Working Group I - Behavior

Strickler (Chair), Batchelder, Jonsson, Kiorboe, Yen

Animal behavior includes a wide range of activities--swimming, feeding activity, migration, mating, reproduction and escape behaviors--that can greatly influence survival, growth, and reproduction. Few of these behaviors have been investigated adequately to permit their inclusion in mechanistic models of secondary production. The working group identified three aspects of animal behavior where intensified research could lead to improved mechanistic models of secondary production.

First, investigation of the mechanisms underlying individual behavior is needed. Individual behavior is influenced by a milieu of environmental factors--hydrography (temperature and salinity), light intensity, food resources (quantity and quality), predator distributions--and factors intrinsic to the individual--general physiological condition, including size (stage or age), hunger, reproductive condition. As an example, it is clear from numerous studies that the timing of diel vertical migration in many species is closely tied to light intensity. In some cases, the depth of daytime residence is adequately explained solely by light intensity, in others it is also dependent upon swimming speed (Buskey et al., 1989). The cues that regulate night-time depth are less clear. Temperature and food concentration and quality have vertical gradients and often large discontinuities at scales of tens of centimeters to meters that may be important (Cowles et al. 1993; Harris, 1988). Vertical migration amplitudes in copepods can be modified by food availability (Daro, 1985). The uneven distribution of food in all three dimensions, its varying quality and composition, and its generally low abundance require a wide behavioral repertoire on the part of consumers to acquire sufficient amounts of food, especially in the presence of predators. Numerical models are useful for exploring the effect of different animal behaviors interacting with the patterns and dynamics of patchy prey and predator aggregations in respect to obtaining resources, growing, reproducing and surviving. For instance, fecundity in the copepod Labidocera is dependent upon the interaction of photoperiod and food patchiness, e.g., the time of the day when food is available (Marcus, 1988).

Second, interactions among individuals need to be examined. These include conspecific interactions such as finding mates (Yen, 1988), cannibalism of younger by older stages, and schooling behavior; and interspecific interactions such as foraging, and avoiding and escaping predators.

Third, behaviors which result in the retention of individuals, patches and populations in favorable environments need investigation. This is perhaps the topic of most immediate relevance to U.S. GLOBEC, in that the interaction of zooplankton behavior and advection can have direct and strong impacts on the survival and productivity of zooplankton. These include behaviors at various temporal and spatial scales. Behavior can maintain individuals in favorable food environments (Price, 1989) and can involve the recognition of and reaction to changing conditions. Well-documented examples whereby zooplankton have behavioral adaptations to maintain themselves in favorable locales include regions of vertically sheared (often reversed) flow like the Oregon upwelling zone (Wroblewski, 1980; 1982), and tidally dominated regions.

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