1. Chapter 14. Parasitism What’s a parasite? – hard to define
Intimate contact (feed off host)
Usually do not kill host (parasitoids do)
Herbivores(?)
Parasitic Plants
Holoparasites (lack chlorophyll) – Rafflesia (biggest flower)
Hemiparasites (photosynthesize) – Mistletoe
Microparasites – reproduce inside host
Bacteria, viruses
Macroparasites – release juvenile outside
E.g. trematodes
Ectoparasites vs. endoparasites

2. “Weird” Parasites Nest Parasites Sexual Parasites Brownheaded Cowbird
European Cuckoo
Sexual Parasites
Gynogenetic fishes
Amazon molly
Resided/Finescale Dace hybrid

3. Parasitism Common Possibly more parasites than anything else
50% of insects parasitic
Potentially 4:1 parasites:free-living forms
Often complex life cycles
E.g. lancet fluke, other trematodes
Several intermediate hosts

6. Modeling Parasitism
Complex because of intermediate hosts, and infection rate
Not usually sensitive to “actual” r for parasite (this is gigantically high)
Important variables:
Rp – number of infected hosts
If Rp > 1 then parasite spreads
For microparasites
Rp = NBL
N – density of susceptible hosts
B – transmission rate of parasite
L – length of time host is infectious
Nt (host pop. size) = 1/BL (if Rp = 1)
Critical host density (upshot is disease cycles as Nt reached by recruitment)

8. Effects on natural populations
Introduced parasites – large effect
Chestnut blight, Dutch elm etc.
Natural systems
Dodder (Cuscuta) – plant parasite – may act to maintain diversity
Fuller and Blaustein – deer mice
Found infected had lower overwinter survival
Hurtrez-Bousses – microwaved blue tit nests
Found higher size at fledging and lower failure rate
Red Grouse

12. Community Effects Brainworm – host is white-tailed deer
Not much effect
All other cervids and pronghorns susceptible
“apparent competition” – as white-tailed deer expand range, other species affected
Other examples of effects
Flour beetles, Anolis lizards

13. Biocontrol Some success (about 16%)
E.g. myxoma and rabbits in Australia
Evolution of reduced virulence
How much of the rest deleterious uncertain
Pesticides degrade in environment
Introduced parasites remain
Switch hosts?? Cause other problems?
Some advocate shotgun approach
Some advocate “targeted” approach
I think – last-ditch effort (and maybe not even then)

15. Mutualism Both species benefit Plant-pollinator
Often tightly coevolved relationships
E.g. figs and fig wasps – 900 species of figs, each with its own pollinating wasp
Yucca plants and yucca moths
Perhaps each trying to “cheat”?
Reciprocal parasitism?

17. Seed Dispersal Fruits attract dispersers Hypotheses for seed dispersal
Color, smell, abundance etc.
Hypotheses for seed dispersal
Reduced competition
Colonization hypothesis
Directed dispersal hypothesis (ants)
Predator escape hypothesis

18. Variety of Mutualisms Resources Protection Obligate mutualisms
Leaf cutting ants/fungus
Nitrogen fixing bacteria / plants
Protection
Cleaner fish and “customers”
Some are mimics (cheaters)
Ants and aphids
Ants and acacia trees (herbivory)
Obligate mutualisms
Lichens (algae and fungus)
Ruminants/bacteria
Deep sea fishes/luminescent bacteria
Corals/zooxanthellae
Endosymbiont theory

19. Modeling Mutualism Similar to Lotka-Volterra comp. eqns.
Replace negative effect with positive
Change K to X (carrying capacity is raised)
Can become weird (unstable) or can become stable when facultative
Obligate mutualisms even more unstable (though obviously there are stable areas)

22. Indirect effects on community
Mycorrhizal fungi / plants
Reduce herbivory
Increased vigor
Increased antiherbivore defenses
Increased mycorrhizal diversity can be positive for community
Or…introduced mutualists can out-compete (endophytes in Indiana)

24. Commensalisms Cattle egrets/cattle Clinging seeds and hosts
Flower mites and hummingbird nostrils