Date of Award

Winter 1990

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

Program/Concentration

Ecological Sciences

Committee Director

Ray S. Birdsong

Committee Member

Jotin J. Govoni

Committee Member

Alan H. Savitzky

Abstract

The feeding ecology of preflexion and flexion-postflexion spot (Leiostomus xanthurus) and Atlantic croaker (Micropogonias undulatus) larvae was evaluated and compared. Nutritional condition of spot larvae from the Gulf of Mexico was high, with no larvae classified as starving. This was probably due to an inability to sample starving larvae at sea because of predation pressure or was indicative of favorable feeding conditions and an absence of starvation in the collection area. In spite of morphological similarities between the species, significant differences in body shape existed.

The diets of the two species converged with age and interspecific dietary overlap was relatively high for both flexion stages. Inter- and intraspecific competition were probably not important determinants of diet composition because of the apparent absence of starvation. In contradistinction, the degree of food selection increased with age in both species. Larvae added larger prey to their diets while continuing to feed on smaller prey, food selection was temporally variable and larvae always fed selectively amongst the available prey. Prey size and shape were important determinants of selectivity, with larvae eating prey that were, on average, larger than those available. The affect of prey size and shape on food selection was probably not related to size-limited ingestion, but to visual profile and reactive distance. These results were in accordance with predictions made by optimal foraging theory and two other food selection models.

The feeding incidence of three age classes of Leiostomus xanthurus, on the rotifer Brachionus plicatilis, was investigated under six different spectral regimes (red, yellow, green, blue and white). Significant sources of variation in feeding incidence were attributed to age and color. Two-three week old larvae did not demonstrate a higher feeding incidence in any regime when compared to the control. Seven and ten week old larvae demonstrated a relatively higher feeding incidence in the yellow and green regimes. Those larvae may have possessed two visual pigments of different maximal absorption that were matched to typical natural background spacelight and that facilitated contrast vision. Differences between the age classes indicated that the ability to perceive prey increased with age.

DOI

10.25777/nxnb-3k67

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