Assessing the invasive potential of Eucalyptus globulus in Australia: quantification of wildling establishment from plantations

Eucalyptus globulus is one of the most widely planted temperate hardwood species in the world, and in Australia there are 538,000 hectares growing in plantations. Although it has been reported as invasive, quantification of E. globulus invasion is rare. We conducted surveys at two geographic scales to assess the level of, and factors influencing, wildling establishment from industrial E. globulus plantations in Australian. We surveyed 290 km of plantation boundary, both within (22 %) and outside (78 %) the species native range. In areas of relatively high establishment, a density triggered paired plot approach (plots with and without wildlings) was used to assess fine-scale factors influencing establishment. We recorded 4,939 wildlings (17/km), 98 % of which occurred within 10 m of the plantation edge (maximum 175 m). Establishment varied between regions, ranging from 1.2 to 39.6 wildlings/km. Generalized linear models showed that the probability of a wildling being present increased with plantation age, that wildling abundance was higher along burnt transects, as well as sites that received regular, relatively high rainfall and had lower mean annual temperatures. The only fine-scale/local factor influencing wildling presence was the reproductive output of the plantation. The current level of E. globulus establishment in Australia is low in comparison to other invasive forestry trees. However, given the relatively young age of the Australian estate, local and regional variation in establishment, and potential future changes in plantation management, monitoring is warranted. Implications for assessing the general invasiveness of Eucalyptus and possibilities for E. globulus wildling control are discussed.     

Variability in size-selective mortality obscures the importance of larval traits to recruitment success in a temperate marine fish

In fishes, the growth-mortality hypothesis has received broad acceptance as a driver of recruitment variability. Recruitment is likely to be lower in years when the risk of starvation and predation in the larval stage is greater, leading to higher mortality. Juvenile snapper, Pagrus auratus (Sparidae), experience high recruitment variation in Port Phillip Bay, Australia. Using a 5-year (2005, 2007, 2008, 2010, 2011) data set of larval and juvenile snapper abundances and their daily growth histories, based on otolith microstructure, we found selective mortality acted on larval size at 5 days post-hatch in 4 low and average recruitment years. The highest recruitment year (2005) was characterised by no size-selective mortality. Larval growth of the initial larval population was related to recruitment, but larval growth of the juveniles was not. Selective mortality may have obscured the relationship between larval traits of the juveniles and recruitment as fast-growing and large larvae preferentially survived in lower recruitment years and fast growth was ubiquitous in high recruitment years. An index of daily mortality within and among 3 years (2007, 2008, 2010), where zooplankton were concurrently sampled with ichthyoplankton, was related to per capita availability of preferred larval prey, providing support for the match–mismatch hypothesis. In 2010, periods of low daily mortality resulted in no selective mortality. Thus both intra- and inter-annual variability in the magnitude and occurrence of selective mortality in species with complex life cycles can obscure relationships between larval traits and population replenishment, leading to underestimation of their importance in recruitment studies.     

Recruitment in the harvester ant, Pogonomyrmex occidentalis: effects of experimental removal

We examined the importance of experimental removal of mature colonies on colony recruitment in the western harvester ant Pogonomyrmex occidentalis. To test the common assumption that established colonies suppress the establishment of new colonies we removed all colonies in ten 0.25 ha plots in 1996 and an additional five plots in 1997 and measured new colony recruitment in 1997, 1998, and 1999. Using a blocked, paired plot design we found that removal of colonies increased new colony recruitment in some areas of the site, but not others. Spatial variation in the importance of established colonies to recruitment was consistent across years; blocks in which density dependence was important in one year exhibited density dependent recruitment in following years. We estimated that in the blocks where recruitment was affected by established colonies, they accounted for less than 10% of the mortality of foundress queens. The increase in the number of new recruits (on average two additional new colonies) was considerably less than the number of colonies removed; average colony density in the removal plots was 14 colonies per 0.25 ha plot. The consistent lack of importance of established colonies to recruitment in one block and the relatively small response to colony removal in the other blocks suggests that the number of new colonies in a year may not be equivalent to the number of deaths of established colonies in that year. Space limitation is an important influence on recruitment in P. occidentalis, but the magnitude of the limitation varies spatially.     

