Download 1 Biology 413 (Zoogeography) Final Exam Winter Term 2

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Biology 413 (Zoogeography) Final Exam
Winter Term 2 - 2015
Directions:
1. Write your name and student number on each page of the exam.
2. All answers should be written in the space provided. If you need extra space, you can use
extra paper, but clearly label your answers.
3. The exam is designed to be completed in 2.5 hours.
4. The exam questions are organized into two parts and consist of seven pages.
5. PART I consists of 10 short-answer questions.
6. PART II consists of two long-answer (essay-form) questions and one multi-part question.
Points
PART I: 30 points
PART II: 45 points
TOTAL: 75 points
PART I
Answer the following 10 questions using 2-3 sentences or less. These questions should take you less
than 5 minutes each. Please use the space provided. Each question in this section is worth 3 points.
Question 1: Define the target effect and the rescue effect, in the context of the equilibrium theory of
island biogeography.
The target effect is the tendency for immigration rates to be higher on larger islands because larger
islands have more shoreline, can be seen from farther away (i.e., create a larger target for colonization).
The rescue effect is the tendency for extinction rates to be relatively low when islands are very close to
the mainland because island populations are augmented by immigration.
Question 2: What are the three dominant cycles that together make up the Milankovitch cycles?
In general, what do these cycles impact to influence the Earth’s climate system and the advance and
retreat of glaciers?
Eccentricity (or ellipticity of orbit); Axial tilt (obliquity); Precession (pole wandering). The cycles
generally impact the seasonality and location of solar energy around the Earth, thereby influencing
Earth’s climate cycles and the advance and retreat of glaciers
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Question 3: In addition to the Milankovitch cycles, what three related feedback mechanisms were
associated with the growth/retreat of ice sheets and also contributed to rates of cooling and warming?
With the growth and retreat of ice sheets, respectively, there was a 1) decrease and increase in plant and
animal life over large areas, 2) decline and increase in production of greenhouse gases and 3) and
increase and decrease in the amount of white surface on the earth, owing to an increase and decrease of
the albedo effect.
Question 4: Haffer’s (1969) hypothesis represents the “old view” that “islands” of Amazonian lowland
rain forest persisted during the last glacial maxima and can be used to explain current patterns of
disjunct taxa and speciation. The “new view” is that the Amazon did not exhibit isolated forest refugia
during the Pleistocene. Provide one specific line of evidence that supports the new view. (Hint: we
discussed two lines of evidence, one from botanical data and one from animal taxa).
From botanical data: fossil pollen data from lake cores shows continuous forest cover and invasion
by cold-adapted species during the last glacial maximum
From animal taxa: range limits of trumpeter species in South America indicate separation by large river
systems, not glacial refugia. The timing of diversification events shows that speciation of trumpeters
occurred before the last glacial maxima.
Question 5: Endemic species are sometimes described as “relicts”. What is the difference between
taxonomic and biogeographic relicts?
Taxonomic relicts are remnants of, at one time, a much more diverse taxon. Biogeographic relicts are
taxa that at one time had a much wider geographic distribution. The difference emphasizes taxa that
were once historically diverse (irrespective of distribution) versus taxa that were historically
widespread (irrespective of diversity).
Question 6: In the development of continental drift theory, many lines of evidence were used to better
understand the mechanism by which continents shifted. We reviewed seven lines of evidence in lecture
– one of these includes patterns of disjunct distributions in extant taxa. List three additional lines of
evidence below.
Can be any three of the following: 1) stratigraphic evidence (alignment of Precambrian shield and flood basalt deposits with
Pangaea/Gondwana); 2) late Paleozoic glacial deposits are found on all continents of Southern Hemisphere/tongue fern fossil
distribution and animal fossils are shared among now separate continents; 3) sea floor mapping; mid-Atlantic Ridge and
other long chains of mid-ocean ridges suggests areas of plate shift; 4) paleomagnetism, magnetic stripes and magnetic
reversals; certain metals are sensitive to polarity of earth’s magnetic field, alternating/symmatric patterns of polarity/direction
on either side of ridges; 5) sea floor spreading; observations of magnetic striping and sea floor terrain suggested process of
spreading; 6) concentration of earthquake activity associated with meeting/spreading of plates.
Question 7: What are three potential causes of disjunction of populations or related species groups?
(Hint: Continental drift represents a more specific case of one of these general potential causes.)
Vicariance; extinction; long-distance dispersal of species (it’s okay to list these)
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Question 8: In the context of conserving biodiversity and evolutionary history, describe the basic
motivation for conservation based on evolutionarily significant units (ESUs) and evolutionarily distinct
and globally endangered (EDGE) species.
