Optimal foraging area: Size and allocation of search effort

A model is derived for the optimal spatial allocation of foraging effort for an animal returning with food to a central place in a uniform habitat. The forager is assumed to maximize its yield of food during a given period. Foraging effort is expended on search for food, and on transportation to the central place. It is shown that the allocation of search has been optimal if and only if the “marginal cost” of additional food is equal throughout the foraging area when the period has elapsed. The model is used to predict the optimal area radius and allocation of search time. With realistic parameter values, the optimal time per unit area roughly decreases linearly with the distance from the central place. The influence of food density and forager characteristics is examined.     

Optimal foraging of a herbivorous lizard,the green iguana in a seasonal environment

Food selection was studied in free living green iguanas (Iguana iguana) throughout the year in a semiarid environment, Curaçao (Netherlands Antilles). Food intake was determined by direct observations and converted into biomass intake. Comparison between intake and biomass availability of the various food items revealed that the lizards were selective, and that changes in seasonal food availability led to periodic switching of food plants. The extent to which nutrient constraints determine iguana feeding ecology was investigated. Potential constraints were the requirements for water, digestible crude protein, and metabolizable energy. By using a linear programming model that incorporates characteristics of the food (chemical composition, energy content, item size) and requirements and constraints of the green iguanas (nutrient and energy requirements digestive tract capacity, feeding rate) it was possible to identify which factors determine food choice over the year. During the dry period, when the iguanas had no access to drinking water they consumed flowers to increase water intake, though the amount of flowers consumed was too low to cover maintenance requirements for either energy or protein. After the young leaf flush, following the early rains in May, the biomass increased, free surface water was available during showers, and the linear programming solutions indicate that food selection conformed to the protein maximization criterion. Reproduction in green iguanas shows an annual cycle, in which oviposition takes place at the end of the dry season, when intake is below maintenance levels. Females show a 8–10 month gap between acquisition of most of the protein required for egg synthesis and the act of laying. Thus, as in avian and mammalian herbivores, food availability during a period prior to the energy and protein demanding reproductive season of iguanas determines reproductive success.     

Semiochemicals and habitat manipulation to support green lacewing activity to reduce aphid infestations in agroecosystems

Conservation biological control (CBC) is a promising tool for ecological intensification that aims to establish resilient natural enemy populations that contribute to pest management with reduced use of pesticides and at the same time support native biodiversity in agroecosystems. Yet the impact of natural enemies in CBC is often limited due to missing resources such as food, habitat, and hibernation shelters. Here, we studied a CBC strategy that incorporates these essential resources combined with semiochemicals, focusing on how the common green lacewing can enhance biological control of aphids.In a 4-year field study conducted at three locations in the region of East Norway, we developed a CBC strategy combining the three measures ATTRACT (a ternary attractant that increase lacewing egg laying), FOOD (floral buffer strips), and SHELTER (insect hotels for overwintering survival) to increase aphid biological control in spring barley. We recorded the number of lacewings, ladybirds, hoverflies, parasitized aphid mummies, and the two cereal aphid species Sitobion avenae and Rhopalosiphum padi. Our CBC strategy resulted in a significant increase in lacewing activity and significant aphid suppression. At all three locations and over the 4-year period, aphid infestation was below the economic damage threshold in the field plots using CBC measures. In contrast, during two of the years, the density of the aphid infestation in the control plots was significantly above the damage threshold. We found evidence that use of the ternary attractant supported green lacewings but led to loss of ladybirds, hoverflies, and parasitoids, even though flower strips were used as alternative resources.Our study shows a promising increase in lacewing activity in the agricultural landscape and high biological control of aphids in barley. Long-term field studies are needed to evaluate the impact on non-target species and the agroecosystem before practical application of this approach can be considered.     

Optimal foraging: a bird in the hand released

Optimal foraging theory aims to elucidate strategies that maximize resource intake. Although traditionally used to understand animal foraging behavior, recent evolutionary experiments with viruses offer a new twist on an old idea.     

