1. Chapter 6 Population and Community Ecology

2. New England Forests Come Full Circle 1620 Over next 200 years – settlers Deforestation peaked in 1800s – 80% of New England forests were cleared Bw 1850-1950 Abandoned farmland slowly recovered – resilient area This created an ever-changing ecosystem

3. Nature exists at several levels of complexity

4. Population Ecologists Study the Factors that Regulate Population Abundance and Distribution Population ecology – the study of factors that cause populations to increase or decrease Why is this important?

5. Population Characteristics Population size (N)- the total number of individuals within a defined area at a given time Population density- the number of individuals per unit area at a given time Population distribution- how individuals are distributed with respect to one another

6. Population Characteristics Population sex ratio- the ratio of males to females Population age structure- how many individuals fit into particular age categories

7. Factors that Influence Population Size Density-dependent factors- the size of the population will influence an individual’s probability of survival Gause Limiting resource Carrying capacity (K) Density-independent factors- the size of the population has no effect on the individual’s probability of survival

8. Population Growth Rate Population growth models Growth rate - the number of offspring an individual can produce in a given time period, minus the deaths of the individual or offspring during the same period Intrinsic growth rate - under ideal conditions, with unlimited resources, the maximum potential for growth Under less ideal conditions

9. Exponential Growth Model Exponential growth model formula What results?  J-shaped curve However…

10. Logistic Growth Model Logistic growth- when a population whose growth is initially exponential, but slows as the population approaches the carrying capacity Produces - S-shaped curve Problem

11. Variations of the Logistic Model Populations do not always level off at carrying capacity Overshooting K – population becomes larger than the K Result? Ie. reindeer on St. Paul Island in Alaska

12. From Environment: Boom-Or-Bust Population Cycles Boom-or-Bust Population Cycles Not well understood Ie. Lemmings and red grouse populations

13. Population Oscillations Predator-Prey Relationships Lynx and Hares (R) Wolves and moose

14. Reproductive Strategies K-selected species- the population of a species that grows slowly until it reaches the carrying capacity. Ex. elephants, whales, and humans R-selected species- the population of a species that grows quickly and is often followed by overshoots and die-offs Ex. mosquitoes and dandelions

16. Survivorship Curves Species have different patterns of survival over time 3 basic curves: Type I Type II Type III

17. Metapopulations Metapopulations- a group of spatially distinct populations that are connected by occasional movements of individuals between them Movement via corridors Connections important

18. Community Ecology Factors to determine distribution of species: Species’ fundamental niche Ability to disperse to an area Interactions with other species Community ecology – study of the interactions of organisms which determine the survival of a species in a habitat

19. Competition Competition- the struggle of individuals to obtain a limiting resource Gause’s Competitive Exclusion Principle

20. From Environment: Anoles in FL Example Green Anole and Brown Anole Fundamental niches of 2 lizards initially overlapped Brown anole eventually out-competed the green anole  reduced the green anole’s realized niche

21. Resource Partitioning Resource partitioning – when 2 species divide a resource based on differences in the species’ behavior or morphology Species in nature reduce resource overlap via: Temporal resource partitioning Spatial resource partitioning Morphological resource partitioning

23. Predation Predation- the use of one species as a resource by another species Organisms of all sizes can be predators Predators can be grouped: True predators Herbivores Parasites Pathogens – parasites that cause disease Parasitoids Awesome video: http://www.youtube.com/watch?v=nZZyJQNmOV8http://www.youtube.com/watch?v=nZZyJQNmOV8

24. Mutualism Mutualism- A type of interspecific interaction where both species benefit Examples: Plants and pollinators Image – Acacia trees and ants Lichen Coral reefs

25. Commensalism Commensalism- a type of relationship in which one species benefits but the other is neither harmed nor helped Examples…

26. Overview of Interspecific Interactions Symbiotic relationship – relationship of 2 species that live in close association with each other Includes: commensalism, mutualism and parasitism

27. Keystone Species Keystone species- a species that plays a role in its community that is far more important than its relative abundance might suggest Usually not the most abundant or major energy producers Roles include: Predators Sources of food Mutualistic Providers of some other essential service

28. Keystone Species The Gray Wolf Where wolves were hunted to extinction  populations herbivores increased explosively Caused overgrazing  some plant species disappeared Many insects were lost Indiana and Montana- hunting of gray wolf ok…

29. Primary Succession Primary succession- occurs on surfaces that are initially devoid of soil Process: Bare rock is colonized by organisms  secrete acids

30. Secondary Succession Secondary succession- occurs in areas that have been disturbed but have not lost their soil Follows events like: forest fires, hurricanes, abandoned fields

31. Climax Stage Climax stage (community) – the community scientists used to believe ended succession Characteristics: Complex structures – many species interactions Narrow niches High species diversity

32. Aquatic Succession Lakes are filled with sediment Slowly become terrestrial habitat Explain the process

33. Factors that determine species richness: Latitude Time Habitat size and distance from habitat from source of colonizing species Basis for the Theory of Island Biography (next slide)

34. Theory of Island Biogeography Theory of island biogeography- the theory that explains that both habitat size and distance determine species richness Larger habitats contain more species Why? Further from colonizing community  the less species