1. Predation

2. – one species feeds on another  enhances fitness of predator but reduces fitness of prey ( +/– interaction)

4. Charles Elton (1942) British ecologist who studied mammalian population data. He concluded that oscillations were common and suggested that predators regulate prey populations. Cycles caused by predator –prey interactions British ecologist who studied mammalian population data. He concluded that oscillations were common and suggested that predators regulate prey populations. Cycles caused by predator –prey interactions predators prey

5. Lotka – Volterra Predation model Lotka – Volterra Predation model Mathematicians who tried to model predator-prey interactions. - to what extent do predators cause these cyclic fluctuations (are they ½ responsible? Completely responsible?) - are other factors important? - do predators keep prey populations below K? (If predators keep prey populations below K then we have no reason to believe completion is important because resources would not be limiting) - if predators are so efficient, why don’t the prey populations go extinct? Mathematicians who tried to model predator-prey interactions. - to what extent do predators cause these cyclic fluctuations (are they ½ responsible? Completely responsible?) - are other factors important? - do predators keep prey populations below K? (If predators keep prey populations below K then we have no reason to believe completion is important because resources would not be limiting) - if predators are so efficient, why don’t the prey populations go extinct?

6. Predator-Prey Interaction Model N = # of prey r 1 = intrinsic rate of increase in prey populations k 1 = constant that measures the ability of the prey to escape predators (0-1) P = # of predators N = # of prey r 1 = intrinsic rate of increase in prey populations k 1 = constant that measures the ability of the prey to escape predators (0-1) P = # of predators r 1 N =density independent growth - k 1 PN = reflects the negative effect of predators on prey r 1 N =density independent growth - k 1 PN = reflects the negative effect of predators on prey Changes in prey population

7. Predator-Prey Interaction Model r 2 = death ratein predator population k 2 = constant that measures the ability of the predators to capture prey (0-1) P = # of predators r 2 = death ratein predator population k 2 = constant that measures the ability of the predators to capture prey (0-1) P = # of predators - r 2 P = negative of density independent growth (drag on predator populations Changes in predator population Assumption: no density dependent effects (no carrying capacity, no competition) only predation dN dt rPkNP  22

8. Predator-Prey Interaction Model This model did produce an oscillation between prey and predator populations (thus, it appeared to reflect natural situations). However, more complicated models they were math. unstable. Gause : 1 st test of model – observed two species of protozoans (prey and predator) grown on an oat medium. Predator always totally consumed the prey, then starved to death.

9. Predator-Prey Interaction Model Gause : By adding sediment to the oat medium (habitat complexity) for hiding places for the prey (paramecium). Predators starved to death, then the prey populations incre ased dra m atically. Gause concluded that the cycles seen in nature are the result of constant migration, because he could not get coexistence in his experiments.

10. Carl B. Huffaker (1950’s) Insect ecologist Used experiments to find predators that controlled prey species that fed on commercially important citrus crops. He concluded that Gause’s experiments were too simple to adequately reflect nature. Insect ecologist Used experiments to find predators that controlled prey species that fed on commercially important citrus crops. He concluded that Gause’s experiments were too simple to adequately reflect nature. He studied 2 species of mites (predator and prey) on oranges. Prey fed on oranges and predators fed on prey. Arenas in the lab had oranges placed in rectangular trays and densities of predators/prey were manipulated. He also increased habitat complexity by adding rubber balls and vasoline barriers. oranges only: predators ate prey and eventually starved to death. oranges, balls and vasoline: coexistence He studied 2 species of mites (predator and prey) on oranges. Prey fed on oranges and predators fed on prey. Arenas in the lab had oranges placed in rectangular trays and densities of predators/prey were manipulated. He also increased habitat complexity by adding rubber balls and vasoline barriers. oranges only: predators ate prey and eventually starved to death. oranges, balls and vasoline: coexistence

11. C. S. Holling (1960’s) Conducted studies on the components of predatory interactions (acts among individual organisms) Worked with vertebrates and invertebrates (entomologist, concerned with the outbreaks of insects in forests which denuded trees.) Conducted studies on the components of predatory interactions (acts among individual organisms) Worked with vertebrates and invertebrates (entomologist, concerned with the outbreaks of insects in forests which denuded trees.) Functional response – relationship between prey density and the rate at which an individual predator consumes prey Numerical response- increase in predator numbers with increases in prey abundance Functional response – relationship between prey density and the rate at which an individual predator consumes prey Numerical response- increase in predator numbers with increases in prey abundance

