Feeding of the Bat,Sturnira lilium,on Fruits of Solanum riparium Influences Dispersal of this Pioneer Tree in Forests of Northwestern Argentina

The influence of fruit ingestion by the bat, Sturnira lilium, on germination of the seeds of the tree Solanum riparium was studied in a secondary rain forest in northwestern Argentina. Bat frequencies in disturbed areas were analyzed by mist net captures. Germination rates were determined for seeds collected from trees and bat feces. S. lilium was the most abundant fruit bat in the study area. Fruit digestion and the passage of seeds through the intestine did not significantly affect germination in S. riparium. In this case the fruit bats, therefore, probably provide only seed dispersal.     

Understanding plant reproductive diversity

Flowering plants display spectacular floral diversity and a bewildering array of reproductive adaptations that promote mating, particularly outbreeding. A striking feature of this diversity is that related species often differ in pollination and mating systems, and intraspecific variation in sexual traits is not unusual, especially among herbaceous plants. This variation provides opportunities for evolutionary biologists to link micro-evolutionary processes to the macro-evolutionary patterns that are evident within lineages. Here, I provide some personal reflections on recent progress in our understanding of the ecology and evolution of plant reproductive diversity. I begin with a brief historical sketch of the major developments in this field and then focus on three of the most significant evolutionary transitions in the reproductive biology of flowering plants: the pathway from outcrossing to predominant self-fertilization, the origin of separate sexes (females and males) from hermaphroditism and the shift from animal pollination to wind pollination. For each evolutionary transition, I consider what we have discovered and some of the problems that still remain unsolved. I conclude by discussing how new approaches might influence future research in plant reproductive biology.     

Biotic and abiotic determinants of the formation of ant mosaics in primary Neotropical rainforests

1. Ants are widespread in tropical rainforests, including in the canopy where territorially dominant arboreal species represent the main part of the arthropod biomass. 2. By mapping the territories of dominant arboreal ant species and using a null model analysis and a pairwise approach this study was able to show the presence of an ant mosaic on the upper canopy of a primary Neotropical rainforest (c. 1 ha sampled; 157 tall trees from 28 families). Although Neotropical rainforest canopies are frequently irregular, with tree crowns at different heights breaking the continuity of the territories of dominant ants, the latter are preserved via underground galleries or trails laid on the ground. 3. The distribution of the trees influences the structure of the ant mosaic, something related to the attractiveness of tree taxa for certain arboreal ant species rather than others. 4. Small‐scale natural disturbances, most likely strong winds in the area studied (presence of canopy gaps), play a role by favouring the presence of two ant species typical of secondary formations: Camponotus femoratus and Crematogaster levior, which live in parabiosis (i.e. share territories and nests but lodge in different cavities) and build conspicuous ant gardens. In addition, pioneer Cecropia myrmecophytic trees were recorded.     

Geographical variation in mandible morphologies specialised for collembolan predation depend on prey size in the ant Strumigenys lewisi

1. Ants in the genus Strumigenys are predator ants that feed on tiny soil arthropods. The mandibles are modified into high‐speed traps to capture swift collembolan prey. The peculiar mandible morphologies of these ants have evolved depending on characteristics of the prey. Specifically, the evolution of mandible size and shape may be directly driven by prey size. 2. In the present study, the intraspecific variation of the morphological traits of Strumigenys lewisi populations were observed in central Japan. The relationships between the morphological variations and the prey body size were analysed. 3. In workers and queens, three morphological traits, head width, mandible length, and mandible width were significantly different among the multiple sites. Specifically, the mandible length was shorter in southwestern Japan than in other sampling locations. The ancova model revealed that the allometry of the mandible length to the head width was different among the sites. 4. As predicted, the mandible length was positively correlated with the average body size of collembolans in the Entomobryidae family. Furthermore, multiple regression analysis showed that the variation of the mandible length was affected by environmental factors represented as location information. However, the effect of collembolan body size was more effective at predicting mandible length. The study suggests that the geographical variation of mandible morphologies in S. lewisi has been selected by predator–prey interactions with collembolans.     

