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AP Environmental Science Gleason Notes 3Population Dynamics and Carrying Capacity

1. What is a kelp forest?

Kelp forests are some of the most productive and dynamic ecosystems on Earth. They provide essential habitats for a variety of species, inhibit soil erosion and reduce the impact of storm waves on the coastlines. Because of this, they are a very important component of underwater coastal ecosystems. (Kelp is a type of macroalgae).

2. What is a sea urchin?

Sea urchins are tiny, spiny globular creatures that feed primarily on algae (as well as some invertebrates such as mussels, sponges and brittle stars). Since kelp is a form of algae, sea urchins consume kelp as a large part of their diet.

3. What is a keystone species?

A keystone species is one that has a disproportionate effect on the environment relative to its abundance. If a keystone species is removed from the ecosystem, many other organisms in the ecosystem will be affected. A perfect example of a keystone species is a grizzly bear, who helps nutrients cycle from aquatic ecosystems to terrestrial ecosystems when it brings fish to shore to eat.

4. How do sea otters serve as a keystone species in kelp forests?

Each day, a sea otter consumes about 25% of its weight in clams, crabs, mussels, abalone and sea urchins. Sea otters are incredibly important for keeping the sea urchin population numbers in check. By helping control the sea urchin population (through predation), the kelp forest (a vital part of coastal underwater ecosystems) can stay healthy and in tact. If the sea otters were removed from the kelp forests, the sea urchin population would increase exponentially, damaging the kelp forests perhaps beyond repair.

5. What is the biotic potential of a population?

The biotic potential of a population is a measure of a population’s capacity for growth. The higher the biotic potential, the larger the population can grow. Access to food, resources, water and space all affect the biotic potential of a population.

6. Do all populations of organisms grow at the same rate?

No they do not. All populations grow at different speeds based on access to resources such as food, light, water, space, etc. If members of a population can’t access the resources they need for survival, the size of the population will not grow.

7. What is the intrinsic rate of increase (r) of a population?

The intrinsic rate of increase is the rate at which a population would grow if it had unlimited resources.

8. What are four factors that would cause for a population of organisms to have a high intrinsic rate of increase?

1. Age of sexual maturity (If members of a population take a short amount of time to reach sexual maturity, the population can grow faster).

2. Generation time (If the amount of time between each successive generation is small, the population is likely growing quickly).

3. Ability to reproduce frequently (The more times a single individual can reproduce, the faster the population will grow).

4. Number of offspring per birth (Generally speaking, organisms that have a large number of offspring per birth have a high intrinsic rate of increase).

9. With respect to population growth, what important rule must we always remember?

With respect to population growth, it is important that we always remember that no population can grow indefinitely. In the real world, a rapidly growing population reaches some size limit imposed by a shortage of one or more limiting factors. There are always limits to population growth in nature.

10. What is environmental resistance?

Environmental resistance is a measure of all the factors acting jointly to limit the growth of a population. Such factors include resource availability, environmental favorability, ability to adapt to change, number of competitors, etc.

11. The population size of a species in a given time is determined by the interplay between its ______________ ______________________ and _______________________ _________________.

Biotic potential; Environmental resistance. The higher the biotic potential, the higher the population size. The lower the biotic potential, the lower the population size.

12. What is the intrinsic rate of increase of a population dependent on?

The intrinsic rate of increase of a population depends on having a “starter population” of minimum size called the minimum viable population (MVP).

13. What is the minimum viable population (MVP)?

The minimum viable population is the minimum size of a population needed for the population to grow at its intrinsic rate of increase.

14. What are three reasons that a population can’t grow at its intrinsic rate of increase if its size falls below the MVP?

1. If the population size is too small, individuals may have a difficult time locating mates. 2. If the population size is too small, genetically related individuals may interbreed and

produce weak or malformed offspring. 3. If the population size is too small, the genetic diversity of the population may be too low

to enable adaptation to new environmental conditions.

15. Bacteria reproduce by splitting in half through a process called binary fission. If bacteria have all of the conditions they need for optimal growth (the right amounts of heat, moisture and light), they can divide every 20 minutes. Suppose Mr. Gleason places one single bacterium in a nutrient dish. How many will be present after 20 minutes?

