Ecology 2 - Energy Transfer and Nutrient Cycles

Open systems

Exchange of matter and energy with the surroundings

Closed system

Exchange of energy with the surroundings

Ecosystems

A community of living organisms (biotic factors) interacting with their non-living (abiotic) physical environment

They are open systems that are interconnected

Mesocosms

A simulation of natural biological systems that contain the abiotic and biotic features, but are RESTRICTED IN SIZE and UNDER CONTROLLED CONDITIONS

Ethics of mesocosm

Is it possible to prevent any organism from suffering as a result of it being placed in the mesocosm? → If so, keep all abiotic factors within the tolerance limits of the organisms

Considerations of mesocosms

• Opaque or transparent sides → glass or plastic jars

• Which organisms must be included to make up a sustainable community?

• Once sealed → no more oxygen can enter, will oxygen supply be sufficient for all the organisms?

Purpose of mesocosms

• Investigate the stability of an ecosystem

• Study ecosystem response to changes in specific factors (e.g. light and nutrient levels)

  • Can control all the factors other than the variable studied.

Food chains

Sequence of organisms, each of which feeds on the previous one

Food webs

Shows multiple food chains and is more realistic

→ Many consumers feed on more than one species and are fed upon by more than one species

Apex predator

A top-tier animal at the very peak of a food chain that has no natural predators of its own in adulthood

Removal of an organism in a food web

• May not be catastrophic to ecosystem → BUT will put new pressures on surviving populations

• Reduces genetic diversity & species richness within the food web

• Fewer alternative food sources

Resilience

The ability of an ecosystem to recover from a disturbance. High biodiversity = high resilience

Removal of producer in food web

Bottom-up effect → If a producer or primary consumer is removed, energy flow to all higher trophic levels is reduced, causing declines higher up the web

Removal of apex predator in food web

Removes top-down control → predators of lower trophic levels increase → overconsumption of lower trophic levels → competition & habitat destruction (less plants less photosynthesis)

Example of key stone species: Pisaster Sea Star

1. Removed starfish → immediate competition for space/resources

2. Species competed against each other to be the dominant species

3. Dominant species reach carrying capacity and die out as resources decrease

4. Species diversity reduced drastically

Example of key stone species: Otters

Habitat: Kelp forests

Top predators that feed on urchins (primary consumer) that eats kelp

No otters = predation pressure decreases on urchins, urchin population increases exponentially

Higher urchin population overgrazes kelp and destroys habitat → lower biodiversity

No kelp = less habitat for fish & food

What is the primary source of energy on Earth?

Light energy

Photosynthesis

Producers converting light energy into chemical energy for most ecosystems on Earth

Chemical energy

Energy stored within bonds of organic compounds (glucose, lipids, and amino acids)and passed from one to another when consumed

Chemical reactions

Use iron, methane, sulfides or other inorganic compounds as substrates to produce organic compounds via chemosynthesis

Chemosynthesis

Where microbes convert carbon molecules → organic matter using energy from inorganic chemical reactions instead of sunlight

Fuels life in dark environments like deep-sea hydrothermal vents

Trophic

Nutrition, food

Autotrophs

Synthesis of organic compounds from inorganic compounds using external energy sources

Photoautrophs

Using the sun’s energy to fix carbon

Carbon fixation

Process by which inorganic carbon (carbon dioxide, CO₂) is converted into organic carbon compounds (such as glucose) during photosynthesis

Chemoautotrophs

Using oxidation of chemicals to produce energy

Oxidation

Loss of electrons

Reduction

Gain of electrons

Heterotrophs

Consumes other organisms to obtain carbon compounds, digested either externally or internally into monomers, and then assimilated into new molecules

Assimilation

Process by which absorbed nutrients are incorporated into the cells and tissues of an organism, becoming part of its biomass

Saprotroph (Hetero)

Secrete enzymes that digest dead organic matter to release carbon and nitrogen into the environment to be absorbed

e.g fungi, some bacteria, decomposers

Decomposition

Breakdown of dead organic matter (detritus) into simpler inorganic substances by saprotrophs (decomposers)

What do decomposers recycle?

• Detritus/feces

• Dead organisms

• Castoffs from organisms (leaves, snake skin etc.)

Internal digestion (heterotrophs)

Breakdown of food inside the body of an organism using enzymes

Holozoic nutrition

Consuming whole pieces of food to digest internally, occurs over 5 stages

Ingestion → digestion → absorption → assimilation → egestion

Ingestion

Bringing food into the gut

Digestion

Breaking large food molecules into smaller molecules

Absorption

Transport of digested food across the plasma membrane of epidermis cells and into the blood/tissues

Assimilation

Using digested foods to synthesise proteins and other macromolecules to make them a part of the body’s tissues

Egestion

Emptying undigested material from the end of the gut

Holozoic → multicellular

Consumes food into gut via swallowing

Mixes food with enzymes from digestive glands

Monomers absorbed into the blood via the small intestine wall

Holozoic → unicellular

Take food via endocytosis

Digest inside phagocytic vacoules

Absorb products of digestion from vacoules into cytoplasm

Mixotrophs

Can combine autotrophic and heterotrophic modes of nutrition to meet energy needs

Faculative mixtrophs

Survives using either autotrophy or heterotrophy. It does not require both to survive - can swap interchangeably depending on habitat

Obligate mixotrophs

An organism that must use BOTH autotrophy and heterotrophy to survive. It cannot rely on just one mode

Prokaryote domains

1. Archaea

2. Eubacteria

Archaea

Prokaryote → no nucleus

Archaea → phototrophic energy source

Absorption of light energy by pigments, but pigments other than chlorophyll are used

Archaea → chemotrophic energy source

Oxidation of inorganic chemicals

Archaea → heterotrophic energy source

Oxidation of carbon compounds obtained from other organisms

Archaea energy source types

1. Phototrophic

2. Chemotrophic

3. Heterotrophic