C6

Human Ecology and Ecosystem Components

• Ecology: The study of the relationships between living organisms, including humans, and their physical environment.

• Human Ecology: Specifically refers to the relationships between people and their environment. In this field, the environment is perceived as an ecosystem.

• Ecosystem: Everything in a specified area, including air, soil, water, living organisms, and physical structures, as well as everything built by humans. An ecosystem can vary in size from a drop of pond water to the Amazon rainforest.

• Biological Community: The living parts of an ecosystem, which include microorganisms, plants, and animals (including humans).

• Human-Environmental Interaction: It is useful to conceptualize this as a relationship between the human social system and the rest of the ecosystem.

• Social System: Everything about people, their population, psychology, and social organization that shapes their behavior. This system is central to human ecology because society strongly influences human activities that impact ecosystems.

• Abiotic Components: All nonliving elements of an ecosystem. These include:

  • Water (fresh water or salt water).
  • Air.
  • Temperature.
  • Rocks and minerals that make up the soil.
  • Precipitation levels (rain fall).
  • Sunlight exposure.
  • Frequency of freezing and thawing.

• Biotic Components: The living organisms that live on and interact with the abiotic components.

Trophic Levels and Nutrient Cycling

• Producers: These organisms are at the base of the food web and are generally the largest group by weight or biomass. They take in energy from sunlight to transform carbon dioxide ($CO_2$) and oxygen ($O_2$) into sugars. Examples include:

  • Plants.
  • Algae.
  • Photosynthetic bacteria.
  • Producers act as an interface with abiotic components during nutrient cycles by incorporating inorganic carbon and nitrogen from the atmosphere.

• Consumers: Living organisms that obtain energy by consuming other organisms. They are subdivided by diet:

  • Herbivores: Eat producers.
  • Carnivores: Eat other animals.
  • Omnivores: Eat both producers and animals.
  • Energy Transfer: Consumers can only harvest about $10\%$ of the energy contained in what they eat, leading to less biomass at each successive stage of the food chain.

• Decomposers: The living component that breaks down waste material and dead organisms. Examples include earthworms, dung beetles, and many species of fungi and bacteria. They perform a vital recycling function:

  • Returning nutrients from dead organisms to the soil for plant uptake.
  • Harvesting the final sunlight energy initially absorbed by producers.
  • Representing the final step in many cyclical ecosystem processes.

Adaptation and Resilience

In biology, adaptation has three related meanings:

1. Dynamic Evolutionary Process: The process that fits organisms to their environment, enhancing evolutionary fitness.
2. State Reached: The specific state a population reaches during the evolutionary process.
3. Phenotypic/Adaptive Trait: A functional role in an individual organism maintained and evolved by natural selection.

• Adaptive Plasticity: Traits that develop in response to imposed environmental challenges as an organism grows, providing resilience to varying environments.

Conservation and Its Types

Conservation is the scientific study of nature aimed at protecting species, their habitats, and ecosystems from extinction.

1. Environmental Conservation: The practice of saving the environment from collapsing due to loss of species and ecosystems caused by pollution and human activity. A key focus is saving trees, which convert $CO_2$ produced by factories into $O_2$ for respiration. Preventing species extinction is critical for scientific study and to avoid disrupting food webs.

2. Animal Conservation: The practice of protecting endangered wild animal species and their habitats. Conservationists identify species in need and may keep them in captivity until safe wild habitats are available.

3. Marine Conservation: The protection of species and ecosystems in oceans and seas by reducing human activities such as fishing, whaling, and water pollution.

4. Human Conservation: Efforts to keep human communities alive, particularly those at risk of losing traditional culture.

   • Example: The Tsachila tribes in Ecuador, who once had a prolific presence but now only have $7$ remote settlements due to European and North American influence. Conservation involves living with these communities, learning traditions, and improving standards of living.

Climate Change: Definition and Causes

• Definition: A change in the statistical distribution of weather patterns when that change lasts for an extended period of time.

• Causes:

  • Biotic processes.
  • Variations in solar radiation received by Earth.
  • Plate tectonics.
  • Volcanic eruptions.
  • Human activities (often referred to as global warming).

• Scope: Shifting weather patterns threatening food production and rising sea levels increasing the risk of catastrophic flooding. Global warming may have localized benefits (fewer winter deaths in temperate climates), but overall health effects are expected to be overwhelmingly negative.

