The impact of redefined species limits in Palame (Coleoptera: Cerambycidae: Lamiinae: Acanthocinini) on assessments of host, seasonal, and stratum specificity

Assumptions about the host and stratum specificity of tropical insects are routinely incorporated into estimates of global species richness, but few empirical studies reliably assess tropical insect specificity. In French Guiana, cerambycid beetles in the genus Palame reproduce exclusively in trees belonging to the Brazil nut family (Lecythidaceae). During a year-long rearing project, Palame anceps (Bates) emerged exclusively from a single host species, but P. crassimana Bates and P. mimetica Monné appeared to make seasonal changes in host affiliation. In the case of P. crassimana , dry season specimens could be distinguished from rainy season specimens by subtle differences in pubescence, but it was difficult to find diagnostic morphological characters supporting their delimitation as separate species. In order to detect genetic differentiation in Palame , 1049 bp of mitochondrial DNA (COI gene) were sequenced. The three nominal species of Palame yielded six haplotype groups, with sequence divergences among groups ranging from 8.27 to 17.56%. Species with apparent seasonal changes in host use included multiple distinct haplotype groups that I interpret to represent multiple species-level taxa. Insects considered generalized owing to temporal or geographical changes in host association may, with improved resolution in species limits, prove to be assemblages including relatively specialized cryptic species. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 76 , 195–209.     

The influence of tree species on canopy soil nutrient status in a tropical lowland wet forest in Costa Rica

The canopy is host to a large percentage of the flora and fauna in tropical wet forests and is distinct from the forest floor in plant richness, soil type and microclimate. In this study, we examined the influence of tree species and season on soil nutrient cycling processes in canopy soils of four tree species common to Costa Rican wet forests. We also compared the canopy soils to the associated forest floor mineral soils. Both tree species and season had strong effects on canopy soil nutrients and processes. Canopy soils from trees with high litter lignin concentrations had higher net N-mineralization rates and higher dissolved inorganic N concentrations than those with low lignin concentrations. During the dry season, net N-immobilization occurred and dissolved organic and inorganic N and available P concentrations were significantly higher than during the wet season. Overall, canopy soils had higher N levels and higher fungi + bacteria richness than forest floor mineral soils. The differences in canopy soil properties observed among tree species indicates that these species have distinct N cycles that reflect differences in both soil origin and biological controls.     

Leaf flushing phenology and herbivory in a tropical dry deciduous forest,southern India

Patterns of leaf-flushing phenology of trees in relation to insect herbivore damage were studied at two sites in a seasonal tropical dry forest in Mudumalai, southern India, from April 1988 to August 1990. At both sites the trees began to flush leaves during the dry season, reaching a peak leaf-flushing phase before the onset of rains. Herbivorous insects emerged with the rains and attained a peak biomass during the wet months. Trees that flushed leaves later in the season suffered significantly higher damage by insects compared to those that flushed early or in synchrony during the peak flushing phase. Species whose leaves were endowed with physical defenses such as waxes suffered less damage than those not possessing such defenses. There was a positive association between the abundance of a species and leaf damage levels. These observations indicate that herbivory may have played a major role in moulding leaf flushing phenology in trees of the seasonal tropics.     

Stratification in French Guiana: Cerambycid Beetles Go Up When Rains Come Down

When tropical rain forest insect species are associated with a particular season or forest stratum, it can imply tolerance for heat and drought—or moisture dependence; attributes that may predict their responses to global climate change. In French Guiana (1995–1996), wood‐boring cerambycid beetles made a seasonal shift in stratum. During the dry season, ground stratum bait branches were densely colonized, but during the rainy season almost all cerambycids emerged from canopy stratum branches. Because the same substrate was available at both levels, abiotic factors probably influenced branch selection. In this study, cerambycids were reared at the same site (2007–2008) to determine if the seasonal shift recurred. Microclimate data (temperature, relative humidity, and wind speed) were collected with portable weather meters to test the hypothesis that microclimate would be similar at ground stratum during the dry season, and at canopy stratum during the rainy season. The seasonal shift in stratum did recur; many cerambycid individuals (56%) belonged to species classified as ‘seasonal shifters’. Temperatures in the preferred microhabitats were intermediate, but relative humidity remained high during the rainy season (regardless of stratum) and it was windier in the canopy (regardless of season). The shifters preferentially colonized branches at moderate mean temperatures (23.0–24.3°C) and high mean relative humidities (91.3–100%). Shifters were considered season and stratum generalists because they were reared at both strata and were present in both seasons, but they may actually track a narrow microclimate window. Should the regional climate become warmer and drier, it would probably favor species currently restricted to the dry season or canopy stratum.     

