Common Native Species Research Articles

Historical land use and present-day canopy thinning differentially affect the distribution and abundance of invasive and native ant species

Disturbance may play a key role in affecting animal invasions; less appreciated is that past and present disturbances might interact to affect invasion. For example, although large portions of forest ecosystems worldwide are jointly affected by a history of past agricultural land use as well as contemporary timber harvest, it is unclear whether these disturbances facilitate biological invasions. We conducted a large-scale experiment that coupled adjacent non-agricultural and post-agricultural sites and a factorial canopy-thinning manipulation to understand how past agricultural land use might interact with contemporary canopy thinning to affect the distribution (i.e., presence/absence of mounds) and abundance of a highly invasive ant species, Solenopsisinvicta, and common native ant species, Dorymyrmexbureni. Mounds of S. invicta were more likely to be present in unthinned post-agricultural habitats than unthinned non-agricultural habitats, but this legacy effect disappeared with canopy thinning. In unthinned habitats, the presence of D. bureni mounds did not differ based on past land use. However, presence of D. bureni mounds was greater in thinned non-agricultural habitats than thinned post-agricultural habitats. Once present in an area, mound abundance was largely related to temperature near the ground for both species, and negatively related to soil compaction for D. bureni. Our results provide large-scale evidence that an understanding of anthropogenic events that occur decades before present may be essential for interpreting contemporary invasion dynamics and the distribution of some species, and that local contemporary habitat characteristics play a key role in determining ant abundance once an area is colonized.

Commonness and rarity of alien and native plant species – the relative roles of intraspecific competition and plant–soil feedback

The success of invasive alien and common native species may be explained by the same underlying mechanisms. Differences in intraspecific competition as well as differences in plant–soil feedback have been put forward as potential determinants of plant success. We teased apart the relative roles of competition and plant–soil feedback in a greenhouse experiment with 30 common and rare alien and native species from nine plant families. We tested whether plant biomass decreased less for common than rare species, regardless of origin, when grown at higher relative frequencies (1, 3 or 6 out of 9 plants per pot) in a community and in soil previously conditioned by the same species at different frequencies (0, 1, 3 or 6 out of 9 plants per pot) in an orthogonal design for these two factors. Plant survival decreased slightly, but non‐significantly, for all species when grown in soil previously occupied by conspecifics. Among surviving plants, we found a decrease in biomass with increasing intraspecific competition across all species (regardless of origin or commonness), and alien species were more negatively affected by previous high plant frequency than native species, but only marginally significantly so. Our findings suggest that, while intraspecific competition limits individual biomass in a density‐dependent manner, these effects do not depend on species origin or commonness. Notably, alien species but not natives showed a decrease in performance when grown in soil pre‐conditioned with a higher frequency of conspecifics. In conclusion, soil‐borne pathogen accumulation might be weak in its effects on plant performance compared to intraspecific competition, with neither being clearly linked to species commonness.

Effects of entrance size, tree size and landscape context on nest box occupancy: Considerations for management and biodiversity offsets

The effectiveness of nest boxes as a management and biodiversity offset tool remains equivocal and controversial. Improving nest box programs requires urgent empirical research to identify the spatial factors that affect occupancy outcomes. Understanding which fine, local and landscape-level attributes influence nest box selection by wildlife can assist practitioners in refining nest box designs and placement in the field. We asked: Does entrance size, tree size and landscape context affect nest box occupancy? We monitored 144 nest boxes with six different entrance sizes (20, 35, 55, 75, 95 and 115mm diameter), secured to individual trees of three sizes (small 20–50cm DBH, medium 51–80cm and large >80cm) situated in four different landscape contexts with varying degrees of modification (reserves, pasture, urban parklands and urban built-up areas). We found that six common native and exotic species accounted for 89% of nest box occupancies. Entrance size had a significant effect on overall occupancy. Nest boxes with larger entrance sizes (115, 95, 75 and 55mm) were occupied more (⩾77% of nest boxes occupied) than nest boxes with smaller entrance sizes (35 and 20mm; ⩽45% of nest boxes occupied). Tree size and landscape context had no significant effect on overall occupancy. However, multinomial analysis revealed that entrance size and landscape context affected occupancy by common fauna (i.e. species that occupied ⩾5% of nest boxes). Nest boxes with small (20 and 35mm), intermediate (55 and 75mm) and large (95 and 115mm) entrance sizes were predominately occupied by the European honey bee Apis mellifera, common exotic (e.g. common myna Acridotheres tristis) and native birds (e.g. eastern rosella Platycercus eximius), and the common brushtail possum Trichosurus vulpecula, respectively. Nest boxes in reserves and pasture had near equal occupancy by common fauna while nest boxes in urban parklands and urban built-up areas were predominately occupied by the common brushtail possum and the European honey bee. Establishing nest boxes with different entrance sizes could maximise occupancy by a variety of common hollow-nesting species. Targeting occupancy by some species requires consideration of landscape context but not tree size. Nest boxes were predominately occupied by a few common native and exotic species, suggesting that nest boxes may not be highly effective management and biodiversity offset tools for rare and threatened taxa in modified landscapes. Management policies and practices aimed at avoiding the loss of large, hollow-bearing trees must be prioritised.

