Envi Sci Week 1

Environment and Ecology

• Environment: the habitat where organisms live, consisting of biotic (living) and abiotic (non-living) components.
• Ecology: the study of interactions between organisms and their environment.

Ecosystems and Communities

• Ecosystem: includes biological communities and abiotic components (e.g., rock, air, water, soil) along with energy and matter fluxes.
• Population: a group of similar organisms in a specific area at a given time.
• Community: an interaction of multiple populations within the same environment.

Population Dynamics

• Change is constant in nature with all components interconnected.
• Factors affecting population size include:
  • Resource availability (food, water)
  • Competition for limited resources among individuals
  • Interspecific interactions (predation, parasitism)
  • Environmental conditions (weather, natural disasters)

Population Fluctuations

• Density-dependent fluctuations: population size changes based on the density of another population (e.g., predator-prey interactions).
• Density-independent fluctuations: population size changes in response to environmental factors (e.g., climate, fire).

Carrying Capacity

• Carrying capacity (K): maximum sustainable population size where births equal deaths.
• Known as density-dependent equilibrium.

Life History Strategies

• R-selected species: focus on rapid reproduction in harsh environments; characteristics include quick development, small body size, many offspring, minimal parental care (e.g., American toad).
• K-selected species: emphasize growth and survival in stable environments; characteristics include slow development, larger size, fewer offspring, substantial parental care (e.g., bears).

Energy Flow and Photosynthesis

• Energy flow in ecosystems starts with photosynthesis, where green plants convert solar energy into chemical energy.
• Biomass represents the organic matter, measured in grams of carbon per square meter per year (gC/m²/yr).

Primary Production Metrics

• Gross Primary Production (GPP): total photosynthesis in an ecosystem.
• Net Primary Production (NPP): the balance of photosynthesis minus respiration (NPP = GPP - R).

Trophic Levels and Food Webs

• Autotrophs (primary producers): organisms that perform photosynthesis.
• Heterotrophs: consumers of other organisms (herbivores as primary consumers, carnivores as secondary consumers).
• Decomposers: organisms that break down dead organic material.
• Food webs represent interconnected food chains and trophic levels within ecosystems.

Ecosystem Productivity

• Ecosystem productivity varies by region, with tropical forests showing the highest (1000-3500 g/m²/year) and tundras the lowest (100-250 g/m²/year).
• Microscopic algae (phytoplankton) are primary producers in ocean ecosystems.

Biogeochemical Cycles

• Biogeochemical cycles involve the movement of chemical elements between living and non-living parts of the environment.
• Sources produce elements, while sinks remove them. Flux indicates movement between sources and sinks.

Carbon Cycle

• Major reservoirs of carbon: atmosphere, land (biosphere and lithosphere), oceans; fossil fuels act as a fourth reservoir.
• Atmospheric CO₂ concentration has risen from 280 ppm to over 400 ppm primarily due to fossil fuel emissions.

Nitrogen Cycle

• Nitrogen is crucial for proteins, DNA, RNA, and chlorophyll, making it essential for life.
• Despite its abundance in the atmosphere (78%), nitrogen must be converted to usable forms for organisms.
• Nitrogen fixation converts inert atmospheric nitrogen into forms that plants can absorb.
• Decomposition of dead organisms returns nitrogen to the soil, while denitrification converts nitrates back to atmospheric nitrogen.
• Human activity, specifically fertilizer use, adds nitrogen to the cycle.

Interspecific Interactions

• Various interactions in communities:
  • Predation: (+/-) one species benefits at the expense of another.
  • Parasitism: (+/-) one organism benefits, harming the other.
  • Competition: (-/-) both species are harmed by sharing limited resources.
  • Commensalism: (+/0) one species benefits while the other is unaffected.
  • Mutualism: (+/+) both species benefit from the interaction.