ICA 09 SPECIES DIVERSITY 2
Group ____________Name__________________
REGIONAL DIVERSITY
1. Figure 1. What is the pattern? Species # increases as island size increases
What two equilibrium factors may explain it?
A. More habitat heterogeneity on larger islands yields
more niches/less competitive exclusion (extinction) and more species
B. Larger islands have larger population sizes less prone to stochastic extinction.
(or Larger islands are bigger targets for successful immigration).
2. Figure 2. Describe what predicts S(hat): the equilibrium number of species on an
island. When the rate of immigration equals the rate of extinction, an equilibrium of
species number is reached.
3. Figure 3. How/why is island biogeography theory modified by proximity to
mainland? S(hat) is greater for islands near than far to the mainland because of
greater dispersal potential.
Figure 4. How/why is it modified by size of island? S(hat) is greater with
larger than smaller islands because of lower extinction rates on large islands.
4. Figure 5. Which hypothesis is illustrated in 5A? Species diversity increases with
(island) area. Why is the pattern altered in 5B? Islands are different distances from
the mainland.
5. Figure 7. What are three patterns in regional species diversity and what factor
accounts for each?
A. More species as decrease in latitude – climate less stressful.
B. More species in topographically heterogeneous western mountains.
C. Decrease in species down the Baja peninsula due to dispersal limitation.
6. Figure 9. (20.12) Describe two patterns of species turnover (beta diversity) at larger scales.
1. Species turnover is more rapid in N-S than E0W direction.
2. Species turnover is greater in both directions in Asia than NA; Asia has higher SR.
Figure 10. (20.13) What is the major change in longitudinal beta diversity as latitude
increases in NA? Species turnover (beta diversity) decreases from S to N.
Which latitude has least climatic uniformity? Most S latitude (dry to wet)
How does that explain the pattern? In S a strong gradient in water availability causes
big change in species composition from W to E. In N climate is more uniform; there
not all species have moved back in areas previously covered with ice.
LATITUDINAL SCALE
7. Figure 11. Describe the major latitudinal pattern of species diversity.
For most taxa, species diversity increases from the poles to the equator.
The hypotheses in ICA 8 that explain local diversity were derived by considering
about why the tropical biome has the greatest species diversity.
What must be true of those hypotheses for them to explain the latitudinal pattern?
They must be more ‘intense’ processes than in the temperate zone.
How does TIME contribute to more species in the tropics. It refers to a long period
of stability without climatic disruption, allowing much time for speciation and low
amounts of extinction, resulting in a high species diversity in the tropics. However,
the tropics may also have been affected by glacial history – with dry periods during
cold periods to the N. The tropical climate has not been stable.
CONTINENTAL SCALE
8. Figure 14. Has diversity been constant for long periods? Yes
Have mass extinctions occurred – in marine invertebrates? Yes terrestrial plants? No
What is the relative role of extinction vs. additions on diversity of these groups?
Diversity of marine invertebrates has been greatly affected temporarily by a mass
extinction, but additions via speciation have more than replaced extinctions so their
species diversity has continued to rise.
GLOBAL
9. Figure 16. In what ways does continental drift change climate of a region?
Continents move to different latitudes with different angles of sun, affecting
temperature and rainfall. They change in amount of contact with large bodies of
water affecting specific heat and heat transfer to land. They change global ocean
currents that affect land climates.
10. Figure 17. By what means did continental drift change routes of dispersal?
What are some examples of separation? Africa and S.A.; N and S
America; Australia, SA and Antarctica.
Joining? Europe and Africa; India and Asia; Australia and SE Asia
11. Figure 20. How do birds of the same body form occur on separate continents?
Did they converge or divergence? Divergence. They have a common widespread
ancestor that developed on Gondwana before the Southern continents separated.
After separation the body form was largely retained with diversification of minor
modifications on the fragmented continents.
12. Figure 23. Give an example of how climate change plays a role in explaining
species diversity in North America: In Miocene with warmer, drier conditions,
grasslands spread with an accompanying increase in herbivore species richness.
13. Figure 27. How does ‘dispersal limitation’ explain differences in post-glacial
expansion of tree species in Europe? Small-seeded species spread far N after the
glaciers receded, but the large-seeded species faced dispersal limitation and are in
more S areas of Europe.
14. Figure 29. How has climate changed the relative size of biomes over time?
Tropical climates were much more extensive during the Eocene and slowly
contracted . Boreal biome is relatively recent. Present-day species richness of trees
is predicted better by area occupied by these forest types during the past than by their
area at present.
15. Figure 31. Where does more diversification occur? In ecological zone of origin.
Why? Adaptive shifts to a new ecological zone are more difficult as they face more
stressful conditions, and hence are infrequent.
How does this hypothesis explain why species diversity is highest in the tropics?
Evolution has had more time to operate in the tropics and a large proportion of
ancestral lineages were adapted to tropical conditions. Few lineages made adaptive
shifts to new ecological zones, so species diversity remains highest in the tropics.