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NEW AIM: How do scientists describe population growth?

NEW AIM: How do scientists describe population growth?. Population Ecology. - The study of changes in population size and the environmental factors that regulate it. Population. - group of individuals of a single species that occupy the same general area. 1. Rely on same resources.

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NEW AIM: How do scientists describe population growth?

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  1. NEW AIM: How do scientists describe population growth? Population Ecology - The study of changes in population size and the environmental factors that regulate it. Population - group of individuals of a single species that occupy the same general area 1. Rely on same resources 2. Influenced by the same biotic and abiotic factors 3. High likelihood of interbreeding

  2. NEW AIM: How do scientists describe population growth? Population Density - Number of individuals per unit area or volume How can we determine this? 1. Count all individuals (not always possible) 2. Count individuals in several random spots and then extrapolate 3. mark-recapture: - Capture some animals and mark (left) - Release back to population - Let animals mix back for days/weeks - Randomly catch animals again - Now you get mix of marked and unmarked Great, but what does that do for me?

  3. NEW AIM: How do scientists describe population growth? Population Density - Number of individuals per unit area or volume How can we determine this? 1. Count all individuals (not always possible) 2. Count individuals in several random spots and then extrapolate 3. mark-recapture: - Capture some animals and mark (left) - Release back to population - Let animals mix back for days/weeks - Randomly catch animals again - Now you get mix of marked and unmarked - The ratio of marked to unmarked gives population estimate

  4. NEW AIM: How do scientists describe population growth? Population Dynamics - Pop. Density is obviously not going to be static Additions/subtractions occur through 1. Birth/Death 2. Immigration / Emigration

  5. AIM: What are some of the factors that limit population growth? Dispersion - Pattern of spacing among individuals in a population What types of patterns are observed? 1. Clumped - Most common (we do this of course) - Can be associated with: 1. Resource location like food or water 2. mating - Improve odds of finding a mate 3. Improve odds of predators - Pack of wolves more likely than single wolf to capture a prey animal 4. Improve odds of prey - Herding behavior = use genetically unrelated individuals as shield against predators

  6. AIM: What are some of the factors that limit population growth? Dispersion - Pattern of spacing among individuals in a population What types of patterns are observed? 2. Uniform - Can be associated with: 1. Direct interaction of population members - Some plants secrete chemicals that inhibit germination of seeds - Territoriality – defending a space against encroachment by other members of population - Penguins to right will aggressively defend their space from other penguins

  7. AIM: What are some of the factors that limit population growth? Dispersion - Pattern of spacing among individuals in a population What types of patterns are observed? 3. Random - Can be associated with: 1. Absence of strong attraction/repulsion amongst individuals 2. Key biotic/abiotic factors are homogenous (equally distributed) throughout area – food, water, etc…

  8. AIM: What are some of the factors that limit population growth? Demography - Study of statistics of populations and how they change over time. What influences density and dispersion of populations? 1. Ecological needs of a species (food, water, sunlight, humiditiy, etc…) 2. Structure of the environment (are resources evenly distributed, are they found in certain areas, are there predators, etc…) 3. Interactions between individuals of population These factors will be the cause of vital statistics like: 1. Death Rates (Survivorship)

  9. AIM: What are some of the factors that limit population growth? Demographers construct Life Tables Life tables - Age specific summaries of the survival patterns of a population that allow one to estimate how long a person of a given age will live – great for life insurance companies Cohort - Group of individuals the same age that demographers follow from birth to death for each age group. Let’s take this life table data and look at it graphical in what are called survivorship curves…

  10. AIM: What are some of the factors that limit population growth? Demographers construct Life Tables Survivorship curves - Graphical representations of life tables Survivorship curves for male and female Belding’s ground squirrels. Be aware that Y-axis is logarithmic. Survivorship curves can be classified into three general types as shown on the next slide…

  11. AIM: What are some of the factors that limit population growth? Demographers construct Life Tables Survivorship curves Three general types: Type I - Flat at start meaning low death rate at early and middle life and then drops steeply - Ex. Humans, many other large mammals with high parental care Type III - Drops steeply reflecting high death rate in young individuals, but then flattens out for those few individuals that make it to a critical age. - Ex. Organisms producing many offspring, but little parental care like fish, marine invertebrates like oysters, which release millions of eggs of which most are eaten by predators. Type II - Between type I and type III with a fairly constant death rate over a lifetime - Ex. Annual plants, some rodents, some lizards, etc…

  12. AIM: What are some of the factors that limit population growth? Demography - Study of statistics of populations and how they change over time. What influences density and dispersion of populations? 1. Ecological needs of a species (food, water, sunlight, humiditiy, etc…) 2. Structure of the environment (are resources evenly distributed, are they found in certain areas, are there predators, etc…) 3. Interactions between individuals of population These factors will be the cause of vital statistics like: 1. Death Rates (Survivorship) 2. Reproductive Rates

  13. AIM: What are some of the factors that limit population growth? Demographers construct Reproductive Tables Reproductive tables - Fertility schedule, age-specific summary of reproductive rates in a population Constructed by measuring reproductive output of a cohort from birth to death – the number of offspring a group has in a lifetime.

