Ivan Sazima

Underwater observations of piranhas in western Brazil

SynopsisThe behaviour of three piranha species,Serrasalmus marginatus, S. spilopleura, andPygocentrus nattereri, and their prey fishes was studied underwater in the Pantanal region, Mato Grosso, Brazil. General habits, predatory tactics, feeding behaviour, and social interactions while foraging, as well as defensive tactics of prey fishes were observed.S. marginatus is solitary whereas the other two species live in shoals; their agonistic behaviour varies accordingly, the simplest being displayed by the solitary species. Predatory tactics and feeding behaviour also vary:S. spilopleura shows the most varied diet and highly opportunistic feeding strategy, which includes aggressive mimicry. The solitaryS. marginatus, besides fin and scale-eating, occasionally cleans larger individuals ofP. nattereri. Several cichlid species display defensive tactics clearly related to piranha attacks: tail protecting, watching, and confronting the predator are the most commonly observed behaviours. Piranhas seem to strongly influence use of habitat, social structure, and foraging mode of the fish communities.

Scale-eating in characoids and other fishes

SynopsisScale-eating is known for several unrelated fish groups, but few data are available on the habits of most species. General habits and feeding behavior of some lepidophagous characoids are presented and compared to other scale-eating species. The diversity of morphology, habits, and behavior of scale-eating fishes is great, and few patterns are shared by the specialized scale-eaters. Except for modified teeth, no morphological characteristic permits identifying a fish as a specialized lepidophage. Hunting tactics consist mainly of ambush, stalking, or disguise (aggressive mimicry). Scale-removal may be accomplished by a jarring strike with the snout, generally directed at the preys flank, or by biting or rasping. The mode of scale-removal seems to reflect primarily the disposition of the jaws and the teeth. Scales are swallowed directly if taken in the mouth; if not, they are gathered as they sink, or picked up from the bottom. Scale-eating is probably a size-limited habit. Specialized scale-eaters rarely exceed 200 mm, most ranging near 120 mm. Some species eat scales only when young; most take other food items in addition to scales. Scale-eating habits probably arose from trophic or social behaviors. These are not mutually exclusive and, indeed, may have acted together during the evolution of lepidophagy. Suggested trophic origins include scraping epilithic algae, modified piscivory, and necrophagy. Social origins include intra- and interspecific aggressive behavior during feeding.

Structure of an anuran community in a montane meadow in southeastern Brazil: effects of seasonality, habitat, and predation

In order to assess the main factors influencing its structure, an anuran community was studied from August 1996 to July 1997, in a 1200 m high rocky meadow site at the Serra do Cipo, Minas Gerais, Brasil, a region with markedly seasonal climate. The study site included three temporary habitats: a stream, a puddle, and a swamp. Thirteen anuran species were recorded at the study site. Species of tadpoles differed in microhabitat as to their position in water column, annual occurrence period, and water flow in the occupied sites. Aquatic vegetation, depth and occupied habitat (stream, swamp, or puddle) were of secondary importance in telling species apart. Calling sites of males were distinguished based on occupied habitat and annual activity period. Most species started their reproductive activities at the onset of the rains, in an opportunistic way. Water availability in the habitat seems to be the most important factor affecting temporal distribution of reproductive activities in the anuran community. Competitive interactions could not be detected in the community. The most important tadpole predators recorded at the study site were belostomatid water bugs and dragonfly nymphs. Their abundance peaks occurred after those of tadpoles, as predicted for predator-prey populations with interconnected cycles. Mortality rates were high for tadpoles, and predation is the most likely cause. Differences recorded among species, considering time of occurrence, tadpole microhabitats, and male calling sites, may reflect distinct specific adaptations and preferences.

