Populations

1. 43 Populations

2. Chapter 43 Populations • Key Concepts • 43.1 Populations Are Patchy in Space and Dynamic over Time • 43.2 Births Increase and Deaths Decrease Population Size • 43.3 Life Histories Determine Population Growth Rates • 43.4 Populations Grow Multiplicatively, but Not for Long

3. Chapter 43 Populations Key Concepts 43.5 Extinction and Recolonization Affect Population Dynamics 43.6 Ecology Provides Tools for Managing Populations

4. Chapter 43 Opening Question How does understanding the population ecology of disease vectors help us combat infectious diseases?

5. Concept 43.1 Populations Are Patchy in Space and Dynamic over Time Population—all the individuals of a species that interact with one another within a given area at a particular time. Humans have long been interested in understanding species abundance: to increase populations of species that provide resources and food and to conserve species for ethical and aesthetic reasons to decrease abundance of crop pests, pathogens, etc.

6. Concept 43.1 Populations Are Patchy in Space and Dynamic over Time Population density—number of individuals per unit of area or volume Population size—total number of individuals in a population Counting all individuals is usually not feasible; ecologists often measure density, then multiply by the area occupied by the population to get population size.

7. Concept 43.1 Populations Are Patchy in Space and Dynamic over Time Abundance varies on several spatial scales. Geographic range—region in which a species is found Within that region, it’s range, species may be restricted to specific suitable environments or habitats which may be scattered across the species geographic range. Habitat patches are “islands” of suitable habitat separated by areas of unsuitable habitat.

8. Figure 43.1 Species Are Patchily Distributed on Several Spatial Scales (Part 1)

9. Concept 43.1 Populations Are Patchy in Space and Dynamic over Time Population densities are dynamic—they change over time. Density of one species population may be related to density of other species populations.

10. Read the acorn connection.

11. Figure 43.2 Population Densities Are Dynamic and Interconnected

12. Concept 43.2 Births Increase and Deaths Decrease Population Size Change in population size depends on the number of births and deaths over a given time. “Birth–death” or BD model of population change: N =pop size B=number of births in the time interval from t to t+1 D = number of deaths in the same time interval

13. Concept 43.2 Births Increase and Deaths Decrease Population Size Population growth rate (how fast it is changing): a pop of red foxes is at 100. 1 year later after 65 babies are born at 25 fatalities, the population is at _____? 140 – 100 =40 =Change N To figure out the rate of population change we simply divide the change in N (pop), by the change in T(time). 40/1year =40foxes per year. This is the pop growth rate.

14. Concept 43.2 Births Increase and Deaths Decrease Population Size Per capita birth rate (b)—number of offspring an average individual produces 65 foxes added/100 foxes initial. B=.65 Per capita death rate (d)—average individual’s chance of dying 25 foxes died/100 intial foxes Per capita growth rate (r) = (b – d) = average individual’s contribution to total population growth rate

15. Concept 43.2 Births Increase and Deaths Decrease Population Size Lets not over complicate things. Its really simple. If b > d, then r > 0, and the population grows. If per capita birthrate > per capita death rate, population grows. If b < d, then r < 0, and the population shrinks. If per capita births is less than per capita deaths, pop shrinks. If b = d, then r = 0, and population size does not change.

16. Concept 43.3 Life Histories Determine Population Growth Rates Life history—time course of growth and development, reproduction, and death during an average individual’s life Life histories are quantitative descriptions of life cycles. Example: the life cycle of the black-legged tick.

17. Figure 43.3 Life History of the Black-Legged Tick

18. Concept 43.3 Life Histories Determine Population Growth Rates A life table shows ages at which individuals make life cycle transitions and how many individuals do so successfully. Life tables have two types of information: survivorship—fraction of individuals that survive from birth to different life stages or ages fecundity—average number of offspring each individual produces at those life stages or ages

19. Birth and Death Rates Lesson 4.3 Population Growth • A population’s relative birth and death rates (mortality and natality) affect how it grows. • Survivorship curves show how the likelihood of death varies with age.

20. Concept 43.3 Life Histories Determine Population Growth Rates Life histories vary among species: how many and what types of developmental stages, age of first reproduction, frequency of reproduction, how many offspring they produce, and how long they live. Life histories can vary within a species. For example, different human populations have different life expectancies and age of sexual maturity.

21. Concept 43.3 Life Histories Determine Population Growth Rates Individual organisms require resources (materials and energy) and physical conditions they can tolerate. Rate at which an organism can acquire resources increases with the availability of the resources. Examples: photosynthetic rate increases with sunlight intensity, or an animal’s rate of food intake increases with the density of food.

22. Population Density Lesson 4.2 Describing Populations • Measure of how crowded a population is • Larger organisms generally have lower population densities. • Low population density:More space, resources; finding mates can be difficult • High population density:Finding mates is easier; tends to be more competition; more infectious disease; more vulnerability to predators Northern pintail ducks

23. Figure 43.4 Resource Acquisition Increases with Resource Availability (Part 1)

24. Figure 43.4 Resource Acquisition Increases with Resource Availability (Part 2)

25. Figure 43.4 Resource Acquisition Increases with Resource Availability (Part 3)

26. Figure 43.4 Resource Acquisition Increases with Resource Availability (Part 4)

27. Concept 43.3 Life Histories Determine Population Growth Rates Principle of allocation—once an organism has acquired a unit of some resource, it can be used for only one function at a time: maintenance, foraging, growth, defense, or reproduction. In stressful conditions, more resources go to maintaining homeostasis. Once an organism has more resources than it needs for maintenance, it can allocate the excess to other functions.

