Nitrogen Fertilization Effects on Productivity and Nitrogen Loss in Three Grass-Based Perennial Bioenergy Cropping Systems

Nitrogen (N) fertilization can greatly improve plant productivity but needs to be carefully managed to avoid harmful environmental impacts. Nutrient management guidelines aimed at reducing harmful forms of N loss such as nitrous oxide (N₂O) emissions and nitrate (NO₃^-) leaching have been tailored for many cropping systems. The developing bioenergy industry is likely to make use of novel cropping systems, such as polycultures of perennial species, for which we have limited nutrient management experience. We studied how a switchgrass (Panicum virgatum) monoculture, a 5-species native grass mixture and an 18-species restored prairie responded to annual fertilizer applications of 56 kg N ha^-1 in a field-scale agronomic trial in south-central Wisconsin over a 2-year period. We observed greater fertilizer-induced N₂O emissions and sub-rooting zone NO₃^- concentrations in the switchgrass monoculture than in either polyculture. Fertilization increased aboveground net primary productivity in the polycultures, but not in the switchgrass monoculture. Switchgrass was generally more productive, while the two polycultures did not differ from each other in productivity or N loss. Our results highlight differences between polycultures and a switchgrass monoculture in responding to N fertilization.     

A novel polyculture growth model of native microalgal communities to estimate biomass productivity for biofuel production

Native polyculture microalgae is a promising scheme to produce microalgal biomass as biofuel feedstock in an open raceway pond. However, predicting biomass productivity of native polycultures microalgae is incredibly complicated. Therefore, developing polyculture growth model to forecast biomass yield is indispensable for commercial-scale production. This research aims to develop a polyculture growth model for native microalgal communities in the Minamisoma algae plant and to estimate biomass and biocrude oil productivity in a semicontinuous open raceway pond. The model was built based on monoculture growth of polyculture species and it is later formulated using species growth, polyculture factor (k_value), initial concentration, light intensity, and temperature. In order to calculate species growth, a simplified Monod model was applied. In the simulation, 115 samples of the 2014–2015 field dataset were used for model training, and 70 samples of the 2017 field dataset were used for model validation. The model simulation on biomass concentration showed that the polyculture growth model with k_value had a root-mean-square error of 0.12, whereas model validation provided a better result with a root-mean-square error of 0.08. Biomass productivity forecast showed maximum productivity of 18.87 g/m²/d in June with an annual average of 13.59 g/m²/d. Biocrude oil yield forecast indicated that hydrothermal liquefaction process was more suitable with a maximum productivity of 0.59 g/m²/d compared with solvent extraction which was only 0.19 g/m²/d. With satisfactory root-mean-square errors less than 0.3, this polyculture growth model can be applied to forecast the productivity of native microalgae.     

Floral neighborhood influences pollinator assemblages and effective pollination in a native plant

Pollinators represent an important intermediary by which different plant species can influence each other’s reproductive fitness. Floral neighbors can modify the quantity of pollinator visits to a focal species but may also influence the composition of visitor assemblages that plants receive leading to potential changes in the average effectiveness of floral visits. We explored how the heterospecific floral neighborhood (abundance of native and non-native heterospecific plants within 2 m × 2 m) affects pollinator visitation and composition of pollinator assemblages for a native plant, Phacelia parryi. The relative effectiveness of different insect visitors was also assessed to interpret the potential effects on plant fitness of shifts in pollinator assemblage composition. Although the common non-native Brassica nigra did not have a significant effect on overall pollinator visitation rate to P. parryi, the proportion of flower visits that were made by native pollinators increased with increasing abundance of heterospecific plant species in the floral neighborhood other than B. nigra. Furthermore, native pollinators deposited twice as many P. parryi pollen grains per visit as did the nonnative Apis mellifera, and visits by native bees also resulted in more seeds than visits by A. mellifera. These results indicate that the floral neighborhood can influence the composition of pollinator assemblages that visit a native plant and that changes in local flower communities have the potential to affect plant reproductive success through shifts in these assemblages towards less effective pollinators.     

