1. food and drink

FOOD WEBS
READINGS:
FREEMAN
Chapter 54
What is a Biological Community (I)?
• An assemblage of many populations, each of
different species, that have similar
requirements or tolerances.
• All species that interact with each other in a
local area (acres or 1,000’s of square meters
or smaller).
What is a Biological Community (II)?
• Has a few species that are common (represented by
many individuals), many more that are rare
(represented by a few individuals) and most with
intermediate population sizes.
• Named on the basis of vegetative type, prevalent
species, moisture gradient, or geographical location.
• Characterized by productivity, key species, and/or
species diversity.
Milkweed Community: A
Model for Study of Species
Interactions
Summer and fall insect visitors at milkweeds come to
forage. The interactions that occur between species
include herbivory, predation, parasitoidism and
scavenging. These interactions can be summarized
in a simple food web.
Biotic Interactions in a
Milkweed Community (Summer)
• Common milkweeds1 attract a number of
species of insect14 and arachnid1 species.
• Milkweeds act as resources for bees3,
wasps2, ants2, butterflies2 and moths3.
• Crab spiders1 prey on visiting insects.
• Wasps and flies2 are parasitoids on eggs and
larvae of insects and spiders.
Number of species in a particular milkweed community.
Scientific American 253(1): 112-119
Biotic Interactions in a
Milkweed Community (Summer)
• Pollinators/Nectar
Feeders
- Bumble Bees2
- Moths3 (night)
- Honeybees1
• Nectar Feeders (only)
- Ants2
Scientific American 253(1): 112-119
Biotic Interactions in a
Milkweed Community (Summer)
• Major Herbivores
-Monarch Butterflies1
Larvae eat leaves and
young pods.
Adults collect necter
and pollen.
Scientific American 253(1): 112-119
Biotic Interactions in a
Milkweed Community (Summer)
• Predator
- Crab Spider1
• Parasitoids
- Trachinid Flies2
- Ichneumon
Wasps1
Scientific American 253(1): 112-119.
Biotic Interactions in a Milkweed
Community (Fall)
• Milkweed1 community in fall has a
different assemblage of species8.
• Nectar feeders are gone. Aphids1 (&
mosquities1) feed on plant sap.
• Milkweed bugs1 suck on developing
seeds.
• Milkweed beetles1 eat foliage
Biotic Interactions in a Milkweed
Community (Fall)
• Crab spiders1 continue to ambush prey.
• Ichneumon1 and mud-dauber1 wasps
are parasitoids and predators.
• Daddy longlegs1 scavenge on insect
remains, capture small prey, sip nectar
from the few remaining flowers.
Number of species
Scientific American July 1985
Biotic Interactions in a Milkweed
Community (Fall)
• Primary Consumers
(plant sap, seeds,
leaves, etc)
- Aphids1
- Mosquitos1
- Milkweed Bugs1
- Milkweed Beetles1
Biotic Interactions in a Milkweed
Community (Fall)
• Predator
- Crab Spider1
- Mud-dauber wasp1
• Parasitoid
- Ichneumon Wasp1
• Scavenger
- Daddy Longlegs1
FOOD WEB
• A food web provides a summary of important
eating (trophic) relations between populations
of different species in a community.
• A complex pathway along which matter and
energy moves among many different species
at different trophic levels.
• It is a network of interlinked food chains.
• It links primary producers with primary
consumers, secondary consumers and higher
level (3rd, 4th …) consumers.
• A given species can be included in several
trophic levels in a food web.
A Milkweed Community Food Web
Trachinid
Flies2
Ichneumon
Wasps1
Monarch
Butterfly1
Larvae
(Leaves)
Crab
Spiders1
Honeybees1
Moths3
Bumblebees2
Ants2
(Flowers)
Common Milkweed1
Producer
Primary Consumer Secondary Consumer
Defining Community Structure
• Several approaches have been used to
define community structure. They are:
- species composition;
- successional stage;
- species richness and species diversity;
- food web complexity.
• Each approach has strengths and
weaknesses. Thus, community ecology is
currently in a state of active investigation.
Species Composition
• Species lists serve as the simplest
versions of species composition in most
biological communities.
