Understory Of Tropical Rainforests Research Articles

Drought Reduces the Growth and Health of Tropical Rainforest Understory Plants

Drought Reduces the Growth and Health of Tropical Rainforest Understory Plants

Tradescantia-based models: a powerful looking glass for investigation of photoacclimation and photoadaptation in plants.

Here, we summarize diverse evidence from species that belong to the genus Tradescantia, which we propose as handy and versatile models for studies of the ecology of photosynthesis and the mechanisms of photoacclimation in higher plants. A valuable feature of this genus is the amazingly broad range of ecological niches occupied by its species: from shady understory of tropical rainforest to deserts and semideserts. The former habitats demand shade tolerance (e.g. that featured by Tradescantia fluminensis), whereas the latter requires succulence and/or high light stress tolerance (evident in e.g. Tradescantia navicularis). At the same time, the acclimative traits of Tradescantia species seem quite moderate at first glance. Certainly, their basic principles of acclimation seem to differ in some aspects from the ones typical for most of other higher plants. This review presents a systematic analysis of irradiance responses of Tradescantia species studied on different timescales. The specifics of Tradescantia responses to irradiance make the plants of this genus a 'multitool' for studies in this field. Similarity of irradiance acclimation patterns is a characteristic feature in the ecologically contrasting Tradescantia species, which may inspire further insights into physiology and evolution of plants.

Una nueva especie de Allomaieta (Melastomataceae- Cyphostyleae) del piedemonte amazónico de los Andes de Colombia

Allomaieta javierbarrigae , a new species from the Amazonian foothills of the state of Putumayo, Colombia, is described. This is the first record of the genus Allomaieta from the Amazonian flank of the Andes of Colombia. It is characterized by strigose indumentum of the vegetative parts, inflorescence and hypanthium, leaves with basal or slightly plinervate venation, 5-merous flowers, and rose-coloured petals. It grows in the shade of the understory of tropical rainforests between 700 and 900 m a.s.l. Given its limited distribution and habitat specificity, the categorization of this species as Endangered (EN) is recommended.

Stomatal opening in response to the simultaneous increase in vapor pressure deficit and temperature over a 24-h period under constant light in a tropical rainforest of the central Amazon

Stomatal functioning is modulated by several factors and, in most circumstances, stomatal aperture declines with increasing leaf-to-air vapor pressure difference (VPDL) and temperature, but stomatal functioning under the humid conditions of the tropical rainforest understory has been scarcely investigated. The aim of this study was to determine how stomatal conductance of saplings responds to the changing understory temperatures of a tropical rainforest. We measured gas-exchange in four saplings of Guarea carinata (1–2 m tall). On each plant, stomatal conductance (g s), VPDL and leaf temperature were measured continuously at 3-min intervals during 24 h. We used a constant irradiance of 50 µmol m−2 s−1 and nearly constant relative humidity (75.8 ± 1.9%). Within the leaf chamber, leaf temperature over plants varied from 25.8 to 30.7 °C and VPDL from 0.62 to 0.93 kPa. Contrary to expectations, g s increased with the increase in leaf temperature and VPDL, and throughout the 24-h cycle, g s was maximum (0.123 mol m−2 s−1) at midday when temperatures were higher and minimum (0.016 mol m−2 s−1) after midnight, when the lower temperatures were recorded. There was a positive relationship between g s and both leaf temperature (p < 0.0001) and VPDL (p < 0.0001). If global temperature continues to increase as predicted by models, the direct increase in g s of saplings associated with an increase in temperature can be nullified if global warming negatively affects the water balance of plants (e.g. Guarea carinata) in this part of the Amazon.

Frugivory-related traits promote speciation of tropical palms.

Animal-mediated seed dispersal by frugivorous birds and mammals is central to the ecology and functioning of ecosystems, but whether and how frugivory-related traits have affected plant speciation remains little explored. Fruit size is directly linked to plant dispersal capacity and therefore influences gene flow and genetic divergence of plant populations. Using a global species-level phylogeny with comprehensive data on fruit sizes and plant species distributions, we test whether fruit size has affected speciation rates of palms (Arecaceae), a plant family characteristic of tropical rainforests. Globally, the results reveal that palms with small fruit sizes have increased speciation rates compared with those with large (megafaunal) fruits. Speciation of small-fruited palms is particularly high in the understory of tropical rainforests in the New World, and on islands in the Old World. This suggests that frugivory-related traits in combination with geography and the movement behaviour of frugivores can influence the speciation of fleshy-fruited plants.