ESUs are intraspecific groups that represent distinct characteristics and tendencies, occupy unique
habitats or display unusual phenotypes. Phenotypic distinctiveness is often correlated with genetic
distinctiveness. When considering conservation priorities, ESUs should be examined to capture an array
of intraspecific diversity, and thus evolutionary potential for adaptation. EDGE species are recognized
for the amount of unique evolutionary history that they represent, as well as their level of endangerment
(e.g., based on the IUCN). For EDGE species, we ask how much evolutionary history would be lost if
that species were to go extinct, as well as the likelihood of extinction given current and future threats.
Question 9: What are the two metrics used to assess a mass extinction, and what to they measure?
Extinction is measured by rate and magnitude. Rate measures the number of extinctions over a period
of time in which the extinctions occurred (or the fraction of species that have gone extinct per unit time).
Magnitude is the percentage of species that have gone extinct.
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Question 10: Provide a brief definition for the three “shortfalls” (Wallacean, Linnaean and
Hutchinsonian) with respect to predicting changes in species distributions.
The Wallacean shortfall refers to the deficit of lack of knowledge of explicit spatial distributions of
species (i.e., where do species occur, what is the extent of distribution and patterns of density across a
species range?). The Linnaean shortfall refers to shortcomings in the discovery and description of new
species, or the deficit in knowing what species exist, as well as in classifying them as distinct from other
species. The Hutchinsonian shortfall refers to our lack of knowledge of attributes of species niches and
their interactions with the environment and other species, particularly in what species require for
sustainable/persistent populations.
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PART II
Answer the following 3 questions using the space provided, with complete sentences as necessary.
Each question in this section is worth 15 points.
Question 11: We have discussed Janzen’s hypothesis with respect to several different themes in
biogeography. Describe the predictions derived from Janzen’s hypothesis for tropical and temperate
mountains and/or montane species with respect to the following: (1) physiological barriers to dispersal;
(2) breadth of elevational ranges; (3) beta diversity (or change in species composition) along elevational
gradients; (4) potential for allopatric speciation and (5) sensitivity of species to climate warming.
[3 points each – 15 points total]
(1) Janzen’s hypothesis predicts that mountains are “higher” in the tropics. Specifically, species
occurring in the tropics experience and are specialized to a narrower range of thermal conditions
annually compared to temperate species. Therefore a mountain of a given height in the tropics would
pose a greater barrier to dispersal for a species compared to a mountain in the temperate zone, because a
given tropical species would likely need to disperse through regions outside of its physiological
tolerance to colonize new areas beyond mountain passes, more so than species in temperate regions,
which would be less likely to encounter thermal regimes outside of its physiological range of tolerance.
(2) A direct consequence of the narrower physiological tolerances of species in the tropics should be
that tropical species also show narrower elevational ranges compared to temperate species.
(3) If species, on average, have narrower elevational ranges in the tropics, then we would expect beta
diversity (or spatial species turnover, or change in species composition at the community level) to be
higher in the tropics compared to the temperate zone, where species on average have broader elevational
ranges.
(4) With mountains being more significant dispersal barriers and with species having narrower
elevational ranges in the tropics, we would expect the potential for allopatric speciation to also be higher
in the tropics, compared to the temperate zone, simply because we would expect more opportunity for
isolation, either through vicariance, or through infrequent successful dispersal across barriers.
(5) Following Janzen’s hypothesis, if species have narrow physiological tolerances in the tropics, then
any incremental change in temperature may bring species closer to their physiological limit, compared
to species in temperate areas with broader physiological tolerances. Therefore, we would expect tropical
species to be more sensitive to a similar magnitude of climate warming, compared to temperate species.
This hypothesis has been supported in various species of ectotherms, including insects and lizards.
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PART II (continued)
Question 12: Relying on what you know about the Theory of Island Biogeography and the information
provided in the questions, reconstruct the box exhibiting MacArthur and Wilson’s
Immigration/Extinction dynamics. [15 points total, including parts a - d]
(a) The empty box below is labeled with arrows that represent increasing isolation on the x-axis and
increasing area on the y-axis. At the top of the box (upper portion of the box opposite the x-axis)
indicate one of two rates associated with increasing isolation (immigration or extinction) with an arrow
showing the rate as increasing. Draw another arrow on the right-hand side of the graph (opposite the
y-axis) indicating the other rate (immigration or extinction) showing the rate as increasing (2 points).
(b) The following three terms can be used to describe the composition of the communities found in each
corner of the box. Match one term to each corner by writing the term in the box, based on the axes
provided and the axes you created. The term for the lower right-hand corner is provided (3 points).
High endemism
Mainland like
Species poor/Highly transient
(c) The following terms describe the processes that largely shape the composition of communities in
three corners of the box you filled in above. Indicate which process is associated with each corner, based
on the axes that are provided and the axes you have created in part (a) above (3 points).
