Wildlife Ecology - Community & Ecosystem Ecology: Energy

Energy Source from Outside System: Such as sunlight or fossil fuel.
Energy Storage: Dead wood and litter are types of energy storage in ecosystems.
Heat Sink: Represents the loss of maintenance energy as heat; can also represent wasted energy.
Production Subsystem: In ecosystems, autotrophs.
Consumption Subsystem: In ecosystems, heterotrophs.
Interaction: The interaction of two or more types of energy flows.

"Trophic" means "feeding."
The trophic (feeding) structure of communities is based on the food chain.
Food Chain: The sequence of organisms in which one organism feeds on the one preceding it.
Food Web: In most communities, several or many interconnected food chains exist at different points.

Organisms are grouped into categories known as trophic levels:
- Producers
- Consumers
- Decomposers

Producers (autotrophs, e.g., green plants): Organisms that make food from simple inorganic materials.
Food refers to complex organic compounds such as carbohydrates, fats, and proteins.
Photosynthesis: Plants use carbon dioxide, water, and minerals to produce carbohydrates and other organic materials, releasing oxygen.

Consumers: Organisms that obtain food by consuming other organisms.
Herbivores (Primary Consumers): Consume plants.
Carnivores (Secondary and Tertiary Consumers): Obtain food by eating other animals.
Heterotrophs: All organisms that must obtain at least some of their food prefabricated.
All animals are heterotrophs, including fungi and bacteria.
Larger heterotrophs break down food partially in their digestive tracts and absorb it into the blood.
The absorbed food is used as building blocks or broken down to yield energy.
Respiration: Organic compounds are combined with oxygen; stored energy is released, and carbon dioxide, water, and mineral wastes are formed.
Energy is used for repairing and constructing cells, moving, courting, fighting, and catching food and is given off as heat into the environment.
Respiration is a universal process for every organism, including green plants.

Include saprobes – scavengers and decay organisms (bacteria, actinomycetes, and fungi).
Decomposers use dead plants, animals, and excreta as their food source.
Digestion, respiration, and excretion are similar in all kinds of heterotrophs.
Decay bacteria secrete digestive enzymes into dead material outside their bodies and absorb the food molecules.

Pyramid of Numbers: More producers (plants) than primary consumers (herbivores), and more primary consumers than secondary and tertiary consumers (carnivores).
Pyramid of Biomass: Dry weight is used instead of numbers.

The starting point for energy flow is sunlight.
Of the solar radiation reaching Earth’s atmosphere:
- $30\%$ is reflected into space.
- $20\%$ is absorbed by the atmosphere.
- $50\%$ is absorbed as heat by ground, water, or vegetation.
- Far less than $1\%$ of the sunlight reaching the atmosphere is fixed in photosynthesis.

Green plants use some of the energy stored in organic compounds (photosynthesis) for their own respiration, releasing heat.
Primary consumers (herbivores) eat plants.
Energy obtained is stored in new tissue growth (and reproduction), and used for repair, locomotion, and other activities. This energy is eventually converted to heat.
Herbivores have less energy available than plants originally produced because plants used some energy in respiration and some plant parts become food for decomposers.
A good part of the plant is indigestible to most herbivores, forming the major part of the faeces of herbivores and becoming food for decomposers.
Carnivores (secondary consumers) get their energy from herbivores.
Carnivores use digested herbivore tissue for making new cells and tissue and for reproducing; the rest is respired to provide energy for activities.
Energy available to carnivores is much less than that taken in by herbivores.
Less and less food energy is available at each level.
If a herbivore needs 1 ha for food, a secondary consumer of the same size will need 10 ha, and a tertiary consumer will need 100 ha.
This is why hawks, eagles, and trout are rarer, and mice and bluegill sunfish are common.
Two people per square kilometer can live on trout, but 2000 must eat rice.

Detritus: Dead organic matter; the starting point in most ecosystems for a series of complex food chains.
In most ecosystems, the total energy flowing along detritus pathways is greater than that which travels from live plant to grazer.
Bacteria, fungi, and actinomycetes grow on dead leaves, twigs, fruits, pollen, and other organic debris.
Examples include earthworms, isopods, and slugs.
Detritus food chains are especially important in streams.
A high percentage of stream invertebrate fauna (caddis flies, mayflies, midges, stone flies, and isopods) are detritus feeders.
In streams, much of the organic matter is imported (leaves, twigs, and logs) rather than being produced by the stream’s own algae and macrophytes.

At any one time, each trophic level contains some amount of energy stored as biomass, often referred to as the standing crop.
The pyramid of biomass indicates the amount of energy present at a particular time.
Energy is deposited in the producer trophic level by photosynthesis and in a consumer trophic level by assimilation.
Energy is withdrawn from a specific trophic level by respiration and consumption by the organisms of the next higher level.