Positive interaction between invasive plants: The influence of Pyracantha angustifolia on the recruitment of native and exotic woody species

Abstract: Positive interactions between species are known to play an important role in the dynamics of plant communities, including the enhancement of invasions by exotics. We studied the influence of the invasive shrub Pyracantha angustifolia (Rosaceae) on the recruitment of native and exotic woody species in a secondary shrubland in central Argentina mountains. We recorded woody sapling recruitment and micro‐environmental conditions under the canopies of Pyracantha and the dominant native shrub Condalia montana (Rhamnaceae), and in the absence of shrub cover, considering these situations as three treatments. We found that native and exotic species richness were higher under Pyracantha than under the other treatments. Ligustrum lucidum (Oleaceae), an exotic bird‐dispersed shade‐tolerant tree, was the most abundant species recruiting in the area, and its density was four times higher under the canopy of Pyracantha. This positive interaction may be related to Pyracantha's denser shading, to the mechanical protection of its canopy against ungulates, and/or to the simultaneous fruit ripening of both woody invaders.     

Additive and interactive effects of plant genotypic diversity on arthropod communities and plant fitness

Recent research suggests that genetic diversity in plant populations can shape the diversity and abundance of consumer communities. We tested this hypothesis in a field experiment by manipulating patches of Evening Primrose ( Oenothera biennis ) to contain one, four or eight plant genotypes. We then surveyed 92 species of naturally colonizing arthropods. Genetically diverse plant patches had 18% more arthropod species, and a greater abundance of omnivorous and predacious arthropods, but not herbivores, compared with monocultures. The effects of genotypic diversity on arthropod communities were due to a combination of interactive and additive effects among genotypes within genetically diverse patches. Greater genetic diversity also led to a selective feedback, as mean genotype fitness was 27% higher in diverse patches than in monocultures. A comparison between our results and the literature reveals that genetic diversity and species diversity can have similar qualitative and quantitative effects on arthropod communities. Our findings also illustrate the benefit of preserving genetic variation to conserve species diversity and interactions within multitrophic communities.     

物种多样性及环境因子对入侵植物空心莲子草群落稳定性的影响

为探讨外来入侵植物空心莲子草群落稳定性的驱动机制,在中国21°N-37°N范围内设置73个面积为10 mX 10 m的空心莲子草群落样地(陆生39个,水生34个),分别计算其Godron群落稳定性坐标值和4个α-物种多样性指数,并测定各样地的7项环境因子(经度、纬度、海拔、铵态氮、硝态氮、年均温和年均降雨量),采用回归...     

Efficiency of biochar,nitrogen addition,and microbial agent amendments in remediation of soil properties and microbial community in Qilian Mountains mine soils

Lacking systematic evaluations in soil quality and microbial community recovery after different amendments addition limits optimization of amendments combination in coal mine soils. We performed a short‐term incubation experiment with a varying temperature over 12 weeks to assess the effects of three amendments (biochar: C; nitrogen fertilizer at three levels: N‐N1~N3; microbial agent at two levels: M‐M1~M2) based on C/N ratio (regulated by biochar and N level: 35:1, 25:1, 12.5:1) on mine soil properties and microbial community in the Qilian Mountains, China. Over the incubation period, soil pH and MBC/MBN were significantly lower than unamended treatment in N addition and C + M + N treatments, respectively. Soil organic carbon (SOC), total nitrogen (TN), available nitrogen (AN), available phosphorus (AP), available potassium (AK), microbial biomass carbon (MBC), and nitrogen (MBN) contents increased significantly in all amended treatments (p < .001). Higher AP, AK, MBC, MBN, and lower MBC/MBN were observed in N2‐treated soil (corresponding to C/N ratio of 25:1). Meanwhile, N2‐treated soil significantly increased species richness and diversity of soil bacterial community (p < .05). Principal coordinate analysis further showed that soil bacterial community compositions were significantly separated by N level. C‐M‐N treatments significantly increased the relative abundance (>1%) of the bacterial phyla Bacteroidetes and Firmicutes, and decreased the relative abundance of fungal phyla Chytridiomycota (p < .05). Redundancy analysis illustrated the importance of soil nutrients in explaining variability in bacterial community composition (74.73%) than fungal composition (35.0%). Our results indicated that N addition based on biochar and M can improve soil quality by neutralizing soil pH and increasing soil nutrient contents in short‐term, and the appropriate C/N ratio (25:1) can better promote microbial mass, richness, and diversity of soil bacterial community. Our study provided a new insight for achieving restoration of damaged habitats by changing microbial structure, diversity, and mass by regulating C/N ratio of amendments.     