Propagule pressure and native species richness effects drive invasibility in tropical dry forest seedling layers

Understanding the factors that encourage or inhibit plant invasions is vital to focusing limited invasive control efforts within areas where they are most practical and cost-effective. To extend the range of contexts in which invasibility is studied and aid the development of practical strategies to limit damaging plant invasions, we set out to test the relative importance of native species richness, native seedling density, and invasive propagule pressure, on the invasibility of artificial assemblages of naturally occurring tropical woody seedling communities. Our greenhouse mesocosms included a species pool of twelve trees and woody shrubs native to South Florida's tropical hardwood hammocks, and an increasingly prevalent noxious woody invader of this system, Ardisia elliptica. We found that invader propagule pressure was the single most important factor determining community invasibility. We also revealed a positive relationship between invasibility and native species richness in our polyculture mesocosms. Because A. elliptica biomass production significantly differed among different native monocultures and was not related to overyielding in native polycultures, we suggest that the effect of species richness on invasibility in this experiment was the result of sampling effects rather than a true effect of diversity.Three broad findings hold potential for application in preventing and controlling plant invasions, especially in the seedling layers of tropical dry forests: (1) effective invasive control efforts will likely benefit from measures to minimize propagule pressure; (2) managers might do well to prioritize invasive monitoring and removal efforts on the most diverse habitats within a management region; and (3) while more data are necessary to further understand our finding of a lack of association between productivity and invasibility, management regimes aimed at maximizing primary productivity might not increase invasibility, and in fact, strategies for controlling invasive plants via the management of ecosystem productivity may be ineffective.     

Ectomycorrhizal fungal communities of native and non-native Pinus and Quercus species in a common garden of 35-year-old trees

Non-native tree species have been widely planted or have become naturalized in most forested landscapes. It is not clear if native trees species collectively differ in ectomycorrhizal fungal (EMF) diversity and communities from that of non-native tree species. Alternatively, EMF species community similarity may be more determined by host plant phylogeny than by whether the plant is native or non-native. We examined these unknowns by comparing two genera, native and non-native Quercus robur and Quercus rubra and native and non-native Pinus sylvestris and Pinus nigra in a 35-year-old common garden in Poland. Using molecular and morphological approaches, we identified EMF species from ectomycorrhizal root tips and sporocarps collected in the monoculture tree plots. A total of 69 EMF species were found, with 38 species collected only as sporocarps, 18 only as ectomycorrhizas, and 13 both as ectomycorrhizas and sporocarps. The EMF species observed were all native and commonly associated with a Holarctic range in distribution. We found that native Q. robur had ca. 120% higher total EMF species richness than the non-native Q. rubra, while native P. sylvestris had ca. 25% lower total EMF species richness than non-native P. nigra. Thus, across genera, there was no evidence that native species have higher EMF species diversity than exotic species. In addition, we found a higher similarity in EMF communities between the two Pinus species than between the two Quercus species. These results support the naturalization of non-native trees by means of mutualistic associations with cosmopolitan and novel fungi.     

Density of Anomoea flavokansiensis on Desmanthus illinoensis in monoculture and polyculture

The effect of plant species diversity on the density of the herbivore, Anomoea flavokansiensis Moldenke (Coleoptera: Chrysomelidae), on Desmanthus illinoensis (Michaux) MacMillan (Mimosaceae), a promising North American legume for exploring the principles of diverse, perennial grain agriculture was examined. From mid-June to early August A. flavokansiensis feeds on young leaves and inflorescences of D. llinoensis. At high density, A. flavokansiensis potentially reduces seed yield and is thus an important consideration for long-term stands that are to be grown without insecticides. The potential to manage this insect via intercropping its host species with other, non-host perennial species by monitoring A. flavokansiensis density on D. illinoensis within experimental monocultures, two-species mixtures with Tripsacum dactyloides, and three-species mixtures with T. dactyloides and Leymus racemosus was examined. Insects were censused 2–3 times weekly from mid-June to early August at two sites from 1991 to 1995. In the first three years, beetle density was generally low (<1 per plant), and did not differ among treatments. In the fourth year, however, beetle density peaked at 15 and 25 insects per plant at the two sites, and was highest within monoculture for most dates. In 1995, density was again low, but tended to remain higher in monoculture at one site. The results suggest that beetle density on D. illinoensis can be reduced in polyculture and may hold promise for the management of this insect herbivore within perennial grain polycultures.     

