Cafeteria Experiments Research Articles

Dispersal by ants inCentaurea corymbosa(Asteraceae): What is the elaiosome for?

AbstractThis paper reports on different observations and experiments examining the role of ants in the seed dispersal of the rare and endemic speciesCentaurea corymbosa. Direct observations of seed manipulation by ants in natural populations showed that dispersal distances are very limited, and many ants did not disperse seeds at all. Cafeteria experiments failed to demonstrate: (i) that the elaiosome represents the attractive part of the achene; and (ii) that seeds ofEuphorbia characias,a common species occurring in the same habitat, are more attractive than achenes ofC. corymbosadespite a 10‐fold difference in elaiosome size. However, ants show a foraging behavior to collect seeds ofC. corymbosabecause seed removal is greater at the foot of a fruiting plant than further away. Experiments in controlled conditions were also carried out to investigate the secondary benefits of seed manipulation by ants. Two independent experiments showed that, in contrast to many other myrmecochorous species, elaiosome removal decreases germination rate. Finally, the effects of burial at low depth (2 cm) on seed emergence are limited; however, as ants rarely move seeds to their nest, this secondary benefit of myrmecochory is unlikely. Therefore, it can be concluded that the functional role of an elaiosome in this species is not evident. However, ants clearly contribute to seed dispersal inC. corymbosa.

Oribatid mite predation by small ants of the genus Pheidole

Using “cafeteria experiments” with forest soil and litter, I obtained evidence that at least some small Neotropical species of Pheidole prey on a wide array of slow-moving invertebrates, favoring those of approximately their own size. The most frequent prey were oribatid mites, a disproportion evidently due in part to the abundance of these organisms. The ants have no difficulty breaking through the calcified exoskeleton of the mites.

Insect feeding preferences and plant phenolic glucosides in the system Gonioctena linnaeana–Salix triandra

AbstractThe aim of this study was to investigate the preference of a leaf beetle to different Salix clones, and to relate this preference to plant chemistry. The preference of Gonioctena linnaeana Schrank (Coleoptera: Chrysomelidae) was tested in cafeteria experiments using its host Salix triandra L. (Salicaeae) from three Swedish isolated populations and one Russian population from the main distribution range of the host. The leaves from the different host clones were used to analyse the content of phenolic glucosides and the amount of condensed tannins. The larvae did not show any feeding preferences for host clones from the population they originated from, but all Swedish host populations were preferred over the Russian host population. This suggests a preference for regional hosts. We analyzed whether leaf chemistry parameters may explain host plant preferences. Chemical analysis of the leaves showed that the quantities, but not the quality, of the phenolic compounds differed between populations. A Principal Component Analysis of the chemical data also highlighted a difference between the Swedish and Russian host plant populations. The two most important compounds separating Russian from Swedish clones were gallocatechin and salidroside. However, the difference in preference could also be a result of, for example, nutritional quality, water content, or leaf texture. The relative importance of these different factors should be evaluated in future experiments.

Post‐dispersal predation ofTaraxacum officinale(dandelion) seed

SummaryThe importance of predation in determining the fate of post‐dispersal dandelion (Taraxacum officinale) seed was investigated. Flowering, seed dispersal, seedling establishment, seed predation and seed predator abundance were recorded in 2002 and 2003, at two sites. Number of flowers were counted in 1‐m2plots, wind‐borne seeds were collected in water traps, invertebrate seed predation was estimated from the rate of removal of dandelion seeds exposed on the ground and invertebrate activity density was determined by using pitfall traps. The censuses were made at 2‐ to 3‐day intervals.Seed dispersal occurred 10 days after flowering. Although some seeds were blown away, 3.7–24.2 × 103seeds m−2fell to the ground. Four weeks after the peak in seed dispersal 0.7–3.1% of these seeds germinated. Three weeks later only 11–13% of the dispersed seed remained on the ground and most of these were damaged, the remainder presumably having been removed by predators.Predation of exposed seeds was low before seed dispersal but increased after its onset, in parallel with increases in the number of seeds present on the ground and in the activity density of adults of a seed‐consuming carabid,Amara montivaga.In cafeteria experiments in which the seeds of 28 perennial and annual herbs were providedA. montivagaconsumed the most dandelion seeds, followed by nine otherAmaraspecies. In no‐choice experiments, under field conditions,A. montivagaconsumed six seeds day−1.Post‐dispersal predation, mainly due to aggregation of a single ground beetle species, was more important than that which occurred prior to dispersal. Although predators destroyedc. 97% of the seeds, the effect on dandelion population biology is likely to be small.Post‐dispersal seed predation may nevertheless be important in other species, as aggregates of large invertebrate predators can consume large quantities of seed.