Belowground competition among invading detritivores.

The factors regulating soil animal communities are poorly understood. Current theory favors niche complementarity and facilitation over competition as the primary forms of non-trophic interspecific interaction in soil fauna; however, competition has frequently been suggested as an important community-structuring factor in earthworms, ecosystem engineers that influence belowground processes. To date, direct evidence of competition in earthworms is lacking due to the difficulty inherent in identifying a limiting resource for saprophagous animals. In the present study, we offer the first direct evidence of interspecific competition for food in this dominant soil detritivore group by combining field observations with laboratory mesocosm experiments using 13C and 15N double-enriched leaf litter to track consumption patterns. In our experiments, the Asian invasive species Amynthas hilgendorfi was a dominant competitor for leaf litter against two European species currently invading the temperate deciduous forests in North America. This competitive advantage may account for recent invasion success of A. hilgendorfi in forests with established populations of European species, and we hypothesize that specific phenological differences play an important role in determining the outcome of the belowground competition. In contrast, Eisenoides lonnbergi, a common native species in the Eastern United States, occupied a unique trophic position with limited interactions with other species, which may contribute to its persistence in habitats dominated by invasive species. Furthermore, our results supported neither the hypothesis that facilitation occurs between species of different functional groups nor the hypothesis that species in the same group exhibit functional equivalency in C and N translocation in the soil. We propose that species identity is a more powerful approach to understand earthworm invasion and its impacts on belowground processes.

Aboveground biomass equations for sustainable production of fuelwood in a native dry tropical afro-montane forest of Ethiopia

Biomass equations are presented for five tree species growing in a natural forest in Ethiopia. Fitted models showed more accurate estimations than published generalized models for this dry tropical forest. Biomass equations are needed to correctly quantify harvestable stock and biomass for sustainability efforts in forest management, but this kind of information is scarce in Ethiopia. This study sought to develop biomass models for five of the most common native tree species in the Chilimo dry afro-montane mixed forest in the central highlands of Ethiopia: Allophyllus abyssinicus, Olea europaea ssp. cuspidata, Olinia rochetiana, Rhus glutinosa, and Scolopia theifolia. Comparison with generalized models was intended to show the greater accuracy of the specific models. A total of 90 trees from different diameter classes were selected, felled, and divided into different biomass compartments. Biomass equation models were fitted using joint-generalized least squares regression to ensure the additivity property between the biomass compartments and total biomass. These were the first models developed for these species in African tropical forests. Models were including diameter at breast height and total height as independent variables, obtaining more accurate biomass estimations using these models than from generalized models. Fitted models are reliable for estimating aboveground biomass in the Chilimo forest and for more general application in similar forest types. Model applicability for biomass or carbon estimation is high within forest inventory data contexts.

Growth of native tree species planted in montane reforestation projects in the Colombian and Ecuadorian Andes differs among site and species

