The cooling of convolvulaceous flowers in a tropical environment

The temperatures of flowers of Ipomoea pes‐caprae ssp. brasilensis, Ipomoea aquatica and Merremia borneensis in bright sunshine, were studied to determine the role of corollas and sepals in cooling the gynoecium. The corollas and sepals were prevented from transpiring by greasing, to investigate the extent of evaporative cooling. In the exposed natural habitats of these flowers the maximum temperatures of air and soil were high (32 and 42 °C, respectively) and corolla, sepal and gynoecium temperatures were often intermediate. Despite being almost astomatous, significant evaporative cooling was observed in the corolla. Between 20 and 80% of the energy absorbed by the corollas was dissipated as evaporation. The sepals were stomatous and their evaporative cooling was very important in reducing the temperature of the gynoecium. The temperatures of the non‐transpiring gynoecia and corollas were significantly higher than the temperatures of the normally transpiring corollas and gynoecia. Furthermore, the gynoecia temperatures were significantly higher with non‐transpiring corollas than with normally transpiring corollas, suggesting that the corollas alone play a role in maintaining the gynoecium within optimal temperatures levels. It was shown in an incubation experiment that temperatures exceeding 32 °C may damage the carpels, and temperatures exceeding 42 °C may damage sepals. Pollen grains were killed after 200 min of exposure to temperatures in the range 32 to 47 °C. It is concluded that the cooling mechanisms (evaporation and self‐shading) are critical for the reproductive success of these flowers in their natural environment.     

The role of termites in tropical forestry

Summary Tropical forestry is influenced by termites in widely differing ways.Large mounds constructed byMacrotermes in Africa and Asia are ecological factors which influence the natural regeneration of forests and the vegetation patterns of savanna woodlands and grasslands.Economic losses in timber caused by termite attack on mature trees are restricted to those areas in Australia, Asia and Central America where particular species ofCoptotermes are present.Afforestation withEucalyptus in less humid areas of Africa, India and South America has been greatly facilitated by the use of organochlorine insecticides to protect seedlings and saplings from attack by ground-dwelling termites.

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Zusammenfassung Für die tropische Forstwirtschaft ist eine Reihe von Termitenarten in unterschiedlicher Weise bedeutsam.Dis grossen Termitenhügel vonMacrotermes sind in Afrika und Asien ökologisch von grosser Wichtigkeit, indem sie die Regeneration des Waldes und die Vegetationsverteilung in Trockensavannen und Grasland beeinflussen.Wirtschaftliche Holzschäden durch Termitenangriff auf stehende Waldbäume beschränken sich in Australien, Asien und Zentralamerika auf solche Gebiete, in denen best-immteCoptotermes-Arten vorkommen.Die Aufforstung mit Eucalyptusarten in Afrika, Indien und Südamerika ist wesentlich erleichtert worden, seitdem man dazu übergegangen ist, die Sämlinge und Jungbäumchen durch verschiedene organischsynthetische-Boden-Insektizide zu schützen.

     

Flower orientation enhances pollen transfer in bilaterally symmetrical flowers

Zygomorphic flowers are usually more complex than actinomorphic flowers and are more likely to be visited by specialized pollinators. Complex zygomorphic flowers tend to be oriented horizontally. It is hypothesized that a horizontal flower orientation ensures effective pollen transfer by facilitating pollinator recognition (the recognition-facilitation hypothesis) and/or pollinator landing (the landing-control hypothesis). To examine these two hypotheses, we altered the angle of Commelina communis flowers and examined the efficiency of pollen transfer, as well as the behavior of their visitors. We exposed unmanipulated (horizontal-), upward-, and downward-facing flowers to syrphid flies (mostly Episyrphus balteatus), which are natural visitors to C. communis. The frequency of pollinator approaches and landings, as well as the amount of pollen deposited by E. balteatus, decreased for the downward-facing flowers, supporting both hypotheses. The upward-facing flowers received the same numbers of approaches and landings as the unmanipulated flowers, but experienced more illegitimate landings. In addition, the visitors failed to touch the stigmas or anthers on the upward-facing flowers, leading to reduced pollen export and receipt, and supporting the landing-control hypothesis. Collectively, our data suggested that the horizontal orientation of zygomorphic flowers enhances pollen transfer by both facilitating pollinator recognition and controlling pollinator landing position. These findings suggest that zygomorphic flowers which deviate from a horizontal orientation may have lower fitness because of decreased pollen transfer.     

