The dispersal rate of a beetle, Osmoderma eremita, living in tree hollows

The dispersal of an endangered beetle, Osmoderma eremita, that lives in tree hollows, was studied by mark-release-recapture with pitfall traps. As only a small proportion of all dispersals is observed by this method, a simulation model was constructed to estimate the dispersal rate per individual. The model results suggest that 15% of the adults leave the original tree for another hollow tree, and consequently most individuals remain in the same tree throughout their entire life. This suggests that each hollow tree sustains a local population with limited connection with the populations in surrounding trees. It supports the view that O. eremita has a metapopulation structure, with each tree possibly sustaining a local population, and with the population in an assemblage of trees forming a metapopulation. Low dispersal rate and range make the species vulnerable to habitat fragmentation, probably at a scale of only a few hundred meters.     

Regulation of xylem sap flow in an evergreen, a semi-deciduous, and a deciduous Meliaceae species from the Amazon

The significance of phenological characteristics, stomatal conductance of the leaves, and stem water storage fluctuations for the regulation of xylem sap flow in an evergreen (Carapa guianensis Aubl.), in a semi-deciduous (Swietenia macrophylla King), and in a deciduous (Cedrela odorata L.) Meliaceae species was studied in a 7-year-old plantation near Manaus, Brazil. The study responds to the increasing demand for knowledge on the water relations of highly exploited timber trees of the Amazon. Xylem sap flow measurements indicated that the daily sap flow of Carapa (3.8 l day^-1 tree^-1 to 16.4 l day^-1 tree^-1) exceeded the daily sap flow of Swietenia (2.4 l day^-1 tree^-1 to 7.0 l day^-1 tree^-1) and Cedrela (1.6 l day^-1 tree^-1 to 11.6 l day^-1 tree^-1) during the entire year, although the highest flux densities were measured in Cedrela. The decrease in xylem sap flow observed in periods with low soil water potentials and high atmospheric vapor saturation deficits was more pronounced in the deciduous (Cedrela) and semi-deciduous species (Swietenia) than the evergreen species (Carapa). Carapa, which has the highest daily sap flow, had the highest biomass and sapwood portion. The high flux densities measured in Cedrela most likely result from the large earlywood vessels in this species. The seasonal variation of xylem sap flow of the three species was correlated with the stomatal conductance of the leaves measured by infiltration experiments. Stem water storage fluctuations in Carapa and Swietenia were predominantly due to transpiration; in Cedrela it was predominantly due to evaporative water loss on the stem surface during dry periods.     

Microclimate in hollow trees and how it affects an inhabiting beetle species,Osmoderma eremita

1. Studies of species' responses to microclimatic conditions have increased our understanding of their habitat requirements and possible responses to climate warming. However, little is known about the role of microclimate for insects inhabiting hollow trees.
2. We explored the relationship between tree characteristics and microclimate, and analysed how the microclimate in tree-hollows affects the occurrence and body size of an endangered beetle species, Osmoderma eremita.
3. We placed temperature data-loggers in wood mould (= loose material in tree-hollows) and surveyed O. eremita in 47 hollows in oak pastures in south-eastern Sweden. We found that tree characteristics previously known to be associated with occurrence of beetle species confined to tree-hollows (larger diameters, more wood mould, entrances higher up, and not directed upwards) tend to decrease moisture and moisture variation, while their effects on temperature and temperature fluctuations differ during different seasons. This indicates that microclimatic conditions are important for beetles in hollow trees, and many specialised species seem to avoid conditions that are too moist.
4. O. eremita occurred more frequently in trees with a warmer and more stable microclimate, while adult body size decreased with a warmer microclimate. A positive effect of a warmer microclimate was expected, since the study was done near the northern margin of the species' range.
5. O. eremita is confined to living in hollow trees, which may be due to the microclimate there being more stable in comparison to both the ambient climate and the microclimate in standing and downed dead wood.

