Population Ecology

1. Population Ecology Study of the factors that affect the population dynamics of any species! Current Population Clock

2. Overview of Chapter 8 • Principles of Population Ecology • Reproductive Strategies • The Human Population • Demographics of Countries • Demographics of United States

3. Principles of Population Ecology • Population Ecology • Study of populations and why their numbers change over time • Important for • Endangered species • Invasive species • Population • Group of individuals of same species living in the same geographic area at the same time

4. Population Dynamics: • Several factors are included: • Population density • Birth rate • Death rate • Growth rate • Age structure • Resources (quantity, type, quality)

5. How a Population Responds to the Environment Depends Upon Several Interactions: • How individuals compete for food • How disease, predation, and other environmental pressures affect population • Reproductive success (or failure) • Management of populations for ecosystem health and/or human needs • forestry management – tree populations, • agronomy – pest and crop populations • wildlife management – animal and fish populations

6. Population Density • the number of individuals of a species per unit of area or volume at a given time • Population density can change dramatically in different habitats, or in the same habitat over a short distance • Population density can indicate a potential pollution source in a river or stream

7. Population Density • Population density • The number of individuals of a species per unit area or volume at a given time • Ex: minnows per Liter of pond water • Ovals below have same population, and different densities

9. Birth Rate • the rate at which individuals produce offspring • Birth rate in humans: (b) = the number of births per 1000 people per year (human terms)

10. Death Rate • = the rate at which organisms dieDeath rate in humans: (d) = the number of deaths per 1,000 people per year

11. Growth Rate • the rate of change (increase or decrease) in a population; • Formula: Growth rate (r) = b-d Growth rate in humans is also called the “natural increase” in the population

12. Example Growth Rate Problem: • Population of 40,000 people; 800 births per year; 400 deaths per year • b = 800/40,000 = 0.02 • d = 400/40,000 = 0.01 • r = 0.02 – 0.01 = 0.01 or 1.0% per year population growth rate • r is positive if people are born faster than they die; r is negative is people die faster than they are born

13. Dispersal • the movement of individuals from one location to another, which affects the population at either location • Immigration (i) – individuals entering a population • Emigration (e) – individuals leaving a population

14. Global Populations vs. Local Populations… • Global populations depend purely on birth and death rates • Local populations depend on birth and death rates plus immigration and emigration rates

16. Example Growth Rate Problem 2: • Population of 250,000; 1400 births per year; 900 deaths per year; 100 immigrants and 200 emigrants yearly • b = 1,400/250,000 = 0.0056 • d = 900/250,000 = 0.0036 • i = 100/250,000 = 0.0004 • e = 200/250,000 = 0.0008 • r = b – d + i –e = 0.0056 – 0.0036 + 0.0004 – 0.0008 = 0.0016 • **Note: This is equivalent to 0.16% growth

17. Birth Rate & Death Rate Calculations…Points to Consider • NOTE: Sometimes birth and death rates are simply given as percentages, which indicates how many people were born (or died) out of 100. Either way of reporting (rate or number per 1,000 living) is acceptable. • Example: Birth rate of 1.1% means 1.1 people were born for every 100 people living in area under consideration. • Typically reported as 11 births per 1,000 people living.

18. Example Growth Rate Problem 3: Note: NOT on your packet… • Birth rate = 1.1% (NOTE: this would be 1.1 per 100; or 11 per 1,000) • Death rate = 0.8% • Immigration = 0.08% • Emigration = 0.04% • Growth rate = 1.1 – 0.8 + .08 - .04 = 0.34% This means that 0.34 people are added to the population for every 100 living; or 3.4 people per 1,000 living.

19. Calculating Future Populations • Extending population growth into the future utilizes a physical constant e = 2.7183 • Formula: Population (final) = Population (initial) x e (r * t) Pf = Pi x e (r * t) Where r is the growth rate IN PERCENT expressed in DECIMAL form, and t is the time (number of years) NOTE: On a calculator, you plug in the r x t first, then raise 2.7183 to that number, then multiply result by the initial population!

20. Calculating Future Populations • EXAMPLE: • 2002 Pakistan population = 143.5 million • Pakistan population growth rate is 2.1% • 2010 population: • P = 143.5 million x 2.7183 (.021 x 8 yrs) • P = 143.5 million x 2.7183 (0.168) • P = 143.5 million x 1.182937939 • P = 169.8 million

21. Estimating Animal Populations: • Most of the time, determining animal populations in an ecosystem setting is difficult unless the animal is sessile (immobile) and easy to count. • Tag & Recapture is often the preferred method used to estimate animal populations • Works by catching an initial sample, “tagging” with some identification mark or tag, releasing them, and recapturing them later. • A simple ratio is used to determine final population.

