BIOS 6150: Ecology

BIOS 6150: Ecology

Dr. Stephen Malcolm, Department of Biological Sciences

•   Week 9: Decomposers,

Detritivores & Mutualists.

•   Lecture summary:

•   Decomposition &

detritivory:

•   Examples & resources.

•   Comparisons.

•   Model of detritivory.

•   Mutualism:

•   Non-symbiotic.

•   Symbiotic.

Slide - 1 BIOS 6150: Ecology - Dr. S. Malcolm. Week 9: Decomposers, detritivores & mutualists

2. Decomposers and detritivores:

•   Decomposers are saprobes like bacteria and

fungi that feed on dead or dying plant and

animal tissues.

•   Detritivores feed on the same material once

it has been fragmented and processed to

varying extents by both these

decomposers and physical events.

•   Interactions tend to be very general.

•   Taxonomic origin usually unimportant.

•   Result in release of nutrients (Fig. 11.2).

BIOS 6150: Ecology - Dr. S. Malcolm. Week 9: Decomposers, detritivores & mutualists Slide - 2

3. Resources include:

•   1. Dead bodies of animals:

•   carrion

(Fig. 11.18)

•   2. Feces & other excreted products

(Fig. 11.15)

•   Australia was nearly covered with sheep/cow feces because of a lack of dung beetles!

•   3. Dead plant material:

•   Trees, roots, stems, leaves as standing material

•   Litter, and ripe fruit separated from the parent

•   Fig. 11.11.


4. Resource decomposition rates:

•   Resistance of resources to decomposition

increases in the order:

•   sugars < starch < hemicelluloses < pectins and proteins < cellulose < lignins < suberins < cutins

•   Shown partially in Fig.11.2

for 2 different ecosystems.

•   Cellulose is difficult to break down:

•   Cellulose catabolism (cellulolysis) requires cellulase

enzymes which most animals don’t have:

•   1 cockroach & a few termites.

•   Complex mechanisms have evolved as in Fig. 11.12.


5. Differences from other consumers:

•   Although predators and herbivores also eat

dead food after they have caught and

killed it, the primary distinction between

these consumers and decomposers/

detritivores is that the latter do not affect

the rate at which their resources are

produced, but of course predators and

herbivores do.

•   In addition, while mutualists may increase

resource availability, decomposers and

detritivores do not have an influence.


6. A continuous model of detritivory:

•   Represent resource ( R ) renewal as F(R).

•   P as the number of predators.

•

•   a as the efficiency with which individuals find and capture

their food resource.

  For exploiters , such as predators, herbivores and parasites , the rate of resource renewal dR/dt is: dR/dt = F(R) - aP

•   for mutualists , where M is the number of mutualists and

is a measure of mutual benefit dR/dt is:

δ dR/dt = F(R) + δ M

•   for decomposers and detritivores that have no influence

on resource renewal, dR/dt is: dR/dt = F(R)


7. Size classification and biomass of

detritivores:

•   Detritivores and microbivores (tiny

detritivores that feed on bacteria and

fungi rather than larger particulate

detritus - but their food is often alive!).

•   Taxonomically diverse and can be classified

by size from:

•   microfauna (<100 µ m) through,

•   mesofauna (100 µ m-2mm) to,

•   macrofauna (2-20 mm) (Fig. 11.3).


8. Distributions of detritivore size

classes:

•   The relative distribution of micro- meso- and

macro-detritivores among biomes related to

temperature, rainfall and latitude is shown in

Fig 11.4

:

•   Most macrofauna in tropics.

•   Most microfauna in cold regions.

•   Mesofauna dominant in temperate zones.

•   Darwin (1888) estimated that earthworms near his

house formed new soil layers at the rate of 18

cm/30 years and bring up 5.1Kg soil/m 2 .


9. Diversity & abundance of detritivores:

•   In 1m 2 of temperate woodland soil there could be:

•   10 million nematodes and protozoans.

•   100,000 springtails (Collembola) and mites

(Acari).

•   50,000 other invertebrates.

•   In woodlands, microbial decomposition is

highest (Fig. 11.7), but larger detritivores can

enhance microbial respiration and so the

different species function as a connected

community (Fig. 11.8).


10. Diversity & abundance of detritivores:

•   In freshwater ecosystems, detritivores are

also diverse.

