Reducing the impact of insect herbivory in eucalypt plantations through management of extrinsic influences on tree vigour

In this paper it is argued that concepts developed in ecologically derived insect–plant interaction models can contribute directly to the management of insect herbivory in eucalypt plantations. Common to most species of commercially planted eucalypt is their genetic potential for early rapid growth. Several plant defence theories predict that intrinsically fast growing plants are able to tolerate relatively high levels of herbivory. The risk of this strategy failing increases when plants are exposed to external stressful factors that reduce canopy growth and vigour. Results from a young Eucalyptus camaldulensis plantation stressed by moisture deficit and two young Eucalyptus dunnii plantations, stressed by flooding and weed competition, respectively, are summarized. In all three cases, the stress‐inducing agents reduced canopy growth rates and architecture so that the proportion of leaf tissue damaged by insects increased and the tree’s ability to tolerate this damage decreased. Therefore, alleviating tree stress through improved silvicultural practices or improved site selection techniques may indirectly reduce the impact of insect herbivory. In resource‐limiting environments, an alternative approach may be to plant eucalypt species that although slower growing, are predicted to have better defended foliage. Manipulation of these natural antiherbivore plant strategies are not exclusive of other management approaches, such as the need for routine surveillance of key pest insects or the genetic selection of natural insect resistance and selective chemical control techniques, but should be viewed as an overarching concept for plantation health.     

Hollow occurrence and abundance varies with tree characteristics and among species in temperate woodland Eucalyptus

Tree hollows are a critical but diminishing resource for a wide range of fauna around the world. Conservation of these fauna depends on sustainable management of tree species that produce the hollows on which they depend. This study addressed the need for empirical data about intraspecific and interspecific variation in hollow occurrence and abundance in woodland trees in Australia. We measured and performed hollow surveys on 1817 trees of seven species of woodland Eucalyptus in central‐western New South Wales, Australia. Trees were surveyed at 51 one‐hectare sites and about 30% of trees surveyed had multiple stems. Generalized linear mixed models that accounted for nestedness of stems within trees and trees within sites detected a significant amount of variation in hollow occurrence and abundance. Models for individual tree stems of live trees showed hollow probability and abundance increased with diameter at breast height (DBH) and with increasing senescence (form). Stems of Eucalyptus microcarpa Maiden had a higher probability of having hollows than similar DBH stems of Eucalyptus camaldulensis Dehnh., Eucalyptus melliodora A.Cunn. ex Schauer or Eucalyptus populnea ssp. bimbil L.A.S.Johnson & K.D.Hill. Dead stems in live trees were more likely to have hollows than live stems of similar DBH. Each stem in a multi‐stemmed tree had a lower probability of hollow occurrence and lower abundance of hollows than single‐stemmed trees of similar DBH. For stems of dead trees, hollow occurrence and abundance increased with DBH and differed depending on stage of senescence. A comparison of our data with other studies indicates regional variation of hollow abundances within tree species.     

First record of the Red Gum Lerp Psyllid,Glycaspis brimblecombei Moore (Hem.: Psyllidae), in Europe

The eucalypt‐feeding psyllid Glycaspis brimblecombei Moore (Hom.: Psyllidae), an Australian insect, is reported for the first time in Europe. It was initially detected in Portugal and Spain, in September 2007, on Eucalyptus camaldulensis Dehn. At present, G. brimblecombei has only been found associated with E. camaldulensis and E. tereticornis Smith, being apparently absent from E. globulus Labill., the main eucalypt species planted on the Iberian Peninsula. Generalist predators, such as ants, spiders and ladybeetles, were observed in trees attacked by G. brimblecombei, but no psyllid parasitoids were detected.     