Factors limiting rosette recruitment in scarlet gilia, Ipomopsis aggregata: seed and disturbance limitation

We performed a factorial combination of seed additions, surface soil disturbance, and protection from potential seed predation in experimental plots to elucidate the relative importance of each factor in the recruitment of scarlet gilia seedlings. We detected a significant interaction between seed addition and surface soil disturbance on seedling recruitment over 2 years of establishment. Plots that received both supplemental seed addition and disturbance established 10.5 times as many rosettes as control plots. We did not detect main or interactive effects of caging on seedling establishment. We explored the importance of density-dependent recruitment by investigating the number of rosettes per experimental plot through time. In addition, we used planned contrasts to compare the absolute and percent changes in control and treatment plot rosette densities between the study years. We found significant downward concave curvature to the seedling recruitment curve, suggesting negative density-dependent recruitment across the experimental range of rosette densities. We found a significant difference between the control plots and the seed addition-disturbance plots in terms of absolute changes in plot density from 1997 to 1998. Greater net mortality occurred in plots that received both seed addition and disturbance. However, we found no differences among treatments in the percent change in rosette density across the study years. Our study demonstrates that seedling recruitment in natural plant populations may be limited by the interaction of seed and microsite availability, and that seedling recruitment in scarlet gilia may be negatively density dependent. Our results suggest that the fecundity effects of particular plant-animal interactions (e.g., pollination, herbivory) may affect scarlet gilia population dynamics, particularly under conditions of high soil disturbance. Received: 11 June 1999 / Accepted: 24 November 1999     

Invasion dynamics on a temperate rocky shore: from early invasion to establishment of a marine invader

Populations of invading Asian shore crabs (Hemigrapsus sanguineus) and resident crabs (European green crab Carcinus maenas or species in the family Panopeidae) were monitored for up to 12 years along a south to north orientation on the open coast of Massachusetts and within the Narragansett Bay estuary, Rhode Island. At all sites, densities of resident crabs declined as H. sanguineus increased in abundance. Population dynamics were divided into 3 stages of the invasion (early, mid, late) based on statistically different densities of invading and resident crabs. Early in the invasion on the open coast, the relatively few H. sanguineus present had a wide range of individual sizes. By late in the invasion, relatively small crabs [<10 mm carapace width (CW)] constituted half of the population. Few seasonal differences occurred. Carcinus maenas, dominant at the coastal sites early in the invasion, showed strong recruitment of small individuals in the fall early in the invasion. Overall numbers of C. maenas declined as the H. sanguineus invasion progressed, and very few crabs >10 mm CW were present late in the invasion. In Narragansett Bay, a recruitment peak of H. sanguineus occurred shortly before it surged in population size, and large crabs were abundant late in the invasion. Geographic comparisons of H. sanguineus populations in southern New England showed similar growth trajectories. Monitoring populations of resident and invading species at multiple locations from early invasion through clear establishment of the invader allows a more complete understanding of the population dynamics of marine species invasions.     

Impact of plot shape and size on the evaluation of treeline dynamics in the Tibetan Plateau

Key message

Field survey methods influence the assessment of treeline structure and inferences on reconstructed treeline dynamics.

Abstract

Numerous field studies have described the structure of alpine treeline ecotones encompassing the forest limit and treeline to infer their dynamics in response to climate warming. However, the inferred treeline dynamics may be biased due to the selection of different plot sizes and shapes. Rectangular large plots including the whole treeline ecotone, i.e., encompassing the forest limit and the treeline, and square small plots located at current treeline have been widely used. Nevertheless, little is known about how large a plot must be to capture the main features of treeline structure and dynamics. Here, we investigate this question at Smith fir treelines located in the Sygera Mountains, southeastern Tibetan Plateau. Six rectangular large treeline plots (30 × 150 m) were sampled and compared with six square small treeline plots (30 × 30 m). Six rectangular plots with lengths shorter than the treeline ecotone span (100–135 m) were also sampled and compared with the other two plot types. Dendrochronology was used to reconstruct the recruitment dynamics of treelines, which were related to summer mean minimum temperatures. Rectangular large plots better captured the main features of recent treeline dynamics such as the abundance of recruits from the 1950s onwards and the establishment of old trees. Therefore, large plots allowed reaching more robust conclusions on treeline dynamics as compared to small plots. On the other hand, smaller rectangular plots revealed similar findings to those inferred from large rectangular plots but with a much lower survey cost. We propose using smaller rectangular plot with its longest side being shorter than the ecotone span as the most reliable and practical method to characterize alpine treeline dynamics.

