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Ecology > Chapter 21: Energy Flow and Food Webs > Flashcards

Chapter 21: Energy Flow and Food Webs Flashcards

1
Q

The Artic is…

A

one of the msot remote and pristine areas on Earth

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2
Q

How much more PCB concentration were in breast milk from Inuit women than Quebec women?

A

7 times higher

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3
Q

PCBs

A

type of industrial chemicals called persistent organic pollutants (POPs)

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4
Q

Can POPs remain in the envrionment for a long time?

A

Yes

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5
Q

What form are POPs produced in at low latitudes?

A

they are produced in gaseous form and enter the atmosphere

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6
Q

Atmospheric circulation patterns

A

they carry them to the Artic, where they condense to liquid and fall from the atmosphere

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7
Q

What has been banned in North America but some developing countries still use them?

A

Manufacture and use of POPS

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8
Q

What is the correlation between POPs and diet?

A

-Inuit communities that ate mostly marine mammals had the highest levels of POPs
-Communities that ate herbiovorous caribou had lower levels
-Inuit community diets were centered around different trophic levels

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9
Q

Trophic Levels

A

describe the feeding positions of groups of organisms in ecosystems

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10
Q

The ecological roles of organisims are determined by…

A

their trophic interactions (what they eat and what eats them)

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11
Q

What is trophic level based on?

A

the number of feeding steps by which it is seperated from autotrophs

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12
Q

What does the 1st trophic level consists of…?

A

autotrophs or primary producers

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13
Q

Autotrophs

A

generate chemical energy from sunlight or inorganic chemical compounds

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14
Q

What trophic level generates most of the dead orgnaic matter in an ecosystem?

A

autotrophs

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15
Q

2nd Trophic Level

A

Herbivores that consume autotrophs; also includes detritivores that consume dead organic matter

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16
Q

3rd and higher trophic levels

A

Carnivores that consume animals from the level below

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17
Q

Ominvores

A

feed at multiple trophic levels

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18
Q

Omnivores Example

A

coyotes are opportunistic feeders, consuming vegetation, mice, other carnivores, and ond leather boots

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19
Q

Detritus

A

all arganisims are either consumed by other organisims or enter the pool of dead organic matter

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20
Q

What portion of biomass is consumed in terrestrial ecosystems?

A

small portion

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21
Q

Where does most of the energy flow pass through in the trophic levels?

A

detritus

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22
Q

What do detritivores consume?

A

dead organisims and feces

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23
Q

What are detritivores?

A

primarily bacteria, archaea, and fungi

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24
Q

What tropic level is detritus considered to be part of?

A

1st trophic level

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25
Q

What trohic level are detritivores part of?

A

2nd level

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26
Q

Where is much of the detritus in streams, lakes, and estuaries derived from?

A

terrestrial organic matter

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27
Q

Allochthonous Inputs

A

external energy inputs from detritus

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28
Q

Autochthonous Energy

A

energy produced by autotrophs

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29
Q

Where are allochthounous inputs most important?

A

stream ecosystems

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30
Q

River Continuum Concept

A

states that the importance of autochthonous energy inputs increases from the headwaters toward the lower reaches of a river

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31
Q

What increases and decreases as you go downstream?

A

-water velocity decreases
-nutrient concentrations increase

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32
Q

How is the amount of energy transferred from one trophic level to the next?

A

depends on the food quality and consumer abundunce and physiology

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33
Q

Second Law of Thermodynamics

A

states that during any transfer of energy, some is dispersed and becomes unusable

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34
Q

Available energy _____ with each trophic level

A

decrease

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35
Q

What portrays the relatice amounts of energy or biomass in each trophic level?

A

trophic pyramid

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36
Q

Is all of the biomass at each trophic level consumed?

A

no. Some of the energy is dispersed in the transfer to the next level

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37
Q

Why are energy and biomass pyramids similar in terrestrial ecosystems?

A

biomass is closely associated with energy production

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38
Q

What does the biomass pyramid look like in aquatic ecosystems?

A

Inverted

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39
Q

What are the primary producers?

A

phytoplankton

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40
Q

What is the life span of phytoplankton?

A

short life spans and high turnover

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41
Q

Where are inverted biomass pyramids most common?

A

productivity is lowest, such as nutrient-poor regions of the open ocean

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42
Q

Factors that determine how much energy flows from one trophic level to the next:

A

-Amount of NPP at basse of food web
-Proportion of each trophic level consumed by the one above it
-Nutritional content of autotrophs, detritus, and prey
-Efficiency of energy transfers

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43
Q

Do land herbivores or aquatic herbivores consume a lower proportion of autotrophs?