12. Components of Functional Responses (for individual predators) Components of Functional Responses (for individual predators) 1.Rate of successful search a. ratio of the speed of predator to prey b. size of the field of reaction of the predator (distance at which the predator can perceive the prey) c. success rate of capture (does a predator get a prey every time he encounters it) 1.Rate of successful search a. ratio of the speed of predator to prey b. size of the field of reaction of the predator (distance at which the predator can perceive the prey) c. success rate of capture (does a predator get a prey every time he encounters it)

13. Why are predators size-selective? Encounter frequency: Encounter of large prey is higher than small prey Encounter frequency: Encounter of large prey is higher than small prey Reaction distance —how close to the fish does a prey item have to be for the fish to see it and react to (eat) it? Pumpkinseed Lepomis gibbosus Pumpkinseed Lepomis gibbosus Confer and Blades 1975 (L&O)

14. Reaction distance translates to overall volume searched, which influences vulnerability of the prey Longer radius = higher encounter rate Reaction distance = radius of sphere

15. It is not just size that matters, it is overall visibility Zaret 1972 Fish always took the big-eye form. Fish always took the big-eye form. Two morphs of Ceriodaphnia Big eyeSmall eye Two morphs of Ceriodaphnia Big eyeSmall eye Artificially made small-eye morph more visible by feeding them india ink. Predation rate increased

16. Components of Functional responses (for individual predators) Components of Functional responses (for individual predators) 2.Time available for hunting verses other activities other activities necessary for an organism to carry on to reproduce is going to influence the amount of time available to hunt a. avoiding other predators b. time looking for a mate c. patrolling a territory 2.Time available for hunting verses other activities other activities necessary for an organism to carry on to reproduce is going to influence the amount of time available to hunt a. avoiding other predators b. time looking for a mate c. patrolling a territory

17. Components of Functional Responses (for individual predators) Components of Functional Responses (for individual predators) 3. Time spent handling prey amount to time it takes to capture a prey after recognizing a potential food source a. pursuit of prey b. subduction of prey c. eating prey d. digesting prey 4. Hunger level – function of the size of the gut of the predator and the time spent in digestion and assimilation (rapid verses slow metabolsim) 3. Time spent handling prey amount to time it takes to capture a prey after recognizing a potential food source a. pursuit of prey b. subduction of prey c. eating prey d. digesting prey 4. Hunger level – function of the size of the gut of the predator and the time spent in digestion and assimilation (rapid verses slow metabolsim)

18. Type I: Functional Response Linear increase; same assumptions as the Lotka-Votera growth models Linear increase; same assumptions as the Lotka-Votera growth models No examples of Type I functional response curve observed in natural systems

19. Type II: Functional Response Leveling off of # of prey eaten even though the # of prey increases (satiation of predators or time spent hunting prey) Leveling off of # of prey eaten even though the # of prey increases (satiation of predators or time spent hunting prey) Holling found Type II curve with invertebrate predators

20. Type III: Functional Response Lag period: even as density of prey increases the # of prey eaten doesn’t increase dramatically (thought to result from the formation of search image by predators ) Lag period: even as density of prey increases the # of prey eaten doesn’t increase dramatically (thought to result from the formation of search image by predators ) These were all the results of laboratory experiments that Holling conducted. People later found a few examples of Type II and more examples of Type III.

21. Search image – when prey are rare there is no value in hunting for them. Only when the prey population increases above some threshold level does the predator form a search image and begin to recognize that particular prey item as a valuable food source. The Predator then focuses on and begins to exploit that food source heavily. Search image – when prey are rare there is no value in hunting for them. Only when the prey population increases above some threshold level does the predator form a search image and begin to recognize that particular prey item as a valuable food source. The Predator then focuses on and begins to exploit that food source heavily.

22. Numerical response – when there is a large increase in prey density, the predators present can become satiated as prey densities increase and the rate of prey eaten is not going to increase for each individual predators. However, if predators are added to the population increased exploitation of the prey can occur (due to immigration not reproductive increase in the population)

23. Switching If predators exploit prey populations heavily and drive prey populations down, eventually prey densities will decline below some threshold value and predators will switch to another prey item. If switching occurs then more than one prey species can coexist (many studies have found switching to take place).

