7760 - Laserfiche WebLink

Home Browse Search

occurred in those treatments as well. Several explanations can be offered to account for the insensitivity of diet overlap under the experimental conditions. First, diet overlap may have been insensitive to changes in resource availability because only one type of food, zooplankton, was introduced into aquaria. Wild Colorado squawfish and fathead minnow larvae also consume benthic invertebrates, phytoplankton, and detritus. Lack of alternative prey may have compelled study fish to partition what would normally be perceived as one resource type. Consequently, diet overlap would not be expected to change until competition was extreme. An alternative explanation for the insensitivity of diet overlap is related to its uncertain relation to resource availability (Schoener 1983; Wiens 1992). Diet overlap may not decrease monotonically with resource availability. As resource availability declines, competition may foster decreasing overlap, or, if a resource is scarce (as was the case in the lowest feeding regime), increasing overlap. This hypothetical relation, and example data, are depicted in Figure 3. The relative position of example data correspond to those observed in our experiment. The position of the response at the lowest feeding regime is uncertain and cannot be assigned without additional information (i.e., more responses where the slope is non-zero). At the lowest feeding regime, zooplankton availability may have been sufficiently low to push the response of diet overlap into the realm of starvation. Indeed, growth and survival were poor in the lowest feeding regime. Simultaneously, the two highest resource availabilities may have corresponded with opportunistic responses, and an intermediate response may not have been observed. This interpretation implies that competition for zooplankton did not occur at the two highest feeding regimes; however, analysis of relative 19