Study Guide 9 Community Ecology

Question 1

fundamental niche

Answer 1

abiotic conditions in which a species can survive and reproduce (determined by physiological tolerance)

Question 2

realized niche

Answer 2

the biotic interactions that determine where a species can survive and reproduce (determined by species interactions)

Question 3

carrying capacity

Answer 3

the maximum number of organisms of a given species that a habitat can support (determined by resource availability)

Question 4

Draw a hypothetical fundamental niche for a species and use this diagram to depict how species interactions could shrink or expand the fundamental niche to produce the realized niche.

Answer 4

Question 5

Draw a hypothetical logistic growth curve for a species and use this diagram to depict how species interactions could increase or decrease the carrying capacity

Answer 5

-parasites or pathogens (like the aphids) my lower carrying capacity if individuals must spread out to avoid infecting others
-mutualist relationships (like mycorrhizae) can raise carrying capacity by improving resource efficiency or access

Question 6

the roles organisms can play in ecosystems: keystone species

Answer 6

Keystone species have a high impact on ecosystem richness or evenness despite being rare.

ex: seastars enhance species richness in tidepools by eating various species, preventing any one prey from outcompeting the others.

Question 7

the roles organisms can play in ecosystems: foundation species

Answer 7

Foundation species create habitats for other species through their physical presence and are common in the ecosystem, unlike keystone species

ex: Coral reefs, where corals create the habitat structure and provide spaces for other species to inhabit.

Question 8

the roles organisms can play in ecosystems: ecosystem engineers.

Answer 8

An ecosystem engineer is a species that physically alters or modifies its habitat in significant ways.

ex: beavers, which alter river flow by building dams.

Question 9

Species A and B are lizards that eat insects. The figures at right show the preferred prey size of each species for populations living on Islands 1, 2, and 3.

Determine if each of the statements below is true of these species on these islands

A. In allopatry, species A and B eat mostly the same prey
B. In sympatry, resource partitioning has occurred
C. In sympatry, species A and B diverge in prey choice
D. Competition between species A and B affects prey choice in this group of islands
E. Character displacement has decreased competition between species A and species B in allopatry

Answer 9

A. True
B. True
C. True
D. True
E. False

Question 10

What is the competitive exclusion principle?

Answer 10

The competitive exclusion principle states that two species requiring the same limiting resource cannot coexist; one will outcompete the other, driving it to extinction.

Question 11

How can organisms avoid the outcome predicted by
the competitive exclusion principle?

Answer 11

limiting competition through character displacement
or resource partitioning

Question 12

resource partitioning

Answer 12

Occurs when species divide a limiting resource, with each accessing a different component.

ex: include species occupying different areas of a habitat (e.g., lizards and birds) or utilizing different types or sizes of resources (e.g., bats feeding on different insect types).

Question 13

character displacement

Answer 13

Form of resource partitioning where species evolve morphological traits to access different resource components.

ex: include beak shape and size changes in finches and honeycreepers to specialize in different food sources.

Question 14

The figure below shows the population size of hares in orange and lynx in blue in northern Canada from 1840-1940

a. What drives the oscillations in population size in these two species?

Answer 14

In both species, population size is driven by the size of the other species. When lynx are abundant, hare numbers decline, reducing lynx. When lynx decrease, hare numbers rise, increasing lynx.

Question 15

The figure below shows the population size of hares in orange and lynx in blue in northern Canada from 1840-1940

b. Why do the high and low points of the lynx population generally fall shortly after the high and low points of the hare population?

Answer 15

The lag between population changes occurs because when prey populations rise, it takes time for predators to consume them and produce offspring. This delay causes a lag in the maximum and minimum population sizes.

Question 16

Write out the Lotka-Volterra equations for population growth in predators and prey.

Answer 16

prey: dV/dt =rV -pVP

predators: dP/dt = cpVP-dpP

Question 17

Write out the Lotka-Volterra equations for population growth in predators and prey.

a. What term(s) in these equations represent reciprocal density dependence in population sizes of predators and prey?

Answer 17

prey: the variable P (pop size of predators)

predators: the variable V (pop size of victims/prey)

Question 18

Write out the Lotka-Volterra equations for population growth in predators and prey.

b. What term represents the growth rate of the predator population?

Answer 18

cpV is equivalent to r for the predator population.

B/C these contribute to how quickly predator population can increase
-victim population size
-predation rate
-conversion efficiency

Question 19

Write out the Lotka-Volterra equations for population growth in predators and prey.

c. Why are these equations formulated from the exponential growth equation and not from the logistic growth equation?

Answer 19

Because they assumed predator and prey populations primarily drive each other and neither reaches the ecosystem’s carrying capacity, making K irrelevant.

Question 20

Why might natural selection favor a predator that is LESS efficient, or a disease/pathogen that is LESS virulent?

Answer 20

In the orange mite experiment, overly efficient predators drove prey to extinction, leading to their own extinction.
Similarly, pathogens that kill hosts too quickly die out.
Natural selection favors reduced efficiency or virulence to avoid exhausting resources.

