Population and Community Ecology

1. Population and Community Ecology

2. Complexity

3. Population Ecology

4. Population Change = (births + immigrations) – (deaths + emigrations)

5. Population Characteristics • Population Size (N) is the total number of individuals within a defined area at a given time • Population Density is the number of individuals per unit area (or volume) • Used to determine rarity/abundance, impact • Important for wildlife managers

6. Population Characteristics • Population Distribution is a description of how individuals are distributed with respect to one another; 3 types: • Uniform • Random • Clumped

7. Population Characteristics • Population Sex Ratio is the ratio of males to females (duh); usually 50:50 • Population Age Structure is a description of how many individuals fit into particular age categories

8. Factors Influencing Population Size • Density-Dependent Factors influence an individual’s probability of survival and reproduction that depends on size of the population • Limiting resource is a resource a population cannot live without; food, water nutrients • Carrying capacity (K) is the limit to how many individuals the food supply can support

9. Factors Influencing Population Size • Density-Independent Factors influence an individual’s probability of survival and reproduction regardless of population density • Factors include tornadoes, hurricanes, fires, volcanic eruptions and other climatic events

10. Growth Models

11. The Exponential Growth Model • Growth Rate = No. of births – No. of deaths • Intrinsic Growth Rate (r)is the maximum potential for growth of a population under ideal condition • J-shaped Curve results when rapid growth of a population not limited by resources occurs

13. The Exponential Growth Model • Mathematically, The exponential growth model is: Nt = N0ert • Nt = future population • N0 = current population • r = intrinsic growth rate • t = time • e = natural log

14. The Logistic Growth Model • Logistic Growth Model describes a population whose growth is initially exponential, but slows as the population reaches carrying capacity • S-shaped curve is the graphical result • Variations on the Logistic Model: • Overshoot occurs when a population temporarily exceeds its carrying capacity (ex. – spring births); die-off occurs

18. Reproductive strategies

19. K-Selected Species • Abundance determined by carrying capacity • Low intrinsic growth rate • Typically are large organisms • Late reproductive maturity • Produce few, large offspring • Provide substantial parental care

20. r-Selected Species • High intrinsic growth rate (r) • Rapid population growth followed by overshoots and die-offs • Tend to be small organisms • Early reproductive maturity • Reproduce frequently, producing many offspring • Provide little or no parental care

21. Survivorship Curves

22. Species interactions

23. Competition • The struggle of individuals to obtain a limiting resource • Competitive exclusion principle states that two species competing for the same limiting resource cannot coexist • Resource partitioning can result if two species divide a resource based on differences in behavior and morphology

24. Competition • Temporal partitioning different species hunt at different times • Spatial partitioning different species reduce competition by using different habitats • Morphological partitioning over time, species evolve morphologically to reduce competition (Darwin’s finches)

26. Predation • True predators kill their prey and consume most • Herbivores consume plants • Parasites live on or in the organism (host); rarely kill the host; a type of symbiosis • Pathogens are parasites that cause disease • Parasitoids lay eggs inside other organisms

27. Mutualism • Will benefit two interacting species by increasing both species’ chances of survival • Example – pollinators • A type of symbiosis

28. Commensalism • Relationship in which one of the interacting species benefits but the other is neither harmed nor helped • A type of symbiosis

29. Keystone Species • Species that plays an important role in a community • Typically exist in low numbers • May be predators, sources of food, mutualistic species, or providers of some other essential service • Ecosystem engineers

30. Invasive Species • Invasive Species

31. Communities change over time

32. Primary Succession • Occurs on surfaces initially devoid of soil • Examples: abandoned parking lot, rock after glacial retreat, newly cooled lava • Type of community that develops depends on climate

33. Secondary Succession • Occurs in areas that have been disturbed but have not lost their soil • May follow events such as hurricanes, tornadoes, etc • Pioneer species colonize new areas rapidly

34. Aquatic Succession • Most common example: freshwater lakes

35. Factors affecting species richness

36. Latitude • Number of species declines as one moves northward/southward of the equator • Southern U.S.: 12,000 species, Canada: 1,700 species

37. Time • The longer a habitat exists, the more the colonization, speciation, and extinction can occur

38. Habitat Size and Distance • Theory of island biogeography: dual importance of habitat size and distance from colonizing species determines species richness • Larger habitats can support larger populations • Oceanic islands farther from continents tend to have fewer species