How do Populations Grow?

1. How do Populations Grow? • Three factors that help to predict how population may change • Number of individuals already present (N) • Population’s carrying capacity (K) • Growth rate (r)

2. K-Selection & r-Selection • Species are K-selected • When they have adaptations that permit them to live in a state of equilibrium • Close to carrying capacities for long periods • Species are r-selected • When they have adaptations that permit them to rapidly increase their numbers • When their populations are below their carrying capacities K r

3. K-Selected Species Live in stable environment Ecological specialists Have populations stable in size Compete well against other species Are restricted in where they can live K & r–Selected Species Comparison of Characteristics r-Selected Species Live in disturbed environments Ecological generalists Have populations that fluctuate rapidly in size Do not compete well against other species Are widely distributed

4. K-Selected Species Take rapid advantage of ecological opportunities Are long-lived Have few, relatively large young Have long periods of embryonic development K & r–Selected Species Comparison of Characteristics r-Selected Species Are slow to respond to ecological opportunities Are short-lived Have many, relatively small young Have short periods of embryonic development

5. K-Selected Species Reach adulthood slowly Invest intensive care in young Reproduce throughout lifetime K & r–Selected Species Comparison of Characteristics r-Selected Species Reach adulthood rapidly Invest little or no parental care in young Reproduce once per lifetime

6. Application to Fisheries Management

7. Is the coastal shark fishery sustainable?Why not? Spiny Dogfish http://www.nefsc.noaa.gov/sos/spsyn/op/dogfish Spiny dogfish, Squalus acanthias, are distributed in the western North Atlantic from Labrador to Florida and are considered to be a unit stock in this region. During spring and autumn, they are found in coastal waters between North Carolina and Southern New England. Dogfish migrate northward to the Gulf of Maine-Georges Bank region and into Canadian waters in summer and southward in autumn and winter. They tend to school by size and, when mature, by sex. Dogfish are known to feed on many species of fish and crustaceans, but generally target the most abundant species. In the Northwest Atlantic, maximum ages reported for males and females are 35 and 40 years, respectively. The species bears live young, with a gestation period of about 18 to 22 months, producing 2 to 15 pups with an average of 6.

8. Interactions of Populations • When populations compete, both are harmed • Two types of competition: • Competition between individuals within their own species for food, space, mates • Competition between species for food, space, but never for mates

9. Interactions of Populations • G. Gause, 1930s • Studied effects of competition on populations of 2 different species of Paramecium • When grown alone • Each species’ population showed S-shaped population growth curve • When grown together • Both species initially expressed in S-shaped growth pattern, but with time • One species survived & other became extinct

10. Interactions of Populations • Further experiments led G. Hardin to state Competitive Exclusion Principle, 1960 • Two species cannot coexist while exploiting same limiting resource

11. Competition among species • Ecological niche 1. No two species ever occupy exactly the same niche 2. Niches of different species will overlap

12. Cape May warbler Blackburnian warbler black-throated green warbler bay-breasted warbler myrtle warbler

13. III. Competition among species • Species compete for resources 1. Competitive exclusion 2. Resource partitioning is the outcome of coevolution

14. Interactions of Populations • What are the results of competition? • It is density-dependent • In ideal environment competition is not a factor • As populations grow, interactions between competitors intensify • One species will exclude the other • They will partition resources so that competition is minimized & tolerable

15. Predator & Prey Interactions • Populations regularly • Exploit other populations as sources of nutrients & energy • One population (predator) • Benefits at expense of other (prey)

16. Predator & Prey Interactions • Predation is density-dependent factor • Predator/prey relationships • Can be used to control unwanted populations 144Afsy4.MOV

17. Competition among species 1. Predator–prey interactions shape evolutionary adaptations a. Development of defenses (prey) b. Overcoming defenses (predators) 2. Camouflage—both predator and prey 3. Warning coloration 4. Mimicry—prey species "evolve" characteristics to mimic a dangerous/poisonous species 5. Aggressive mimicry—predators resemble harmless species or objects 6. Chemical warfare a. Bombardier beetle b. Plant chemicals, secondary metabolites c. Venoms/poisons

18. (b)

19. (a)

20. (b)

21. (b)

22. (c)

23. Competition among species 7. Complex predator–prey relationships involving more than two species a. Plants, herbivores, and coevolution b. Species use other species to protect themselves

24. Plants & Herbivores • Plant/herbivore interaction • Most herbivores prefer specific type of plant species & seek them out • Herbivores responded evolutionarily • That plant cells have cellulose • That is difficult to digest • Herbivores digestive systems are more complex than those of carnivores

25. Plants & Herbivores • Plants may respond to herbivores • In passive fashion – make enough tissue to feed herbivores & still live • Plants may also respond in less passive way • By releasing hormones that deter further feeding • Some are distasteful & avoided by herbivores

26. Herbivores & Carnivores • Herbivore/carnivore interactions • Carnivores must find, approach, & secure prey • Herbivores must sense presence of predators & avoid them

27. Herbivores & Carnivores • Carnivores get more energy from animal material • It is easier to digest & nutrients are highly concentrated

28. Herbivores & Carnivores • It is to carnivore’s advantage to secure most food while expending least energy • Energy expenditure is important to prey species too • Carnivore initiates chase & prey responds • Being inconspicuous is important to both prey & predators

29. Symbioses • Some populations form intimate associations • Interactions between a pair of species can become so intimate • That one or both become dependent on the other • This is called symbioses

30. Symbioses • There are 3 basis types of symbioses: • Parasitism • Commensalism • Mutualism

31. Symbioses • Parasitism • Interaction between parasite & host • Parasites have at least one host, some may have multiple hosts The pearl fish lives in the anus of the sea cucumber and feed on the Sea Cucumbers respiratory tissues and gonads.

32. Symbioses • Commensalism • One species benefits while other is seemingly unaffected

33. Symbioses • Mutualism • Both species benefit • Partnerships in life are formed • Corals and Algae • Coral gain carbon compounds, Zooxanthellae receive nutrients especially P & N that coral get from eating zooplankton. • Coral use of carbon compounds controls growth and density of the algae

34. III. Competition among species • Keystone predators and community structure • Exotic species and community structure • 1. Zebra mussels • 2. Kudzu

35. (a)

36. (b)

37. IV. Succession—community changes over time as changes in plant communities occur • 1. Occurs over a longer period of time (thousands of years) • 2. Pioneer species • 3. Climax community • a. Environment (temperature/precipitation) influences type of climax community in an area

38. lichens and moss on bare rock bluebell, yarrow blueberry, juniper jack pine, black spruce, aspen balsam fir, paper birch, white spruce, climax forest

39. blackberry blackberry blackberry plowed field plowed field plowed field plowed field plowed field plowed field ragweed, crabgrass and other grasses ragweed, crabgrass and other grasses ragweed, crabgrass and other grasses ragweed, crabgrass and other grasses ragweed, crabgrass and other grasses asters, goldenrod, broom sedge grass asters, goldenrod, broom sedge grass asters, goldenrod, broom sedge grass asters, goldenrod, broom sedge grass Virginia pine, tulip poplar, sweet gum Virginia pine, tulip poplar, sweet gum oak-hickory climax forest