Responses of tropical fruit bats to monoculture and polyculture farming in oil palm smallholdings

The oil palm industry is one of the main economic drivers in Southeast Asia. The industry has caused tropical deforestation on a massive scale in producing countries, and this forest conversion to oil palm agriculture has decimated the habitat of numerous native species. Monoculture and polyculture practices are two distinctive oil palm production systems. We hypothesize that polyculture farming hosts a greater diversity of species than monoculture farming. Habitat complexity in smallholdings is influenced by multiple farming practices (i.e. polyculture and monoculture). However, little is known about the effects of such farming practices in smallholdings on mammalian biodiversity, and particularly frugivorous bats. Our study aimed to find the best farming practice to reconcile oil palm production with biodiversity conservation. Mist-nets were used to trap frugivorous bats at 120 smallholdings in Peninsular Malaysia. We compared species richness and the abundance of frugivorous bats between monoculture and polyculture smallholdings. We investigated their relationships with vegetation structure characteristics. Our results revealed that species richness and abundance of frugivorous bats were significantly greater in polyculture smallholdings than monoculture smallholdings. We also found that 28.21% of the variation in species richness was explained by in situ habitat characteristics, including the number of dead standing oil palms and immature oil palms, non-grass cover, height of non-grass cover, and farming practices. The in situ habitat quality was closely associated with oil palm farming management. Commercial growers should implement polyculture rather than monoculture farming because polyculture farming has positive effects on the abundance and species richness of bats in oil palm production landscapes.     

Ecological niche differentiation between native and non-native shrimps in the northern Baltic Sea

Invasions of non-native species are modifying global biodiversity but the ecological mechanisms underlying invasion processes are still not well understood. A degree of niche separation of non-native and sympatric native species can possibly explain the success of novel species in their new environment. In this study, we quantified experimentally and in situ the environmental niche space of caridean shrimps (native Crangon crangon and Palaemon adspersus, non-native Palaemon elegans) inhabiting the northern Baltic Sea. Field studies showed that the non-native P. elegans had wider geographical range compared to native species although the level of habitat specialization was similar in both Palaemon species. There were clear differences in shrimp habitat occupancy with P. elegans inhabiting lower salinity areas and more eutrophicated habitats compared to the native species. Consequently, the non-native shrimp has occupied large areas of the northern Baltic Sea that were previously devoid of the native shrimps. Experiments demonstrated that the non-native shrimp had higher affinity to vegetated substrates compared to native species. The study suggests that the abilities of the non-native shrimp to thrive in more stressful habitats (lower salinity, higher eutrophication), that are sub-optimal for native shrimps, plausibly explain the invasion success of P. elegans.     

Epifaunal and algal assemblages associated with the native Chondrus crispus (Stackhouse) and the non-native Grateloupia turuturu (Yamada) in eastern Long Island Sound

Although the spread of non-native algae is rapidly escalating, relatively few ecological studies have been done to gauge the impacts incurred to native flora and fauna. A reduction in the dominance of a native habitat-forming macroalga due to the replacement by an introduced species can have adverse effects on the community. The non-native red alga Grateloupia turuturu, first reported in Rhode Island, USA in 1994, has since extended its southern range into eastern Long Island Sound. This large alga has the potential to impact coastal communities by altering the floristic composition important to associated flora and fauna. A comparison of algal and epifaunal assemblages was made during 2006 and 2007 between native and non-native algal communities dominated by either G. turuturu or the native, Chondrus crispus at two sites in Long Island Sound. We found that within Grateloupia-dominated habitat, there was a large decrease in overall macrophyte biomass as compared to native habitat. We also found that habitat dominated by the non-native alga reduced species richness and total abundance of invertebrates relative to nearby habitats dominated by C. crispus. In addition, we found that the dominant mesofaunal species, important to higher trophic level consumers, had greatly reduced densities in communities dominated by the non-native alga.     

