The relationship between copepod foraging behavior and their microscale distribution

This dissertation examines foraging strategies for copepods, detailing the foraging behavior of one copepod species, Acartia clausi. At the microscale (cm's), I propose that copepods use area-restricted search as their foraging mechanism to find patches of food and remain within them. Area-restricted search (ARS) means that the organism takes shorter steps, and turns at greater angles as the concentration of food it encounters increases.; The modeling studies in Chapters 2, 3, and 4, suggest that ARS is a useful behavior for copepods which swim similar to Acartia sp. In Chapter 2, using a vertical 1D model, it was found that there is a tradeoff between net foraging efficiency and the rate of dispersal through an environment. ARS also leads to a distribution of copepods relative to the their food's distribution which mimics the relationship that would be predicted by the Ideal-Free Distribution, although intake rates among the individual copepods are vastly different between these models. In Chapter 3, a 2D (horizontal and vertical) model of copepods foraging in patchy environments was developed, which is general enough that it can be used by others to answer questions concerning foraging behavior of any organism thought to use ARS, terrestrial or marine. Using this model in Chapter 4, it was found that when phytoplankton is intensely patchy in 2D, it is essential to sample the environment on the same spatial scale as the step length of the copepods, or the success of the copepods will be underestimated. Decreasing the relative intensity of food patches over background levels decreases foraging efficiency more than decreasing the total number of patches available.; In the laboratory studies conducted for Chapters 5 and 6, it was found that A. clausi exhibited a large difference in its swimming behavior when feeding on phytoplankton versus when no phytoplankton was available. When filter-feeding on phytoplankton, A. clausi moves shorter distances and more frequently than when not filter-feeding. There was no significant trend in any metrics describing the copepods' swimming behavior as the concentration of food given to the copepods increased. As the copepods were starved longer, the change in their swimming behavior versus unfed controls became significantly greater, although this may have been due to differences in the quality of the food. The vertical displacement of the copepods over very short times (∼10s) was adequately described by a 1D vertical unbiased random walk. Predictions of displacement over longer periods of time suggest that the foraging strategy of A. clausi is consistent with ARS, and that this strategy is adequate for finding and remaining within phytoplankton patches on the scales at which we might expect them to encounter patchiness.