Altitudinal differences in bud burst and onset and cessation of cambial activity of four subalpine tree species

This study investigated bud burst and onset and cessation of radial growth (i.e., secondary xylem cell production by cambium) along an altitudinal gradient (1,600–2,800 m a.s.l.) in central Japan, to examine whether timing of the three phenological events are controlled by thermal conditions alone, irrespective of altitude. Measurement was done at biweekly intervals during 3 years (2006–2008) for four subalpine tree species at their upper and lower distribution limits, except for bud burst in 2006. Although bud burst and onset of radial growth were later at higher altitudes in the combined data of the four species, cessation of radial growth occurred in mid-August, irrespective of altitude. Coefficients of variation of timing of the phenological events decreased in the order bud burst, onset of radial growth, and cessation of radial growth in combined data of the four species. Growing degree days (GDD) for bud burst did not differ greatly along the altitudinal gradient for each species. However, GDD for the onset of radial growth was lower at higher altitude. This study suggests that the effects of thermal conditions on the phenological events along the altitudinal gradient might decrease in the order bud burst, onset of radial growth and cessation of radial growth. Probably not only temperature, but also other factors such as day length, may affect onset and cessation of radial growth. However, further research is necessary to examine the altitudinal differences in timing of the phenological events more accurately, by measurements at shorter time intervals than the biweekly intervals of this study.     

Water relations of five tropical tree species on Barro Colorado Island,Panama

Summary Diurnal curves of xylem pressure potential (P) and leaf conductance (C) were measured for five tree species of the lowland tropical forest on Barro Colorado Island, Panama. Measurements were taken just before and just after the beginning of the rainy season. The species studied were: Cordia alliodora, Faramea occidentalis, Heisteria concinna, Macquira costaricana, and Trichilia cipo.For all species, predawn (base P) and daytime values of P increased markedly after the beginning of the rainy season. Diurnal patterns of C were quite diverse. C. alliodora showed a decline in C during the day whereas F. occidentaus, H. concinna, and M. costaricana showed little change. Conductance of the last three species was lower before the first rains. T. cipo exhibited more complicated behavior for P and C. Before the rainy season, low values of base P and midday P were observed (-26 bars and-39 bars, respectively). Conductance was also low. After the first rains, base P increased to-4 bars. At this time, midday P and C appeared to respond to vapor pressure deficit (VPD), being less on a day with high VPD than on a day with low VPD.     

Seasonal activity and energetics of two species of varanid lizards in tropical Australia

The field metabolic rates (FMR) and rates of water flux were measured in two species of varanid lizards over five periods of the year in tropical Australia. The energetics of these species were further investigated by directly measuring activity (locomotion) and body temperatures of free-ranging animals by radiotelemetry, and by measuring standard metabolic rate (over a range of body temperatures) and activity metabolism in the laboratory. Seasonal differences in the activity and energetics were found in these goannas despite similar, high daytime temperatures throughout the year in tropical Australia. Periods of inactivity were associated with the dry times of the year, but the onset of this period of inactivity differed with respect to habitat even within the same species. Varanus gouldii, which inhabit woodlands only, were inactive during the dry and late dry seasons. V. panoptes that live in the woodland had a similar seasonal pattern of activity, but V. panoptes living near the floodplain of the South Alligator River had their highest levels of activity during the dry season when they walked long distances to forage at the receding edge of the floodplain. However, during the late dry season, after the floodplain had dried completely, they too became inactive. For V. gouldii, the rates of energy expenditure were 196 kJ kg^–1 day^–1 for active animals and 66 kJ kg^–1 day^–1 for inactive animals. The rates of water influx for these groups were respectively 50.7 and 19.5 ml kg^–1 day^–1. For V. panoptes, the rates of energy expenditure were 143 kJ kg^–1 day^–1 for active animals and 56 kJ kg^–1 day^–1 for inactive animals. The rates of water influx for these two groups were respectively 41.4 and 21.0 ml kg^–1 day^–1. We divided the daily energy expenditure into the proportion of energy that lizards used when in burrows, out of burrows but inactive, and in locomotion for the two species during the different seasons. The time spent in locomotion by V. panoptes during the dry season is extremely high for a reptile (mean of 3.5 h/day spent walking), and these results provide an ecological correlate to the high aerobic capacity found in laboratory measurements of some species of varanids.     