•   Different “guilds” according to feeding

methods:

•   “shredders”, “collecto-gatherers”, “grazer-

scrapers”, and “collecto-filterers” (Fig. 11.5).

•   Together this community breaks down detritus in

a stream (Fig. 11.6).


11. Mutualism:

•   Mutualism is an interaction in which both

partners benefit:

•   “ … individuals in a population of each

mutualist species grow, survive and

reproduce at higher rates when in presence

of individuals of the other species”

•   Note: it is not a “cosy” relationship - each

species acts completely selfishly.


12. Mutualism and symbiosis:

•   Symbiosis just means "living together" in

close association (excluding parasitism).

•   Mutualism is a special kind of symbiosis,

but mutualists don’t have to be symbionts

to benefit each other.

•   So mutualisms can be either symbiotic or non-symbiotic.


13. Abundance of mutualists:

•   Most of the world's biomass is made of

mutualists:

•   Most plants, coral reefs, pollinators.

•   Nonsymbiotic mutualisms are common:

•   E.g.

cleaner fish, ants tending aphids, or pollinator-flower interactions.

•   Symbiotic mutualisms also common:

•   Include fungus-alga associations in lichens

(Fig. 13.21), fungus-plant associations in mycorrhizae, or animal-alga associations such as the flatworm Convoluta roscoffensis .


14. Nonsymbiotic

mutualisms:

•   Bull's horn acacia and

Pseudomyrmex ants:

•   Figs. 13.2 & 13.3 (4 th )


15. Nonsymbiotic mutualisms:

•   shrimps and gobiid fish

•   Fig. 13.3 (3 rd )

•   clown fish & anemones

•   cleaner fish & customers

•   honey guide and ratel


16. Nonsymbiotic

mutualisms:

•   Defense mutualisms:

•   E.g.

Müllerian mimicry in heliconiid butterflies:

•   Eltringham (1916), from cover of

Futuyma & Slatkin

(1983) Coevolution .

•   Group defense:

•   E.g.

musk oxen or sawflies.


17. Agricultural/domestic mutualists:

•   Are domestic crops and domestic animals

examples of mutualisms with man?

•   Is your dog or cat a mutualist?

•   If there are many more of a species than

there would have been without the

association it must be a mutualism!

•   “Farming” also occurs in termites and ants

where they “tend” aphids and butterfly

larvae and fungus gardens (Fig. 13.5).


18. Fruit dispersal and

pollination:

•   Fruit dispersal is mostly a generalist

phenomenon Fig. 13.7.

•   Pollination:

•   Charles Darwin was fascinated by pollination and he

described the specialized floral structure of the

Madagascar star orchid in 1859 with nectar tubes

approx. 30 cm long.

•   He suggested that a pollinator must exist with an

appropriately long proboscis and 40 years later a

hawkmoth with a 25cm proboscis was found:

•   see Fig. 8.5 Howe & Westley 1988 for floral diversity in relation to pollinators & Fig. 7.7 for fig wasp mutualism.


19. Symbiotic mutualisms:

•

 

Degrees of symbiotic association.

•   Fig. 13.10.

•

 

Such a range of association

dependence implies that closer

associations might benefit the

interactants:

•   Greater stability for the symbiont or the

opportunity to control environmental

conditions through the association.


20. Gut mutualists:

•   Gut inhabitants in plant-feeding vertebrates and

invertebrates:

•   Problem is coping with cellulose - a very hard to digest polysaccharide.

•   Many animals have solved the problem by hosting

bacterial microcosms in their guts.

•   Ruminants (deer, cattle and antelope) have a 4chambered stomach of which the rumen harbors a complete ecological community of protozoa and bacteria that compete, predate and cooperate through mutualisms, all driven by cellulose.


21. Termite and aphid mutualists:

•

 

Termites are “insect deer” with their

own microflora that digest cellulose:

•   Figs 13.11 & 13.14

of termite gut flora.

•

 

Aphids also have tightly associated

symbiotic mutualists:

•   Fig. 13.12.


22. Mycorrhizae:

•   Sheathing ectomycorrhizae and vesicular arbuscular

(VA) endomycorrhizae:

•   Found in majority of plant species (Figs 13.15

& 13.17).

•   Clearly benefit plants (Fig. 13.18) by providing P, N & Ca.

•   Ectomycorrhizae:

•   Occur as a sheath most often on roots of trees.

•   Can be cultured in isolation from their hosts

•   Require soluble carbohydrates as carbon resource from

host (not cellulose like free-living fungi).

