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Chapter 14

BIOLOGY 2F03 Chapter Notes - Chapter 14: Flour Beetle, Caddisfly, Red Fox

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D R.Kajura

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CHAPTER 14- Herbivory and Predation
Herbivores consume plants but don’t usually kill plant
Predators kill and consume their organisms
Parasites live on the tissues within the host, reducing their fitness
Parasitoid, an insect whose larva consumes the host and kills it in the process
Pathogens: induce disease in a host
Complex interactions
Exploitative interactions weave populations into a web of relationships that
defy easy generalization
Parasites Manipulating Host Behavior: some species alter the behavior of
animals they exploit
Alter behavior to benefit transmission of the parasite
Acanthocephalans change behavior of amphipods in a way so that they are
more likely to be eaten so that the life cycle can be completed
They induce positive phototaxis, a behavior which puts the amphipods on the
surface of the lake, making them more likely to be eaten
Transmission to the host as well as size may be a faction
Moore: Control and infected group
Infected some and some not, then mixed, parasite puts it in less sheltered
environment and more out in the open
Birds more likely to eat infected individuals
Altered behavior increases probability of being eaten, continuing the parasite
life cycle
Another example of a parasite is the Wild flowers produced by a fungus
Promotes growth of fungus but kills the plant
Entangling of Exploitation and competition
Flour beetles, depended on temperature and moisture
Cannibalism differs based on temperature
Completing the life cycle of adeline means being ingested by a beetle
Adelina reduces tribolium populations (competition in different conditions)
Here susceptibility to parasitism completely destroys the competitive
advantage, as some species may be better under certain environmental
conditions but at these conditions are also more likely to get a parasite
Exploitation to Abundance
Predators, parasites and pathogens influence the distribution, abundance and
structure of prey and host populations
Herbivorous Stream Insect and Algal food: the insect was caddisfly, forms a
shell-like structure around the larvae grow and feeds on algae during
To look at the effects of predators on theses algae, researchers placed tiles at
the botton of the creek to watch them develop (algae was to grow on these
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After population reached its peak, the algal population was decreased in 2
weeks by the caddisfly, they depleted their own food supply
Restricted caddisfly so they couldn’t get to the tiles and looked at the algal
development (took away the predator)
Without the predator the population of algae was higher (tiles were more
densely covered)
Another Example of predators on species abundance: Cactus and moth in
Cactus and a herbivorous moth: growth of Catcus resulted from lack of natural
By inducing the months (whose larvae digest the inside of the cactus) they
were able to greatly reduce the population density of this plant
Summary: Moths are parasitic to cactus
Pathogenic parasite, predator and prey: mite infesting foxes, killed 40% of
British foxes
Following the decrease in the red fox population by the mites, there was an
increase in the hares (predator decreases their prey increases)
Red fox cyclically affects prey species
Predator-prey, host-parasite and host-pathogen relationships are dynamic
Temporal dynamics
Snowshoe hares and predators: lynx is a big predator, they share population
Thought that the solar radiation affected the food supply of the hares and thus
the lynx – disproved
Decimation by disease, physiological stress at high pop, starvation due to
reduced food quality
This was the overpopulation hypothesis
Their is the cyclic hypothesis which states that as prey increases so will
They can grow fast and exhaust their own food supplies (hares)
They have other predators
Lynx and coyotes populations increase with increasing hares
They hypothesis are not mutually exclusive but linked
Food and predication impacts
They created blocks of forest minimum of 1 km, to test the impact of food and
plant tissue quality on hare numbers, only hare predators were hawks and
Hares peaked then declined
Predator reduction and food study plots had the greatest hares
Mathematical models
Hares: can mathematical models on predatory or parasite cycles can be
Predator increase can be correlated with prey decrease
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