Decomposers and Detritivores

Question 1

What is the main distinction between decomposers and detritivores and the herbivores, carnivores and parasites? How are decomposers and detritivores donor-controlled?

Answer 1

• Herbivores, carnivores, and parasites all directly affect the rate at which their resources are produced
• Decomposers and detritivores don’t directly control the rate at which their resources are made available or regenerate, they are dependent on the rate at which some other force releases the resource on which they live, they are donor-controlled
  o Ex. the release of nutrients from decomposing litter may ultimately affect the rate at which trees produce more litter

Question 2

What role do decomposers play in nutrient recycling and what is meant by the “mineralization of chemical nutrients”?

Answer 2

• It’s in nutrient recycling that decomposers and detritivores play their most fundamental role
• Decomposition involves the release of energy and the mineralization of chemical nutrients, the conversion of complex, organic elements into their simpler, inorganic constituents that can be used by plants

Question 3

What are the principal decomposers?

Answer 3

• Bacteria and fungi, they are found everywhere and are usually present in dead material

Question 4

Describe the process of degradative succession.

Answer 4

• A number of different microorganisms are required to completely remove a source of dead organic material from the environment. Each organism specializes in processing different components of that resource.
  o Pattern of succession, one species replaces another over time as the resource is degraded

Question 5

Describe the first organisms to exploit a source of dead organic matter.

Answer 5

• They tended to use soluble materials, mainly sugars and amino acids that are freely diffusible. Thought of as opportunist, r-selected species among the decomposers
• Molds that grow on stale bread
• Lactobacilli that turn green fodder into silage for feeding livestock and cabbage into sauerkraut

Question 6

What types of decomposer organisms are favored under conditions of low pH?

Answer 6

• Lowering the pH favors fungal activity as opposed to bacterial activity

Question 7

What kinds of organic materials are particularly difficult for decomposers to break down?

Answer 7

• Cellulose, lignin, chitin and keratin

Question 8

What do detritivors feed on?

Answer 8

• Detritus (dead organic matter) and the microflora (bacteria and fungi) growing on the detritus

Question 9

Give examples of each of the following types of terrestrial detritivores: micorfauna, mesofauna, macrofauna, and megafauna.

Answer 9

• Microfauna—protozoans, microscopic nematodes and rotifers
• Mesofauna—littermites and springtails
• Macrofauna—larger nematodes (easily seen)
• Megafauna—woodlice, millipedes, snails, slugs, and earthworms

Question 10

What role do earthworms play in the process of decomposition?

Answer 10

• Bury litter, mix it with the soil, and expose it to other decomposers and detritoveres
• Create burrows to increase soil aeration and drainage and deposit feces rich in organic matter

Question 11

The relative importance of the microfauna is greatest in the soils of what biomes?

Answer 11

• Microfauna dominate the soils of boreal forests and tundra

Question 12

The relative importance of the mesofauna is greatest in the soils of what biomes?

Answer 12

• Mesofauna are the most important in the deep organic soils of temperate forests

Question 13

The relative importance of the macrofauna is greatest in the soils of what biomes?

Answer 13

• Macrofauna are most important in tropical forests and grasslands

Question 14

How are aquatic detritivores classified?

Answer 14

• Aquatic detritivores are classified according to their feeding mode

Question 15

Describe the feeding styles of each of the following: shredders, collector-gathers, collector-filters, grazer-scrapers.

Answer 15

• Shredders—feed on coarse particulate organic matter
• Collector-gathers—obtain dead organic particles from the debris and sediments of the beads of streams
• Collector-filters—sift small particles from the flowing water column
• Grazer-scrapers—consume the organic matter attached to rocks and stones

Question 16

How does the decomposition of dead material depend on the interaction between decomposers and detritivores?

Answer 16

• The decomposition of dead material results from the interaction between decomposers and detritivores
  o Ex. the shredding action of detritivores produces smaller particles with larger surface area thus increased opportunities for microbial growth
  o Fragmentation by detritivores plays a key role in terrestrial situations because of the tough cell walls of vascular plant detritus
  o The activity of both fungi and bacteria are enhanced by the addition of mineral nutrient in feces and urine produced by the detritivores

Question 17

How do the dung of carnivores and herbivores differ in terms of food quality and types of organisms that exploit these resources?

Answer 17

• Dung of carnivores is poor quality, assimilate food with high efficiency, 80% digested, less produced which isn’t enough to support a specialist detritivore fauna
  o Most of its decomposition falls on bacteria and fungi
• Herbivore dung abundant in organic matter, thickly spread in environment supporting own characteristic fauna
  o Dung beetles of the tropics best known consumers
  o Temperate regions: other invertebrates (earthworms), bacteria, fungi consume dung

Question 18

How did the Australians solve their problem with accumulating cow dung?

Answer 18

• Importing species of African dung beetles as dung eaters

- Also reduced fly population

Question 19

What types of components of animal corpses are most resistant to attack by decomposers?

Answer 19

• Bone, hair, feathers