2.6.1-.2 Populations

1. 2.6.1-.2 Populations

2. Population Dynamics A look at the factors that tend to increase or decrease the size of a population.

3. The population size of a species in a given space at a given time is determined by the interplay between BIOTIC POTENTIAL and ENVIRONMENTAL RESISTANCE. Biotic potential = growth rate with unlimited resources. Environmental resistance = all the factors acting jointly to limit population growth.

4. POPULATION SIZE Growth factors (biotic potential) Decrease factors (environmental resistance) Abiotic Abiotic Too much or too little light Temperature too high or too low Unfavorable chemical environment (too much or too little of critical nutrients) Favorable light Favorable temperature Favorable chemical environment (optimal level of critical nutrients) Biotic Biotic High reproductive rate Generalized niche Adequate food supply Suitable habitat Ability to compete for resources Ability to hide from or defend against predators Ability to resist diseases and parasites Ability to migrate and live in other habitats Ability to adapt to environmental change Low reproductive rate Specialized niche Inadequate food supply Unsuitable or destroyed habitat Too many competitors Insufficient ability to hide from or defend against predators Inability to resist diseases and parasites Inability to migrate and live in other habitats Inability to adapt to environmental change

5. Four variables change population size: • NATALITY = birth rate • MORTALITY = death rate • IMMIGRATION = rate of organisms moving in • EMIGRATION = rate of organisms moving out

6. Carrying capacity K K species; experience K selection Number of individuals r species; experience r selection Time REPRODUCTIVE STRATEGIES

7. Opportunistic or r-Selected Species cockroach dandelion 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

8. Competitor or K-Selected Species elephant saguaro 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

9. SURVIVORSHIP CURVES

10. Population density affects population growth.

11. DENSITY INDEPENDENT FACTORS = affect a populations’ size regardless of its population density. • Weather • Earthquakes • Floods • Fires • . . . Natural disasters R-strategists populations are most affected by these.

12. DENSITY DEPENDENT FACTORS = affect a populations’ size depending on its population density. • Predation • Disease • Availability of food and water • Space Negative Feedback!!

13. INTERNAL FACTORS = might include density-dependent fertility or size of breeding territory. EXTERNAL FACTORS = might include predation and disease.

14. High High Paramecium aurelia Paramecium aurelia Paramecium caudatum Relative population density Relative population density Paramecium caudatum Low Low 0 2 4 6 8 10 12 14 16 18 0 2 4 6 8 10 12 14 16 18 Days Days Both species grown together Each species grown alone Species interactions influence population growth and carrying capacity = SYMBIOSIS Competition for resources.

15. Resource Portioning

16. PREY POPULATION PREDATOR POPULATION PREDATION

17. Bombardier beetle Span worm Wandering leaf insect Foul-tasting monarch butterfly When touched, the snake caterpillar changes shape to look like the head of a snake Poison dart frog Viceroy butterfly mimics monarch butterfly Hind wings of io moth resemble eyes of a much larger animal Avoiding predators

18. Parasitism

19. Oxpeckers and black rhinoceros Clown fish and sea anemone Mutualism

20. Shark and ramora

21. Cleaning station Cleaner blenny Sabertooth blenny

22. Commensalism

23. Herbivory

24. Population Growth change in the size of a population over time.

25. resources  pop. size • resources  pop. size • POPULATION = a group of interbreeding organisms (same species) that live in the same place at the same time and compete for the same resources. • Resources = food, water, shelter, mates, and so on . . .

26. Clumped (elephants) Uniform (creosote bush) Random (dandelions) • Populations change in response to environmental stress or changes in environmental conditions. • In size = # of individuals • Density = # of individual / specific space • Age distribution = proportions / age group • Dispersion =

28. 2.0 1.5 Number of sheep (millions) 1.0 .5 1800 1825 1850 1875 1900 1925 Year No population can grow indefinitely! Every environment has a CARRYING CAPACITY = the maximum number of individuals of a given species that can be sustained indefinitely in a given space.

29. Factors that affect carrying capacity: • Competition with/in and between species. • Natural and human caused catastrophes. • Immigration and emigration. • Seasonal fluctuations in food, water, shelter, and nesting sites.

30. Population size (N) “J” population growth curve Time (t) A population that has few if any resource limitations grows exponentially. EXPONENTIAL GROWTH starts out slowly and then proceeds faster and faster as the population increases.

31. 1024 Bacteria population 24 hours later 8

33. LOGISTIC GROWTH involves initial exponential growth and then there is a steady decrease in growth as the population encounters environmental resistance and approaches carrying capacity and levels off. K Population size (N) “S or sigmoid” population growth curve Time (t)

34. K Population size (N) Time (t) Plateau phase Transitional phase Exponential phase

35. 2,000 1,500 Number of reindeer 1,000 500 1910 1920 1930 1940 1950 Year

36. Kaibab Plateau

37. Kaibab Plateau