     

Non-native liana, <Emphasis Type="Italic">Euonymus fortunei</Emphasis>, associated with increased soil nutrients,unique bacterial communities,and faster decomposition rate

Invasive plants have wide-ranging impacts on native systems including reducing native plant richness and altering soil chemistry, microbes, and nutrient cycling. Increasingly, these effects are found to linger long after removal of the invader. We examined how soil chemistry, bacterial communities, and litter decomposition varied with cover of Euonymus fortunei, an invasive evergreen liana, in two central Kentucky deciduous forests. In one forest, E. fortunei invaded in the late 1990s but invasion remained patchy and we paired invaded and uninvaded plots to examine the associations between E. fortunei cover and our response variables. In the second forest, E. fortunei had completely invaded the forest by 2005; areas where it had been selectively removed by 2010 were paired with an adjacent invaded plot. Where E. fortunei had patchily invaded, E. fortunei patches had up to 3.5× nitrogen, 2.7× carbon, and 1.9× more labile glomalin in soils than uninvaded plots, whereas there were no differences in soil characteristics between invaded and removal plots. In the patchily invaded forest, bacterial community composition varied among invaded and non-invaded plots, whereas bacterial communities did not vary among invaded and removal plots. Finally, E. fortunei leaf litter decomposed faster (k = 4.91 year^?1) than the native liana (k = 3.77 year^?1), Vitis vulpina; decomposition of both E. fortunei and V. vulpina was faster in invaded (k = 7.10 year^?1) than removal plots (k = 4.77 year^?1). Our findings suggest that E. fortunei invasion increases the rate of leaf litter decomposition via high-quality litter, alters the decomposition environment, and shifts in the soil biotic communities associated with a dense mat of wintercreeper. Land managers with limited resources should target the densest mats for the greatest restoration potential and remove wintercreeper patches before they establish dense mats.     

Roadside Revegetation in Glacier National Park, U.S.A.: Effects of Herbicide and Seeding Treatments

From 1992 to 1995 we experimentally evaluated the effectiveness of several revegetation treatments along a segment of Going-to-the-Sun Highway in Glacier National Park, U.S.A. This segment, reconstructed during the spring and summer of 1992, is bordered by fescue prairie vegetation and is known to be susceptible to invasion by several alien species, including Centaurea maculosa (spotted knapweed) and Phleum pratense (common timothy). We used a split plot study design to evaluate the effectiveness of herbicide and seeding treatments on assisting recovery of native flora and limiting the establishment of alien species. The herbicide treatment consisted of a yearly herbicide spray application of clopyralid (3,6-dichloropicolinic acid). Five seeding treatments were evaluated, three of which included an indigenous graminoid-forb seed mix. Percent canopy coverages of four species groups—alien graminoids, native graminoids, alien forbs, and native forbs—were determined in July 1995. In addition, community-level patterns in sprayed plots and unsprayed plots were compared with a reference site of native fescue prairie. Herbicide treatments decreased mean canopy coverage of alien forbs (treated = 4.2%, untreated = 23.4%) and increased mean canopy coverage of native graminoids slightly (treated = 6.3%, untreated = 4.0%). But herbicide treatments reduced mean coverage of native forbs (treated = 3.9%, untreated = 8.9%) and likely increased coverage of alien graminoids. Treatments that included a fall 1992 seed mix increased native graminoid coverages 2.8–4.6 times, although coverages were still lower than those attained by alien graminoids. Native and alien forb coverage appeared unaffected by seeding treatments. Species composition was less diverse in sprayed plots and more dominated by alien grasses than in unsprayed plots and the reference site. Areas for additional study are suggested, including seed bank assays to determine treatment effects on recruitment of alien versus native species and the use of native graminoids to create low-diversity communities with high canopy coverages to resist establishment of alien species.     

