Pietro K. Maruyama

Processes entangling interactions in communities: forbidden links are more important than abundance in a hummingbird -plant network

Understanding the relative importance of multiple processes on structuring species interactions within communities is one of the major challenges in ecology. Here, we evaluated the relative importance of species abundance and forbidden links in structuring a hummingbird–plant interaction network from the Atlantic rainforest in Brazil. Our results show that models incorporating phenological overlapping and morphological matches were more accurate in predicting the observed interactions than models considering species abundance. This means that forbidden links, by imposing constraints on species interactions, play a greater role than species abundance in structuring the ecological network. We also show that using the frequency of interaction as a proxy for species abundance and network metrics to describe the detailed network structure might lead to biased conclusions regarding mechanisms generating network structure. Together, our findings suggest that species abundance can be a less important driver of species interactions in communities than previously thought.

Floral resource availability and hummingbird territorial behaviour on a Neotropical savanna shrub

The influence of floral resource availability on behaviour and dominance hierarchy of hummingbirds has seldom been investigated in open tropical environments. We evaluated the behavioural changes of hummingbirds associated with Palicourea rigida, a shrub common in the Cerrado, the open savanna areas in Central Brazil. We observed the foraging behaviour as a function of resource availability and experimentally manipulated floral display and nectar in order to define resource thresholds associated with territorial behaviour and territory intruding behaviour. Territorial behaviour was observed only in patches with high floral abundance and was restricted to some hummingbird species. The large Eupetomena macroura seems to be the dominant species in the community, excluding other hummingbirds and holding the richest patches. The experimental reduction in the floral abundance and nectar led to the abandonment of territory by these hummingbirds, which reinforces the idea that a certain threshold is necessary to maintain territorial defence. Higher floral display, on the other hand, seems to lead to higher frequency of intrusions and higher behavioural complexity of territory defenders, possibly meaning greater energy expenditure. The flower number and nectar manipulation affected visitation rates of territorial hummingbirds, but the frequency of intruders was affected only by the former manipulation. This indicates that territorial intruder use visual cues (floral abundance) as indicators of resource availability in order to estimate cost–benefit of territory invasion. Although territorial behaviour could limit pollen flow in patches with larger floral displays, this may be compensated by the territory invaders, which bring pollen from other patches.ZusammenfassungDer Einfluss von Ressourcenverfügbarkeit von Blüten auf das Verhalten und die Dominanzhierarchie von Kolibris in offenen, tropischen Landschaften ist bisher nur selten untersucht worden. Wir erfassten Verhaltensveränderungen von Kolibris in Assoziation mit Palicourea rigida, einem häufiger Strauch in der Cerrado, der offenen Baumsavanne in Zentralbrasilien. Wir untersuchten das Foragierverhalten als eine Funktion der Ressourcenverfügbarkeit. Dazu manipulierten wir Blüten- und Nektarverfügbarkeit experimentell um Schwellenwerte von Ressourcenverfügbarkeit, assoziiert mit Territorialverhalten, zu schätzen. Territorialverhalten wurde nur an Stellen mit hoher Blütenabundanz beobachtet, und war beschränkt auf nur einige Kolibriarten. Der große Eupetomena macroura scheint die dominante Art in der Gemeinschaft zu sein: diese Art schloss andere Kolibriarten aus und besetzte die reichsten Stellen. Die experimentelle Verringerung von Blüten- und Nektarverfügbarkeit führte zum Verlassen von Territorien durch diese Kolibris, welches die Idee eines Schwellenwertes, für die Entstehung von Territorialverhalten unterstützt. Vermehrte Blütenverfügbarkeit jedoch führte scheinbar zu einer höheren Frequenz von Intrusions, und zu höherer Komplexität des Verhaltens des Verteidigers des Territoriums, was möglicherweise auf einen erhöhten Energieverbrauch hinweist. Die Blütenanzahl und die Nektarmanipulationen beeinflussten die Besuchsraten von territorialen Kolibris; die Frequenz der Eindringlinge jedoch wurde nur von der Blütenmanipulation beeinflusst. Dies suggeriert das die Eindringlinge visuelle Hinweise (Blütenabundanz) als Indikator für die Ressourcenverfügbarkeit verwenden, um die Kosten und den Nutzen einer Eindringung in ein Territorium abzuschätzen. Obwohl Territorialverhalten Pollenverbreitung limitieren kann, ist es möglich dass dieses durch die Eindringlinge kompensiert wird, welche Pollen von anderen Stellen mitbringen.

