Ostracoda and Amphibia in temporary ponds: who is the prey? Unexpected trophic relation in a mediterranean freshwater habitat |
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Authors: | Dario Ottonello Antonio Romano |
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Institution: | 1.Pietra Ligure (SV),Italy;2.Dipartimento di Biologia,Università di Roma “Tor Vergata”,Rome,Italy |
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Abstract: | Small and temporary freshwater ecosystems are important biodiversity “hot spots” of the Mediterranean region, and their food
webs are considered as very complex systems. Amphibians and ostracods are two highly ubiquitous classes of metazoans adapted
to live in temporary ponds. Their trophic interactions are considered unidirectional, the amphibians acting as predators and
the ostracods as preys. In the field, we observed the opposite interaction in few ponds in Northern Italy. To confirm this
qualitative evidence, we set up laboratory experiments to investigate the predation by the Ostracod mussel shrimp (Heterocypris incongruens) on eggs and tadpoles of Common toad (Bufo bufo) and Stripless tree frog (Hyla meridionalis). Amphibian eggs of both species were offered to ostracods either as unique trophic resource or, alternatively, together
with another kind of food. Similarly, tadpoles of both species were simultaneously offered to ostracods (with alternative
food) to disclose their preferences. Ostracods preyed mainly on amphibian eggs and no significant differences in the rate
of predation between toad and treefrog eggs were detected. However, ostracods preferred Bufo when offered along with Hyla tadpoles. Toad eggs and larvae are commonly considered highly unpalatable, but our results contrasted this view. The difference
in the predation rate between the two tadpole species is discussed in the light of their swimming behaviour. We show that
feeding relationships between Amphibia and Ostracoda are much more complex than expected and depend on both the ecological
context and amphibian life stage. The knowledge of the trophic connections among taxa is a fundamental prerequisite to further
and more exhaustive studies on community ecology. |
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