The snake assemblage of the Pantanal at Poconé, Western Brazil: Faunal composition and ecological summary

The faunal composition and ecological features were studied in a snake assemblage in the Pantanal, an open and seasonally flooded area in western Brazil. Twenty six species of snakes in 19 genera and five families, and their use of habitat, substrate, time, and food were recorded. Hydrodynastes gigas and Eunectes notaeus, the two commonest and largest species, explore the widest range of habitats and food resources. Trends in use of substrate, time of activity and food were compared to those known for snake assemblages from two open and two forested areas in the neotropics. The comparisons indicate that features such as vertical distribution may be viewed essentially from an ecological perspective, while trends in food use benefit from the addition of a faunal perspective.

Specialization in Plant-Hummingbird Networks Is Associated with Species Richness, Contemporary Precipitation and Quaternary Climate-Change Velocity

Large-scale geographical patterns of biotic specialization and the underlying drivers are poorly understood, but it is widely believed that climate plays an important role in determining specialization. As climate-driven range dynamics should diminish local adaptations and favor generalization, one hypothesis is that contemporary biotic specialization is determined by the degree of past climatic instability, primarily Quaternary climate-change velocity. Other prominent hypotheses predict that either contemporary climate or species richness affect biotic specialization. To gain insight into geographical patterns of contemporary biotic specialization and its drivers, we use network analysis to determine the degree of specialization in plant-hummingbird mutualistic networks sampled at 31 localities, spanning a wide range of climate regimes across the Americas. We found greater biotic specialization at lower latitudes, with latitude explaining 20–22% of the spatial variation in plant-hummingbird specialization. Potential drivers of specialization - contemporary climate, Quaternary climate-change velocity, and species richness - had superior explanatory power, together explaining 53–64% of the variation in specialization. Notably, our data provides empirical evidence for the hypothesized roles of species richness, contemporary precipitation and Quaternary climate-change velocity as key predictors of biotic specialization, whereas contemporary temperature and seasonality seem unimportant in determining specialization. These results suggest that both ecological and evolutionary processes at Quaternary time scales can be important in driving large-scale geographical patterns of contemporary biotic specialization, at least for co-evolved systems such as plant-hummingbird networks.

Bat Pollination of the Passion Flower, Passiflora mucronata, in Southeastern Brazil

The pollination by bats of the passion flower, Passiflora mucronata, has been studied in southeastern Brazil. Experiments indicate that the flowers are self-incompatible. They are typically chiropterophilous being white, long-stalked, and exserted from the foliage canopy, opening after dark, and producing nectar throughout the night. The flower opens in less than 15 seconds and shows subsequent movements of the anthers and stigmas which results in a zygomorphic flower, an uncommon condition in Passiflora. The grouping of anthers and stigmas increases the deposition of pollen on the head of the visiting bat and offers the greatest stigmatic surface to be brushed with pollen already deposited on the bats head. Two species of phyllostomid bats, Glossophaga soticina (long-tongued) and Caorollia perspici iata (short-tongued), were observed pollinating the flowers. Other nocturnal visitors were sphingid and noctuid moths, and wasps, but all were ineffectual pollinators. The flowers of P. mucronata remain open until mid-morning and are visited by diurnal bees, wasps, butterflies, and hummingbirds, but it seems that only honeybees effect pollination, and their active foraging for pollen may prevent much of the potontial pollination by hummingbirds.

The nested structure of marine cleaning symbiosis: is it like flowers and bees?

In a given area, plant–animal mutualistic interactions form complex networks that often display nestedness, a particular type of asymmetry in interactions. Simple ecological and evolutionary factors have been hypothesized to lead to nested networks. Therefore, nestedness is expected to occur in other types of mutualisms as well. We tested the above prediction with the network structure of interactions in cleaning symbiosis at three reef assemblages. In this type of interaction, shrimps and fishes forage on ectoparasites and injured tissues from the body surface of fish species. Cleaning networks show strong patterns of nestedness. In fact, after controlling for species richness, cleaning networks are even more nested than plant–animal mutualisms. Our results support the notion that mutualisms evolve to a predictable community-level structure, be it in terrestrial or marine communities.