Opposed latitudinal patterns of network‐derived and dietary specialization in avian plant‐frugivore interaction systems

Latitudinal patterns of biodiversity have been studied for centuries, but it is only during the last decades that species interaction networks have been used to examine the proposed latitudinal gradient of biotic specialization. These studies have given idiosyncratic results, which may either be because of genuine biological differences between systems, different concepts and scales used to quantify biotic specialization or because the methodological approaches used to compare interaction networks were inappropriate. Here we carefully examine the latitudinal specialization gradient using a global dataset of avian plant-frugivore assemblages and interaction networks. In particular, we test whether network-derived specialization patterns differ from patterns based on assemblage-level information on avian dietary preferences on specific food types. We found that network-derived measures of specialization (complementary specialization H2’ and , modularity Q) increased with latitude, i.e. frugivorous birds divide the niche of fruiting plants most finely at high latitudes where they also formed more modular interaction networks than at tropical latitudes. However, the strength and significance of the relationship between specialization metrics and latitude was influenced by the methodological approach. On the other hand, assemblage-level information on avian specialization on fruit diet (i.e. the proportion of obligate frugivorous bird species feeding exclusively on fruit diet) revealed an opposed latitudinal pattern as more bird species were specialized on fruit diet in tropical than in temperate assemblages. This difference in the latitudinal specialization gradient reflects that obligate frugivores require a high diversity of fruit plants, as observed in tropical systems, and fulfil more generalized roles in plant-frugivore networks than bird species feeding on different food types. Future research should focus on revealing the underlying ecological, historical and evolutionary mechanisms shaping these patterns. Our results highlight the necessity of comparing different scales of biotic specialization for a better understanding of geographical patterns of specialization in resource-consumer interactions. . This article is protected by copyright. All rights reserved.

Avian frugivory in Miconia (Melastomataceae): contrasting fruiting times promote habitat complementarity between savanna and palm swamp

Species of Miconia are considered keystone plant resources for frugivorous birds in Neotropical forests, but for other ecosystems little of their ecological role is known. The fruiting phenology and the composition of frugivores of four Miconia species in savanna and palm swamp from the Brazilian Neotropical savanna were studied in three sites from November 2005 to May 2011. The hypothesis tested was that plants from different habitats share their frugivores and consequently promote links between habitats. Through focal plant observations (30-50 h per species in each site), 668 visits by 47 species of birds were recorded and plants from different habitats shared most of the frugivores (49-97%). The fruiting of Miconia chamissois in the palm swamp during the period of fruit scarcity (dry season) was accompanied by an enhancement in the frugivore bird richness and abundance in this habitat, providing indirect evidence of resource tracking. Bird species which primarily dwell in savanna recorded consuming fruits in palm swamps during the resource-scarce season is taken as evidence of landscape supplementation. Miconia assemblage studied here seems to promote a link between two adjacent habitats in the Neotropical savanna from Central Brazil, a link which is likely to be common in this naturally patchy ecosystem.

Relation of group size and daily activity patterns to southern lapwing ( Vanellus chilensis ) behaviour

Behavioural patterns of birds commonly vary according to flock size and daily activity pattern. Southern lapwing behaviours and their relation with flock size were studied, as well as the relationship between the frequency of behaviours and the period of the day. Results showed that the proportion of time spent in foraging and vigilance was higher during the morning, when small groups were more common, and decreased from midday on, when group size increased. Maintenance and inactivity (sleeping) behaviours presented the opposite pattern. Correlation between flock size and period of the day, and their similar effects on bird behaviour may be evidence that groups of different sizes could have different functions throughout the day. Our results show that southern lapwings seem to form smaller flocks for feeding in the beginning of the day and larger flocks later for different activities (e.g., maintenance and sleeping). In this sense, it is possible that group size variation throughout the day is related to different demands for specific behaviours (functions) of groups, according to the daily activity patterns of the birds.

When hummingbirds are the thieves: visitation effect on the reproduction of Neotropical snowbell Styrax ferrugineus Nees & Mart (Styracaceae)

The spectrum of floral visitors associated with a particular plant is frequently larger than predicted by the traditional concept of floral syndromes and the role that unpredicted visitors play in plant reproduction deserves attention. Hummingbirds are frequently recorded visiting flowers with distinct floral syndromes, especially in some hummingbird flower poor ecosystem such as the Cerrado. In this study we investigated the effect of frequent hummingbird visits on the reproduction of melittophilous Styrax ferrugineus. The flowers were visited by many different insect groups and visits by hummingbirds were frequent, especially early in the morning when nectar availability was higher. Nectar parameters varied considerably during the flower life span, and was probably affected by the temperature variation during the day. Hummingbird exclusion experiments showed no effect in the fruit-set of the plant. The inability of hummingbirds to deplete all of the nectar produced in this mass-flowering plant, and the existence of another resource (pollen) for the primary pollinator (large bees), are possible reasons why there was no perceptible hindrance of plant reproduction by the hummingbirds. Although no effect in the fruit-set was observed, the use of non-ornithophilous flowers must be important for hummingbirds, which are specialized nectar consumers.