Visitor assemblages at flowers in a tropical rainforest canopy

Abstract Canopy crane‐based studies have been carried out to quantify the sets of arthropods that visit the flowers of a suite of common species of trees, palms and vines within the Cape Tribulation study area. Those Orders that increase significantly in abundance between the budding and flowering stages of inflorescences are identified, and multivariate and univariate comparisons have been made first, among coflowering plant species and second, at different seasons for the same plant species. The analysis has been repeated for both the profile of higher arthropod taxa in the samples and for the relative abundances of families of Coleoptera: one of the Orders most frequently suggested as critical in the pollination biology of Australian rainforests. In all cases significant differences are identified among species confirming that the visitor profile is a plant species‐specific phenomenon. Profiles within plant species at different times also differed. At the ordinal level significant differences in visitor profiles associated with coflowering plants, were observed, variously, in Thysanoptera, Diptera, Lepidoptera, Coleoptera and Hymenoptera. Within the Coleoptera significant differences occurred in relative abundances of Scarabaeidae, Phalacridae, Latridiidae and Curculionidae. Seasonal differences in visitation to Syzygium gustavioides, Normanbya normanbyi and Calamus radicalis, reflected differences in Diptera, Lepidoptera, Homoptera, Thysanoptera, Hymenoptera and Araneida. Within the Coleoptera, the Elateridae and Curculionidae varied significantly between occasions. The various forms of flower/arthropod interaction that may be represented in these results are discussed, as are the implications for pollination.     

Biodiversity in tropical agroforests and the ecological role of ants and ant diversity in predatory function

Abstract.  1. Intensive agricultural practices drive biodiversity loss with potentially drastic consequences for ecosystem services. To advance conservation and production goals, agricultural practices should be compatible with biodiversity. Traditional or less intensive systems (i.e. with fewer agrochemicals, less mechanisation, more crop species) such as shaded coffee and cacao agroforests are highlighted for their ability to provide a refuge for biodiversity and may also enhance certain ecosystem functions (i.e. predation).
2. Ants are an important predator group in tropical agroforestry systems. Generally, ant biodiversity declines with coffee and cacao intensification yet the literature lacks a summary of the known mechanisms for ant declines and how this diversity loss may affect the role of ants as predators.
3. Here, how shaded coffee and cacao agroforestry systems protect biodiversity and may preserve related ecosystem functions is discussed in the context of ants as predators. Specifically, the relationships between biodiversity and predation, links between agriculture and conservation, patterns and mechanisms for ant diversity loss with agricultural intensification, importance of ants as control agents of pests and fungal diseases, and whether ant diversity may influence the functional role of ants as predators are addressed. Furthermore, because of the importance of homopteran-tending by ants in the ecological and agricultural literature, as well as to the success of ants as predators, the costs and benefits of promoting ants in agroforests are discussed.
4. Especially where the diversity of ants and other predators is high, as in traditional agroforestry systems, both agroecosystem function and conservation goals will be advanced by biodiversity protection.     

Nectarless flowers: ecological correlates and evolutionary stability

In animal-pollinated flowers, the pollinators cannot detect the presence of nectar before entering flowers, and therefore flowers may cheat by not producing nectar. An earlier model suggested that a mixed strategy of producing nectarful and nectarless flowers would be evolutionarily stable. Here we compare nectarless flowers as a cheating strategy with three competing hypotheses namely "visit-more-flowers", "cross-pollination enhancement" and "better contact". We collected field data on 28 species of plants to test some of the differential predictions of the hypotheses. Nectarless flowers were detected in 24 out of 28 plant species. Correlations of percent nectarless flowers with floral and ecological variables support the cheater flower hypothesis. We further model the cost-benefits of cheating and show that an evolutionary stable ratio of nectarless to nectarful flowers can be reached. The equilibrium ratio is mainly decided by factors associated with pollinator density and pollinator learning.     

Water relations of tropical dry forest flowers: pathways for water entry and the role of extracellular polysaccharides

Many trees in tropical dry forests flower during the dry season when evaporative demand is high and soil water levels are low. In this study the factors influencing the water balance of flowers from three species of dry forest trees were examined. Flowers had greater mucilage contents than leaves, high intrinsic and absolute capacitances, long time constants for water exchange and high transfer resistances. Flower water potentials were higher than in leaves and did not fluctuate over the lifespan of the flower. Flower water content also remained constant even though evaporation rates were high, suggesting that water was being supplied from the stem. In two of the species, the water potential gradient between flowers and leaves was opposite to that necessary for water transport from stem to flowers through the xylem, and it was therefore hypothesized that water may enter the flower through the phloem. Calculations showed that nectar production in these flowers could drive a sink of sufficient magnitude to allow water input via the phloem equal to water lost from the flower to the atmosphere.     