Competition intensity at local versus regional spatial scales

Studies of competition intensity over natural (i.e. topographic) gradients often contradict the results from studies where artificial (i.e. fertilizer) gradients have been used. Why should the type of gradient matter? To explore the possibilities, we performed experiments to measure competition intensity experienced by tree seedlings from grass competitors across a natural resource gradient, and simultaneously across artificial soil nutrient (fertiliser) gradients. We measured various functional traits (i.e. specific leaf area, leaf area, leaf nitrogen content, δ¹⁵N, δ¹³C, RGR) to gain mechanistic insight into the nature of competition across these gradients. Competition intensity increased with increasing resource availability, unequivocally at the local scale (i.e. with fertilizer application) but not at the regional scale (i.e. across the natural productivity gradient). Our measurements of plant traits were generally consistent with measurements of competition intensity, and demonstrate that competition occurs even when resource levels are low. Competition mainly acted to reduce the growth of Eucalyptus seedlings. Functional (physiological) traits in the Eucalyptus seedlings were not strongly affected by competitors, with the possible exception of δ¹⁵N, which may effectively integrate information on soil nutrient, moisture and leaf processes.     

Does rapid utilization of elevated nutrient availability allow eucalypts to dominate in the tropical savannas of Australia?

Northern Australia's savannas are among the most fire‐prone biomes on Earth and are dominated by eucalypts (Eucalyptus and Corymbia spp.). It is not clear what processes allow this group to dominate under such extreme fire frequencies and whether a superior ability to compete for nutrients and water might play a role. There is evidence that eucalypts are adapted to frequent fires; juvenile eucalypts escape the fire trap by growing rapidly in height between fires. However, non‐eucalypts are less able to escape the fire trap and tend to have stand structures strongly skewed toward suppressed juveniles. The mechanisms that drive these contrasting fire responses are not well understood. Here, we describe the results of a controlled glasshouse seedling experiment that evaluated the relative importance of nutrient and water availability in determining height growth and biomass growth of two eucalypt and one noneucalypt tree species, common in northern Australian savannas. We demonstrate that growth of eucalypt seedlings is particularly responsive to nutrient addition. Eucalypt seedlings are able to rapidly utilize soil nutrients and accumulate biomass at a much greater rate than noneucalypt seedlings. We suggest that a seasonal spike in nutrient availability creates a nutrient‐rich microsite that allows eucalypt seedlings to rapidly gain height and biomass, increasing their likelihood of establishing successfully and reaching a fire‐resistant size. Our results extend our understanding of how eucalypts dominate northern Australian savannas under extremely high fire frequencies.     

Climate and geochemistry as drivers of eucalypt diversification in Australia

Eucalypts cover most of Australia. Here, we investigate the relative contribution of climate and geochemistry to the distribution and diversity of eucalypts. Using geostatistics, we estimate major element concentrations, pH, and electrical conductivity at sites where eucalypts have been recorded. We compare the median predicted geochemistry and reported substrate for individual species that appear associated with extreme conditions; this provides a partial evaluation of the predictions. We generate a site‐by‐species matrix by aggregating observations to the centroids of 100‐km‐wide grid cells, calculate diversity indices, and use numerical ecology methods (ordination, variation partitioning) to investigate the ecology of eucalypts and their response to climatic and geochemical gradients. We find that β‐diversity coincides with variations in climatic and geochemical patterns. Climate and geochemistry together account for less than half of the variation in eucalypt species assemblages across Australia but for greater than 80% in areas of high species richness. Climate is more important than geochemistry in explaining eucalypts species distribution and change in assemblages across Australia as a whole but there are correlations between the two sets of environmental variables. Many individual eucalypt species and entire taxonomic sections (Aromatica, Longistylus of subgenus Eucalyptus, Dumaria, and Liberivalvae of subgenus Symphyomyrtus) have distributions affected strongly by geochemistry. We conclude that eucalypt diversity is driven by steep geochemical gradients that have arisen as climate patterns have fluctuated over Australia over the Cenozoic, generally aridifying since the Miocene. The diversification of eucalypts across Australia is thus an excellent example of co‐evolution of landscapes and biota in space and time and challenges accepted notions of macroecology.     