A

land herbivores consume a much lower proportion of biomass

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44
Q

How much terrestrial NPP is consumed on average?

A

about 13%

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45
Q

How much NPP is consumed in aquatic ecosystems?

A

35% on average

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46
Q

What kind of relationship does NPP and amount of biomass consumed by herbivores have?

A

positive relationship

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47
Q

What may be limited by the amount of food available?

A

Herbivore production

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48
Q

Hypotheses for why terrestrial herbivores consume less of the available biomass?

A

-Herbivores are constrained by predators and never reach carrying capacity
-Autotrophs have defenses against herbivory, such as secondary compounds, spines, etc.
-Phytoplankton are more nutritious for herbivores than terrestrial plants

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49
Q

What hypothesis is suppourted by predator removal experiments?

A

Herbivores are constrained by predators and never reaching carrying capacity

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50
Q

What is the main difference in resource-poor environment plants and resource-rich environment plants?

A

resource poor plants have stronger defenses

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51
Q

What do unicellular algae generally lack?

A

chemical and structural defenses

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52
Q

Why are terrestrial plants not as nutritious as phytoplankton?

A

terrestrial plants have structural components, such as wood, which have few nutrients

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53
Q

What is an indicator of food quality?

A

the ratio of carbon to nutrients such as N and P

54
Q

What has a closer carbon to nutrient. ratio to herbivores?

A

freshwater phytoplankton

55
Q

Trophic efficiency

A

amount of energy at one trophic level divided by amount of energy at the trophic level immediately below it

56
Q

Three components of trophic efficency

A

-proportion of available energy that is ingested (consumption efficiency)
-proportion of ingested food that is assimilate (assimilation efficiency)
-proportion of assimilated food that goes into new consumer biomass (production efficiency)

57
Q

Consumption efficency

A

-higher in aquatic ecosystems than in terrestrial ecosystems
-consumption efficencies also tend to be higher for carnivores than for herbivores

58
Q

Assimilation efficiency

A

is determined by food quality and consumer physiology

59
Q

Why is the food quality of plants and detritus low?

A

because of complex compounds such as cellulose, lignins, and humic acids, which are not easily digested, and low concentrations of N and P

60
Q

Animals have __________ similar to the animals consuming them

A

carbon to nutrient ratios

61
Q

Assimilation efficencies of herbivores and detritivores

A

20-50%

62
Q

Assimilation efficiencies of carnivores

A

about 80%

63
Q

Endotherm vs Ectotherm digestion

A

-Endotherms digest food more quickly than ectotherms and thus have higher assimilation efficiencies

64
Q

What do mutualistic symbioints help herbivores digest?

A

cellulose

65
Q

How do ruminants break down cellulose?

A

they have a modified foregut with bacteria and protsists that break it down

66
Q

What has higher assimilation efficencies than all other herbivores?

A

ruminants

67
Q

What is production efficeiency strongly related to?

A

thermal physiology and size of the consumer

68
Q

What do endotherms allocate more energy to than ectotherms?

A

heat production, so they have less for growth and reproduction

69
Q

What size endotherm loses a grerater proportion of its heat across is body surface?

A

small endotherm lose a greater proportion of its heat than large endotherms
-lower production efficiency

70
Q

What can impact trophic efficiency can can determine consumer population size?

A

change in food quantity or quality

71
Q

How much did Steller sea lion populations in Alaska decline by over 25 years?

A

about 80%

72
Q

What seemed to be the cause of the smaller body size and decreased birth rates of Steller sea lions in Alaska?

A

food quantity or quality problems (decline in trophic efficiency)

73
Q

What did the change in diet of Stellar sea lions reflect in the fish community?

A

it reflected a shift in the fish community

74
Q

What can influence the flow of energy at multiple trophic levels?

A

changes in the abunduances of organisims at one trophic level

75
Q

The “bottom up” view

A

resources that limit NPP determine energy flow throught an ecosystem

76
Q

The “top down” view

A

-energy flow is governed by rates of consumption and other interactions at the highest trophic level
-this influences multiple trophic levels below them

77
Q

What control affects energy flow in an ecosystem?

A

Both controls are operating simultaneously (bottom up and top down)

78
Q

What control has implications for the effects of trophic interactions on energy flow?