The tropical Andes in Ecuador and Colombia are a biodiversity hotspot that has endured centuries of forest clearance and degradation. Forest restoration has been identified as a regional conservation priority; in recent decades, native species reforestation projects have proliferated, but little information exists on growth performance of commonly planted tree species in relation to site and soil nutrient status. This study analyzed growth of seven common native species (Alnus acuminata, Baccharis bogotensis, Cedrela montana, Myrica pubesens, Quercus humboltii, Sambucus nigra, Smallanthus pyramidalis) on 12 montane forest sites across the northern region of the tropical Andes. Andean alder (A. acuminata) was the most commonly planted species, and grows at a mean annual diameter increment (MAI-d) of 1.81 cm y−1 and a mean annual height increment (MAI-h) of 0.95 m y−1. S. pyramidalis, a short lived pioneer of the Asteraceae family, also exhibited fast growth rates of 1.64 cm MAI-d and 1.21 m MAI-h. Andean oak (Q. humboltii) was the second-most commonly planted species, growing with an MAI-d of 0.99 cm and MAI-h of 0.56 m. Soil magnesium and potassium were significant predictors of MAI-d and MAI-h for A. acuminata, while soil nitrogen, phosphorous, sodium, and calcium were negatively associated with growth (p < .001). We speculate that A. acuminata did not grow as well on soils richer in calcium and phosphorus because they were less conducive to nitrogen symbiosis common to this species. Soil magnesium and calcium were significant predictors (p < .05) of diameter growth for Q. humboltii. For both species, we attribute growth responses to soil nutrients as a result of the variable nature of fertility in the complex and variable soils that make up the volcanic and surficial geological landscape of the northern Andes. Results indicate that native species can grow in a variety of soil conditions, and exhibit growth rates comparable to non-native species. However, our results suggest native species are site restricted for best growth and should be planted on particular soils. We make recommendations for reforestation for the species in this study.

Distribution, diversity, and traits of native, exotic, and invasive climbing plants in Michigan

We compiled records of all the known climbing plant species both native and non-native in the state of Michigan, USA. County-level distributions and a broad suite of traits related to ecological and reproductive success were individually scored for each species. Non-native climbing species were subdivided and classified as either invasive or exotic. A total of 103 climbing species are present in the state, 50% of which are native. We classified only ten climbing species as currently invasive: of those 40% are woody, compared to 31% woody native and 33% woody exotic species. Our research asks whether latitude is correlated with either species richness or mode of dispersal among climbers. We also asked whether sexual system, dispersal mode, and unit of dispersal are different in native versus non-native climbers, and whether the dispersal mode of common trees is different from that of common climbers. We found latitudinally bimodal species richness for all classes of climbers, which we propose is due to collecting effort, growing season length, and human population density. We found surprisingly high numbers of climbing species at northern latitudes, in spite of harsh winter conditions, especially for climbing plants whose vascular tissues are compromised by freezing temperatures. Native species are significantly more often dioecious (27%) than non-natives (6%); however one of the woody invasive species, Celastrus orbiculatus, is functionally dioecious. Collectively, climbers include more abiotically dispersed species (62%) than biotically dispersed (38%). However, the 18 most common native species (found in more than 40 of 83 counties) are 61% biotically dispersed. Native woody climbers are 81% biotically dispersed, whereas native trees include 38–40% biotically dispersed species. Native climbing species are more often dispersed as fruits (52%) than are non-native climbers (37%), which are more often dispersed as seeds. Climbing mechanism is generally achieved by stem apical twining in both native and non-native species; however when tendrils are produced, native species produce similar proportions of leaf, petiole, and axillary tendrils, while non-native species largely produce leaf tendrils, a mechanism that is phylogenetically concentrated in the crop and crop-weed family, Fabaceae. Based on traits of the ten currently invasive climbing species in Michigan, we identify ten exotic species that are most likely to become invasive, most of which are perennials, hermaphroditic, with abiotically dispersed fruits, and modified climbing organs. Climbing species add significantly to biodiversity in Michigan, comprising 3.6% of the 2858 vascular plants. Climbing guilds in the temperate zone are more morphologically diverse and species rich than broadly recognized.

Genetic variation of Central European oaks: shaped by evolutionary factors and human intervention?

