Name:
NRES 441/641 – Spring 2007
Ecology and Management of Invasive Plants
First Mid-term Exam – Place your name at the top of this page in the space provided and on any other
sheets of paper that you use. (Total of 50 points)
I. Multiple Choice. Circle the most correct answer for each question below (one answer only).
(1 pt each)
1. Which of the following elements does the Federal Executive Order 13112 NOT contain:
a. provides for legal action taken by a group against a federal agency
b. definition of invasive species
c. details of the stakeholders involved in carrying out the order
d. provisions for an Invasive Species Management Plan
2. Invasive species tend to have characteristics of:
a. high phenotypic plasticity and be dioecious
b. high seed production and a short juvenile period
c. low seed production and long flowering periods
d. seed dormancy mechanisms and be monoecious
3. In the Great Basin, juniper is an example of a _ that is also a _
a. native, invasive
b. immigrant, invasive
c. native, casual
d. alien, transfomer
4. Callaway and Aschehoug (2000) tested the allelopathy hypothesis. Which of the following is
true about the effect of diffuse knapweed (Centaurea diffusa) on either the Montana grass
species or Eurasian grass species:
a. activated carbon in the soil increased the biomass of the Montana grasses when
grown in the presence of C. diffusa, but decreased the biomass of the Eurasian
grasses
b. activated carbon enhanced the uptake of phosphorus for both the Eurasian grasses and
Montana grasses
c. the seeds of C. diffusa attacked the seeds of the Montana grasses
d. the biomass of C. diffusa decreased when grown in the presence of the Montana
grasses as compared to when it was grown with Eurasian grasses
5. A difference between a noxious weed and an invasive plant is:
a. there is no difference between the two; it is only a result of inconsistent scientists
b. an invasive species is legally defined in the Nevada Revised Statutes – Chapter 555,
while a noxious weed is not
c. “noxious weed” implies that the plant has a negative economic or environmental
impact, whereas the name “invasive” does not require a negative impact
d. noxious weeds disperse naturally while invasive species are dispersed by humans
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6. Which of the following would be evidence that a species came from a disjunct population and
is therefore an alien?
a. similar genetic diversity between two populations
b. insects that only utilize that species
c. systematic floral survey showing an absence of the species 100 years ago
d. nearby pack-rat midden containing a fragment of the species
7. Changes in vegetation related to increases in atmospheric CO2 are examples of the:
a. environmental change hypothesis
b. disturbance and land use hypothesis
c. limiting resource hypothesis
d. biodiversity hypothesis
8. In a new environment, an alien plant may potentially encounter new enemies. If the new alien
species is to be successful, the potential enemies would:
a. feed on foliage
b. be dioecious
c. have a large population size
d. be generalists
9. According to Alpert (2000), which of these hypotheses of invasion requires no advantage to
being introduced?
a. allelopathy
b. vacant niche
c. competition
d. enemy release
Note: the paper specifically mentions the competition hypothesis in this category, but I
also accepted ‘vacant niche’ as a correct answer because this hypothesis also does not
imply that there is an advantage simply to being introduced.
10. How would you best explain the contradictions in the biodiversity hypothesis?
a. higher biodiversity implies higher levels of competition and fewer unused resources,
but invaders from rich floras are more competitive and successful
b. biodiversity conveys community stability, but reduces the realized niches of native
plants
c. areas of higher biodiversity have already undergone invasion in the past and are no
longer easily invaded
d. local diversity conveys resistance to invasion while between-community diversity
implies higher resources and increased invasion Note – this is in the paper by
Shea and Chesson.
11. Which of the following statements about alien species is true?
a. aliens are currently easy to detect by remote sensing
b. all alien species are dependent on disturbance by human activities
c. aliens are generally considered to be colonizers
d. most alien species that become naturalized also become invasive
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12. The idea that a community becomes more susceptible whenever there is an increase in the
amount of unutilized resources is a basic concept from:
