Environmental Engineering Reference
In-Depth Information
Table 5.1
A classification of rare species based on three characteristics: geographic range, habitat specificity and
local population size. From Krebs (2001); after Rabinowitz (1981).
Geographic range
Large
Small
Habitat specificity . . .
Wide
Narrow
Wide
Narrow
Population size
Large, dominant
somewhere
Locally abundant
over a large
range. In several
habitats
geographically.
Locally abundant
over a large
range. In a
specific habitat
geographically.
Locally
abundant in
several habitats,
but restricted.
Locally
abundant in a
specific habitat,
but restricted.
Small,
non-dominant
Constantly sparse
over a large
range and in
several habitats.
Constantly sparse
in a specific
habitat but over
a large range.
Constantly
sparse and
geographically
restricted in
several habitats.
Constantly
sparse and
geographically
restricted in a
specific habitat.
geographically more widespread. This suggests that
similarities in species-abundance distributions and
species-range-size distributions could have some
common mechanistic basis. Whatever the causes, the
strong right skew to species-range-size distributions
has some important consequences, particularly for
inventories of faunas and floras and for conservation.
ies in a strict sense (taxonomically defined; see the
introduction to this chapter), including guilds, and
leaving interspecific interactions in biotic communit-
ies (representing all the biota in an ecosystem) out of
scope.
Competitive interactions are mutually detrimental,
or one species is inhibited and the other is not
affected. The latter is sometimes called amensalism,
but we avoid using this term, because this can be
caused by either competition or allelopathy. It seems
useful to distinguish between the latter two, because
competition is mostly two-sided and refers to space
or resources, while allelopathy is one-sided and
results from the release of toxic organic compounds
from one of the species into the environment.
Parasitism is a relationship where one of the
species, the consumer, benefits, whereas the other, the
resource, suffers. This can be a relationship between
trophic levels in a biotic community, like predation
and herbivory, but it can also take place within a
community, for example among plants.
Facilitation and mutualism are interactions where
one, two or more species benefit. We avoid the term
commensalism for a one-sided advantage, because it
5.3 The niche-assembly perspective:
interspecific interactions in
communities
5.3.1 Types of interaction
When individuals of two species meet, the interaction
between these two can be positive, which results in
advantage, negative, which is disadvantageous, or
indifferent to one or both interacting species. The
advantage or disadvantage can be measured in terms
of an increase or decrease in fitness or fitness com-
ponents, as compared to a control with no interac-
tion (see Table 5.2). In the present chapter, I will confine
myself to interspecific interactions within communit-