Oak species (Quercus spp.) in Central Europe grow on a relatively wide range of sites. Due to the economic importance of oak for its wood and other products, oak forests have long been managed by humans. This raises the question whether adaptation and/or human activities—especially the moving of propagules—have left their footprints on the genetic variation of oak populations. To address this question, we focused on the Upper Rhine Valley, a densely populated area today that was settled by humans early on. Here, the three most common native Central European oak species can be found. We studied their genetic variation across a large number of oak stands, growing on different sites and having different silvicultural histories, using neutral and EST-derived microsatellite markers. At the interspecific level, we showed that Quercus robur is relatively well delimited, while Quercus petraea and Quercus pubescens are more closely related. Natural hybridization might explain the increased genetic introgression between these two species. Within species, we found a low differentiation among populations of Q. robur and Q. petraea. In spite of forest fragmentation, we detected no spatial genetic barriers. However, we found that populations of Q. pubescens, a species with a marginal distribution in the study area were spatially structured. Genetic drift but also unidirectional introgressive hybridization with Q. petraea may account for this. Regarding the question of adaptation, we considered soil flooding, texture, drainage, and calcium carbonate in the upper horizons as physiologically important site condition variables. But with multivariate statistics, we could not find any significant effects of these parameters on genetic differentiation. Although there was no evidence for natural selection due to adaptation in stands of Q. robur, we demonstrated that age had a significant effect on their genetic variation and that stands established after the end of the Second World War had higher genetic diversity. We interpret these findings as being the result of an increase in large-scale transfers of reproductive materials during this time period and discuss arguments supporting this hypothesis. Finally, we consider the implications of these results for forest management.

Asteraceae invaders have limited impacts on the pollination of common native annual species in SW Western Australia’s open woodland wildflower communities

The York gum–jam woodlands of southwest Western Australia support diverse annual wildflower communities despite extensive habitat fragmentation, remnant isolation and the invasion of many exotic annual plant species. Few studies have explored the pollinator–plant relationships maintaining these persistently species-rich ‘novel’ communities. We examine the pollination ecology of five native species common to York gum–jam woodland annual communities to determine whether native pollinators may be mediating impacts of exotic annual plants on native wildflower species. We determined the pollination requirements of native focal species and the diversity and frequency of pollinator visitation to these focal plant species across invasion gradients. We also recorded the pollinator community of a dominant exotic herb in this system: Arctotheca calendula (cape weed). Only two of the five native species examined had significant seed set benefits attributable to insect pollination. One native plant species, Podotheca gnaphalioides, had pollinator assemblages that overlapped significantly with exotic A. calendula, with some reduction in pollinator visitation evident. One species, Waitzia acuminata, was found to benefit from insect pollination only in the larger of two surveyed remnants, which may reflect emerging reproductive polymorphism among geographically isolated populations. We highlight two mechanisms in this system that may buffer pollinator-mediated impacts of exotic species on native species: autonomous seed production, which may be increasingly prevalent in isolated populations, and segregation of pollinator resources among species. Our findings illustrate the ways that pollinator-mediated interactions can affect seed set within plant communities persisting in highly fragmented and invaded agricultural landscapes.

Impacts of Celastrus-primed soil on common native and invasive woodland species

Invasive plant species have been shown to alter soil environments resulting in changes in soil chemistry, biota, and nutrient cycling. Few studies have focused on how soil changes affect co-occurring native species or plants of different growth forms. This study, located in Connecticut, USA, focused on the soil effects of the liana, Celastrus orbiculatus (oriental bittersweet), a prominent invader of eastern North America, using two different approaches. In a litter addition experiment, addition of C. orbiculatus leaf litter to uninvaded field soils showed an increase in soil nutrients, pH, and nitrogen mineralization over 2 years across a range of soil and forest community types. In a complimentary common garden-pot experiment, a suite of common, ecologically similar, native and invasive lianas and shrubs were grown in soils primed with C. orbiculatus. Invaded soil was compared to uninvaded field and control potting soils. The change in soil attributes was not significantly different when grown with native or invasive plants; however, soils grown with lianas had a greater decrease in nutrients than those grown with shrubs. Although soils from locations with C. orbiculatus were higher in nutrients than uninvaded soils, plant growth, as measured in root:shoot, root and stem biomass, relative growth rate of volume, and final biomass were not different in invaded and uninvaded soils for either lianas or shrubs. However, lianas had similar growth patterns in nutrient-sparse potting soil, while shrubs growing in potting soil had lower growth. Thus, negative impacts of invaded soils on plant growth are not universal, and the plant community may show a varied response to C. orbiculatus-primed soils depending on the level of resource competition.

Early physiological responses of Pinus pinea L. seedlings infected by Heterobasidion sp.pl. in an ozone-enriched atmospheric environment.

