BIOS 3010: Ecology Lecture 12: Decomposition and Detritivory: 2. Decomposers and detritivores: 3. Resources of decomposers: Lecture summary:

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1 BIOS 3010: Ecology Lecture 12: Decomposition and Detritivory: Lecture summary: Decomposers & detritivores: Resources. Characteristics. Model of detritivory. Size of detritivores. Diversity & abundance. Dr. S. Malcolm BIOS 3010: Ecology Lecture 12: slide 1 2. Decomposers and detritivores: Decomposers are saprobes like bacteria & fungi that feed on dead or dying plant & animal tissue. Detritivores feed on the same material once it has been fragmented and processed to varying extents by both decomposers and physical events. These interactions tend to be very general. Taxonomic origin is usually unimportant. Result in release of nutrients (Fig. 11.2). Dr. S. Malcolm BIOS 3010: Ecology Lecture 12: slide 2 3. Resources of decomposers: (1) Dead bodies of animals/carrion (Fig ) Also manipulation of other interactions such as mites reducing fly competitors of beetles (Figure 11.17). (2) Feces & other excreted products (Fig ) 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 or litter, and ripe fruit separated from the parent (Fig ). Dr. S. Malcolm BIOS 3010: Ecology Lecture 12: slide 3 1

2 4. Resources of decomposers: Resistance of resources to decomposition increases in the order: sugars < starch < hemicelluloses < pectins and proteins < cellulose < lignins < suberins < cutins As shown partially in Figure 11.2 for 2 different ecosystems. Cellulose is difficult to break down. Cellulose catabolism (cellulolysis) requires cellulase enzymes which most animals don t have. Cellulases in 1 cockroach sp. & a few termite spp. So complex mechanisms have evolved as in Figure Dr. S. Malcolm BIOS 3010: Ecology Lecture 12: slide 4 5. Differences from other consumers: Decomposers/detritivores eat dead food. Predators and herbivores also eat dead food after they have caught and killed it. Primary distinction is that: Decomposers/detritivores 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. Dr. S. Malcolm BIOS 3010: Ecology Lecture 12: slide 5 6. A continuous model of detritivory: If we represent: Resource (R) renewal as F(R) or a function of the amount of resource R P as the number of predators, and a as the efficiency with which individuals find and capture their food resource Then for exploiters, such as predators, herbivores and parasites, the rate of resource renewal dr/dt is: dr /dt = F(R) - ap like the Lotka-Volterra predation model dn/dt = rn-apn Dr. S. Malcolm BIOS 3010: Ecology Lecture 12: slide 6 2

3 7. A continuous model of detritivory: For mutualists, where M is the number of mutualists and δ is a measure of mutual benefit dr/dt is: dr/dt = F(R) + δm For decomposers and detritivores that have no influence on resource renewal, dr/dt is: dr/dt = F(R) Dr. S. Malcolm BIOS 3010: Ecology Lecture 12: slide 7 8. Size classification and biomass of detritivores: Detritivores and microbivores: Tiny detritivores that feed on bacteria and fungi rather than larger particulate detritus Their food is often alive! Taxonomically diverse Can be classified by size: Microflora & fauna (<100µm) Mesoflora & fauna (100µm-2mm) Macroflora & fauna (2-20 mm) (Fig. 11.3). Dr. S. Malcolm BIOS 3010: Ecology Lecture 12: slide 8 9. Size classification and biomass of detritivores Micro-, meso-, and macro-detritivores vary among biomes with latitude (Figure 11.4). Most macrofauna in the 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 5.1 Kg soil/m 2 each year. Dr. S. Malcolm BIOS 3010: Ecology Lecture 12: slide 9 3

4 10. Diversity & abundance of detritivores: Terrestrial: 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) Larger detritivores can enhance microbial respiration and so function as a connected community (Fig. 11.8). Perhaps allantoin excreted by woodlice at high density kills microbes? Dr. S. Malcolm BIOS 3010: Ecology Lecture 12: slide Diversity & abundance of detritivores: Aquatic: Similarly in freshwater ecosystems, detritivores are diverse and separate into different guilds according to feeding methods as: shredders, collector-gatherers, grazer-scrapers, and collector-filterers (Fig. 11.5). Together this community breaks down detritus in a stream as shown in Figure Dr. S. Malcolm BIOS 3010: Ecology Lecture 12: slide 11 Figure 11.2 (3 rd ed.): Decomposition of oak leaf litter. Dr. S. Malcolm BIOS 3010: Ecology Lecture 12: slide 12 4

5 Figure 11.18: Mouse burial by Necrophorus beetles. Dr. S. Malcolm BIOS 3010: Ecology Lecture 12: slide 13 Figure (3 rd ed.): Influence of mites on Necrophorus beetle fitness at different soil depths + mites - mites Dr. S. Malcolm BIOS 3010: Ecology Lecture 12: slide 14 Figure 11.15: African dung beetles roll balls of mammalian dung for larval food resources Dr. S. Malcolm BIOS 3010: Ecology Lecture 12: slide 15 5

6 Figure 11.11: Decomposition of detritus land, water Dr. S. Malcolm BIOS 3010: Ecology Lecture 12: slide 16 Figure 11.12: Methods of detritivore digestion of cellulose Dr. S. Malcolm BIOS 3010: Ecology Lecture 12: slide 17 Figure 11.3: Sizes of terrestrial decomposers Dr. S. Malcolm BIOS 3010: Ecology Lecture 12: slide 18 6

7 Figure 11.4: Latitudinal and biome changes in decomposer communities Dr. S. Malcolm BIOS 3010: Ecology Lecture 12: slide 19 Figure 11.7: Significance of microflora in forest litter decomposition Dr. S. Malcolm BIOS 3010: Ecology Lecture 12: slide 20 Figure 11.8 (3 rd ed.): Influence of woodlice on microbial decomposition in microcosms Dr. S. Malcolm BIOS 3010: Ecology Lecture 12: slide 21 7

8 Figure 11.5: Freshwater invertebrate feeding guilds Dr. S. Malcolm BIOS 3010: Ecology Lecture 12: slide 22 Figure 11.6: Detrital energy flow in a stream (---- feces) Dr. S. Malcolm BIOS 3010: Ecology Lecture 12: slide 23 8