The role of experimental microcosms in ecological research

A number of recent and important developments in community ecology have been derived from experiments conducted in microcosms. Studies with microcosms have addressed a broad range of phenomena, including climate change, biodiversity, assembly rules, habitat restoration, trophic dynamics and mycorrhizal associations. The common factor linking these studies is that they manipulate an individual environmental axis and explore the role that axis plays in structuring communities. We discuss six recent studies to illustrate the use and design of microcosms for community ecology research.     

The role of ecological theory in microbial ecology

Microbial ecology is currently undergoing a revolution, with repercussions spreading throughout microbiology, ecology and ecosystem science. The rapid accumulation of molecular data is uncovering vast diversity, abundant uncultivated microbial groups and novel microbial functions. This accumulation of data requires the application of theory to provide organization, structure, mechanistic insight and, ultimately, predictive power that is of practical value, but the application of theory in microbial ecology is currently very limited. Here we argue that the full potential of the ongoing revolution will not be realized if research is not directed and driven by theory, and that the generality of established ecological theory must be tested using microbial systems.     

The ecological role of bacteriocins in bacterial competition

Bacteriocins are an abundant class of antimicrobial molecules that appear to mediate population dynamics within species. The bacteriocins of Escherichia coli have served as a model for exploring the ecological role of these potent toxins. Studies suggest that colicins provide a competitive edge in nutrient-poor environments and that there might be a trade-off between the costs and benefits of colicin production.     

The role of frugivorous bats in tropical forest succession

Discussion of successional change has traditionally focused on plants. The role of animals in producing and responding to successional change has received far less attention. Dispersal of plant propagules by animals is a fundamental part of successional change in the tropics. Here we review the role played by frugivorous bats in successional change in tropical forests. We explore the similarities and differences of this ecological service provided by New and Old World seed-dispersing bats and conclude with a discussion of their current economic and conservation implications. Our review suggests that frugivorous New World phyllostomid bats play a more important role in early plant succession than their Old World pteropodid counterparts. We propose that phyllostomid bats have shared a long evolutionary history with small-seeded early successional shrubs and treelets while pteropodid bats are principally dispersers of the seeds of later successional canopy fruits. When species of figs (Ficus) are involved in the early stages of primary succession (e.g. in the river meander system in Amazonia and on Krakatau, Indonesia), both groups of bats are important contributors of propagules. Because they disperse and sometimes pollinate canopy trees, pteropodid bats have a considerable impact on the economic value of Old World tropical forests; phyllostomid bats appear to make a more modest direct contribution to the economic value of New World tropical forests. Nonetheless, because they critically influence forest regeneration, phyllostomid bats make an important indirect contribution to the economic value of these forests. Overall, fruit-eating bats play important roles in forest regeneration throughout the tropics, making their conservation highly desirable.     

The role of growth regulators in the differentiation of flowers and inflorescences

Growth regulators participate in the differentiation of floral parts, determining the developmental path of the respective type of inflorescence. The effect depends on the expression of the peculiarities of floral part differentiation, the recognition of the character of endogenous substances in certain stages and the choice of the suitable regulator for application. In the primitive flower ofPapaver petals and stamens are formed from the peripheral meristem with a lower content of auxins and a higher level of gibberellic substances. The pistil arises later from central tissues with a higher level of auxins and inhibitory substances. The stamens are more sensitive to the higher level of auxin substances, and by a suitable application of GA₃ and BAP they can be transformed into petals; in this way double flower forms arise. In the differentiation of floral parts ofCampanula, Rosa andMelandrium similar regularities assert themselves in time successions, but in another spatial arrangement. Sex differentiation of diclinous flowers ofMelandrium is based on differences in heterochromosomes XY and XX. The rise of the zygomorphic flower ofVeronica is accompanied by a different distribution of endogenous substances which affect the development of petals, stamens and the pistil. The differentiation of flowers in the racemose inflorescence occurs in the acropetal succession, and lateral primordia inCampanula develop into actinomorphic regular flowers, whereas inDigitalis they are zygomorphic and only the terminal flower is peloric. In the initial phases the staminate tassel and the pistillate ear in maize are identical. Earlier differentiation of the terminal pistillate tassel is connected with a higher level of gibberellins and the later development of the lateral pistillate ear is accompanied by the increase in auxin-like substances and inhibitions. Similar correlations were found in the development of staminate catkins and the differentiation of pistillate flowers in terminal buds ofJuglans regia. By the application of auxin-like substances it is possible to achieve the transformation of primordia of the staminate tassel into the pistillate ear in maize or to regulate the number of staminate catkins and pistillate flowers on twigs of the walnut tree. In the capitulum of the sunflower differences arise between peripheral pistillate ray flowers and hermaphrodite tubular ones. By applying GA₃ and BAP the number of ray flowers is increased. If the normal course of inflorescence differentiation is affected with a suitable type of regulator, a range of floral abnormalities appears which permit to assess the intervention in different developmental stages and the reaction of the primordium to the applied type of regulator. Abnormalities also suggest some phylogenetic correlations.     

