1. Predation Great White Shark and Fur Seal

2. Predator-Prey Interactions

3. Effects on populations Population regulation refers to the tendency of a population to decrease in size when above a particular level, and to increase in size when below that level. Population regulation can only occur as a result of one or more density dependent processes acting on birth or death rates. Population abundance is determined by the combined effects of all factors and processes that influence population size, whether they are density dependent or density independent.

4. Mink Muskrat

5. Arctic Ground Squirrel – Predator population is self-limited

6. Red Grouse in Heather – Predator population is self-limited

7. Tawny Owl Bank vole Predator Switching Regulates Prey Population

9. Cinnabar Moth and Caterpillar on Ragwort Tansy

10. Snowshoe hare and Lynx

13. Lynx Ruffed GrouseSnowshoe hare

14. Sea Otter

15. Sea Urchin

16. Kelp Forest

17. Sea Otter eating Sea Urchin in Kelp Forest

18. Comparison of kelp and urchin biomass with and without sea otters

19. Kelp forest ecsystems with and without sea otters

20. Sea Urchin Barren

21. Plant Resource Defense Qualitative defense - highly toxic substances, small doses of which can kill predators high nutrient environment/fast growth (high turnover in plants) - use toxins (plant secondary compounds) that often require N, expensive to make (must be replaced often), but can be made rapidly - cyanide compounds, cardiac glycosides, alkaloids - small molecules

22. Plant Resource Defense Quantitative defense - substances that gradually build up inside an herbivore as it eats and prevent digestion of food low nutrient environment/slow growth (low turnover in plants) - primarily use carbon structures - wood, cellulose, lignin, tannins - large molecules - makes plant hard or unpleasant to eat (woodiness, silica), but plants are slow to make these defenses

23. Evolutionary “Arms” Races Monarch and milkweed

24. Evolutionary “Arms” Races

25. California garter snakePacific newt

26. Other Plant Defenses Include: mechanical defenses - plant thorns and spines deter many vertebrate herbivores, but may not help much against invertebrate herbivores failure to attract predators - plants somehow avoid making chemicals which attract predators reproductive inhibition - some plants such as firs (Abies) have insect hormone derivatives which if digested, prevent successful metamorphosis of insect juveniles masting - the synchronous production of very large numbers of progeny (seeds) by trees of one species in certain years

27. Eurasian Jay with Acorn

28. Masting

30. Fagus sylvaticus – European Beech

31. Dipterocarp distribution

32. Dipterocarp trees

33. Beech seeds and boring moth

34. Lyme’s disease life cycle

35. Masting and Human Health - Lyme’s Disease

36. Induced Defenses Another aspect of plant defenses is that plants do not always have tissues loaded with defensive chemicals - in many plants, defensive chemicals are only produced when they are needed, usually after the plant has experienced some herbivory - this is an induced defense

37. Impact of Herbivores Is Not Uniformly Experienced

38. Aphids attacking Alfalfa Spotted Alfalfa Aphid

39. Induced defenses in Birch Trees

42. Rubus prickles

43. Acacia depanolobium

44. Plant defenses are developed at a cost to fitness when: 1. Organisms evolve more defenses if they are exposed to much damage and fewer defenses if cost of defense is high 2. More defenses are allocated within an organism to valuable tissues that are at risk 3. Defense mechanisms are reduced when enemies are absent and increased when plants are attacked - mostly true for chemicals not structures 4. Defense mechanisms are costly and cannot be maintained if plants are severely stressed by environmental factors