Recent theoretical studies have shown the potential for chaotic dynamics in simple three‐species food chains. Most of these studies have focused on linear food chains, although natural food chains are seldom isolated from the surrounding food web. There is a growing awareness that food web dynamics can be strongly influenced by the behavior and movement of predators, energy, and nutrients across ecosystem and subecosystem boundaries. Motivated by observations from lakes, where the pelagic food web is often linked to the littoral food web by mobile predators, we constructed a simple model to evaluate the dynamics of two food chains linked by a top predator with prey preference. Linking the two food chains had no qualitative effect on model dynamics, although it did increase the density of the top predator. Instead, the prey preference of the top predator changed the system dynamics. We found a range of prey preferences that could eliminate chaos, dampen oscillations, and even produce point stability in a previously oscillatory system. The strength of prey preference required to produce a point attractor in a previously chaotic system was positively related to the dimension of chaos (a measure of the complexity of chaos). Our results suggest that, although chaos is possible in food webs, common processes like prey preference reduce the potential for chaos.

Conners, M. E., and R. ). Naiman. 1984. Particulate allochthsnous inputs: relationships with stream size in an undisturbed watershed. Can. ). Fish. Aquat. Sci. 41 : 1473-1484.Four streams of a pristine boreal watershed in eastern Quebec were examined to assess the composition, seasonal pattern, and ash-free dry mass (AFBM) of particulate allochthonous input. Study sites on streams ranging from first to sixth order exhibited significant differences in the types and magnitude of litter input. Composition of Bitterfall varied according to vegetation and physical structure of the riparian zone. Although the forest in the watershed is dominated by conifers, deciduous leaves dominated annual budgets and seasonal input patterns. Annual litterfall per unit area of stream surface declined exponentially with increasin~ stream order (3 = 0.98) from 307-5348 AFDM-m-2-yr-' in a first-order stream to 15-13 g AFDM m-syr-' in a sixth-order stream. Lateral inputs of 25-70 g AFDM . m-' .yr-' were not related to stream size, but were strongly influenced by riparian structure and entrainment of organic matter during spring flooding. Total input per unit stream length increased logarithmically with increasing order (3 = 0.87), appr~aching 1000 g AFDA4.m-I-yr-' in the fifth-and sixth-order streams. A watershed budget calculated from these results estimates a total input of 729 t~~r -' to streams of this 673-km2 watershed. When particulate allochthonous input is compared with primary production measurements in these streams, 81-95' 36 of the organic carbon supplied to the first-and second-order streams is allochthonous, but 85-95% of the supply ts the fifth-and sixth-order streams is autochthonous. While these trends agree with predictions of the synthetic continuum model, the importance of local effects in our results illustrates the need for a more mechanistic apprsch In allochthonous input research.Quatre cours d'eau d'un bassin versant boreal non perturbe de Vest du Quebec ont fait l'olsjet d'une etude visant a determiner ia composition, I'allure saisonniere et la masse seche sans cendre (MSSC) des apports aliochtones particulaires. Les endroits etudies de cours d'eau, dont I'srdre allait d'un &six, presentaient des differences appreciables quant au type et a I'importance de I'apport de litiere. La composition de I'apport de litiere etait fonction de la veg6tation et de la structure physique des rives. La for& du bassin versant est dominee par les coniferes, mais O e s feuilles de decidus s'averaient dominantes dans les bilans annuelset les allures saisonnieres des apports. L'apport annuel par precipitation de litiere par unit4 de surface de cours d'eau diminuait de fason exponentielle en fonction de I'accroissement de I'ordre du cours d'eau (r2 = 0,98) ; ii etait de 307-534 g ~SSC-rn-~.an-' dans un cours d'eau d'crrdre un et de 15-17 g ~~~C -r n -~. a n -' dans un cours d'eau d'ordre six. Les apports lateraux de 25-70 g MSSC-m-' .an-' n'etaient pas lies B la taille du cours d'eau, mais dependaient fortement de la structure des riv...

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The goals of this research were to investigate geographic patterns in the Aleutian Island region's demersal ichthyofauna and to determine whether they reflected the physical and biological oceanographic patterns documented by other authors in this volume. The analyses were structured according to the level of organization: at the community level, patterns in species occurrence and community structure were investigated; at the population level, distribution and abundance were examined; at the individual level, food habits and growth were studied. There were stepchanges in species occurrence, diversity, population distribution and food habits at Samalga Pass and at sites farther west. These longitudinal trends indicated physical and biological variation along the length of the Aleutian Islands chain; however, depth-related patterns were as common as longitudinal patterns in demersal fish distribution. In addition, high catches of patchily distributed species occurred in areas expected to be biological 'hot spots' because of increased productivity and prey availability. These patterns suggest linkages between demersal fish ecology and the biophysical processes described by other authors in this volume and indicate that inter-disciplinary research is needed to elucidate the underlying mechanisms.

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