22. Biotic Potential: • the maximum rate at which a population can increase • Life History Characteristics that Influence biotic potential: • Age at which reproduction begins • Amount of life that reproduction is possible • Number of reproductive periods per lifetime • Number of offspring per reproductive event • Larger organisms generally have smallest biotic potential, while microorganisms have the highest

23. Life history traits –characteristics of an individual that influence survival and reproduction Age at maturity Atlantic Salmon African elephant House Mouse 3-6 years 2 months 11 - 20 years

24. Life history traits –characteristics of an individual that influence survival and reproduction Number of offspring produced Atlantic Salmon African elephant House Mouse 1 calf every 3-8 years 5-8 young every month 1,500 to 8,000 eggs once

25. Life history traits –characteristics of an individual that influence survival and reproduction Number of reproductive events Atlantic Salmon African elephant House Mouse ~6-12 1 ~3 - 10

26. Life history traits –characteristics of an individual that influence survival and reproduction Lifespan Atlantic Salmon African elephant House Mouse 60 - 70 years 3-6 years ~2 years

27. Exponential Population Growth: • Populations with a constant reproductive rate will have an accelerating population growth under optimal conditions • doubling of population occurs in successively shorter intervals

29. Numbers of Bacteria During 10 hour Period (growing exponentially!)

30. Environmental Resistance: • limits to exponential population growth occur when population reaches a size that allows environmental limits to take effect • Environmental limits include: • Space • Food • Exposure to toxins, etc. • Increase in population of predators

31. Carrying Capacity: • Carrying Capacity (K) = the largest population that can be maintained for an indefinite period of time in a particular environment • Carrying capacity changes with changes in the environment, either natural or artificial • Droughts, pollution, excess rainfall, etc.

32. Carrying Capacity

33. S-Shaped Population Curves… • Graphs of populations influenced by environmental limitations show a characteristic S shape curve • Shows an initial exponential growth, followed by slowed growth and then a flattening of the curve as environmental limits are reached

34. S-Shaped Growth Curve (paramecia):

35. Example 1: bacterial population crash due to toxic waste accumulation

36. Reproductive Strategies: • Nature forces organisms to make tradeoffs in the expenditure of energy • Only some energy can be used for reproduction, since each organism must uptake nutrients to grow, hunt for food, etc. • “r-selected” and “k-selected” species have developed over time in response to energy requirements

37. r – Selected Species: • Those species that have traits that favor growth rate strategies (“r-strategists) • Typical r-selected strategies: • Small body size • Early maturity • Short life span • Large broods • Minimal required parental care • Live in unpredictable or temporary environments • Opportunists (like mosquitos, insects, weeds, etc.)

38. K-Selected Species • Called “K-strategists” • Species that try to maximize the chances of survival, especially in environments where the number of individuals (N) is near the carrying capacity (K) of the environment

39. K-Selected Strategies… • Long life span, slow development • Late reproduction • Large body size • Low reproductive rate • Examples: redwood trees, animals requiring long parental care (Tawny owls pair for life!)

40. Survivorship: • Life tables are constructed by ecologists to indicate the relative chances of survival at any time during the life of the organism • Each organism is classified as a Type I, Type II, or Type III Survivorship organism

41. Survivorship = the probability that a given individual in a population will survive to a particular age. Type I Survivorship: the young and those at reproductive age have a high chance of living Type II Survivorship: the probability of survival does not change with age Type III Survivorship: the probability of death greatest early in life, those that survive have high survival rate until old age

42. Factors That Affect Population Size • Density-Dependent Factors: • A change in population density initiates some factor, which subsequently has a counter-effect on the population • Examples of D-D Factors: • Disease, predation, competition for resources • Predator-prey relationships involve dynamics of density-dependent factors.

43. Predator-Prey on Isle Royale… • From 1960 to the mid 1980’s…this is a simple predator-prey dynamic relationship • Mid 1980’s the wolf population crashed…later confirmed to be the result of a deadly canine parvovirus disease… • This allowed moose to flourish…but by mid-1990’s there were so many that they literally overgrazed their main food source (ash and aspen)…which led to a sudden collapse, which then triggered a die-off of the already struggling wolves by 1998 (only 14 individuals were counted!)

44. Population Cycles – Hares/Lynx Example

45. Example 2: Population cycling due to organism interaction Start: both have low population density • Hares – high food, low predators = pop increase over next generations • Lynx – as hares increase, more food = pop increase • Hares – when high pop density, increased competition for food and increased predation = low birth rate & high death rate = sharp pop decrease • Lynx – when high pop density and few hares, low food = low birth rate & high death rate = sharp pop decrease • Back to start

46. Population Cycles

47. Density-Independent Factors… • Any environmental factor that affects the size of a population but is not influenced by changes in population density • Usually abioticfactors, such as random severe weather, fires, timing & severity of winter season, etc. • Cause distress to a population

48. Human Population • Right now at over 6.6 billion and counting… • Scientific advances have enabled us to improve the productivity of the land…so food production has kept pace…not a limiting factor for much of the world • However, have we reduced the ability of the land to sustainably feed future generations?

49. Exponential growth so far • Should “level out” sometime during the 21st century • S-curve may be developing already • What will cause the S-curve????

50. The Human Population Clock…