28. Figure 43.5 The Principle of Allocation

29. Concept 43.3 Life Histories Determine Population Growth Rates In general, as average individuals in a population acquire more resources, the average fecundity, survivorship, and per capita growth rate increase.

30. Concept 43.3 Life Histories Determine Population Growth Rates Life-history tradeoffs—negative relationships among growth, reproduction, and survival Example: investments in reproduction may be at the expense of adult survivorship or growth. For example a tree expends lots of energy producing flowers to attract pollinators and fruit to protect seed. That energy cannot be directed for any other function, ie growth of the parent organism. Environment is also a factor: if high mortality rates are likely, it makes sense to invest in early reproduction. These species have high fecundity, but relatively short lifespans (spiders).

31. You have 100 to invest. Option A will give you 10% interest per day Option B will give you $10 per day

32. Concept 43.4 Populations Grow Multiplicatively, but Not for Long Population growth is multiplicative—an ever-larger number of individuals is added in each successive time period. This is exponential growth, growth at a constant rate In additive growth, a constant number (rather than a constant multiple) is added in each time period.

33. In-Text Art, Ch. 43, p. 850

34. Exponential Growth Lesson 4.3 Population Growth • Population increases by a fixed percentage every year. • Normally occurs only when small populations are introduced to an area with ideal environmental conditions • Rarely lasts long. Once resources are used up, a pop crash usually follows.

35. Human Population Growth Lesson 1.1 Our Island, Earth •Tremendous and rapid human population growth can be attributed to: •The Agricultural Revolution: About 10,000 years ago; humans began living in villages, had longer life spans, and more surviving children. • Industrial Revolution: Began in early 1700s; driven by fossil fuels and technological advances Did You Know? The human population increases by about 200,000 people every day.

36. Concept 43.4 Populations Grow Multiplicatively, but Not for Long Charles Darwin was aware of the power of multiplicative growth: “As more individuals are produced than can possibly survive, there must in every case be a struggle for existence.” This ecological struggle for existence, fueled by multiplicative growth, drives natural selection and adaptation.

37. Concept 43.4 Populations Grow Multiplicatively, but Not for Long Populations do not grow multiplicatively for very long. Growth slows and reaches a more or less steady size:

38. Logistic Growth and Limiting Factors Lesson 4.3 Population Growth • Growth almost always slows and stops due to limiting factors. • Limiting factors:Environmental characteristics slow population growth and determine carrying capacity. • Density-dependent:Influence changes with population density. • Density-independent:Influence does not change with population density.

39. Concept 43.4 Populations Grow Multiplicatively, but Not for Long r decreases as the population becomes more crowded; r is density dependent. As the population grows and becomes more crowded, birth rates tend to decrease and death rates tend to increase. When r = 0, the population size stops changing—it reaches an equilibrium size called carrying capacity, or K.

40. Figure 43.8 Per Capita Growth Rate Decreases with Population Density (Part 1)

41. Figure 43.8 Per Capita Growth Rate Decreases with Population Density (Part 2)

42. Concept 43.4 Populations Grow Multiplicatively, but Not for Long Spatial variation in environmental factors can result in variation of carrying capacity. Temporal variation in environmental conditions may cause the population to fluctuate above and below the current carrying capacity. Example: the rodents and ticks in Millbrook, New York.

43. Figure 43.2 Population Densities Are Dynamic and Interconnected

44. Concept 43.4 Populations Grow Multiplicatively, but Not for Long The human population is unique. It has grown at an ever-faster per capita rate, as indicated by steadily decreasing doubling times. Technological advances have raised carrying capacity by increasing food production and improving health.

45. Figure 43.9 Human Population Growth (Part 1)

46. Concept 43.4 Populations Grow Multiplicatively, but Not for Long In 1798 Thomas Malthus pointed out that the human population was growing multiplicatively, but its food supply was growing additively, and predicted that food shortages would limit human population growth. His essay provided Charles Darwin with a mechanism for natural selection. Malthus could not predict the effects of technology such as medical advances and the Green Revolution.

47. Concept 43.4 Populations Grow Multiplicatively, but Not for Long Many believe that the human population has now overshot its carrying capacity for two reasons: Technological advances and agriculture have depended on fossil fuels, a finite resource. Climate change and ecosystem degradation have been a consequence of 20th century population expansion.

48. Concept 43.4 Populations Grow Multiplicatively, but Not for Long If the human population has indeed exceeded carrying capacity, ultimately it will decrease. We can bring this about voluntarily if we continue to reduce per capita birth rate.

49. Figure 43.10 A Metapopulation Has Many Subpopulations

50. Concept 43.5 Extinction and Recolonization Affect Population Dynamics Regional populations (metapopulations) are made up of subpopulations in habitat patches. Individuals may move in or out of subpopulations.