Drivers of Central European urban land snail faunas: the role of climate and local species pool in the representation of native and non-native species

The importance of macroclimate and dispersal limitation in the broad-scale variation of European urban land snail assemblages is likely to differ between native and non-native species because of the southern origin of many non-native snails, often spread by humans. We sampled land snails in each of 32 European cities and compiled from the literature a list of land snail species reported from the surroundings of each city. To quantify the predictive power of climate and local species pools, beta-sim dissimilarity matrices of both native and non-native species were explored using MDS and RDA ordination methods, Mantel tests with bootstrapping of each dataset, and multivariate homogeneity analysis of group variances. We observed no significant relation between the numbers of non-native species found in the cities and their surroundings (p > 0.133), while the percentage of native species in the cities derived from their local species pools decreased significantly with the increasing species richness of local faunas (r_S = ?0.75, p < 0.001). Assemblage variation of urban native species was explained mostly by the difference between mean January and July temperatures (21.3 %), with the major role of July temperature (18.0 %). In contrast, variation of non-native species assemblages was mainly explained by January temperature (19.9 %). The congruence in faunal similarities between the cities and the surrounding areas was higher in native (r = 0.46, p < 0.001) than in non-native species (r = 0.36, p < 0.001). Overall native faunas were significantly more homogeneous than the non-native faunas. Our results suggest that recent climate warming may foster geographical expansions of many non-native land snail species as their distributions are controlled mainly by January temperature.     

Local and regional differences in abundance of co-dominant grasses in the shortgrass steppe: a modeling analysis of potential causes

The shortgrass steppe is co-dominated by two C₄perennial grasses, Bouteloua gracilis andBuchloë dactyloides. At our site and throughouteastern Colorado Bouteloua gracilis has higher cover andbiomass than Buchloë dactyloides. We hypothesizedthatthe interaction between seedling recruitment differences and disturbance regimeand tolerance to drought conditions were the most likely causes of the observeddifferences in relative abundances. We used a simulation model to investigatethe relative importance of the three factors. We studied plant biomass of thesetwo species in 18 simulated treatments that resulted from a factorialcombination of seedling recruitment differences, disturbance regime, andtolerance to drought conditions. Analysis of the simulation outputs with ANOVAindicated that biomass of each species responded positively to increases inrecruitment probability. Increasing disturbance frequency favoredBuchloë dactyloides over Boutelouagracills, whereas the susceptibility Buchloëdactyloides to drought favored Boutelouagracilis. The results indicated that differences in droughttoleranceand seedling recruitment probabilities along with their interactions withdisturbance regimes exert a major control on the biomass of the species. In theabsence of or with intermediate disturbance, a higher recruitment probabilityand greater tolerance to drought of Bouteloua gracilisthanBuchloë dactyloides yielded patterns of relativebiomass similar to the patterns observed in the shortgrass steppe.     

Repeated mowing to restore remnant native grasslands invaded by nonnative annual grasses: upsides and downsides above and below ground

California grasslands have been severely impacted by the invasion of nonnative annual grasses, which often limit restoration of this important ecosystem. In this study, we explored the use of mowing as a restoration tool for native perennial grasslands at the Santa Rosa Plateau Ecological Reserve in southern California. We sought to evaluate if, over time, mowing would reduce nonnative annual grass cover and benefit native species, especially the native bunchgrass Stipa pulchra. We hypothesized that repeated mowing, carefully timed to target nonnative annual grasses prior to seed maturation, would reduce nonnative seed inputs into the soil and eventually lead to diminished abundance of these species. We monitored vegetation in mowed and unmowed plots for 4 years, and conducted a seed bank study after 5 years to better understand the cumulative effects of mowing on native and nonnative seed inputs. Consistent with our hypotheses, we found that mowing successfully reduced nonnative annual grass cover and benefitted some native species, including S. pulchra. However, we also found that nonnative forb species showed progressive increases in mowed plots over time. We observed similar patterns of species composition in the soil seed bank. Together, these results suggest that mowing can be used to control nonnative annual grasses and increase the abundance of native bunchgrasses, but that this method may also have the unintended consequence of increasing nonnative forb species.     