Evolution
Stochastic events/neutrality
Ecological interactions
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PART II (continued)
(d) Now, put your ideas together to explain the box you reconstructed above. For each of the three
corners that you filled in, explain why we see predictable patterns in composition within each
community (part b), which are generally shaped by each process (part c). Also explain why we see
depauperate islands in the lower right-hand corner. Be sure to relate the terms in each corner to both the
area/isolation axes provided and the immigration/extinction rate axes you created in part (a). Use
complete sentences (7 points).
Top left corner: With islands that are large in size and close to the mainland (low isolation), we expect
the composition of communities to be more representative of mainland communities, due to higher rates
of immigration/exchange of individuals and low rates of extinction. Thus, the processes that largely
govern the composition of these communities are ecological in nature (lots of species are present to
interact, plus there is less opportunity for these species to be isolated for any long period of time;
selection is less effective in the face of high gene flow).
Top right corner: These islands will experience lower rates of colonization due to high isolation, but also
lower rates of extinction due to larger size. As such, the species that are able to reach the island are more
likely to persist there over time. Without constant gene flow from the mainland, these communities are
more subject to evolutionary pressures like selection, and such islands, given enough time should host
high numbers of (in-situ) endemic species, showing communities that are more distinct from the
mainland.
Bottom left corner: Because these islands are small, they will experience higher extinction rates, but due
to their close proximity to the mainland, they will be more readily colonized by individuals dispersing
from the mainland. The resulting community should be one that is relatively species poor, because the
island is small and cannot support many species overall, but also one that is also highly transient and
subject to stochastic events, due to continual/repeated colonization and higher extinction. (Ecological
interactions are not as important in determining species composition of these islands, because the
transient nature of the community with high colonization/extinction rates leads to unpredictable
dynamics of populations for most species).
Bottom right corner: these islands are both small in area and far from the mainland. We expect few
species to be able to reach these islands in the first place (low colonization), and because the islands are
small, they experience higher extinction rates. This results in species poor/depauperate faunas overall.
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PART II (continued)
Question 13: The latitudinal gradient in species diversity is sometimes considered the only true law in
biogeography. Explain what this gradient is (3 points) and provide a discussion of four major
hypotheses to account for it (including their weaknesses or exceptions to the general patterns; 3 points
per hypothesis). We discussed more than four hypotheses in class, but choose four among those
presented. You may use illustrations to help make your points. [15 points total]
The latitudinal gradient in species diversity is the well-established pattern that areas/habitats at lower
latitudes (tropical regions, towards the equator) tends to be higher in species richness than areas/habitats
at higher latitudes (temperate regions, towards the poles). The hypotheses can be generally categorized
into null hypotheses, deterministic/non-equilibrial and deterministic/equilibrial hypotheses. Looking for
specific hypotheses within these broad categories.
Null hypotheses:
(1) Mid-domain effect. Given any bounded gradient, such as a latitudinal gradient, we would expect the
greatest range of species overlap at a mid-point between the extremes of the gradient, or in the case of
latitude, mid-way between the poles. Thus the pattern is an artifact with no underlying biological
significance.
Deterministic, non-equilibrial hypotheses:
(2) Communities have not reached a steady state; communities, and species diversity is still in the
process of increasing (or decreasing) following historical disturbance or dynamics.
Deterministic, equilibrial hypotheses (assumes a steady state has been reached):
(3) Higher productivity (i.e., solar radiation, potential evapotranspiration) in the tropics leads to
higher resource availability, such that species can more finely partition a resource gradient (increased
species packing). Exceptions to this include shallow eutrophic lakes and salt marshes, which are
extremely productive, but have low species diversity.
(4) Harsh environments, characteristic of the temperate zone (e.g., icy and cold), have higher
extinction rates, lower colonization potential, and less opportunity for resource specialization than more
benign environments.
(5) Temporal stability is higher in the tropics. Variable climates prevent resource specialization, and
hence are able to support fewer species. Temporal variability tends to favour generalists at the expense
of specialists. Exceptions include the deep ocean, which is stable, but has low diversity (but also lower
productivity).
(6) Tropical habitats are more structurally diverse, with higher habitat heterogeneity. Diverse
physical environments promote isolation, resource specialization, speciation, and co-existence.
Exceptions include marine plankton communities, which are highly diverse despite low heterogeneity.
(7) Interspecific Interactions (and feedback). More species in tropical communities create a positive
feedback of diversification through increased competition, predation, and parasitism. Not certain if this
is a cause for tropical diversity or a consequence of it (chicken – egg).
(8) Area. Tropics have greater area than either polar region due to curvature of the earth. Species-area
relationship is well established. However, tropical latitudes have much less terrestrial area.
(9) Age. Latitudinal gradients for clades originating in warm climates are steeper, with a strong tropical
affinity. For a variety of plants and animals of both marine and terrestrial realms, most clades radiated in
tropical climates. Extant tropical diversity peak is created from lineages that adapted to a planet with
tropical climate. Higher diversities have arisen among tropical clades because the earth has been
predominantly tropical throughout most of its history.
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