Ecology Lecture 6

Parasite/host interactions

Parasites hard to define, sometimes considered a special case of predation.

One definition: ‘An organism which uses the metabolism of another organism to the detriment of its host without immediately killing it.

Some plant examples. e.g. Toothwort - woodland plant parasite of Hazel, Elm etc.

Broomrapes: 150 spp, tap in directly to host roots. (host legumes).

Indian-Pipe. Parasite of trees via their mycorrhizae fungi.  

Mistletoe: semiparasitic (can photosynthesise).

Endoparasites (‘protozoa’ in blood)

Protists are examples of ‘microparasites’ - along with viruses, bacteria, some fungi etc. 

Ectoparasite- Mite, Hippoboscid fly, Flea.

Evolutionary effects; microparasites are key to one important explanation for why sex exists.

Sex is a problem

-Maynard Smith’s idea

-Imagine a sexual population with N females and N males

-Each female produces K eggs

-Eggs have a survival probability S

=Thus in the next generation there will be KSN sexual individuals

Parthenogenetic mutant

-Females produce offspring without sex (a parthenogen)

-n parthenogenetic females

-Each produce K eggs with survival rate S

=Thus in the next generation there will be KSn parthenogenetic females 

If the parthenogen is a mutant- then it will…