     

Physiological basis of spacing effects on tree growth and form in Eucalyptus globulus

We examine the effects of spacing and layout on the growth and form of 3- to 4-year-old Eucalyptus globulus in a farm forestry context. Four planting layouts were chosen. These represented the range commonly in use in farm forestry: block plantings (2Ǹ m), triple rows (2Ǹ m) at 10-m intervals, single rows (2᎒ m) and isolated trees (10᎒ m). The physiological significance of key results is interpreted in terms of changes in the parameters of a simple plantation growth model. Under conditions where levels of direct light are high, for example during summer, block-planted trees intercepted only 38% of the light intercepted by isolated trees. On a stand basis, however, the combination of incident radiation and ground coverage declined with lower stand densities. While stand leaf area index declined from around 6 to 1 with increased spacing, individual tree leaf areas rose from around 50 m² in block plantings to 150 m² in isolated trees. The proportion of above-ground biomass found in stems declined with increasing spacing as the mass in foliage and branches increased. Stems accounted for 65% of above-ground biomass in block-planted trees but only 35% in isolated trees. The contributions of leaves and branches correspondingly rose from 19% to 35% and from 16% to 29%, respectively. Changes in biomass distribution were accompanied by increasing branch number, branch thickness, flatter branch angles and the longer retention of lower branches with greater spacing. These changes have implications for the merchantability of the timber. The efficiency of above-ground radiation conversion was constant at 0.67 g MJ^-1 irrespective of spacing. We estimated that foliar maintenance respiration (R_m) accounted for about 90% of above-ground R_m. On a stand basis R_m costs block plantings 23.90 t DM ha^-1 year^-1 (50% annual above-ground photosynthetic production) compared with 6.22 t DM ha^-1 year^-1 (40% annual above-ground photosynthetic production) in stands of isolated trees.     

Enhanced growth and ethylene increases spiral grain formation in Picea abies and Abies balsamea trees

Spiral grain angle in Norway spruce (Picea abies) trees and balsam fir (Abies balsamea) seedlings was investigated in relation to growth rate, endogenous and applied ethylene. Trees from stands of Norway spruce, which were irrigated and fertilised in order to enhance growth, and trees having different growth rates in non-treated stands were studied. Stem growth rate at the stand level (m³ ha^-1 year^-1) was measured annually, or by means of microscopy on stem sections as the number and size of tracheids produced. Enhanced growth increased ethylene evolution and maintained a high level of left-handed spiral grain angle in comparison to slower-growing trees. An increased number of earlywood tracheids in fast growing trees was correlated to a more left-handed spiral grain angle. Ethrel, applied to stems of balsam fir seedlings, increased the internal ethylene levels in parallel with increased left-handed spiral grain angle. The results indicate that ethylene regulates the extent of spiral grain angle.     

Surveying an endangered saproxylic beetle, Osmoderma eremita, in Mediterranean woodlands: a comparison between different capture methods

Measuring population size is riddled with difficulties for wildlife biologists and managers, and in the case of rare species, it is sometimes practically impossible to estimate abundance, whereas estimation of occupancy is possible. Furthermore, obtaining reliable population size estimates is not straightforward, as different sampling techniques can give misleading results. A mark-recapture study of the endangered saproxylic beetle Osmoderma eremita was performed in central Italy by applying four independent capture methods within a study area where 116 hollow trees were randomly selected to set traps. Detection probability and population size estimates were drawn from each of these four capture methods. There were strong differences in detection probability among methods. Despite using pheromone and beetle manipulation, capture histories were not affected by trap-happiness or trap-shyness. Population size estimates varied considerably in both abundance and precision by capture method. A number of 0.5 and 0.2 adult beetles per tree was estimated using the whole data set by closed and open population models, respectively. Pitfall trap appeared the optimal method to detect the occurrence of this species. Since in the southern part of its distribution range, a single population of O. eremita is widespread in the landscape, and includes beetles from more than one hollow tree, conservation efforts should focus not only on preserving few and isolated monumental hollow trees, but should be extended to large stands.     