An unlikely silk: the composite material of green lacewing cocoons

Spiders routinely produce multiple types of silk; however, common wisdom has held that insect species produce one type of silk each. This work reports that the green lacewing ( Mallada signata, Neuroptera) produces two distinct classes of silk. We identified and sequenced the gene that encodes the major protein component of the larval lacewing cocoon silk and demonstrated that it is unrelated to the adult lacewing egg-stalk silk. The cocoon silk protein is 49 kDa in size and is alanine rich (>40%), and it contains an alpha-helical secondary structure. The final instar lacewing larvae spin protein fibers of approximately 2 microm diameter to construct a loosely woven cocoon. In a second stage of cocoon construction, the insects lay down an inner wall of lipids that uses the fibers as a scaffold. We propose that the silk protein fibers provide the mechanical strength of the composite lacewing cocoon whereas the lipid layer provides a barrier to water loss during pupation.     

The diet and foraging behaviour of the Dunnock Prunella modularis in a hedgerow habitat

The diet and foraging behaviour of a population of Dunnocks inhabiting hedgerows was studied between November 1981 and December 1983 at Nedge Hill, Shropshire. Invertebrates were most abundant in hedgerows and adjacent vegetation during the summer when the diet of the Dunnock was largely insectivorous. Beetles (Coleoptera) were the main taxa in the diet, with weevils (Curculionidae) and rove beetles (Staphylinidae) predominating. Arachnids were important, and snails (Gastropoda), earthworms (Oligochaeta), springtails (Collembola) and flies (Diptera) were taken. Seeds were available in the study area from July and featured in the diet from August to April. Nettle Urtica dioica comprised the main seed in the diet. Other important seeds included Yorkshire fog Holcus lanatus , elder Sambucus nigra and dock Rumex obtusifolius. Stomach stones were most common in the faeces in winter. The Dunnocks were predominantly ground feeders and mainly used a hop-picking technique. Some seeds and invertebrates were picked directly off plants by Dunnocks above the ground. Most feeding occurred in hedgerows, which formed a small proportion of the study area. Overgrown hedgerows were the most important of the five hedgerow types. Nettle patches were an important feeding habitat. Dunnocks usually foraged alone or in pairs and rarely fed in association with other bird species. The highest proportion of time spent feeding was in January and the lowest in May.     

Structure of the subgenual organ in the green lacewing, Chrysoperla carnea

REM and TEM studies of the subgenual organ in Chrysoperla carnea (Neuroptera: Chrysopidae) show that it is composed of three scolopidia, each with one sensory, one scolopale and one cap cell. The distal part of the dendrite shows a cilium with a '9 + 0' structure. The cross-handing pattern of the ciliary root has a periodicity of bands of about 61 nm. The scolopale material in a certain part of the scolopale cell is organized into five rods. The cell bodies of all three cap cells form a lens-like structure. the velum, which is fixed to the leg wall and the trachea with an extracellular material. The importance of the velum is discussed. Four types of intercellular junction are found; spot desmosomes. belt desmosomes, septate junctions and gap junctions.     

Isopropanol attracts the green lacewing,Chrysopa quadripunctata (Neuroptera: Chrysopidae)

Adult female green lacewings, Chrysopa quadripunctata Burmeister, were attracted to traps baited with 45% isopropanol in an unsprayed apple orchard in Missouri, USA. No lacewings were attracted to the unbaited traps. To the best of our knowledge this is the first report on a semiochemical that attracts lacewings of this species.     

The role of behavior in evolution: a search for mechanism

Behavior has been viewed as a pacemaker of evolutionary change because changes in behavior are thought to expose organisms to novel selection pressures and result in rapid evolution of morphological, life history and physiological traits. However, the idea that behavior primarily drives evolutionary change has been challenged by an alternative view of behavior as an inhibitor of evolution. According to this view, a high level of behavioral plasticity shields organisms from strong directional selection by allowing individuals to exploit new resources or move to a less stressful environment. Here, I suggest that absence of clear mechanisms underlying these hypotheses impedes empirical evaluation of behavior’s role in evolution in two ways. First, both hypotheses focus on behavioral shifts as a key step in the evolutionary process but ignore the developmental mechanisms underlying these shifts and this has fostered unwarranted assumptions about the specific types of behavioral shifts that are important for evolutionary change. Second, neither hypothesis provides a means of connecting within-individual changes in behavior to population-level processes that lead to evolutionary diversification or stasis. To resolve these issues, I incorporate developmental and evolutionary mechanisms into a conceptual framework that generates predictions about the types of behavior and types of behavioral shifts that should affect both micro and macroevolutionary processes.     

Adaptive dispersal and appetitive flight in the green lacewing, Chrysopa cornea

Abstract.

