Section 3: Predation (part B), Herbivory, parasitism, popn. Regulation, biocontrol, fisheries, conservation biology.
PREDATION… Continued (Part B)
C. Studying predator effects on prey populations in the field.
1. Manipulative experiments
2. Accidental Experiments
3. Comparative Studies- woodland caribou
D. Optimal Foraging theory: how do predators choose their diets? (see chapter 3)
*What is the optimum strategy?
= Energy maximization or time minimization
Assumptions about the predator (forager):
-Eating and searching for the next food (prey) item are mutually exclusive activities.
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1. If defenses are costly then expression of defense will depend upon the degree of herbivore damage.
2. If defense are costly, plants will allocate more defensive mechanisms to more valuable tissues.
1. Structural: some evidence indicates that spines protect plants against herbivores.
2. Chemical: plants also invest in chemical defenses
Common metabolites are….
Alkaloids-------nicotine, morphine, caffeine.
**Mutualism: mutual positive interactions between species.
The production and accumulation of some secondary metabolites seems to be advantageous for determining herbivores.
Evidence for cost of chemical defenses
-Plants species either allocate energy to growth or defense but not both.
Slow growing plants do not (CANNOT) replace tissue quickly.
3. Associational defenses
Defense by association with another species
Acacias and ants: a classic example of MUTUALISTIC symbiosis
Ants- protection from herbivores and remove competitors
Acacia- ant food (beltian bodies and extra floral nectaries) and homes.
D. Herbivores on the Serengeti plains
1. Zebra-200, 000
2. Wildebeest--- 1,000,000
3. Thomson’s gazelles----------600,000
ALL MIGRATE IN RESPONSE TO GROWTH OF GRASSES (RAINFALL)
Competition is weak each different part of the plant.
5. Grazing facilitation?
Wildebeest grazing facilitates a short green lawn of herbs and new grass shoots,
E. Can herbivory benefit plants?
The overcompensation hypothesis: plant growth is stimulates by moderate amounts of grazing. (little evidence for this hypotheses)
Snow Geese as herbivores
F. Herbivores are choosy
Decline in preferred forage was correlated with high population densities.
G. Herbivore irruptions (non-interactive predator-prey systems)
Interacting grazing- Predator (-) (_+) Prey
Non-interactive grazing---- Predator + Prey (+/-) annual weather patterns
Diseases and Parasitism (chapter 13) Dr. Dorn
- Parasitism: relationship between 2 species in which the parasite depends metabolically on the host and usually harms the host
-Disease: an interaction in which a disease organism lives on or within a host plant or animal, to the benefit of the disease agent and to the detriment of the host
**Disease agents are microparasites (viruses, bacteria, fungi)
** Parasitism normally refers to MACROPARASITES (ticks, tapeworms, trematodes)
B. Compartment models
SIR model with fixed population size
Per capita rates are used to model transitions of hosts and persistence of the disease in the host population
Beta- transmission rate per encounter
Growth of infected category: dY/dt=(BXY)/N –VY
Where X= susceptible and Y= infected
**With fixed host population size...