Seedling growth of five tropical dry forest tree species in relation to light and nitrogen gradients

Aims Increasing anthropogenic nitrogen (N) deposition has been claimed to induce changes in species composition and community dynamics. A greenhouse experiment was conducted to examine the effect of increased N availability on growth and functional attributes of seedlings of five tree species with different life history characteristics under varying irradiances. The following questions have been addressed: (i) how do the pioneer and non-pioneer species respond in absolute growth and relative growth rate (RGR) to the interaction of light and nitrogen? (ii) how does the interaction between irradiance and nitrogen availability modulate growth attributes (i.e. functional attributes)? (iii) is there any variation in growth responses between leguminous and non-leguminous species along the light and nitrogen gradients?Methods Seedlings of five tree species (Acacia catechu, Bridelia retusa, Dalbergia sissoo, Lagerstroemia parviflora and Terminalia arjuna) were subjected to twelve combinations of irradiance and N levels. Various growth traits, including height (HT), basal area (BA), whole plant dry biomass (M D), leaf mass per unit area (LMA), leaf area ratio (LAR), net assimilation rate (NAR), RGR, biomass fractions, root-to-shoot ratio (R:S) and leaf nitrogen content, were studied to analyse intra- and inter-specific responses to interacting light and N gradients.Important findings Significant interactions for irradiance and N availability for majority of growth attributes indicates that growth and biomass allocation of seedlings were more responsive to N availability under high irradiance. However, species responded differentially to N addition and they did not follow successional status. Slow growers (B. retusa, a shade-tolerant species and L. parviflora, a light demander) exhibited greater response to N enrichment than the fast growers (A. catechu, D. sissoo and T. arjuna). However, N-mediated increment in growth traits was greater in non-legumes (B. retusa, L. parviflora and T. arjuna) compared with that of legumes (A. catechu and D. sissoo). Allocation of biomass to root was strongly suppressed at the highest N supply across species; however, at high irradiance and high N availability, a greater suppression in R:S ratio was observed for B. retusa. NAR was a stronger determinant of RGR relative to LAR, suggesting its prominent role in increased RGR along increasing irradiances. Overall, a higher growth response of slow-growing species to elevated N levels, particularly the non-pioneers (B. retusa and L. parviflora) suggests that future N deposition may lead to perturbations in competition hierarchies and species composition, ultimately affecting community dynamics in nutrient-poor tropical dry forests.     

Leaf-cutting ant preferences for five native tropical plantation tree species growing under different light conditions

To examine the susceptibility of five Costa Rican tree species to leaf-cutter ants (Atta cephalotes L.: Formicidae, Attini), young and mature leaves from trees that were grown in a plantation under full sun and partial shade were offered to six leaf-cutter colonies located in full sun and six in patial shade. In addition to offering leaf disks to the ants, we offered large pieces of leaves to assess the effect of cutting leaves on food choices. Leaf-cutters responded differently to each plant species, preferring Virola koschyni Warburg (Myristicaceae) and Hyeronima alchorneoides Allemao (Euphorbiaceae) over Stryphnodendrum microstachyum Poeppig & Endlicher (Mimosoideae), Pentaclethra macroloba Willdenow (Fabaceae) and Vochysia ferruginea Martius (Vochysiaceae). In agreement with previous studies, interspecific differences among the tree species in water and saponin content appeared to account for the observed ant preferences among the five tree species: leaf-cutter ants preferred leaves and disks with more water and less saponins and the five tree species varied significantly in these traits. An observed positive correlation between preference and phenolic/nitrogen ratio appears to be spurious, and is instead due to a negative correlation between water content and nitrogen content. For the first time, Atta nest location has been shown to affect consumption: nests located in partial shade removed more leaf material than those from the sun plots. However, nest location had no effect on preference ranking of the tree species tested. Pieces of leaves from all the tree species grown in partial shade were significantly more removed than those trees grown in full sun. Leaf age, toughness, leaf specific weights, ant activity, and colony were not correlated with food choices. Because of the observed preferences, the five tree species should not be considered as equal candidates for plantation purposes. However, complete characterization of the candidate status of tree species for plantations in the neotropics must include information on the ability of such species to tolerate pest attacks in addition to their natural defenses to attack.     

Diverse scaling relationships of tree height and diameter in five tree species

Background: Allometric scaling relationships are important in ecology and forestry. The metabolic scaling theory (MST) predicts a universal invariant scaling relationship for tree growth, relating height and diameter to each other.

Aims: Data on five tree species (Pinus taeda L., Pinus virginiana Mill., Liquidambar styraciflua L., Liriodendron tulipifera L., and Pinus palustris Mill.) were used to test the predictions from MST on the scaling of height–diameter and also diameter growth.

