Ecosystems: Biogeochemical Cycles

How Ecosystems Work

• Biogeochemical cycles explain the cycling of matter in an ecosystem.
• Key cycles include biogeochemical, sulfur, carbon, nitrogen, and phosphorus.
• Success depends on understanding biogeochemical cycles, how climate affects them, and their similarities/differences.

Cycling of Matter in Ecosystems

• Biogeochemical cycles involve biological, geological, and chemical processes.
• Humans greatly influence these cycles.
• Matter cycles through ecosystems, moving from the abiotic environment to organisms and back.
• Energy flows through ecosystems, from producers to consumers to decomposers, and is released as heat.

Real Life Question

• Disruptions like deforestation or pollution to biogeochemical cycles affect ecosystems' biodiversity and functioning.

The Carbon Cycle

• Carbon is vital for organisms' molecules and the abiotic environment.
• Global movement of carbon occurs between the atmosphere, ocean, and organisms.
• This involves photosynthesis, cellular respiration, combustion, and decomposition.
• Carbon makes up 0.04% of the atmosphere.
• Needed to make proteins and carbohydrates.
• Carbon is present as CO2, HCO3, and CaCO3.
• Photosynthesis uses CO2 to produce carbohydrates.
• Fossil fuels (coal, oil, natural gas) store carbon compounds.

The Hydrologic Cycle

• Water circulates between the ocean, land, and atmosphere, renewing water supply for land organisms.
• Runoff is the movement of water from land to rivers and lakes.
• Watersheds are land areas where runoff drains.

The Nitrogen Cycle

• Nitrogen is an essential part of proteins and nucleic acids.
• The atmosphere is 78% nitrogen gas.
• Nitrogen gas must be broken down to be used in proteins and nucleic acids.
• Nitrogen cycles between the abiotic environment and organisms in five steps:
• Nitrogen fixation.
• Nitrification.
• Assimilation.
• Ammonification.
• Denitrification.
• Nitrogen fixation converts atmospheric nitrogen gas into a usable form (NH3).
• Nitrogen-fixing bacteria perform nitrogen fixation in soil and aquatic environments.
• Photochemical smog and acid deposition are nitrogen-based air pollutants.

The Sulfur Cycle

• The sulfur cycle is a bacteria-driven cycle.
• Sulfur is primarily found underground in sedimentary rocks and minerals.
• It can be found in forms such as SOX, H2SO4, and H2S.
• Sulfur gas is a minor component of the atmosphere but has substantial movement in and out.
• Sulfur is necessary for proteins.
• Animals get sulfur from plant protein.

The Phosphorus Cycle

• No atmospheric component.
• Phosphorus cycles between land and organisms.
• Phosphorus in soil is absorbed by plant roots.
• Necessary to make nucleic acids and ATP.
• Humans accelerate loss of phosphorus from the land.
• Phosphorus in fertilizers can cause eutrophication.

Ecological Niches

• An ecological niche is the sum of an organism's adaptations, resource use, and lifestyle.
• Describes an organism's place and function in an ecosystem.
• Takes into account all aspects of an organism's existence.
• Habitat: the place where an organism lives; part of its niche.
• Niches can be expressed as:
• Fundamental niche - The potential, idealized niche.
• Realized niche - The actual niche an organism occupies.

Resource Partitioning

• Resource partitioning helps species avoid or reduce niche overlap.
• Reduces competition for resources.
• Includes timing of feeding, nest sites, and location of feeding.

Interactions Among Organisms

• Organisms in an ecosystem interact and form associations.
• Three main types of interactions:
• Symbiosis.
• Predation.
• Competition.

Symbiosis

• Symbiosis involves two species living in close association.
• It is a result of coevolution where both species adapt to each other.
• Three main types of symbiosis:
• Mutualism: both organisms benefit.
• Commensalism: one benefits, the other is unaffected.
• Parasitism: one benefits at the expense of the other.
• Mutualism benefits both organisms
• Is common in Central America, where acacia ants get shelter and nutrients from acacia plants and protect the plant from predators.
• Commensalism benefits one organism without harming or helping the other.
• Ex: Epiphytes attach to the branches and trunks of larger trees.
• Parasitism benefits one organism (the parasite) and harms the host.

Predation

• Predation is where one species (predator) consumes another (prey).
• Often leads to a coevolutionary "arms race" where predators and prey evolve to better catch or escape each other.
• Examples: Cheetahs sprinting to catch prey; spiders using camouflage to ambush prey.
• Avoiding predation can involve various strategies:
• Social behavior.
• Chemical defenses.
• Camouflage.

Competition

• Competition is the interaction among organisms vying for the same resources like food or living space.
• This can manifest as:
• Intraspecific competition: competition within the same species.
• Interspecific competition: competition between different species.

Keystone Species

• Keystone species are vital for maintaining the structure and function of an ecosystem.
• They might not be the most abundant, but greatly impact the entire ecosystem.
• Can be top predators or affect the availability of essential resources.
• Ex: The gray wolf is a keystone species.

Case Study: Global Climate Change

• The biggest factor in climate change is increased atmospheric CO2.
• CO2 has increased 20% in 50 years.
• Generated by burning fossil fuels and forests.
• Stabilization wedges are approaches to reduce carbon emissions, aiming for a 1-billion-ton-per-year reduction.