Class Notes (839,081)
Canada (511,183)
BIOB50H3 (258)
Lecture 16

BIOB50Winter2012 Lecture 16/20 (he redid it as Lecture 20 later) - includes pictures and complementary readings from text.docx

12 Pages

Biological Sciences
Course Code
Marc Cadotte

This preview shows pages 1,2 and half of page 3. Sign up to view the full 12 pages of the document.
BIOB50Winter2012 Lecture 1620 Energy Flow and Food Webs Chapter 20 Introduction o What links organisms together in the context of ecological functioning is their trophic interactionswhat they eat and what eats themo The influence of an organism on the movement of energy and nutrients through an ecosystem is determined by the type of food it consumes and by what consumes itFeeding Relationshipso Trophic levels describe the feeding positions of groups of organisms in ecosystemso Each feeding category called a trophic level is based on the number of feeding steps by which it is separated from autotrophs o The first trophic level consists of autotrophs primary producers o Figure 203 Trophic Levels in a Desert Ecosystemeach trophic level is characterized by the number of feeding steps by which it it removed from autotrophs primary producers o detritus is considered part of the first trophic level and detritivores are grouped with herbivores in the second trophic level o All organisms not consumed by other organisms end up as detrituso Some organisms do not conveniently fit into trophic levels o Omnivores feed at multiple trophic levelso Example coyotes are opportunistic feeders consuming vegetation mice other carnivores and old leather bootso All organisms in an ecosystem are either consumed by other organisms or enter the pool of dead organic matter detritus o In terrestrial ecosystems only a small portion of the biomass is consumed and most of the energy flow passes through the detritus1o Figure 204 Ecosystem Energy Flow Through DetritusB numerous studies of both terrestrial and aquatic ecosystems have found that in most ecosystems most of the NPP ends up as detritusC relatively little of the the NPP in an ecosystem is consumed by herbivoresomore than 50 of NPP ends up as detritus the up and down trend is stronger for aquatic ecosystemsin most of the studies only a small proportion of NPP is consumed by herbivores o Much of the input of detritus into streams lakes and estuarine ecosystems is derived from terrestrial organic matter o Those external energy inputs are called allochthonous inputs o Energy produced by autotrophs within the system is autochthonous energy Energy Flow among Trophic Levels o The amount of energy transferred from one trophic level to the next depends on food quality and consumer abundance and physiologyo A trophic pyramid is a graphical representation of trophic relationshipso Energy will decrease with each trophic levelo Figure 205 Trophic Pyramid Schemes2
More Less
Unlock Document

Only pages 1,2 and half of page 3 are available for preview. Some parts have been intentionally blurred.

Unlock Document
You're Reading a Preview

Unlock to view full version

Unlock Document

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.