Abundance and Leaf Damage Caused by Gall‐Inducing Insects in a Mexican Tropical Dry Forest1

We evaluated the temporal and spatial patterns of abundance and the amount of damage caused by gall‐inducing insects (GII) in deciduous and riparian habitats in a seasonal tropical dry forest in Mexico. Plants occurring in these habitats differ in their phenology and moisture availability. Deciduous habitats are seasonal and xeric, while riparian habitats are aseasonal and mesic. We found 37 GII species and each one was associated with a specific plant species. In total, 19 species (51.3%) were present in deciduous habitats, 13 species (35.2%) in riparian habitats, and only 5 species (13.5%) occurred in both. Abundance and leaf damage by GII were greater in deciduous than in riparian habitats during the wet season. For each GII species that occurred in both habitats, host plant species supported greater abundance and leaf damage by GII in deciduous habitats during the wet season. These results indicate a greater association of GII species with host plants in deciduous than in riparian habitats during the wet season. In riparian habitats, 11 plant species (61.1%) had greater density of GII in the dry than in the wet season. Similarly, leaf damage by GII was significantly greater in the dry than in the wet season in riparian habitats for 12 plant species (66.7%). Dry forest plants of riparian habitats presented two peaks of leaf‐flushing: GII colonized leaves produced in the first peak at the beginning of the wet season, and accumulated or recolonized leaves in the second peak at the beginning of the dry season. The levels of leaf damage by GII detected in this study in the rainy season were considerably higher than those obtained for folivorous insects in other neotropical forests, suggesting that this GII guild might have an important impact on their host plant species in this tropical community.     

Phytophagous insect-woody sprout interactions in tropical eucalypt forest. II. Insect community structure

Abstract Sucking insects constituted 79% of all phytophagous insects collected from woody sprouts in the ground layer of a tropical eucalypt forest. Mobile insect groups such as non-psyllid Hemiptera and Orthoptera were relatively frequent in this environment compared to temperate, Eucalyptus-dominated vegetation. The high fire frequency of the tropical eucalypt forest may favour mobile insect groups. The capture of sucking insects and caterpillars peaked in dry season samples. Other patterns of abundance of phytophagous insect groups showed little consistency in their seasonal trends between host species or between vegetation types within host species. Disparities between chewing insect abundance in daytime samples and the damage chewing insects cause, may result from disproportionate consumption by large, mainly nocturnal insects, such as members of the Orthoptera. In this study, 21% of insect species were specialists on single plant species. This study suggested that insect abundance reflected the growth patterns of woody sprouts after regular burning, rather than that plant growth and development were tuned to the pressures of insect herbivory.     

What shapes cerambycid beetle communities in a tropical forest mosaic? Assessing the effects of host tree identity,forest structure,and vertical stratification

Due to anthropogenic activities, tropical rain forests face many challenges in sustaining biodiversity and maintaining global climates. This study explores how forest successional stage, tree composition, and stratum affect communities of saproxylic cerambycid beetles—concealed feeders that play important roles in forest nutrient cycling. Forty trees in five families (Fabaceae, Lecythidaceae, Malvaceae, Moraceae, and Sapotaceae) were sampled in a mosaic of old‐growth and secondary forest on the Osa Peninsula, Costa Rica. Bait branches yielded 3549 cerambycid individuals in 49 species. Species richness was almost identical in old‐growth and secondary forest, and both yielded specialists, but abundance was higher in old‐growth forest. Overall community structure was most strongly influenced by host plant species; within most plant families it was also impacted by forest successional status. Moraceae was the exception, presumably because the focal tree species was abundant in both old‐growth and secondary forest. Several host and old‐growth specialist species reached high densities within patches of old‐growth forest, but seldom colonized apparently suitable trees within secondary forest. This suggests that even small areas of old‐growth forest can act as refuges, but that secondary forest may act as a barrier to dispersal. The vulnerability of specialized saproxylic insects to land use change will be linked to the ability of their preferred hosts to disperse to and persist in successional habitats; rearing studies may provide the most accurate method to monitor community changes over time.     