Trait values and not invasive status determine competitive outcomes between native and invasive species under varying soil nutrient availability

Invasion by exotic plants is often associated with nutrient enrichment of soils, particularly on soils of naturally low fertility. As a consequence, it is likely that the outcome of competitive interactions between native and invasive plants may be mediated by soil nutrient availability. We independently investigated competitive effect and response as well as the occurrence of asymmetric competition among native and invasive plants on soils of varying nutrient availability, using a glasshouse experiment. Seedlings of eight co‐occurring pairs of invasive and native species from low fertility Hawkesbury Sandstone‐derived soil were grown under low and high nutrient availability. We tested the hypotheses that native species would be competitively superior at low nutrient availability and have trait values associated with a resource conservation strategy while invasive species would be competitively superior at high nutrient availability and have trait values associated with a resource acquisition strategy. We found that nutrient availability did not mediate competitive interactions between invasive and native species. Instead, two invasive and one native species were always competitively superior irrespective of nutrient availability. Competitively superior species displayed a mixture of both resource conservation and acquisition strategies at low and high nutrient availability. In support of previous studies, we found that the a priori classification of invasive and native species does not predict competitive superiority at varying nutrient levels. Rather, species specific differences in trait values provide a competitive advantage in response to nutrient availability.     

Outbreak of an invasive paropsine beetle in south‐west Ireland: preference,performance and damage to Eucalyptus

An exotic, paropsine beetle –Paropsisterna nr. gloriosa Blackburn – occurred at high densities in south‐west Ireland in 2007. In bioassays, adults and larvae fed on foliage from a variety of eucalypt species. Eggs and neonates occurred only in association with new foliage. Despite their ability to consume old foliage, adult beetles had a high preference for new leaves with low specific leaf weights (softer leaves). In choice tests, adults that depleted new foliage of their preferred host, moved to new foliage of a second host but not older foliage of the preferred host. A 2008 survey of southern Ireland indicated that P. nr. gloriosa was restricted to County Kerry, largely associated with foliage plantations in that county. The distribution of damage suggests that the initial spread of the beetle was facilitated by foliage‐trade activities. Eucalyptus parvula L.A.S. Johnson & K.D. Hill was the most heavily damaged species at many plantations. Eucalyptus pulverulenta Sims and Eucalyptus cordata Labill. were highly resistant to the beetle as indicated by low levels of damage in the field and reduced fitness of larvae in feeding trials. Nevertheless, at the plantation with the highest overall levels of damage, adult beetles moved to feed on E. pulverulenta. A progressive dispersal from plantations also caused slight damage to neighbouring ornamental eucalypts. Clear preferences by P. nr. gloriosa for new foliage, irrespective of eucalypt species, suggests that pollarding – the removal of top branches to produce dense juvenile foliage – accelerated population build‐up during 2007.     

Why do some species in arid lands increase under grazing? Mechanisms that favour increased abundance of Maireana pyramidata in overgrazed chenopod shrublands of South Australia

While the abundance of some plant species decreases under high grazing intensity, others become more abundant. Release from competition by decreaser species contributes to this pattern in mesic systems, but this may not be the case in xeric systems where competition may be less intense. Here we examine three mechanisms that may be involved: (i) increased recruitment and growth because of soil changes produced by grazing, for example, increased soil nutrient availability through dung accumulation; (ii) increased recruitment favoured by the breaking up of the lichen crust; and (iii) reduced competition because of the decline of decreaser species. We used field and glasshouse experiments to determine the possible contribution of these mechanisms to the increase of the chenopod Maireana pyramidata around a watering point in a chenopod shrubland of South Australia. There was no evidence of nutrient accumulation close to the watering point, and while seedlings of M. pyramidata responded to nutrient addition, their growth was the same in soil collected from areas with different grazing intensity. While a broken lichen crust increased the emergence of both M. pyramidata and the decreaser Atriplex vesicaria, the effect was larger for the former. We found no competition between seedlings of the two species or between juveniles of A. vesicaria and seedlings of M. pyramidata in glasshouse experiments. Adult plants of both A. vesicaria and M. pyramidata produced similar growth reduction in seedlings of M. pyramidata. Furthermore, a field removal experiment failed to detect any competitive effect of A. vesicaria on M. pyramidata. Our data indicate that the disintegration of the soil crust by grazer activities can be a major factor controlling floristic changes in overgrazed rangelands. These results imply that factors that control establishment may be more important than competition in shaping shrub population dynamics in these systems. Ground surface itself can affect establishment opportunities, and this should be taken into account in management and restoration efforts in arid lands.     

