Bio 213-McKee
Community Ecology Review
name___Claudia Esteves______________________
Read each scenario below and identify any of the following ecological principles that might
apply.
Ecological principles:
Bottom-up controls
Character displacement
Coevolution
Competition
Competitive exclusion
Disturbance
Fundamental niche
1.
Keystone species
Primary succession
Realized niche
Resource partitioning
Secondary succession
Top-down controls (trophic cascade model)
Trophic levels
Two species of closely-related swallows live in England. The black swallow lives in
coniferous forests, and the yellow swallow lives in deciduous forests. In Ireland, where the
black swallow has never been introduced, only the yellow swallow is present and it lives in
both coniferous and deciduous forests.
In this scenario the ecological principles that might apply are resource partitioning, competitive
exclusion, fundamental and realized niche. The closely-related swallows living in England could
be the result of resource partitioning, the closely-related species are able to coexists in the same
place because of the different resources available. Since both species share an environment,
each species concentrates in the forest they are best adapted to survive. In the case of the
yellow swallow species living in Ireland, we can observe the species fundamental niche which
includes coniferous and deciduous forests, and their realized niche in the deciduous forests of
England.
2.
In a woodland community, three species of rodents coexist: voles, field mice, and shrews.
All three species eat seeds and nuts. Each species has a preference for seeds of the most
appropriate sizes for their teeth and mouths; however, all three species compete for the
same kinds of nuts. An owl species also lives in this woodland community. The owl preys
on all three rodent species. During one particular year, a parasite that causes pneumonia in
birds is introduced into the community. This parasite dramatically reduces the owl
population, which remains low for several years as a result. Following the initial reduction in
the owl population, there is a dramatic increase in the population of field mice and a
dramatic decrease in the populations of both voles and shrews
In this scenario the ecological principles that might apply are keystone species, top-down
controls (trophic cascade model), and competitive exclusion. The owl in this case is considered a
keystone species, by preying in all three species of rodents the owl population holds a strong
Bio 213-McKee
control on the rodent communities. In this scenario the owl population declined after a parasite
was introduced in the population, the low populations of owls led to a dramatic increase in field
mice population in comparison to the other two rodent species, indicating top-down control;
where the owl population influences other species populations. Since the population of field
mice had a disproportional increase, we might say that the field mice, in the absence of a
predator is able to use resources efficiently showing competitive exclusion.
3.
A researcher conduced an experiment on two desert islands. The islands were of similar
size, climate, and species composition and richness. Originally, the same species of snake
was present on both islands (A and B). In her experiment, the researcher removed the snake
species from island A. For comparison, the snake species was not removed from island B.
She then recorded the number of species on each island each month, for 2 years. Data are
presented in the graph below.
45
N
u
m
b
e
r
s
p
e
c
i
e
o s
f
40
35
30
25
20
A
15
B
10
5
0
0
5
10
15
20
25
30
Week
Construct a hypothesis that explains the difference between the numbers of species present on
island A versus B over the 2-year period.
Over the 2 year- period the difference between the number of species present on island A in
comparison with Island B, can be the result of the disturbance in the Island A population. We
may hypothesize that the disturbance in the Island A resulted in a decline of species numbers, a
sharp decline in the population can be observed when species were removed from the Island A.
Over time the species population in Island A was able to stabilize at low levels without
disappearing. In comparison, the undisturbed Island B remained at a constant number of 33 to
45 number of species present in Island B.