Communities of insect herbivores foraging on saplings versus mature trees of Pourouma bicolor (Cecropiaceae) in Panama

The arthropod fauna of 25 saplings and of three conspecific mature trees of Pourouma bicolor (Cecropiaceae) was surveyed for 12 months in a tropical wet forest in Panama, with particular reference to insect herbivores. A construction crane erected at the study site provided access to tree foliage in the upper canopy. A similar area of foliage (ca. 370 m²) was surveyed from both saplings and trees, but samples obtained from the latter included 3 times as much young foliage as from the former. Arthropods, including herbivores and leaf-chewing insects with a proven ability to feed on the foliage of P. bicolor were 1.6, 2.5 and 2.9 times as abundant on the foliage of trees as on that of saplings. The species richness of herbivores and proven chewers were 1.5 (n=145 species) and 3.5 (n=21) times higher on trees than on saplings, respectively. Many herbivore species preferred or were restricted to one or other of the host stages. Host stage and young foliage area in the samples explained 52% of the explained variance in the spatial distribution of herbivore species. Pseudo-replication in the two sampling universes, the saplings and trees studied, most likely decreased the magnitude of differences apparent between host stages in this forest. The higher availability of food resources, such as young foliage, in the canopy than in the understorey, perhaps combined with other factors such as resource quality and enemy-free space, may generate complex gradients of abundance and species richness of insect herbivores in wet closed tropical forests.     

The negative effect of lianas on tree growth varies with tree species and season

Lianas reduce tree growth, reproduction, and survival in tropical forests. Liana competition can be particularly intense in isolated forest fragments, where liana densities are high, and thus, host tree infestation is common. Furthermore, lianas appear to grow particularly well during seasonal drought, when they may compete particularly intensely with trees. Few studies, however, have experimentally quantified the seasonal effects of liana competition on multiple tree species in tropical forests. We used a liana removal experiment in a forest fragment in southeastern Brazil to test whether the effects of lianas on tree growth vary with season and tree species identity. We conducted monthly diameter measurements using dendrometer bands on 88 individuals of five tree species for 24 months. We found that lianas had a stronger negative effect on some tree species during the wet season compared to the dry season. Furthermore, lianas significantly reduced the diameter growth of two tree species but had no effect on the other three tree species. The strong negative effect of lianas on some trees, particularly during the wet season, indicates that the effect of lianas on trees varies both seasonally and with tree species identity. Abstract in Portuguese is available with online material.     

Observations of canopy bromeliad roots compared with plants rooted in soils of a seasonal tropical forest,Chamela, Jalisco,Mexico

Roots of canopy bromeliads of a seasonal tropical forest were observed for mycorrhizal activity and compared with plants rooted in the soil during the later part of the growing season. No vesicular-arbuscular mycorrhizae or ectomycorrhizae were observed in the bromeliads. However, some interesting septate fungi were observed within the cortex of all samples where the roots were present in organic matter trapped in the canopy. All 15 soil-rooted plant species we observed were vesicular arbuscular mycorrhizal. While no known mycorrhizal types were apparently present in these canopy epiphytes, we cannot rule out the possible formation of symbioses between canopy epiphytes and other fungi in these habitats.     