Leaf traits and herbivore selection in the field and in cafeteria experiments

Abstract Despite the vast diversity and complexity of herbivores, plants and their interactions, most authors agree that a small number of components of leaf quality affect preference by generalist herbivores in a predictable way. However, herbivore preference is determined not only by intrinsic plant attributes and herbivore biology but also by the environmental context. Within this framework, we aimed to analyse general interspecific trends in the association between herbivory and leaf traits over a wide range of angiosperms from central Argentina. We (i) tested for consistent associations between leaf traits, consumption in the field, and preference of generalist invertebrate herbivores in cafeteria experiments; (ii) assessed how well herbivore preferences in cafeterias matched leaf consumption in the field; and (iii) developed a simple conceptual model linking leaf traits, herbivore preference in cafeterias and consumption in the field. In general, we found that tender leaves with higher nutritional quality were preferred by herbivores, both in the field and in cafeteria experiments. According to our model, this relationship between field and cafeteria consumption and leaf quality is observed when generalist herbivores and plants of high accessibility are considered. However, differences between leaf consumption in the field and in cafeteria experiments can also be found. At least two reasons can account for this: (i) specialized plant–herbivore relationships often occur in the field, whereas cafeteria experiments tend to consider only one or a few generalist herbivores; (ii) different plant species growing in the field often differ in their degree of accessibility to herbivores, whereas in cafeteria experiments all species are equally accessible. Our results add new evidence to a growing consensus that, although herbivory in the field is determined by many factors, consistent patterns of differential susceptibility to foliar feeders can be found in leaves differing in nutritional quality and thus in resource‐use strategy.

RESOURCE-DEPENDENT INTERACTIONS AND THE ORGANIZATION OF DESERT ANT COMMUNITIES

Resources influence consumer physiology, behavior, population growth, interspecific interactions, and community structure. To understand fully the influence of resources on interactions among consumer populations and community structure, it may be necessary to understand the influence of resources on individual behavior. In the first part of this study, we examined how resource type influenced foraging behavior and interactions in a guild of omnivorous desert ants. Cafeteria experiments showed that Myrmecocystus depilis, M. mimicus, and Aphaenogaster cockerelli prefer protein resources to seed resources. However, A. cockerelli collects mostly seed resources, and M. depilis and M. mimicus collect mostly protein resources when faced with competition from one another. A temporary removal experiment showed that the effect of M. mimicus and M. depilis on A. cockerelli depended on resource type. At protein resources, Myrmecocystus foragers tended to displace A. cockerelli foragers, but at seed resources, there ...

Seed dispersal in Erythronium dens-canis L. (Liliaceae): variation among habitats in a myrmecochorous plant

Erythronium dens-canis is a geophyte which produces a single flower each season. The fruits produce small seeds with relatively large elaiosomes. We performed experiments to investigate primary and secondary seed dispersal mechanisms of this species in different habitats in the western part of the Cantabrian Range in northwest Spain. Sticky traps were used to measure primary dispersal of seeds up to 0.5 m from mother plants. Seed cafeteria experiments were performed in different habitats to examine the role of ants and rodents in secondary seed transport and seed predation. Our results indicate that: (a) primary seed dispersal is positively skewed (99% of seeds fall within 20 cm of the mother plant) and seed dispersal distances vary significantly among plants; (b) secondary dispersal is exclusively by myrmecochory, although the proportion of seeds removed by ants differs significantly among habitats; (c) ant species composition and abundances vary among habitats; and (d) freshly dropped seeds are more likely to be removed than seeds that have begun to dry out. We conclude that secondary dispersal of seeds is greatly influenced by habitat but not by small-scale microhabitat.

Selection and capture of prey in the African ponerine antPlectroctena minor (Hymenoptera: Formicidae)

Prey selection by Plectroctena minor workers is two-fold. During cafeteria experiments, the workers always selected millipedes, their essential prey, while alternative prey acceptance varied according to the taxa and the situation. Millipedes were seized by the anterior part of their body, stung, and retrieved by single workers that transported them between their legs. They were rarely snapped at, and never abandoned. When P. minor workers were confronted with alternative prey they behaved like generalist species: prey acceptance was inversely correlated to prey size. This was not the case vis-à-vis millipedes that they selected and captured although larger than compared alternative prey. The semi-specialised diet of P. minor permits the colonies to be easily provisioned by a few foraging workers as millipedes are rarely hunted by other predatory arthropods, while alternative prey abound, resulting in low competition pressure in both cases. Different traits characteristic of an adaptation to hunting millipedes were noted and compared with the capture of alternative prey. We also noted the parsimony of the behavioural phases during their capture compared to the capture of alternative prey.

Clonal Variation in Susceptibility of White Birches (Betula Spp.) to Mammalian and Insect Herbivores

Abstract Resistance of small micropropagated plantlets and seedlings of white birch (Betula pendula Roth and B. pubescens Ehrh.) to hares (Lepus timidus L.), voles (Microtus agrestis L.) and weevils (Phyllobius and Polydrosus spp.) was determined. Field and cafeteria experiments were conducted over 2 yr period at several locations near Punkaharju Forest Research Station, Eastern Finland. There were significant differences among clones and seedlots (forest seed origins) in susceptibility to hares, voles, and weevils. One of the eight clones studied in detail was resistant to most tested agents (clone 39), whereas two clones were susceptible to each agent (clones 36 and JR/1). However, there was only one significant correlation (hare vs. Polydrosusweevil) among rankings of clones in susceptibility to different pests. Generally the differences among clones were similar in different experimental situations, indicating a genetic basis to variation in resistance. No difference in the susceptibility was observed between seedlots from natural forest and micropropagated plantlets from rapidly growing plus trees, suggesting that selecting for rapid growth did not compromise resistance as predicted by some theories. For. Sci. 43(3):396-402.