Methods: Data on tree height and diameter for five tree species from both natural forests and plantations were collected to study two types of scaling relationships: tree height–diameter and stem diameter growth. A reduced major axis of regression analysis model type II was used to determine scaling exponents from each species under different environmental conditions.

Results: No universal invariant scaling exponent was found in height–diameter and diameter growth for the five species. The scaling varied across natural forests, plantations and scales (e.g., time and number of measured trees). However, in some situations the scaling exponents failed to show significant difference with the predicted values (e.g., 2/3 or 1).

Conclusions: Diverse scaling exponents were observed for the five tree species with the scaling relationships varying with environmental settings.     

Decline of photosynthetic capacity with leaf age in relation to leaf longevities for five tropical canopy tree species

The effect of leaf aging on photosynthetic capacities was examined for upper canopy leaves of five tropical tree species in a seasonally dry forest in Panama. These species varied in mean leaf longevity between 174 and 315 d, and in maximum leaf life span between 304 and 679 d. The light-saturated CO2 exchange rates of leaves produced during the primary annual leaf flush measured at 7-8 mo of age were 33-65% of the rates measured at 1-2 mo of age for species with leaf life span of < 1 yr. The negative regression slopes of photosynthetic capacity against leaf age were steeper for species with shorter maximum leaf longevity. In all species, regression slopes were less steep than the slopes predicted by assuming a linear decline toward the maximum leaf age (20-80% of the predicted decline rate). Maximum oxygen evolution rates and leaf nitrogen content declined faster with age for species with shorter leaf life spans. Statistical significance of regression slopes of oxygen evolution rates against leaf age was strongest on a leaf mass basis (r = 0.49-0.87), followed by leaf nitrogen basis (r = 0.48-0.77), and weakest on a leaf area basis (r = 0.35-0.70).     

Seasonal variation of black fly (Diptera: Simuliidae) species diversity and community structure in tropical streams of Thailand

Seasonal variation of the physicochemical conditions of streams plays an important role in aquatic insect diversity and community structure. Asian tropical streams profoundly change between seasons due to the effects of monsoons. However, little is known about how these changes affect aquatic insect diversity and community structure. The objectives of this study are to examine seasonal variations of the physicochemical conditions in tropical streams in Thailand and to assess the effects of these changes on black fly community structure and diversity. Black flies were sampled and physicochemical conditions recorded at eight sites between December 2007 and December 2008. A total of 10 black fly species were found. Comparisons of the streams between seasons revealed that physical conditions related to rainfall rate were significantly different. Canonical correspondence analysis differentiated sampling sites from each season. Streams in the rainy season were faster and deeper, with higher discharge and conductivity than those of the cold and dry seasons. Species richness was significantly higher in the rainy season than in the cold and dry seasons ( F  = 6.23, P  = 0.004). Community structure profoundly changed between the low-flow season (cold and dry) and high-flow season. Black fly species found predominantly in the low-flow season ( Simulium siamense "cytoform A", S. aureohirtum ) decreased dramatically during the high-flow season. In contrast, species found at high frequency during the high-flow season ( S. nakhonense , S. angulistylum ) disappeared in the low-flow season. The study demonstrates the importance of seasonal variation of stream conditions on black fly community structure and diversity.     

Seasonal and spatial functional shifts in phytoplankton communities of five tropical reservoirs

Trait-based approaches have become increasingly important and valuable in understanding phytoplankton community assembly and composition. These approaches allow for comparisons between water bodies with different species composition. We hypothesize that similar changes in environmental conditions lead to similar responses with regard to functional traits of phytoplankton communities, regardless of trophic state or species composition. We studied the phytoplankton (species composition, community trait mean and diversity) of five reservoirs in Brazil along a trophic gradient from ultra-oligotrophic to meso-eutrophic. Samples at two seasons (summer/rainy and winter/dry) with a horizontal and vertical resolution were taken. Using multivariate analysis, the five reservoirs separated, despite some overlap, according to their environmental variables (mainly total phosphorus, conductivity, pH, chlorophyll a). However, between the seasonal periods, the reservoirs shifted in a similar direction in the multi-dimensional space. The seasonal response of the overall phytoplankton community trait mean differed between the ultra-oligotrophic and the other reservoirs, with three reservoirs exhibiting a very similar community trait mean despite considerable differences in species composition. Within-season differences between different water layers were low. The functional diversity was also unrelated to the trophic state of the reservoirs. Thus, seasonal environmental changes had strong influence on the functional characteristics of the phytoplankton community in reservoirs with distinct trophic condition and species composition. These results demonstrate that an ataxonomic trait-based approach is a relevant tool for comparative studies in phytoplankton ecology.     

