Ch. 14

Question 1

oscillating dynamics.

Answer 1

What is beneficial at one time point, is not at the next due to alterations in
environmental conditions over time.

Question 2

coexistence can be

Answer 2

stable or unstable.

Question 3

Stable coexistence

Answer 3

means that species tend to recover from low densities and that
species densities may fluctuate over time, but don’t disappear.

Question 4

Equalizing Mechanisms

Answer 4

Reduce fitness difference between species

All species in the community respond in the same way to the environment

The more similar species are in fitness the longer it would take for competition to favor one species at the expense of another

Cannot facilitate the recovery of species from low densities

Cannot lead to stable coexistence

Question 4

Unstable coexistence

Answer 4

means that even if species coexist for long periods of time
there are no ecological mechanisms that will promote species recovery when at
low abundance leading to species extinction and decline in species richness.

Question 5

Stabilizing Mechanisms

Answer 5

Stable coexistence requires stabilizing mechanisms

The species similar in fitness requires less stabilizing mechanisms to maintain coexistence

Include: resource partitioning and frequency-dependent selection – because these operate whether the environment fluctuates or not
and thus are called fluctuation-independent mechanisms.

Mechanisms that depend on population densities and environmental factors are called fluctuation-dependent mechanisms.

Question 6

fluctuation-dependent mechanisms.

Answer 6

Mechanisms that depend on population densities and environmental factors

Question 7

Origins of the Idea of the Storage Effect

Answer 7

Discovered by Peter Chesson in the 1980’s
He was exploring a hypothesis proposed by another scientist: Peter Sale

Sale’s hypothesis stated that temporal variation in recruitment could allow the
coexistence of many species of fish competing for territories on a coral reef.

Question 7

fluctuation-independent mechanisms.

Answer 7

resource partitioning and frequency-dependent selection – because these operate whether the environment fluctuates or not

Question 8

Fluctuation-Dependent Mechanisms

Can be classified into two categories:

Answer 8

Nonlinearity of competition

Storage Effect

Question 9

The storage effect

Answer 9

temporal variation in environmental conditions leads to
species coexistence

Question 10

competition for territories on the reef is intense; once a territory is
obtained

Answer 10

it is held until the death of the individual

Question 10

Sale predicted that even if fish have generalized diets and habitat usage….

Answer 10

as long as there is
temporal variation in the availability of territories (due to death of individuals) and variation in the
settlement of fry of different fish species on those territories, a wide diversity of species can
coexist within the coral reef habitat.

Question 11

‘lottery model’

Answer 11

territory establishment is on a
first-come-first serve basis.

Question 12

Temporal variation in recruitment, coupled with relatively long-lived adult stage
that can “store” the population contributions allows these temporal fluctuations to be

Answer 12

a stabilizing mechanism.

Question 12

Key features of the Lottery Model (fix)

Answer 12

Adult fish hold territories on the reef until death. Adults are iteroparous (reproduce
more than once), and each species has overlapping generations.

2. To survive and reproduce territories are necessary. Space is limiting. There are
   always more fry fish attempting to establish territories than there are territories.
   Allocation of territories is a first-come-first-serve basis.

Fry are produced in abundance and dispersed.

Fry survival depends on environmental conditions, which fluctuate over time, species
differ in their response to those conditions. So this means that all species have relatively
“good” and “bad” years for fry survival and territory recruitment.

Question 13

Adler (2006)

Answer 13

Empirical testing of the storage effect: Prairie Grasses

Question 14

Adler (2006) tested this idea in prairie plants in plots in Kansas. what did he find

Answer 14

All three species have long life spans, differential species-specific responses to
environmental variation (i.e. precipitation and temperature).

Found that the effects of competition were more severe in more favorable years,
but neighboring species had weak or even facilitative effects during bad years.

Question 15

Environmental variation may promote

Answer 15

species coexistence

Question 16

Environmental variation can have important consequences

Answer 16

on a global scale over
geologic time in shaping:

Glacial cycles

Shift in species ranges

Species extinction

Alterations to biodiversity

Question 17

An equilibrium, or stable state, is a state in which

Answer 17

the population isn’t changing.

Question 18

Alternative stable state

Answer 18

describes a situation where communities may exist in
different configurations (of species richness, species composition, food web
structure, size structure) and these different community configurations represent
different equilibrium states.

Question 19

who determines that alternative states may exist?

Answer 19

Mathematical modeling by Robert May first elucidated that in fact, alternative
states may exist.

Question 20

The concept of alternative stable states is represented by a ball on a landscape of
hills and valleys.

Answer 20

Here the picture shows that communities remain stable if in the valley until an
environmental disturbance or changes causes it to shift to a new state.

Question 21

A change from one community state to another is termed

Answer 21

Regime Shift or

Phase Shift

Question 22

The critical threshold at which a system undergoes a regime shift is referred to as the

Answer 22

tipping point.

Question 23

Resistance is the term used to describe

Answer 23

the strength of perturbation needed to shift a community from one
state to another.

Question 24

the strength of perturbation needed to shift a community from one
state to another is called

Answer 24

resistance

Question 25

Resilience is the term used to describe

Answer 25

the speed at which a community recovers after a perturbation.

Question 26

the term used to describe the speed at which a community recovers after a perturbation.

Answer 26

Resilience

Question 27

Ecological Resilience

Answer 27

the magnitude of a perturbation that a system can withstand before
undergoing a regime shift.

Question 28

Engineering Resilience –

Answer 28

the time it takes for a system to recover from a perturbation.

Question 29

Two definitions of resilience

Answer 29

Engineering Resilience and Ecological Resilience

Question 30

Ecological shifts can be at

Answer 30

the macro or microscales:

Coral reef systems → macroalgae

Savannas → Deserts

Microbial communities in the gut of Humans after antibiotics

Question 31

Anthropogenic changes have resulted in

Answer 31

an increase in regime shifts in recent years over shorter
periods of time.

Question 32

Rate of change to environments can happen

Answer 32

smoothly, gradually over time

OR

In large steps, abruptly over time

Question 32

Mechanisms that lead to alternative stable states

Answer 32

Positive Feedbacks

Nonlinear Species Interactions (remember the species that are better competitors
at low resource levels vs species that are better competitors at high resource
levels)

Size-based refuges from predation

Priority Effects (who arrives in an ecosystem first)

Question 33

( see slide) Zooplankton community composition changes

Answer 33

smoothly with changes in planktivore density

Question 34

Environments are always

Answer 34

changing

Question 35

Environments are always changing, and as a result, communities of organisms

Answer 35

also change