Chapter 9 Mutualism

1. Chapter 9 Mutualism 鄭先祐 生態主張者 Ayo Japalura@hotmail.com

2. RoadMap • Mutualism: an association between two organisms that benefits both • Seed dispersal mutualism: disperser acquires a meal and the plant gets its seed dispersed • Through mutualism, species are better able together to secure resources or better able to defend themselves • Mutualism is difficult to model; models tend to result in runaway densities Chap.9 Mutualism

3. RoadMap • Mutualism between two species can affect the entire community • Commensalism is an association between two species that benefits only one, with the other species unaffected Chap.9 Mutualism

4. 9.1 Plant-Pollinator Mutualism • Most frequent type of mutualism (Figure 9.1) • 45% of all studies of mutualism • Coevolved systems • Selective pressures for plants to develop intimate relationship with pollinators (Figure 9.2) • More than 900 species of Ficus exist and virtually all must be pollinated by its own species of agaonid wasp • Yucca plants and yucca moths - highly coevolved • The distribution of each species is controlled by the availability of the other species • Ex. Yucca flower abortion if too many eggs are laid Chap.9 Mutualism

5. 0.5 0.4 0.3 Proportion of mutualism articles 0.2 0.1 0 Grazing Nutritional Other Seed dispersal Ant-plant protection Ant-insect protection Mycorrhizal Pollination Fig. 9.1 Frequency of articles on different forms of mutualism published in 675 papers. Chap.9 Mutualism

6. Fig. 9.2 Blastophaga psenes, a tiny fig wasp, which crawl inside the captifig in California to lay her eggs. Chap.9 Mutualism

7. Cheating in pollination • In the Bogs of Maine • Grass-pink orchid produces no nectar, but mimics the nectar-producing rose pogonia • Some Bombus species cheat by biting through the base of the flowers, taking the nectar without entering the plant nor assisting with pollination Chap.9 Mutualism

8. 9.2 Seed Dispersal • Seed dispersal systems account for almost 30% of all mutualisms • In tropics some fruits are dispersed by birds that are frugivorous • Fruit provides balanced diet for birds • Birds disperse seeds • Mechanisms for attraction • Birds and mammals - attractive colors, and odorless (Birds) • Nocturnal bats - give off pungent odor Chap.9 Mutualism

9. Seed dispersal mechanisms are not as obligatory as plant-pollinator systems • Performed by more generalist agents • Wide array of adaptations • Ex. parrot beaks to crack and peel fruits • A berry-eating fish from the Amazon. Ex. Figure 9.3 Chap.9 Mutualism

10. A Variety of Mutualisms • Mutualisms and resources • Neotropical leaf-cutting ants and fungus (Figure 9.4) • Typical ant colony: 9 million • Typical biomass of colony: Equivalent to a the biomass of a cow • Typically cuts the equivalent of a cow's daily requirement of fresh vegetation • Leaf-cutting ants harvest 17% of the total leaf production in the forest • Ants take cut vegetation underground to grow special fungal crops (nature's farmers?) • Fungus grows specialized structures called gongylidia, which serve as food for the ants Chap.9 Mutualism

11. Fig. 9.4 Leaf-cutting ants Atta cephalotes, in South America, chew up leaves and cultivate fungus gardens underground. Chap.9 Mutualism

12. Leaf-cutting ants and the parasitic fungus, Escovopsis • Escovopsis can infest the ants' fungi gardens, destroying the fungi inside • A mutualisitic streptomyces • Occurs on the bodies of ants • Produces antibodies that keep Escovopsis in check Chap.9 Mutualism

13. Nitrogen • Vital to plant and animal growth • Most species can not fix atmospheric nitrogen • Fixation is carried out by soil bacteria and archaebacteria • Most live in the roots of plants • Mutualistic relationship with plant • Excess nitrogen is available to plant • Ex. Rhizobia bacteria in legumes • Figure 9.5 Chap.9 Mutualism

14. Mutualism under harsh environmental conditions • Strong facultative mutualism • Leguminous shrub, Retama, and an understory plant, Marrubium vulgare • Grow in a semiarid region of Spain • Retama shades Marrubium, provides favorable microclimate • Marrubium enhances the availability of water for Retama Chap.9 Mutualism

15. Retama Marrubium 1.0 30 20 Leaf mass (g) Leaf mass (g) 0.5 10 0.0 0 100 20 2 2 15 75 Leaf area (cm /g) Leaf area (cm /g) 50 10 25 5 0 0 3 0.6 2 0.4 N content (g / plant) N content (g / plant) 0.2 1 Fig. 9.6 0 0.0 +M -M +R -R Environment Chap.9 Mutualism

16. Mutualism and protection from natural enemies • Common example: ants and aphids(Figure 9.7) • Aphids feed on plant sap and excrete honeydew • Ants drink the honeydew and in return protect the aphids Chap.9 Mutualism

17. Mutualism and herbivory • Ants protect plants from herbivores • Common in the tropics • 377 myrmecophytic plants per hectare in a Brazilian Rain Forest (Fonseca and Ganade, 1996) • 312 ant-plant associations at a single coastal site in Mexico (Rico-Grey, 1993) Chap.9 Mutualism

18. Fig. 9.8 Thorns on Acacia collinsii in Paloverde National Park in Costa Rica. • Example: Ants and the Central American acacia trees • Acacia trees provide food and shelter for the ants inside large thorns • Ants protect the acacia tree from other insects and vertebrate herbivores • Ants also trim foliage away from competing plants and kill neighboring plant shoots • Figure 9.8 Chap.9 Mutualism