Chlorophyll fluorescence and photosynthetic response to light in 1-year-old needles during spring and early summer in <Emphasis Type="Italic">Pinus leucodermis</Emphasis>

Ten-year-old trees from four Italian populations of Pinus leucodermis (populations A, B, C and D), which were collected from different sites at different altitudes, were grown near Florence, Italy. Needle CO₂ gas exchange and chlorophyll fluorescence response to increasing light intensities were evaluated; gas exchange and chlorophyll fluorescence variation between April and July were also monitored. Populations A, B and C showed a similar photosynthetic response to increasing photosynthetic photon flux density (PPFD) intensities, while at various light intensities population D, which originated from the highest altitude, showed the highest photosynthetic rates. In this population photosynthesis was saturated at PPFDs higher than 900 µmol m^-2s^-1 and a slow decrease of effective photosystem II quantum yield and F'_V/F'_M in response to increasing PPFDs were found. The same trees also showed a faster recovery in photosynthesis from limitations induced by winter temperatures than the other three populations. This work showed that photosynthetic response to light in population D was different from the other populations; trees from this population were probably naturally selected to prevent photoinhibition due to excess light.     

Monitoring spatiotemporal variation in abundance and dispersal by a pheromone-kairomone system in the threatened saproxylic beetles <Emphasis Type="Italic">Osmoderma eremita</Emphasis> and <Emphasis Type="Italic">Elater ferrugineus</Emphasis>

Pheromone monitoring could provide unique spatial and temporal information about rare and threatened insect species for conservation purposes. Pheromone traps may be especially valuable in detecting fluctuations and declines in vulnerable species, if trap catch can be related to population density. We exploited the pheromone-kairomone system of the hermit beetle Osmoderma eremita and its predator, the red click beetle Elater ferrugineus, to monitor variation in their flight activity during 7 years (2001–2002, 2005–2009). Spatial and temporal flight activity of O. eremita and E. ferrugineus were highly correlated over individual trap replicates and trap days. Yearly flight activities of both species were correlated within two core sites included during all years of the study, and positively affected by temperature both within and between years. Flight activity could not be directly translated to variation in abundance in either species, however. Dispersal rate was likely the main factor explaining flight activity in O. eremita. Normalizing the flight activity of E. ferrugineus against that of O. eremita did not eliminate most of the variability, however, suggesting that flight activity of E. ferrugineus was governed both by dispersal rate and by population density. Higher fluctuations in population density of E. ferrugineus likely render it more vulnerable to local extinction, which may explain the greater rarity of this species. We suggest that preserving large assemblies of suitable hollow trees would be absolutely essential for buffering against stochastic population fluctuations and securing the long-term persistence of E. ferrugineus.     

The influence of climatic variability on local population dynamics of Cercidium microphyllum (foothill paloverde)

This study investigated correlations among climatic variability, population age structure, and seedling survival of a dominant Sonoran Desert tree, Cercidium microphyllum (foothill paloverde), at Tucson, Arizona, USA. A major goal was to determine whether wet years promote seedling establishment and thereby determine population structure. Plant age was estimated from basal circumference for a sample of 980 living and dead trees in twelve 0.5-ha plots. Ages ranged from 1 to 181 years. Age frequency distribution showed that the population is in decline. Most (51.2%) of the 814 living trees were 40-80 years old; only 6.5% were younger than 20 years. The average age of the 166 dead trees was 78 years. Fifty-nine percent of dead trees were aged 60-100 years. Survival of newly emerged seedlings was monitored for 7 years in a 557-m² permanent plot. Mean survival in the 1st year of life was 1.7%. Only 2 of 1,008 seedlings lived longer than 1 year. Length of survival was not correlated with rainfall. Residual regeneration, an index of the difference between predicted and observed cohort size, showed that regeneration was high during the first half of the twentieth century and poor after the mid-1950s. Trends in regeneration did not reflect interannual variation in seasonal temperature or rain before 1950, that is, in the years before urban warming. Taken together, the seedling study and the regeneration analysis suggest that local population dynamics reflect biotic factors to such an extent that population age structure might not always be a reliable clue to past climatic influences.     