  14. AIM: What are some of the factors that limit population growth? Review Demography

  15. AIM: What are some of the factors that limit population growth? Life History Traits Life History Traits of a population that affect reproduction and survival What are the three general traits affecting life history? 1. Age at which reproduction begins 2. How often organism reproduces 3. Number of offspring produced during each reproductive episode ***Excluding humans, organisms do not choose consciously when to reproduce or how many offspring to have…

  16. AIM: What are some of the factors that limit population growth? Life History Traits Life History Traits of a population that affect reproduction and survival 1. Semelparity (big-bang reproduction) - “one-shot” pattern of reproduction - Ex. Pacific salmon will produce thousands of eggs one time and then die. Under what environmental conditions would this be a good strategy to evolve? - When survival rate of offspring is low due to highly variable / unpredictable environment.

  17. AIM: What are some of the factors that limit population growth? Life History Traits Life History Traits of a population that affect reproduction and survival 2. Iteroparity (repeated reproduction) - Individuals will have smaller numbers or offspring, but consistently over a lifetime - We obviously display iteroparity along with birds, most reptiles, all mammals, and most fish. Under what environmental conditions would this be a good strategy to evolve? - When environment is more dependable and competition against other individuals is critical - A few, relatively large, well-provisioned individuals will stand a better chance of survival and reproduction

  18. AIM: What are some of the factors that limit population growth? Life History Traits Life History Traits of a population that affect reproduction and survival Why are there not species that combine the two and have tons of offspring regularly? Evolutionary trade-offs, there is just not enough time, energy and nutrients available to do this.

  19. AIM: How do scientists describe population growth? Let’s look at population growth of bacteria starting from a single bacterium - binary fission every 20 minutes under ideal conditions Q: How many will there be after 36 hours?

  20. AIM: How do scientists describe population growth? 2n Where n = # of divisions Let’s look at population growth of bacteria starting from a single bacterium - binary fission every 20 minutes under ideal conditions Q: How many will there be after 36 hours? A: 2108 (enough to cover the planet one foot deep) Graph it:

  21. AIM: How do scientists describe population growth? 1. Exponential Growth Model (J-shaped curve) What does the rate of growth depend on in this model? The number of individuals ONLY So why is Earth not covered in bacteria?

  22. AIM: How do scientists describe population growth? 2. Population limiting factors - environmental factors that restrict population growth Ex. Fur seals on St. Paul Island

  23. AIM: How do scientists describe population growth? 2. Population limiting factors - environmental factors that restrict population growth Ex. Fur seals on St. Paul Island 1. Uncontrolled hunting until 1925 2. Population jumped until 1935 - Almost exponential 3. Population stabilized - Some hunting - limited breeding grounds

  24. AIM: How do scientists describe population growth? 2. Population limiting factors - environmental factors that restrict population growth 3. Logistic Growth Model (S - shaped curve) Q: How does the logistic model differ from the exponential model?

  25. AIM: How do scientists describe population growth? 2. Population limiting factors - environmental factors that restrict population growth 3. Logistic Growth Model (S - shaped curve) Q: How does the logistic model differ from the exponential model? A: It accounts for limiting factors in the environment

  26. AIM: How do scientists describe population growth? 2. Population limiting factors - environmental factors that restrict population growth 3. Logistic Growth Model (S - shaped curve) Carrying capacity (K) - max. population the environment can support without degrading the habitat Determined by: The species itself and the environment (resources available, predation, etc…) **Carrying capacity if obviously not fixed. It depends on abundance of limiting resources at a particular space and time. Figure out way to make or get more food…carrying capacity increases.

  27. AIM: How do scientists describe population growth? 2. Population limiting factors - environmental factors that restrict population growth 3. Logistic Growth Model When is growth rate the lowest? 1. When population is small or large Limited number of individuals and then limited resources When is it the highest? 1. Population at intermediate level relative to carrying capacity. 2. Plenty of resources NO POPULATION FITS EITHER MODEL PERFECTLY

  28. AIM: How do scientists describe population growth? Population limiting factors - environmental factors that restrict population growth Human Population We have a major problem here. What is our future? The number one problem on this planet for humans and many, many other species is our own overpopulation. What is the solution?