日本中部10种树木叶片中氮和磷的季节变化及其转移

从叶完全展开到生长季结束,对常绿阔叶树种日本米储、具柄冬青、铁冬青、红楠和海桐及落叶阔叶树种袍栎、栓皮栎、日本朴、银杏和日本树五加的叶N和P含量进行了测定．结果表明,在整个生长季中,常绿阔叶树种中的日本米储和铁冬青的新叶和老叶的N和P含量呈现初期高、中期较低、后期上升的趋势;具柄冬青和海桐新叶的N和P含量的变化趋势与日本米储和铁冬青相似,而其老叶的N和P含量随季节推移而逐渐下降;红楠新叶和老叶的N含量呈现上升的趋势,其新叶和老叶的P含量则呈下降趋势;落叶阔叶树种的叶N和P含量随着时间的推移不断减少．各树种的N转移率为43％～75％,P为62％～84％．常绿阔叶树种的N平均转移率与落叶阔叶树种相似,而其P平均转移率大于落叶阔叶树种．所有树种的N平均转移率小于P平均转移率．     

Seasonal drought limits tree species across the Neotropics

Within the tropics, the species richness of tree communities is strongly and positively associated with precipitation. Previous research has suggested that this macroecological pattern is driven by the negative effect of water‐stress on the physiological processes of most tree species. This implies that the range limits of taxa are defined by their ability to occur under dry conditions, and thus in terms of species distributions predicts a nested pattern of taxa distribution from wet to dry areas. However, this ‘dry‐tolerance’ hypothesis has yet to be adequately tested at large spatial and taxonomic scales. Here, using a dataset of 531 inventory plots of closed canopy forest distributed across the western Neotropics we investigated how precipitation, evaluated both as mean annual precipitation and as the maximum climatological water deficit, influences the distribution of tropical tree species, genera and families. We find that the distributions of tree taxa are indeed nested along precipitation gradients in the western Neotropics. Taxa tolerant to seasonal drought are disproportionally widespread across the precipitation gradient, with most reaching even the wettest climates sampled; however, most taxa analysed are restricted to wet areas. Our results suggest that the ‘dry tolerance' hypothesis has broad applicability in the world's most species‐rich forests. In addition, the large number of species restricted to wetter conditions strongly indicates that an increased frequency of drought could severely threaten biodiversity in this region. Overall, this study establishes a baseline for exploring how tropical forest tree composition may change in response to current and future environmental changes in this region.     

Seasonal change in group size amongst five wild herbivore species

Species group size, a parameter increasingly used in mammal census work is discussed in the light of 47 months' data for five gregarious species. It is shown that group size parameters fluctuate seasonally, can be correlated with social and reproductive behaviour and are basically predictable. Species with a closed family unit structure exhibit a constant group size whilst those with an open structure exhibit large seasonal changes. Group density and group size for two finite animal populations are compared and the two dependent variables are found to be significantly correlated.     

Predispersal seed predation on five Piper species in tropical rainforest

Absolute number of seeds lost to predispersal seed predators and proportion of total seeds lost per infructescence were compared among five Costa Rican Piper species of different annual fecundities. Mean seed number and mean seed size in the five species were negatively correlated. The impact of predation on these species was inversely related to the number of seeds they produced. The two early successional species had very high fecundities, a combination of many seeds per infructescence, many infructescences per plant, and, in one species, year-round reproduction. Although seed predators destroyed as many or more seeds of these early successional species than they did of the less fecund, late successional species, this loss accounted for a relatively minor proportion (9 and 12%) of the seeds of the early successional species. In contrast, late successional species produced fewer, larger seeds in a smaller number of infructescences and were not continually in fruit. One of these species, which produced intermediate numbers of intermediately sized seeds, lost 30% of the seeds in each infructescence on average. Seed predators destroyed a larger proportion (65 and 76%) of the seeds per infructescence in the two species with fewest seeds per infructescence. High levels of insect damage in these late successional species caused many of their infructescences to abort prematurely. Taken together these factors resulted in annual fecundities several orders of magnitude smaller in shade-tolerant Piper species than the annual fecundities of shade-intolerant, early successional species. Seedlings of the two early successional species were common in large gaps and other sunny clearings and seedlings of the species with 30% seed loss were occasional, whereas no seedlings were seen of the two species with the highest proportional seed loss, suggesting that seed predation on the latter species may limit seedling recruitment.