24. Murdoch (1960’s) Conducted the 1 st switching experiments – examined gastropods that feed on mussels and barnacles and found that switching took place. best candidate for switch occurred when the predator exhibited a weak preference for prey species Conducted the 1 st switching experiments – examined gastropods that feed on mussels and barnacles and found that switching took place. best candidate for switch occurred when the predator exhibited a weak preference for prey species

25. Prudent Predator Predators can influence prey populations dramatically (can drive them to extinction). You might conclude that there is some optimal level of predation intensity that will serve to maximize the # of predators without driving the prey populations to extinction. The idea was suggested that predators might “manage” prey populations and that this might explain why predators and prey coexist. Predators can influence prey populations dramatically (can drive them to extinction). You might conclude that there is some optimal level of predation intensity that will serve to maximize the # of predators without driving the prey populations to extinction. The idea was suggested that predators might “manage” prey populations and that this might explain why predators and prey coexist. Problem: individuals would have to cooperate with each other (no penalty for cheaters in the short term) Problem: individuals would have to cooperate with each other (no penalty for cheaters in the short term) Some evidence: predators can be prudent without “altruistic behavior” because exploitation of the prey is determined by the ability of predators to capture prey. Which individuals are removed from prey populations?

26. Back to the Rocky Intertidal Early work by Connell (1970) Conducted a 9 year study of barnacles and predatory whelks (San Juan Island, Washington) Early work by Connell (1970) Conducted a 9 year study of barnacles and predatory whelks (San Juan Island, Washington)

27. Observations Juveniles barnacles Adults barnacles Adults barnacles Predatory Whelks

28. Model Model: Lower limit of adults caused by predation H 1 : Excluding predators in low areas leads to presence of adults Experiment: predator exclusion cages on a pier piling Model: Lower limit of adults caused by predation H 1 : Excluding predators in low areas leads to presence of adults Experiment: predator exclusion cages on a pier piling Results Midshore level: excluding whelks resulted in an adult population Lowshore: small whelks got into cages Midshore level: excluding whelks resulted in an adult population Lowshore: small whelks got into cages

29. Conclusion Predation controls lower limit of barnacle population Contrast with Connell (1961) - competition controlled lower limit of Chthamalus Reason for difference? - predation reduced density below which competition could occur - space not limiting Predation controls lower limit of barnacle population Contrast with Connell (1961) - competition controlled lower limit of Chthamalus Reason for difference? - predation reduced density below which competition could occur - space not limiting

30. Effects of predation on morphology, distribution and abundance 1.Change in size structure of prey population (if predator prefers the largest individuals in a prey population) or shifts in the relative abundance of prey species (such that smaller species become quite abundant and the larger prey species becomes rare). 1.Change in size structure of prey population (if predator prefers the largest individuals in a prey population) or shifts in the relative abundance of prey species (such that smaller species become quite abundant and the larger prey species becomes rare). Brooks and Dodson 1965 (over 1350 citations) Lakes in North America When fish introduced there were huge changes - predators preferred the larger zooplankton - small zooplankton became dominant - large phytoplankton become abundant Lakes in North America When fish introduced there were huge changes - predators preferred the larger zooplankton - small zooplankton became dominant - large phytoplankton become abundant

31. Effects of predation on morphology, distribution and abundance 2. Decreases in overall diversity – if predators are very efficient at removing prey, they drive populations to extinction which reduces diversity 3.Increase in diversity – in simple systems with few potential prey species, one of which is a dominant competitor. If we introduce a predator system and it prefers the dominant competitor it can reduce the population of the dominant competitor, allowing the inferior competitors to exist. All three of these can occur in “ecological time” = one to a few generations 2. Decreases in overall diversity – if predators are very efficient at removing prey, they drive populations to extinction which reduces diversity 3.Increase in diversity – in simple systems with few potential prey species, one of which is a dominant competitor. If we introduce a predator system and it prefers the dominant competitor it can reduce the population of the dominant competitor, allowing the inferior competitors to exist. All three of these can occur in “ecological time” = one to a few generations

32. Paine 1966 Effect of Pisaster on intertidal assemblage 15 species coexist in intertidal Food web: Pisaster the most important consumer Effect of Pisaster on intertidal assemblage 15 species coexist in intertidal Food web: Pisaster the most important consumer

