Energy Transfer through Food Webs
Objective:
 Understand how energy is transferred through a food
chain or web
 Be able to use a dichotomous key
 Be able to construct the food web of barn owl
 Be able to estimate the producer biomass needed to
support a barn owl for one year
Owl Pellet Safety
 Wearing gloves
 Washing hands after use
 Allergic to pet: contains hair of
the prey
 Pellets: heat sterilized
Terminologies
 Species →
Population →
Community
 Autotrophs/ producers
 Consumers
 Primary- herbivores
 Secondary-carnivores
 Tertiary)-omnivores
 Detrivores /
decomposers :
recycles nutrients
Background
 Food chain:
 Energy moves through a community as organisms feed
on one another.
 Simplified, linear representation of energy flow
• Food web:
• complex and
realistic
• shows all possible
flow path
 First Law of
Thermodynamics:
 Conservation of energy
 Quantity and quality of energy
transferred


efficiency
heat
 Second Law of
Thermodynamics:
 Entropy: degree of disorder
within a system
Energy Flow
Eagle/
Trophic Structure
 Pyramid of Number
 Pyramid of Biomass
 Pyramid of Energy
Top
Predato
r
Chinook
(0.1
Salmon/
Calories
Tertiary
)
consumer
(1 Calories)

Example:
School of minnows/
Secondary consumer
(10 Calories)
Zooplankton/
Primary Consumers
(100 Calories)
Phytoplankton/Producers
(1000 Calories)
Trophic Level: position in the feeding hierarchy
Pyramid of Biomass
Pyramid of Energy
Constructing a food web and pyramid of biomass
for Barn Owl (Tyto alba)
 Top predator
 Nocturnal
 Hunt at night
 Have an excellent vision
 Acute sense of hearing
 Feathery depressions around
eyes
 Swallow whole prey
 Digest only fleshy parts
 Indigestible portions of prey :
PELLETS or CASTING
 Needs 6-12 hours to form
casting
 Casting become a home and
source of food for a variety of
insects
 Prey:10-15 per night
 Herbivores: Rodentia
eg: mice, voles, rats, pocket
gophers.
 Carnivores: Insectivora
eg: moles, shrews
 Life expectancy: 7-8 years
 Cosmopolitan Species
Procedure
 Dissect an owl casting
 Identify the animal remains
contained within the casting
using a DICHOTOMOUS KEY
 INSECTIVORA :No
Gap(Diastema) between
incisors and cheek teeth
 Zygomatic Arch
 RODENTIA: Gap (Diastema)
between incisors and cheek
teeth
 Infraorbital Canal
Hypothesis
 H1:the number of producers that it takes to support a
barn owl with a diet consisting Rodent is higher than a
diet consisting of Insectivores
 H0:the number of producers that it takes to support a
barn owl with a diet consisting Rodent is NOT higher
than a diet consisting of Insectivores
 Homework : Page 41 through 43
Page 44 (Education Majors Only)