Impacts of Climate Change on Human Health

Climate change affects the social and environmental determinants of health: clean air, safe drinking water, sufficient food, and secure shelter.

• Temperature-Related Impacts: Warmer average temperatures lead to more frequent and longer heat waves. Projected increases in heat-related deaths are not expected to be offset by reductions in cold-related deaths. Adaptive responses like air conditioning are expected to mitigate some heat-related deaths.

• Extreme Weather Events: Extreme precipitation, flooding, droughts, and storms. These events affect health by:

  • Reducing availability of safe food and drinking water.
  • Damaging infrastructure (roads, bridges) and disrupting access to hospitals/pharmacies.
  • Interrupting communication, utilities, and healthcare services.
  • Causing carbon monoxide poisoning from improper portable generator use.
  • Increasing stomach and intestinal illnesses (especially after power outages).

• Air Quality Impacts: Warmer temperatures and shifting weather patterns worsen air quality.

  • Ground-Level Ozone: A harmful air pollutant in smog created more frequently in heat. It can damage lung tissue, reduce function, and inflame airways, aggravating asthma and chronic lung diseases.
  • Particulate Matter (PM): Extremely small particles (fine particles are smaller than $2.5\,\mu m$) and liquid droplets. Sources include dust, wildfires, sea spray, and fossil fuel combustion. Inhaling these can lead to lung cancer, Chronic Obstructive Pulmonary Disease (COPD), and cardiovascular disease.

• Allergens and Asthma Triggers: Climate change may lengthen the ragweed pollen season. Rising $CO_2$ and temperatures lead to earlier flowering and increased pollen levels.

  • Common Asthma Triggers: Colds, furry pets, strong emotions, exercise, cockroaches, weather changes, cold weather, mold and mildew, food allergies, strong smells, and dust.

• Vector-Borne and Water-Borne Diseases:

  • Vector-Borne: Malaria, dengue, encephalitis, hantavirus, Rift Valley fever.
  • Water-Borne: Cholera, cryptosporidioses, campylobacter, leptospirosis, and harmful algal blooms.

• Mental Health and Displacement: Increases in anxiety, despair, depression, and Post-Traumatic Stress Disorder (PTSD). Climate change also creates environmental refugees through forced migration and civil conflict.

Vulnerable Populations

While climate change poses threats globally, certain populations face increased risks:

• People in developing countries.
• Children.
• Pregnant women.
• Older adults.
• People with low incomes.
• Outdoor workers.
• People with disabilities or existing medical conditions.

Pyramid of Effects From Air Pollution

The impacts of air pollution can be visualized as a pyramid, where the severity of effects increases toward the top, while the proportion of the population affected increases toward the base:

• Severity (High to Low):
  1. Death (Thousands affected).
  2. Emergency Room (ER) visits and Hospital admissions (Tens of thousands affected).
  3. Heart attacks (Magnitude: Millions affected at various lower levels).
  4. Doctor visits, school absences, and lost work days.
  5. Respiratory symptoms and medication use.
  6. Asthma attacks.
• Monetized Benefits: Over $90\%$ of monetized benefits of pollution reduction are associated with preventing deaths at the top of the pyramid.

Questions & Discussion

1. Why do epidemics and pandemics occur?

Epidemics and pandemics occur when infectious diseases spread rapidly across populations. Factors contributing to this include human ecology interactions, where changes in the social system or environment allow agents to reach susceptible hosts more easily, or when new pathogens emerge that the human population has no immunity against.

2. Explain how the agent, host, and environmental factors interrelate in producing a disease?

The interrelation is often described via the epidemiological triad. The agent (the cause of the disease), the host (the organism harboring the disease), and the environment (external factors that allow transmission) must overlap for disease to occur. A change in the environment, such as climate change, can expand the habitat of an agent (like a mosquito) and increase its interaction with the host (humans).

3. From an analytic viewpoint, why is the cross-sectional study considered weaker than either a cohort or a case-control study?

A cross-sectional study is considered weaker because it captures data at a single point in time, making it difficult to establish a temporal relationship between exposure and outcome. In contrast, cohort studies follow subjects over time, and case-control studies look back at exposure history, providing stronger evidence for causality.