Extinction risks in metapopulations of a beetle inhabiting hollow trees predicted from time series

Ancient and dead trees are declining habitats harbouring many threatened species. These habitats are naturally patchy, and inhabiting species might exhibit metapopulation dynamics at a small spatial scale. In this study, the demography and metapopulation dynamics was analysed for Osmoderma eremita , which is an endangered beetle species associated with tree hollows in Europe. Extinction risks of O. eremita populations were predicted using Monte Carlo simulations based on time series of population assessments. Predicted occurrence patterns were consistent with field observations from an area with many small stands in which the populations are believed to have been more or less isolated from each other during the last 150–200 yr. Population growth was found to be density dependent. Carrying capacity was proportional to the volume of wood mould (i.e. loose material of dead wood in the tree hollows), which varied widely between hollow trees. This generates large differences in local extinction risks between hollow trees. The predicted metapopulation extinction risk was much higher if the habitat dynamics (formation, gradual increase and deterioration of tree hollows) were taken into consideration than in predictions yielded by models in which the amount of wood mould was assumed to be constant over time. Thus, this system has features from both mainland-island metapopulations and habitat-tracking metapopulations, and is rather far from a classic metapopulation. For the long-term persistence of the species in hollow trees, the habitat dynamics seem to be more important than demographic processes. Since the formation and deterioration of suitable tree are partly stochastic processes, there is a considerable extinction risk for many O. eremita populations, because they mainly rely on only one or a few trees with large amounts of wood mould.     

Fluctuations of macrobenthic populations: a link between climate-driven river run-off and sole fishery yields in the Gulf of Lions

The Rhone river is the most important input to the Mediterranean Sea, responsible for 50% of the primary productivity of the Gulf of Lions. A highly variable amount of 1-23᎒⁶ t year^-1 of terrestrial material is exported to the sea by the Rhone and stocked on the continental shelf for the most part. Soft-bottom communities off the Rhone delta were dominated by polychaetes both in species richness and abundance, and exhibited strong temporal fluctuations mainly related to flooding events. Floods caused pulses of organic matter followed, with different time lags, by peaks of polychaetes. Opportunistic, short-lived species, such as Mediomastus sp. and Aricidea claudiae, exhibited high short-term peaks in density and biomass a few months after flooding events. Conversely, long-lived species, such as Laonice cirrata and Sternaspis scutata, peaked in density and biomass with a time lag of 1-3 years, and their population increase lasted for a few years. The common sole, Solea solea, is a voracious predator of polychaetes which represent >80% of its prey. A positive correlation was found between the mean annual discharge of the Rhone river and the annual commercial landings of S. solea with a time lag of 5 years in the two fishing harbours (Sete and Martigues) located close to the Rhone delta. The long-term increase in food (i.e. polychaete density and biomass) after flooding events might favour the different stages of the sole life cycle, enhancing its population size for several years. Fluctuations of sole fishery yields in the Gulf of Lions could be influenced by climate, as the Rhone river flow is related to the North Atlantic Oscillation that drives precipitation over Western Europe.     

Restricted dispersal in a flying beetle assessed by telemetry

Many insects living in ancient trees are assumed to be threatened as a result of habitat loss and fragmentation. It is generally expected that species in habitats with low temporal variability in carrying capacity have lower degree of dispersal in comparison to those in more ephemeral habitats. As hollow trees are long-lived, species in that habitat are expected to be sensitive to habitat fragmentation, due to a low capacity to establish new populations far from present ones. Using radio telemetry, we studied the dispersal for a beetle, Osmoderma eremita, living in hollow trees. O. eremita exhibited philopatry and only dispersed over short ranges. About 82–88% of the adults remained in the tree where they were caught. All observed dispersal movements ended up in nearby hollow trees and 62% in the neighbouring hollow tree. These results corroborate the suggestion that habitat fragmentation may be detrimental to insects living in temporally stable but spatially variable habitats. In order to preserve such species, we propose that conservation efforts should be focused on maintaining or increasing the number of suitable trees in and near presently occupied stands.     