热带季节雨林优势树种叶片和冠层尺度二氧化碳交换特征

采用叶室法和涡度相关法分析了西双版纳热带季节雨林优势树种绒毛番龙眼和大叶白颜树冠层及其叶片在不同季节的CO₂交换量,并拟合得到主要特征值.结果表明：以叶室法测得的两树种冠层最大净光合速率(P_{max A})为雨季>雨季末>雾凉季>干热季,叶片暗呼吸速率(R_d)为雨季>雨季末>干热季>雾凉季;以涡度相关法得到的两树种冠层最大净光合速率(P_{max B})为雨季>雨季末>雾凉季>干热季,而冠层呼吸速率(R_e)则是雨季>干热季>雾凉季>雨季末.两种方法得到的不同季节植物冠层最大净光合速率相差0.9～2.0 μmol·m^-2·s^-1.     

Field water relations of a wet-tropical forest tree species,Pentaclethra macroloba (Mimosaceae)

Summary The water relations of Pentaclethra macroloba (Willd.) Kuntze, a dominant, shade-tolerant, tree species in the Atlantic lowlands of Costa Rica, were examined within the forest canopy. Pressure-volume curves and diurnal courses of stomatal conductance and leaf water potential were measured in order to assess differences in water relations between understory, mid-canopy and canopy leaves. Leaves in the canopy had the smallest pinnules but the largest stomatal frequencies and stomatal conductances of the three forest levels. Osmotic potentials at full turgidity decreased with height in the forest; in the canopy and midcanopy they were reduced relative to those in the understory just enough to balance the gravitational component of water potential. Consequently, maximum turgor pressures were similar for leaves from all three canopy levels. Bulk tissue elastic modulus increased with height in the canopy. Leaf water potentials were lowest in the canopy and highest in the understory, even when the gravitational component was added to mid-canopy and canopy values. As a result, minimum turgor pressures were also lowest in the canopy compared to those at lesser heights, and approached zero in full sunlight on clear days.Osmotic potentials at each canopy level were similar for both wet and dry season samples dates suggesting that seasonal osmotic adjustment does not occur. Despite lowered predawn water potentials during the dry season, turgor was maintained in the understory by reduced stomatal conductances.     

Insect diversity: facts,fiction and speculation*

Biologists are still trying to grasp the global dimensions of the phylum Arthropoda and its major class the Insecta, in spite of the fact that over a million species of arthropods have been described. The canopy of rain forest trees is believed by many to hold the key to the immense diversity of insects. In recent years the use of knock-down insecticides to sample insects from rain forest canopy has revealed information on the canopy's arthropod inhabitants and community structure. The sampling techniques involved are outlined and data reviewed on taxonomic and guild structure, species abundance, body size and biomass of insects, and the faunal similarity of trees. Calculations by Erwin (1982), based on knock-down insecticide studies of the beetle fauna of one species of Central American tree, suggest there may be 30 million species of tropical forest arthropods. Reanalysis of these calculations, using additional data, produces a range of possible estimates from about 10 to 80 million. The unknown range of plant host-specificities of tropical insects is the main weakness of this method of calculation. Assessment of the faunal importance of the canopy in relation to that of other rain forest biotopes requires comparative quantitative studies. The preliminary results of one such simple study suggest that over 42 million arthropods may be found in a hectare of Seram rain forest (at the time of study), and that 70% occur in the soil and leaf litter and 14% in the canopy. They also suggest that Collembola and Acarina are the dominant groups in this hectare, and that there are as many ants as all the other insects (excluding Collembola).     

How much have we learned about seasonality in tropical insect abundance since Wolda (1988)?

Seasonal patterns in climatic conditions affect the life cycles and temporal patterns in the abundance of most temperate insect species. In tropical regions where there is no winter season, the situation may be different. For a better understanding of the evolution of seasonal life cycles, and the dynamics affecting temporal patterns in abundance of tropical insect populations and assemblages, it is important to study the life cycles of tropical insects and the presence or absence of seasonality in relation to climatic conditions. By reviewing studies on temporal patterns of abundance, this article examines the patterns of seasonality in adult tropical forest insects and discusses the variation in such patterns in various forest types. Seasonal and aseasonal patterns were found to be common in tropical dry and wet regions, respectively. In wet regions, which lack a distinctive dry season, there exists a wide variety of temporal patterns in addition to aseasonal patterns: distinctively seasonal and supra‐annual fluctuations in some insect species. Some of the problems of hidden ecological mechanisms underlying seasonal patterns in abundance are discussed, and the definition of seasonality in temporal patterns of insect abundance at a particular stage in the life cycle is considered. Methodological problems are also discussed.     