The role of plant hormones and carbohydrates in the growth and survival of coppiced Eucalyptus seedlings

Depending on the species, coppicing (decapitation) may promote vigorous growth (Eucalyptus camaldulensis Dehn), or cause rapid senescence and death (Eucalyptus obliqua L'Herit). In seedlings of the latter species, the presence of a small upwardly directed shoot on the decapitated stump prevents or delays decline. Coppiced seedlings of E. camaldulensis and E. obliqua, with and without a remaining shoot, were analyzed for starch and soluble sugars (with the anthrone method), gibberellin-like substances (GAs) and cytokinin-like substances (by bioassay), and ethylene (by gas-liquid chromatography) before and after decapitation. Levels of soluble sugars declined similarly in both varieties of eucalypts, and starch reserves appeared adequate for sprouting, and did not diminish following decapitation of the susceptible species. Decapitation did not markedly alter the relatively high amounts of GAs in roots and shoots of E. obliqua, the susceptible species, although increased levels of Gas were observed in the stumps of seedlings left with 1 shoot after decapitation. The overall levels of GaS were relatively low in the roots and stems of the resistant E. camaldulensis, but higher in the shoots. Marked qualitative changes in GAs with decapitation were apparent in the shoots of E. camaldulensis. A single major GA peak occurred prior to decapitation but afer decapitation several additional peaks of GA-like activity appeared. Cytokinin-like activity was initially low in all tissues, but increased dramatically in stump and shoot tissue following decapitation. Increases ranged from approximately 5-fold (stump tissue of either species, minus-shoot treatment) to approximately 40-fold (shoot tissue of the resistant E. camaldulensis seedlings left with 1 shoot). In both E. camaldulensis and E. obliqua ethylene production increased to a peak 7 days after decapitation provided a shoot had been retained. This ethylene peak precedes a marked upturning of the retained shoot, and was not present in the stumps of totally decapitated seedlings. For totally decapitated seedlings ethylene evolution in E. obliqua (the susceptible species), but not E. camaldulensis (the resistant species), had ceased by 15 days.     

Effects of aluminium on growth and cation uptake in seedlings of Eucalyptus mannifera and Pinus radiata

This experiment was designed to examine the effects of aluminium (Al) on the growth of Pinus radiata (D. Don) and Eucalyptus mannifera subsp. mannifera (Mudie) seedlings in culture solutions in a glasshouse to help explain the failure of radiata pine trees on some acid, low fertility soils in Australia on which the native eucalypts flourish. Aluminium (Al) in culture solution increased the growth of roots and shoots of seedlings of both species but while growth of the eucalypt continued to increase with increases in Al to 2.222 μM, growth of the pine was largest at 370 μM Al. In addition to total root length, specific root length (length per unit dry weight), a measure of fineness of the root, increased in the eucalypt seedlings as the substrate Al increased. Growth of the shoots and roots of the pine in the absence of any added Al was extremely poor suggesting that Al, in low concentrations, may be an essential element or ameliorate some other factors in solution culture at low pH. Root and shoot concentrations of K increased with increasing Al, whilst Ca and Mg Concentrations decreased and Mn concentrations were unaffected in both species. Tissue Ca and Mg concentrations were 2 to 3 times higher in the eucalypt seedlings than the pine at all levels of added Al due to greater uptake of these elements by the eucalypt. In contrast, at the highest concentration of Al in the medium, shoot Al concentrations were lower in the cucalypt than in the pine due to a greater proportion of Al being retained in the eucalypt roots. These differences between the seedlings in terms of root growth and tissue cation concentrations may help explain the ability of eucalypt species to maintain vigorous growth on acid soils high in Al and low in Ca and P, where growth of the pines failed.     