Osmoderma eremita as an indicator of species richness of beetles in tree hollows

The beetle Osmoderma eremita has received much attention in the last few years, as it is among those species with the highest priority in the European Union's Habitat Directive. In this paper the species is evaluated as a potential indicator and umbrella species for the endangered beetle fauna in tree hollows. To be useful as an indicator of a species-rich fauna it should be easy to inventory and be strongly correlated with the presence of other species. An umbrella species is a species which is so demanding that the protection of this species will automatically save many others. The species richness of saproxylic beetles and occupancy of O. eremita were surveyed in tree hollows in an area in southeastern Sweden by assessing the presence/absence of living and dead adults (including fragments) and larvae. The species richness was higher when O. eremita was present, both at tree and stand level. Several threatened species were associated with the presence of O. eremita, whereas others did not correlate with the occurrence of O. eremita. As O. eremita is easy to find and identify, it is useful as an indicator of stands with a rich beetle fauna in tree hollows. Osmoderma eremita can be used as an umbrella species, because if measures are taken to conserve O. eremita, many other species in the same habitat are also conserved. However, there are some beetles in tree hollows which seem to be more sensitive to habitat fragmentation than O. eremita, and may go extinct if only O. eremita is taken into consideration.     

Causes and consequences of small population size for a specialist parasitoid wasp

The parasitoid wasp Cotesia melitaearum lives in extremely small extinction-prone populations in the Åland islands of southwest Finland. Intensive observational data from two generations, a laboratory competition experiment, and 8 years of survey data were used to measure the causes, extent and consequences of small population size for this parasitoid. In the spring generations of 1999 and of 2000 we observed 21 out of 23 and 26 populations respectively, ranging in size from 2 to 103 parasitoid cocoons. Within these populations the fraction of individuals surviving to adulthood decreased with increasing parasitoid population size. The largest source of mortality was predation (44%) followed by parasitism (20%) and unknown causes (10%). In the field about 30% of the host butterfly larvae are parasitized by a competing parasitoid, Hyposoter horticola. A laboratory competition experiment showed that C. melitaearum eggs died when laid in post-diapause host larvae occupied by H. horticola. Consequently one-third of the progeny of the over-wintering generation of C. melitaearum from the field die as a result of larval competition. The survey of host and parasitoid population dynamics over 8 years showed that extinction of local host butterfly populations occupied by the parasitoid was not associated with current parasitoid population size. Over the same period small parasitoid populations were more likely to become extinct than large populations. However, parasitoid population size was not related to parasitoid extinction when the host also became extinct. These data suggest that the parasitoid populations are kept small through the action of natural enemies and competitors, some of which are density dependent. Local populations are so small that they become extinct frequently and rarely measurably affect the population dynamics of their host. It is likely that this parasitoid persists in Åland because of the spatial asynchrony of local population dynamics.     

Nutrient partitioning and storage in arid-zone forests of the mangroves Rhizophora <Emphasis Type="Italic">stylosa</Emphasis> and <Emphasis Type="Italic">Avicennia</Emphasis><Emphasis Type="Italic">marina</Emphasis>

Mangrove partitioning and storage of macronutrients and trace metals were examined in different arid coastal settings of Western Australia. Total living biomass in three Rhizophora stylosa forests, which ranged from 233 to 289 t DW ha^-1, was significantly greater than biomass in three Avicennia marina forests (range: 79-155 t DW ha^-1). Although prop roots and stems were the largest single tree components for R. stylosa and A. marina, respectively, most nutrients were stored in leaves and living roots of both species. However, only a small fraction of the total nutrient pool was vested in tree biomass; the vast bulk was in soils. A large below-ground pool of dead fine roots was identified at all stands, equivalent to 36-88% DW of total living tree biomass. The amount of Ca, S, Cl, Na, Si, Fe, Mn, Zn, B, Mo and Cu vested in dead roots of both species was greater than in the total living tree biomass. The proportion of Fe and S vested in live and dead roots was exceptionally large, consistent with previous evidence of metal plaques on mangrove roots. Sulphur, iron and zinc in dead roots of both species constituted the bulk of these metals. R. stylosa trees preferentially accumulated more Mg, S, Cl, Na, Si, Fe, Mn, B and Mo than A. marina trees. Proportionally greater storage of P, N, Ca, K, Cu and Zn occurred in two of the three A. marina forests. Foliar concentrations of Mg, S, Mn, B and Mo in mangrove leaves were at the high end of the range reported for other tropical trees, but other elemental concentrations were at the low or mid-range. Nitrogen limitation in these forests is implied by a positive correlation between total tree N and net canopy production and by a lower percentage of ecosystem N in tree biomass as compared with other forests. Unlike terrestrial forests where a large proportion of nutrient capital is vested in floor litter, most elements in these mangrove forests are stored in dead roots. A large reservoir of dead roots below the forest floor may serve as a conservation mechanism, particularly in such arid oligotrophic environments.     

