Ecological and Evolutionary Consequences of Species Interactions

1. 44 Ecological and EvolutionaryConsequences of SpeciesInteractions

2. Chapter 44 Ecological and Evolutionary Consequences of Species Interactions • Key Concepts • 44.1 Interactions between Species May Be Positive, Negative, or Neutral • 44.2 Interspecific Interactions Affect Population Dynamics and Species Distributions • 44.3 Interactions Affect Individual Fitness and Can Result in Evolution • 44.4 Introduced Species Alter Interspecific Interactions

3. Chapter 44 Opening Question How could the intricate ecological relationship between leaf-cutter ants and fungi have evolved?

4. Concept 44.1 Interactions between Species May BePositive, Negative, or Neutral Interspecific interactions (between individuals of different species) affect population densities, species distributions, and ultimately lead to evolutionary changes. The interactions can be beneficial or detrimental to either of the species.

5. Figure 44.1 Types of Interspecific Interactions (Part 1)

6. Concept 44.1 Interactions between Species May BePositive, Negative, or Neutral Interspecific competition refers to–/– interactions Members of two or more species use the same resource. At any one time there is often one limiting resource in the shortest supply relative to demand.

7. Figure 44.1 Types of Interspecific Interactions (Part 2)

8. Concept 44.1 Interactions between Species May BePositive, Negative, or Neutral Consumer–resource interactions—organisms get their nutrition by eating other living organisms. +/– interactions—the consumer benefits while the consumed organism loses Includes predation, herbivory, and parasitism.

9. Figure 44.1 Types of Interspecific Interactions (Part 3)

10. Concept 44.1 Interactions between Species May BePositive, Negative, or Neutral Mutualism benefits both species: +/+ interaction Examples: Leaf-cutter ants and the fungi they cultivate Plants and pollinating or seed-dispersing animals Humans and bifidobacteria in our guts Plants and mycorrhizal fungi Lichens Corals and dinoflagellates

11. Figure 44.1 Types of Interspecific Interactions (Part 4)

12. Concept 44.1 Interactions between Species May BePositive, Negative, or Neutral Commensalism—one species benefits while the other is unaffected (+/0 interaction). Brown-headed cowbird follows grazing cattle and bison, foraging on insects flushed from the vegetation. Cattle convert plants into dung, which dung beetles can use. Dung beetles disperse other dung-living organisms such as mites and nematodes, which attach themselves to the bodies of the beetles.

13. Concept 44.1 Interactions between Species May BePositive, Negative, or Neutral Amensalism—one species is harmed while the other is unaffected (–/0 interactions). Tend to be more accidental than other relationships. Example: a herd of elephants that crush plants and insects while moving through a forest.

14. Concept 44.1 Interactions between Species May BePositive, Negative, or Neutral Relationships between species do not always fit perfectly into these categories. Fish that live with sea anemones escape predation by hiding in the anemone tentacles. Effects of this on the anemones is unclear. Do the fish steal some of their prey? Do they get nutrients from fish feces? It may depend on the availability of nutrients.

15. Figure 44.2 Interactions between Species Are Not Always Clear-Cut

16. Concept 44.2 Interspecific Interactions Affect Population Dynamics and Species Distributions Density-dependent population growth reflects intraspecific (within-species) interactions among individuals in a population. They are usually detrimental because per capita resource availability decreases as population density increases.

17. Concept 44.2 Interspecific Interactions Affect Population Dynamics and Species Distributions Interspecific interactions also modify per capita growth rates: Interspecific competition—effect of the other species would be subtracted in the growth model. Consumer–resource interactions—effect of the consumer is subtracted in the equation for the resource species; the effect of the resource is added in the equation for the consumer, since the consumer benefits.

18. Concept 44.2 Interspecific Interactions Affect Population Dynamics and Species Distributions Populations show different dynamics in the presence or absence of other species. This was demonstrated in classic experiments with species of Paramecium.

19. Figure 44.3 Interspecific Competition Affects Population Growth (Part 1)

20. Figure 44.3 Interspecific Competition Affects Population Growth (Part 2)

21. Concept 44.2 Interspecific Interactions Affect Population Dynamics and Species Distributions Conclusions from the Paramecium studies, and from mathematical models: Presence of a competitor always reduces population growth rate. When two species coexist, they have lower equilibrium population densities than either would alone. In some cases, competition causes one species to go extinct.

22. Concept 44.2 Interspecific Interactions Affect Population Dynamics and Species Distributions Other types of interspecific interactions have similar consequences: Per capita growth rate of each species is modified by the presence of the other, positively or negatively. Population densities are increased in positive interactions and decreased in negative interactions. In interactions with negative effects, extinction of one or both species is possible.

23. Concept 44.2 Interspecific Interactions Affect Population Dynamics and Species Distributions Interspecific interactions can affect the distributions of species. Competitive interactions can restrict the habitats in which species occur. Two barnacle species compete for space on the rocky shorelines of the North Atlantic, with no overlap between zones occupied. A classic experiment removed each species and observed response of the other species.

24. Figure 44.4 Interspecific Competition Can Restrict Distributions

25. Concept 44.2 Interspecific Interactions Affect Population Dynamics and Species Distributions Two competitors can coexist when each species suppresses its own per capita growth rate more than it suppresses the per capita growth rate of its competitor. Intraspecific competition must be stronger than interspecific competition.