Growth and Hare Resistance of Birches: Testing Defense Theories

We tested resistance to the hare (Lepus timidus) of one-year-old seedlings of ten birch (Betula) species showing different life history strategics. Also, we tested the effect of fertilization and shading on the resistance and growth of eight species, including several geographic origins of some. Resistance varied substantially and consistently among the ten birch species. both in field and in cafeteria experiments. Three species exhibited high resistance (B. ermanii. B. platyphylla, and B. resinifera), and six high susceptibility (B. alleghaniensis, B. grossa, B. maximowicziana. B. papyrifera, B. pubescens and B. schmidtii). B. pendula exhibited substantial variation in resistance among individuals and origins. Inherently fast-growing species showed a strong response to fertilization. Growth rate was not related to resistance/susceptibility at the species level. Fertilization significantly lowered the apparent resistance of two of the three resistant species (B. resinifera was invariant), but did not change the susceptible species. Shading substantially decreased seedling mass at high, but not at low nutrient levels, and generally had only a minor effect on resistance. The resistance of B. pendula and B. platyphylla seedlings from different geographic origins varied significantly, but growth and resistance of these seedlings were not related. There was no significant difference in resistance between the easternmost of the western Siberian and the Finnish origins of B. pendula, nor was there any east-west (55°-78°E longitude) clinal trend in its resistance. The resistance of progeny from fast growing Finnish B. pendula families (plus trees) was similar to that of randomly selected forest origins from Finland and western Siberia. Resistance and growth were not related in this comparison either. These results emphasize the great genetic and phenotypic variabiiity both within and among birch species but lend little support for the hypothesis predicting a trade-off between growth and hare defense investments in one-year-old birch scedlings.

Worker Size Polymorphism Conditioning Size Matching in Two Sympatric Seed-Harvesting Ants

The relationship between size matching and degree of polymorphism in two sympatric seed-harvesting ants, Messor bouvieri and M. capitatus is discussed. The two species converged in the use of seeds as their main food resource, but they collected differentsized items, those of M. capitatus being larger than those of M. bouvieri. Size matching of forager size and seed size was also greater in M. capitatus than in M. bouvieri. It was related to the specific worker caste polymorphism of each species: M. bouvieri showed a monophasic allometry, while M. capitatus displayed a diphasic allometry with two segments of different slope meeting at an intermediate point. Small M. capitatus workers, in the same size range as M. bouvieri workers, showed a similar weak size matching, while there was greater correlation between worker size and seed size for bigger M. capitatus individuals. This indicates that size matching is only rewarding when the loads carried are quite large. The role of major M. capitatus workers in increasing the range of sizes carried to the nest was evaluated by means of cafeteria experiments: M. capitatus colonies with major workers were able to transport large seeds (20-30 mm length), while M. bouvieri colonies and M. capitatus colonies without majors were only able to collect smaller seeds.

Twelve New Ant-Dispersed Species from the Southern Appalachians

GADDY, L. L. (Consulting Biologist, Route 1, Box 223, Walhalla, S. C. 29691). Twelve new ant-dispersed species from the southern Appalachians. Bull. Torrey Bot. Club 113:247-251. 1986-Through the use of cafeteria experiments with the diaspores of 17 herbaceous species and with 3 species of ants, 12 southern Appalachian herbs, unreported as myrmecochores, were found to be ant-dispersed. The 12 species included three species of the genus Carex and Scleria triglomerata (Cyperaceae), three species of Panicum (Poaceae), two species of Hexastylis (Aristolochiaceae), Chrysogonum virginianum var. au.strale (Asteraceae), Disporum lanuginosum (Lilaeaceae), and Galium circaezans (Rubiaceae). Here, myrmecochory is reported for the first time in the genera Galium and Panicum. The structure of the elaiosome in each species is also discussed. Galium circeazans and Disporum lanuginosum seem to have elaiosomes that are structurally different from any that have been heretofore described.

Influence of Anise Oils on the Palatability of Calf Starters

Summary Two imitation anise oils and U.S.P. anise oil were used in cafeteria experiments which involved a wide range of basal starters. In each of four experiments, anise oil significantly depressed palatability. Anise oil was more detrimental in one experiment than in the others. In one experiment U.S.P. anise oil and one of the imitations lowered palatability highly significantly more than did another imitation. Two pounds of imitation anise oil per ton of starter lowered palatability highly significantly more than did one-half pound per ton.