Developmental responses of portulaca seedlings to conflicting spectral signals

Summary Portulaca oleracea seedlings avoid growing in the direction of neighbouring plants even when they are very small or remote. The present study was designed to determine the relative effect on the development of Portulaca seedlings of light availability (i.e. the resource level) as compared with spectral composition (i.e. the signal of future competition for the resource). The plants were subjected to various intensities of photosynthetic light and red/far-red (R/FR) ratios from opposite directions. The seedlings became recumbent preferentially towards the direction with the lower FR light, even when this meant growing towards plastic that absorbed 20 times more photosynthetic light. A preference for the direction with higher photosynthetic light over lower FR was also found, though only under extreme light differences. The response of the seedlings was not absolute: the orientation chosen depended on the light received from other alternative directions.     

Growth rate and basal area response curves of four Eucalyptus species on Mt. Wellington,Tasmania

Abstract. The heights, diameters and regrowth basal areas of 22-yr old fire-initiated regeneration of Eucalyptus delegatensis ssp. tasmaniensis, E. urnigera, E. coccifera and E. johnstonii were measured over altitudinal, solar radiation and drainage gradients on Mt. Wellington, Tasmania. The growth rate responses to the altitude gradient-complex vary from linear to curved depending on the performance measure, the species and the gradient. Much of the variation in growth rate appears to be a direct response to the physical environment. However, disparities between trends in growth rate and trends in re-growth basal area are consistent with the hypothesis that competition (sensu Grime 1979) is more important in productive environments and less important in stressful environments. A glasshouse trial with Eucalyptus seedlings indicated that potential growth rates decline with increasing altitude of seed source.     

Comparison of habitat selection by two sympatric macropods,Thylogale billardierii and Macropus rufogriseus rufogriseus,in a patchy eucalypt‐forestry environment

Abstract Population density estimates and patterns of habitat selection by sympatric red‐bellied pademelons (Thylogale billardierii (Marsupialia: Macropodidae)) and red‐necked wallabies (Macropus rufogriseus rufogriseus (Marsupialia: Macropodidae)) were examined within a patchy forestry environment in north‐west Tasmania. Population density of both species was relatively high. Selection indices from both population surveys and animal movement data showed that T. billardierii and M. rufogriseus had similar patterns of habitat selection at two spatio‐temporal scales; home range within the study area and habitats selected while foraging at night. Both species selected for young Eucalyptus nitens plantation with high weed‐cover within their home range. At night, T. billardierii and M. rufogriseus selected for open habitats (young plantation and grassland) and avoided closed habitats (native forest and 5–7 years old E. nitens plantation). There was no evidence for resource partitioning between species at these scales. In contrast, the two species differed in their selection for daytime sheltering habitat; T. billardierii selected native forest while M. rufogriseus selected older plantation. This may reflect differences in their predator avoidance strategies; that is, crypsis versus flight, rather than resource partitioning as a result of interspecific competition. The environment appears to be of high quality for both species, with patches of feeding and shelter habitats within close proximity of one another.     

Effects of flooding on Eucalyptus camaldulensis and Eucalyptus globulus seedlings

Summary Flooding for up to 40 days induced morphological changes and reduced growth of 6-week-old Eucalyptus camaldulensis and Eucalyptus globulus seedlings. However, the specific responses to flooding varied markedly between these species and with duration of flooding. Both species produced abundant adventitious roots that originated near the tap root and original lateral roots, but only E. camaldulensis produced adventitious roots on submerged portions of the stem. Flooding induced leaf epinasty and reduced total dry weight increment of seedling of both species but growth of E. globulus was reduced more. In both species dry weight increment of shoots was reduced more than dry weight increment of roots, reflecting compensatory growth of adventitious roots. Adaptation to flooding appeared to be greater in E. camaldulensis than in E. globulus. the importance of formation of adventitious roots in flooding tolerance is emphasized.Research supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison; CEPEC (Cacao Research Center), Bahia, Brazil; and BMBRAPA (Brazilian Research Institute), Brasilia, Brazil     

