1. Chapter 6 Population and Community Ecology

2. Nature exists at several levels of complexity

3. Populations Can Grow, Shrink, or Remain Stable Population size governed by Births Deaths Immigration Emigration Population change = (births + immigration) – (deaths + emigration)

4. Factors that Regulate Population Abundance and Distribution Population size ( N )- the total number of individuals within a defined area at a given time. Trying to Save the California Condor Nearly extinct (22) by 1987 Birds captured and bred in captivity By 2009, 180 in the wild (348 total) Threatened by lead poisoning

5. Factors that Regulate Population Abundance and Distribution Population density- the number of individuals per unit area at a given time. Population distribution- how individuals are distributed with respect to one another. Commonly see in plant species Commonly see in territorial or toxic species Provides extra protection Gather around resources

6. Most Populations Live Together in Clumps or Patches 1. Species tend to cluster where resources are available 2. Groups have a better chance of finding clumped resources (such as grass and water) 3. Protects some animals from predators 4. Packs allow some to get prey

7. Generalized Dispersion Patterns Fig. 5-12, p. 112 Where resources are scarce, uniform dispersion is more common. Where resources are plentiful, random dispersion is more likely.

8. Factors that Regulate Population Abundance and Distribution Population sex ratio- the ratio of males to females Population age structure- how many individuals fit into particular age categories. Age structure Pre-reproductive age Reproductive age Post-reproductive age Age Structure Pyramid

9. Factors that Influence Population Size Density-dependent factors- the size of the population will influence an individual’s probability of survival. Limiting factor principle Too much or too little of any physical or chemical factor can limit or prevent growth of a population, even if all other factors are at or near the optimal range of tolerance

10. Limiting Factors that Control Population Growth Precipitation (most important terrestrial) Light Water Space Nutrients Exposure to too many competitors, predators or infectious diseases Specific to aquatic ecosystems: DO, salinity

11. No Population Can Grow Indefinitely Environmental resistance All factors that act to limit the growth of a population Carrying capacity (K) Maximum population a given habitat can sustain Intrinsic rate of growth (r) Maximum potential for growth for a population under ideal conditions, with unlimited resources available

12. Some Factors Can Limit Population Size Range of tolerance Variations in physical and chemical environment Trout Tolerance of Temperature

13. Factors that Influence Population Size Density-independent factors- the size of the population has no effect on the individual’s probability of survival. Often include climatic events

14. Population calculations Growth rate = births - deaths Percent growth = (final / initial) x 100 Exponential growth = N t = future population N 0 = present population e = 2.72 (e x ) r = growth rate t= time

15. Exponential Growth Model J-shaped curve- when graphed the exponential growth model looks like this. Exponential growth Starts slowly, then accelerates to carrying capacity when meets environmental resistance

16. Logistic Growth Model Logistic growth- when a population whose growth is initially exponential, but slows as the population approaches the carrying capacity. S-shaped curve- when graphed the logistic growth model produces an “S”.

17. Variations of the Logistic Model If food becomes scarce, the population will experience an overshoot by becoming larger than the spring carrying capacity and will result in a die-off, or population crash.

18. Several Different Types of Population Change Occur in Nature Stable Irruptive Population surge, followed by crash Cyclic fluctuations, boom-and-bust cycles Top-down population regulation Bottom-up population regulation Irregular Fig. 5-18, p. 118

19. Humans Are Not Exempt from Nature’s Population Controls Ireland Potato crop in 1845 Bubonic plague Fourteenth century AIDS Global epidemic

20. Species Have Different Reproductive Patterns A species’ biotic potential is the fastest rate at which its populations can grow. This rate is limited by reproductive potential. Reproductive potential is the maximum number of offspring that a given organism can produce. Reproductive potential increases when 1. individuals produce more offspring at a time, 2. Reproduce more often, and 3. reproduce earlier in life.

21. K-selected species Live right below carrying capacity in stable, predictable environment Small number of offspring with long life spans Populations are constant & competitive Long time to maturity Reproduce later in life Protected by parents, and potentially groups Elephants, humans

22. r-selected species Usually live in unstable or unpredictable environments Ability to disperse offspring widely Many, usually small, offspring Little or no parental care Massive deaths of offspring Short generation time High fecundity Insects, bacteria, algae

23. Types of Survivorship Curves

24. Metapopulations Metapopulations- a group of spatially distinct populations that are connected by occasional movements of individuals between them. Usually healthier than a single population Animals can follow resources Greater sources for genetic diversity Could be detrimental to small populations

25. Species Interact in Five Major Ways

26. Competitive Exclusion Principle Specialist Species of Honeycreepers Fig. 5-3, p. 107 two species competing for the same limiting resource cannot coexist

27. Resource Partitioning Among Warblers Fig. 5-2, p. 106 Resource partitioning Using only parts of resource Using at different times Using in different ways

28. Three Types of Resource Partitioning

29. Types of Predation Predation- the use of one species as a resource by another species. True predators- kill their prey. Herbivores- consume plants as prey. Parasites- live on or in the organism they consume (rarely kill host, much smaller than host). Parasitoids- lay eggs inside other organisms.

30. Prey avoid capture by: 1. Run, swim, fly 2. Protection: shells, bark, thorns 3. Camouflage 4. Chemical warfare 5. Warning coloration 6. Mimicry 7. Deceptive looks 8. Deceptive behavior Fig. 5-5, p. 109

31. In Some Interactions, Both Species Benefit Mutualism Nutrition and protection relationship Gut inhabitant mutualism Not cooperation: it’s mutual exploitation Fig. 5-8, p. 110

32. In Some Interactions, One Species Benefits and the Other Is Not Harmed Commensalism Epiphytes Birds nesting in trees Fig. 5-10, p. 111

33. Keystone Species Keystone species- a species that plays a role in its community that is far more important than its relative abundance might suggest. I’m an ecosystem engineer!

34. PREDATOR-MEDIATED COMPETITION

35. Primary Succession Primary succession- occurs on surfaces that are initially devoid of soil. No soil in a terrestrial system Takes hundreds to thousands of years Need to build up soils to provide necessary nutrients

36. Aquatic Succession No bottom sediment in an aquatic system Takes hundreds to thousands of years Need to build up sediments to provide necessary nutrients

37. Secondary Succession Secondary succession- occurs in areas that have been disturbed but have not lost their soil. Some soil remains in a terrestrial system Ecosystem has been Disturbed Removed Destroyed

38. Some Ecosystems Do Not Have to Start from Scratch: Secondary Succession Primary and secondary succession Tend to increase biodiversity Increase species richness and interactions among species Primary and secondary succession can be interrupted by Fires Hurricanes Clear-cutting of forests Plowing of grasslands Invasion by nonnative species Fig. 5-21, p. 120 Secondary Ecological Succession in Yellowstone Following the 1998 Fire

39. Factors that determine species richness: Latitude As we move from the equator towards the poles, the number of species declines. Time The longer a habitat exists, the more colonization, speciation, and extinction can occur there. Habitat size Larger habitats usually contain more species.

40. Species Richness on Islands Theory of island biogeography Dispersing species are more likely to find larger islands than smaller islands. Larger habitats can support more species Larger habitats contain more varied environmental conditions. Oceanic islands that are more distant from continents generally have fewer species than islands that are closer.