Nutrient use preferences among soil Streptomyces suggest greater resource competition in monoculture than polyculture plant communities

Background an aims

Nutrient use overlap among sympatric Streptomyces populations is correlated with pathogen inhibitory capacity, yet there is little information on either the factors that influence nutrient use overlap among coexisting populations or the diversity of nutrient use among soil Streptomyces.

Methods

We examined the effects of plant host and plant species richness on nutrient use of Streptomyces isolated from the rhizosphere of Andropogon gerardii (Ag) and Lespedeza capitata (Lc) growing in communities of 1 (monoculture) or 16 (polyculture) plant species. Growth on 95 carbon sources was assessed over 5d.

Results

Cumulative growth was significantly greater for polyculture vs. monoculture isolates, and for Lc vs. Ag isolates. Isolates from monocultures, but not polycultures, exhibited a drop in growth rates between 24 h and 72 h post-inoculation, suggesting resource allocation to non-growth functions. Isolates from high-carbon (polyculture) or high-nitrogen (Lc) soils had larger niche widths than isolates from low-C (monocultures) or low-N (Ag) soils. Sympatric isolates from polycultures were significantly more differentiated from one another in preferred nutrients for growth than sympatric isolates from monocultures.

Conclusions

These results suggest that Streptomyces populations respond to selection imposed by plant host and plant community richness and that populations from polyculture but not from monoculture, mediate resource competition via niche differentiation.

     

Differential effect of wave stress on the physiology and behaviour of native versus non-native benthic invertebrates

In fresh waters, non-native invertebrate species preferentially spread via navigation waterways, where they often dominate assemblages. Littoral habitats in navigation waterways are regularly exposed to ship-induced waves. We conducted experiments to test the effects of artificial wave exposure on the relative performance of wide-spread native and non-native species. We compared physiological and behavioural response variables (i.e. growth rate, glycogen content, feeding and swimming activity) of two amphipods (native Gammarus roeselii and non-native Dikerogammarus villosus) and two gastropods (native Bithynia tentaculata and non-native Physella acuta) subject to wave and control (i.e. no wave) treatment flumes across a 6-week period. Growth, and in part glycogen content (as a measure of energy storage), were significantly reduced after exposure to waves in native invertebrates, but not in non-native invertebrates. The reduction in growth may be associated with the disturbance effects of waves, such as the higher swimming activity of G. roeselii and lower food uptake of B. tentaculata. In comparison, the effective hiding behaviour observed for D. villosus and good swimming ability of P. acuta, were identified as important traits facilitating the successful colonisation of the harsh habitat conditions of littoral waterways. Our study demonstrates that artificial wave regimes may contribute significant selective pressure, thus explaining the observed dominance of non-native species in navigational waterways. The success of non-native species under the harsh hydraulic habitat conditions of these socio-economically driven ecosystems may consequently be traced directly to behavioural and/or physiological traits.     

Trait-based plant mortality and preference for native versus non-native seedlings by invasive slug and snail herbivores in Hawaii

