Chapter 4 Evolution, Biodiversity, and Community Ecology

1. Chapter 4 Evolution, Biodiversity, and Community Ecology

2. Where we’re going • We’ll look at populations and communities- from the perspective of Joe Rabbit • Lots of terms! But I’ll try to integrate them better. • Diversity, niche, reproductive capacity, models for growth, competition, predation, etc.

3. Nature exists at several levels of complexity Joe- or Bunny Fu-Fu

4. Nature exists at several levels of complexity Here’s Joe. He lives in my back yard. He lives there because it’s a good habitat- it’s his ecological niche Joe’s niche is constrained by both Biotic and Abiotic factors. Joe’s not picky, so he can live just about anywhere! Other creatures are more specialized. Niche might be easier to consider if you think about a plant- it grows better under some conditions than others- it might still grow, but poorly, in one type of soil, for instance.

5. All sorts of conditions make for a good niche- there are some places that Joe tolerates, others that he thrives in

6. Niches Realized niche―the range of abiotic and biotic conditions under which a species lives. This determines the species distribution, or areas of the world where it lives. Niche generalist―species that live under a wide range of conditions Niche specialist―species that live only in specific habitats

7. Nature exists at several levels of complexity Joe and the other rabbits in the backyard ecosystem make up a population- set of interbreeding organisms of the same species that live in the same area at a particular time. So we could talk about the Duluth Rabbit population, Superior Rabbit population, etc. We might want to know the population’s SIZE and/or DENSITY- just like in human populations. Your book talks about other things we might measure if we wanted to take the time to do so. We also want to know how the population GROWS

8. What controls the Rabbit Population? • Optimum Reproductive rate- growth rate • Density dependent things (changes with the density of rabbits): • Available food • Predators! • Disease • Density independent things- harsh winters, floods, etc. • A habitat will have a maximum carrying capacity (denoted K)

9. How do populations grow? • When not restrained- J curves • When restrained- more typically- S curves.

10. Exponential Growth Model J-shaped curve: when graphed, the exponential growth model looks like this:

13. Variations of the Logistic Model Overshoot and die-off.

14. Reproductive Strategies K-selected species (strategists):the population of a species that grows slowly until it reaches the carrying capacity. Abundance is determined by carrying capacity, hence the use of “K”. (Also, “Karing” Examples include elephants, whales, and humans.

15. Reproductive Strategies R-selected species: the population of a species that grows quickly, and is often followed by overshoots and die-offs. So-called because “r” denotes the intrinsic growth rate. Lots of reproduction, little care for young Examples include mosquitoes and dandelions.

16. So is Joe a K or R strategist?

17. Nature exists at several levels of complexity Joe lives in a community of interacting species- both plants and animals- Together with the abiotic elements, they would make up an ecosystem. How can we characterize his community? By SPECIES DIVERSITY Two measurements- species RICHNESS and EVENNESS Think of a LAWN vs a MEADOW

18. Species richness―the number of species in a given area Species evenness―the measure of whether a particular ecosystem is numerically dominated by one species or are all represented by similar numbers of individuals

19. Community ecologists study species interactions.Competition PredationMutualism and commensalism

20. Competition Competition: individuals struggling to obtain a limiting resource.

21. Competition

22. Competition Competitive exclusion principle: two species competing for the same limiting resources cannot coexist. This can lead to resource partitioning. Resource partitioning: two species co-evolve to divide a limiting resource, through differences in species behavior or form.

23. Resource Partitioning

24. Predation Predation: the use of one species as a resource (food!) by another species. Predators are found in four forms: true predators, herbivores, parasites, and parasitoids.

25. Predation True predators: kill their prey. Herbivores: consume plants as prey. Parasites: live on or in the organism they consume. If they cause disease, they are pathogens. Parasitoids: lay eggs inside other organisms.

26. Commensalism Commensalism:a type of relationship in which one species benefits but the other is neither harmed nor helped.

27. Symbiosis Symbiotic relationships: two species live in close association. Commensalism, mutualism, and parasitism are all examples of symbiotic relationships.

28. Summary of Species Interactions + is a positive effect,  negative, and 0 is neutral.

29. Keystone Species Keystone species: a species that plays a role in its community that is far more important than its relative abundance might suggest.

30. Keystone Species Keystone species typically exist in low numbers. They may be predators, sources of food, mutualistic species, or providers of other ecological services. For instance, North American beavers can act as ecological engineers, modifying their environment in ways that create and maintain their habitat.

31. The Composition of a Community Changes over Time and is Influenced by Many Factors

32. Ecological Succession Ecological succession occurs as: Primary succession Secondary succession Aquatic succession

33. Primary Succession Primary succession: occurs on surfaces that are initially devoid of soil. This might happen after a volcano eruption, or a long time ago

34. Primary Succession

35. Secondary Succession Secondary succession: occurs in areas that have been disturbed but have not lost their soil.

36. Factors that determine species richness Latitude: moving north or south away form the equator, species richness declines. Time: older habitats show more variety of species.

37. Factors that determine species richness Habitat size and distance: size of the habitat and distance from the colonizing species affects the number and types of species. This is the basis for the theory of island biogeography.

38. Review Questions 1. What are three forms of biodiversity? 2. What is the difference between species richness and species evenness? 3. Distinguish macroevolution form microevolution. What is the result of each process? 4. What are genes? What is meant by “genotype”?

39. Review Questions 14. List the levels of complexity that make up the biosphere. 15. What are the three ways in which a population can be distributed? 16. What is the difference between a density-dependent and a density-independent factor?

40. Review Questions 17. What is the difference between a density-dependent and a density-independent factor? 18. Give an example of each type of factor. 19. The J-shaped curve is associated with what model? 20. The S-shaped curve is associated with what model?

41. Review Questions 21. How is a die-off associated with carrying capacity? 22. What are some characteristics of an r- selected species? Give an example. 23. Name and describe the four forms of predation.

42. Review Questions 24. What is a pathogen? 25. Distinguish mutualism from commensalism. 26. What is a keystone species? Why are they important in ecosystems?

43. Review Questions 27. What is primary succession? 28. What are the two factors underlying the theory of island biogeography?