Invasion Pattern of Herb Garlic Mustard (Alliaria petiolata) in High Quality Forests

The invasion of non-indigenous plant species poses a severe threat to native plant communities. Garlic mustard (Alliaria petiolata) is a naturalized European biennial herb that has spread rapidly through the eastern US and adjacent Canada. To determine garlic mustard rate of spread, eleven permanent plots (50×25 m) were located in seven high quality (relatively undisturbed) forests in the early stages of invasion. Garlic mustard presence was recorded within six 50×2 m permanent belt transects, and density and percent cover by age class were recorded in 36 permanent 1 m² quadrats, between 1989 and 1992, and again in 1997. Garlic mustard spread at an average rate of 5.4 m per year between 1989 and 1992, in all plots combined. Within individual plots rate of spread varied substantially, with location of the front increasing up to 36 m and decreasing as much as 18 m between years. While the front alternately advanced and retreated, over time garlic mustard consistently advanced through all forests. Rate of spread was influenced by establishment of satellite populations, and disturbance (wind-throw and flooding). The pattern of spread within plots was one of a ragged advancing front, supplemented by establishment of satellite populations 6–40 m distant from the front, which then coalesced with the main population. Garlic mustard presence between 1989 and 1997 increased significantly within all plots, and in each age class within each plot. The greatest increases occurred in plots where this plant was initially rarest. Garlic mustard cover and density varied nonsignificantly during the same time period. These results indicate that after garlic mustard invades a forest it becomes a permanent part of the community, annually increasing in presence but fluctuating in cover and density. Garlic mustard maintains a low profile under low disturbance conditions, but increases rapidly with periodic disturbance. This study monitored garlic mustard invasion in high quality relatively undisturbed forests, and may underestimate the rate of spread in low quality highly disturbed forests.     

The thermal tolerance of crown-of-thorns (Acanthaster planci) embryos and bipinnaria larvae: implications for spatial and temporal variation in adult populations

To understand the role of sea temperature on the population biology of the crown-of-thorns sea star Acanthaster planci, the thermal window for embryonic and larval development was investigated. In two experiments, the response of embryos and larvae across 12 temperatures from 19.4 to 36.5 °C was quantified as the percentage of individuals reaching cleavage stage embryos, blastula, gastrula, early-bipinnaria, late-bipinnaria larvae or abnormal. Measurements were made at 7 times up to 72 h post-fertilisation, with the morphometrics of larvae measured in the 72-h sample. Acanthaster planci developed at temperatures between 19.4 and 33.2 °C, with a thermal window for development to the late-bipinnaria stage between 25.6 and 31.6 °C. Development rate, normal development and larval size were optimal at 28.7 °C, with development rates remaining relatively constant up to 31.6 °C. Rates of abnormality increased steadily (early embryonic stages) above 28.7 °C and was 100 % at temperatures approaching 33 °C. These experiments provide a more detailed insight into the response of A. planci developmental stages to temperature. The present day distribution of the species in eastern Australia overlap with the optimal thermal window for development to the late-bipinnaria stage (≈25–32 °C), implying a role of temperature in controlling population distributions and abundances. Despite this, short- or long-term temperature increases may not be a major modulator of the crown-of-thorns recruitment success, population dynamics and distribution in the future as no significant change in development rates, larval survival and growth occurred within this thermal window. Therefore, moderate (1–2 °C) increases in sea temperatures caused by El Niño or near-future ocean warming may not drive an increase in developmental and settlement success. Indeed, without any acclimation to warmer temperatures expected under near-future warming (+2 to 4 °C), climate change could ultimately reduce larval survival due to elevated mortality above the optimal development temperature.     

Canopy gaps facilitate establishment,growth, and reproduction of invasive <Emphasis Type="Italic">Frangula alnus</Emphasis> in a <Emphasis Type="Italic">Tsuga canadensis</Emphasis> dominated forest

The primary objective of this study was to determine whether the exotic, invasive shrub, glossy buckthorn (Frangula alnus), is more abundant in canopy gaps created by logging than in uncut forests. Secondary objectives were to determine whether buckthorn abundance in gaps is related to gap size, and whether or not buckthorn exhibits advanced regeneration. The abundance of glossy buckthorn was estimated in five patch cuts and three single-tree cuts in a 90 year old eastern hemlock–eastern white pine–sweet birch forest at the Woodman Horticultural Farm in Durham, NH, USA. Glossy buckthorn was 96 times more abundant in logged areas than in uncut control plots. The three largest but youngest gaps (>0.08 ha; 5 years old) had the greatest proportion of tall (>2 m), reproductively mature glossy buckthorn individuals, with 18.4% fruiting. The older, medium-sized gaps (ca. 0.03 ha; 10 years old) contained the highest overall densities of glossy buckthorn, but few stems were flowering (~2%) and none were fruiting at the time of sampling. Small gaps (<0.01 ha; 10 years old) appeared to be sinks for glossy buckthorn, as all individuals were <0.5 m tall and none were >4 years old. As age and size of gaps were correlated, it was difficult to determine which factor played a larger role in the establishment and persistence of glossy buckthorn. However, the greater proportion of individuals >2 m tall and greater reproductive vigor of glossy buckthorn in large gaps relative to small gaps—despite fewer years available for growth—suggest that larger disturbances lead to more resources available for buckthorn growth, survival, and reproduction. Individuals <0.5 m tall were observed in uncut control plots at low density (<30 stems/ha) and 5% of stems in large gaps were older than the gaps themselves, suggesting that gap formation released previously established glossy buckthorn individuals (i.e., advanced regeneration).     