Behavioural defences of anurans: an overview

Among vertebrates, defensive behaviours have been reviewed for fishes, salamanders, reptiles, birds, and mammals, but not yet for anuran amphibians. Although several defensive strategies have been reported for anurans, with a few exceptions these reports are limited in scope and scattered in the literature. This fact may be due to the lack of a comprehensive review on the defensive strategies of anurans, which could offer a basis for further studies and insights on the basic mechanisms that underlie these strategies, and thus lead to theoretical assumptions of their efficacy and evolution. Here we review the present knowledge on defensive behavioural tactics employed by anurans, add new data on already reported behaviours, describe new behaviours, and speculate about their origins. A total of 30 defensive behaviours (some with a few sub-categories) are here recognised. The terminology already adopted is here organised and some neologies are proposed. Some of the behaviours here treated seem to have an independent origin, whereas others could have evolved from pre-existent physiological and behavioural features. The role of predators in the evolution of defensive behaviours is still scarcely touched upon and this overview adds data to explore this and other evolutionary unsolved questions.

Bat pollination ofEncholirium glaziovii, a terrestrial bromeliad

The many-flowered, brush-like spikes ofEncholirium glaziovii, a ground-dwelling pitcairnioid bromeliad of the “campo rupestre” formation of southeastern Brazil, was observed being pollinated by the glossophagine bat,Lonchophylla bokermanni, in the Serra do Cipó (Minas Gerais). Nectar feeding was while hovering, and the pollen was preferentially transferred by the bats snout. The floral pattern is chiropterophilous; unlike known tillandsioid bat flowers, stamens and style are protrusive beyond a small, persistent perigon, and anthesis, apparently protogynous, extends over several nights, with gradual onset and cease. Although various other flower-visitingChiroptera are known to occur in the area and are not mechanically precluded from exploitingEncholirium glaziovii, no one seems to compete withLonchophylla bokermanni. This species, a trap-liner, habitually forages in open habitats, a possible reason for its exclusiveness.—Flower details of two other species ofEncholirium from the same locality including one with the bat pollination syndrome, are given.

The Saw-billed HermitRamphodon naevius and its flowers in southeastern Brazil

The large Saw-billed HermitRamphodon naevius and its foraging behaviour on a variety of ornithophilous flowers were studied at one site in the Atlantic rainforest in southeastern Brazil. The flower assemblage visited by this endemic hermit throughout the year is composed mainly by epiphytes and herbs, Bromeliaceae and Heliconiaceae being the staple foodplants. Most of the plant species present steady-state, long-tubed and high-reward flowers, and bloom sequentially. The Saw-billed Hermit is a year-round resident and traplining forager, behaves aggressively over its feeding routes, and excludes conspecifics and other hummingbird species from its main flower sources. This large hermit regularly visited and pollinated about 45 % of the native ornithophilous plants at the study site, thus acting as the major pollinator on this flower assemblage. Der große in Südbrasilien endemische Sägeschnabel-Schattenkolibri (Ramphodon naevius) und dessen Nahrungsverhalten an ornithophilen Blüten einer Pflanzengesellschaft des atlantischen Regenwaldes wurde untersucht. Die von ihm besuchten Blüten gehören hauptsächlich zu Kräutern und Epiphyten, wobei Bromeliaceen und Heliconiaceen die Hauptnahrungspflanzen bilden. Diese Arten haben eine lange Blühperiode und blühen konsekutiv. Die Blüten besitzen lange Kronröhren und sondern reichlich Nektar ab. Der standortstreue Kolibri hält eine bestimmte Route und einen Zeitplan bei der Nahrungsaufnahme ein; er verhält sich aggressiv sowohl gegenüber Individuen seiner eigenen Art als auch solchen anderer Kolibriarten, die er von den wichtigsten Nahrungsquellen vertreibt. Der Sägeschnabel-Schattenkolibri besuchte regelmäßig ca. 45 % der ornithophilen einheimischen Pflanzen einer bestimmten Gesellschaft. Damit ist er der wichtigste Bestäuber dieser Pflanzen.