Non-native herbivores may alter plant communities through their preferential consumption of seedlings of different species. We assessed seedling herbivory by two invasive gastropod species in Hawaii, the giant African snail (Achatina fulica) and the Cuban brown slug (Veronicella cubensis). We hypothesized that six native species would suffer greater gastropod herbivory than four non-native species, and that species with short stature, thin leaves, and lacking physical defenses would suffer the greatest mortality from gastropods. Herbivory was measured during 13-day preference trials using enclosures that each contained four different woody species (two native, two non-native) and were assigned to one of three treatments: giant African snail, Cuban brown slug, or control (no gastropod). Discriminant function analysis was used to predict gastropod-induced seedling mortality from a suite of seedling characteristics. Native species did not always experience greater herbivory than non-natives species, and seedling mortality was 0–100 %. Native Pipturus albidus and Clermontia parviflora suffered 100 % mortality from V. cubensis herbivory, and P. albidus, Psychotria hawaiiensis, and Myrsine lessertiana suffered ≥80 % mortality from A. fulica. Two non-natives (Fraxinus uhdei, Clidemia hirta), and two natives (Metrosideros polymorpha, Diospyros sandwicensis), suffered little damage and no mortality. Non-native Ardisia elliptica suffered 10–30 % gastropod mortality, and non-native Psidium cattleianum mortality was 0–50 %. Leaf thickness best predicted species mortality caused by slugs and snails; some thicker-leaved species suffered most. Invasive snails and slugs threaten some native and non-native seedlings by directly consuming them. Current and future plant community structure in Hawaii may in part reflect the feeding preferences of invasive gastropods.     

Native Alternatives for Non-Native Turfgrasses in Central Florida: Germination and Responses to Cultural Treatments

Little information exists about the establishment of native longleaf pine flatwoods species for use in restoration efforts and as buffers around natural areas in the southeastern United States. Composition of groundcover in these systems is dominated by perennial graminoid species. Vegetation in current buffers is generally non‐native turfgrass that can escape into natural areas, often reducing establishment and survival of native species. Where management objectives involve actively restoring native groundcover or reducing the probability of invasion by these non‐native turfgrasses, identification of native species and restoration methods is needed. We investigated seed germination and establishment of four species native to longleaf pine flatwoods in central Florida and one species native to the adjacent wetland communities. Paspalum setaceum, Panicum anceps, Eustachys petraea, and Eragrostis refracta were directly seeded, and P. distichum was planted as sprigs into three former P. notatum pastures. Irrigation, fertilization, weed control, and mowing treatments were assessed in terms of cover development of the sown species. Paspalum distichum developed the highest percent cover—over 80% in wet areas after 1 year. Mowing had mixed impacts depending on the species, and fertilization never significantly increased cover. Directly seeded species developed sparse cover (0–40%), probably as a result of drought conditions. However, E. petraea and E. refracta appeared more promising for use on rights‐of‐way when using high sowing rates. A second experiment conducted on a roadside included these two species and sprigged P. distichum. Both E. petraea and P. distichum developed more than 45% cover on the roadside. Establishment of these natives from seed or sprigs was significantly enhanced when site preparation effectively reduced the seedbank of other species present in the soil.     

The impact of weed diversity on insect population dynamics and crop yield in collards, Brassica oleraceae (Brassicaceae)

Vegetational diversity within agricultural fields is often suggested as a means to reduce insect herbivore populations and to increase their natural enemies. In this paper we compare population densities of herbivores, predators, and parasitoids on collards in monocultures and on collards interplanted with two different groups of weeds, one with weed species from the same plant family as the collards (Brassicaceae) and one with weed species from unrelated plant families (non-Brassicaceae). The collards in the Brassicaceae weed polyculture had higher densities (number of herbivores/mean leaf area (cm²) per plant) of specialist herbivores than collards in the non-Brassicaceae weed polyculture and in collard monoculture. The “resource concentration” hypothesis is supported by the observation of higher populations of Phyllotreta spp., acting as facultative polyphages, in the Brassicaceae weed polyculture than in the non-Brassicaceae weed polyculture where Phyllotreta spp. are facultative monophages. Population densities of natural enemies (mostly coccinellids, carabids, and staphylinids) were higher in the polycultures than in the monoculture: carabid and staphylinid predators may be responsible for larval mortality in the imported cabbage worm, Pieris␣rapae, and in the diamondback larvae, Plutella xylostella. In spite of differences in densities of specialist herbivores across treatments, crop yield, leaf area (cm²), the proportion of leaf area damaged, and the number of leaves undamaged did not differ. These findings suggest that plant competition may interfere with attempts to reduce herbivore damage. We conclude that the use of weedy cultures can provide effective means of reducing herbivores if the crop and weed species are not related and plant competition is prevented. Received: 25 December 1995 / Accepted: 24 February 1997     