Quantifying micro-environmental variation in tropical rainforest understory at landscape scale by combining airborne LiDAR scanning and a sensor network

We combined aerial LiDAR and ground sensors to map the spatial variation in micro-environmental variables of the tropical forest understory. We show that these metrics depend on forest type and proximity to canopy gaps. Our study has implications for the study of natural forest regeneration. Light impacts seedling dynamics and animals, either directly or through their effect on air temperature and relative humidity. However, the micro-environment of tropical forest understories is heterogeneous. We explored whether aerial laser scanning (LiDAR) can describe short-scale micro-environmental variables. We also studied the determinants of their spatial and intra-annual variation. We used a small-footprint LiDAR coverage combined with data obtained from 47 environmental sensors monitoring continuously understory light, moisture and temperature during 1 year over the area. We developed and tested two models relating micro-environmental conditions to LiDAR metrics. We found that a volume-based model predicts empirical light fluxes better than a model based on the proportion of the LiDAR signal reaching the ground. Understory field sensors measured an average daily light flux between 2.9 and 4.7% of full sunlight. Relative seasonal variation was comparable in the understory and in clearings. In canopy gaps, light flux was 4.3 times higher, maximal temperature 15% higher and minimal relative humidity 25% lower than in the forest understory. We found consistent micro-environmental differences among forest types. LiDAR coverage improves the fine-scale description of micro-environmental variables of tropical forest understories. This opens avenues for modelling the distribution and dynamics of animal and plant populations.

Ecology and conservation of avian insectivores of the rainforest understory: A pantropical perspective

Avian insectivores of the tropical rainforest understory (“understory insectivores”) are common, diverse, and often sensitive to disturbance of tropical forest, making them useful as sentinels of rainforest ecosystem change. At the 2013 joint American Ornithologists’ Union and Cooper Ornithological Society meeting in Chicago, USA, researchers convened a symposium to address the ecology and conservation of understory insectivores. This Special Issue of Biological Conservation is the result of that symposium: a collection of articles that unites our efforts to further understand and conserve understory insectivores. In this introductory paper, we review the diversity and ecology of understory insectivores, identify threats to the guild, discuss hypotheses on drivers of population declines, and make suggestions for future research. Deforestation and forest degradation are the immediate threats to this guild, with agricultural expansion (particularly oil palm plantations), urbanization, road expansion and logging leading the list. Although vulnerabilities of this guild are most evident in the Neotropics, there are few studies from Asia and fewer still from Africa—we recommend increased geographic coverage. If we are to understand the vulnerabilities of understory insectivores from a pantropical perspective, researchers should prioritize understanding the most serious threats (e.g., edge effects, deforestation, fragmentation, etc.) and standardize efforts to gauge understory insectivores’ response to these threats (e.g., via species richness, abundance, demographic metrics). A coordinated approach by researchers working in tropical rainforests across the globe can help us understand the ecology of understory insectivores and meaningfully apply conservation and management actions.

Forest fragmentation alters microhabitat availability for Neotropical terrestrial insectivorous birds

Many insectivorous birds of the tropical rainforest understory, particularly terrestrial species, are prone to local extinctions in fragmented forests. We evaluated the hypothesis that vegetation structural changes in rainforest fragments reduce the availability of microhabitats used by terrestrial insectivores. Near Manaus, Brazil, we compared the vegetation in forest fragments to the vegetation in a continuous forest site where nine species of terrestrial insectivores were observed foraging. Our focal species included those that are extinction prone in fragments (Myrmornis torquata [Wing-banded Antbird], Grallaria varia [Variegated Antbird], Hylopezus macularius [Spotted Antpitta]), a fragmentation-tolerant species (Myrmothera campanisona [Thrush-like Antpitta]), and species that have and intermediate response (Myrmeciza ferruginea [Ferruginous-backed Antbird], Formicarius colma [Rufous-capped Anttrush], Formicarius analis [Black-faced Antthrush], Conopophaga aurita [Chestnut-belted Gnateater], and Corythopis torquata [Ringed Antpipit]). To quantify vegetation, we measured sixteen habitat variables in 8-m radius plots where birds were observed foraging as well as random points in continuous forest and forest fragments of 1-, 10-, and 100-ha. Four principal components were produced from a principal component analysis and we selected a variable (leaf litter depth, plant cover 3–10m, density of plants 1–2m, and plant cover >20m) from each principal component for our fragment vs continuous forest comparisons. Using Markov chain Monte Carlo (MCMC) simulation, we estimated the probabilities that the density of plants 1–2m, proportion of plant cover 3–10m, and leaf litter depth increased with decreasing fragment area and also exceeded the values associated with fragmentation-sensitive species. We also tested the prediction that plant cover >20m decreased in forest fragments and that those sites became more open than typical sites used by our focal species. Our predictions were strongly supported: decreasing fragment size was correlated with increasing density of tall plants, increasing mid-story vegetation cover, decreased canopy cover, and increasing leaf litter depth. Even if our focal species are able to disperse to small forest fragments, our results suggest that they may not find enough appropriate habitat.

