Ecology and Ecosystems Overview

Ecology

• Study of organism-environment relationships, a systematic and quantitative field.

Environmental Factors

• Abiotic factors: Influence organisms (temperature, moisture, nutrients, radiation, wind, water currents, fire, toxins).
• Biotic factors: Influence organisms through interactions like competition, herbivory, predation, parasitism, disease, mutualism.

Ecosystems

• Fundamental unit in ecology.
• Include abiotic and biotic components.
• Range from large (biosphere) to small (pitcher plant).
• Described by productivity, nutrient changes (e.g., nitrogen fixation), energy flow, and water flow.

Mangroves

• Brackish water ecosystem of mangrove trees.
• Adapted to intertidal zones (mixing of salt and fresh water).
• Salt tolerance: Excrete salt through leaves, utilize pneumatophores (lung roots) for oxygen in high tides, filter water through roots absorbing nutrients and eliminating unwanted elements.
• Seed dispersal: Carried by high tides.

Limiting Factors

• Often, mineral nutrients limit ecosystem productivity.
• Limiting factor: resource with lowest availability relative to need.
• Phosphorus often limits lake productivity, excess can lead to eutrophication.
• Growth depends on the scarcest resource.

Niche

• All environmental factors restricting a species' distribution, growth, reproduction.
• Physical space occupied by an organism or species.
• Fundamental niche: Complete range of conditions for a species to survive without competition.
• Realized niche: Observed resource use in nature, affected by environmental restrictions.

Stressors

• Chronic stressors: Long-term influence (e.g., water nutrient levels).
• Disturbance stressors: Powerful, short-lived events (e.g., storms, fire).
• Natural stressors: Present for long time periods.
• Anthropogenic stressors: Human-created.
• Types: Climatic (temperature, radiation, wind, moisture), chemical (toxicity), wildfire, physical (volcanic eruption), biological (inter-organism interaction).
• Effects: Decreased productivity, increased mortality, reproductive failure.
• Species response: Sensitive species replaced by tolerant ones; loss of top predators and large-bodied species; reduced species diversity.

Ecological Energetics

• Ecosystems are open systems needing continuous energy input.
• Primary source: Solar radiation.
• Amount & transmission: Varies with latitude.
• Photosynthesis: Uses visible light, autotrophs fix energy.
• Energy flow: Organisms use fixed solar energy for processes, release as heat.
• This is how most ecosystems operate using solar energy utilized by autotrophs. Stored energy can be stored for extended periods (peat, fossil fuels).

Thermodynamics

• First Law: Energy transformation, not creation or destruction. Input = stored + output.
• Second Law: Natural processes only increase universe's entropy. Energy for order requires energy transformations are never fully efficient.
• Life: Needs continual energy input, primarily solar.

Greenhouse Gases

• Natural greenhouse gases (CO2, water, methane) absorb infrared radiation, re-radiating it.
• Thermal blanket effect: Warms Earth's average temperature (from -18°C to +15°C).
• Human activities (fossil fuel combustion, deforestation, agriculture) increase concentrations of these gases.

Ecological Productivity

• Rate at which energy is fixed (autotrophs) and biomass accumulates.
• Measured in dry weight per area (t/ha or tons/ha), per unit time (e.g. t/ha/year).
• Gross Primary Production (GPP): Total solar energy fixed.
• Respiration (R): Energy autotrophs use for metabolism.
• Net Primary Production (NPP): GPP minus respiration (NPP = GPP - R).
• Low NPP in open oceans (low nutrient availability); High NPP in reefs and estuaries.

Biomagnification

• Humans introduce unnatural substances (organochlorides, DDT, mercury).
• Bioaccumulation in food chains, dramatic effects on top predators, e.g., DDT affected hawks and eagles.

Cycles

• Carbon cycle: Fixation through photosynthesis, release through decomposition and respiration. Storage in biomass, eventually fossil fuels.
• Methane production: By bacteria, fossil fuel combustion, and autotrophs.
• Nitrogen cycle: Often a growth limitation. Nitrogen fixation converts N2 (atmospheric nitrogen) to usable forms. Natural and industrial fixation. Rhizobium and Bradyrhizobium bacteria in root nodules.
• Phosphorus cycle: Essential for cells and biomolecules. Limited in lakes, primarily in sediments. One-way transport from land to oceans, with biovectors (birds, fish).
• Sulfur cycle: Important for proteins and other chemicals. Volcanic emissions, bacterial production, human impact through fossil fuel combustion and ore smelting.

Population Ecology

• Study of population dynamics and environment interactions. Populations can increase or decrease in short term and long term.
• Closed population: Nt+1 = Nt + (B-D).
• Open population: Nt+1 = Nt + (Bt - Dt) + (It - Et).

Population Growth

• Exponential growth: Resources eventually limit growth with increased competition.
• Logistic growth: Carrying capacity (K) is the maximum sustainable population size in an environment where N (population size) = K in equilibrium. When N < K populations grow, and when N > K populations shrink down until N = K.