Beginning with Emlen (1966) and MacArthur and Pianka (1966) and extending through the last ten years, several authors have sought to predict the foraging behavior of animals by means of mathematical models. These models are very similar,in that they all assume that the fitness of a foraging animal is a function of the efficiency of foraging measured in terms of some "currency" (Schoener, 1971) -usually energy- and that natural selection has resulted in animals that forage so as to maximize this fitness. As a result of these similarities, the models have become known as "optimal foraging models"; and the theory that embodies them, "optimal foraging theory." The situations to which optimal foraging theory has been applied, with the exception of a few recent studies, can be divided into the following four categories: (1) choice by an animal of which food types to eat (i.e., optimal diet); (2) choice of which patch type to feed in (i.e., optimal patch choice); (3) optimal allocation of time to different patches; and (4) optimal patterns and speed of movements. In this review we discuss each of these categories separately, dealing with both the theoretical developments and the data that permit tests of the predictions. The review is selective in the sense that we emphasize studies that either develop testable predictions or that attempt to test predictions in a precise quantitative manner. We also discuss what we see to be some of the future developments in the area of optimal foraging theory and how this theory can be related to other areas of biology. Our general conclusion is that the simple models so far formulated are supported are supported reasonably well by available data and that we are optimistic about the value both now and in the future of optimal foraging theory. We argue, however, that these simple models will requre much modification, espicially to deal with situations that either cannot easily be put into one or another of the above four categories or entail currencies more complicated that just energy.

Citation classic - optimal foraging - a selective review of theory and tests

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Temperature and Organism Size—A Biological Law for Ectotherms?

Many taxa of both marine and freshwater zooplankton perform diel vertical migrations with amplitudes from a few to 100 metres (Hutchinson, 1967). The 'normal' pattern is an evening ascent and a morning descent, though several cases of 'reversed' migrations have been described (Ohman, Frost & Cohen, 1983; Bayly, 1986). Migrating animals spend the day in deep waters but stay near the surface at night. The amplitude of the movements and the shape of the vertical distribution of the population may be very different between species and between ontogenetic stages of the same species and may be influenced by factors like turbitiy and food abundance (Bohrer, 1980; George, 1983). Zooplankton may either migrate up and down together in a narrow band or may be sharply stratified in deep waters during the day but spread throughout the entire water column at night. However, what we observe are only changes in the population density at different depths of the water column. When taking plankton samples from different water layers, we obtain a vertical profile of animal abundances. Shifts in these vertical distributions are usually interpreted as movements of the population and day-night differences between means or medians of the distributions serve as measures of the vertical range of migration. However, such population responses may be seriously misleading in terms of the behaviour of constituent individuals (Pearre, 1979a). Individuals may vary speed and direction of their movements, so that at any time some animals move upwards while others rest or move downwards. The movement of the population reflects only the net effect. The distance between the mean depths of a population at different times equals the distance travelled by an individual only if all animals migrate synchronously. Otherwise, the movement of an individual can be considerably underestimated. As it is not possible to track small individual zooplankton in situ, this problem is still not solved. In the sixties, the main concern of investigators of vertical migration was the neurophysiological basis of the rhythmic behaviour. Behavioural physiology tried to identify the stimuli for initiation and direction of the migration. The relative change of light intensity has been found to be the proximate cue that controls the upwards and downwards movements. At least in Daphnia, the reaction depends on the level of light adaptation of the animal's eye (Siebeck, 1960; Ringelberg, 1964; McNaught & Hasler, 1964; Ringelberg, Van Kasteel & Servaas, 1967). Today the focus of most research on vertical migration has shifted from the environmental control towards the search for ultimate reasons.