Benthic foraminifera associated with the invasive ascidian, Didemnum sp. A

The invasive ascidian, Didemnum sp. A, first appeared in New England bays and harbors in the early 1990s, and in the waters around Cape Cod in 1993. While ship traffic was the likely vector introducing the species, its origin and precise date and location of its introduction are presently unknown. Colony surfaces of Didemnum sp. A appear very clean and not favorable substrates for epibiota settlement, but closer inspection revealed the presence of benthic foraminifera. During 2003 and 2004, 52 samples of Didemnum sp. A and other ascidians were collected to determine whether or not the foraminiferal assemblages might also be non-native and thus provide a potential clue to the place of origin of Didemnum sp. A. Sample locations included the New England coast from Connecticut to Maine (with a concentration in the Cape Cod area), northern California, Zeeland, The Netherlands, and Shakespeare Bay, New Zealand. From New England samples, 18 species of benthic foraminifera were identified. The most common species represented were Cornuspira involvens, C. planorbis, Elphidium galvestonense, E. margaritaceum, Glabratellina lauriei, Miliolinella subrotunda, Quinqueloculina bicornis, and Rosalina floridana. Foraminiferal assemblages on Didemnum sp. A from other regions sampled were composed of the same cosmopolitan species found in New England, plus other species which were indigenous to each region. Because no exotic foraminifera species were found it is concluded that Didemnum sp. A likely did not introduce non-native foraminifera originating from their native habitats into the New England region.     

Introduced species provide a novel temporal resource that facilitates native predator population growth

Non-native species are recognized as important components of change to food web structure. Non-native prey may increase native predator populations by providing an additional food source and simultaneously decrease native prey populations by outcompeting them for a limited resource. This pattern of apparent competition may be important for plants and sessile marine invertebrate suspension feeders as they often compete for space and their immobile state make them readily accessible to predators. Reported studies on apparent competition have rarely been examined in biological invasions and no study has linked seasonal patterns of native and non-native prey abundance to increasing native predator populations. Here, we evaluate the effects of non-native colonial ascidians (Diplosoma listerianum and Didemnum vexillum) on population growth of a native predator (bloodstar, Henricia sanguinolenta) and native sponges through long-term surveys of abundance, prey choice and growth experiments. We show non-native species facilitate native predator population growth by providing a novel temporal resource that prevents loss of predator biomass when its native prey species are rare. We expect that by incorporating native and non-native prey seasonal abundance patterns, ecologists will gain a more comprehensive understanding of the mechanisms underlying the effects of non-native prey species on native predator and prey population dynamics.     

The impact of two non-native plant species on native flora performance: potential implications for habitat restoration

Both Impatiens glandulifera and Fallopia japonica are highly invasive plant species that have detrimental impacts on native biodiversity in areas where they invade and form dense monocultures. Both species are weakly dependent on arbuscular mycorrhizal fungi (AMF) for their growth and, therefore, under monotypic stands, the AMF network can become depauperate. We evaluated the impact of I. glandulifera and F. japonica on the performance (expressed as shoot biomass) of three UK native species (Plantago lanceolata, Lotus corniculatus and Trifolium pratense) grown in soil collected from under stands of both invasive plants and compared to plants grown in soil from under stands of the corresponding native vegetation. All native species had a higher percentage colonisation of AMF when grown in uninvaded soil compared to the corresponding invaded soil. P. lanceolata and L. corniculatus had a higher biomass when grown in uninvaded soil compared to corresponding invaded soil indicating an indirect impact from the non-native species. However, for T. pratense there was no difference in biomass between soil types related to I. glandulifera, suggesting that the species is more reliant on rhizobial bacteria. We conclude that simply managing invasive populations of non-native species that are weakly, or non-dependent, on AMF is inadequate for habitat restoration as native plant colonisation and establishment may be hindered by the depleted levels of AMF in the soil below invaded monocultures. We suggest that the reintroduction of native plants to promote AMF proliferation should be incorporated into future management plans for habitats degraded by non-native plant species.