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Lecture 18

BIOL 215 Lecture Notes - Lecture 18: Intertidal Zone, Ecosystem Engineer, Biogeography

Biology (Sci)
Course Code
BIOL 215
Neil Price

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BIOL215 Lecture 18 Notes
In food chain or food webs, the concept means transferring energy
from plants to herbivores and carnivores
Food chain is looking more at the linear connection between two
species while food web is looking more at the big community and
the multiple food chains within the food web
When we talk about food chains, we use trophic levels (the
positions in the food chain/food web) to describe who eats who
In trophic levels, the position tells you the function of the
individual in the food chain
What is the limit to food chain complexity? As the richness of a community increases, the number of
links in species tends to increase as well. Essentially, each species is connected to more and more
species as diversity increases. In addition, chain length is the number of links running from the top
predator to the basal species
In general, at any trophic level, many more species interacting (not much longer food web). On
average, in a food web, every species is linked to anywhere between 8-12 species, but the trophic
chain levels is anywhere between 4-5 levels
Two hypothesis to explain why food chains aren't longer:
The energetic hypothesis: Length is limited by inefficient transfer of energy
The dynamic stability hypothesis: long food chain are not stable
For those in community ecology, it's important to understand that when looking at the community,
we are expecting a relatively constant relative-prey and herbivore-plant ratio. It follows the transfer
of energy concept where there has to be an equilibrium of predator-prey/herbivore-plant ratio
Generalization (page 407-409):
As diversity increases a species is connected to more and more species
Food chains tend to be short
There is a constant proportions of top predator, intermediate species and basal species in a
community at equilibrium
Keystone species: Is a species that plays a role in a structural role in a community that is completely
disproportionate to its abundance. It is a species that ends up structuring the community due to its
function, not because of its abundance
Paine's experiment demonstrated the effects of keystone species in the sense that the control
(containing starfish) contained on average 15 species, while the starfish removal trials only contained
8 species with mussels dominating the majority of the species. The reason was because starfish
mediating coexistence by preferentially feeding on mussels and barnacles
There are various categories of keystone species:
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