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Lecture 18

BIOL215 Lecture 18 Notes.pdf

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McGill University
Biology (Sci)
BIOL 215
Neil Price

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: • A major predator: (i.e. Pisaster ochraceus) which preys on the rocky inte
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