Question 21

Using your understanding of density dependent interactions, explain how herd immunity protects susceptible individuals in the population from contracting a disease.

Answer 21

Pathogen infection is density-dependent; frequent contact increases spread. Herd immunity reduces the density of susceptible individuals through vaccination, lowering the chance of disease transmission b/c coming into contact with susceptible individuals is unlikely

Question 22

The graph Laci showed in lecture (and included
below) shows how the R0 value of different
pathogens determines the degree of immunity that
individuals in a population must meet in order to
reach herd immunity. Use this graph to explain why
vaccination for measles and rubella is required for
public school children in the United States, but flu
vaccination is not.

Answer 22

Measles and rubella have high R0 values, requiring over 90% vaccination to protect others. A high
R0 value and severe illness impacts make measles and rubella vaccines mandatory for public school children, while flu vaccine is optional.

Question 23

The graphs below show growth of Species 1 in Habitats A and B when Species 2 is present and absent (left graph) and the growth of Species 2 in Habitats A and B when Species 1 is present and absent (right graph). Complete the bar graphs with data that represent the following species interactions: Competition

Answer 23

Competition occurs when both species negatively impact each other, though the effects may differ in magnitude across species or habitats.

Question 24

The graphs below show growth of Species 1 in Habitats A and B when Species 2 is present and
absent (left graph) and the growth of Species 2 in Habitats A and B when Species 1 is present and absent (right graph). Complete the bar graphs with data that represent the following species interactions: Mutualism

Answer 24

Mutualism occurs when both species benefit from each other, though the magnitude of benefits may vary between species or habitats.

Question 25

The graphs below show growth of Species 1 in Habitats A and B when Species 2 is present and absent (left graph) and the growth of Species 2 in Habitats A and B when Species 1 is present and absent (right graph). Complete the bar graphs with data that represent the following species interactions:Commensalism

Answer 25

Commensalism/facilitation occurs when one species benefits while the other is unaffected, though the benefit’s magnitude may vary between habitats.

Question 26

The graphs below show growth of Species 1 in Habitats A and B when Species 2 is present and
absent (left graph) and the growth of Species 2 in Habitats A and B when Species 1 is present and absent (right graph). Complete the bar graphs with data that represent the following species interactions: Predation/Herbivory/Parasitism

Answer 26

Parasitism, predation, or herbivory occurs when species 1(pred) benefits while species 2(prey) is harmed, with impact magnitudes varying across habitats.

Question 27

Describe how species interactions produce the following evolutionary trajectories in two species
and explain how we know if these processes are occurring or have occurred in two species.
a. Character displacement

Answer 27

Character displacement occurs when similar species compete for a resource, and natural selection favors different phenotypes to reduce overlap. In allopatry (species not in contact), traits and resource use often overlap, but in sympatry (species in contact), traits diverge to minimize competition, like changes in beak shape.

Question 28

Describe how species interactions produce the following evolutionary trajectories in two species
and explain how we know if these processes are occurring or have occurred in two species.
b. Trait matching

Answer 28

Trait matching occurs when two species coevolve traits to strengthen a mutualistic interaction, like flowers evolving to attract specific pollinators and pollinators adapting to access nectar. Evidence includes interaction specificity and phenotype changes tailoring each species to the other, benefiting both.

Question 29

Describe how species interactions produce the following evolutionary trajectories in two species
and explain how we know if these processes are occurring or have occurred in two species.
c. Evolutionary ‘arms race’

Answer 29

An evolutionary arms race occurs when predator-prey, herbivore-plant, or parasite-host traits evolve oppositely. Prey develop defenses (e.g., toxicity), while predators evolve resistance, driving reciprocal selection over time. Evidence includes strong prey defenses (toxins, chemicals) and predator adaptations (resistance, tolerance).

Question 30

Crypsis

Answer 30

Crypsis is when an organism mimics its environment to avoid detection. It helps prey evade predators and predators ambush prey.

Question 31

Masquerading

Answer 31

Masquerading is when an organism mimics another object or structure, appearing as something it’s not (e.g., leaves, sticks, bird poop). Unlike crypsis, it’s noticeable but misidentified, helping prey evade predators and predators ambush prey.

Question 32

Müllerian mimicry

Answer 32

Müllerian mimicry occurs when multiple defended species share visible warning signals, like bright coloration in poison dart frogs, to deter predators. Unlike crypsis or masquerading, it highlights danger through honest communication of toxicity or other defenses

Question 33

Batesian mimicry

Answer 33

Batesian mimicry occurs when a harmless species mimics a defended one, like ground-burrowing owls imitating rattlesnake sounds. Unlike Müllerian mimicry, it’s dishonest, as the mimic lacks actual defenses but benefits from predator avoidance.

Question 34

What is the difference between being poisonous and being venomous?

Answer 34

Poisonous species use toxins defensively to avoid being eaten, while venomous species use toxins offensively to immobilize or consume prey.