Modeling the predation, growth and population dynamics of fish within a spatially-resolved shelf-sea ecosystem model

The development and analysis of a fish population module within the European Regional Seas Ecosystem Model (ERSEM) is described. Fixed predation rates on ERSEM zooplankton and zoobenthos, which may be used in place of this dynamic module of fish, are described also. The dynamic module is age-structured, with state variables for the number of individuals and their weight, the latter partitioned into structural (skeletal, essentially) and remobilizable 'reserve' components. It is capable of prediction of observed patterns of both positive and negative changes in individual weight. The fish are modelled as one population for the whole North Sea, superimposed on the ERSEM box structure. Parameters have been derived from the literature where possible and, for herring, certain parameters have been adjusted to match independent estimates of growth in the field. Preliminary results show that herring growth rate depends inversely on biomass, when changes in the latter are caused by altered fishing mortality. The magnitude of these effects is in agreement with historical data for herring in the North Sea. The model is discussed in relation to previous attempts to model fish population dynamics, particularly in the North Sea

The third trophic level of plant defence: neotropical social wasps\u27 use of odours of freshly damaged leaves when hunting

An important aspect of the hunting strategy of neotropical social wasps (Hymenoptera: Vespidae) is where they hunt. Three species used two behavioural components in their selection of a place to search for prey. The wasps uti lizcd the odour of freshly damaged leaves as cues (which could be synomones) to select which leaves to inspect and also they remembered a place to which they were strongly attracted to hunt recently and returned there. Polybia ignobilis (Haliday, 1836) and Polistes satan Bequaert, 1940 hunted on a lawn of Digitaria diversinervis Stapf immediately after it was mown in significantly larger numbers than at other times. P. ignobilis and Polistes versicolor (Olivier, 1791) hunted in significantly greater numbers on freshly cut leaves of passion vine (Passiflora edulis Sims) than on uncut leaves. Sometimes wasps inspected cards rubbed with freshly crushed leaves of P. edulis, but not control cards. Preliminary data suggest that several other species of social wasps around Brasilia hunt in a similar manner on native and exotic plants. Apparently the production of ephemeral odours by freshly cut leaves attract generalist insectivorous predators which perceive these scents and the social wasps investigated are members of the third trophic level of the plants' defence against attacks by herbivores. Available information suggests a difference between the behaviour of generalists and that of specialist arthropod predators which arc attracted to the odour emitted after their particular prey have damaged the leaves