  29. AIM: How do scientists describe population growth? Review Population ecology Exponential growth model - J-shaped - NO limiting factors - Growth rate determined by population size and type of organism Logistic Growth Model - S-shaped - Population limiting factors FEW POPULATIONS FIT EITHER MODEL PERFECTLY AS YOU WILL SEE ON THE NEXT SLIDE…

  30. AIM: How do scientists describe population growth? FEW POPULATIONS FIT EITHER MODEL PERFECTLY:

  31. AIM: How do scientists describe population growth? K-selection (quality) vs r-selection (quantity) K-selection - Population selected for fewer offspring and higher parental care. - Typically found when environments are stable resulting in high population density and therefore intense competition – fighting other individuals, not the environment - iteroparity - Traits typically large body size, long life expectancy, fewer offspring, higher parental care. r-selection - Population selected for having many offspring with low parental care. - Typically found when environments are unstable/unpredictable resulting in lower population densities – have many and hope something makes it – fighting the environment , not other individuals. - semelparity - Traits typically large body size, long life expectancy, fewer offspring, higher parental care.

  32. AIM: How do scientists describe population growth? Let’s look at some specific population limiting factors and examples.

  33. NEW AIM: What are some of the factors that limit population growth? Population limiting factors 1. Biotic factors a. Competition among members (intraspecific) - food supply, water, space, energy (oil), mates, etc… Song Sparrow Population Experiment (small island in British Columbia) - add food - Clutch size increased Fig. 35.4A

  34. AIM: What are some of the factors that limit population growth? Population limiting factors 1. Biotic factors a. Competition among members (intraspecific) - food supply, water, space, energy (oil), mates, etc… Competition for space…

  35. AIM: What are some of the factors that limit population growth? Population limiting factors 1. Biotic factors a. Competition among members (intraspecific) i. food supply ii. space (territory) A. Dispersion patterns 1. clumped 2. uniform 3. random

  36. AIM: What are some of the factors that limit population growth? Dispersion patterns

  37. AIM: What are some of the factors that limit population growth? Population limiting factors 1. Biotic factors b. Health - increased spread of disease with increased pop. density - accumulation of waste

  38. AIM: What are some of the factors that limit population growth? Population limiting factors 1. Biotic factors c. Predation As the hare population increases, so does the Lynx population, which will cause the hare population to decrease and in turn the lynx population decreases, etc… “boom-and-bust” cycles Fig. 35.5

  39. AIM: What are some of the factors that limit population growth? Population limiting factors 1. Biotic factors d. Physiological factors White-footed mouse experiment 1. Enclose in a small field 2. Reproduce quickly to 30 or 40 3. Reproduction declines and pop. stabilizes around 40 4. Add more food and water - no change RESULT: high population induces stress syndrome (hormonal changes) - sexual maturity delayed, reproductive organs shrink, depressed immune system

  40. AIM: What are some of the factors that limit population growth? Population limiting factors 2. Abiotic factors a. Climate and weather Ex. Aphids Fig. 35.4B - insects that feed on phloem sap of plants 1. Exponential growth in spring 2. Rapid die out in hot, dry summer 3. A few individuals survive and reproduce when conditions improve What happens to mosquitoes and grasshoppers during winter? - die out completely, leaving only fertilized eggs

  41. AIM: What are some of the factors that limit population growth? Population limiting factors 2. Abiotic factors b. Fire, flood, etc…

  42. AIM: What are some of the factors that limit population growth? Population limiting factors 1. Biotic factors a. Competition among members - food supply - space Fig. 35.4C b. Health c. Predation d. Physiological factors 2. Abiotic factors a. Climate and weather b. Natural disasters (25-year study of the song sparrow) Almost all populations are regulated by a mixture of these and other factors

  43. AIM: What are some of the factors that limit population growth? Age Structure of HUMAN populations Age structure of a given population can indicate if the population is growing or declining as well as current social structures… Indicate if the above human populations are growing or declining.

  44. AIM: What are some of the factors that limit population growth? Age Structure of HUMAN populations What do these allow us to predict about social structure? Ex. Afghanistan is going to have issues with opportunities for jobs and education with the huge influx of young people. In the US, a smaller population of working people will be supporting a larger population of retired people…

  45. AIM: What are some of the factors that limit population growth? Ecological footprint The amount of land required to sustain an individual or a population/nation in terms of food/water and absorbing generated waste in hectares (ha; 1 hectare = 100m x 100m) Ecological capacity How much land a country actually has per person (US has 6.2 ha/person, but uses 8.4 ha/person on average) Calculate your footprint online…

  46. AIM: What are some of the factors that limit population growth? “Milestone QUESTIONS” 1. One species of forest bird is highly territorial, while the second lives in flocks. What is each species’ likely pattern of dispersion? Explain. 2. Each female of a particular fish species produces millions of eggs per year. What is its likely survivorship pattern? Explain. 3. Consider two rivers: One is spring fed and is constant in water volume and temperature year-round; the other drains a desert landscape and floods and dries out at unpredictable intervals. Which is more likely to support many species of iteroparous animals and why? Would you guess this to be an r-selection or K-selection species and why? 4. Where is exponential growth by a plant population more likely – on a newly formed island or in a mature, undisturbed rain forest? 5. Identify three factors that limit population size.

  47. AIM: What are some of the factors that limit population growth? “Milestone QUESTIONS” on next slide…study, study…

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