Double sampling to assess the accuracy of ground‐based surveys of tree hollows in eucalypt woodlands

Ground‐based surveys of tree hollows often give poor estimates of hollow abundance in forests. Woodlands have shorter trees and a more open structure than forests, which may make hollows easier to detect. Therefore, one would expect ground‐based surveys of tree hollows to be more accurate in woodlands than in forests. We compared hollow counts from ground‐based and climbing surveys (double sampling) for four species of Eucalyptus trees in woodlands of central‐western New South Wales, Australia: E. camaldulensis Dehnh, E. melliodora A. Cunn. ex Schauer, E. microcarpa Maiden and E. populnea F. Muell. ssp. bimbil L.A.S. Johnson & K.D. Hill and E. melliodora A. Cunn. ex Schauer. Overall, 83% of hollow‐bearing trees and 93% of trees without hollows were correctly classified by ground‐based surveys. Mean difference in hollow counts of ground‐based surveys to climbed surveys was 1.7 hollows ± 0.2 SE (all species combined) with 91% of ground‐based hollow counts being within five of the actual number of hollows. The error in ground‐based counts of hollows in E. microcarpa was larger than for the other three species. Errors in all species resulted from both overestimation and underestimation of hollow abundance by ground‐based surveys. A larger error was associated with the detection of hollows located in branches compared with hollows located in the main trunk(s). Total number of hollows in the tree (based on climbing surveys), crown area or maximum trunk diameter were significant predictors of ground‐based survey accuracy. Overall, the accuracy associated with ground surveys was relatively high and generally error rates were lower than those published for forests.     

Simulated effects of herb competition on planted Quercus faginea seedlings in Mediterranean abandoned cropland

Abstract. We tested simulated effects of herb competition on the performance of planted seedlings of Quercus faginea ssp. faginea in Mediterranean abandoned cropland. We produced three types of environment with respect to herb competition: absence of competition (AC), below‐ground competition (BGC), and total competition (TC). We assessed the performance of Q. faginea seedlings in each treatment in five ways: (1) seedling mortality, (2) leaf length and total plant leaf area, (3) water potential, (4) total biomass and biomass allocation, and (5) non‐structural carbohydrate storage in different plant organs. We also measured (6) soil moisture at different depths and (7) biomass production of herbs. The TC treatment reduced water availability more than the BGC treatment, in agreement with the most pronounced water stress in seedlings under TC conditions. BGC and TC treatments showed a high and similar seedling mortality, which was one order of magnitude higher than that in the AC treatment. Competition treatments affected glucose concentration in both shoots and roots, and followed the rank TC > BGC > AC. Q. faginea seedlings might compensate a lower water availability through glucose accumulation in leaves to reduce the osmotic potential. There was a maximum starch concentration in the BGC treatment that hints that a moderate resource limitation would limit tissue growth but not carbon assimilation. We conclude that the negative effects of herbs on Q. faginea seedlings are mostly a result of competition for water, and that this competition is noticeable since the earliest stages of the establishment. Complete weed removal is a technique that would strongly improve seedling survivorship.     

Is decline in high altitude eucalypt forests related to rainforest understorey development and altered soil bacteria following the long absence of fire?

