Chapter 52 Reading Quiz

2. Chapter 52 Reading Quiz • A group of individuals of the same species hanging out in the same area at the same time is called a ____. • A bunch of nesting penguins would exhibit which pattern of dispersion? • Describe under what condition “zero population growth” occurs. • The maximum population that a particular environment can sustain is called ______. • The world population increases by about how many people per year?

3. 1. What is a population? Distinguish between density and dispersion. • Population  individuals of one species simultaneously occupying the same general area, utilizing the same resources, and influenced by similar environmental factors • Density  the number of individuals per unit area or volume • Dispersion  the pattern of spacing among individuals within the geographical boundaries of the population 

5. 2. How do scientists measure density? • May count all the individuals in a sample of representative plots; estimates become more accurate as sample plots increase in size or number • May estimate by indirect indicators such as number of nests or burrows, or by droppings or tracks • May use the mark-recapture method 

6. 3. Describe the various patterns of dispersion. • Clumped pattern  “patchy” groupings of organisms • Uniform pattern  spacing of individuals is even • Random pattern  spacing of animals varies in an unpredictable way - very uncommon in nature 

8. 4. What is demography? Why is it important to study the age structure and sex ratio of a population? • Demography  the study of the vital statistics affecting population size • Age structure  relative numbers of individuals of each age in a population • Sex ratio  the proportion of individuals of each sex found in a population 

10. 5. Overview the various survivorship curves, and list examples. • Type I curve  flat during early and middle life and drop suddenly as death rates increase among the older individuals • Type II curve  intermediate with mortality being more constant over the life span • Type III curve  show very high death rates for the young followed by lower death rates after individuals have survived to a certain critical age 

12. 6. Overview how life histories are diverse yet exhibit patterns. • Life history  an organism’s schedule of reproduction and death - life histories often vary in parallel with environmental factors - tropical birds lay fewer eggs than those in higher latitudes, which reflects the number of offspring that can successfully be fed (parent birds can gather more food) 

14. 7. Describe the concept of a trade-off between reproduction and survival. What does this have to do with offspring produced, number of matings, and age of maturation? • Relates to the principle of allocation • Episodes of reproduction  - semelparity: invest most in growth & development, then reproduce before dying - iteroparity: fewer offspring produced over many seasons • # of offspring per episode • Maturation age  balances the cost between current reproduction and survival plus future reproduction 

15. 8. Describe the conditions for the exponential model of population growth. • Describes an idealized population in an unlimited environment • Birth rates must be higher than death rates • Produces a J-shaped curve 

17. 9. Describe the concept of “carrying capacity” and logistic population growth. How does this model fit with real populations? • The “carrying capacity” of a habitat is the maximum stable population size that the particular environment can support over a relatively long time period • A “logistic population growth” model assumes the rate of population growth (r) slows as the population size reaches the carrying capacity of the environment • Some assumptions do not hold true for all populations  Ex: Populations approach carrying capacity smoothly 

19. 10. Differentiate between K-selected populations and r-selected populations. • K – selected  “equilibrium populations” - live at a density near the limits of their resources • r – selected  “opportunistic populations” - more likely to be found in variable environments where population densities fluctuate or in open or disturbed habitats where individuals have little competition 

21. 11. Describe how density-dependent factors regulate population growth. • A density-dependent factor intensifies as the population size increases, affecting each individual more strongly • Seen in intraspecific competition, where two or more individuals of the same species rely on the same resource • Ex: disease, competition 

23. 12. Describe the effects of density-independent factors on population size. • Density-independent factors are unrelated to population size and affect the same percentage of individuals regardless of the size of the population • Ex: weather, climate, natural disasters 

24. 13. How are most populations in nature regulated? • A mix of density-dependent and density-independent factors probably limits the growth of most populations • Many populations remain fairly stable in size, close to the carrying capacity determined by the density-dependent factors • Show short-term fluctuations due to the density-independent factors 

25. 14. Describe how some populations have regular boom and bust cycles. • Lemmings have a 3 – 5 year cycle • Snowshoe hares have a 9 – 11 year cycle • Crowding may regulate cyclical population by affecting the organisms endocrine systems (stress due to high density) • May result from a time lag in response to density-dependent factors, causing the population to overshoot and undershoot the carrying capacity • Cicadas have a 13 – 17 year cycle, probably an adaptation to reduce predation 

27. 15. Overview the history of human population growth. • The human population has been growing exponentially for centuries (since 1650) but will not be able to forever • The advent of agriculture 10,000 years ago increased birth rates and decreased death rates • Better sanitation and nutrition since Industrial revolution • Scientists can not agree on what the carrying capacity of humans on earth might be…hopefully it will be a smooth leveling out once we get there 