1. Population Ecology The struggle between the biotic potential of a species and the environmental resistance that it encounters

2. Population Ecology Population – all of the individuals of a particular species that live together in one place at one time. Population ecology explores how biotic and abiotic factors influence the density, distribution, size and age structure of populations

3. Population Ecology Principles of population ecology may be used to: Principles of population ecology may be used to: –manage wildlife, fisheries, and forests for sustainable yield –reverse the decline of threatened or endangered species –reduce pest populations –IPM = Integrated Pest Management Integrated pest management (IPM) uses a combination of biological, chemical, and cultural methods to control agricultural pests Integrated pest management (IPM) uses a combination of biological, chemical, and cultural methods to control agricultural pests

4. count all the individuals in a population count all the individuals in a population estimate by sampling estimate by sampling mark-recapture method depends on likelihood of recapturing the same individual mark-recapture method depends on likelihood of recapturing the same individual How are populations measured?

5. Population Ecology Three fundamental characteristics of the organisms in a population DensityDensity DispersionDispersion DemographyDemography

6. Population Size … is the number of individuals present at a given time. The passenger pigeon was once North America’s most numerous bird, but it is now extinct.

7. Population Density … is the number of individuals per unit area. In the 19th century, the flocks of passenger pigeons showed high population density. Increases by births and immigration Increases by births and immigration Decreases by deaths and emigration Decreases by deaths and emigration

8. Population Dispersion The dispersion pattern of spacing among individuals within the boundaries of the population

9. Population Dispersion Clumped Clumped – Individuals in patches or groups – Usually resource related – Example: Bluestripe snappers (Lutjanus kasmira) – Schooling of some fish is a protective strategy – Herd mentality – protection of young

10. Population Dispersion Uniform Uniform – Often the result of antagonistic interactions – Animals that defend territories oftens show a uniform patters – Example: Cape gannets (Morus capensis) – These birds space their nests out evenly – Plants - alleleopathy

11. Population Dispersion Random Dispersion Random Dispersion – Unpredictable spacing – Not usual in nature because there is usually a reason for a pattern of spacing

12. Carrying Capacity refers to the size of a population that can live indefinitely in an environment without doing that environment any harm. This applies to all organisms. # of individuals in a population that an environment can support.

13. Hunting Hunting Amount of space suitable for breeding Amount of space suitable for breeding Food availability - limited food supply Food availability - limited food supply Preditors Preditors The buildup of toxic wastes The buildup of toxic wastes Increased disease Increased disease What limits the carrying capacity of an ecosystem? Limiting Factor: is any biotic or abiotic resource that limits a populations size.

14. More Limiting Factors Terrestrial Terrestrial – Sunlight – Temperature – Precipitation – Soil nutrients – Fire frequency – Wind – Latitude – Altitude Aquatic/Marine Aquatic/Marine – Light penetration Water clarity Water clarity – Water currents – Dissolved nutrient concentrations Esp. N, P, Fe Esp. N, P, Fe – Dissolved Oxygen concentration – Salinity

15. Limits on Population Growth: Biotic Potential vs. Environmental Resistance  No population can increase its size indefinitely. The intrinsic rate of increase ( r ) is the rate at which a population would grow if it had unlimited resources. The intrinsic rate of increase ( r ) is the rate at which a population would grow if it had unlimited resources. Carrying capacity ( K ): the maximum population of a given species that a particular habitat can sustain indefinitely without degrading the habitat. Carrying capacity ( K ): the maximum population of a given species that a particular habitat can sustain indefinitely without degrading the habitat.

16. Idealized models describe two kinds of population growth 1. exponential growth - the rate of expansion of a population under ideal conditions 2. logistic growth - idealized population growth slowed by limiting factors as the population size increases How do populations grow?

17. A J-shaped growth curve A J-shaped growth curve – G = the population growth rate – r = the intrinsic rate of increase, or an organism's maximum capacity to reproduce – N = the population size Exponential Growth Curve

18. Logistic growth is slowed by population-limiting factors Logistic growth is slowed by population-limiting factors – K = carrying capacity - maximum population size that an environment can support – ( K - N )/ K accounts for the leveling off of the curve Logistic Growth Curve

19. Exponential and Logistic Population Growth: J-Curves and S-Curves  Populations grow rapidly with ample resources, but as resources become limited, its growth rate slows and levels off.