Fruiting phenology in a tropical dry evergreen forest on the Coromandel coast of India in relation to plant life-forms,physiognomic groups,dispersal modes,and climatic constraints

The fruiting phenology of 22 woody plant species belonging to 19 families was studied with respect to life-forms, physiognomic groups and dispersal modes, for 1 year at monthly intervals, in a tropical dry evergreen forest at Oorani (12°11′N, 79°57′E) on the Coromandel coast of India. At the community level, bimodal fruiting pattern prevailed, with a major peak in the dry season and a minor one in the early rainy season. An annual fruiting pattern was observed in many species and among the studied species fruiting lasted for 2–9 months. There was no significant difference in the frequency of species at three fruiting stages across the life-form categories and many species of upper and lower canopy trees and lianas were in the ripe fruiting phase during the late dry season. Plant physiognomic groups displayed distinct seasonality in fruiting pattern. The fruit maturation period was much longer for the wet season fruiting brevi-deciduous species than evergreen and deciduous species that fruited during the dry season. The variation in timing of fruiting behaviour among zoochorous species demonstrated less seasonality and zoochorous fruits were available throughout the year. Fruiting in anemochorous species peaked during the driest months and dryness favoured the dissemination of seeds. The fruiting patterns observed in the studied tropical dry evergreen forest across various plant traits were comparable with patterns recorded in other tropical seasonal forests.     

Geological History,Flora, and Vegetation of Xishuangbanna,Southern Yunnan,China1

Xishuangbanna of southern Yunnan is biogeographically located at a transitional zone from tropical Southeast (SE) Asia to subtropical East Asia, and is at the junction of the Indian and Burmese plates of Gondwana and the Eurasian plate of Laurasia. The flora of the region consists of a recorded 3336 native seed plant species, belonging to 1140 genera in 197 families, among which 83.5 percent are tropical genera and 32.8 percent are endemic to tropical Asia, suggesting a strong affinity to tropical Asian flora. The vegetation of Xishuangbanna is organized into four forest types: tropical rain forest, tropical seasonal moist forest, tropical montane evergreen broad‐leaved forest, and tropical monsoon forest. The tropical rain forest in Xishuangbanna has the same floristic composition of families and genera as some lowland equatorial rain forests in SE Asia, and is dominated (with a few exceptions) by the same families both in species richness and stem dominance. The exceptions include some deciduous trees in the canopy layer, fewer megaphanerophytes and epiphytes, and a higher abundance of lianas and microphyllic plants. We consider the tropical rain forest of Xishuangbanna as a type of tropical Asian rain forest, based on their conspicuous similarities in ecological and floristic characteristics.     

Diversity and seasonal variation of ground and understory spiders from a tropical mountain cloud forest

We made intensive samplings to study the seasonal response of spiders across different forest strata (ground and understory) in a tropical mountain cloud forest from Mexico. We sampled spiders from ten plots in six sampling events during the dry and rainy season, to analyze their abundance, structure (distribution of abundance among species), diversity and the response of the five dominant species at each stratum. Results demonstrated that seasonal patterns of spider communities differed among strata, revealing a complex spatiotemporal dynamic. Abundance, structure, diversity of ground spiders, as well as the responses of four dominant species at this stratum, showed low seasonal variations. In contrast, a strong seasonal variation was observed for the understory assemblage, with lowest abundance and highest diversity in the rainy season, and different assemblage structures for each season. Seasonal patterns of each assemblage seem linked to the responses of their dominant species. We found high co‐occurrence among most of the ground dominant species with similar habitat use and with multivoltine patterns, contrasting with low co‐occurrence among most of the understory dominant species with similar habitat use and univoltine patterns. Our results showed that the spiders’ assemblages of tropical mountain cloud forest (opposed to what is found in temperate and boreal forests) increase their species richness with the height, and that their responses to seasonal change differ between strata. Management programs of these habitats should consider the spatial and temporal variations found here, as a better understanding of their ecological dynamics is required to support their sustainable management.     