Sexual ratio and floral biology of the dioecious Neea theifera Oerst. (Nyctaginaceae) in a cerrado rupestre of central Brazil

Dioecy is characterized by a complete separation of sexual functions on male and female plants. It has evolved many times in flowering plants and is widespread among distinct Angiosperm families. It is viewed as a reproductive strategy to reduce endogamy, and to promote optimal resource allocation between male and female sexual functions. Neea theifera is a common species in Cerrado, neotropical savannas in Brazil, but information regarding its reproductive biology is still incomplete. In order to investigate how environmental conditions possibly affect this dioecious species, we studied its floral biology, sex ratio and spatial distribution of sexual morphs along a soil-altitudinal gradient. The sex ratio did not significantly deviate from the expected 1:1 ratio. However, flower abundance in the population was significantly biased towards staminate flowers. Female individuals were larger than male individuals and plant size was negatively correlated with altitude, but did not differ between sexual morphs. The population did not show spatial segregation of sexes and male individuals were sexually mature earlier than female ones. Staminate flowers were larger than pistillate flowers and presented high pollen viability. Meliponini bees, small flies and thrips were potential pollinators, but pollination success was very low. Dioecy in N. theifera corroborates many general features of this reproductive strategy, such as woody habit, inconspicuous flowers, pollination by small generalist insects and differential resource allocation between male and female plants. However, reproduction in this species seems to be impaired by pollinator limitation. The results showed that the soil-altitude gradient influenced the growth pattern of the species and may play an important role in its reproductive biology but did not affect dioecy directly.

Flower stage and host plant preference by floral herbivore thrips (Insecta: Thysanoptera: Frankliniella) in a Brazilian savanna

This study shows that three Frankliniella (Thysanoptera) species have species-specific associations with their hosts: F. varipes–Faramea cyanea (Rubiaceae); F. musaeperda–Hancornia speciosa (Apocynaceae) and F. fulvipes–Solanum lycocarpum (Solanaceae). All thrips species had a marked preference for flowers in anthesis, as in this stage flowers provide food and protection from environment. Frankliniella musaeperda and F. varipes populations were female-biased while F. fulvipes was male-biased. Since many species of Frankliniella have economic importance, studies on the ecology of these species are essential, given the possibility of invasion of agricultural systems in the future.

Gall-inducing nematodes as ecosystem engineers for arthropods associated with its host plant in the Cerrado of Brazil

In this study we examined the role of a gall-inducing nematode on the diversity of arthropods associated with Miconia albicans (Melastomataceae), acting as an ecosystem engineer. Nematode galls (i.e. leaves and infructescences) supported higher arthropod diversity than healthy plant structures, and some species were found only in the gall. Galled leaves and infructescences harbored species of different trophic levels, suggesting that galls provide distinct resources, such as food tissue and refuge. We conclude that the presence of gall has a strong effect on the diversity and composition of arthropod fauna and a gall inducer can be important microhabitat engineers where they are abundant, having considerable influence on the diversity of small organisms inhabiting plants.

Trait evolution, resource specialization and vulnerability to plant extinctions among Antillean hummingbirds

Species traits are thought to predict feeding specialization and the vulnerability of a species to extinctions of interaction partners, but the context in which a species evolved and currently inhabits may also matter. Notably, the predictive power of traits may require that traits evolved to fit interaction partners. Furthermore, local abiotic and biotic conditions may be important. On islands, for instance, specialized and vulnerable species are predicted to be found mainly in mountains, whereas species in lowlands should be generalized and less vulnerable. We evaluated these predictions for hummingbirds and their nectar-food plants on Antillean islands. Our results suggest that the rates of hummingbird trait divergence were higher among ancestral mainland forms before the colonization of the Antilles. In correspondence with the limited trait evolution that occurred within the Antilles, local abiotic and biotic conditions—not species traits—correlate with hummingbird resource specialization and the vulnerability of hummingbirds to extinctions of their floral resources. Specifically, hummingbirds were more specialized and vulnerable in conditions with high topographical complexity, high rainfall, low temperatures and high floral resource richness, which characterize the Antillean Mountains. These findings show that resource specialization and species vulnerability to extinctions of interaction partners are highly context-dependent.