiversity

Economic Management: Organisms like honeybee colonies and domestic livestock are managed for economic returns, which often reduces their genetic diversity.
Plants/Crops: Humans grow significantly fewer species of plants today. Genetic variation is reduced due to selective breeding and the use of $GMOs$ .
Livestock: Raising a small number of species with low genetic variability makes them highly vulnerable to disease and environmental shifts.

Strategies to Mitigate Biodiversity Loss

Direct Conservation: Creating protected areas and restoring lost habitats.
Structural Connectivity: Using habitat corridors to link fragmented landscapes.
Land Use Practices: Promoting sustainable land use and sustainable agriculture techniques (e.g., $IPM$ or Integrated Pest Management, permaculture).
Urban Management: Implementing urban growth boundaries. Decreasing urban sprawl by "building up, not out." Expanding urban parks, gardens, and green roofs. Preserving existing habitats within developed areas.