The presence of the American root-rot disease fungus Heterobasidion irregulare Garbel. & Otrosina was detected in Italian coastal pine forests (Pinus pinea L.) in addition to the common native species Heterobasidion annosum (Fries) Brefeld. High levels of tropospheric ozone (O3) as an atmospheric pollutant are usually experienced in Mediterranean pine forests. To explore the effect of interaction between the two Heterobasidion species and ozone pollution on P. pinea, an open-top chamber (OTC) experiment was carried out. Five-year-old P. pinea seedlings were inoculated with the fungal species considered (H. irregulare, H. annosum and mock-inoculation as control), and then exposed in charcoal-filtered open-top chambers (CF-OTC) and non-filtered ozone-enriched chambers (NF+) from July to the first week of August 2010 at the experimental facilities of Curno (North Italy). Fungal inoculation effects in an ozone-enriched environment were assessed as: (i) the length of the inoculation lesion; (ii) chlorophyll a fluorescence (ChlF) responses; and (iii) analysis of resin terpenes. Results showed no differences on lesion length between fungal and ozone treatments, whereas the short-term effects of the two stress factors on ChlF indicate an increased photosynthetic efficiency, thus suggesting the triggering of compensation/repair processes. The total amount of resin terpenes is enhanced by fungal infection of both species, but depressed by ozone to the levels observed in mock-inoculated plants. Variations in terpene profiles were also induced by stem base inoculations and ozone treatment. Ozone might negatively affect terpene defences making plants more susceptible to pathogens and insects.

An exploration of hypotheses that explain herbivore and pathogen attack in restored plant communities.

Many hypotheses address the associations of plant community composition with natural enemies, including: (i) plant species diversity may reduce enemy attack, (ii) attack may increase as host abundance increases, (iii) enemy spillover may lead to increased attack on one host species due to transmission from another host species, or enemy dilution may lead to reduced attack on a host that would otherwise have more attack, (iv) physical characteristics of the plant community may influence attack, and (v) plant vigor may affect attack. Restoration experiments with replicated plant communities provide an exceptional opportunity to explore these hypotheses. To explore the relative predictive strengths of these related hypotheses and to investigate the potential effect of several restoration site preparation techniques, we surveyed arthropod herbivore and fungal pathogen attack on the six most common native plant species in a restoration experiment. Multi-model inference revealed a weak but consistent negative correlation with pathogen attack and host diversity across the plant community, and no correlation between herbivory and host diversity. Our analyses also revealed host species-specific relationships between attack and abundance of the target host species, other native plant species, introduced plant species, and physical community characteristics. We found no relationship between enemy attack and plant vigor. We found minimal differences in plant community composition among several diverse site preparation techniques, and limited effects of site preparation techniques on attack. The strongest associations of community characteristics with attack varied among plant species with no community-wide patterns, suggesting that no single hypothesis successfully predicts the dominant community-wide trends in enemy attack.

Chamaenerion danielsii (D. Löve) Czerep. (Onagraceae) во флоре Восточной Европы

The species status of Chamaenerion danielsii (D. Löve) Czerep., a tetraploid in the Chamaenerion angustifolium-complex, is reasoned. C. danielsii occurs in the Eastern Europe, being in the Crimea a common native species, and a rare introduced plant in the rest of the Eastern Europe. Distribution map of the species, its synonymy and morphological description are given.

Trade-offs in seedling growth and survival within and across tropical forest microhabitats.

For niche differences to maintain coexistence of sympatric species, each species must grow and/or survive better than each of the others in at least one set of conditions (i.e., performance trade-offs). However, the extent of niche differentiation in tropical forests remains highly debated. We present the first test of performance trade-offs for wild seedlings in a tropical forest. We measured seedling relative growth rate (RGR) and survival of four common native woody species across 18 light, substrate, and topography microhabitats over 2.5 years within Hawaiian montane wet forest, an ideal location due to its low species diversity and strong species habitat associations. All six species pairs exhibited significant performance trade-offs across microhabitats and for RGR versus survival within microhabitats. We also found some evidence of performance equivalence, with species pairs having similar performance in 26% of comparisons across microhabitats. Across species, survival under low light was generally positively associated with RGR under high light. When averaged over all species, topography (slope, aspect, and elevation) explained most of the variation in RGR attributable to microhabitat variables (51–53%) followed by substrate type (35–37%) and light (11–12%). However, the relative effects of microhabitat differed among species and RGR metric (i.e., RGR for height, biomass, or leaf area). These findings indicate that performance trade-offs among species during regeneration are common in low-diversity tropical forest, although other mechanisms may better explain the coexistence of species with small performance differences.

