Environmental Engineering Reference
In-Depth Information
A
B
C
D
(a)
(a)
(a)
(a)
Competition
Realized
niche
Recruitment
limitation
Facilitation
0
Predation
LOW
HIGH
Fundamental
niche
(b)
Disease and parasitism
Productivity
LOW
HIGH
LOW
HIGH
Environmental
stress
HIGH
LOW
(b)
(b)
(b)
Resource enhancement
LOW
HIGH
Realized
niche
(c)
Predation
refuge
Recruitment
enhancement
0
Fundamental
niche
Competition
Habitat amelioration
Productivity
LOW
HIGH
LOW
HIGH
LOW
HIGH
Resident species richness
Intensity or frequency of
disturbance or predation
Environmental
stress
HIGH
LOW
Fig. 5.3
Four fundamental models of ecology, with and without facilitation, illustrating paradigm shifts if
facilitation is included. (A) The realized niche can be larger than the fundamental niche due to facilitation; (Aa)
without facilitation, (Ab) with facilitation. (B) Facilitation may affect the competitive abilities of species along an
environmental gradient; (Ba) facilitation weak, constant, (Bb) facilitation strong, variable. (C) Facilitation may have
an impact on the success of invaders; (Ca) without facilitation, (Cb or Cc) with facilitation. (D) Facilitation may
change the relationship between species richness and ecosystem productivity; (Da) without facilitation, (Db) with
facilitation (lower line, primary space holders; upper line, secondary space holders). From Bruno
et al.
(2003).
Reproduced by permission of Elsevier.
This may imply, for instance, that the realized niche
of a species can be larger than its fundamental niche,
affecting the net effect of competition. Positive inter-
actions could also affect the relationship between
diversity and invasibility.
complex balance of competition and facilitation. For
example,
Quercus douglasii
trees have the potential
to facilitate understorey herbs by adding consider-
able amounts of nutrients to the soil beneath their
canopies. However, experimental tree-root exclusion
increased understorey biomass under trees with high
shallow-root biomass, but had no effect on understorey
biomass beneath trees with low shallow-root biomass.
Thus, the overall effect of an overstorey tree on
its herbaceous understorey is determined by the
balance of both facilitation and competition. In wet-
lands, shifts in facilitation and competition among
aerenchymous plants were shown to occur in anaer-
obic substrates when temperatures change.
Myosotis
laxa
, a small herb common in wetlands of the north-
ern Rocky Mountains, benefits from soil oxygenation
when grown with
Typha latifolia
at low soil tem-
peratures in greenhouse experiments. At higher soil
5.4 Complex species interactions affect
community structure
The intensity of interspecific interactions, be it
competition, facilitation, parasitism or any other
relationship, may change during community devel-
opment, and several interactive mechanisms may be
at work simultaneously, structuring communities
in space and in time (e.g. van Andel
et al
. 1993).
Callaway and Walker (1997) provided many examples
to illustrate that species interactions may involve a