33. Experimental Design 8 x 2 m Plots in intertidal Control Piaster removal 8 x 2 m Plots in intertidal Control Piaster removal Monitored changes over one year

34. Results Control plot: no change Removal plot: 80% barnacles (3 months) Mussels starting to dominate (1 yr) Species diversity decreased 15 to 8 spp. Predicted mussel population would dominate available space Control plot: no change Removal plot: 80% barnacles (3 months) Mussels starting to dominate (1 yr) Species diversity decreased 15 to 8 spp. Predicted mussel population would dominate available space

35. Conclusions Pisaster interrupts successional process After removal, superior competitor dominates Pisaster interrupts successional process After removal, superior competitor dominates Limitations: no replication did not examine microfauna (can be very diverse) Produced the concept of the “keystone predator” Produced the concept of the “keystone predator”

36. Keystone species paradigm Pisaster become known as a “keystone species” Paine (1966) cited 850 times 1970 –1979 Defined as “a single native species, high in the food web … which greatly modifies the species composition and physical appearance of the system” (Paine 1969) Pisaster become known as a “keystone species” Paine (1966) cited 850 times 1970 –1979 Defined as “a single native species, high in the food web … which greatly modifies the species composition and physical appearance of the system” (Paine 1969)

37. Is the keystone a useful concept? Paine intended the term as metaphor – rarely used it himself Others picked up on it (particularly conservation literature) (conserving keystones to maintain diversity) Problems: - identifying them - context dependent - may overlook other important species Criticized by Hurlburt (1997) Paine intended the term as metaphor – rarely used it himself Others picked up on it (particularly conservation literature) (conserving keystones to maintain diversity) Problems: - identifying them - context dependent - may overlook other important species Criticized by Hurlburt (1997)

38. Menge (1994) Effects of Pisaster under different conditions Transplanted mussel clumps Hypothesis: Pisaster will consume mussels at all locations where it is present

39. Boiler Bay Strawberry Hill Sheltered Exposed PredNo pred Turf Bare Experimental Design Replicates (n=5)

40. Results Pisater more important at exposed sites Other sites: diffuse predation - strong effect shared among species “Keystone” effect context dependent Why? – low productivity Pisater more important at exposed sites Other sites: diffuse predation - strong effect shared among species “Keystone” effect context dependent Why? – low productivity Predation can regulate assemblage structure - Directly: influences prey distribution - Indirectly: can mediate competition Keystone concept – beware of generality Predation can regulate assemblage structure - Directly: influences prey distribution - Indirectly: can mediate competition Keystone concept – beware of generality Take home message

41. Trophic Cascade in Kelp Forests When the keystone sea otter is removed, sea urchins overgraze kelp and destroy the kelp forest community. Figure 5.15b

42. Effects of predation on morphology, distribution and abundance 4.Morphological modifications – inference from observation a. protective devices (spines on sea urchins; strong shells) 4.Morphological modifications – inference from observation a. protective devices (spines on sea urchins; strong shells)

43. Effects of predation on morphology, distribution and abundance 4.Morphological modifications – inference from observation b. mimicry – organisms that resemble unpalatable species (usually because they contain toxic compound) 4.Morphological modifications – inference from observation b. mimicry – organisms that resemble unpalatable species (usually because they contain toxic compound)

44. Effects of predation on morphology, distribution and abundance 4.Morphological modifications – inference from observation c. crypsis – organisms match the color and surroundings of their background. Believed this morphology shaped by predatory pressure over time. 4.Morphological modifications – inference from observation c. crypsis – organisms match the color and surroundings of their background. Believed this morphology shaped by predatory pressure over time.

45. Artificial camouflage Decorator crabs  Crabs put algae on their backs, which increases their survival  In areas with Dictyota algae, use this species for decoration, but rarely food

46. Optimal Foraging - types of feeding behaviors that would maximize food intake rate. Important because increased food intake results in larger and healthier organisms with more energy for growth and reproductive output. (maximize fitness) Is taking the largest prey item the best strategy? - types of feeding behaviors that would maximize food intake rate. Important because increased food intake results in larger and healthier organisms with more energy for growth and reproductive output. (maximize fitness) Is taking the largest prey item the best strategy?