http://myweb.facstaff.wwu.edu/shulld/ESCI%20432/Lampert1989.pdf

The adaptive significance of diel vertical migrations

In order to study the size dependency of grazing and growth rates in zooplankton, data wcrc collected from laboratory studies in the literature, covering both limnic and marinc organisms. Data were obtained from about 60 species of nano-, micro-, and mesozooplankton, representing flagellates, ciliates, rotifers, meroplankton larvae, copepods, and cladocerans. Estimates of maximum ingestion and clearance were extracted from functional responses (ingestion rates as a function of food density) cstablishcd from laboratory experiments. Maximum specific rates were expressed as a function of predator body volume. Maximum specific clearance and ingestion rates decreased with predator volume within each group of zooplankton, with a-common exponent (scaling factor) of -0.23 (SE = 20.12) in accordance with previous findings. However, significant differences wcrc found between groups. In particular, among the protists, ciliates display maximum ingestion, growth, and clearance rates that exceed those of dinoflagellates by a factor of 2-4. Among the metazooplankton, Calanoid copepods have maximum clearance rates that cxcccd those of filter-feeding cladocerans and meroplankton larvae by a factor of 10. Because of these differenccs between the groups, the entire set of observations could not be fitted by an overall regression.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1997.42.4.0687

Zooplankton grazing and growth: Scaling within the 2-2,-μm body size range

Climate warming will adversely affect Canadian water quality and water quantity. The magnitude and timing of river flows and lake levels and water renewal times will change. In many regions, wetlands will disappear and water tables will decline. Habitats for cold stenothermic organisms will be reduced in small lakes. Warmer temperatures will affect fish migrations in some regions. Climate will interact with Overexploitation, dams and diversions, habitat destruction, non-native species, and pollution to destroy native freshwater fisheries. Acute water problems in the United States and other parts of the world will threaten Canadian water security. Aquatic communities will be restructured as the result of changes to competition, changing life cycles of many organisms, and the invasions of many non-native species. Decreased water renewal will increase eutrophication and enhance many biogeochemical processes. In poorly buffered lakes and streams, climate warming will exacerbate the effects of acid precipitation. Decreases in dissolved organic carbon caused by climate warming and acidification will cause increased penetration of ultraviolet radiation in freshwaters. Increasing industrial agriculture and human populations will require more sophisticated and costly water and sewage treatment.

The cumulative effects of climate warming and other human stresses on Canadian freshwaters in the new millennium

A complete analysis of the macro- and microzooplankton of a warm monomictic lake indicates that Protozoa dominate the community numerically. During winter mixis, ciliates are found at densities of l-8 x 103*liter-’ and constitute up to 32% of the zooplankton community biomass, With summer stratification crustaceans decline, while both the relative and absolute abundance of protozoans and rotifers increase. Densities of protozoans are highest (l-2 x 105* liter-l) in the metalimnion where scuticociliates bloom in zones of intense bacterial activity. During the period of these blooms (July-October), Protozoa account for 15-62% of the zooplankton biomass. This suggests that Protozoa make a significant contribution to rates of grazing, nutrient regeneration, and secondary productivity and should not be overlooked in

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1981.26.5.0822

The relative importance of protozoans, rotifers, and crustaceans in a freshwater zooplankton community1

Abstruct Swimming patterns, fecging behaviors, and ingestion, filtering, assimilation, and respiration rates were measured for Daphnia mugnu in food concentrations from 0 to 10” Chlamydomonas reinhnrdi cells * cm-“, equivalent to O-20 mg C* liter-‘. A Helling type 2 functional response curve or an Ivlev model without a threshold appear to be biologically meaningful descriptions of Daphnia feeding response to different food concentrations. Daphnia has no feeding threshold or reduced filtering activity at low concentrations such as are predicted by optimal foraging models. Above the incipient limiting concentration, constant ingestion rates and an over-collection of food result in increased rejection rates. These behaviors may cause high respiratory rates and reduced net assimilation rates at the highest food concentration. Daphnia does not orient to or alter swimming patterns in response to algal patches.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1982.27.5.0935

The effect of food concentration on swimming patterns, feeding behavior, ingestion, assimilation, and respiration by Daphnia1

