Konrad Fiedler

COMPETITION FOR COMPOSITION: LESSONS FROM NECTAR-FEEDING ANT COMMUNITIES

Studies of the relationship between the composition of nectar and its consumers often focus on single or very few species, thus ignoring dynamics in diverse assemblages. Conversely, most documented patterns of nectarivore communities have not been linked to nectar quality measures. In a study of nectar-foraging ant communities in an Australian rain forest, we found that nectar source partitioning between consumers may be driven by two factors: (1) variation in nectar composition preferences mediated by taste and physiological requirements, and (2) severe asymmetrical competitive interactions within the community. Ant communities are strongly shaped by competitive hierarchies. When foraging for extrafloral and floral nectar sources, wound sap, and homopteran honeydew, competitively superior weaver-ants (Oecophylla smaragdina) showed a significant preference for nectar composition, whereas most other common community members were nonselective. Nectars frequently used by O. smaragdina were characterized by s...

Response of the copper butterfly Lycaena tityrus to increased leaf nitrogen in natural food plants: evidence against the nitrogen limitation hypothesis

Abstract This study examined the effects of increased leaf N in natural food plants on oviposition, preimaginal survival, growth, and adult size of the butterfly Lycaena tityrus. Female butterflies did not discriminate between leaves of high and low N content. In accordance with previous studies, we found higher growth rates and concomitantly decreased development times at a high N level. However, because of high pupal (and larval) mortality (overall 73.0%) as well as a reduction in adult size (by ca. 8%) this was, overall, not beneficial to the butterflies. Thus, our results were not consistent with the broad interspecific trend that insect herbivore performance is positively correlated with leaf N. These findings undermine the general applicability of the N limitation hypothesis. As the detrimental effects were largely confined to the pupal and adult stages, results obtained from the larval phase only may not yield reliable results and must therefore be interpreted with caution. If negative effects of N enrichment are found more frequently in declining species inhabiting nutrient poor grassland, this will have major implications for the conservation of these species.

Physiological costs of growing fast : does accelerated growth reduce pay-off in adult fitness?

Accumulating evidence suggests that, in contrast to earlier assumptions, juvenile growth rates are optimised by means of natural and sexual selection rather than maximised to be as fast as possible. Owing to the generally accepted advantage of growing fast to adulthood, such adaptive variation strongly implies the existence of costs attached to rapid growth. By using four populations of protandrous copper butterflies with known differences in intrinsic growth rates within and across populations, we investigate a potential trade-off between rapid growth and the proportionate weight loss at metamorphosis. While controlling for effects of pupal time and mass, we demonstrate that (1) protandrous males, exhibiting higher growth rates, suffer a higher weight loss than females throughout, that (2) population differences in weight loss generally follow known differences in growth rates, and that (3) males have by 6 higher metabolic rates than females during pupal development. These results support the notion that a higher weight loss during the development to adulthood may comprise a physiological cost of rapid development, with the pay-off of accelerated growth being reduced by a disproportionally smaller adult size

Reaction norms for age and size at maturity in response to temperature: a test of the compound interest hypothesis

In ectotherms, temperature induces similar developmental and evolutionary responses in body size, with larger individuals occurring or evolving in low temperature environments. Based on the occasional occurrence of opposite size clines, showing a decline in body size with increasing latitude, an interaction between generation time and growing season length was suggested to account for the patterns found. Accordingly, multivoltine species with short generation times should gain high compound interest benefits from reproducing early at high temperatures, indicating potential for extra generations, even at the expense of being smaller. This should not apply for obligatorily monovoltine populations. We explicitly test the prediction that monovoltine populations (no compound interest) should be selected for large body size to maximise adult fitness, and therefore size at maturity should respond only weakly to temperature. In two monovoltine populations (an Alpine and a Western German one) of the butterfly Lycaena hippothoe, increasing temperatures had no significant effect on pupal weight and caused a slight decrease in adult weight only. In contrast, two closely related, yet potentially multivoltine Lycaena populations showed a greater weight loss at increasing temperature (in protandrous males, but not in females) and smaller adult sizes throughout. Thus, the results do support our predictions indicating that the compound interest hypothesis may yield causal explanations for the relationship between temperature and insect size at maturity. At all temperatures, the alpine population had higher growth rates and concomitantly shorter development times (not accompanied by a reduction in size) than the other, presumably indicating local adaptations to different climates.

The symbiosis between the weaver ant, Oecophylla smaragdina, and Anthene emolus, an obligate myrmecophilous lycaenid butterfly

Females of Anthene emolus use the presence of the weaver ant, Oecophylla smaragdina, as oviposition cue. Ovipositing females are not attacked by the ants. The first instar larvae are adopted by the ants and carried into their pavilions where the caterpillars feed. Outside the pavilions the larvae cannot survive. The older larvae leave the pavilions and are carried by the ants to their feeding places or back into the pavilions. The larvae are constantly attended by the ants. During the 3rd and 4th instar the caterpillars secrete high amounts of nutritive liquids representing an estimated energy content of 200 J per larva. Thus the larvae are important trophobionts of Oe. smaragdina and attract the ants by releasing food recruitment behaviour. The pupae are not attractive for ants, but are not attacked, either. The emerging adults are not protected from ant attacks and are sometimes killed by their host ants. The costs and benefits of this close obligate myrmecophilous relationship for both the ants and lyc...