20. What does the logistic growth model suggest about real populations in nature? A population’s growth rate will be small when the population size is either small or large The growth rate will be highest when the population is at an intermediate level relative to the carrying capacity. Limiting factors make the birth rate decrease, the death rate increase or both Eventually the population will stabilize at the carrying capacity when the birth rate equals the death rate These are mathematical models and no population fits either perfectly

21. Exponential and Logistic Population Growth: J-Curves and S-Curves  As a population levels off, it often fluctuates slightly above and below the carrying capacity.

22. Types of Population Change Curves in Nature  Population sizes may stay the same, increase, decrease, vary in regular cycles, or change erratically. Stable : exhibits dynamic equalibrium. Stable : exhibits dynamic equalibrium. Irruptive : when populations explode and crash. Irruptive : when populations explode and crash. Cyclic : populations fluctuate up and down Cyclic : populations fluctuate up and down Irregular : erratic changes. Irregular : erratic changes.

23. Some factors that limit population growth Competition for resources Competition for resources As density of song sparrows increase, the number of eggs laid decreases because of food shortages As density of song sparrows increase, the number of eggs laid decreases because of food shortages Plants grown under crowded conditions tend to be smaller and less likely to survive Plants grown under crowded conditions tend to be smaller and less likely to survive Disease transmission or accumulation of toxic waste products can increase mortality Disease transmission or accumulation of toxic waste products can increase mortality

24. Some factors that limit population growth A predator may capture more of a particular kind of prey as the prey becomes abundant A predator may capture more of a particular kind of prey as the prey becomes abundant White-footed mice stop reproducing at a colony size of 30-40 even when food and shelter are provided. Stress? White-footed mice stop reproducing at a colony size of 30-40 even when food and shelter are provided. Stress? The graph shows aphids which feed on the phloem sap of plants increase in population in the summer and then die-off in the fall and winter The graph shows aphids which feed on the phloem sap of plants increase in population in the summer and then die-off in the fall and winter

25. Some factors that limit population growth Some populations remain fairly stable in size close to carrying capacity Some populations remain fairly stable in size close to carrying capacity Most populations fluctuate as seen at the left Most populations fluctuate as seen at the left This graph shows song sparrow populations, with periodic catastrophic reductions due to severe winter weather This graph shows song sparrow populations, with periodic catastrophic reductions due to severe winter weather

26. Hare cycles may be caused by increasing food shortages during winter caused by overgrazing Hare cycles may be caused by increasing food shortages during winter caused by overgrazing They may be due to predator-prey interactions They may be due to predator-prey interactions Cycles could be affected by a combination of food resource limitation and excessive predation Cycles could be affected by a combination of food resource limitation and excessive predation Predators reproduce more slowly than their prey so they always lag behind prey in population growth. Predators reproduce more slowly than their prey so they always lag behind prey in population growth. Boom and bust cycles

27. Population growth crash Some populations that rise too fast and deplete resources may then crash, as with reindeer on St. Paul Island. St. Paul reindeer, Rangifer tarandus

28. This is when a population is controlled by natural events other than population density. This is when a population is controlled by natural events other than population density. Natural disasters are examples of density independent factors Natural disasters are examples of density independent factors fires fires Floods Floods Earthquakes Earthquakes Hurricanes Hurricanes Volcanoes Volcanoes Drought Drought Density Independent

29. This occurs when the density of the population controls the total population of individuals in a species. This occurs when the density of the population controls the total population of individuals in a species. Stress Stress Disease Disease Competition for resources Competition for resources Lack of space Lack of space Density Dependent

30. Life history traits are products of natural selection Life history traits are products of natural selection Traits that affect an organism’s schedule of reproduction and survival make up its life history Traits that affect an organism’s schedule of reproduction and survival make up its life history Life history traits are evolutionary outcomes, not conscious decisions by organisms Life history traits are evolutionary outcomes, not conscious decisions by organisms Life History

31. r- and K- Survivorship Strategies r-selected species Many offspring Many offspring Fast growing Fast growing No parental care No parental care K-selected species Few offspring Few offspring Slow growing Slow growing Parental care Parental care Terms come from: r = intrinsic rate of population increase. (Populations that can potentially grow fast, have high r.) K = symbol for carrying capacity. (Populations tend to stabilize near K.)