After 20 minutes, the population of bacteria will have doubled to two. After forty minutes, the population of bacteria will have doubled to four. After one full hour, the population of bacteria will have doubled to eight.

16. Please fill in the table below that describes the number of bacteria that will be present in Mr. Gleason’s nutrient dish after each of the time intervals listed.

Time Interval Number of Bacteria20 minutes 240 minutes 460 minutes 880 minutes 16100 minutes 32120 minutes 64140 minutes 128160 minutes 256

One Full Day 4,720,000,000,000,000,000,000

17. Please draw a graph that below that represents how the population of bacteria grew over the course of a full day.

Number of Bacteria

Time 18. With respect to environmental science, what is exponential growth?

Exponential growth is growth that starts out slowly and then proceeds faster and faster as the population increases. Exponential growth is characterized by the J-shaped curve seen above.

19. Under ideal conditions, will all populations grow exponentially?

Yes, under ideal conditions, all populations will experience the exponential growth seen by the bacteria population. At first the number of individuals in an exponentially increasing population increases slowly. But, over time, the population becomes larger and larger until it approaches an indefinitely large size.

20. Unlike bacteria, elephants reproduce much more slowly. It takes approximately two years to produces an infant elephant and another ten years for the elephant to reach sexual maturity. In the unlikely event that a single pair of elephants survived and reproduced for 750 years, how many elephants would roam the planet?

If optimal conditions existed, there would be approximately 20 million elephants after 750 years!!

21. In spite of the above-described scenarios, we know that the planet is not covered in elephants and bacteria. Why is this? What inhibits the exponential growth of a population?

In life, resources aren’t inexhaustible. In other words, in life, individuals have to compete for food, space, shelter and fresh water. This competition for resources and the fact that resources are limited prohibits true exponential growth from occurring often times.

22. What is the carrying capacity of a population?

The carrying capacity of a population is the maximum number of individuals that a given environment can support. The carrying capacity of a population is usually determined by environmental factors such as availability of certain resources.

23. As resources become less available, what happens to the growth of a population?

As resources become less available, the growth of a population generally slows down or stops.

24. What is logistic population growth?

Logistic growth is characterized by exponential growth when the population is small, and a steady decrease in population growth with time as the population encounters environmental resistance and approaches the carrying capacity of the environment. Logistic growth is characterized by an S-shaped curve.

25. Please draw a logistic growth curve on the graph below and circle the area in which the population has reached its carrying capacity.

Number of Organisms

Time

26. Can a population ever exceed its carrying capacity?

Yes, a population most definitely can exceed its carrying capacity. Most populations do not make a smooth transition between exponential and logistic growth. Usually a population will temporarily overshoot or exceed its carrying capacity because of reproductive lag time, the period needed for the birth rates to fall and the death rates to rise in response to resource overconsumption.

27. When a population overshoots its carrying capacity, what usually follows?

When a population overshoots its carrying capacity, a crash usually follows. A population crash is caused by a lack of resources available and competition between members of the population for these resources.

28. Please draw a logistic growth curve that represents a typical population at its carrying capacity experiencing overshoot and crash.

Number of Organsims

Time

Pg 201 Miller APES

29. Is the carrying capacity of a population a fixed quantity? Can the carrying capacity for a population fluctuate?

The carrying capacity for a population is not a fixed quantity. The carrying capacity is affected by competition within and between species, natural and human-caused catastrophic events, immigration and emigration and seasonal fluctuations in the supply of food, water, hiding places, etc.

30. There are two main types of population controls that limit population growth. What are these two types of factors?

A. Density Independent Population ControlsB. Density Dependent Population Controls

31. What are density independent population controls?

Density independent population controls affect a population’s size regardless of how dense the population is.

32. What are density dependent population controls?

Density dependent population controls have a greater effect on the population as the population’s density increases.

33. Please determine if the following are density dependent or density independent population controls.

1. Flood2. Disease3. Predation4. Competition5. Hurricanes6. Fire

1. Independent, 2. Dependent, 3. Dependent, 4. Dependent, 5. Independent, 6. Independent

34. In order for populations to grow, species must reproduce. What are the two main types of reproduction that a species can participate in?