Abstruct The thermal demographic advantage of vertical migration was tested using life-table studies of Daphnia parvula cohorts fed on Chlamydomonas reinhurdi. At a high food level, lifespan and body size at death were relatively insensitive to temperature differences. Fecundity parameters (brood size, brood number, total number of young per reproductive female, and net reproduction rate) were highest at an optimal midrange temperature (15°C). However, age at onset of reproduction, instar at first reproduction and brood duration decreased with increasing temperature, resulting in an overall increase in the realized rate of increase (r) with increasing temperature. Realized rates of increase were higher in fluctuating temperatures than at comparable average constant temperatures but were always lower than those at the highest constant temperature in each range. A low food level reduced the effect of temperature on some growth and fitness parameters from those at a high food level, but T was still greater at the higher temperatures. Therefore, there is no apparent thermal demographic advantage to vertical migration at either a high or low food level within the natural range experienced by D. purvulu. Maximum fitness is achieved by remaining in the warmest surface waters at all times.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1983.28.4.0720

Diel vertical migration by zooplankton: Constant and fluctuating temperature effects on life history parameters of Daphnia1

The functional response of an organism is often assumed to maximize its fitness. We examined the relationship between functional response and body growth, survivorship, and repro- duction in Daphnia magna under controlled and comparable conditions. In a previous study we determined that D. magna exhibits a Holling Type II functional response with an asymptotic increase in ingestion rate with increasing food concentration to a maximum rate at an incipient limiting con- centration of lO 104 Chlamydomonas reinhardi cells/cm3 (measured as carbon, 0.2 mg/L) and that observed feeding activity does not follow the predictions of energy optimization models. In this study, we determined the fitness response for cohorts of D. magna (n = 20-30) at 0, 103, 104, 105, and 106 Chlamydomonas reinhardi cells/cm3 using life table methods. Most parameters indicative of fitness (e.g., body growth, fecundity, survivorship, r, and RO) were maximal at 105 cells/cm3 (2.0 mg/L). The optimum food concentration for growth and reproduction remained at )05 cells/cm3 when cohort life spans were truncated in a simulation of mass mortality due to predation or environmental deterio- ration. The fitness optimum occurred above the incipient limiting concentration and below the max- imum food concentration encountered in nature. These appear to be "suboptimal" behavioral and reproductive responses. However, reproductive modes of parthenogenesis and resting egg formation along with these feeding, growth, and reproductive responses suggest that Daphnia track the envi- ronment in that they are adapted for rapid population increase and for recovery from mass mortality in cyclical environments with conditions for optimal growth that can be expected to reoccur but are of highly variable duration.

https://www.jstor.org/stable/info/1937196

Functional Response and Fitness in a Generalist Filter Feeder, Daphnia Magna (Cladocera: Crustacea)

Daphnia parvula experiences a wide range of thermal (4°–30°C) and food conditions during its annual population cycle. We used cohort life table experiments to determine the synergistic effects of temperature and food concentration on its life history parameters. A 3×3 factorial design experiments was conducted with animals raised at all combinations of three naturally experienced temperatures (10°, 15° and 25° C) and food levels (0.02, 0.20 and 2.0 mg C/l). D. parvula showed an increase in survivorship with decreasing temperature at all food levels. Fecundity parameters (number of broods/female, brood size and net reproductive rate) increased with increasing food at the two lower temperatures but showed a mid-range food optimum at the highest temperature. Development rates and realized rates of increase (r) showed an increase with both increasing temperature and food such that they were maximum at the highest temperature-food level treatment. The life history parameters, average lifespan, age at first reproduction, brood duration time, brood size and number of young per reproductive female all showed significant interaction between temperature and food as was suggested by trends in Ro and r. Temperature had a reduced effect on fecundity, development rates and realized rates of increase at the low food level.

John D. Orcutt

Papers

The relative importance of protozoans, rotifers, and crustaceans in a freshwater zooplankton community1

The effect of food concentration on swimming patterns, feeding behavior, ingestion, assimilation, and respiration by Daphnia1

Diel vertical migration by zooplankton: Constant and fluctuating temperature effects on life history parameters of Daphnia1

Functional Response and Fitness in a Generalist Filter Feeder, Daphnia Magna (Cladocera: Crustacea)

The synergistic effects of temperature and food concentration of life history parameters of Daphnia.