Species Interactions

1. Species Interactions

2. Interactions • Populations do not exist in isolation. • All populations are tightly linked to other populationsthat share the same habitat.

3. Parasitism • Parasites are extremely diverse. • All parasites acquire resources from their host.This is always detrimental to the host. A “coevolutionary arms race” exists between parasitesand their hosts. • Parasites develop better ways to attack and use the host,while hosts develop better defenses. • Example: Plasmodium and the human immune system. (Fig. 49.3a,b) • Parasites can manipulate the behavior of their host.(Fig. 49.4)

4. Figure 49.1 middle 1437 nm

5. Human host 1. Sporozoites are injected from salivary gland of mosquito into human. Mosquito host 7. Male and female gametocytes fuse in mosquito’s gut. Gametocytes Sporozoites in salivary glands Gut 4. Merozoites reproduce asexually until they cause red blood cells to rupture (causing anemia in human host). 2. Sporozoites reproduce asexually to form merozoites in human liver. 8. After meiosis, resulting cells develop into sporozoites and migrate to salivary glands. 3. Merozoites are released into blood- stream where they infect red blood cells. 6. When a mosquito bites the human host, gametocytes enter the mosquito as part of a blood meal. 5. Merozoites surviving human immune system become male or female gametocytes.

6. Cytotoxic T cell HUMAN IMMUNE DEFENSE AGAINST PLASMODIUM Cytotoxic T cell Plasmodium sporozoites cp26 protein from Plasmodium HLA-B53 HLA-B53 Healthy liver cell Infected liver cell Infected liver cell Dead liver cell 1. Healthy liver cell has an HLA-B53 protein on its membrane. 2. HLA-B53 protein displays cp26 protein from Plasmodium, indicating that the liver cell is infected. 4. Cytotoxic T cell kills liver cell before merozoites are produced. 3. Cytotoxic T cell recognizes HLA-B53 and cp26 complex.

7. In The Gambia, West Africa, different strains of Plasmodium have different versionsof the cp protein. How successful are these different strains at infecting people? Plasmodiumstrain Infectionrate Interpretation cp26 Low HLA-B53 binds to these proteins.Immune response is effective. cp29 Low Immune response fails when thesestrains infect the same person. cp26 and cp29strains together High cp27 High HLA-B53 does not bind to theseproteins. Immune response is notas effective. cp28 Average

8. Birds that prey on snails arethe next host for the parasite Infected snails move to opensunny areas; tentacles wiggle. Uninfected snails stay in shadedareas; tentacles do not wiggle.

9. Predation • When predation occurs, a predator kills and consumesa prey individual. • Predators can regulate prey populations and/or reducethem to below carrying capacity. • Prey have a wide array of mechanisms that they use todefend themselves from predation. • Keystone predators are those that have an exceptionallygreat impact on all the other surrounding species.

10. Regulated prey population Carrying capacity Prey population size Population fluctuates within a narrow range Time

11. Predator behavior Prey population size Time

12. 20 15 Predation rate (number of moosekilled/moose density) 10 5 0 High Medium Low Moose density

13. Camouflage

14. Mimicry

15. Weapons

16. Prey and predator

17. Correlation between predation rate and prey defense Attachment strength (N) Shell mass (g) Low predation High predation Low predation High predation Site type Site type

18. Is prey defense induced by presence of predator? Are mussel defenses induced by the presence of crabs? Are mussel defenses induced by the presence of broken mussel shells? Seawater Seawater Broken mussel shells Crab (fed fish, not mussels) Intact mussel shells No crab Mussels Mussels Mussels Mussels Shell thickness HIGH Shell thickness LOW Shell thickness HIGH Shell thickness LOW Yes Yes

19. Keystone predator present

20. Keystone predator absent

21. Keystone predator present

22. Keystone predator absent

23. Herbivory • Unlike predators, herbivores are plant-eaters that removetissue from their prey, but rarely kill them.

24. Figure 49.11 Predator Herbivore Primary producer(plants)

25. Competition • Competition is detrimental to both of the individuals orspecies involved because it reduces available resources. • Every species has a unique niche, or set of habitat requirements. • Competition occurs when niches overlap. • Competitive exclusion results when niches completely overlap. • Coexistence is possible if niches do not overlap completelyand the species involved partition the available resources. • Coexistence is also possible if other factors serve to limit the better competitor in some way.

26. One species eats seeds of one size range Number consumed Seed size

27. Partial niche overlap: competition for seeds ofintermediate size Species 2 Species 1 Number consumed Seed size

28. Complete niche overlap Species 1: Strong competitor Species 2: Weak competitor,driven to extinction Number consumed Seed size

29. Consumptive competition occurs when organisms compete for the same resources. These trees are competing for nitrogen and other nutrients.

30. Preemptive competition occurs when individuals occupy space and prevent access to resources by other individuals. The space preempted by these barnacles is unavailable to competitors.

31. Overgrowth competition occurs when an organism grows over another, blocking access to resources. This large fern has overgrown other individuals and is shading them.

32. Chemical competition occurs when one species produces toxins that negatively affect another. Note how few plants are growing under these Salvia shrubs.

33. Territorial competition occurs when mobile organisms protect a feeding or breeding territory. These red-winged blackbirds are displaying to each otherat a territorial boundary.

34. Encounter competition occurs when organisms interfere directly with each other’s access to specific resources. Here, spotted hyenas and vultures fight over a kill.

35. Mutualism • Mutualism is a type of interaction that is beneficial to both species involved. • It does not involve altruism. The benefits are a by-product of each species’ own self-interest. • The costs and benefits of mutualism vary widely between partners, over time, and from one area to the next.

36. Mutualism between ants and fungus

37. Mutualism between fish

38. Treehopper excreting honeydew, which is harvested by ants

39. Are ants beneficial to treehoppers? 1000 m2study plot Plants withants Plants withants removed

40. Which treatment contained more treehoppers? 100 80 Plantswithants 60 Average number of youngtreehoppers per plant Plantswithoutants 40 20 0 25 30 10 20 20 5 July August