Environmental Engineering Reference
In-Depth Information
Figure 7.4
Mismatches between the effects of decreased population size of white campion (
Silene latifolia
) on its fruit
herbivore
Hadena bicruris
and on the hebivore's parasitoids
Microplitis tristis
and
Eurylabus tristis
. (a) Presence (closed dots)
and absence (open dots) of
M. tristis
as a function of plant population size and connectivity. Lines indicate population sizes
required for 25%, 50% and 75% presence. (b) Same for
E. tristis
. (c) Effect of plant population size on the proportion of
herbivores that is parasitized. (d) Effect of plant population size on the proportion of fruits predated by the herbivore. Lines
indicate estimates for three levels of connectivity (distance to nearest population 0.2-2.0 km). (Modifi ed from Elzinga
et al
.
2005, 2007 .)
Populations with low levels of genetic variation at both
neutral markers and functional genes of the immune
system show high incidence of the parasite-induced
disease ' feline peritonitis ' , although causal relation-
ships have yet to be proven. Another way in which
inbreeding affects the outcome of species interactions
is through effects on the extent of adaptive plasticity.
The fresh-water tadpole snail (
Physa acuta
) shows
adaptive morphological and behavioural responses in
the presence of predatory fi sh that contribute to preda-
tor avoidance. Inbreeding reduces the extent of these
responses by half (Auld & Relyea 2010) thereby imped-
ing its induced defense responses. But not only animals
experience genetic consequences of fragmentation that
impact their interactions with pests and predators. Also
in plant populations, low levels of genetic variation and
inbreeding (resulting in loss of heterozygozity) can
decrease their resistance to herbivores and pathogens
(Spielman
et al
. 2004b). For instance, inbred plants of
monkey fl ower (
Mimulus guttatus
) show increased
suceptibility to spittlebugs (
Philaenus spumarius
) (Carr
& Eubanks 2002). However, the magnitude and even
the direction of the effect of inbreeding on resistance
commonly vary among and even within populations.
An illustrative example is the study of effects of experi-
mental inbreeding in white campion,
Silene latifolia
(Ouborg
et al
. 2000), using a large number of inbred
lines created by brother-sister matings for four genera-
tions, resulting in a range of inbreeding levels within
each line. Contrary to expectation, experimental
inbreeding on average slightly increases resistance of
S.
latifolia
to one of its common pathogens, the anther
smut fungus
Microbotryum violaceum
. But most strik-
ingly, the effect of inbreeding is inconsistent among