32. Many small offspring Little or no parental care and protection of offspring Early reproductive age Most offspring die before reaching reproductive age Small adults Adapted to unstable climate and environmental conditions High population growth rate (r) Population size fluctuates wildly above and below carrying capacity (K) Generalist niche Low ability to compete Early successional species r-Selected Species Cockroach Dandelion

33. More examples… Dandelions and salmon produce many, tiny offspring with low survivorship probabilities

34. Fewer, larger offspring High parental care and protection of offspring Later reproductive age Most offspring survive to reproductive age Larger adults Adapted to stable climate and environmental conditions Lower population growth rate (r) Population size fairly stable and usually close to carrying capacity (K) Specialist niche High ability to compete Late successional species K-Selected Species SaguaroElephant

35. More examples… Coconut palms and kiwis produce a few, big offspring with high survivorship probabilities

36. Study of vital statistics Birth and Death rate –Type I curve – low death rate early and midlife. Death rate increases sharply at older age –Type II curve -probability of survival does not change with age; no age bias –Type III curve – high death rates for very young then a period when death rates are lower for those who survive to a certain age

37. Collapse of northern cod fishery – Renewable resource management – harvesting crops without damaging the resource Renewable resource management – harvesting crops without damaging the resource Maximum sustainable yield – harvest at a level that produces a consistent yield without forcing a population into decline Maximum sustainable yield – harvest at a level that produces a consistent yield without forcing a population into decline

38. In 1890, a group of Shakespeare enthusiasts released about 120 starlings in New York's Central Park In 1890, a group of Shakespeare enthusiasts released about 120 starlings in New York's Central Park The Spread of Shakespeare Starlings

39. Today over 100 million starlings are spread over North America Current 1955 1945 1935 1925 1935 1915 1905 1925 1935 1945 1955 Current

40. The starling population in North America has some features in common with the global human population The starling population in North America has some features in common with the global human population –Both are expanding and are virtually uncontrolled –Both are harming other species

41. The history of human population growth Throughout human history parents had many children but only two on average survived to adulthood Throughout human history parents had many children but only two on average survived to adulthood Estimates that by 2025 the world will have to double food production, 2/3 of the available fresh water on earth will be in use, 60,000 plant species will be lost to support the population Estimates that by 2025 the world will have to double food production, 2/3 of the available fresh water on earth will be in use, 60,000 plant species will be lost to support the population Issues: overgrazing, rivers running dry, decrease in groundwater, energy? Issues: overgrazing, rivers running dry, decrease in groundwater, energy?

42. Demographic Transition Going from high birth rates and high death rates to low birth rates and low death rates Going from high birth rates and high death rates to low birth rates and low death rates May take 150 years to complete May take 150 years to complete “Death rate falls due to increased medical care and sanitation “Death rate falls due to increased medical care and sanitation Falling birth rate takes longer, thus delaying transition. Falling birth rate takes longer, thus delaying transition.

43. Population pyramids for Canada and Madagascar. Canada (a) shows a balanced age structure, with relatively even numbers of individuals in various age classes. Madagascar (b) shows an age distribution heavily weighted toward young people. Madagascar's population growth rate is nine times that of Canada's. Data from U.N. Population Division.

44. As China's population ages, older people will outnumber the young Age pyramids show the predicted graying of the Chinese population between 2005 (a) and 2030 (b). Data from U.N. Population Division.

45. USA Baby Boom 2005 The "baby boom" is visible in the 2005 age pyramid for the United States, in the age brackets between 40 and 50. The nation is experiencing an aging population as baby-boomers grow older. Data from U.N. Population Division.

46. The Ecological Footprint (carrying capacity) Amount of productive land and water needed to support the people in a population Amount of productive land and water needed to support the people in a population Currently 1.7 hectares per person is considered suitable Currently 1.7 hectares per person is considered suitable A typical American has a footprint of 10 hectares A typical American has a footprint of 10 hectares

47. What next?

48. Conclusion Natural selection, speciation, and extinction help determine Earth’s biodiversity.Natural selection, speciation, and extinction help determine Earth’s biodiversity. Understanding ecological processes at the population level is crucial to protecting biodiversity.Understanding ecological processes at the population level is crucial to protecting biodiversity. Understanding population ecology also helps us understand human population growth.Understanding population ecology also helps us understand human population growth.