Interspecific Competition

Question 1

Define interspecific competition

Answer 1

competition between individuals by the shared use of one or more resources that are in limited supply, resulting in a mutual reduction in fitness

Question 2

What are the two main types of competition

Answer 2

1. exploitation competition
2. interference competition

Question 3

Define exploitation competition

Answer 3

(also known as resource or scramble competition)
when individuals interact indirectly as they compete for a common limiting resource

Question 4

What are examples of common limiting resources in exploitation competition

Answer 4

food/nutrients, habitat, space, light
limiting resources mean that they do not have ample amount (ex. even though need oxygen, there is lots of it so doesn’t count)

Question 5

Define interference competition

Answer 5

(also known as contest competition)
is direct competition when individuals interfere or impede the access of others to a resource even if the resource is not in limited supply

Question 6

Examples of interference competition

Answer 6

tree canopies blocking light, territoriality, changes to the environment such as plants releasing chemicals to forbid other plants to grow there, or direct fighting/hoarding

Question 7

Explain example of exploitation and interference competition in dung beetles

Answer 7

use feces to feed themselves and their larvae

exploitation = dung is a limited resource and quickly removed (rolled, buried. etc).
interference = beetles often fight over dung

Question 8

exploitation and interference competition often occur ______

Answer 8

simultaneously

Question 9

they found that beetles who “won” in interference competition were often ____

Answer 9

larger and have a higher body temperature

Question 10

Explain how competition can be size-symmetric or size-asymmetric

Answer 10

size symmetric = the resource acquired is proportional to the size of the individuals, structure, etc. ex. root nutrients because if they are 2x larger they will get 2x more nutrients

size asymmetric = the resource acquired is not proportional to the size of individuals, structures, etc. ex. large canopy gets all the light, small canopy gets little to none

Question 11

Explain example of exploitation and interference competition in plants

Answer 11

exploitation = roots competing for limiting resource of nitrogen. root competition is size symmetric, while shoots compete for access to light and is size-asymmetric.

interference = plants produce toxic chemicals to inhibit other plants from living there (allelopathy)

Question 12

Define the Lokta-Volterra model

Answer 12

model that describes the outcome of competition between two species over ecological time

Question 13

Explain the competition coefficients a and b for interspecific competition

Answer 13

a = makes species 2 individuals equivalent to species 1 individuals in terms of their effect on the population growth of species 1

b = opposite

they measure the competitive effects of one species on another in terms of effect on population growth

Question 14

If each individual of species 2 has the same effect as 2.5 individuals of species 1 on the population growth of species 1, then what are the coefficients

Answer 14

a = 2.5

Question 15

What is the goal of the lokta-volterra model

Answer 15

to determine the equilibrium when the 2 species have reached their combined saturation densities

Question 16

When do equilibriums occur to give a zero-growth isoclines for both species

Answer 16

N1 = 0 (extinction)
N1 = K1-aN2

N2 = 0 (extinction)
N2 = K2-bN1

Question 17

Explain Case 1 and 2 of competition

Answer 17

competitive dominance
case 1 = species 1 outcompetes species 2
case 2 = species 2 outcompetes species 1
the winner is the growth rate that is further out
stable equilibrium = K1 for N1 (x-axis) and K2 for N2 (y-axis)

Question 18

Explain Case 3 of competition

Answer 18

bistability
the winner depends on initial conditions
unstable equilibrium is where they cross
stable are at either species K1 or K2
the winner is whichever is further out, changes for vertical or horizontal
outcome indeterminant in bottom corner because doesn’t favour either

Question 19

Explain case 4 of competition

Answer 19

stable coexistence
species 1 and 2 coexist stably
the stable equilibrium is where they cross compared to unstable being either K1 or K2

Question 20

In case 3, what type of competition is typically stronger

Answer 20

interspecific because the equilibrium is when only 1 or the other species exists

Question 21

In case 4, what type of competition is typically stronger

Answer 21

intraspecific competition because the equilibrium is when both species can exist stably

Question 22

Explain Case 5 of competition

Answer 22

neutral coexistence
Species 1 and 2 coexist neutrally the whole time along their coincident isoclines

Question 23

What are the 2 comments about Case 5

Answer 23

1. probably not likely that the isoclines are exactly coincident
2. not stable coexistence, but neutral coexistence meaning random fluctuations so do not tend to return to the same equilibrium, exclusion can occur under extreme conditions

Question 24

What are the 4 cons of LV model

Answer 24

1. all individuals are equivalent (no age or stage structure or individual variability)
2. assumes inhibitory functions of intra and interspecific competition are linear functions of density
3. real ecosystems vary over space and time, but the model assumes K and competition coefficients are constant
4. difficult to apply to multiple species

Question 25

What are the 5 pros of the LV model

Answer 25

1. simple
2. makes testable predictions
3. often successfully predicts patterns of exclusion and coexistence
4. sometimes predicts equilibrium densities
5. explains outcome of competition and related to intra and inter, carrying capacity and effect of others

Question 26

linking competition and community structure is an application of _____ theory

Answer 26

niche

Question 27

Define ecological niche

Answer 27

describes both the range of conditions necessary for persistence of a species, where it lives, and the resources it requires (what, where, how it acquires)

Question 28

Explain the graph of the generic description of a niche

Answer 28

peak is the level/value that the species uses the resource most. intraspecific competition and generalization highest in the middle and specialization and interspecific competition higher on the outside

Question 29

if interspecific competition is greater than intraspecific competition, it predicts

Answer 29

exclusion
or natural selection could act on the niches and allow for coexistence

Question 30

why is important that niches have multiple dimensions that do not overlap

Answer 30

niches can overlap in certain dimensions, but not all because then would be exact same and couldn’t coexist

Question 31

Explain how competition can be size-symmetric or size-asymmetric

Answer 31

size symmetric = the resource acquired is proportional to the size of the individuals, structure, etc. ex. root nutrients because if they are 2x larger they will get 2x more nutrients

size asymmetric = the resource acquired is not proportional to the size of individuals, structures, etc. ex. large canopy gets all the light, small canopy gets little to none