26. Concept 44.2 Interspecific Interactions Affect Population Dynamics and Species Distributions A species has a growth advantage when it is at a low density and its competitor is at a high density. This rarity advantage prevents the species from decreasing to zero. Result is coexistence.

27. Concept 44.2 Interspecific Interactions Affect Population Dynamics and Species Distributions Resource partitioning—different ways of using a resource. Example: Paramecium caudatum can coexist with P. bursaria. P. bursaria can feed on bacteria in the low-oxygen sediment layer at the bottom of culture flasks. P. bursaria has symbiotic algae that provides it with oxygen from photosynthesis.

28. Figure 44.5 Resource Partitioning Can Result in Intraspecific Competition Being Greater than Interspecific Competition

29. Concept 44.2 Interspecific Interactions Affect Population Dynamics and Species Distributions Prey species may gain a rarity advantage that prevents them from being driven extinct by their predators. They may be harder to find and predators may switch to other prey species. They may invest in more defenses—low density means more resources per capita. Other limiting factors may prevent predators from becoming numerous enough to eat all the prey

30. Concept 44.3 Interactions Affect Individual Fitnessand Can Result in Evolution Species interactions can affect individual fitness. Phenotypes that gain the most from a positive interaction or suffer least from a negative interaction will increase in frequency in the population, and the population will evolve.

31. Concept 44.3 Interactions Affect Individual Fitnessand Can Result in Evolution Intraspecific competition—density-dependent growth models assume all individuals in a population are equally affected by density. But individuals vary, and some traits may increase the ability to obtain resources. Natural selection will favor the trait and its frequency will increase in the population (directional selection). More resources will be available for this phenotype, increasing the carrying capacity.

32. Concept 44.3 Interactions Affect Individual Fitnessand Can Result in Evolution Interspecific competition Variation in traits can affect sensitivity to interspecific competition. Resource partitioning as an evolutionary response: Finch species in the Galápagos Islands have varying beak sizes; beak sizes match sizes of available seeds.

33. Figure 44.6 Resource Paritioning Allows Competitors to Coexist (Part 1)

34. Figure 44.6 Resource Paritioning Allows Competitors to Coexist (Part 2)

35. Figure 44.6 Resource Paritioning Allows Competitors to Coexist (Part 3)

36. Concept 44.3 Interactions Affect Individual Fitnessand Can Result in Evolution In one finch species on the Galápagos Islands, small individuals feed more on nectar, larger individuals feed more on seeds. On islands where carpenter bees are present and compete for nectar, the finches tend to be larger and eat more seeds. The finch resource use has diverged from their bee competitors on islands where they coexist.

37. Figure 44.7 Finch Morphology Evolves in Response to Competition with Carpenter Bees (Part 1)

38. Figure 44.7 Finch Morphology Evolves in Response to Competition with Carpenter Bees (Part 2)

39. Figure 44.7 Finch Morphology Evolves in Response to Competition with Carpenter Bees (Part 3)

40. Concept 44.3 Interactions Affect Individual Fitnessand Can Result in Evolution Consumer–resource interactions The opposing interests of the consumer and the resource species can lead to an “evolutionary arms race,”—prey continually evolve better defenses and predators continually evolve better offenses.

41. Concept 44.3 Interactions Affect Individual Fitnessand Can Result in Evolution Strategies of resource species: Use speed, size, or weapons to thwart predators. Hide or use camouflage Mimic unpalatable species Sessile species have thick armor or are non-nutritive or poisonous.

42. Figure 44.8 Defense Mechanisms and “Arms Races” (Part 1)

43. Concept 44.3 Interactions Affect Individual Fitnessand Can Result in Evolution Strategies of consumers: Greater speed, size, or strength Keen senses Armor-piercing or crushing tools Means of detoxifying poisons

44. Figure 44.8 Defense Mechanisms and “Arms Races” (Part 2)

45. Concept 44.3 Interactions Affect Individual Fitnessand Can Result in Evolution Plants produce a variety of toxic chemicals against herbivores and pathogens. Some of these chemicals we use as spices, etc.: black pepper, chili peppers, caffeine. Herbivores evolve ways to deal with the chemicals.

46. Concept 44.3 Interactions Affect Individual Fitnessand Can Result in Evolution Heliconius butterflies store or detoxify the cyanide compounds of passionflower and use them as defense against their own predators. Some passionflower species have leaf structures that resemble butterfly eggs. Females will not lay eggs on a plant that already has eggs.

47. Figure 44.9 Using Mimicry to Avoid Being Eaten

48. Concept 44.3 Interactions Affect Individual Fitnessand Can Result in Evolution Mutualisms Species benefit other species because acting in their own self-interest happens to benefit others. Most pollinators visit flowers to get food and happen to pollinate the flowers in the process; flowers provide food (usually as little as possible) to lure the animals.

49. Concept 44.3 Interactions Affect Individual Fitnessand Can Result in Evolution All mutualisms involve the exchange of resources and services. The fitness effect of the mutualism can vary depending on environmental conditions. Example: Mycorrhizae benefit plants in nutrient-poor soils, but can be a liability in nutrient-rich soils, where the cost of feeding the mycorrhizae outweighs their value in nutrient uptake.

50. Concept 44.3 Interactions Affect Individual Fitnessand Can Result in Evolution Cheating in mutualisms: Some flowers mimic the form and smell of female insects and are pollinated when males attempt to copulate with them. Some bees bite holes in the base of flowers and eat the nectar without pollinating the flower.