Air Quality Criteria for Lead Volume II of II - (NEPIS)(EPA) - US ...

• Predator-prey interactions (e.g., reduced avoidance of predators)
• Prey consumption rate (e.g., increase or decrease in feeding)
• Species competition (e.g., interference with another species, increased aggressive
behavior)
• Species tolerance/sensitivity (e.g., the emergence of a dominant species due to
contaminant tolerance or sensitivity)
Species interactions are highly relevant to a discussion about the effects of Pb on natural
aquatic ecosystems, because effects on species interactions could potentially affect ecosystem
function and diversity. Some examples of Pb induced changes in species interactions are
presented below (see summary in Table AX7-2.5.2).
Predator-prey Interactions
Lefcort et al. (1999) examined the competitive and predator avoidance behaviors of snails
and tadpoles in outdoor mini-ecosystems with sediment from a metals-contaminated Superfund
site (i.e., Pb, Zn, Cd). Previous investigations of aquatic invertebrates and vertebrates yielded Pb
tissue concentrations of 9 to 3800 mg/kg dw and 0.3 to 55 mg/kg dw, respectively. Several
species interactions were studied in the presence of metal-contaminated sediment:
Snails and tadpoles have similar dietary behaviors. Thus, when placed in the same habitat
they will compete for the same food items and negatively affect one another. However, when
tadpoles exposed to a predator (i.e., through biweekly additions of 20 mL of water from tanks
housing sunfish—10 mL from sunfish-fed snails, 10 mL from sunfish-fed tadpoles) were placed
with snails, the tadpoles reduced sediment ingestion, while snails increased ingestion. Thus,
snails were exposed to greater quantities of metals in sediment.
In an uncontaminated environment, snail recruitment (i.e., reproduction) was reduced in
the presence of tadpoles. The addition of tadpoles increased the competition for food in the form
of floating algae and the snails switched to feeding on algae that grew on the sediment. This
decrease was due to competition alone. The effects on snail recruitment were even higher when
tadpoles, the influence of a predator (i.e., sunfish extract), and metals in the sediment were all
present. However, the predator effect was indirect in that the tadpoles hid in the algal mats
forcing the snails to feed primarily on the benthic algae that grew on the sediment with high
AX7-207