Vacuum cleaning for conservationists: a new method for inventory of Osmoderma eremita (Scop., 1763) (Coleoptera: Scarabaeidae) and other inhabitants of hollow trees in Natura 2000 areas

Recording the insect species of hollow trees, particularly in larger cavities, presents a major methodological challenge. A whole range of endangered saproxylic beetles and other wood-inhabiting species live together in this habitat. In order to conduct preliminary surveys and monitor populations of the hermit beetle (Osmoderma eremita) in Natura 2000 areas designated for nature conservation according to the EU Habitats Directive, a vacuum cleaner has been used for the first time. Sampling of 127 trees with cavities revealed 39 trees in which O. eremita was present and for which submission of a report is mandatory. A total of 35 species was found, including 17 species in the German red data book as well as six species which are classified as relict species of ancient woodland. The method has therefore proved itself to be very appropriate and is now routinely used in southern Germany.     

Air sampling of its pheromone to monitor the occurrence of Osmoderma eremita, a threatened beetle inhabiting hollow trees

Osmoderma eremita is a threatened scarab beetle living in the hollows of old deciduous trees and is regarded as an umbrella species of the beetle fauna associated with this habitat. Several methods like pitfall trapping and wood mould sampling have been used to monitor the occurrence of O. eremita, but these methods cannot be applied for trees with certain characteristics. Recently, (R)-(+)--decalactone was identified as a male-produced sex pheromone of the species. Here, we show that -decalactone can be detected in hollow trees by air sampling and that the presence of the compound is strongly correlated with the occurrence of living male beetles in the same trees. Air was sampled from tree cavities and extracts analysed using gas chromatography–and mass spectrometry. There was a 89% match between the detection of -decalactone in extracts and the occurrence of male O. eremita±2 days from the sampling event. In the absence of males, samples never contained -decalactone, and the presence of this compound in a tree cavity appears to be a good predictor of O. eremita occupancy. Air sampling can be a useful complement to other methods when trying to detect as many trees housing this beetle as possible, which is crucial when estimating populations sizes and developing conservation strategies for this species.     

Influence of climate-driven shifts in biomass allocation on water transport and storage in ponderosa pine

Conifers decrease the amount of biomass apportioned to leaves relative to sapwood in response to increasing atmospheric evaporative demand. We determined how these climate-driven shifts in allocation affect the aboveground water relations of ponderosa pine growing in contrasting arid (desert) and humid (montane) climates. To support higher transpiration rates, a low leaf:sapwood area ratio (A_L/A_S) in desert versus montane trees could increase leaf-specific hydraulic conductance (K_L). Alternatively, a high sapwood volume:leaf area ratio in the desert environment may increase the contribution of stored water to transpiration. Transpiration and hydraulic conductance were determined by measuring sap flow (J_S) and shoot water potential during the summer (June-July) and fall (August-September). The daily contribution of stored water to transpiration was determined using the lag between the beginning of transpiration from the crown at sunrise and J_S. In the summer, mean maximum J_S was 31.80LJ.74 and 24.34Dž.05 g m^-2 s^-1 for desert and montane trees (a 30.6% difference), respectively. In the fall, J_S was 25.33NJ.52 and 16.36dž.64 g m^-2 s^-1 in desert and montane trees (a 54.8% difference), respectively. J_S was significantly higher in desert relative to montane trees during summer and fall (P<0.05). Predawn and midday shoot water potential and sapwood relative water content did not differ between environments. Desert trees had a 129% higher K_L than montane trees in the summer (2.41᎒^-5 versus 1.05᎒^-5 kg m^-2 s^-1 MPa^-1, P<0.001) and a 162% higher K_L in the fall (1.97᎒^-5 versus 0.75᎒^-5 kg m^-2 s^-1 MPa^-1, P<0.001). Canopy conductance decreased with D in all trees at all measurement periods (P<0.05). Maximum g_C was 3.91 times higher in desert relative to montane trees averaged over the summer and fall. Water storage capacity accounted for 11 kg (11%) and 10.6 kg (17%) of daily transpiration in the summer and fall, respectively, and did not differ between desert and montane trees. By preventing xylem tensions from reaching levels that cause xylem cavitation, high K_L in desert ponderosa pine may facilitate its avoidance. Thus, the primary benefit of low leaf:sapwood allocation in progressively arid environments is to increase K_L and not to increase the contribution of stored water to transpiration.     

