The effect of food web structure on community stability and resilience
has rarely been examined using empirical data. Yet there is a practic
al application for such studies insofar as resistance stability determ
ines the ability of a system to ''absorb'' anthropogenic stress and ad
justment stability determines the reversibility of resulting damage. T
he stability of zooplankton food webs in 46 Precambrian Shield lakes w
as examined using data collected in the 1970s, when pH ranged from 3.8
to 7.0, and in 1990, when pH had increased by up to two units in some
lakes. Acidification overcame resistance stability at pH < 5.0, as ev
idenced by decreases in species richness, numbers of predatory and com
petitive links, directed connectance, predator generalization, and lin
kage density, identified by analysis of variance. Adjustment stability
was demonstrated by changes in food web attributes in lakes with high
er pH in 1990 than in the 1970s. Species richness, numbers of predator
y and competitive links, linkage density, and predator generalization
all increased relative to the 1970s values. Food web attributes of ''r
ecovering'' lakes were statistically indistinguishable from those of l
akes of similar pH that had not been more acidic in the 1970s. Similar
trajectories of food web change were followed during environmental de
gradation and recovery. Planktonic food webs of anthropogenically acid
ified lakes may eventually recover to resemble their pre-acidification
condition, given sufficient time without acidic inputs. Whether adjus
tment stability is a general feature of anthropogenically stressed sys
tems remains to be determined.