The role of pollinators in floral diversification in a clade of generalist flowers

Pollinator‐mediated evolutionary divergence has seldom been explored in generalist clades because it is assumed that pollinators in those clades exert weak and conflicting selection. We investigate whether pollinators shape floral diversification in a pollination generalist plant genus, Erysimum. Species from this genus have flowers that appeal to broad assemblages of pollinators. Nevertheless, we recently reported that it is possible to sort plant species into pollination niches varying in the quantitative composition of pollinators. We test here whether floral characters of Erysimum have evolved as a consequence of shifts among pollination niches. For this, we quantified the evolutionary lability of the floral traits and their phylogenetic association with pollination niches. As with pollination niches, Erysimum floral traits show weak phylogenetic signal. Moreover, floral shape and color are phylogenetically associated with pollination niche. In particular, plants belonging to a pollination niche dominated by long‐tongued large bees have lilac corollas with parallel petals. Further analyses suggest, however, that changes in color preceded changes in pollination niche. Pollinators seem to have driven the evolution of corolla shape, whereas the association between pollination niche and corolla color has probably arisen by lilac‐flowered Erysimum moving toward certain pollination niches for other adaptive reasons.     

The ecological role of secondary lichen substances

Considerable evidence, both direct and indirect, supports the hypothesis that many lichen secondary substances have significant ecological roles. Thus secondary chemistry may be important in determining the relative ecological success of individual lichen species and thus the structure and diversity of natural lichen communities. Primary ecological roles of secondary lichen substances can be classified into four groups: light-screen compounds, chemical weathering compounds, allelopathic compounds, (including antibiotic compounds), and anti-herbivore defense compounds.     

Some ecological aspects of fish populations in tropical ricefields

Fish yields from the captural method of rice-fish farming system were monitored from 1985 to 1987. Seven species were obtained, with Trichogaster pectoralis, Clarias macrocephalus, and Channa striatus dominant and economically important. Low number of species is due to double cropping of rice resulting in increased human activities. The maximum yield obtained, 174.6 kg ha^–1, is probably near the maximum for this type of rice-fish farming and the harvests have also stabilised when compared to those obtained in the early 1970s. Fish populations included more than one year-class in each harvest. A decline in individual weight, especially of herbivores, was recorded and correlated to the abundance of the species, and hence, to food supply.     

The role of phenotypic plasticity in shaping ecological networks

Plasticity-mediated changes in interaction dynamics and structure may scale up and affect the ecological network in which the plastic species are embedded. Despite their potential relevance for understanding the effects of plasticity on ecological communities, these effects have seldom been analysed. We argue here that, by boosting the magnitude of intra-individual phenotypic variation, plasticity may have three possible direct effects on the interactions that the plastic species maintains with other species in the community: may expand the interaction niche, may cause a shift from one interaction niche to another or may even cause the colonization of a new niche. The combined action of these three factors can scale to the community level and eventually expresses itself as a modification in the topology and functionality of the entire ecological network. We propose that this causal pathway can be more widespread than previously thought and may explain how interaction niches evolve quickly in response to rapid changes in environmental conditions. The implication of this idea is not solely eco-evolutionary but may also help to understand how ecological interactions rewire and evolve in response to global change.     

