Ch. 7

Question 1

competitive exclusion

Answer 1

“two species cannot exist on one limiting resource”.

Question 2

David tilman quote to be familar with

Answer 2

“Multispecies stable equilibrial coexistence
requires interspecific tradeoffs. If a species arose
that was able to avoid such tradeoffs and be a
superior competitor relative to all other species, it
would eliminate its competitors.”

Question 3

major factor influencing
community structure.

Answer 3

Historical perspective:
Gause (1934) conducting experiments on competitive exclusion

Lotka/Volterra (1925, 1926) independently develop mathematical theory of interspecific
competition

Question 4

Interspecific competition is the
( def 1 ) grover 1997

Answer 4

interaction occurring between species when increased
abundance of a first species causes the population growth of a second to decrease, and
there is a reciprocal effect of the second on the first. (Grover, 1997)

Question 5

Interspecific competition
( cas 2000)

Answer 5

Interspecific competition between two species occurs when individuals of one species
suffer a reduction in growth rate from a second species due to their shared use of limiting
resources (exploitative competition) or active interference (interference competition).
(Case, 2000)

Question 6

two special cases of competition

Answer 6

Exploitative competition (a.k.a. resource competition)

Interference competition (a.k.a. contest competition)

Question 7

Exploitative competition (a.k.a. resource competition)

Answer 7

When a species consumes a shared resource that limits its and other species’ population growth
making that resource less available to other species.

Question 8

Interference competition (a.k.a. contest competition)

Answer 8

Occurs when one species restricts another species’ access to a limiting resource.

Can encompass overt aggression such as in territorial defense or just occupying the space another
individual needs.

Question 9

Lotka-Volterra competition model

Adds in the term α which is a

Answer 9

competition coefficient and this constant reflects the effect
of an individual species on the per capita growth rate of the alternative species.

Question 10

Lotka-Volterra competition model is based on what type of model

Answer 10

Based on logistic growth model

Question 11

Lotka-Volterra competition model on density and population between species

Answer 11

the density of one species has a negative effect on the population
growth of the second species.

Question 12

zero growth isoclines of species

Answer 12

see slides

Question 13

Founder control

Answer 13

the outcome is dependent on the
initial starting abundances of species 1 and
species 2.

Question 14

What is a resource?

Answer 14

A resource is any substance or factor which can lead to increased population growth rates as its
availability in the environment is increased, and which is consumed by an organism (Tilman,
1982).

Resources are entities which contribute positively to population growth, and are consumed in the
process (Grover, 1997).

Question 15

two properties that define a resource:

Answer 15

A resource contributes positively to the growth rate of the consumer population

2. a resource is consumed (and is thus made unavailable to other individuals or species).

Question 16

Resource types

Answer 16

biotic and abiotic

Question 17

examples of biotic resource types

Answer 17

Prey (for predators)

Plants (for herbivores)

Seeds (for granivores)

Question 18

examples of abiotic resource types

Answer 18

Minerals

Light

Space (although stronger for sessile
organisms like sponges)

Question 19

One consumer, one resource: R*

Answer 19

R* is the intersection of mortality and per capita birth rate

Presumably there is an upper limit to per capita birth rates, and is generally approached in an asymptotic fashion as limiting resources become less available.

Question 20

If R > R*

Answer 20

Then, the consumer population will increase over time and the abundance of resources
will decline to the R* point (the equilibrium point).

see graphs

Question 21

two species competing
for one resource

Answer 21

Conclusions from this analysis

1. Two species cannot exist on one limiting resource.
2. The species that can maintain population growth with the lowest resource level (R*)
   will win.

Question 22

what can maintain coexistence of two species then?

Answer 22

?

One species has relatively greater
population growth rate at low resource
levels and the other has relatively
greater population growth rate at high
resource levels.

Question 23

Gleaners

Answer 23

– grow relatively well when
resources are scarce (here that is
species 2).

Question 24

Opportunists

Answer 24

grow relatively well
when resources are abundant (here
that is species 1).

Question 25

If resources fluctuate between high and low,

Answer 25

then two species might coexist because each has an advantage under different resource conditions.

Question 26

Essential resources:

Answer 26

required for growth and one essential resource cannot substitute for another. Example: plants require 20 different mineral resources (i.e. nitrogen, phosphorus, etc.)

Question 27

Substitutable resources:

Answer 27

one resource can take the place of another. Example: a fox predator might consume a number of different prey species to fulfill its nutritional needs (i.e. rabbits, squirrels, or mice)

Question 28

ZNGI

Answer 28

zero net growth isocline

Question 29

ZNGI defines

Answer 29

an equilibrium point at which the densities of species 1 and species 2 are unchanging (births = deaths for both species).

Question 30

Interspecific Competition results in an inverse relationship in density between the two competing species. This competition can come in the form of

Answer 30

exploitative competition or interference competition.

Question 30

C1 and C2 are

Answer 30

the consumption vectors for the two species. The equilibrium point is potentially stable because each species consumes more of the resource that most limits its own growth.

Question 31

R* is the point at which

Answer 31

per capita birth rate equals per capita death rate (know how to find R* on a graph.

Question 31

Resources are

Answer 31

entities that contribute positively to the consumer’s growth.

Question 32

When in competition for resources, two species

Answer 32

cannot be maintained on the same limiting resource & the one that can maintain itself on a lower amount of resource will be the one that wins.

Question 33

if resources fluctuate and are not stable,

Answer 33

it is possible that one species will have increased growth when resources are scarce (gleaners) and the other will have increased growth when resources are abundant (opportunists). This may lead to coexistence.

Question 34

When we expand the model further, we see that some resources may be substituted. And, under this relaxed assumption we see that the two species may coexist when each consumes more of the resource that limits its own growth. (Be able to point out the area on the graph where stable coexistence could be achieved.)

Answer 34

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