Linking size‐dependent growth and mortality with architectural traits across 145 co‐occurring tropical tree species

Tree architecture, growth, and mortality change with increasing tree size and associated light conditions. To date, few studies have quantified how size-dependent changes in growth and mortality rates co-vary with architectural traits, and how such size-dependent changes differ across species and possible light capture strategies. We applied a hierarchical Bayesian model to quantify size-dependent changes in demographic rates and correlated demographic rates and architectural traits for 145 co-occurring Malaysian rain-forest tree species covering a wide range of tree sizes. Demographic rates were estimated using relative growth rate in stem diameter (RGR) and mortality rate as a function of stem diameter. Architectural traits examined were adult stature measured as the 95-percentile of the maximum stem diameter (upper diameter), wood density, and three tree architectural variables: tree height, foliage height, and crown width. Correlations between demographic rates and architectural traits were examined for stem diameters ranging from 1 to 47 cm. As a result, RGR and mortality varied significantly with increasing stem diameter across species. At smaller stem diameters, RGR was higher for tall trees with wide crowns, large upper diameter, and low wood density. Increased mortality was associated with low wood density at small diameters, and associated with small upper diameter and wide crowns over a wide range of stem diameters. Positive correlations between RGR and mortality were found over the whole range of stem diameters, but they were significant only at small stem diameters. Associations between architectural traits and demographic rates were strongest at small stem diameters. In the dark understory of tropical rain forests, the limiting amount of light is likely to make the interspecific difference in the effects of functional traits on demography more clear. Demographic performance is therefore tightly linked with architectural traits such as adult stature, wood density, and capacity for horizontal crown expansion. The enhancement of a demographic trade-off due to interspecific variation in functional traits in the understory helps to explain species coexistence in diverse rain forests.

Dispersal of butterflies in a New Guinea rainforest: using mark–recapture methods in a large, homogeneous habitat

In an intensive mark‐release‐recapture study of all butterfly species in a tropical rainforest understory, 5903 individuals from 90 butterfly species (from the estimated total of 104 ± 9 species present in understory habitat) were marked, and 1308 recaptured at least once. The study proved that mark‐recapture methods are feasible in tropical rainforests, but also showed its limitations, as after 232 person‐days of sampling we could only characterise dispersal for one‐third of the species present. The mean dispersal distance was 184 ± 46.1 m per species, while for six of the 14 species studied &gt;1% of individuals were estimated to disperse 1 km or more. These parameters are, however, strongly dependent on the size and spatial configuration of the study plots, particularly in large homogeneous habitats. A new method proposed here to correct this bias revised the mean distance between two captures from 135 ± 33.6 to 325 ± 87.0 m per species. These results, in combination with data from large permanent rainforest plots, suggest that most woody plant species in tropical forests are sufficiently abundant to serve as host plant species even to monophagous Lepidoptera species.

Breeding system and fruit set in African Marantaceae

Marantaceae are a pantropically distributed family of perennial herbs and lianas in the understory of tropical rainforests. They are characterized by a unique pollen transfer mechanism. To understand its functional significance and evolution, field investigations have been conducted in Gabon.Data from 28 (of 35) species from Central Africa are achieved. The pollen–ovule ratio (34–140:1; exception Sarcophrynium 2.5:1) falls into the range of facultative autogamous species. All investigated species were proven to be self-compatible; however, only two were autogamous. Natural fruit set was generally low (10.9±10%). The highest natural fruit set was found in Marantochloa purpurea (29.7%), Ma. grandiflora (33.5%) and the two autogamous species Halopegia azurea (31%) and Marantochloa leucantha (35%). Considerable higher fruit set could be reached in all species by hand-self-pollination.We conclude that autogamy is generally avoided through herkogamy based on secondary pollen presentation on the back of the style head – a central component of the specific pollen transfer mechanism. However, with respect to the consecutive visit of pollinators to several flowers of the same individual geitonogamy cannot be excluded. The aggregated pollen transfer via the explosive pollination mechanism might be interpreted as an adaptation to low pollinator visitation rate, pollen limitation might explain the low fruit set.

How Did the Swiss Cheese Plant Get Its Holes?

