Ch. 9

Question 1

Mutualism

Answer 1

a reciprocally positive interaction between species (Bronstein, 2009).

Question 2

Examples of facilitation

Answer 2

Nitrogen-fixing plants that release nitrogen into the soil that benefits non-nitrogen-fixing neighbors; salt marsh plants that provide shade and reduce evapotranspiration, thus reducing soil salinity and allowing less salt-tolerant species to survive.

Question 2

Facilitation

Answer 2

s an interaction in which the presence of one species alters the environment in a way that enhances growth, survival, or reproduction of a second, neighboring species (Bronstein, 2009).

Question 3

Foundational species

Answer 3

generally provide modified environments so that whole communities can develop within the environment.

provide structural habitat for other species

Question 4

Ecosystem Engineers

Answer 4

modify the environment in a way that makes it more or less suitable for other species.

Question 5

symbiosis

Answer 5

An intimate and persistent association between two species.

Could be positive or negative, and can exist on a continuum. Some debate about the definition in terms of whether or not it includes both positive and negative relationships.
For the purposes of this chapter we will only examine positive symbioses

Question 6

Most mutualisms depend on

Answer 6

costs/benefits of the relationship.

Question 7

Members of each species exchange resources or services, but

Answer 7

are vulnerable to exploitation.

Question 8

How is cheating by one species or the other minimized?

Answer 8

Partner choice, partner fidelity

Question 9

what is the modificed lotka-volterra model for two-species interactions

Answer 9

Used Lotka-Volterra model of two-species interactions; changed the sign of the interactions from negative to positive.
Species 1 equation: dN1/dt = r1N1 {K1 – N1 + α12 N2 / K1}
Species 2 equation: dN2/dt = r2N2 {K2 – N2 + α21 N1 / K2}

Question 10

partner Choice - Example

Answer 10

Simms et al. 2006 found the yellow bush lupine preferentially allocates resources (makes larger nodules) to strains of Rhizobia bacterial strains (live in nodules on roots) that provided the greatest benefits to the plants.

Question 11

When interaction coefficients are positive

Answer 11

both species together attain larger biomasses than separately, and a “stable knot” (equilibrium point) occurs.

Question 12

As α and β increase

Answer 12

the equilibrium point continuously moves up and rightwards and finally passes into infinity.

Question 13

Gause and Witt showed that

Answer 13

considering mutualisms within the L-V framework is unrealistic

Question 14

For stable species coexistence to occur,

Answer 14

the positive effects of mutualism must be balanced by negative density dependence in some other area.

Question 15

Examples of negative density dependence that could limit population growth:

Answer 15

Strong intraspecific competition (competition within species)

Feedbacks from other life stages (i.e. nurse plants benefit seedlings, but not adults)

Fluctuating environments (sometimes good for participating mutualistic species, sometimes bad)

Competition from other members within the community

Question 16

Nurse plants

Answer 16

species whose canopies provide protective microclimate promoting the germination and growth of other species

Question 17

more recently models have shown that mutualisms can evolve from

Answer 17

negative relationships like parasitism and competition.

Question 17

This analysis (that the L-V elicits an unrealistic outcome), may be why beneficial interactions have been ignored in ecological theory.

Answer 17

??????

Question 18

Mutualisms can be context dependent

Answer 18

One example: mycorrhizal fungi & land plants
In this relationship:
Plants deliver carbon compounds to their associated fungi
Fungi deliver mineral nutrients (commonly phosphorous, sometimes nitrogen)
In nutrient-poor soils plants may obtain up to 80% of their requirements for nitrogen and up to 90% of phosphorous from their fungi.
BUT, this is context dependent and may shift when in nutrient-rich soils. No benefit to mineral provisions to plants, and plant growth may be slightly inhibited due to carbon demands of the fungus.

Question 19

A biotic example of context-dependent mutualisms

Answer 19

Ant-acacia mutualism
Acacia tree provides a nursery for ant broods. Ants will raise broods in the tree’s specialized thorns and are nourished by the tree’s extrafloral nectaries and Beltian bodies.
see slides

Question 20

Mutualistic interactions often depend on

Answer 20

the inclusion of other species, which can influence positive/negative effects of the interaction.

Question 21

Both biotic and abiotic factors can influence

Answer 21

the interaction between species to result in a beneficial or antagonistic relationship.

Question 23

changes from positive to negative interactions can be altered across

Answer 23

life stages and environmental conditions
see slide

Question 24

Mutualisms are extremely common in nature, but

Answer 24

much less work has been done to understand the complexities of their existence.

Question 25

Mutualisms can involve complex, multi-species interactions creating

Answer 25

ecological networks

Question 26

Gause & Witt (1935) utilized the Lotka-Volterra interspecific competition model and simply switched

Answer 26

the negative interaction to positive ones. But, the outcome seemed biologically unrealistic because it lead to an equilibrium point that would migrate upward.

Question 26

Gause & Witt (1935) All likely because trade-offs (particularly negative density-dependent effects)

Answer 26

were not taken into account in the model.

Question 27

Johnson (2010) developed a conceptual model to account for

Answer 27

trade-offs & the ant-acacia model is an example of a context-dependent mutualism.

Question 28

Palmer (2008) found

Answer 28

the ant-acadia model is dependent upon herbivore presence.

Question 29

minor differences in biotic or abiotic contexts can significantly alter

Answer 29

the mutualism context, leading to the evolution of antagonistic relationships.