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

Parasitoids and predators of herbivores have evolved and function within a multitrophic context. Consequently, their physiology and behavior are in­ fluenced by elements from other trophic levels such as their herbivore victim (second trophic level) and its plant food (first trophic level) (126) . Natural enemies base their foraging decisions on information from these different trophic levels, and chemical information plays an important role. This review is restricted to the ecology of chemical information from the first and second trophic levels. The importance of so-called infochemicals, a subcategory of semiochemicals, in foraging by parasitoids and predators has been well documented (e.g. reviewed in 31, 78, Il l , 183, 185) , and we do not intend to repeat the details. But because of a lack of testable hypotheses, all this research is conducted rather haphazardly: the total puzzle of infochemical use has not been solved for any natural enemy species. Here we approach the use of infochemicals by natural enemies from an evolutionary and ecological standpoint. Our basic concept is that information from the first and second trophic levels differs in availability and in reliability, a difference that shapes the way infochemicals are used by a species. We generate hypotheses on (a)

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Ecology of infochemical use by natural enemies in a tritrophic context.

Part I: Theoretical bases of population dynamics. Basic properties and structure of population processes. Structures and patterns of population processes. Statistical analysis of population fluctuations. Population process models. Part II: Analysis of classic cases. Analysis of lynx 10-year cycle. Snowshoe hare demography. Density effects on the dynamics of a single-species population: Utida's classic experiments on the azuki bean weevil. Dynamics of a host-parasitoid interaction system: Utida's experimental study. Dynamics of the spruce budworm outbreak processes. Epilogue. Bibliography. Index.

Analytical population dynamics

Sexual size dimorphism (SSD) is common in both plants and animals, and current evidence suggests that it reflects the adaptation of males and females to their different reproductive roles. When species are compared within a clade, SSD is frequently found to vary with body size. This allometry is detected as β ≠ 1, where β is the slope of a model II regression of log(male size) on log(female size). Most frequently, β exceeds 1, indicating that SSD increases with size where males are the larger sex, but decreases with size where females are larger, a trend formalized as “Rensch's rule.” Exceptions are uncommon and associated with female-biased SSD. These trends are derived from a sample of 40 independent clades of terrestrial animals, primarily vertebrates. Their extension to plants and aquatic animals awaits quantitative assessments of allometry for SSD within these groups. Many functional hypotheses have been proposed to explain the evolution of allometry for SSD, most featuring sexual selection on males ...

https://www.jstor.org/stable/pdfplus/2952508.pdf

Allometry for Sexual Size Dimorphism: Pattern and Process in the Coevolution of Body Size in Males and Females

land Writing in 1980, Professor Per Brinck drew attention to "that coherent system of ideas and approaches which is necessary to shape any branch of science. " As he also pointed out in the same paper, the science of ecology has developed greatly over the last few decades, and recently many have sought theoretical concepts that would bring a coherence to our subject - to avoid, in Watt's (1971) words, being washed out to sea in an immense tide of unrelated information. The most modest role for theories is to provide a classification into which facts can be arranged serving, as T. H. Huxley pointed out (in the days before computers), as an aid to the memory. Such a function alone would only justify the description 'schema'; strictly a theory must permit predictions that can be tested and found true. There are many philosophical and methodological difficulties surrounding the application of what are perceived as strict

Tactics, strategies and templets

We develop a natural selection model for sex ratio control in a spatially variable environment. Predictions of sex ratio alteration as a function of environmental change are tested in laboratory experiments with two parasitic wasps. Field data from a variety of other organisms also support the model. Finally, we discuss possibilities and difficulties for testing this type of evolutionary model.