The ecological role of ants in two Mexican agroecosystems

Summary The development of the ant communities and their foraging dynamics were studied in two annual agroecosystems of the Mexican tropical lowlands: a forest milpa of corn, beans, and squash made by cutting and buring 40-year-old forest, and a field milpa of corn, beans, and squash made by plowing 1-year-old second growth. The ant community was sampled using tuna fish baits 26, 52, 110 and 353 days after planting. Although immediately after planting the same number of ant species occurred in each milpa type, thereafter the ant faunas diverged. The field milpa became completely dominated by the native fire ant, Solenopsis geminata, while the number of ant species in the forest milpa gradually increased over time, reaching eight species 110 days after planting and 14 species by 353 days. Initially S. geminata dominated the ant fauna in the forest milpa (occurring on 90% of the baits), but by 353 days planting it was found on only 26% of the occupied baits. Ant foraging efficiency, as measured by proportion of tuna baits occupied and the removal rates of dead Drosophila fly baits, was much higher (by a factor of 2 to 3) in the field than the forest milpa. This was caused by the extremely high density of S. geminata colonies in the field milpa. The simple Solenopsis-dominated community of the field milpa may be much more effective in biological control than the more diverse community of the forest milpa. Although S. geminata has potential negative impacts in annual agroecosystems (it stings, eats corn seeds, and guards homopterams), its overall impact appears to be beneficial. As forested areas of the lowland wet tropics are increasingly cut and converted to annual agriculture, the primary ant inhabitant of these highly disturbed environments, S. geminata, will necessarily play a much more significant ecological role in agroecosystems.     

Elephants versus butterflies: the ecological role of large herbivores in the evolutionary history of two tropical worlds

Aim Large herbivores have important effects upon Paleotropical ecosystems, but attain much lower biomass densities in the Neotropics. We assess how this difference in herbivore activity has generated different ecological and evolutionary trajectories in the New and Old World tropics. We also propose an explanation for how the greater biomass density in the Old World came about. Location Data were compiled primarily from moist tropical forests, although more of the relevant information to address most of our hypotheses was available from the mainland areas of Africa, Asia, and South America than elsewhere. Methods We gleaned data from published information and personal communication. We compared body masses and a variety of other types of information for the New‐ and Old‐World tropics. We proposed that interhemispheric differences exist in a variety of processes, including herbivory, frugivory, and flower visitation. We erected hypotheses and evaluated them qualitatively, and, when information was available, tested them using simple ratios of species in various taxonomic and trophic categories. To make the comparisons more meaningful, we specified appropriate data selection criteria. Results A general pattern of differences emerges from this review. Compared with Neotropical forests, the much greater biomass densities of large herbivores in Paleotropical forests are associated with a lesser diversity of small herbivores, different hunting methods used by indigenous humans, larger arboreal vertebrates, larger fruits, different patterns of fruit and flower dispersion in space and time, a lesser abundance of most types of reproductive plant parts, and other features. The existence of a species‐rich fauna of large herbivores in the pre‐Holocene Neotropical rain forest was not supported. Main conclusions The potential for large herbivores to cause functional differences between the New and Old World tropical forests has been virtually unexplored, despite the well‐known importance of large herbivores in the Old World tropics. The evaluations of our hypotheses suggest that the abundance of large herbivores in the Old World tropics has launched it onto a different evolutionary trajectory than that of the NewWorld tropics. The relevant evidence, although scanty, suggests that the interhemispheric ecological differences are not an artefact of recent megafaunal extinctions in the New World. Recent human activities have, however, reduced population sizes of large wild herbivores in the Old World, and increased population sizes of livestock. This has likely created a rather homogeneous, anthropogenic selection pressure that tends to erase the evolutionary differences between the two tropical worlds.     

The role of remnant forest trees in tropical secondary succession

This paper emphasizes the contribution of remnant trees to the establishment of woody species during succession on abandoned fields and pastures in the Mexican rain forest area, Los Tuxtlas, Veracruz. Remnant trees, original large forest trees left in the clearings by traditional farmers will become natural perching sites for both passing and resident birds. Frugivorous birds drop or regurgitate seeds and fruits which fall under the canopies of remnant trees during their stay, thus contributing to an accumulation of species, which make these remnant trees into ‘regeneration nuclei’. The species transported into these sites belong chiefly to older stages of successional development and reach these otherwise isolated areas, counteracting the depauperization of tropical land, brought about by both intensive and extensive clearing. In a study of seven remnant trees, 29 woody species and two climbers were found, 86% of which are bird dispersed. The total number of species per tree varied from 6 to 15 and was higher under remnant trees with fruits attractive to birds. Floristic variations of the understorey as detected by detrended correspondence analysis was correlated with the relative amount of shade-tolerant primary and late secondary trees versus light dependent pioneers and early successional trees.     

The role of indirect interactions in structuring tropical insect communities

Apparent competition is a form of indirect interaction among species that can potentially structure biological communities. In insect communities, parasitoid-mediated apparent competition has been proposed as a particularly important structuring force. We argue that short-term apparent competition may be less important in structuring insect communities in tropical regions, compared with temperate regions. This prediction arises because, compared with temperate insects, tropical insects that share natural enemies are more likely to be isolated in both space and time.