• Only crude estimates of population
sizes of species within communities
have been attempted.
Successional Stages
• Succession is a non-seasonal,
directional and continuous change due
to extinction and colonization of a site
by species populations.
• Ecologists distinguish between primary
succession and secondary succession.
Early Stages of Secondary
Succession
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Late Stages of Secondary
Succession
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Simple Model of Primary
Succession
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More Complex Model of
Primary Succession
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Species Richness and Species Diversity
• Species richness is a simple count of
how many species are present in a
given area.
• Species diversity is a measure of the
relative abundance of species.
• These two aspects of community
structure will be studied in more detail
later on in BioS 101.
Species Richness in a Biological
Community
• Over 10,000 species have been
documented in the Great Smoky
Mountains National Park (520,004
acres). Scientists believe an additional
90,000 species may live here.
• Wolf Road Prairie Preserve (80 acres) has a
plant species list that contains 327 scientific
names of native plants.
Species Richness and
Productivity
60
TOTAL PLANT COVER (%)
• Increasing species richness
has been shown to increase
community productivity.
• Note productivity is
measured as % of plot
covered by plants rather
than biomass.
• Freeman (2005) describes
this experiment and reports
the results in Figure 53.24.
50
40
30
20
10
0
1
3
5
7
9
11
13
15
17
19
21
NUMBER OF PLANT SPECIES PER PLOT (S)
23
Species Richness and
Community Stability (I)
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Species Richness and
Community Stability (II)
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FOOD WEB COMPLEXITY
• A food web is one of the most basic and
revealing description of community structure.
• In most communities, a few keystone species
control population dynamics within the
community.
• Thus, even in communities that contain
1,000’s of species, only a few have
populations that account for the majority of
matter and energy transactions.
Some Food Webs in Hubbard Brook
• The Hubbard Brook
Experimental Forest, a
7,800 acre New
Hampshire reserve, has
been a study site for
matter and energy
studies for over 50
years.
• The food web studies of
the reserve serve as a
model for the study of
community structure.
An Ariel View of
3 Study Sites
Green Food Web in Hubbard Brook
• Food webs that begin
with primary producers
are often called GREEN
or GRAZING food
webs.
• In Hubbard Brook,
deciduous northern
hardwood trees
including sugar maple,
beech, yellow birch and
some white ash are the
dominant producers.
Green Food Web in Hubbard Brook
• White-tailed deer and
saddled prominent moth
(caterpillar) are two
herbivores.
• Eastern chipmunk and
scarlet tanager feed on
both plant and insects.
• Red-tailed hawks are
top level consumers.
Green Food Web in Hubbard Brook
Red-tailed Hawk
Eastern
Chipmunk
White-tailed
Deer
Scarlet Tanager
Saddled Prominent
Moth (Caterpillar)
Maple, Beech, Ash, Cherry, Blackberry
(Leaves, Fruits, Seeds)
A food chain from producers to highest level consumers.
Brown Food Web in Hubbard Brook
• A BROWN or
DECOMPOSER food
web begins with dead
plant and animal
remains (detritus).
• Leaf litter (detritus)
provides an important
food source in a
deciduous forest.
Brown Food Web in Hubbard Brook
• Bacteria and fungi are
important primary
decomposers in forest litter.
• Earthworms,sow bugs and
beetles play a primary role
in decomposition.
• Other species of beetles,
spiders, salamanders and
shrews feed on the larger
invertebrates on the forest
floor.
Brown Food Web in Hubbard Brook
Red-tailed Hawk
Eastern Chipmunk
Scarlet Tanager
Red-backed
Salamander
Spiders
Ground Beetles
Tiger Beetles
Wood boring, Stag,
& Scarab Beetles
Short-tailed Shrew
Earthworms
Fungi
Sow Bugs
Bacteria
Litter
(Dead parts of Maple, Beech, etc.)
Dead plant parts and the remains and droppings of animals are
At the base of brown or decomposer food webs.
Another View of the Brown
(Decomposer) Food Web(I)
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Another View of the Brown
(Decomposer) Food Web(II)
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Food Webs Consist of Short
Food Chains
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FOOD WEBS
READINGS:
FREEMAN
Chapter 54