Local and regional dynamics of a specialist herbivore: overexploitation of a patchily distributed host plant

This study reports a rare example where a native herbivorous insect frequently overexploits local populations of its perennial host. Local dynamics of a flightless weevil (Hadramphus spinipennis, Curculionidae) and its host plant (Aciphylla dieffenbachii, Apiaceae) were assessed for one discrete patch. In this main study site local weevil population structure, dynamics and movement were investigated using a capture-recapture study. Local plant dynamics were studied by mapping plant location, size, sex and the phenological stage of each plant. Regional weevil and plant dynamics were studied for six plant patches using line-transect counts to estimate local weevil numbers and repeated counts of the number of flowering adult plants to assess plant numbers. Dispersal was assessed by regularly searching all plant patches for marked weevils that emigrated from the main study site. Prior to extinction, local weevil abundance, survival and recruitment rates increased continuously. At the same time the feeding damage on the plants increased and the area covered by A. dieffenbachii decreased until no plants were left. An increase in weevil abundance was clearly associated with the extinction of the local host plant population. Weevils stayed in their local host plant patch whilst food was available and dispersed only after local extinction of the plant. Over a 4-year period four local population extinctions were observed. This study was too short to allow explicit conclusions to be drawn about the ratio of extinction to colonisation rates for both the weevil and the host plant populations. However, persistence of this locally unstable system appears possible only in a fragmented habitat where asynchrony in local dynamics is maintained.     

Photosynthesis, photoinhibition, and nitrogen use efficiency in native and invasive tree ferns in Hawaii

Photosynthetic gas exchange, chlorophyll fluorescence, nitrogen use efficiency, and related leaf traits of native Hawaiian tree ferns in the genus Cibotium were compared with those of the invasive Australian tree fern Sphaeropteris cooperi in an attempt to explain the higher growth rates of S. cooperi in Hawaii. Comparisons were made between mature sporophytes growing in the sun (gap or forest edge) and in shady understories at four sites at three different elevations. The invasive tree fern had 12-13 cm greater height increase per year and approximately 5 times larger total leaf surface area per plant compared to the native tree ferns. The maximum rates of photosynthesis of S. cooperi in the sun and shade were significantly higher than those of the native Cibotium spp (for example, 11.2 and 7.1 µmol m^-2 s^-1, and 5.8 and 3.6 µmol m^-2 s^-1 respectively for the invasive and natives at low elevation). The instantaneous photosynthetic nitrogen use efficiency of the invasive tree fern was significantly higher than that of the native tree ferns, but when integrated over the life span of the frond the differences were not significant. The fronds of the invasive tree fern species had a significantly shorter life span than the native tree ferns (approximately 6 months and 12 months, respectively), and significantly higher nitrogen content per unit leaf mass. The native tree ferns growing in both sun and shade exhibited greater photoinhibition than the invasive tree fern after being experimentally subjected to high light levels. The native tree ferns recovered only 78% of their dark-acclimated quantum yield (F_v/F_m), while the invasive tree fern recovered 90% and 86% of its dark-acclimated F_v/F_m when growing in sun and shade, respectively. Overall, the invasive tree fern appears to be more efficient at capturing and utilizing light than the native Cibotium species, particularly in high-light environments such as those associated with high levels of disturbance.