The two main types of reproduction that a species can participate in are:A. Asexual Reproduction B. Sexual Reproduction

35. What is asexual reproduction?

Asexual reproduction is reproduction in which all offspring are exact genetic copies (clones) of a single parent. This type of reproduction is common in single-celled species such as bacteria, in which the mother cell divides to produce two identical cells that are genetic clones or replicas of the mother cell.

36. What are the advantages of asexual reproduction?

Asexual reproduction is advantageous in that no energy needs to be invested in attracting a partner. Additionally, asexual reproduction is usually a much quicker process than sexual reproduction.

37. What are the disadvantages of asexual reproduction?

The disadvantages of asexual reproduction are that the offspring show no genetic variation, as each offspring is genetically identical to the parent. Because of this, the population will be more susceptible to environmental stresses.

38. What is sexual reproduction?

Sexual reproduction is reproduction in which organisms produce offspring by combining the gametes from both parents. This produces offspring that have combinations of traits from each parent. About 97% of known organisms use sexual reproduction to perpetuate their species.

39. What are the advantages of sexual reproduction?

Sexual reproduction increases the genetic variation of the offspring. This means that sexually reproducing organisms have “many different eggs in their genetic basket” and have a greater chance of reproducing when environmental conditions change that does a brood of genetically identical clones. Another advantage of sexual reproduction is that males can gather food for the female and the young and may help protect and train the young.

40. What are the disadvantages of sexual reproduction?

The disadvantages of sexual reproduction are as follows:

Females have to produce twice as many offspring to maintain the same number of young in the next generation as an asexually reproducing organism.

The chances of genetic errors and defects increase during the splitting and recombination of chromosomes.

Mating entails huge energy costs such as time-consuming courtship and mating rituals, disease transmission, and injury inflicted by males during mating.

41. Each species has a characteristic mode of reproduction. Some species reproduce early in life and have multiple offspring, whereas others reproduce later in life and have fewer offspring. With respect to reproductive strategies, what are the two types of species?

The two types of species are:A. r-selected speciesB. K-selected species

42. What is an r-selected species?

R-selected species are species that have a capacity for a high rate of increase. R-selected species have:

Many offspring Small offspring Early reproductive age Most offspring die before reaching reproductive age Small adults Population varies wildly above and below carrying capacity Low Ability to Compete

Instead of investing energy in making sure a few offspring have a high chance of survival, r-selected species produce a large number of offspring in hopes that as many of them as possible will survive until adulthood.

43. R-selected species are often called opportunists. Why is this?

R-selected species are often called opportunists because they are very good at gaining a “foothold” in an area after a large disturbance. Because they reproduce quickly and can have many offspring, r-selected species can move into and populate a new area quickly. However, when resources become depleted, their numbers can fluctuate wildly.

44. What is a K-selected species?

A K-selected species is the opposite of an r-selected species. K-selected species tend to do well in competitive conditions when their population size is near the carrying capacity for the environment. Their populations typically follow a logistic growth curve. K-selected species are characterized by the following:

Fewer, larger offspring Higher parental care and protection of offspring Later reproductive age Larger adults Most organisms survive to reproductive age Lower population growth rate High ability to compete.

45. What key problem affects K-selected species more easily than r-selected species?

K-selected species are more easily affected by extinction than r-selected species. Since r-selected species can reproduce more quickly, they can repopulate their populations quickly. K-selected species aren’t as good at this.

46. Please determine if the following are r-selected or K-selected species:

A. Black Widow SpiderB. ElephantC. CockroachD. Saguaro CactusE. GrassF. HumansG. BacteriaH. Annual Plants

47. Below is a list of environmental events. Please determine which type of species (r-selected or K-selected) would be best at surviving the event.

A. FireB. FloodC. Limited SpaceD. DiseaseE. Lack of Food

R-selected species are better at surviving environmental stress so they would do better after a fire, flood or disease, as they are opportunists. Since a K-selected species thrives when the population is at or near its carrying capacity, they would do better when there is lack of food or space.

48. What is a survivorship curve?

A survivorship curve is a representation of the number of survivors of each age group for a particular species. Survivorship curves are a way to represent the age structure of a population.

49. What are the three types of survivorship curves? Please draw the three types on the graph provided below.

A. Late Loss B. Early Loss

C. Constant Loss

Percentage Surviving

Age

50. What types of organisms have early loss survivorship curves?

Organisms that have early loss survivorship curves have many offspring, high juvenile mortality and high survivorship once the surviving young reach a certain age and size.