Improved Feedstock Option or Invasive Risk? Comparing Establishment and Productivity of Fertile <Emphasis Type="Italic">Miscanthus × giganteus</Emphasis> to <Emphasis Type="Italic">Miscanthus sinensis</Emphasis>

The perennial grass genus Miscanthus has great promise as biomass feedstock, but there are concerns about potential invasion outside production fields. While the sterile hybrid Miscanthus × giganteus is currently one of the leading feedstock options due to its low invasive potential, fertile varieties are being developed to reduce establishment costs, and their invasive risks need to be further assessed. We performed seed addition experiments in Ohio and Iowa, USA to examine the establishment, flowering, persistence, and shoot biomass per plot of a fertile M. × giganteus biotype (‘PowerCane’) and two Miscanthus sinensis biotypes, one feral, and one ornamental. Seeds were added to small, replicated plots in each of the 2 years under two seeding densities and two competition treatments, and plots were monitored for 2–3 years. The ‘PowerCane’ biotype established better, survived better, and produced greater amounts of biomass per plot than both M. sinensis biotypes. All three biotypes flowered by the second or third year after establishment, with inflorescences more numerous in ‘PowerCane’ and the Ornamental M. sinensis biotypes. Effects of seeding density and competition on these patterns were minor in most cases. Our research suggests that ‘PowerCane’ exhibits many traits shared by both biomass crops and invasive species: multi-year persistence, high biomass potential, and fertility. We suggest that the benefits of a seeded M. × giganteus should be carefully weighed against its increased invasive risk prior to deployment across the landscape.     

红火蚁入侵强度对本地蚂蚁群落物种的发现-支配权衡的影响

【目的】发现-支配权衡(discovery-dominance trade off)在物种间的竞争起着重要作用。本研究旨在了解不同强度的红火蚁Solenopsis invicta入侵对本地蚂蚁群落物种的发现-支配权衡的影响,从而探讨红火蚁与本地蚂蚁的竞争机制。【方法】于2017年10-11月,在云南省楚雄州牟定县的一滇橄榄种植基地利用诱饵法和陷阱法结合的方式引诱和收集蚂蚁,观察并记录常见蚂蚁种类的发现能力、招募能力、支配能力、最早发现诱饵的时间段及个体数。【结果】红火蚁的入侵显著影响了本地蚂蚁群落物种的发现-支配权衡。强入侵区(5.6个活动蚁巢/100 m²)蚂蚁群落中物种的相对发现能力和相对支配能力不存在相关性;弱入侵区(0.14个活动蚁巢/100 m²)蚂蚁群落中两者存在较弱的负相关性,但不显著;对照区(无蚁巢)中两者存在显著负相关性(强入侵区:r=-0.01,P=0.97;弱入侵区:r=-0.60,P=0.21;对照区:r=-0.81,P=0.04)。强入侵区的红火蚁种群普遍在5 min之内就能发现诱饵,而弱入侵区的种群需要10～60 ...     

