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Relationships between the occurrence of Chaetogammarus ischnus (Stebbing, 1898) and Pontogammarus robustoides (G. O. Sars, 1894) (Crustacea, Amphipoda) in a lowland Polish dam reservoir

Żytkowicz J., Kobak J.

Oceanological and Hydrobiological Studies

2008

Vol. 37, No.2

39-50

Populations of Chaetogammarus ischnus and Pontogammarus robustoides living in the middle part of the Włocławek Dam Reservoir (on the lower Vistula River, central Poland) were studied. The two species coexisted at offshore sites of the reservoir, with P. robustoides being much more abundant than C. ischnus. In samples collected from the bare bottom of the reservoir (sandy or covered by zebra mussel shells) and macrophytes a negative relationship between the two species was observed: C. ischnus occurred in high numbers in those samples in which abundance of P. robustoides was low. This phenomenon is postulated as resulting from the larger size and more predatory nature of P. obustoides, limiting the occurrence of C. ischnus.

Size-structured interactions and the dynamics of aquatic systems

Persson Lennart, Roos André M.

Polish Journal of Ecology

2006

Vol. 54, nr 4

621-632

Size variation within species as a result of individual growth and development over the life cycle is a ubiquitous feature of many aquatic organisms. We review the implications of this size variation for the dynamics of aquatic systems. Ontogenetic development results in differences in size dependent competitive abilities between differently sized individuals giving rise to cohort cycles that are qualitatively different from traditional predator prey cycles. Size-dependent interactions also mean that the type of interaction - competitive or predatory - changes over the life cycle as a result of an increase in size. At the intraspecific level, cannibalistic interactions may, depending on the life history characteristics of the cannibal, give rise to either equilibrium or cycles driven by a mixture of inter-cohort cannibalism and competition. In multispecies contexts, size variation and particularly food dependent growth lead to the presence of alternative states involving catastrophic collapses. These size-structured interactions have so far been mainly demonstrated for fish and cladocerans, but do have whole lake food web ramifications.