•   VA endomycorrhizae:

•   Extremely widespread and penetrate host cells.

•   Makes them very difficult to culture.


23. Nitrogen fixation:

•   Bacteria associated with roots of some

plants can fix atmospheric nitrogen and

make it available to the plant:

•   Fig. 13.19.

•   Benefits plant and influences outcome of

other ecological processes:

•   Fig. 13.21.


24. Postscript on mutualisms:

•   Ultimate symbiotic mutualism may be

evolution of the eukaryotic cell.

•   “tit-for-tat”

•   Axelrod & Hamilton demonstrated

theoretically the increased stability

generated from cooperation.

•   Sex may have evolved through parasitism

that lead to cooperation and mutualism

because of mutual benefit.


Figure 11.2 (3 rd ). Release of resources

during decomposition of oak leaves.


Figure 11.18 (4 th ). Mouse burial by

Necrophorus beetles.


Figure 11.15 (4

th

). African dung beetle.


Figure 11.11 (4 th ). Detritus decomposition rates.


Figure 11.12 (4 th ). Mechanisms of

cellulose digestion.


Figure 11.3 (4 th ). Sizes

of decomposers.


Figure 11.4 (4 th ). Faunal variation of

decomposers among biomes.


Figure 11.5 (4 th ). Freshwater

invertebrate feeding guilds.


Figure 11.6 (4 th ). Energy flow in a stream.


Figure 11.7 (4 th ). Forest litter decomposition.


Figure 11.8 (3 rd ). Influence of isopods

on microbial breakdown of leaf litter.


Figure 13.21 (3

rd

). Lichen structure.


Figure 13.5 (3 rd ). Feeding by Atta ants

at their fungus garden.


Figure 13.7

(3

rd

).

•   Diet breadth of fruit feeders in Malaysia.


Figure 8.5 (Howe & Westley, 1988).

Floral diversity and pollinators.


Figure 7.7 (Howe & Westley, 1988).

Fig wasp mutualism.


Figure 13.10

(3 rd ).

•   Degrees of symbiotic association.


Figs 13.11 (4 th ) &13.14 (3 rd ). Symbiotic

mutualists in termite intestines.

BIOS 6150: Ecology - Dr. S. Malcolm. Week 9: Decomposers, detritivores & mutualists

E – endospore-forming

bacteria

S – spirochaetes

Others are anaerobic,

flagellate protozoa

Figure 13.12 (4 th ). Congruent phylogenies of

aphids and their bacterial endosymbionts.


Figure 13.15 (4

th

). Sheathing

ectomycorrhiza of pine roots.


Figure 13.17 (3 rd ). Vesicular

arbuscular mycorrhiza.


Figure 13.18 (3 rd ). Effect of mycorrhizae on

phosphate concentration in leek roots.


Figure 13.19 (4 th ). Rhizobial bacteria in

root nodules of legume roots.


Figure 13.21 (4 th ). Influence of rhizobia on

plant performance and competition.


BIOS 6150: Ecology •

2. Decomposers and detritivores:

3. Resources include:

4. Resource decomposition rates:

5. Differences from other consumers:

6. A continuous model of detritivory:

7. Size classification and biomass of

detritivores:

8. Distributions of detritivore size

classes:

11. Mutualism:

12. Mutualism and symbiosis:

13. Abundance of mutualists:

14. Nonsymbiotic

mutualisms:

15. Nonsymbiotic mutualisms:

16. Nonsymbiotic

mutualisms:

17. Agricultural/domestic mutualists:

19. Symbiotic mutualisms:

•

Degrees of symbiotic association.

•

Such a range of association

dependence implies that closer

associations might benefit the

interactants:

20. Gut mutualists:

21. Termite and aphid mutualists:

•

Termites are “insect deer” with their

own microflora that digest cellulose:

•

Aphids also have tightly associated

symbiotic mutualists:

22. Mycorrhizae:

23. Nitrogen fixation:

24. Postscript on mutualisms:

Figure 11.15 (4

). African dung beetle.

Figure 13.21 (3

). Lichen structure.

Figure 13.7

(3

).

Figure 13.15 (4

). Sheathing

ectomycorrhiza of pine roots.

Related documents

Add this document to collection(s)

Add this document to saved

Suggest us how to improve StudyLib

BIOS 6150: Ecology •  