Species Interactions: Herbivory & Disease/Parasitism (Pt. 1)

I. Herbivores important selective agents plants � Evolutionary time

            1. Structural - spines

            2. Chemical -secondary plant compounds

                        a. Byproducts of metabolic pathways

            3. Two views: function compounds:

                        a. Waste products - avoid autotoxication

                        b. Chemicals specifically evolved

            4. If plant defenses are cost plant fitness:

                        a. Evol. > defenses if exposed > damage

                        b. Defense chemicals concentrated valuable tissue

                                    i. growing regions (tannins, resins, alkaloids)

                        c. Defense mechanisms reduced enemies absent

                        d. Defense mech. costly not present > stress env.

            5. Research shown latter

                        a. Chemicals specifically evolved

                        b. Primarily plants easily located

                        c. Fast vs slow growing plants

            6. Herbivores evolve adaptations to plant chemicals

                        a. Enzymes to detoxify plant chem.

                        b. Timing life cycle eat plants

                        c. Evolve way eat and get nutrition

            7. Mutualistic system of Defense

                        a. Ants and Acacias-New World tropics

                                    i. Ants depend Acacias food

                                    ii. Acacias depend ant protection

            8. Herbivore Interactions:

                        a. Ungulates on Serengeti Plains Africa

                                    i. Migratory respond fixed times grass dev.

                                    ii. Part of grass eat

                                    iii. Most are ruminants (bact. protozoa, cellulose)

                                    iv. Zebras not, > like horses

                                    v. Hypothesized grazing facilitation (obligatory)

            9. Plant-herbivore systems: 2-types

                        a. Interactive herbivore system (herb. influence growth)

                                    i. Irruption - 4 stages

                                    ii. Can stabilize at low levels & oscillate

                                    iii. Insect-plant interactions

                                                -Plants stressed: low toxic compounds

                                                -Concentrate proteins aa leaves & stems

                        b. Noninteractive herbivore system (no influence)

                                    i. Finches feeding on seeds trees shrubs

                                    ii. No affect on prod. of food plants

            10. Plant-herbivore coevolution mutualism

                        a. Seed dispersal - fruit - discrete package seeds

                        b. Fruit toxic some animals not others - "choose" agent disp.

II. Disease & Parasitism

Disease = Assoc. b/t pathogenic microorganism & host; host suffers physiologically.

Parasitism = One spp. lives in obligatory assoc. with another, metabolically depends host

            1. Disease � Great preoccupation humans through time

i.  Black death 14th century

ii.  Smallpox scourge 19th century

iii.  Great Influenza Pandemic 1918

iv.  AIDs epidemic, tuberculosis, mad-cow today

2. Disease agents (microparasites):

i.  bacteria

ii.  viruses

iii.  pathogenic fungi

iv.  prions (protein bodies)

v.  (May be lethal maybe not)

3. Parasitic agents (macroparasites):

i.  multicellular organisms

ii.  tapeworms

iii.  Middle ground

iv.  spirochetes � syphilis

v.  (Mostly not lethal)

4. Humans- concentrate on lethal diseases

5. Ecology- sublethal stress more important populations wild

6. Mathematical models of host-disease interaction:

i.  Human epidemiology focus disease research

ii.  Focus on continuous populations (differential equations)

iii.  Start with box models or compartmental models

vi.  Divide host population-susceptibles, infected, recovered

v.  Based size of population and rates of birth & death

vi.  Various other parameters in model:

-transmission rate, recovery rate, mortality rate, loss immunity rate

7. Mathematical equations for simple box model � microparasitic infection

8. Trajectory of this simple epidemic:

            i.  The infected number of individuals rises to some peak

ii.  The susceptible individuals decline so no contact with infected indiv.

iii.  Organisms become immune and disease dies out

9. How might we control disease described by this simple model?

i.  Vaccinate individuals

ii.  Cull susceptibles from population

iii.  Example fish aquaculture important parameters