a. variable resource hypothesis
b. vacant niche hypothesis
c. disturbance and land use hypothesis
d. environmental change hypothesis
13. Which of the statements about the micro-evolutionary change hypothesis is true?
a. because of the things like genetic drift, founder effects and hybridization, microevolutionary changes that occur in aliens are always beneficial
b. hybridization allows the alien species to incorporate potentially advantageous
local adaptations into its genome
c. this hypothesis is scientifically well-documented
d. repeated introductions are necessary for alien establishment
14. Disturbances:
a. create a temporary effect, and even with the introduction of invasive species, the area
usually returns to its previous state
b. are often caused by humans
c. decrease the chance of ruderals establishing
d. discourage invasions by increasing or altering available resources
15. Which of the following is NOT true of the anthropogenic hypothesis?
a. there is substantial and widespread evidence for this hypothesis
b. evidence in support of this hypothesis is that the most-visited natural areas have the
most exotic species
c. humans have intentionally introduced exotic species
d. humans are vectors for introduction
Note: introductions are both deliberate and accidental in this hypothesis.
II. Matching. Below is a list of words and phrases. For each of the numbered statements, write
on the line at the end of that statement the word or phrase from this list that best matches the
statement. (1 pt each)
(-)-catechin
Crowding index
Introgressants
Realized niche
Allelopathy
Allopolyploid
Saltation
Fundamental niche Genetic bottleneck Hybridization
Naturalized
Phylogenetic distance C3
Ruderal
Transformer
Weed
C4
1. Subset of invasive plants that change ecosystems. Transformers
2. One reason why plants may be more invasive in some communities than in others (Strauss et
al 2006). Phylogenetic distance (Strauss et al is the paper about relatedness and invasion
ability)
3. Plants having this photosynthetic pathway are predicted by the global change hypothesis to
benefit from an increase in atmospheric CO2. C3
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First Mid-term Exam
4. A decrease in reproductive barriers is a consequence of this process. Hybridization
5. A life history strategy in which the goal is to grow quickly and have a high fecundity,
particularly under stress. Ruderal
6. The theoretical limits of existence for a species along n resource axes. Fundamental niche
7. An individual formed by two different species that can still back cross with 1 or more parent.
Introgressant
8. An alien species that can reproduce consistently and can create self-replacing populations
without human-intervention. Naturalized
9. The actual limits of existence for a species along n resource axes. Realized niche
10. When one plant releases chemicals that are toxic to another. Allelopathy
III. Short Answer: Data Interpretation. This section involves a series of graphs and questions
related to those graphs. On a blank piece of paper, answer each of the questions related to the
graphs in 1 or 2 sentences. Be sure to clearly number each question (for example, “Short answer
1a”), make sure your name is at the top of each page, and number each page in consecutive
order. (10 pts).
At the top of the next page of this exam are two figures. Fig A shows growth of grass tillers of
five U.S. native grasses grown in competition with Centaurea maculosa, both with and without
activated carbon in the soil. Fig B shows growth of C. maculosa with and without activated
carbon, and with and without native competitors. “Naïve” plants are from un-invaded native
populations, “experienced” plants are from populations growing with C. maculosa in the wild.
Answer the following questions about these graphs.
(a) What is the effect of activated charcoal on the growth of native grasses grown with C.
maculosa? What does this imply about the effect of C. maculosa on native prairie grasses?
(b) What do you notice about the effect of C. maculosa on ‘naïve’ plants VS ‘experienced’
plants, in general?
(c) What do you notice about the growth of C. maculosa when grown with naïve VS experienced
native competitors?
(d) What do the results you noted in (b) and (c) tell you about the long-term response of
vegetation to invasion by C. maculosa?
(e) The authors of this paper suggest that ‘maternal effects’ could be a confounding factor in this
study. How would you design an experiment to verify that maternal effects do not come into
play?
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Fig B
Fig A
(From Callaway et al 2005. Journal of Ecology 93:576-583).
