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52 Cards in this Set
- Front
- Back
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symbionts |
-organisms that live in/on other organisms -50% species=symbionts -own bodies can host other species |
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parasite |
-consumes tissues/body fluids of organism on which it lives (host) -negative effects on host |
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pathogens |
parasites that cause diseases |
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commensals |
symbionts w/ neutral effects on their hosts |
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mutalists |
symbionts w/ net + effect on their hosts |
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typically harm but don't immediately kill the organisms they eat |
parasites |
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parasitoids |
insects whose larvae feed on single host and almost always kill it |
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macroparasite |
large species such as arthopods and worms |
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microparasite |
microscopic, such as bacteria |
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diversity of parasites |
most species are attacked by more than 1 kind of parasite; even parasites have parasites |
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specialists that are closely adapted to particular host species |
parasites |
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ectoparasites |
live on outer body surface of host |
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endoparasites |
live inside hosts, w/in cells/tissues, alimentary canal |
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mistoles are hemiparasitic |
they get water/nutrients from host but can also photosynthesize |
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dodder gets water/food from host plant via specialized roots called |
haustoria |
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ectoparasite advantages |
-ease of dispersal -safe from host's immune system |
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endoparasite advantage |
-ease of feeding -protecting from external env't -safer from natural enemies |
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ectoparasite disadvantages |
-vulnerability to natural enemies -exposure to external environment -feeding more difficult
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endoparasite disadvantage
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-vulnerability to host's immune system
-dispersal more difficult |
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parasite-host co-evolution b/w rabbits & their viral pathogen |
-rabbits introduced to Australia 1859 -population exploded, control methods failed -Myxoma virus introduced 1950; 99.8% infected rabbits died |
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Coevolution |
when populations of 2 interacting species evolve together, each in response to selection imposed by the other |
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Change in frequencies of host and parasite genotypes were shown in a trematode worm and its snail host in New Zealand lakes |
found parasites infected snails from home lake more effectively than snails from other lakes |
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trematode-snail coevolution |
-parasite genotypes in each lake evolved rapidly enough to overcome defenses of snail genotypes found in that lake -snails also evolved in response to parasites -over period of 5 years, most abundant genotype changed year to year |
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lab experiments for trematode-snail coevolution |
showed parasites infect snails w/ common genotype more often than snails w/ rare genotype -common genotypes attacked by many parasites, genotype frequencies vary yearly |
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outcome of parasite-host coevolution |
-ever-escalating arms races rarely occur -common host genotypes decrease in frequency bc are attacked by many, leads to increase in previously rare genotypes
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in fruit flies and their parasitoids, costs for encapsulation and avoiding it |
-ability to encapsulate associated w/ lower larval survival rates -wasp eggs avoiding encapsulation by embedding in host tissue take longer to hatch than other eggs |
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studies of wild flax/rust pathogen |
some rust genotypes=more virulent (overcome plant resistance genes) -virulent rust genotypes=common in host population dominated by plants w/ many resistance genes |
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wild flax/rust pathogen trade off |
-virulent rust genotypes produce fewer spores than other genotypes -in flax pops w/ few resistance genes, no advantage to being virulent |
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ecological effects of parasites |
can reduce survival/reproduction of their host |
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parasites impact population cycles of their hosts |
-manipulated #s of parasites in red grouse pops, which crash every 4 years -parasitic trematode was known to decrease survival/reproductive success |
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effects of parasites on physical environment |
burrows built by Corophium hold mud together, preventing erosion and forming mud islands at low tide |
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when parasite drives Corophium pops to extinction, ___ increases and __ disappear |
erosion; islands |
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susceptible individuals |
(S) |
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infected individuals |
I |
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recovered/immune individuals |
R |
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complications to SIR model |
1) host age may affect likelihood of infection 2) latent period in which individual is infected but can't spread disease 3) vertical transmission |
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vertical transmission |
disease is passed from mother to newborn |
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Probability of infected individuals encountering susceptible individuals |
SI |
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a disease will spread when |
dI/dt = >0 BSI-di= 0 S> d/b |
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disease will establish/spread when # of susceptible individuals exceeds |
threshold density St=d/B |
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alternative 1 to keep susceptible individuals below threshold |
-susceptible domestic animals can be slaughtered to reduce density -vaccinations for human populations |
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alternative 2 to keep susceptible individuals below threshold |
raise St: -increase recovery rate by early detection/improved treatment -decrease B by quaranting infected individuals |
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case study in wild population: threshold densities determined for bison populations susceptible to bacterial disease brucellosis |
smaller the held, less individuals= exposed to brucellosis |
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no practical control for brucellosis |
-herd sizes in parks were 1-3K -vaccine unavailable -killing large # bison=unacceptable |
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immune system driven evolution in pathogen feeds recovered and immune individuals back into |
pool of susceptibles |
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lab experiments on population cycles |
-difficult to achieve in laboratory -mite experiment both populations went extinct -when prey=easy for predators to find, predators drive prey to extinction then go extinct |
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effects of prey resource spacing |
-prey mites persisted longer if oranges they fed on were widely spread (took predators longer to find their prey) |
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more complex habitat structure for experiment |
both populations persisted, cycles resulted |
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other factors involved in population cycles |
-evolution -food supply for prey can fluctuate -some pop cycles caused by 3-way feeding relationships; predators/prey, prey/food plants |
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experiments w/ rotifer predator/algal pray species |
-populations cycled, not synchronously -predator pops peaked when prey pops reached lowest levels, vice versa |
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4 possible mechanisms rotifer experiment |
1) egg viability increases w/ prey density 2) algal nutritional quality increases w/ N concentrations 3) accumulation of toxins alter algal physiology 4) algae might evolve in response to predation |
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hypotheses tested in 2 ways |
1) data compared w/ mathematical models; only model including evolution in prey pop provided good match to data 2) manipulated ability of prey pop to evolve by using single algal genotype; when prey couldn't evolve, typical predator-prey cycles resulted, when prey could evolve cycles became asynchronous |