Abstract The objective of this study was to identify attributes of the understorey vegetation, soil root biomass, soil chemistry and microbial community that may be associated with tree decline in high altitude eucalypt forests in Tasmania. The sites studied were in healthy eucalypt forest, forest in decline and forest containing dead eucalypts dominated by rainforest, in north‐east (Eucalyptus delegatensis forest) and in north‐west (Eucalyptus coccifera forest) Tasmania. In both regions bare ground, rock and shrubby species were associated with healthy sites whereas decline sites were associated with moss and a tall understorey with a high percentage cover of rainforest species. Healthy sites had low root biomass in the top 10 cm of the soil profile relative to decline and rainforest sites. Seedlings of high altitude species were grown in rainforest soil (0.314% N and 0.060% P) and healthy eucalypt soil (0.253% N and 0.018% P). The four eucalypt species studied had similar root to shoot ratio in the two soils, but the rainforest species, Nothofagus cunninghamii and Leptospermum lanigerum, had higher root to shoot ratio in the healthy eucalypt than in the rainforest soil. We produced three soil filtrates: (i) fungi and bacteria present; (ii) bacteria only present and; and (iii) sterile, from healthy, decline and rainforest sites in north‐east and in north‐west Tasmania and used linseed as a germination bioassay. Filtrates from the north‐east decline and rainforest sites induced a significantly greater dysplastic germination response than healthy sites in (i) and (ii) filtrates, but this was not found in filtrates from sites in the north‐west. We conclude that while the development of a rainforest understorey and elevated soil root biomass in the long absence of fire is generally associated with high altitude eucalypt decline, altered bacterial and/or chemical attributes of soil are not always associated with high altitude eucalypt decline.     

Intrinsic competition among solitary and gregarious endoparasitoid wasps and the phenomenon of ‘resource sharing’

1. Intrinsic competition was compared in three species of braconid wasps, the solitary Meteorus pulchricornis Wesmael, and the gregarious Cotesia kariyai (Watanabe) and Cotesia ruficrus Haliday in caterpillars of their common host, the armyworm Mythimna separata Walker. Competition was determined in pair‐wise contests consisting of simultaneous and subsequent parasitisms at various time intervals between the first and second attacks (<1, 24, 48, 72, and 96 h). 2. The experiment revealed that the solitary M. pulchricornis parasitoid was generally superior over the other two gregarious Cotesia species, although, in some cases C. kariyai out‐competed M. pulchricornis when ovipositing first. In contrast, irrespective of the time interval between parasitism and multiparasitism, C. ruficrus always lost in competition with M. pulchricornis. 3. Remarkably, both C. kariyai and C. ruficrus occasionally emerged from the same multiparasitised caterpillar when the time interval between the first and second attacks was small. However, cumulative brood sizes of both species were generally less than when C. kariyai and C. ruficrus developed alone, suggesting that some competition did occur between these two species. 4. Inter‐specific ‘resource sharing’ amongst parasitoid larvae has rarely been described in the literature. In the present study, the conditions in which ‘resource sharing’ in parasitoids can evolve are discussed. Further, we describe differing host usage strategies in parasitoids and how these can affect the outcome of aggressive larval competition.     

Characterisation of Adaptive Genetic Diversity in Environmentally Contrasted Populations of Eucalyptus camaldulensis Dehnh. (River Red Gum)

As an increasing number of ecosystems face departures from long standing environmental conditions under climate change, our understanding of the capacity of species to adapt will become important for directing conservation and management of biodiversity. Insights into the potential for genetic adaptation might be gained by assessing genomic signatures of adaptation to historic or prevailing environmental conditions. The river red gum (Eucalyptus camaldulensis Dehnh.) is a widespread Australian eucalypt inhabiting riverine and floodplain habitats which spans strong environmental gradients. We investigated the effects of adaptation to environment on population level genetic diversity of E. camaldulensis, examining SNP variation in candidate gene loci sampled across 20 climatically diverse populations approximating the species natural distribution. Genetic differentiation among populations was high (F_ST = 17%), exceeding previous estimates based on neutral markers. Complementary statistical approaches identified 6 SNP loci in four genes (COMT, Dehydrin, ERECTA and PIP2) which, after accounting for demographic effects, exhibited higher than expected levels of genetic differentiation among populations and whose allelic variation was associated with local environment. While this study employs but a small proportion of available diversity in the eucalyptus genome, it draws our attention to the potential for application of wide spread eucalypt species to test adaptive hypotheses.