Adult leaf fenestration in "Swiss cheese" plants (Monstera Adans.) is an unusual leaf shape trait lacking a convincing evolutionary explanation. Monstera are secondary hemiepiphytes that inhabit the understory of tropical rainforests, where photosynthesis from sunflecks often makes up a large proportion of daily carbon assimilation. Here I present a simple model of leaf-level photosynthesis and whole-plant canopy dynamics in a stochastic light environment. The model demonstrates that leaf fenestration can reduce the variance in plant growth and thereby increase geometric mean fitness. This growth-variance hypothesis also suggests explanations for conspicuous ontogenetic changes in leaf morphology (heteroblasty) in Monstera, as well as the absence of leaf fenestration in co-occurring juvenile tree species. The model provides a testable hypothesis of the adaptive significance of a unique leaf shape and illustrates how variance in growth rate could be an important factor shaping plant morphology and physiology.

Graveyards on the Move: The Spatio-Temporal Distribution of Dead Ophiocordyceps-Infected Ants

Parasites are likely to play an important role in structuring host populations. Many adaptively manipulate host behaviour, so that the extended phenotypes of these parasites and their distributions in space and time are potentially important ecological variables. The fungus Ophiocordyceps unilateralis, which is pan-tropical in distribution, causes infected worker ants to leave their nest and die under leaves in the understory of tropical rainforests. Working in a forest dynamic plot in Southern Thailand we mapped the occurrence of these dead ants by examining every leaf in 1,360 m2 of primary rainforest. We established that high density aggregations exist (up to 26 dead ants/m2), which we coined graveyards. We further established that graveyards are patchily distributed in a landscape with no or very few O. unilateralis-killed ants. At some, but not all, spatial scales of analysis the density of dead ants correlated with temperature, humidity and vegetation cover. Remarkably, having found 2243 dead ants inside graveyards we only found 2 live ants of the principal host, ant Camponotus leonardi, suggesting that foraging host ants actively avoid graveyards. We discovered that the principal host ant builds nests in high canopy and its trails only occasionally descend to the forest floor where infection occurs. We advance the hypothesis that rare descents may be a function of limited canopy access to tree crowns and that resource profitability of such trees is potentially traded off against the risk of losing workers due to infection when forest floor trails are the only access routes. Our work underscores the need for an integrative approach that recognises multiple facets of parasitism, such as their extended phenotypes.

Fitness Consequences of Herbivory: Impacts on Asexual Reproduction of Tropical Rain Forest Understory Plants

ABSTRACTAlthough herbivory can affect plant fitness, few studies have investigated the effects of herbivory on the fitness of plants that reproduce vegetatively via fragmentation. Plants that reproduce in this manner are common in tropical wet forest understories, where they are subject to damage from falling branches and other debris. For these species, the ability to reproduce via fragmentation may be affected by the extent of herbivory. In this study, we determined the effects of natural and artificial herbivory on plant fragments. The leaves of four tropical understory plant species were either damaged artificially or chosen based on the extent of existing damage. Effects of real and artificial herbivory ranged from strong to no effects depending on the plant species and biotic conditions. Insect‐damaged fragments showed stronger effects than artificially damaged fragments. Herbivory may be an important predictor of mortality in reproductive fragments of understory plants.RESUMENAunque la herviboria puede afectar el vigor de las plantas, pocos estudios han investigado sus efectos en plantas que se reproducen vegetativamente por fragmentación. En el sotobosque de la selva tropical, donde las plantas están expuestas a ramas y otras partes de los árboles que les caen encima, es comün encontrar especies que se reproducen de esta manera. En estas especies, la herviboria puede afectar la habilidad de reproducirse por fragmentación. En este estudio, se determinaron los efectos de herviboria tanto natural como artificial en fragmentos de plantas. Las hojas de cuatro especies de plantas del sotobosque tropical fueron dañadas artificialmente o escogidas según su nivel de herviboria. Los efectos, tanto en hojas con daños naturales como artificiales, variaron desde grandes efectos a inexistentes, dependiendo de la especie de planta y las condiciones bióticas. Los fragmentos que fueron dañados por insectos presentaron efectos mayores que los segmentos que fueron dañados artificialmente. La herviboria puede ser un factor importante para predecir la mortalidad de fragmentos de plantas características del sotobosque.

Is elevation of carbon dioxide concentration beneficial to seedling photosynthesis in the understory of tropical rain forests?

