Vascular Epiphyte Communities in the Inner-Crown of Hyeronima alchorneoides and Lecythis ampla at La Selva Biological Station, Costa Rica

The community composition and percent cover of vascular epiphytes were examined in relation to photosynthetic photon flux density (PFD), temperature, vapor pressure, and tree characteristics in the inner-crown of two emergent tree species, Hyeronima alchorneoides and Lecythis ampla, at La Selva Biological Station, Costa Rica. A total of 53 species were found in a total sampled branch area of 32 m² in eight trees—four trees per species. Community composition varied both among individuals of the same tree species and between tree species. However, percent cover patterns of vascular epiphytes were significantly different between the two tree species; Hyeronima had a significantly greater percent cover of epiphytes than Lecythis . The higher percent light transmittance as well as lower humidity in Lecythis are likely causes of its lower percent cover of epiphytes.     

Stomatal response to humidity in a sugarcane field: simultaneous porometric and micrometeorological measurements*

Abstract. Gas exchange data obtained with wellventilated leaf cuvettes provide clear evidence of a stomatal response to leaf-air vapour pressure difference (V). In contrast, remotely sensed leaf temperatures with specific assumptions regarding canopy boundary layer characteristics, have been interpreted to mean that stomata do not respond to V. We address this apparent discrepancy in a sugarcane field by simultaneous application of a single-leaf, porometric technique and a whole-canopy, Bowen ratioenergy balance technique. These methods indicated significant stomatal response to V in well-irrigated sugarcane. Stomatal responses to V in the field were obscured by strong covariance of major environmental parameters so that opening responses to light and closing responses to V tended to offset each other. Low boundary layer conductance significantly uncoupled V at the leaf surface (V_s) from V determined in the bulk atmosphere (V_a). This reduced the range of the stimulus, V_s, thereby reducing the range of the stomatal response, without indicating low stomatal sensitivity to V. Stomatal responses to V_a may be smaller than expected from V response curves in cuvettes, since V_s rather than the conventionally measured V_a is analogous to V in a well-stirred cuvette. Recently published conclusions that remotely sensed canopy temperatures are inconsistent with stomatal response to V may be based on erroneous estimates of canopy boundary layer conductance and thus of V_s, use of air saturation deficit rather than V to express evaporative demand, and investigation at higher levels of evaporative demand than those eliciting maximal stomatal response.     

Host utilization of the Brazil nut family (Lecythidaceae) by sympatric wood-boring species of Palame (Coleoptera, Cerambycidae, Lamiinae, Acanthocinini)

Estimates of the total number of arthropod species in existence are based, in part, upon assumptions about both the host specificity of tropical insects and their restriction to the forest canopy. It has been difficult to evaluate these estimates because of the paucity of available data. A newly discovered association between wood-boring beetles (Cerambycidae) and their host plants in the Brazil nut family (Lecythidaceae) inspired a year-long rearing project in the Neotropical rain forest of French Guiana. Branches severed from five species of Lecythidaceae yielded 1813 cerambycids belonging to 37 species. Three cerambycid species– Palame anceps (Bates), P. crassimana Bates, and P. mimetica Monné–accounted for almost half of the individuals reared. Each demonstrated a different pattern of host fidelity. Palame crassimana emerged from four of the five potential hosts, P. anceps emerged exclusively from a single host, and P. mimetica made a seasonal change in host affiliation. Although Palame spp. emerged from both ground level and canopy branches, they made a seasonal shift in stratum: they reproduced at both levels during the dry season, but exclusively at canopy level during the rainy season. Even specialized tropical insects may show greater flexibility in host utilization than some current hypotheses suggest.     

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.     

Sex ratios and Ophryocystis elektroscirrha infection levels of Danaus plexippus during spring migration through Oklahoma,USA

Monarch butterflies, Danaus plexippus L. (Lepidoptera: Nymphalidae), have a multiple brood migration in the spring as they move between their overwintering grounds and summer breeding grounds. In Oklahoma, USA, monarchs produce at least one generation in the spring, which develops and continues the northward migration, leaving Oklahoma without a breeding population during the hot summer months. Female monarchs leave the overwintering grounds prior to males, but it is not clear whether females re‐colonize areas along the migration route prior to, or at the same time as males. Male‐to‐female ratios are 1:1 at emergence, but studies have identified a male‐biased sex ratio in the field. Both males and females are susceptible to infection by the obligate protozoan parasite, Ophryocystis elektroscirrha McLaughlin & Myers (OE), which reduces flight abilities and life spans of infected individuals. We examine sex ratios during the spring migration through Oklahoma and whether sex ratios or OE infection estimates vary with capture technique (active or passive). Our data suggest populations are male‐biased during the 1st week of spring migration in Oklahoma, but shift to female‐biased by the 3rd week in both cool and warm springs. Therefore, males may leave southern areas prior to females or migrate longer distances per day. Active sampling (i.e., netting) did not bias sex compared to passive sampling (i.e., sticky traps). Significantly fewer OE‐carrying monarchs (with two or more spores) were captured via netting than by sticky traps which may be caused by sticky trap glue affecting tape sampling effectiveness, but there was no difference in the number of heavily infected individuals (more than 100 spores). Therefore, data from netted monarchs may underestimate OE infection rates within populations.     

