Jerry C. Tash

Feeding by Arizona trout (Salmo apache) and brown trout (Salmo trutta) at different light intensities

SynopsisBrown trout (Salmo trutta) were more efficient than Arizona trout (Salmo apache) in eating brine shrimp at starlight (10−4 fL) light levels. Arizona trout required light levels ≥ moonlight (10−3 fL) to feed. In bright light (50 fL), brown trout utilized cover to a much greater extent in both field and laboratory. Our study indicates that factors other than competition for food or habitat are probably causing the displacement of Arizona trout by brown trout when browns are stocked into the native habitat of Arizona trout.

Experimental Analysis of the Role of Emigration in Population Regulation of Desert Pupfish

Pupfishes (genus Cyprinodon) have existed for long periods in small desert springs and streams that often lack competitors, major predators, and large environmental changes. How their populations are regulated in these systems is poorly known. We ex- perimentally examined the role of emigration in regulating populations of pupfish by (1) comparing the dynamics of populations held in four pools open to emigration with those of populations held in four pools closed to emigration over a 22-mo period and (2) com- paring the rates of emigration from open pools having different densities of pupfish in relation to resources. When pupfish populations were prevented from emigrating, they exhibited symptoms of overpopulation similar to those well documented for fenced populations of small mam- mals. Their numbers increased more than populations in open pools, mortality was high, and body condition and recruitment were low. Again, as in small-mammal populations, these responses were absent in pupfish populations in open pools, where 84% of the total numbers of fish produced emigrated. The timing and magnitude of pupfish emigration was similar in all four open pools and was related to seasonal temperature changes. More males emigrated than females, and emigrants had significantly lower condition factors than res- idents. When densities of pupfish in relation to resources were doubled in two open pools, the percentages of pupfish that emigrated (41.8 and 42.2%) were almost equal to the 50% drop in resources. In contrast, only 15.5 and 16.0% emigrated from two control pools, where pupfish densities in relation to resources were left unchanged. Our results, demonstrating that emigration is a potentially significant mechanism for regulating populations of desert pupfish, are consistent with data from a variety of other animals (small mammals, hydra, roe deer), suggesting that population regulation via a behavioral spacing mechanism may be common among mobile animals.

Food and Habitat Use by Different Sizes of Largemouth Bass (Micropterus salmoides) in Alamo Lake, Arizona

ABSTRACT Each of three size groups of largemouth bass (Micropterus salmoides) differed in foraging behavior and habitat use in an Arizona reservoir. Small bass ( 38 cm TL) were generally found as solitary individuals near submerged structures suitable for ambush feeding. The allometric growth of these fish may have rendered them too bulky to effectively forage in the limnetic zone. Differences in habitat use and foraging behavior for different sizes of largemouth bass in the reservoir appear to be the result of the interaction of the behavioral flexibility of the species, site-specific resources and ecomorphological constraints.

Impact of Threadfin Shad on Macrocrustacean Zooplankton in Two Arizona Lakes

ABSTRACT Analysis of data on macrocrustacean zooplankton in two Arizona lakes provided field evidence that large populations of threadfin shad (Dorosoma petenense) are capable not only of causing species shifts in zooplankton, but also of virtually eliminating zooplankton communities for extended periods as long as 2 years. Our analysis suggests that the long-term negative effects of stocking threadfin shad may greatly outweigh the short-term positive benefits to piscivores.

Unusual diel pHs in water as related to aquatic vegetation

High diel pHs (% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGabmiwayaara% aaaa!36E2!\[\bar X\] > 9.0) showing little or no fluctuation were observed in several impoundments. This phenomenon was experimentally produced in water that contained only Myriophyllum spicatum or species of filamentous algae. Diel pHs ⩾ 9.0 were produced in the laboratory with as little as 0.2 g/1 of algae or vascular plants. The ability of these plants to cause high diel pHs in water may have evolved in response to competition with phytoplankton for carbon.

A Laboratory Approach for Studying Emigration

Angevine, M. W., and S. N. Handel. 1986. Invasion of forest floor space, clonal architecture, and population growth in the perennial herb Clintonia borealis. Journal of Ecology 74:547-560. Batschelet, E. 1965. Statistical methods for the analysis of problems in animal orientation and certain biological rhythms. Monograph, American Institute of Biological Sciences, Washington, D.C., USA. 1981. Circular statistics in biology. Academic Press, London, England. Cain, M. L. 1985. Random search by herbivorous insects: a simulation model. Ecology 66:876-888. 1989. Empirical description and quantitative models of clonal growth in the tall goldenrod, Solidago altissima. Journal of Ecology, in press. Cain, M. L., and R. E. Cook. 1988. Growth in Medeola virginiana clones. II. Stochastic simulation of vegetative spread. American Journal of Botany 75:730-736. Ginsberg, H. 1986. Honeybee orientation behaviour and