Biomarkers of Defense, Tolerance, and Ecological Consequences - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 59

initially identical, but which has never been exposed to this toxicant. This interspecific
variability of tolerance is the basis of the pollution-induced community tolerance (PICT)
concept proposed by Blanck et al. (1988). PICT has been demonstrated in many studies of
microbial communities (reviewed by Tlili and Montuelle in Amiard-Triquet et al. 2011),
and nematodes (Millward and Grant 1995, 2000). Considering macrofauna, in a river
impacted by mining, Cain et al. (2004) have shown that insect species that incorporate met-
als in nondetoxified form were rare or absent from the most contaminated areas, whereas
tolerant species equipped with efficient mechanisms of detoxification were present along
the whole watercourse. Depending on the ecological role of tolerant species in the com-
munity, such community-level effects can manifest themselves in various ways (Fleeger
et al. 2003). If the sensitive species is a host or a prey, its extinction will lead to a depletion
of the populations of its symbionts or predators (Figure 3.2). Population modeling of cod
larvae shows their high sensitivity to loss of zooplankton prey, for example, after an oil
spill (Stige et al. 2011). On the contrary, if the sensitive species is a competitor or a predator
of a tolerant species, the latter will be favored.
Among organisms able to cope with chemical stress, some might be keystone species
with important roles in ecosystem functioning. Thus, resistant bacteria will be able to
maintain their role in biogeochemical cycling of nutrients. By using these nutrients, pri-
mary producers at the base of food webs will function normally, and so on (Chapter 7).
However, in certain environments where the level of natural stress is high, the number of
species is restricted even in the absence of any pollutant impact. In estuarine waters, the

T

Different effects Other species Tolerant species

Loss of sensitive species

S

S

T

- Loss of prey-species Population

depletion

S T

- Loss of host-species

p - Loss of competing species

S T Population

increase

- Loss of predator

T

S

Food chain contamination

P

T

- Tolerance due to elimination

- Tolerance due to storage under nontoxic form

P T

Organochlorines in lipid reserves

P

T

Bound to metallothionein

Metals

Biomineralized

P T

P

Limited transfer Predator

p

Biomagnification Prey

Simple bioaccumulation Disruption of the relationship

FIGURE 3.2
Community effects of tolerance. (Modified after Moore, N.W., Advances in Ecological Research , Academic Press,
New York, 1967.)