Priority effects vary with species identity and origin in an experiment varying the timing of seed arrival

Exotic species are sometimes phenologically distinct from native species in the invaded community, allowing them to be active when there may be reduced competition for resources. In southern California, annual species are particularly problematic invaders, and prior work has shown that these species germinate earlier in the growing season, giving them a competitive advantage over later‐germinating native species. This result begs the question, if being active earlier is advantageous, why have not native species adapted earlier cues for germination? We hypothesized native species would benefit less from earlier germination than exotic species (potentially due to slower growth following germination), thus negating potential selection for early germination. Here we manipulated planting time for common native and exotic species, growing them in all possible species pairs, to evaluate how competitive outcomes were altered by the time of arrival and the origin of competing species. In contrast to our hypotheses, the exotic species often had lower biomass when planted first, potentially due to disturbance when the second species was planted. In contrast, three out of our four native species benefited from earlier planting (a priority effect). Unlike the potential benefit of arriving early, we found no evidence that being planted one week later resulted in a competitive disadvantage, when compared to being planted simultaneously with a competitor. Further, we found that the magnitude and even direction of priority effects varied depending on the identity of the interacting species. Together these results suggest that a lack of directional selection may prevent adaptation towards earlier germination times of native species. Although this experiment was conducted with a limited suite of species, the results show that the role of seasonal priority effects varies among species, and that native species could benefit from seasonal priority effects in restoration efforts even when in competition with fast‐growing exotic annual species.

Urbanization breaks up host-parasite interactions: a case study on parasite community ecology of rufous-bellied thrushes (Turdus rufiventris) along a rural-urban gradient.

Urbanization drastically alters natural ecosystems and the structure of their plant and animal communities. Whereas some species cope successfully with these environmental changes, others may go extinct. In the case of parasite communities, the expansion of urban areas has a critical effect by changing the availability of suitable substrates for the eggs or free-larval stages of those species with direct life cycles or for the range of hosts of those species with complex cycles. In this study we investigated the influence of the degree of urbanization and environmental heterogeneity on helminth richness, abundance and community structure of rufous-bellied thrushes (Turdus rufiventris) along a rural-urban gradient in the metropolitan region of Porto Alegre, State of Rio Grande do Sul, Brazil. This common native bird species of southern Brazil hosts 15 endoparasite species at the study region. A total of 144 thrushes were collected with mist nets at 11 sites. The degree of urbanization and environmental heterogeneity were estimated by quantifying five landscape elements: buildings, woodlands, fields, bare lands, and water. Landscape analyses were performed at two spatial scales (10 and 100 ha) taking into account home range size and the potential dispersal distance of thrushes and their prey (intermediate hosts). Mean parasite richness showed an inverse relationship with the degree of urbanization, but a positive relationship with environmental heterogeneity. Changes in the structure of component communities along the rural-urban gradient resulted from responses to the availability of particular landscape elements that are compatible with the parasites' life cycles. We found that the replacement of natural environments with buildings breaks up host-parasite interactions, whereas a higher environmental (substrate) diversity allows the survival of a wider range of intermediate hosts and vectors and their associated parasites.

Invader traits and community context contribute to the recent invasion success of the macroalga Heterosiphonia japonica on New England rocky reefs

The successful establishment and spread of invasive species may be determined by intrinsic traits of the invader, characteristics of the invaded community, and interactions between the two. The red filamentous macroalga Heterosiphonia japonica has recently invaded and expanded its range in the northwestern Atlantic. We surveyed and compared macroalgal communities at sites with different levels of invasion in Nahant, Massachusetts, and examined potential factors contributing to Heterosiphonia’s successful invasion by assessing its growth rates and rates of herbivory by native grazers in the laboratory. We evaluated growth and herbivory for isolated individuals and for individuals within a macroalgal assemblage comprised of the most abundant species in the native community. We also measured macroalgal nitrate uptake rates to examine a potential mechanism underlying observed differences in growth rate. High abundances of Heterosiphonia were associated with lower native macroalgal species richness, evenness, and diversity and with differences in species composition in the field. Experiments showed that rates of growth and grazing were context dependent. In isolation, Heterosiphonia grew comparably and was grazed similarly to the two native filamentous macroalgae. Within the context of the native macroalgal assemblage, it grew much faster than all common native species, experienced reduced herbivory from one native grazer, and increased herbivory from another. Consistent with its faster growth, Heterosiphonia was the most efficient at nitrate uptake. Our results suggest that multiple interactions between intrinsic traits (e.g., competitiveness for nutrients) and extrinsic factors (e.g., presence of native macroalgal species, identity and relative abundances of native grazers) contribute to Heterosiphonia’s invasion success.