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Data interpretation
a) Figure A shows the percent change in tiller growth (compared to no
competition) for native grasses grown with Centauria maculosa with and
without activated charcoal in the soil – the format is the same as for the
assigned paper Callaway and Ascheoug 2000. In the absence of activated
charcoal, C. maculosa has a strong negative impact on growth of most of the
native grasses. Activated charcoal reduces this negative effect, implying that
the negative impact is due to an allelochemical released by C. maculosa (since
activated charcoal absorbs chemicals from the soil).
b) This question is based on Figure A again. Both naïve and experienced plants
are negatively impacted by C. maculosa and activated charcoal reduces the
negative effect on both naïve and experienced plants, but in general the
negative impact of C. maculosa is greater on naïve plants than it is on
experienced ones.
c) Figure B shows biomass of C. maculosa grown alone (-N) and in competition
with a native grass (+N), either with or without activated carbon, and using
competitors from either experienced or naïve native populations. When
grown with experienced plants, C. maculosa biomass is decreased regardless
of whether activated carbon is present in the soil or not; when grown with
naïve plants, C. maculosa only experiences a decrease in biomass when
activated carbon is present. This implies that experienced plants have a
competitive effect on C. maculosa even when the allelochemical is present,
but naïve plants only have a competitive effect when the allelochemical is
reduced by activated carbon.
d) Taken together, the evidence in a) through c) implies that there is adaptation
for resistance to the allelochemical released by C. maculosa. Experienced
populations (which have been growing with C. maculosa) have undergone
natural selection where more allelochemical-resistant plants have produced
more offspring, resulting in a reduced effect of C. maculosa on the
population. This may mean that there will be evolution of native
communities to become more resistant to C. maculosa through time, and that
those plants surviving the initial invasion may be able to maintain or even
increase their population, thus reducing the invasive ability of C. maculosa.
e) Maternal effects are caused when differences in the environment experienced
by the parent plant result in non-genetically based differences in seed
(weight, protein content, etc) which in turn cause differences in the growth of
the resulting seedlings. To overcome this effect, grow seed from naïve and
experienced populations for one generation in a common environment
(common garden) taking care to avoid cross-pollenation, harvest seed from
those plants, grow the second generation seeds, and conduct the experiment
on the resulting plants.
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NRES 441/641 – Spring 2007
First Mid-term Exam
Short Essay (CHOOSE ONE). On blank pieces of paper, answer one question in about 10-15
sentences. Be sure to clearly label the question at the top of the page (for example, “Short Essay
#1”), make sure your name is at the top of each page, and number each page in consecutive
order. If you require more paper to answer the questions, get additional sheets from the
instructor. (15 pts)
1. Throughout this class, we have discussed the difficulties of concisely defining invasive
species. In the Richardson et al. (2000) paper, the authors first breakdown the barriers that a
species must take if it is to become invasive. These stages are introduction, naturalization and
invasion. Using those stages, they then ascribe different statuses to alien species such as alien
plant, casual alien plant, naturalized plant, invasive plants, and transformers depending on which
barriers they have surmounted. First explain the introduction, naturalization and invasion stages.
Next, detail the types of barriers that an alien must overcome to move to the next step. Then
describe three of the five statuses listed above in detail.
Points breakdown for essay 1: 6 points for explaining the three stages of invasion
(introduction = moving plant to new location and having it survive; naturalization = plant
population reproduces and becomes self-sustaining; invasion = plant population expands
and disperses far from initial introduction, moving into new areas). 3 points for mentioning
3 of the 4 barriers that must be overcome in relation to each stage of invasion (introduction
= geographic barrier; naturalization = environmental and reproductive barriers; invasion
= dispersal barrier). 6 points for describing three of the five statuses (alien = plant
introduced by humans; casual alien = can survive and maybe reproduce but only present
because of repeated introductions; naturalized = established, can reproduce and maintain
population, has become part of the flora; invasive = population is expanding into new
areas, including undisturbed habitats, and may begin to be a pest; transformer = plant is
abundant or different enough to cause dramatic changes in the ecosystem)
2. Many of the hypotheses explaining what makes species invasive discussed in class are not
mutually exclusive of one another. From the list, pick two hypotheses that you believe are not
independent of one another and explain how they are not mutually exclusive. To better illustrate,
use either data presented in class or create a scenario that supports your argument.
Points breakdown for essay 2: 2 points for naming two hypotheses. 4 points for describing
the two hypotheses. 6 points for explaining how the two are related. 3 points for
examples/scenario. The hypotheses are: vacant niche, superior competitor, allelopathy,
environmental change, variable resources, biodiversity, microevolution, enemy release,
disturbance, and anthropogenic. This question was very open-ended, so almost anything
was acceptable as long as you were able to explain the hypotheses, explain the link you saw
between them, and give examples.
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