Long-term Field Efficacy of the Entomogenous Fungus Metarhizium anisopliae against the Subterranean Scarab, Adoryphorus couloni

The efficacy of Metarhizium anisopliae DAT F-001 against Adoryphorus couloni was examined over 4 years on a sheep grazing property ('Inverell') in central Tasmania. Three generations of the primary A. couloni population and two generations of the overlapping population were studied. Application of 5.1 0.7 104 M. anisopliae spores g-1 of soil (2 cm below the soil surface), during midwinter 1989, when the primary population was in the middle of the L3 larval stage, resulted in 30.3% fewer larvae in treated plots by 21 weeks and 57.8% less pupae by 27 weeks. The population decline was consistent with a mortality model developed from laboratory data. In the two subsequent generations of the primary population, there were 63.2% (1991) and 45.0% (1993) fewer larvae in the treated plots before the damaging L3 stage. The two sequential generations of the overlapping A. couloni larval populations had 68% (1990) and 65% (1992) fewer larvae in the treated plots than in the untreated plots. Reductions in larval numbers led to a greater retention of sown perennial grasses, reduced weed invasion and a 23% increase in pasture productivity in the autumn of 1992. Incorporation of M. anisopliae into the soil did not reduce the numbers of non-target invertebrates. The level of M. anisopliae DAT F-001 in the pasture remained at levels close to the applied concentration (5.1 0.7 colony-forming units g-1 of soil), but increased 10-fold when mummified L3 larval, prepupal and pupal cadavers were present from January to June 1990. The level of the fungus in the soil was still twice the original applied concentration at the conclusion of sampling in March 1992.     

The establishment and eradication of an extra-limital population of invasive cane toads

Biological invasions expand not only as a continuous front, but also via translocation of small numbers of individuals to sites far from the main distribution. Detecting and eradicating such satellite populations is critical to curtailing the invasion. Cane toads (Rhinella marina) have been spreading through Australia since 1935, and in 2010 were reported in suburban Sydney, 500 km from the main invasion. The amphibians arrived as stowaways in trucks, and bred successfully in at least 3 years. Local residents noted the toads’ presence long before management authorities. As soon as they recognised the population’s establishment, however, the authorities surveyed locations of toads, assessed toad demography, and culled toads. Radio-tracking revealed the locations of spawning sites, which were then fenced to exclude access. As a result of reproduction, growth, and sex-specific culling (due to sex differences in distribution and catchability), successive years saw major changes in toad abundance, body-size distributions and sex ratios. Rates of infection of toads by parasites (lungworms) increased through time also. Adult male toads were collected primarily from the initial introduction site, whereas adult females were collected from a broader area. A total of > 900 post-metamorphic cane toads and > 5000 earlier life stages were collected, and those efforts (plus predation by rats and birds) exterminated the population (no sightings for the past 3 years). Cane toads will continue to be translocated to sites far outside their main invaded range, but the successful eradication effort suggests that well-integrated programs, with close collaboration among stakeholders, can prevent such populations from establishing.     

Effect of seed predation on seed bank size and seedling recruitment of bush lupine (Lupinus arboreus)

Whether seed consumers affect plant establishment is an important unresolved question in plant population biology. Seed consumption is ubiquitous; at issue is whether seedling recruitment is limited by safe-sites or seeds. If most seeds inhabit sites unsuitable for germination, post-dispersal seed consumption primarily removes seeds that would otherwise never contribute to the population and granivory has minimal impacts on plant abundance. Alternatively, if most seeds ultimately germinate before they lose viability, there is greater potential for seed consumption to affect plant recruitment. Of the many studies on seed consumption, few ask how seed loss affects seedling recruitment for species with long-lived seed banks. We examined post-dispersal seed predation and seedling emergence in bush lupine (Lupinus arboreus), a woody leguminous shrub of coastal grasslands and dunes in California. We followed the fate of seeds in paired experimental seed plots that were either protected or exposed to rodent granivores in grassland and dune habitats. Significantly more seeds were removed by rodents in dunes than grasslands. In dunes, where rodent granivory was greatest (65% and 86% of seeds removed from plots by rodents in two successive years), there is a sparse seed bank (6.6 seeds m⁻²), and granivory significantly reduced seedling emergence (in the same two years, 18% and 19.4% fewer seedlings emerged from exposed versus protected plots), suggesting seed rather than safe-site limited seedling recruitment. In contrast, rodents removed an average of 6% and 56% of seeds from grassland plots during the same two years, and the grassland seed bank is 43-fold that of the dunes (288 seeds m⁻²). Even high seed consumption in the second year of the study only marginally influenced recruitment because seeds that escaped predation remained dormant. Burial of seeds in both habitats significantly reduced the percentage of seeds removed by rodents. Results suggest that granivores exert strong but habitat-dependent effects on lupine seed survival and seedling emergence. Received: 24 October 1996 / Accepted: 4 February 1997     