• 1 The flight behaviour of Chrysopa cornea Steph. (Neuroptera: Chrysopidae) with regard to dispersal activity has been investigated in field experiments. There are three main types of flight activities.
• 2 Shortly after emergence (in the first two nights) the adults perform adaptive dispersal flights which are straight downwind flights mostly at elevations higher than 3 m above ground. The lacewings do not react to the presence of honey dew in the crop.
• 3 After 2—3 days the scent of honeydew becomes a strong landing stimulus. The flight is now an appetitive downwind flight which usually is lower than 3 m above ground.
• 4 Once landed, the lacewings' subsequent flights are toward the source of the kairomone which signals honeydew. This can be termed appetitive upwind flight. It is a low stepwise flight within the ‘boundary layer’ which rarely exceeds 1 m above crop level.
• 5 Dispersal takes place in a continuous ‘rolling’ downwind movement of the whole lacewing population. The immigration rate into a field is thus not a function of the quality of that field but rather of upwind fields. Emigration, however, strongly depends on the presence of honeydew (retaining of ovipositing immigrants) and the density of aphids or other food for the larvae (production of new adults).

     

Optimal foraging in bumblebees: Hunting by expectation

The foraging behaviour literature contains three hypotheses concerned with hunting by expectation. These suggest possible rules animals use to decide when to leave particular feeding sites and search in other places for food. Predictions of the three hypotheses were tested experimentally by varying the quality of plants (amount and distribution of nectar) encountered by bumblebees (Bombus appositus). Results support only a rate expectation hypothesis. Bees left multiflowered plants when the amount of nectar found in the first flower was below a threshold volume. Bees stayed on plants if they received greater than the threshold volume. This threshold nectar volume is close to the amount predicted if a bee forages to maximize its rate of net energy intake.     

A functional response model of a predator population foraging in a patchy habitat

1. Functional response models (e.g. Holling's disc equation) that do not take the spatial distributions of prey and predators into account are likely to produce biased estimates of predation rates. 2. To investigate the consequences of ignoring prey distribution and predator aggregation, a general analytical model of a predator population occupying a patchy environment with a single species of prey is developed. 3. The model includes the density and the spatial distribution of the prey population, the aggregative response of the predators and their mutual interference. 4. The model provides explicit solutions to a number of scenarios that can be independently combined: the prey has an even, random or clumped distribution, and the predators show a convex, sigmoid, linear or no aggregative response. 5. The model is parameterized with data from an acarine predator-prey system consisting of Phytoseiulus persimis and Tetranychus urticae inhabiting greenhouse cucumbers. 6. The model fits empirical data quite well and much better than if prey and predators were assumed to be evenly distributed among patches, or if the predators were distributed independently of the prey. 7. The analyses show that if the predators do not show an aggregative response it will always be an advantage to the prey to adopt a patchy distribution. On the other hand, if the predators are capable of responding to the distribution of prey, then it will be an advantage to the prey to be evenly distributed when its density is low and switch to a more patchy distribution when its density increases. The effect of mutual interference is negligible unless predator density is very high. 8. The model shows that prey patchiness and predator aggregation in combination can change the functional response at the population level from type II to type III, indicating that these factors may contribute to stabilization of predator-prey dynamics.     

Seasonal variation in the migration strategies of the green lacewing Chrysoperla carnea species complex

Abstract.  1. Insect migration strategies are generally poorly understood due to the propensity for high-altitude flight of many insect species, and the technical difficulties associated with observing these movements. While some progress has been made in the study of the migration of important insect pests, the migration strategies of insect natural enemies are often unknown.
2. Suction trapping, radar monitoring, and high-altitude aerial netting were used to characterise the seasonal migrations in the U.K. of an assemblage of aphid predators: three green lacewings in the Chrysoperla carnea species complex.
3. Chrysoperla carnea sens. str . was found to be very abundant at high altitudes during their summer migration, and some individuals were capable of migrating distances of ≈ 300 km during their pre-ovipositional period. In contrast, high-altitude flights were absent in the autumn migration period, probably due to a behavioural adaptation that increases the probability that migrants will encounter their over-wintering sites. The other two species in the complex, C. lucasina and C. pallida , were much rarer, making up ≈ 3% of the total airborne populations throughout the study period.
4. The summer migration of C. carnea sens. str . was not directly temporally associated with the summer migration of its cereal aphid prey, but lagged behind by about 4 weeks. There was also no evidence of spatial association between aphid and lacewing populations.
5. The results show that to understand the population ecology of highly mobile insect species, it is necessary to characterise fully all aspects of their migration behaviour, including the role of high-altitude flights.     