Cuttings of the southeast Asian tropical rain forest tree species, Pongamia pinnata (L.) Pierre were raised in growth chambers providing a photosynthetic photon flux density (PPFD) of 60 micromol m(-2) s(-1) with either a low or a high red:far-red light ratio (LR and HR, repectively). The chambers were supplied with air containing CO(2) at a concentration of either 400 (LR4 and HR4, respectively) or 800 micromol mol(-1) (HR8 and LR8, respectively). After 4 months, leaf morphology and photosynthetic characteristics were determined. Relative to HR4, the LR4 treatment increased leaf area and total chlorophyll concentration (Chl) by 24 and 25%, respectively, but reduced leaf mass per unit area (LMA) by 19%. Elevated [CO(2)] significantly increased leaf area and LMA but did not affect Chl of LR or HR plants. Leaf nitrogen concentration was unaffected by the red:far-red light ratio but decreased significantly in seedlings in the elevated [CO(2)] treatment. Photosynthesis measured in situ under the growth conditions of ambient light and [CO(2)] (A(amb)) was 30% lower on an area basis and 14% lower on a mass basis in LR4 plants than in HR4 plants. Elevated [CO(2)] reduced the activity of ribulose-1,5-bisphosphate carboxylase/oxygenase and thus decreased light-saturated photosynthetic rate in both HR and LR plants. Elevated [CO(2)] increased mean leaf area and decreased respiration rates in both LR and HR plants. The LR8 plants had significantly higher A(amb) than LR4 plants, but similar A(amb) to HR8 plants.

Colony Size and Individual Fitness in the Social SpiderAnelosimus eximius

The effects of colony size on individual fitness and its components were investigated in artificially established and natural colonies of the social spider Anelosimus eximius (Araneae: Theridiidae). In the tropical rain forest understory at a site in eastern Ecuador, females in colonies containing between 23-107 females had india significantly higher lifetime reproductive success than females in smaller colonies. Among larger colonies, this trend apparently reversed. This overall fitness function was a result of the conflicting effects of colony size on different components of fitness. In particular, the probability of offspring survival to maturity increased with colony size while the probability of a female reproducing within the colonies decreased with colony size. Average clutch size increased with colony size when few or no wasp parasitoids were present in the egg sacs. With a high incidence of egg sac parasitoids, this effect disappeared because larger colonies were more likely to be infected. The product of the three fitness components measured-probability of female reproduction, average clutch size, and offspring survival-produced a function that is consistent with direct estimates of the average female lifetime reproductive success obtained by dividing the total number of offspring maturing in a colony by the number of females in the parental generation. Selection, therefore, should favor group living and intermediate colony sizes in this social spider.

RELATIONS BETWEEN SUNFLECK SEQUENCES AND PHOTOINHIBITION OF PHOTOSYNTHESIS IN A TROPICAL RAIN FOREST UNDERSTORY HERB

We report the photosynthetic characteristics of a C3 shade plant native to the tropical rain forest understory. It was shown that Elatostema repens Lour. (Hall) f. (Urticaceae) presents a large light adjustment capacity. The effects of several lightfleck sequences on photoinhibition of photosynthesis and carbon gain are analyzed. Photoinhibition is measured both as a decrease in leaf net CO2 uptake in limiting light (shown to be linearly correlated to quantum yield of O2 evolution measured at saturating CO2) and as a decrease of the ratio of variable fluorescence (Fv) to maximum fluorescence (Fmax) measured in liquid nitrogen. It is shown that lightflecks (from 10 to 30 min in duration) of 700 μmol m–2 s–1 (high light) induce photoinhibition, and that the effects of those successive high light periods are additive; there is apparently no recovery from photoinhibition during the low light periods (from 10 to 45 min in duration). In contrast, the Fv/Fmax ratio, though decreasing similarly to quantum yield of net CO2 uptake on leaves submitted to a continuous illumination of 700 μmol m–2 s–1, is only decreased a little on leaves submitted to lightfleck sequences of the same photon flux density. Lightflecks of 250 μmol m–2 s–1 are not photoinhibitory. Compared to the control maintained under light growth condition (40 μmol m–2 s–1) carbon gain is increased on leaves submitted to lightflecks; this gain remains high throughout the light cycles on leaves submitted to nonphotoinhibitory lightflecks and to the photoinhibitory lightflecks followed by the shortest low light period. In the other cases, carbon gain, higher than that of the control at the beginning of the treatments, decreases and becomes lower than the control carbon gain. Finally, the relevance of photoinhibition in the tropical rain forest understory environment is discussed.

Relations Between Sunfleck Sequences and Photoinhibition of Photosynthesis in a Tropical Rain Forest Understory Herb

Relations Between Sunfleck Sequences and Photoinhibition of Photosynthesis in a Tropical Rain Forest Understory Herb