Biology 252 - Midterm 3 Exam Questions
and Correct Answers
Which statement best describes the difference between the theoretical concept of a
community and the ways in which communities are delineated in practice?
in theory, communities can be defined by physical or biological characteristics, but in
practice, these characteristics are difficult to measure and are not used.
In theory, a community is defined only by abiotic factors of the area; in practice,
communities are delineated by biological attributes as well.
In theory, communities consist of all species present; in practice, biologists usually
study only a subset of the species.
there is no difference between the theoretical concept of a community and how it is
defined in practice. ✅in theory, communities consist of all species present; in practice,
biologists usually study only a subset of the species.
Members of the same functional group must belong to the same
None of the above
guild.
trophic level.
taxonomic group. ✅None of the above
If a biologist wanted to study a hot spring community and were to sample the bacterial
species causing its various colors, this would be an example of what type of subset?
None of the above
taxonomic
Functional
Guild ✅Taxonomic
What is the primary difference between interaction webs and food webs?
Interaction webs do not consider primary producers, where food webs do.
interaction webs include more trophic levels.
Interaction webs include fewer trophic levels.
Interaction webs include non-trophic interactions, where food webs do not.
✅Interaction webs include non-trophic interactions, where food webs do not.
Considering the food web, imagine a circumstance where a new, mutually beneficial
relationship develops between H2 and H3, increasing both of their numbers. The effects
of this on P2 and C2 are best described as
an indirect positive effect on P2 and a direct negative effect on C2.
, a trophic facilitation effect on both C2 and P2.
a direct negative effect on P2 and a trophic facilitation effect on C2.
a direct negative effect on both C2 and P2. ✅a direct negative effect on P2 and a
trophic facilitation effect on C2.
Which web(s) in the figure is(are) an interaction web?
Web I
Web II
Web III
Web II and Web III ✅Web II
The Shannon index is a measure of
species diversity.
species richness alone.
interaction strength.
the extent of trophic facilitation. ✅Species diversity
Mushroom-feeding Drosophila species, including the species D. neotestacea, D. falleni,
D. putrida, and D. recens, are prevalent in the Great Lakes region of the United States.
Suppose a biologist collects flies from three different communities and obtains the
results shown in the tables. Based on the Shannon index, rank the species diversity
from highest to lowest.
Community 1 > Community 3 > Community 2
Community 1 > Community 2 > Community 3
Community 3 > Community 2 > Community 1
Community 2 > Community 1 > Community 3 ✅Community 1 > Community 2 >
Community 3
Mushroom-feeding Drosophila species, including the species D. neotestacea, D. falleni,
D. putrida, and D. recens, are prevalent in the Great Lakes region of the United States.
Suppose a biologist collects flies from three different communities and obtains the
results shown in the tables. What is the Shannon index of community 1?
1.094
1.191
6.519
1.000 ✅1.191
What is the Shannon index value for an area in which only a single species is present?
Infinity
1
0
-1 ✅0
Four species of fish in a pond are found in equal abundance. The Shannon index of the
fish community is therefore
0.25 (ln 0.25).
,1 [4 (ln 4)].
4 [0.25 (ln 0.25)].
0.25 [0.25 (ln 4)]. ✅−4 [0.25 (ln 0.25)].
Suppose you wanted to determine whether you had adequately sampled the species
richness of a given community. Which result would lead most strongly to the conclusion
that the current sampling had adequately assessed the species diversity?
A linear species accumulation curve
A low Shannon index value
A high Shannon index value
A species accumulation curve that leveled off ✅A species accumulation curve that
leveled off
Which of the following examples emphasizes the importance of species composition?
Determining that a particular forest is dominated by one or two species
Knowing that there are seven tree species in a particular forest
Measuring the total abundance of all tree species in a forest
Understanding the influence of the loss of a species of trees on a particular forest
✅Understanding the influence of the loss of a species of trees on a particular forest
Cougars prey on both white-tailed deer and mule deer. Because of their shared
predator, each deer's species abundance is affected by the presence of the other deer
species. The white-tailed and mule deer are engaged in a(n)
trophic facilitation.
indirect interaction.
predator-prey relationship.
direct interaction. ✅indirect interaction.
If another predator were to begin competing with sea otters for the urchins, they would
have a(n) _______ effect on otters and a(n) _______ effect on urchins.
direct negative; direct negative
direct negative; direct positive
direct negative; indirect negative
direct positive; direct negative ✅direct negative; direct negative
The presence of a mutualist spider in a certain area improves the survival of an
herbaceous shrub by reducing the impact of herbivorous insects. These spiders are
preyed on by lizards, and lizards are eaten by birds. The removal of birds from the area
would most likely have a(n) _______ effect on spiders and a(n) _______ effect on the
plant.
indirect positive; indirect positive
indirect negative; indirect negative
indirect negative; indirect positive
direct negative; direct negative ✅indirect negative; indirect negative
, Which statement about the difference between a competitive network and a competitive
hierarchy is true?
in a competitive hierarchy, one species dominates the interaction; in an interaction
network, no one species dominates the interaction.
The interactions are stronger in a competitive network than in interaction networks.
In a competitive hierarchy, indirect species interactions always buffer strong
competition; in interaction networks, they do not.
A competitive network comprises more species than interaction networks. ✅In a
competitive hierarchy, one species dominates the interaction; in an interaction network,
no one species dominates the interaction.
Menge and colleagues performed experiments in which they exposed some populations
of mussels to sea stars and excluded sea stars from other mussel populations. Suppose
two populations of mussels are the same size prior to treatment, and after treatment
there are 600 mussels in the treatment without sea stars and 200 mussels in the
treatment with sea stars. Suppose further that the sea star population consists of 10
individuals. What is the per capita interaction strength of sea stars on mussels?
(ln 600)/(ln 200)
ln (3/10)
ln (0.33/10)
ln (0.33/200) ✅ln (0.33/10)
When wolves were returned to Yellowstone National Park in 1995, some of the effects
noted were increasing levels of berries available to black bears, stabilization of stream
banks, increased nesting habitat for birds, and increasing beaver numbers as a result of
rejuvenating aspen trees. These were later determined to be the results of reduced
numbers and altered feeding behavior of elk as they were preyed upon by the wolves.
Given this information, which of the following best describes wolves in Yellowstone
National Park?
They are an ecosystem engineer.
They are a foundation species.
They are a primary consumer.
They are a keystone species. ✅They are a keystone species.
Where would a keystone species most likely be located in the figure?
Position B
Position A
Position D
Position E ✅Position A
Where would a foundation species most likely be located in the figure?
Position C
Position D
Position A
Position B ✅Position D