47. Elner and Hughes (1978) Used predatory green crabs (Carcinus maenas) and mussels. Several different sizes of mussels were offered (small, medium and large). Feeding trials looked at the amount of energy/unit time. Used predatory green crabs (Carcinus maenas) and mussels. Several different sizes of mussels were offered (small, medium and large). Feeding trials looked at the amount of energy/unit time.

48. Manipulation: Fix the proportion of different sized mussels but varied the overall abundance (# of each size class in a given area) Observation: Proportion of each size class eaten under different abundances. Size Class:123 Low Abundance248 (available) Low Abundance30%65%5% (eaten) High Abundance102040 (available) High Abundance 60%35%5% (eaten) Size Class:123 Low Abundance248 (available) Low Abundance30%65%5% (eaten) High Abundance102040 (available) High Abundance 60%35%5% (eaten)

49. Manipulation: Fixed the proportion of different sized mussels but varied the overall abundance (# of each size class in a given are a) Observation: Proportion of each size class eaten under different abundances. Conclusion: The crabs are foraging in a size-selective manner AND they get more selective at higher abundances However, they still sample unprofitable size classes Conclusion: The crabs are foraging in a size-selective manner AND they get more selective at higher abundances However, they still sample unprofitable size classes

50. Goss-Custard (1977) Studied size selection of polychaete worms on mudflats by redshanks (Tringa totanus). Redshanks selected prey of 7mm more than any other size class even though prey of 8mm were more common. Thus, worms were eaten in proportion to their net energy benefit --not in relation to their abundance. Also…. When large #’s of worms available birds were selective When small #’s of worms were available all were consumed (take what you can get) Studied size selection of polychaete worms on mudflats by redshanks (Tringa totanus). Redshanks selected prey of 7mm more than any other size class even though prey of 8mm were more common. Thus, worms were eaten in proportion to their net energy benefit --not in relation to their abundance. Also…. When large #’s of worms available birds were selective When small #’s of worms were available all were consumed (take what you can get)

51. 2. Optimal foraging — take the prey that provides the greatest energy return for cost of capture/handing. With abundant prey, bigger is better Werner and Hall (1974) Ecology Fed fish choice of three sizes of Daphnia magna

52. Why may organisms not follow predictions of Optimal Foraging Theory 1.The idea that organisms maximize energy uptake is an assumption – other factors may be involved (predator avoidance). An organism may not maximize energy consumption because of the need to minimize predation risk. 2.Organisms may not be able to detect all available prey. 3.Caloric value may not account for all needed resources (essential vitamins). Optimal Foraging needs to be thought of as a concept not a theory. 1.The idea that organisms maximize energy uptake is an assumption – other factors may be involved (predator avoidance). An organism may not maximize energy consumption because of the need to minimize predation risk. 2.Organisms may not be able to detect all available prey. 3.Caloric value may not account for all needed resources (essential vitamins). Optimal Foraging needs to be thought of as a concept not a theory.

53. Inducible versus Constitutive defenses A bryozoan makes spines when placed in contact with a predatory nudibranch. A hydrozoan, Hydractinia, produces defense stolons armed with nematocysts when in contact with another colony.

54. Inducible Defense: The conical (right) and bent (left) forms of the acorn barnacle Chthamalus anisopoma. The animal develops the bent form if predatory snails are present.

55. Mytilus edulis (Blue mussel) Thicker shells Leonard et al (1999) Smith & Jennings (2000) Larger adductor muscle Reimer & Tedengren (1996) Increased gonad ratios Reimer (1999) Increased byssus volume Cote (1995)

56. Predation: Indirect Effects Non-lethal effects –Injury by browsing predators –Trait-mediated indirect effects (TMII) Risk averse foraging More shelter dwelling in the presence of predators –Trophic cascades

58. Emergent Multiple Predator Effects (MPEs) Types of interactions among predators (Soluk and Collins, 1988): –Neutral: predators do not affect one another’s rates of prey consumption –Negative (interference): combined prey consumption less than neutral values  MPE –Positive (facilitation): combined prey consumption greater than neutral values  MPE

59. Parasitism A two species interaction in which one species (parasite) lives in or on a second species (host) for a significant period of time and obtains its nourishment from it.