A

top-down control

79
Q

Trophic cascade

A

series of trophic interactions that result in changes in biomass and species composition

80
Q

Example of a trophic cascase

A

Predation by a top carnivore (4th level)
decreases abundance of 3rd level
carnivores, which leads to an
increase in herbivores (2nd level),
and then a decrease in primary
producers.

81
Q

Where do many examples of trophic cascades come from?

A

accidental introductions of non-native species or extinctions of native species

82
Q

Flecker and Townsend (1994)

A

-compared the effects of brown trout and native galaxies using artificial steam
-brown trout reduced total invertebrate density more than galaxias did
-algal abundance also increased more with brown trout present
-showed a trophic cascade since brown trout had a greater effect on primary production than native fish did

83
Q

What type of ecosystems are more complex and what does this mean for them in terms of trophic cascades?

A

terrestrial ecosystems are more complex than aquatic ecosystems making trophic cascades unlikely

84
Q

Why are trophic cascades unlikely in one species in terrestrial ecosystems?

A

a decrease in one species would be compensated for by increases in similar species that were not being consumed as heavily

85
Q

Dyer and Letourneau (1999)

A

-tropical forest trophic cascade study with four trophic levels
-insecticides were used to kill all ants and beetles were introduced to some plots. Also varied the soil fertility and light lecels to test for bottom up effects
-Found that the trophic cascade was the only significant influence on leaf production by Piper trees
-The predatory beetles decreased ant abundance, which increased rates of herbivory, and decreased leaf area per tree.

86
Q

What factors have a signifciant effect on leaf production?

A

light levels and fertility, but the top-down effects of predation are still persistant

87
Q

What determines the number of trophic levels in an ecosystem?

A

-the number of levels may change due to addition or loss of a top predator or a predator in the middle of the food chain
-omnivore may change food prefrence

88
Q

Factors that control the number of trophic levels

A

-amount of energy entering via primary production
-frequency of distribution
-ecosystem size

89
Q

Why does the amount of energy that enters the ecosystem via primary production affect the number of trophic levels?

A

-more production should allow for more trophic levels
-this appears to be important in resource-poor ecosystems

90
Q

Why does the frequency of disturbance effect the number of trophic levels?

A

-higher trophic levels depend on lower levels and take time to reestablish after disturbance
-if disturbance is frequent, higher levels may never become established

91
Q

Why does the ecosystem size effect the number of trophic levels?

A

larger ecosystems support larger populations, have more habitat heterogeneity, and have higher species diversity

92
Q

Takimoto et al. (2008)

A

-a study of 36 islands in the Bahamas found that island size was correlated with number of trophic levels
-disturbance frequency did not impact trophic levels, but the top predator species changed

93
Q

Food webs

A

-conceptual models of the trophic interactions of organisims in an ecosystem
-diagram showing the connections between organisims and the food they consume
-shows qualitatively how energy flows from one component of this ecosystem to another

94
Q

What is often ignored in food webs?

A

-other interactions like pollination
-the role of microorganisims

95
Q

Interaction strength

A

measure of the effect of one species on the population size of another species

96
Q

Removal experiments

A

can determine interaction strengths, but can’t really be done for all links in a food web

97
Q

What can be used to predict strength of interactions?

A

-predator and prey body size
-this is because feeding rate is realted to metabolic rate, which in turn is governed by body size

98
Q

Paine (1966)

A

-removal of Pisaster sea star in rocky intertidal zone
-mussels become dominant after removal and species richness went from 15 to 8
-called Pisaster a keystone species because it has a greater influence than its abundance or biomass would predict

99
Q

Keystone species concept

A

implies that protecting a keystone species may may be critical for protecting the many other species that depend on it

100
Q

Keystone speices

A

-tend to be top predators but not always
-can be keysonte species in only part of their range which suggest that interaction strength depends on environmental context

101
Q

What can removal experiments provide for determining the strength of indirect effects?

A

can provide estimates of the net effect of a species

102
Q

Net effect

A

sum of the direct effect and all possible indirect effects

103
Q

What does a predator have a direct and indirect effect on?

A

-direct efect on its prey
-indirect effect on other species that compete with, facilitate, or modify the enviornment of the prey species

104
Q

When is the potential for indirect effects to offset or reinforce the direct effect of a predator?

