Advanced Higher/ A-Level Biology course notes. Concise notes covering the topic of parasitism. Notes are easy to follow, highlight key-points, and give supportive question examples where appropriate.
PARASITISM
5 a i Niche
ecological niche a multi dimensional summary of tolerances and requirements of a species
fundamental niche a species has a fundamental niche that it occupies in the absence of
INTERSPECIFIC competition
any
realised niche a realised niche is occupied in response to the presence of INTERSPECIFIC
competition
Competative exclusion principle
As a result of interspecific competition competative exclusion can occur where the niches of
two species are so similar that one population will decline to LOCAL EXTINCTION
Resource Partitioning
where the realised niches of species are sufficiently different potential competitors can
COEXIST by resource partitioning This means different species can exploit different components
of the resource thus reducing potential INTERSPECIFIC competition
,5 a Ii The Parasite Niche
Symbiosis refers to intimate associations between individual organisms of different species
Parasitism is a symbiotic interaction between a parasite and its host Parasites gain
benefits in terms of nutrients at the expense of it's host
The parasite uses the host's resources for ENDOPARASITES
growth and reproduction the host as well live WITHIN their
as losing resources also incurs further host
costs in defending its tissues from parasitic
attack ECTOPARASITES
eg tapeworm
live andfeed on the Plasmodium
Unlike in a predator prey SURFACE of theirhost
relationship the reproductive potential
of the parasite is greater than that eg ticks lice
of the host fleas
Fox parasite
rabbit rabbit
Grass Grass
1
predatorprey
pyramid
p parasitehost
pyramid
CO EVOLUTION 31 THE PARASITE NICHE
Parasite adaptations have been selected in response to the particular adaptations that have evolved in
the host species. Because of this, parasites tend to have a narrow specialised niche: this is true in
terms of both being host-specific and also very specific in their ways of exploiting that host.
Many of a parasites needs are provided by the host, so this means that parasites have become
degenerate - they lack structures and organs that are found in other organisms. For example, the
tapeworm is an endoparasite that ives i the small intestine of its host and is surrounded by ingested
food, so it has no need for a digestive system. The production of unused tissue in an organism is a
waste of resources, so evolution has favoured the loss of these tissues.
, 5 b Parasitic lifecycles
PARASITE LIFECYCLE DEFINITIONS
Some parasites require only one host to complete their lifecycle but many parasitic lifecycles can
involve more than one species.
Definitive host — the organism on which or in which the parasite reaches sexual maturity and so
carries out sexual reproduction.
Intermediate host — the organism on which or in which developmental stages happen to complete
the parasite’s lifecycle.
Parasitic lifecycles may also have species that play an active part in the transmission of the parasite.
These are called vectors and they may also be hosts. For example, the mosquito is the vector for the
malarial parasite, and it is also the definitive host.
MA L AR l A
The human disease malaria is caused by Plasmodium
Definitive host mosquito
Intermediate host human
vector mosquito
An infected mosquito acting as a vector bites a human
Plasmodium enters the human bloodstream
Asexual reproduction occurs in the liver and then in the red blood cells
when the red blood cells burst gameocytes are released into the bloodstream
Another mosquito bites an infected human and the gameocytes enter the mosquito maturing
into male and female gametes allowing sexual reproduction to now occur
The mosquito can then infect another human host
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