3. Population A group of organisms of the same species living in the same area at the same time, interacting with one another. Factors affecting growth rate 1.Birth Rate 2.Death Rate 3.Rates of Migration (Immigration & Emigration)

4. 1.Population distribution = the way individuals are spaced within their area  Clumped  Uniform  Random (no pattern) 2.Population density = number of individuals in a given area or volume  count all the individuals in a population  estimate by sampling How are populations measured?

5. Exponential Growth – “ J ” curve 1.Rapid rate of increase when resources are unlimited and optimal growing conditions are present. 2.The populations double with each generation, such that the larger the population is, the faster it grows. 3.Obviously this rate of growth cannot continue indefinitely.

6. Number of Species over Time

7. Logistic Growth “ S ” Curve 1.This type of growth grows rapidly at first resembling exponential growth, but levels off toward later stages. 2.Related to the fact that resources are limited, and as the population grows larger, it is harder for each individual to get what it needs, so growth slows.

8. 3. Population may slow down either because of decrease in birth rate or an increase in death rate (or both) 4. Populations tend to stabilize around a specific number, although there may be slight fluctuations around that amount.

9. Logistic growth is slowed by population-limiting factors K = Carrying capacity is the maximum population size that an environment can support

10. Logistic growth curve  K = carrying capacity  The term (K - N)/K accounts for the leveling off of the curve

11. Carrying Capacity (CC) The maximum number of organisms of the same species that can be supported in a specific area indefinitely.  Once the carrying capacity is reached, certain factors work to keep population in check (including lack of food, overcrowding, predations, accumulation of waste)  If a natural population overshoots the carrying capacity, three thing can happen: 1.It will die back to the original cc. 2.It will die back, but because of damage to the environment, cc is lower 3.It will become extinct.

12. Factors that Restrict the Size of a Population Limiting Factors

13. Density-Dependent Limiting Factors  The degree of influence depends on the size of the population.  Examples: competition, predation, parasitism, stress caused by crowding, disease  Seldom totally eliminate a population  Some populations are self-controlling in that they have mechanisms to reduce competition – delayed maturation caused by malnutrition, migration, cannibalism.

14. Density-Independent Limiting Factors  The degree of influence is not related to population size.  Examples: pollution, habitat destruction, natural disasters, weather  Usually just reduce the population below the cc. but they have the ability to totally eliminate a population

15. Relationships Within a Population

16. Age Structure Consider especially the pre-reproductive compared to the post-reproductive years. o Very young and very old and more susceptive to disease o If there are huge numbers of young adults, the population will grow; if there are mostly elderly, the population will decline.

17. Sex Ratios In a monogamous species, the ratio of males to females should be about equal. In deer and pheasants, for example, that is not as important, because one male often fertilizes many females.

18. Behavior  Territory- a defended area which insured the occupants will have enough resources for themselves and their offspring.  Social hierarchy – social status determines which individuals eat or breed.  Natural Cycles – increase/decrease in population sizes due to environmental factors or ecosystem interactions (predator/prey)

19. Relationships Between Populations of Different Species  Since two different species cannot indefinitely occupy the same niche, separation of the habitat into microhabitats reduces competition.  Theory of Predation – Predators seldom eat all of their prey. As the prey becomes scarce, it is harder to find something to eat.  Disease, Commensalism, Parasitism, etc.

20. Survivorship Curves Graph of the proportion of individuals alive at each age

21.  Survivorship curves plot the proportion of individuals alive at each age  Three types of survivorship curves reflect important species differences in life history

22. Types of Survivorship Curves Type I: A convex curve. Most individuals live to adulthood with most mortality occurring during old age. i.e., humans, red deer, elephants. Type II: A straight line. An individual ’ s chance of dying is independent of its age. i.e., small birds and mammals. Type III: A concave curve, few individuals live to adulthood, with the chance of dying decreasing with age. i.e., oysters, snapping turtles.

23. Survivorship: Evolution shapes life histories  An organism's life history is the series of events from birth through reproduction to death  Life history traits include  the age at which reproduction first occurs  the frequency of reproduction  the number of offspring  the amount of parental care given  the energy cost of reproduction

24.  Doubled three times in the last three centuries  ~ 6.1 billion and may reach ~ 9.3 billion by the year 2050  Improved health and technology have  Lowered infant mortality rates  Increase life spans (average age)  Lowered death rates Human Populations

25. The history of human population growth…

26. RAPID GROWTH Kenya MaleFemale Percent of population SLOW GROWTH United States MaleFemale ZERO GROWTH/DECREASE Italy MaleFemale Ages 45+ Ages 15–44 Under 15 Ages 45+ Ages 15–44 Also reveals social conditions, status of women The age structure of a population is the proportion of individuals in different age-groups

27. 05101520 0 500 1000 1500 Time (years) Population size r = 0.06 r = 0.02 r = 0 r = -0.05 high intrinsic rate of increase low intrinsic rate of increase zero population growth negative intrinsic rate of increase

28.  Suggests that organisms can be placed into two fundamental groups on the basis of their position on the sigmoid growth curve and the resulting life histories.  r-selected species and K-selected species The Theory of r and K selection

29. Climate  r-selected species live in variable or unpredictable environments  K-selected species live in fairly constant or predictable environment

30. Mortality, Survivorship, & Competition In r-selected species mortality is often catastrophic and subject to density-independent limiting factors. Survivorship is low early in life but increases for those individuals surviving (Type III). Competition lax. In K-selected species mortality is subject to density-dependent limiting factors Survivorship is high throughout life until late in life (Type I). Competition keen.

31. Population Size In r-selected species, population size tends to vary in time and re-colonization occur into unpopulated area frequently (pioneer species) In K-selected species, population size is usually at or near the carrying capacity and colonization is infrequent (keystone species in climax communities)

32. Population Curve

33. Another Population Curve

34. r Species Selection Factors Rapid Development High r = or net reproductive rate Early Reproduction Small Body Size Single Reproduction Many Small Offspring Short Life Span

35. K Species Selection Factors Slow Development Competitive Ability Delayed Reproduction Large Body Size Repeated Reproduction Few Large Offspring Long Life Span

36. A Comparison of r and K selected species

37. Survivorship Curve