Yellow mutant of the Neotropical green lacewing Chrysoperla externa: trait inheritance and predator performance

The Neotropical green lacewing Chrysoperla externa (Hagen) (Neuroptera: Chrysopidae) is a key predator of various small soft‐bodied pest species. Chrysopidae species are known as ‘green lacewings’ due to their overall green body coloration. However, yellow mutant individuals were observed emerging from our lacewing rearing colony. Thus, the mode of inheritance of the yellow trait was studied and the hypothesis of an autosomal recessive allele for yellow color was tested using hybridization and backcrossing techniques. Furthermore, the possible implications of this color variation on specific life‐history characteristics of C. externa and the predation rates of each morph were evaluated. In both yellow and green morphs, basic life‐history characteristics were monitored, including time to hatching and viability of eggs, duration, and viability of larval and pupal stages, emergence rate and survivorship of adults, and fecundity and longevity of females. The yellow and green morphs were indistinguishable with respect to all life‐history traits evaluated and the predation rate of their larvae. Crossing experiments revealed the yellow color to be caused by a homozygous recessive allele, without sex‐linked expression. We conclude that the allele for yellow color is occurring at high frequency in the laboratory colony, supporting the existence of a genetic polymorphism for body ground color.     

The importance of distance to resources in the spatial modelling of bat foraging habitat

Many bats are threatened by habitat loss, but opportunities to manage their habitats are now increasing. Success of management depends greatly on the capacity to determine where and how interventions should take place, so models predicting how animals use landscapes are important to plan them. Bats are quite distinctive in the way they use space for foraging because (i) most are colonial central-place foragers and (ii) exploit scattered and distant resources, although this increases flying costs. To evaluate how important distances to resources are in modelling foraging bat habitat suitability, we radio-tracked two cave-dwelling species of conservation concern (Rhinolophus mehelyi and Miniopterus schreibersii) in a Mediterranean landscape. Habitat and distance variables were evaluated using logistic regression modelling. Distance variables greatly increased the performance of models, and distance to roost and to drinking water could alone explain 86 and 73% of the use of space by M. schreibersii and R. mehelyi, respectively. Land-cover and soil productivity also provided a significant contribution to the final models. Habitat suitability maps generated by models with and without distance variables differed substantially, confirming the shortcomings of maps generated without distance variables. Indeed, areas shown as highly suitable in maps generated without distance variables proved poorly suitable when distance variables were also considered. We concluded that distances to resources are determinant in the way bats forage across the landscape, and that using distance variables substantially improves the accuracy of suitability maps generated with spatially explicit models. Consequently, modelling with these variables is important to guide habitat management in bats and similarly mobile animals, particularly if they are central-place foragers or depend on spatially scarce resources.     

The influence of diet on foraging habitat models: a case study using nursing Antarctic fur seals

Predictable sources of food underpin lifetime reproductive output in long lived animals. The most important foraging areas of top marine predators are therefore likely to be related to environmental features that enhance productivity in predictable spatial and temporal patterns. Even so, although productive areas within the marine environment are distributed patchily in space and time, most studies assess the relationships between feeding activity and proximate, not long term, environmental characteristics. In addition, individuals within a population may exploit different prey types, and these are often associated with different hydrographic features. Until now, models attempting to associate core foraging areas (CFAs) of marine predators with the environmental characteristics of those areas have not considered the diet of individual animals, despite the influence this could have on these relationships. We used bathymetry and multi‐year (n=24) mean sea surface temperature and variability as predictors of CFAs of lactating Antarctic fur seals Arctocephalus gazella at Heard Island. The effect of prey types on the predictability of these models was explored by matching diet and foraging trip data of individual seals (n=40 seals, n=1 trip each). Differences in diet between seals were mirrored by their spatial behaviour. Foraging strategies differed both between and within groups of seals consuming different diets. Long‐term environmental parameters were useful for predicting the foraging activity of seals that consumed a single prey type with relatively specific habitat preferences, but not for those that consumed single or multiple prey types associated with more varied habitats. Ignoring individual variation in predator diet probably contributes to the poor performance of foraging habitat models. These findings highlight the importance of incorporating individual specialization in foraging behaviour into ecological models and management of predator populations.