Dimorphic growth patterns and sex‐specific reaction norms in the butterfly Lycaena hippothoe sumadiensis

Directly developing larvae of the butterfly Lycaena hippothoe sumadiensis exhibited two growth strategies with one cohort passing four larval instars at high growth rates, and the other five instars at lower growth rates. The 4‐instar‐cohort displayed decreased development times, in combination with slightly reduced pupal and adult weights. In addition to adjustment of growth rate, omitting a larval instar may comprise a further mechanism to decrease development time when needed. Using the 4‐instar‐cohort, sex‐related differences in reaction norms were investigated over a temperature gradient. At high temperatures, protandrous males showed early emergence at a reduced size, whereas weight of females remained similar throughout. These differences suggest that large size is more important for female than for male fitness. The pattern is similar to that previously reported for alpine L. tityrus, indicating that sex‐specific reaction norms might be widespread in species living under severe time constraints.

Butterflies and ants: the communicative domain

Associations with ants, termed myrmecophily, are widespread in the butterfly family Lycaenidae and range from mere co-existence to more or less specific mutualistic or even parasitic interactions. Secretions of specialized epidermal glands are crucial for mediating the interactions. Transfer of nutrients (carbohydrates, amino acids) from butterfly larvae to ants plays a major role, but manipulative communication with the help of odour signals is also involved. By means of myrmecophily, lycaenid butterflies largely escape ant predation, and certain species gain protection through attendant ants or achieve developmental benefits from ant-attendance. Benefits to the ants range from minimal to substantial food rewards. While most lycaenid species maintain facultative relationships with a variety of ant genera, highly specific and obligatory associations have convergently evolved in a number of butterfly lineages. As a corollary, communication systems are largely unspecific in the former, but may be highly specialized in the latter. The sophisticated communication between obligate myrmecophiles and their host ants is tightly connected with the evolutionary rise of specialized life-cycles and thus is a source of augmenting diversity within the butterflies.

Functional analysis of the myrmecophilous relationships between ants (Hymenoptera: Formicidae) and lycaenids (Lepidoptera: Lycaenidae). II. Lycaenid larvae as trophobiotic partners of ants—a quantitative approach

SummaryMature larvae of the myrmecophilous lycaenid Polyommatus coridon produce an average of 30.9 droplets of a honeydew-like secretion per hour. They occur in population densities of about 20/m2. The volume of secretion over the whole larval period is estimated to be 22–44 μl with an energy content of 55–110 J. Thus, P. coridon larvae produce carbohydrate secretions with an energy equivalent of 1.1–2.2 kJ/m2. Using data from the literature on ant metabolism, it is shown that these carbohydrate secretions may contribute significantly to the nutrition of attending ants. The myrmecophilous relationship between the larvae of P. coridon and ants should therefore be regarded as a mutualistic symbiosis.

The influence of ants on patterns of colonization and establishment within a set of coexisting lycaenid butterflies in a south-east Asian tropical rain forest

In Peninsular Malaysia ten species of lycaenid butterflies use leaf flushes or inflorescences of the legume tree Saraca thaipingensis as larval hostplant. Resource partitioning among these species is regulated by a complex mixture of patterns of interaction with ants. Females of obligately myrmecophilous species lay their eggs exclusively on trees colonized by their specific host ants. On trees colonized by weaver ants, only specialist mutualists adapted to these territorial ants are able to survive, while larvae of other species are killed. The formicine ant Cladomyrma petalae, which inhabits hollow twigs of the myrmecophytic hostplant, likewise precludes oviposition by female butterflies. Lycaenid larvae confronted with this ant species never survive, but one concealed feeding species (Jamides caeruleus) escapes removal due to the cryptic life-habits of the larvae. Two facultative myrmecophiles associate in a mutualistic way with a wide and largely overlapping range of ant genera which forage at the extrafloral nectaries of leaf flushes. One species (Cheritra freja) is not myrmecophilous, but is tolerated by all but the most territorial ants. Ant-dependent hostplant selection and egg-clustering characterize the obligate mutualists, whereas facultative myrmecophiles and the non-myrmecophile distribute their eggs singly over appropriate hostplants. Signals mediating caterpillar-ant communication are highly specialized in one obligate myrmecophile (Drupadia theda), but rather unspecific in four other species tested. Altogether our observations indicate that colonization and establishment of lycaenid butterflies on S. thaipingensis trees are governed by specializations as well as opportunistic use of resources (ants and hostplant parts). Therefore, the diversity of this species assemblage is maintained by deterministic as well as stochastic factors.

Ordinating tropical moth ensembles from an elevational gradient: a comparison of common methods

The analysis of beta diversity (inter-habitat diversity) of very species-rich and incompletely sampled tropical arthropod communities requires the choice of appropriate statistical tools. The performance of the three commonly employed ordination methods, correspondence analysis (CA), detrended correspondence analysis (DCA), and non- metric multidimensional scaling (NMDS), was compared on a large empirical data set of geometrid moths sampled along an altitudinal gradient in an Andean montane rain forest. Despite the high species richness and incompleteness of the ensembles, all methods depicted the same, readily interpretable patterns. Both CA and NMDS showed an arch-like structure, which hints at an underlying coenocline, whereas this arch was computationally eliminated in DCA. For this particular data set, CA and NMDS both provided convincing results while the detrending algorithm of DCA did not improve the interpretability of the data. Of the large number of similarity indices available to be used in combination with NMDS, the binary Sorensen and the abundance-based Normalized Expected Species Shared (NESS) index were tested. Performance of the indices was measured by comparing stress, a measure of poorness-of-fit in NMDS. NMDS ordinations with lowest values of stress were achieved by the NESS index with the parameter m set to its maximum (mmax). In contrast, ordinations based on NESS values with the parameter m set to 1 (identical with Morisitas index), had consistently higher stress values and performed worse than ordinations using Sorensens index. Hence, if high values of m can be achieved in similar data sets, the NESS index with mmax is recommended for ordination purposes and Morisitas index should be avoided.