/pdf/sex-ratio-evolution-in-a-variable-environment-3wpz7xd1i4.pdf

Sex ratio evolution in a variable environment

We compared the impact of differences in body size on reproductive success of males and females in a species of parasitic wasps (Lariophagus distinguendus; Hym., Chalcidoidea, Pteromalidae), in an effort to obtain an estimate of the consequences of being large or small in terms of classical fitness (the expression of an individual's success of passing on its genes to future generations, DAWKINS, 1982). Body size of male and female Lariophagus may vary over about the same range, but, on average, males are distinctly smaller than females. Sex ratio theory has generated a number of models which predict in what ways a parasite like Lariophagus will treat hosts of variable size (reject, use for a daughter, use for a son) in order to make the most profitable investments (e.g. CHARNOV, 1979, 1982; WERREN, 1984). Assumptions on size and sex-related differential fitness returns underly these models. Our experiments served as a test of CHARNOV'S (1979) hypothesis, that a smaller size may be less of a disadvantage to males than to females. The results give support to this assumption. Large females produced more offspring than small ones because they were more fecund and because they lived longer; large and small differed by a factor 3. Large males lived about twice as long as small ones. Large males were able to inseminate about twice as many females but successful courtship displays of both categories proved to be of equal duration. In competitive situations large males were about 1.2 times more successful to court and copulate first, 1.4 times more successful in stealing a copulation and about twice as successful in obtaining an exclusive copulation without any prior investment in courtship behaviour. Small males were less successful than large ones in avoiding sperm competition; difference were in the order of a factor 2.

Is Being Large More Important for Female Than for Male Parasitic Wasps

The pteromalid Lariophagus distinguendus is able to exploit successfully a wide range of developmental instars of its host (the granary weevil, Sitophilus granarius). On young hosts (L II) only males reached maturity; an increasing proportion of females was found with increasing age of the hosts. At the same time the total yield (numbers of weevils and wasps) of bottles with parasitised young hosts was considerably below that of controls; total yield with older hosts equalled that of controls. It could be proved that the differences in sex ratio as found did not result from a differential mortality of the sexes, but were the outcome of a genuine sex regulation mechanism, operated by the female parent. Rate of oviposition, host density, and degree of superparasitism did not affect the experimental results. There was a considerable variability in size of the adult wasps which could be related to age (size) of the host on which they had developed. Size of the adult female wasp was found to be related to longevity and fecundity. Small females are very probably unable to exploit the different host stages to the same effect as large wasps do. Likewise, the developmental period of the parasite was related to the age of the host on which it had fed; very small adults emerged later than expected, presumably because escaping from the grain took far more time than in normal adults. Some properties of a sex regulation mechanism were discussed. It seems to be improbable that an entirely fixed fertilisation threshold is involved. More likely there is at least an additional mechanism to guarantee the production of a minimum number of males under optimal host conditions. Some arguments were given in support of a fertilisation threshold that, instead of being fixed, may vary according to some quantitative characteristics of hosts dealt with previously.

https://brill.com/downloadpdf/journals/njz/21/4/article-p373_1.pdf

Some Experiments On Sex Ratio and Sex Regulation in the Pteromalid Lariophagus Distinguendus

Courtship and mating behaviour of chalcidoid wasps is species-characteristic. Interactions between conspecific males in competition for inseminable females were observed in the laboratory. We have distinguished six types of interaction. Examples of each type are described and discussed. Some speculation is offered about the conditions under which these types are believed to operate in the field.

Observations On Courtship - and Mating Strategies in a Few Species of Parasitic Wasps (Chalcidoidea)

Chemical stimuli appear to play a role in the reproductive behaviour of the parasitic wasp Nasonia vitripennis. We produced qualitative evidence for their function a) in sex recognition (males discriminate conspecific males and females); b) in courtship (males appear to release a pheromone with the extrusion of their mouth parts during "head nodding") ; and c) in territorial behaviour (males mark the place where they have copulated; they may take up a residence in such a place over days).

J. Van Den Assem

Papers

Sex ratio evolution in a variable environment

Is Being Large More Important for Female Than for Male Parasitic Wasps

Some Experiments On Sex Ratio and Sex Regulation in the Pteromalid Lariophagus Distinguendus

Observations On Courtship - and Mating Strategies in a Few Species of Parasitic Wasps (Chalcidoidea)

Courtship Behaviour of Nasonia Vitripennis (Hym., Pteromalidae): Some Qualitative, Experimental Evidence for the Role of Pheromones