Fluid-mediated dispersal: Effects on the foraging behavior and distribution of stream insects

Dina Medeira Fonseca, University of Pennsylvania


This is the first work on settlement constraints in streams and their influence on the behavior and distribution of lotic organisms that engage in fluid-mediated dispersal. I demonstrate that initiation of fluid-mediated dispersal by first instar black fly larvae is density dependent, and that the strength of the density factor is influenced by current speed. I conclude that dispersal is active, linked to resource limitation, and can be described as a foraging behavior. To understand what factors influence settlement, I developed and tested in the laboratory a model that assesses the effect of local current speed on settlement. I conclude that, above a threshold, settlement rates decrease with increasing local current speed. To assess the relative importance of pre- and post-settlement processes, I altered field distributions by manipulating settlement and made observations over time to determine if the pre-existing patterns reappeared. The new patterns persisted through time, which led me to conclude that field distributions of black fly larvae reflect settlement constraints. Finally, I examined if it was possible to predict field distribution patterns from an optimal foraging model that accounts for settlement constraints. I developed a patch exploitation optimization model for a suspension feeder. I assumed the forager has incomplete information and used Bayes's rule to model the effect of recent experience on the decision process. Used in conjunction with the information on the effect of current speed on black fly settlement the predictions from this model agree with field distributions of larvae. Although I have focused my thesis work on black fly larvae, the information gathered provides insights that may be applied to the ecology of other organisms that are transported by air or water currents in some phase of their life cycle, particularly during foraging movements. I emphasize factors affecting settlement that occur at smaller spatial and temporal scales than the ones commonly included in population models of these types of organisms. By influencing habitat selection and therefore the relationship between consumers and resources, however, spatial heterogeneity and restrictions on dispersal at local scales can influence population dynamics.

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Recommended Citation

Fonseca, Dina Medeira, "Fluid-mediated dispersal: Effects on the foraging behavior and distribution of stream insects" (1996). Dissertations available from ProQuest. AAI9627921.