SEED BANK,SURVIVORSHIP, AND SIZE DISTRIBUTION OF A NEBRASKA POPULATION OF IMPATIENS CAPENSIS (BALSAMINACEAE)

The growth and survivorship of a population of Impatiens capensis were followed in eastern Nebraska. Soil cores were taken within the population to estimate the size of the seed bank. The number of seeds in the soil remained relatively constant from April through October, with a mean of 200 seeds/m². The seed bank size corresponded to observed seedling densities in the following years. Twenty permanent plots were established within the population and censused for three years, 1983–1985. Seedling recruitment to the population was similar in 1983 and 1984 but 30% higher in 1985. The seedling densities of plots were uncorrelated from year to year. Survivorship in 1983 followed a Deevey Type I pattern. Almost one-third of the population survived until chasmogamous reproduction. Plant size (stem height) was measured monthly on all individuals during 1983. The frequency distribution of stem height was positively skewed as long as growth was exponential. When the growth rate slowed, the distribution became more normal.     

Removal of Nonnative Vines and Post‐Hurricane Recruitment in Tropical Hardwood Forests of Florida1

In hardwood subtropical forests of southern Florida, nonnative vines have been hypothesized to be detrimental, as many species form dense “vine blankets” that shroud the forest. To investigate the effects of nonnative vines in post‐hurricane regeneration, we set up four large (two pairs of 30 X 60 m) study areas in each of three study sites. One of each pair was unmanaged and the other was managed by removal of nonnative plants, predominantly vines. Within these areas, we sampled vegetation in 5 X 5 m plots for stems 2 cm DBH (diameter at breast height) or greater and in 2 X 0.5 m plots for stems of all sizes. For five years, at annual censuses, we tagged and measured stems of vines, trees, shrubs and herbs in these plots. For each 5 X 5 m plot, we estimated percent coverage by individual vine species, using native and nonnative vines as classes. We investigated the hypotheses that: (1) plot coverage, occurrence and recruitment of nonnative vines were greater than that of native vines in unmanaged plots; (2) the management program was effective at reducing cover by nonnative vines; and (3) reduction of cover by nonnative vines improved recruitment of seedlings and saplings of native trees, shrubs, and herbs. In unmanaged plots, nonnative vines recruited more seedlings and had a significantly higher plot‐cover index, but not a higher frequency of occurrence. Management significantly reduced cover by nonnative vines and had a significant overall positive effect on recruitment of seedlings and saplings of native trees, shrubs and herbs. Management also affected the seedling community (which included vines, trees, shrubs, and herbs) in some unanticipated ways, favoring early successional species for a longer period of time. The vine species with the greatest potential to “strangle” gaps were those that rapidly formed dense cover, had shade tolerant seedling recruitment, and were animal‐dispersed. This suite of traits was more common in the nonnative vines than in the native vines. Our results suggest that some vines may alter the spatiotemporal pattern of recruitment sites in a forest ecosystem following a natural disturbance by creating many very shady spots very quickly.     

Intraspecific variation influences natural settlement of eastern oysters

As populations decline, their intraspecific diversity also diminishes. Population decline may be exacerbated if a decrease in intraspecific diversity also reduces important ecological functions that maintain population numbers. Oyster reefs are severely overharvested, declining by ~85 % worldwide. We tested how increasing within-species diversity of eastern oysters (Crassostrea virginica) using transplants would affect recruitment of oyster larvae, a key function necessary to maintain future populations. If harvesting reduces population numbers, within-species diversity, and connectivity, then oysters may lose the ability to adapt to changing environmental conditions as well as incur lower levels of recruitment that may hasten their decline. Results from laboratory and field studies indicated that oyster larvae use chemical cues from adult oysters and not from associated fouling communities to select settlement sites. To test how increasing within-species diversity of oysters affected recruitment, we collected oysters from three distinct bay systems in Texas, USA, and compared natural settlement in treatments where all oysters were from a single bay to a mixture of all three bays. Significantly greater recruitment occurred in mixed treatments in 2010, 2011, and 2012 even though oyster recruitment varied by order of magnitude during this time. The net biodiversity effect was positive in all 3 years, indicating that increased recruitment in mixed treatments can be greater than the additive effect of the single bay treatments. Losing intraspecific diversity may reduce recruitment and lead to further declines in oyster populations, illustrating the need for understanding how intraspecific diversity influences ecological functions.