Influence of Colophospermum mopane canopy cover on litter decomposition and nutrient dynamics in a semi‐arid African savannah

The objective of this study was to investigate the influence of mopane canopy cover on litter decomposition in a semi‐arid African savannah. We used a randomized block design with five blocks of 100 × 100 m demarcated in a 10‐ha pocket of open mopane woodland. Litterbags were placed beneath large (8.3 m crown diameter) and small mopane trees (2.7 m crown diameter) and in the intercanopy area. Decomposition was fastest in the intercanopy area exposed to solar radiation (k = 0.35 year^?1), intermediate beneath small trees (k = 0.28 year^?1) and slowest beneath large trees (k = 0.23 year^?1). Soil temperatures beneath small and large trees were 3–5 and 6–9°C lower than in the intercanopy area, respectively. Bacterial and fungal counts were significantly higher (P < 0.05) beneath large than small trees and in the intercanopy area. The amount of N and P released did not vary significantly among sampling sites. Soil moisture in the dry season was similar among sampling sites but rainy‐season soil moisture was significantly greater (P < 0.05) beneath large than small trees and in the intecanopy area. Mopane canopy cover retarded litter decomposition suggesting that photodegradation could be an important factor controlling carbon turnover in semi‐arid African savannahs.     

Herbivory patterns in mature sugar maple: variation with vertical canopy strata and tree ontogeny

1. Although leaf morphology and chemistry show profound changes as trees age, the consequences of such changes to herbivory have received little attention, particularly late in the ontogeny of canopy trees. 2. Using a mobile aerial lift for canopy access, patterns of leaf damage were evaluated in canopy‐dominant mature sugar maple (Acer saccharum Marsh) trees ranging from ～20 to 70 cm in diameter, corresponding to an age range of ～40–180 years. 3. Herbivore damage patterns varied in relation to both vertical canopy position (among upper‐, mid‐, and lower‐canopy positions) and with tree size. Damage types attributable to herbivores active on leaf surfaces, including leaf skeletonizers and leaf cutters (both principally Lepidoptera), and leaf stippling inducers (Hemiptera) showed decreases with tree size, and with increasing height in the canopy. In contrast, leaf damage from the most abundant gall‐forming arthropod in the system, the eriophyid mite Vasates aceriscrumena, increased markedly with tree size. 4. The results indicate that herbivory patterns vary with both canopy stratum and with tree size in sugar maple, and that the relative strength of vertical stratification and tree ontogeny effects are similar in magnitude. The predominant patterns are of a decrease in herbivory with increasing height in the canopy and with tree size, but certain galling arthropods exhibit the reverse trends.     

Phlebotomine sandfly responses to carbon dioxide and human odour in the field

Responses of Lutzomyia sandflies (Diptera: Psychodidae: Phlebotominae) to carbon dioxide (CO2) and human odour were investigated by field experiments in Parana State, southern Brazil. Catches of two predominant species: Lu. intermedia (Antunes & Coutinho) and Lu. whitmani Lutz & Neiva, were compared between traps baited with a human adult or with CO2 emitted at the human-equivalent rate. When the baits were only 40 cm apart, no difference of attractiveness was detected. When baits were separated by 20 m, however, significantly fewer sandflies (44% Lu. intermedia, 46% Lu. whitmani) were trapped with CO2 compared with human bait. This is the first field evidence that anthropophilic sandflies are attracted by human kairomones in addition to CO2. For both species [Lutzomyia intermedia and Lu. whitmani] [corrected], the proportion of human attractiveness attributable to CO2 was significantly more [corrected] for males than females; for Lu. intermedia males human bait was no more attractive than CO2 alone. Gender differences in sandfly olfactory sensitivity are likely to be associated with behavioural differences on the host, where females feed on blood and males find mates. With traps 20 m apart, both Lutzomyia spp. showed roughly linear increased responses (log-log scale) to 0.08-0.55% CO2 equivalent to 0.5-4 humans. This would explain why host size is generally proportional to attractiveness, as observed for other species of phlebotomine sandflies.     

The diversity of hemi-epiphytic figs (Ficus ; Moraceae) in a Bornean lowland rain forest

The diversity and niche specificity of hemi-epiphytic figs in a lowland dipterocarp forest in Sarawak were investigated in 1998. Twenty-seven fig species (264 individuals, c. 120 ha) colonized a diversity of host taxa (35 families), but densities were very low and only 1.77% of trees> 30 cm d.b.h. were occupied. There were no significant associations with host taxa or host-bark roughness but among 11 common species (≥9 individuals) the distributions of all other parameters (host-d.b.h., height and position of colonization, crown illumination, soil-texture and slope-angle) were significantly different, and we identified five fig guilds. The guilds corresponded to canopy strata, and appeared to reflect the establishment microsite requirements of different species. A fundamental trade-off within the hemi-epiphytic habit was revealed: Species colonizing larger hosts were rarer, because of lower host densities and more specific microsite requirements, but had better light environments and attained a larger maximum size. The single strangler species appeared to escape many of these constraints, and an important source of mortality caused by host-toppling, indicating the advantages of this strategy. Thus, the hemi-epiphytic figs in this community have come to fill a remarkable diversity of niches, despite low levels of competition, through the exigencies of a complex environment.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 78 , 439–455