60. Parasitism (cont) Viruses, bacteria and fungi Protozoa, arthropods, helminths (nematodes, cestodes, trematodes, and acanthocephala) Parasites are ubiquitous and should probably be considered in every ecological study (but aren’t)

61. Parasitism (cont) Parasite benefits, the host loses Effects on host –Reduced feeding efficiency –Depletion of food reserves –Reduced reproduction –Lowering of disease resistance

62. Isopods

63. Acanthocephalans In intestine

64. Behaviour and parasitology? Behaviour is ‘the way in which individual organisms interact with other components of their environment, including prey, competitors, predators, potential mates and parasites.

65. 1. Parasites exploit natural patterns of host behaviour to maximise transmission

66. Example 1: The Gasterosteus -Schistocephalus system The types of host behaviour that can be exploited by parasites is variable, but usually involves feeding / foraging. This is especially important for parasites with an indirect life-cycle Free-swimming coracidium Copepod sp. Stickleback

67. Atlantic halibut Hippoglossus hippoglossus Diurnal forager Diurnal forager Rests during night (sand) Rests during night (sand) Infected by: Infected by: Entobdella hippoglossus Common sole Solea solea Nocturnal forager Nocturnal forager Rests during day (sand) Rests during day (sand) Infected by: Infected by: Entobdella soleae Example 2: A tale of two fishes… Parasites are closely related, but cannot successfully infect the ‘wrong’ host

68. Eggs of E. hippoglossus and E. soleae exhibit opposite hatching periodicity, which match host activity patterns Halibut Sole Parasites lay sticky eggs that adhere to sand particles, near their potential hosts E. Soleae hatching E. Hippoglossus hatching

69. We know that host behaviour can influence parasite infectionsWe know that host behaviour can influence parasite infections Therefore…..variation in host behaviour patterns can create variation in parasite infection levels Therefore…..variation in host behaviour patterns can create variation in parasite infection levels

70. 2. Hosts can evolve behavioural resistance as a response to infection threat

71. Behavioural resistance ‘the first line of defence’ Behavioral Defense Prevention better than cure. Least energetically demanding defense Structural Defense Skin of Red Sea cling fish can produce enough anti- parasite mucus to cover its entire body in a few minutes Crinotoxic fishes (sedentary) have epidermal toxins that protect against parasites Immunological Defense Immune defense is important: BUT is energetically expensive, Negative effects regarding growth, fat storage and reproduction

72. Herbivory Herbivory is a special case of predation –herbivory differs from predation in that the prey cannot move, but remember that much herbivory in the ocean is really predation

73. The importance of herbivory to nearshore ecosystems It is the first step in the transfer of energy in nearshore food webs It provides a major trophic link for the cycling of nutrients within these food webs It often affects the productivity and structure of plant communities

74. Plant Community Shifts due to Herbivory Increases prevalence of species with: –Low nutritive value (low nitrogen) –Chemical Defenses (secondary compounds) –Structural Defenses (calcareous skeletons) –Shifts in functional groups (from erect fast growers to prostrate slow growers) –mutualisms between grazers and host plants

75. Why is the world green? Why don’t herbivores consume more of the plants that are available to them? –Maybe herbivores aren’t food limited (predators control herbivore density) –alternatively the plants are not as available as they appear to us

76. Herbivory: Secondary compounds Secondary compounds are not part of primary metabolic pathways so they must be synthesized at some cost to the plant The primary function of these compounds is controversial: –some view them as waste products of plant metabolism that are only coincidentally toxic –others suggests they are so costly as to have evolved specifically to thwart herbivores

77. Herbivory: Secondary compounds cont. Types of chemical defenses: –quantitative examples include tannins and resins which occupy as much as 60% of the plants leaf dry mass these compounds are thought to deter specialized herbivores –qualitative comprise < 2% of a plants leaf dry mass examples include alkaloids and phenols deter generalist herbivores

78. The amount of energy invested in a plant depends on the vulnerability of the tissue –growing shoots and leaves are more heavily defended than old leaves –usually compounds are concentrated near the surface of the plant Because these compounds are expensive to produce (which reduce the competitiveness of some plants) some plants have the ability to turn the production of these compounds on and off (induced defenses) in as little as 12 hours after a bout of herbivory –only studied for a few marine species Herbivory: Secondary compounds cont.

