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Response of potential prey to the introduction of piscivores in a whole ecosystem is generally inferred from small-scale studies. Using distance sampling, two lakes that were initially without predators and three control lakes where predators were previously present were examined for the response of prey species to the introduction of brook trout ( Salvelinus fontinalis). Responses monitored included numerical changes in abundance, changes in habitat use patterns, and changes in the mean shoal sizes of potential prey species. No statistical changes in abundance or habitat use patterns were detected, whereas there was a significant increase in the mean shoal sizes of potential prey species in lakes where predators were added. We conclude that, in some natural systems, shoaling may be the first response potential prey initiate to reduce mortality risk. [ABSTRACT FROM AUTHOR]

The title compound, C(16)H(16)N(2)O(2)S(2), has been synthesized by several different high-yield routes, and has been encountered as a co-product in a number of reaction pathways, ever since it became of inter-est to our research program over 30 years ago. We now confirm the proposed mol-ecular structure in which the mol-ecule exhibits a twofold axis of symmetry through the mid-point of the S-S bond and the two planes defined by the (carbamo-yl)sulfenyl moieties are essentially perpendicular to each other [dihedral angle = 81.55 (14)°].

The title compound, C(16)H(20)O(3), was synthesized to study the hydrogen-bonding inter-actions of the two enanti-omers in the solid state. Inter-molecular O-H⋯O hydrogen bonds produce centrosymmetric R(2) (2)(8) rings which dimerize the two chiral enanti-omers together through their carboxyl groups.

The racemic title compound, C(16)H(20)O(3), was synthesized to study the hydrogen-bonding inter-action of the two enanti-o-mers in the solid state. In the crystal structure, R and S pairs of the racemate are linked by pairs of inter-molecular O-H⋯O hydrogen bonds, producing centrosymmetric R(2) (2)(8) rings.

The title compound, C(16)H(20)O(2), was synthesized to study the hydrogen-bonding inter-action of the two enanti-omers in the solid state. The racemate is made up of carboxylic acid RS dimers. Inter-molecular O-H⋯O hydrogen bonds produce centrosymmetric R(2) (2)(8) rings which dimerize the two chiral enanti-omers through their carboxyl groups. The chirality of this compound is generated by the presence of the double bond in the cyclo-hexene ring and a chiral axis due to the meta-methyl substituent on the aromatic ring.

In the structure of DL-proline, C5H9NO2, the molecules are connected via classical intermolecular N-H...O hydrogen bonds involving the amine and carboxyl groups [N...O = 2.7129 (15) and 2.8392 (16) A], and form chains along the b-axis direction and parallel to (-101). The chains are linked into sheets via weak non-classical hydrogen bonds. The conformation of the molecule and its packing are notably different from the monohydrated DL-proline form.

At room temperature the two title compounds are isomorphous. Both have a disordered structure that includes a major component, one of the title compounds, and a minor component, the 6-halo isomer, occurring at the same site in the crystal. When the chloro compound is cooled to as low as 98 K, there is no change in the structure and no significant change in the degree of disorder. When the bromo compound is cooled, it undergoes a second-order phase transition at 282 K to a second polymorph, structurally very similar, but with two molecules in the asymmetric unit. In both isomorphs and both polymorphs the molecules occur in two-dimensional layers that are essentially the same. In the low-temperature form of the bromo compound the layers have shifted relative to each other by approximately 0.7 A in y. In the low-temperature form the disorder, which is still present after the transition, decreases as the temperature is lowered.

The molecular structures of the title compounds, 2,4, 6-trichlorophenylisonitrile (IUPAC name: 2,4,6-trichlorophenyl isocyanide), C(7)H(2)Cl(3)N, and 2,4,6-trichlorobenzonitrile, C(7)H(2)Cl(3)N, are normal. The two structures are not isomorphous, but do contain similar two-dimensional layers in which pairs of molecules are held together by pairs of Cl.CN [3.245 (3) A] or Cl.NC [3.153 (2) A] interactions. The two-dimensional isomorphism is lost through different layer-stacking modes.