51. What types of organisms typically have early loss survivorship curves?

As a whole, r-selected species typically have early loss survivorship curves as most individuals who are r-selected do not have offspring that survive to adulthood.

52. What types of organisms have constant loss survivorship curves?

Species with constant loss survivorship curves typically have intermediate reproductive patterns with a fairly constant rate of mortality in all age classes and thus a steadily declining survivorship curve. Examples of organisms with these curves are songbirds, lizards and small mammals that face a fairly constant threat from starvation predation and disease throughout their lives.

53. What types of organisms have late loss survivorship curves?

K-selected organisms typically have late loss survivorship curves. Large mammals such as humans, rhinoceroses and elephants have late loss survivorship curves. Organisms survive to a certain age and then there is a high mortality.

54. In the United States, who has a higher life expectancy: men or women?

Women have a higher life expectancy than men by approximately 7 years! Because of this, health insurance generally costs more for a 65 year old man than a 65 year old woman.

55. Where is Easter Island?

Easter Island is an island in the southeastern Pacific Ocean and is a territory owned by Chile. Easter Island is famous for its monumental statues that are sprinkled over this island..

56. What devastating ecological event happened on Easter Island that should serve as a lesson today?

Easter Island was once a palm tree forest, which provided most of the resources needed by the inhabitants. As the population grew, more and more of the palm trees were chopped down to help build shelter, canoes and move the large stone monuments. However, once the trees were gone, the islanders couldn’t build canoes for hunting porpoises or catching fish. Without the forest to slowly absorb and release water, springs and streams dried up, exposed soils eroded and crop yields plummeted causing widespread famine. The starving people turned to warfare and possibly cannibalism.

The lesson from Easter Island should be remembered worldwide, as it shows what can happen if we don’t take care of our resources. We all should realize that the planet Earth is one small island in a vast universe.

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AP Environmental Science Gleason Notes 3 Problem Set, Part APopulation Dynamics Review Problems

Please answer the following questions in complete sentences using your own words.

1. Explain how the populations of sea otters and kelp interact and why the sea otter is considered to be a keystone species.

2. Please write an equation showing how population change is related to births, deaths, immigration and emigration.

3. What is the biotic potential of a population? What are four characteristics of a population with a high intrinsic rate of increase?

4. What are environmental resistance and carrying capacity? How do biotic potential and environmental resistance interact to determine carrying capacity?

5. Please list four factors that can alter an area’s carrying capacity?

6. What is meant by the term minimum viable population size of a population?

7. What is the difference between exponential and logistic growth? Please draw a graph to represent each type.

8. How can a population overshoot its carrying capacity? What are the consequences of doing this?

9. Please distinguish between density dependent and density independent population controls and give an example of each that was not used in class.

10. What are the advantages and disadvantages of sexual reproduction?

11. List the characteristics of an r-selected species. Give an example of an r-selected species. Under what environmental conditions are you likely to find this species?

12. List the characteristics of a K-selected species. Give an example of an K-selected species. Under what environmental conditions are you likely to find this species?

13. What is a survivorship curve? How is it used?

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AP Environmental Science Gleason Notes 3 Problem Set, Part BPopulation Dynamics Critical Thinking Questions

1. What are the advantages and disadvantages of a species undergoing:a. Exponential Growthb. Logistic Growth

2. Why are pest species likely to be r-selected species?

3. Why are many endangered species likely to be K-selected species?

4. Why is an animal that devotes most of its energy to reproduction likely to be small and weak?

5. Given the current environmental conditions, if you had a choice would you rather be an r-selected species or a K-selected species? Please explain your answer. What implications does your decision have for your current lifestyle.

6. If after your death you could come back as a member of a particular type of species, what type of survivorship curve would you like to have and why?

7. Predict the type of survivorship curve you would expect given the descriptions of the following organisms:

A. This organism is an annual plant. It lives only one year. During this time it sprouts, reaches maturity, produces many wind-dispersed seeds and dies.

B. This organism is a mammal. It reaches maturity after 10 year and bears one young every two years. The young are protected by the parents and the rest of the herd.