19. Fig. 9.9 Soay sheep • Example: Fungi and plants • Fungi reduce vertebrate herbivory • Soay Sheep of Hirta Island (in the St. Kilda Archipelago) Figure 9.9 • Sheep overgraze native grasses • Periodically, sheep population crashes Chap.9 Mutualism

20. Mutualism is the chief culprit • The main forage is the grass Festuca rubra • F. rubra contains an endophyte, the fungus Acremonium, inside its blades • The fungus produces toxic alkaloids • These alkaloids function as an anti-herbivory defense • In return, the fungus obtains food from the plant • Frequency of infection correlated to grazing pressure. Heavy grazing causes higher infections • Fungi are in greatest concentration in basal regions. Heavy grazing results in sheep reaching lower blades. Chap.9 Mutualism

21. Obligate mutualism • A mutualistic relationship, in which neither participant could survive without the other • Ex. Lichen: a relationship between algae and fungi • Algae provides the photosynthate • Fungi provides a safe habitat • Ex. Many ruminants and symbiotic bacteria • Bacteria break down plant tissue to provide energy for their hosts • Ex. The roots of most plants and fungi • Mutualistic association between the fungus and root tissue - mycorrhizae • Fungi obtain carbohydrates from their host • Fungi increase access to mineral nutrition and water for the plant Chap.9 Mutualism

22. 9.4 Modeling Mutualism • Uses equations similar to Lotka-Volterra competition equations • For facultative mutualism • dN1 /dt = r1N1 [K1 - N1 + aN2) / K1] • dN2 /dt = r2N2 [K2 - N2 + bN1) / K2] • dNi /dt = change in population size of species 1 or 2 • ri = per capita growth rate for species 1 or 2 • Ni = population size of species 1 or 2 • Ki = Maximum population density of species 1 or 2 • a = Positive effect of species 2 on species 1 • b = Positive effect of species 1 on species 2 Chap.9 Mutualism

23. Facultative mutualism dN N N dN dN a) b) c) 1 1=0 2=0 1= 0 dt dt dt 2 N2 N N 2 2 dN dN 2=0 2=0 dt dt Population density of N2 dN 1=0 dt X2 X X 2 2 X N X N X N 1 1 1 1 1 1 Population density of N1 Fig. 9.10 Graphical models of facultative (a-c) and obligate (d-f) mutualism. Chap.9 Mutualism

24. For obligate mutualism • Different equations are needed • Models of facultative mutualism are, in general, more stable than models of obligate mutualism • Figure (9.10d-f) Chap.9 Mutualism

25. Obligate mutualism N dN 1 dN dN d) e) f) 1= 0 2= 0 1= 0 N dt 2 dt dt N2 N N 2 2 dN dN 2=0 1=0 dt dt Population density of N dN — 2=0 dt N N N 1 1 1 Population density of N1 Chap.9 Mutualism

26. 9.5 Mutualisms and Community Process • Mutualism can have strong indirect effects on the community • Ex. mycorrhizal fungi and herbivory load • Pinyon pines and mycorrhizae: Density of needle scale insect, Matsucoccus acalyptus: • Mycorrhizae can improve pine vigor and/or increase plant investment in antiherbivory defenses • Density of needle scale insects will decrease Chap.9 Mutualism

27. Ex. Endophytes (fungi that live inside leaves) and vascular plant hosts - Defend host against herbivory • Mycorrhizal fungi and plant species diversity (Figure 9.11) Chap.9 Mutualism

28. d) a) 7 0.8 6 0.6 5 Hyphal length (m g soil) -1 0.4 Simpson’s diversity index 4 3 0.2 2 0 0 2 4 8 10 12 14 6 0 2 4 8 10 12 14 6 e) b) 20 130 120 -1 15 110 -2 Shoot biomass (g m ) Soil P (mg kg soil) 100 10 90 5 80 70 0 0 2 4 8 10 12 14 6 0 2 4 8 10 12 14 6 f) c) 2500 160 -2 -2 2000 140 1500 120 Plant P (mg m ) Fig. 9.11 Root biomass (g m ) -2 1000 100 80 500 0 2 4 8 10 12 14 0 2 4 8 10 12 14 6 6 Number of mycorrhizal fungal species Number of mycorrhizal fungal species Chap.9 Mutualism

29. 9.6 Commensalism • Commensal relationship: one members benefits and the other is unaffected • Ex. An orchid and a tropical tree: orchids gain a place to live and the tree gains nothing • Ex. Cattle egrets and cattle: Cattle stir up insect prey for egrets (Figure 9.12) Chap.9 Mutualism

30. 10 Feedings per minute 0 30 20 Steps per prey 10 0 Fig. 9.12 No cow Chap.9 Mutualism Cow

31. Commensalism in the form of phoresy: association is passive and more temporary transport of one organism by another • The transport of flower-inhabiting mites from bloom to bloom in the nares of hummingbirds • Common commensalisms: plant mechanisms of seed dispersal • Ex. Seeds attached to animal fur • Some mechanims can become an antagonistic relationship • Pisonia (cabbage tree) produce a very sticky fruit Chap.9 Mutualism

32. Chap.9 Mutualism

33. Humans in mutualistic relationship • Humans and Agriculture (Box Photo 1) • Origins of world's crops (Box Table 1) • Crops are introduced around the world • Livestock are domesticated • Mutualism • Human population has increased • Crops and livestock populations have increased • Box Table 2 Chap.9 Mutualism

34. Side-Effects of Mutualism • Pollution of bodies of water • Loss of topsoil • Depletion of water supplies • Salting of the land • Desertification • Severe loss of wildlife Chap.9 Mutualism

35. 問題與討論！ Japalura@hotmail.com Ayo 台南站： http://mail.nutn.edu.tw/~hycheng/ Chap.9 Mutualism