哀牢山两类山地森林林冠及林下腐殖质微生物群落比较

中山湿性常绿阔叶林、山顶苔藓矮林是云南哀牢山高海拔山地主要的原生森林植被类型.本文对哀牢山徐家坝地区两类森林林冠及各自林下地表腐殖质的理化特性、微生物组成、数量、生化活性、代谢活性及其季节动态,以及两类森林不同优势树种林冠腐殖质微生物数量及代谢活性进行了研究.结果表明： 两类森林林冠腐殖质的真菌、放线菌的数量、微生物生物量C、N、固氮作用和纤维素分解作用的强度均显著高于林下地表腐殖质;中山湿性常绿阔叶林林冠腐殖质的纤维素分解菌、纤维素分解强度、微生物生物量C、N、有机碳、土壤呼吸强度等指标均显著高于苔藓矮林.在季节变化方面,湿季林冠腐殖质中真菌、细菌及好氧性固氮菌的数量以及呼吸强度均高于干季,放线菌则相反,纤维素分解菌干湿季间差异不显著.两类森林林冠腐殖质微生物数量及生化活性的季节变化幅度均大于林下地表腐殖质.不同树种之间冠层腐殖质的微生物数量差异显著,其中湿季的差异比干季更为明显.林冠层腐殖质的微生物在维系林冠附生植物多样性以及为林冠繁茂的附生植物生长发育提供所需的养分等方面具有重要的生态功能.     

Diversity of gall wasps (Hymenoptera: Cynipidae) associated with oak trees (Fagaceae: <Emphasis Type="Italic">Quercus</Emphasis>) in a fragmented landscape in Mexico

Habitat fragmentation reduces the available habitat area and increases both the distance between fragments and the amount of fragment edges. Therefore, there are more probabilities of plant population size reduction and species extinction. In the same way, biotic and abiotic changes associated with forest fragmentation can dramatically alter plant growth and phenological patterns. We conducted a 3-year study to analyze effects of habitat fragmentation and seasonal variation on host plant quality (quantity of leaves, diameter at breast height, tree height), gall abundance and species richness in a temperate oak forest. Our results show that host plant quality was significantly higher in isolated oaks and small fragments, increasing the abundance and species richness of oak gall wasp species in most fragmented habitats. Oak canopy cover is altered by forest fragmentation, there being higher production of leaves on trees that are more exposed to fragmentation, and can provide important resources for maintaining gall wasp species diversity in a fragmented landscape. We found higher gall wasp richness and abundance in autumn than in the spring, which matches with the higher quantity of leaves in this season.     

Reaching the canopy on the ground: incidence of infection and host-use by mistletoes (Loranthaceae and Viscaceae) on trees felled for timber in Amazonian rainforests

There is a profound absence of knowledge of infestation prevalence and host-use by mistletoes of mature South American tropical rainforests. In this study, we fill this gap using information gathered from felled trees at a logging concession area in Amazonian Brazil. We sampled individuals of 18 tree species, which occurred in two forest physiognomies; open forest with canopy interrupted by palm trees and closed, denser forest, with emergent trees. We hypothesized that infection incidence would be higher in open than in closed forest, irrespective of the mistletoe species involved. In addition, we expected that mistletoe parasitism would be higher on host species that were more abundant, taller, deciduous, and had less dense wood. We sampled 870 individual trees in both sites combined. All but one host species was infected by at least one species of mistletoe. We found 13 mistletoe species/morphospecies, Loranthaceae (7) and Viscaceae (6), parasitizing very different hosts. Mistletoe infection incidence was higher in the closed forest (10.3%) than in the open forest (5.4%). In the closed forest, host height influenced incidence positively, while deciduousness had a negative influence. Our results show that mistletoes are common in the canopy of pristine tropical forests and, contrary to expectations, that infection incidence was higher in the closed forest. The positive relation between infection incidence and host height in this forest type suggests that emergent trees have higher chances of being infected than individuals of correspondent species in the lower forest layers.