Human Interactions with the Biosphere

Population Definitions

  • Population: A group of organisms of the same species living in the same area at the same time.

  • Population Ecology: The study of population dynamics, including disease and interactions.

Factors Controlling Population Size

  • Mortality (Birth): Increases population size.

  • Mortality (Death): Decreases population size.

  • Immigration: Individuals coming into an area, increasing population size.

  • Emigration: Individuals moving out of an area, decreasing population size.

Age Structure Pyramids

  • Graphical representation of human population distribution by age and gender.

  • Males and females are represented on either side with lateral histograms charting age.

  • Developing Population (Pyramid Shape): Wide base indicates a large young population and potential for exponential growth.

  • Demographers use a bilateral histogram. That type of graph is better known as an age pyramid.

Constructing Age Pyramids

  1. Sort by gender (males and females on opposite sides).

  2. Sort by age bracket, with the youngest at the bottom.

  3. Count individuals in each age group.

Pyramid Shapes and Population Trends

  • Pyramid Shape: High birth and mortality rates, typical of developing populations.

  • Cylinder Shape: Decreasing mortality rates lead to a thickening silhouette, indicating an aging population.

  • Spinning Top Shape: Fertility rates drop below two children per woman, resulting in a shrinking base and a more pronounced aging population, seen in countries like Spain, Italy, Japan, and South Korea.

Reasons for Shift from Pyramid to Spinning Top

  1. Improved medical care increases the lifespan of elderly individuals.

  2. Women are more career-oriented, which affects their decision to delaying having children.

  3. Shift from underdeveloped to developed countries.

Population Growth Curves

  • Growth Rate: The rate at which the number of individuals in a population changes.

Exponential Growth Curve (J-Curve)

  • Occurs when resources are abundant, with no limitations.

  • Example: Two elephants introduced to a favorable environment can grow to 8,000 in a few decades.

  • Characterized by mortality exceeding mortality.

  • J curve, exponential growth. These species are abundant. There's no natural predator, no disease. Abundant amount of territory. So it just keeps growing.

Logistic Growth Curve (S-Curve)

  • More realistic model where growth slows down and eventually levels off.

  • Initial exponential growth phase transitions to a slower growth phase as mortality catches up with mortality due to limiting factors.

  • Eventually reaches a carrying capacity (K) where mortality equals mortality, and there is no overall growth.

Carrying Capacity (K)

  • The maximum number of individuals an environment can support.

  • Represented by the leveling-off point on the S-curve.

  • The region between the j curve and the s curve basically it shows the amount of limiting resources. These are selection pressure that was applied to a population.

Phases of the S-Curve

  1. Exponential Phase: mortality is more than mortality.

  2. Transition Phase: mortality is still more, slowing growth.

  3. Plateau Phase: mortality and mortality are equal, stabilizing population size at carrying capacity.

Limiting Factors

  • Factors that restrict population growth.

Biotic Factors

  • Biological factors such as population number, disease, interspecific interactions, predation, and parasitism.

Abiotic Factors

  • Non-biological factors such as hurricanes, floods, and natural disasters.

Population Oscillations

  • Fluctuations in population size due to changing environmental conditions, which affect the carrying capacity.

Earth's Carrying Capacity for Humans

  • Estimated to be around 10,000,000,000, but sustainability is uncertain.

  • Modern medicine has allowed humans to overcome many obstacles, affecting natural selection.

Factors Affecting Earth's Carrying Capacity

  • Food Production: Land degradation and potential inability to maintain current crop yields due to environmental changes.

  • Land being used to raise livestock and put it on one continent, it would take up all of Africa between eight to 9,000,000,000 acres.

  • Land used for crop production would take up an area about the size of South America.

  • Carbon Dioxide Emissions: High emissions, especially in developed countries, contribute to global warming and disrupt food production; global average is about 5 metric tons per person per year, while in America it averages closer to 17 metric tons annually.

  • Water Usage: Humans are using a significant portion of Earth's accessible renewable water supply, with much of it going to agriculture; water scarcity and cleanliness are issues in many countries.

  • If temperatures increase by 2 degrees Celsius by the end of the twenty first century. And with that increase comes more extreme weather conditions, which would inevitably disrupt food production.

Ecological Footprint

  • The amount of resources and land required to support an individual.

  • Affluent countries have larger ecological footprints compared to less developed countries.

Biomagnification

  • The process by which toxins become more concentrated with increasing trophic levels.

DDT Example

  • DDT (dichlorodiphenyltrichloroethane) was used to control the Anopheles mosquito population but affected bird eggshells.

  • Rachel Carson's book Silent Spring theorized that DDT concentrations increased through the trophic levels, affecting bird eggshells and leading to population declines.

  • DDT was banned in 1972 by the EPA, leading to the thickening of eggshells.

  • If we take a look at the picture over here, we can see that the producers, they have round about 0.04 parts per million or DDT in them. A single small fish will eat many of these producers due to which its the concentration in its body is going to increase to 0.23. A big fish is going to eat many small fish. Concentration is going to increase by 2.04. And raptors like falcons, hawks, eagles eat big fish. So they eat many of them as a result of which the concentration of their body of DDT is the highest, which is 13.8 parts per million.

Biodiversity

  • The diversity of taxonomic life in an ecosystem.

Types of Biodiversity

  1. Genetic Diversity: Variation within the gene pool of a species.

  2. Species Diversity: The number of different species in an ecosystem.

  3. Ecosystem Diversity: Variety of habitats within an ecosystem (aquatic, terrestrial, etc.).

Causes of Loss of Biodiversity

  • Environmental disasters (volcanic eruptions, earthquakes).

  • Use of pesticides and herbicides.

  • Pollution (eutrophication from fertilizer runoff).

  • Biomagnification (DDT effects).

  • Hunting and overexploitation (poaching, overfishing).

  • Spread of disease (bird flu, canine distemper).

  • Habitat destruction (deforestation).

  • Invasive species (Australian cane toad, kudzu, phragmites).

  • Overfishing. The North Atlantic cod collapse of the nineteen nineties.

Conservation of Biodiversity

Direct Values

  • Crops and food resources.

  • Natural products (timber, rubber, raisins).

Indirect Values

  • Ecosystem services (pollution regulation, soil conservation, climate regulation, oxygen production).

  • Scientific and educational value (genetic research, medicinal plants like rosy periwinkle).

  • Biological control agents (mongoose controlling snake populations).

  • Environmental indicators (lichen indicating pollution levels).

  • Recreation and ecotourism.

  • Aesthetic values for artists.

  • Intrinsic rights of flora and fauna to exist.

  • Respect for indigenous peoples' beliefs and rights.