A

when the direct effect is weak

105
Q

Berlow (1999)

A

-tested the potential for indirect effects to offest or reinforce the direct effect
-Whelks have a direct negative effect on mussels by eating them
-Barnacles facilitate mussels by providing crevices for mussel larvae to settle in
-when barnacle density is high, they do not attach well and are easily knocked off the rocks, along with the mussel larvae
-when barnacle density is low, whelk predation on barnacles has a negative indirect effect on mussels by providing them with a more stable settlement substrate
-when barnacle density is high, thinning by whelks has a positive indirect effect on mussels by providing them with a more stable settlement substrate

106
Q

If a predator’s effect on a prey species depends on the prescence or absence of other species…

A

the potential for the predator to elimanate that prey species is less

107
Q

What does variation associated with weak interactions promote?

A

coexistence of multiple prey species

108
Q

How is stability measured?

A

how much the populations change over time

109
Q

Charles Elton and Eugene Odum

A

argued that simpler, less diverse food webs should be more easily perturbed

110
Q

Robert May (1973)

A

used random assemblages of organisims to demonstrate that food webs with higher diversity are less stable using mathematical analyses

111
Q

What did strong trophic interactions accentuate in May’s model?

A

population fluctuations

112
Q

The more interacting species there were in May’s model, the more likelu that population fluctuations would reinforce one another. What does this lead to?

A

extinction of one or more species

113
Q

What are the factors that allow naturally complex food webs to be stable?

A

-As shown by Below, weak interactions can stabilize trophic interactions
-newer models and experiments suggest that some food webs may have a structure that allows increased species diversity to have a stabilizing effect
-buffering influence of weak interactions and behavioral or evolutionary changes in prey choice can help reduce population fluctutations

114
Q

Why is the identity of species in a food web important?

A

some species exert a disproportionally greater influence on stability, and others are more likely to go extinct

115
Q

Where is pant production often higher and why is this important?

A

-plant production is often higher in diverse communities
-more diverse communities recover better from disturbances

116
Q

How does increased plant diversity affect other species?

A

-arthropod communities were more stable
-specialist herbivores had lower stability
-all herbivores showed greater stability

117
Q

Mechanisims for how plant diversity influences arthropod community stability

A

-Greater and more stable plant biomass
-increased diversity in the arthropod communities

118
Q

What is higher plant diversity linked to?

A

greater predator abundance and diversity due to its influence on habitat diversity
-these predators may exert top-down effects on herbivore and plant abundances

119
Q

Portfolio effect

A

variation in one species’ population cancels out variation in another so that overall abundance in the communiuty remains the same

120
Q

What would a greater diversity among arthropods lead to?

A

greater probability of the portfolio effect

121
Q

Bioaccumulation

A

some chemicals are not metabolized or excreted, and become progressively more concentrated in tissues over an organisim’s lifetime

122
Q

Biomagnification

A

concentration of these compounds increases in animals at higher trophic levels, as animals at each trophic level consume prey with higher concentrations of the compound

123
Q

Rachel Carson (silent spring 1962)

A

-described the devestating effects of pesticides, espically DDT, on nontarget bird and mammal species
-Silent spring talked about the dangers of bioaccumulation and biomagnifaction of POPS

124
Q

DDT

A

-was thought to be a “miracle” in the 1940-1950 and was used extensively on crops and to control mosquitoes
-but it was building up in top predators, contributing to the near-extinction of peregrine falcons and bald eagles
-eventually banned after Carson’s publication

125
Q

How does biomagnification apply to the Inuit people?

A

-Inuit people that consume marine mammals have higher concentrations of POPs. These animals occupy 3rd,4th, or 5th trophic levels
-Inuits who consume mostly caribou (herbivores) have lower POP levels

126
Q

Where have pollutants been reported on Earth?

A

all environments

127
Q

What concentration of pollutants are found in animals in remote areas?

A

high concentrations espically in top consumers

128
Q

How are ecosystems connected?

A

by the movement of energy and materials

129
Q

How are POPs and other pollutants transported>

A

atmospheric circulation and animals

130
Q

Krummel et al. (2003)

A

-sampled sockeye salmon in eight lakes in southern Alaska. Also collected sediment cores to anylze for PCBs
-sedimentary PCB correlation was positively correlated with salmon density

131
Q

Blais et al. (2005)

A

-found that mercury and POPs are transported by northern fulmars (pelagic fish-eating seabirds) from the ocean to small ponds near their nesting colonies
-showed how behaviors can exacerbate problems of biomagnification

Ecology (12 decks)

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