Study Guide - Chapter 7
Study Guide – Chapter 7
The book talks about the American alligator as a
because of its
pivotal role in the ecosystems in which it lives.
We talked about the importance of
keystone species; these are organisms that we must identify and conserve because
their activities have such an important impact on the structure and function of the
entire biotic community.
Communities are often identified based on dominant species that create the habitat,
e.g., an oak-hickory community, or a
are hundreds of other species of plants and animals present, but identifying the
visually dominant species will often tell us quite a lot about the other types of
organisms that make up that community.
The book talks about
, where two communities meet, e.g., when a forest becomes
We will talk more about edge later, as it has some important effects on
If it is a natural edge, it is much like the ecotone we discussed in class,
which may have unique flora and fauna that are not abundant in either of the other
two community types.
We can use
to describe a biological community, and diversity is
, the number of species, and
, which is the
abundance of individuals within each species.
On page 145, I believe the authors
made a mistake.
In paragraph 3, the book gives and example of a community
composed of 10 individuals within each of 20 species, versus a community with 10
species each containing 2 individuals and 10 other species containing 18 individuals.
Each community has 20 species and 200 individuals, and the book asks which has
the highest richness.
Both communities have 20 species, so the richness is the
same, so unless the book was trying to be clever, a better question is which
community has more evenness?
Even if you do not know how evenness is
calculated, by the nature of the term, a community in which all species are equally
abundant would be as even as you could get.
The book is in error at the bottom of
the first column on p. 145, which talks about a high richness (lots of species)
community with each species having few individuals as low evenness; this is not
correct – evenness refers to the relative abundance among species, not their
If each species in a community has the same number of
individuals, high or low, then the evenness is high
similar concept but is the opposite of evenness, and is easier to understand.
have a community with 10 species, 9 of which have 1 individual, and one that has 91
individuals, this is high dominance and low evenness.
If, however, each species has
10 individuals, this is low dominance and high evenness.
Communities are also characterized by a