79. Secondary compound tradeoffs Reduced competitive capability for the defended plant grazer may seek out defended plants to sequester these compounds for their own defense some grazers are well equipped to defeat chemical defenses

80. The impact of herbivores on plant communities How much plant production is taken: –in macroalgae on reefs and phytoplankton in some estuaries virtually all of the Net Aboveground Primary Production (NAPP) is consumed by herbivores –in seagrass and mangroves less than 30% of NAPP is consumed

81. Population Interactions Competition (--) when both species suffer from an association Predation (+-) when one benefits and one suffers Commensalism (+0) when one species benefits from another Amensalism (-0) when one species negatively affects another Mutualism (++) when both species benefit from another

82. Mutualisms Both species benefit One species provides nutrition while the other provides either protection or cleaning services Examples include: –Clownfish-anemone –Giant clams/corals-zooxanthellae –Goby-shrimp –Decorator crabs-sponges, tunicates and anemones –Deep sea worms-sulphur metabolizing bacteria

83. Mutualisms Classifications of mutualisms –Obligatory At least of the species can not live in the absence of the other –Facultative Each species can survive singly but quality of life is much less

84. Mutualisms How did mutualisms evolve? –Most think they develop as a result of some intense negative interaction (parasitism or predation) –Organisms had two options Escape the interaction Adapt to the interaction

85. Mutualisms Benefits of mutualisms –Each species grows, survives, or reproduces at a higher rates in the presence of the other

86. Mutualisms Mutualisms less important when resources are plentiful They are more common in stressful environments Benefits maybe density-dependent

87. Cleaner Stations An experiment conducted with cleaner fishes and larger predators –Cleaners feed on ectoparasite –In some cases parasites within the mouth When cleaners are removed parasite infestation increase within a very few hours Cleaner stations are sites of very high species richness

88. Another example gobies and snapping shrimp

89. Another example Sea anemone - protection against predators Clown fish highly evolved to survive cnidarian nematocysts Mucus - thicker & lacks sialic acid groups which trigger nematocyst discharge.

90. Algal-Invertebrate Mutualisms Found in protozoans, sponges, cnidarians, asciidians, flatworms, and mollusks. Alga generally lose motility during symbioses and may lose cell walls Animal hosts may change behavior – e.g. Cassiopeia, Convoluta, Tridacna Relationship seems to be mutualism (trading food for food, protection, oxygen, carbon dioxide) Vertical or horizontal transmission possible

91. Algal-Invertebrate Symbioses, cont.

92. Population Interactions Competition (--) when both species suffer from an association Predation (+-) when one benefits and one suffers Commensalism (+0) when one species benefits from another Amensalism (-0) when one species negatively affects another Mutualism (++) when both species benefit from another

93. Commensalism Facultative commensal e.g. – barnacles

94. The Remora fish (Echeniedea) has its dorsal fin modified as a sucker-like attachment organ. It attaches to the sides of larger fish and turtles using them as transport hosts but in addition, obtains food fragments dropped from the host.

95. Trophic amensalism Amensalism is the opposite of mutualism, and occurs when one organism alters the environment such that another type of organism cannot live there. Deposit feeding organisms cause bioturbation, making suspension feeding more difficult or impossible. This is amensalism among trophic levels, or Trophic amensalism.

97. Food chains to food webs Multiple predators and multiple prey Same energy loss as move to higher trophic levels

98. Parasitism (cont) Parasite benefits, the host looses Effects on host –Reduced feeding efficiency –Depletion of food reserves –Reduced reproduction –Lowering of disease resistance

99. Parasitism con’t Parasite classifications –Ectoparasites which live attached to or embedded in the external body surface (gills, body walls etc) of an organism –Endoparasites lie within the body, and may occupy circulatory vessels or internal organs

100. Population Interactions Competition (--) when both species suffer from an association Predation (+-) when one benefits and one suffers Commensalism (+0) when one species benefits from another Amensalism (-0) when one species negatively affects another Mutualism (++) when both species benefit from another

101. Paine 1966- early evidence of important top-down effects Effect of Pisaster on intertidal assemblage 15 species coexist in intertidal Food web: Pisaster the most important consumer Effect of Pisaster on intertidal assemblage 15 species coexist in intertidal Food web: Pisaster the most important consumer

102. Increases prevalence of species with: –Low nutritive value (low nitrogen) –Chemical Defenses (secondary compounds) –Structural Defenses (calcareous skeletons) –Shifts in functional groups (from erect fast growers to prostrate slow growers) Plant Community Shifts due to Herbivory