Mapping habitat suitability for at‐risk plant species and its implications for restoration and reintroduction

The conservation of species at risk of extinction requires data to support decisions at landscape to regional scales. There is a need for information that can assist with locating suitable habitats in fragmented and degraded landscapes to aid the reintroduction of at-risk plant species. In addition, desiccation and water stress can be significant barriers to the success of at-risk plant reintroduction programs. We examine how airborne light detection and ranging (LiDAR) data can be used to model microtopographic features that reduce water stress and increase resource availability, providing information for landscape planning that can increase the success of reintroduction efforts for a dryland landscape in Hawaii. We developed a topographic habitat-suitability model (HSM) from LiDAR data that identifies topographic depressions that are protected from prevailing winds (high-suitability sites) and contrasts them with ridges and other exposed areas (low-suitability sites). We tested in the field whether high-suitability sites had microclimatic conditions that indicated better-quality habitat compared to low-suitability sites, whether plant-response traits indicated better growing conditions in high-suitability sites, whether the locations of individuals of existing at-risk plant species corresponded with our habitat-suitability classes, and whether the survival of planted individuals of a common native species was greater in high-suitability, compared to low-suitability, planting sites. Mean wind speed in a high-suitability field site was over five times lower than in a low-suitability site, and soil moisture and leaf wetness were greater, indicating less stress and greater resource availability in high-suitability areas. Plant height and leaf nutrient content were greater in high-suitability areas. Six at-risk species showed associations with high-suitability areas. The survival of planted individuals was less variable among high-suitability plots. These results suggest that plant establishment and survival is associated with the habitat conditions identified by our model. The HSM can improve the survival of planted individuals, reduce the cost of restoration and reintroduction programs through targeted management activities in high-suitability areas, and expand the ability of managers to make landscape-scale decisions regarding land-use, land acquisition, and species recovery.

Host Range Testing of &lt;I&gt;Tamarixia radiata&lt;/I&gt; (Hymenoptera: Eulophidae) Sourced From the Punjab of Pakistan for Classical Biological Control of &lt;I&gt;Diaphorina citri&lt;/I&gt; (Hemiptera: Liviidae: Euphyllurinae: Diaphorinini) in California

ABSTRACT Tests evaluating the host range of Tamarixia radiata (Waterson) (Hymenoptera: Eulophidae), a parasitoid of the pestiferous Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), sourced from the Punjab of Pakistan, were conducted in quarantine at the University of California, Riverside, CA. Seven nontarget psyllid species (five native and two self-introduced species) representing five families were exposed to T radiata under the following three different exposure scenarios: 1) sequential no-choice tests, 2) static no-choice tests, and 3) choice tests. Nontarget species were selected for testing based on the following criteria: 1) taxonomic relatedness to the target, D. citri; 2) native psyllids inhabiting native host plants related to citrus that could release volatiles attractive to T. radiata; 3) native psyllids with a high probability of occurrence in native vegetation surrounding commercial citrus groves that could be encountered by T. radiata emigrating from D. citri-infested citrus orchards; 4) a common native pest psyllid species; and 5) a beneficial psyllid attacking a noxious weed. The results of host range testing were unambiguous; T radiata exhibited a narrow host range and high host specificity, with just one species of nontarget psyllid, the abundant native pest Bactericera cockerelli Sulc, being parasitized at low levels (< 5%). These results suggest that the likelihood of significant nontarget impacts is low, and the establishment of T. radiata in southern California for the classical biological control of D. citri poses negligible environmental risk.

The illusion of nature: perception and the reality of natural landscapes, as illustrated by vertebrate fauna in the Northern Territory, Australia

SummaryBiomass figures are compared for common native vertebrate species and common non‐native vertebrate species (including fish, amphibian, reptile, bird and mammal species) across the Northern Territory, an area of ostensibly, largely unmodified natural system. The total biomass of the considered non‐native species very substantially surpasses that of the common native vertebrate species considered; hence, the perception that this is a largely intact natural system is, to some extent, an illusion. This preponderance of biomass of non‐native species may help explain the increasing evidence of ecosystem stress and decline of native species. An integrity index based on the relative biomass of native and non‐native species may provide insight into the status and trends of ecological systems across different regions.