Pollination by fungus gnats in four species of the genus Mitella (Saxifragaceae)

The first example of pollination by fungus gnats in the eudicots is reported. The genus Mitella (Saxifragales) is characteristically produces minute, inconspicuous, mostly dull-coloured flowers with linear, sometimes pinnately branched, petals. To understand the function of these characteristic flowers, we studied the pollination biology of four Mitella species with different floral traits and different sexual expression: dioecious M. acerina , gynodioecious M. furusei var. subramosa , and hermaphroditic M. stylosa var. makinoi and M. integripetala. Flower-bagging experiments showed that wind pollination did not occur in the dioecious and gynodioecious species. Two years of observations of flower visitors at six study sites in Japan revealed that the principal pollinators of all four Mitella were specific species of fungus gnats (Mycetophilidae), which landed on the flowers with their long spiny legs settling on the petals. Characteristically, numerous pollen grains were attached to the fungus gnats in specific locations on the body. Although, on average, 1.3–2.6 fungus gnats visited each inflorescence per day, the fruit set of both bisexual and female flowers exceeded 63%. These results suggest that fungus gnats are highly efficient pollinators of Mitella spp., and that Mitella flowers are morphologically adapted to pollination by fungus gnats.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 144 , 449–460.     

Competition for nectar resources does not affect bee foraging tactic constancy

1. Competition alters animal foraging, including promoting the use of alternative resources. It may also impact how animals feed when they are able to handle the same food with more than one tactic. Competition likely impacts both consumers and their resources through its effects on food handling, but this topic has received little attention. 2. Bees often use two tactics for extracting nectar from flowers: they can visit at the flower opening, or rob nectar from holes at the base of flowers. Exploitative competition for nectar is thought to promote nectar robbing. If so, higher competition among floral visitors should reduce constancy to a single foraging tactic as foragers will seek food using all possible tactics. To test this prediction, field observations and two experiments involving bumble bees visiting three montane Colorado plant species (Mertensia ciliata, Linaria vulgaris, Corydalis caseana) were used under various levels of inter- and intra-specific competition for nectar. 3. In general, individual bumble bees remained constant to a single foraging tactic, independent of competition levels. However, bees that visited M. ciliata in field observations decreased their constancy and increased nectar robbing rates as visitation rates by co-visitors increased. 4. While tactic constancy was high overall regardless of competition intensity, this study highlights some intriguing instances in which competition and tactic constancy may be linked. Further studies investigating the cognitive underpinnings of tactic constancy should provide insight on the ways in which animals use alternative foraging tactics to exploit resources.     

Constructing more informative plant–pollinator networks: visitation and pollen deposition networks in a heathland plant community

Interaction networks are widely used as tools to understand plant–pollinator communities, and to examine potential threats to plant diversity and food security if the ecosystem service provided by pollinating animals declines. However, most networks to date are based on recording visits to flowers, rather than recording clearly defined effective pollination events. Here we provide the first networks that explicitly incorporate measures of pollinator effectiveness (PE) from pollen deposition on stigmas per visit, and pollinator importance (PI) as the product of PE and visit frequency. These more informative networks, here produced for a low diversity heathland habitat, reveal that plant–pollinator interactions are more specialized than shown in most previous studies. At the studied site, the specialization index was lower for the visitation network than the PE network, which was in turn lower than for the PI network. Our study shows that collecting PE data is feasible for community-level studies in low diversity communities and that including information about PE can change the structure of interaction networks. This could have important consequences for our understanding of threats to pollination systems.     

Flower change in Oenothera drummondii Hooker as a response to pollinators' visits

Flower change in Oenothera drummondii Hooker as a response to pollinators' visits. The colour and shape of flowers of Oenothera drummondii change owing to senescence, pollination and/or nectar withdrawal. This phenomenon is interpreted as a signal emitted by the plant to 'inform' the potential pollinator of its new status as a rewardless flower. This method of signalling might be important for the pollinators in order to save energy in seeking the correct flowers and for the plant to ensure visits to those flowers that have not yet been visited.