农业景观结构对麦蚜寄生蜂群落组成的影响

麦蚜是中国北方小麦上最重要的害虫之一,既能直接刺吸危害也可传播多种病毒,但麦蚜通常的危害期只有2～3个月。随着现代农业与设施农业的发展,农业景观结构发生了巨大的改变,整个麦蚜寄生蜂群落也随之发生了显著的变化。经典假说认为复杂的农业景观能够维持局部的物种多样性及种间关系,也能够维持更大的天敌资源。作者在4种不同的麦田景观类型下研究了麦蚜及寄生蜂的群落结构,发现简单农业景观与复杂农业景观中寄生蜂寄生率与多样性差异不显著,但初寄生蜂在800m2左右的生境面积中寄生率与多样性最高,重寄生蜂却并没有表现出这种分布,而在更大的生境中重寄生率与多样性更高。研究结果表明:1)生境面积是影响麦蚜及寄生蜂群落的重要因子,2)简单农业景观与复杂农业景观下麦蚜及寄生蜂群落多样性差异不显著,3)一定程度的生境破碎化能够促进初寄生蜂的种群而抑制重寄生蜂的种群,但高度的生境破碎化会同时抑制2种寄生蜂的种群。     

Seed banks on Attalea phalerata (Arecaceae) stems in the Pantanal wetland, Brazil

Background and Aims

Seeds can accumulate in the soil or elsewhere, such as on the stems of palms when these are covered by persistent sheaths. These sheaths could act as a safe site for some species. Here, we studied whether persistent sheaths of the palm Attalea phalerata (Arecaceae) are available sites for seed accumulation in the Pantanal wetland of Brazil. We also investigated whether the composition, richness and diversity of species of seeds in the persistent sheaths are determined by habitat (riparian forest and forest patches) and/or season (wet and dry).

Methods

All accumulated material was collected from ten persistent sheaths along the stems of 64 A. phalerata individuals (16 per habitat and 16 per season). The material was then individually inspected under a stereomicroscope to record seed species and number.

Key Results

Of the 640 sheaths sampled, 65 % contained seeds (n = 3468). This seed bank included 75 species belonging to 12 families, and was primarily composed of small, endozoochoric seeds, with a few abundant species (Cecropia pachystachya and Ficus pertusa). Moraceae was the richest family (four species) and Urticaceae the most abundant (1594 seeds). Stems of A. phalerata in the riparian forest had 1·8 times more seeds and 1·3 times more species than those in forest patches. In the wet season we sampled 4·1 times more seeds and 2·2 more species on palm stems than in the dry season. Richness did not differ between habitats, but was higher in the wet season. Abundance was higher in forest patches and in the wet season.

Conclusions

Attalea phalerata stems contain a rich seed bank, comparable to soil seed banks of tropical forests. As most of these seeds are not adapted to grow in flooding conditions, palm stems might be regarded as safe sites for seeds (and seedlings) to escape from the seasonal flooding of the Pantanal.     

High Bird Species Diversity in Structurally Heterogeneous Farmland in Western Kenya

Tropical ecosystems are globally important for bird diversity. In many tropical regions, land‐use intensification has caused conversion of natural forests into human‐modified habitats, such as secondary forests and heterogeneous agricultural landscapes. Despite previous research, the distribution of bird communities in these forest‐farmland mosaics is not well understood. To achieve a comprehensive understanding of bird diversity and community turnover in a human‐modified Kenyan landscape, we recorded bird communities at 20 sites covering the complete habitat gradient from forest (near natural forest, secondary forest) to farmland (subsistence farmland, sugarcane plantation) using point counts and distance sampling. Bird density and species richness were on average higher in farmland than in forest habitats. Within forest and farmland, bird density and species richness increased with vegetation structural diversity, i.e., were higher in near natural than in secondary forest and in subsistence farmland than in sugarcane plantations. Bird communities in forest and farmland habitats were very distinct and very few forest specialists occurred in farmland habitats. Moreover, insectivorous bird species declined in farmland habitats whereas carnivores and herbivores increased. Our study confirms that tropical farmlands can hardly accommodate forest specialist species. Contrary to most previous studies, our findings show that structurally rich tropical farmlands hold a surprisingly rich and distinct bird community that is threatened by conversion of subsistence farmland into sugarcane plantations. We conclude that conservation strategies in the tropics must go beyond rain forest protection and should integrate structurally heterogeneous agroecosystems into conservation plans that aim at maintaining the diverse bird communities of tropical forest‐farmland mosaics.     

Australian Tropical and Subtropical Rain Forest Community Assembly: Phylogeny,Functional Biogeography,and Environmental Gradients

To compare community assemblage patterns in tropical northeastern and subtropical central eastern Australia across selected gradients and scales, we tested the relationship of species traits with phylogenetic structure, and niche breadth. We considered phylogenetic relationships across current‐day species in assemblages in relation to rain forest species pool sizes, and trait values along gradients including elevation and latitude. Trait values were quantified across scales for seed size, leaf area, wood density and maximum height at maturity for 1137 species and 596 assemblages using trait gradient analysis (TGA). Local assemblages of subtropical species had narrower trait ranges, and higher niche breadth values than corresponding assemblages of tropical species. Leaf size and seed size increased at low latitudes, and community phylogenetic structure was most strongly correlated with seed traits in the subtropics, reflecting dispersal and re‐colonization processes. Elevation accounted for little of the variance in community phylogenetic structure or trait variation across local and regional scales. Stable moist forest areas retained many species from ancestral rain forest lineages across a range of temporally conserved habitats; species within assemblages were less related; and rain forest assemblages had higher functional diversity, but lower niche breadth. This suggests that on average, assemblages of species in stable areas had greater trait variation and narrower distributions. Historic and recent rain forest contraction and re‐expansion can result in recolonized areas that are dominated by species that are more related (phylogenetically) than by chance, have smaller, widely dispersed seeds, and greater niche breadth (broader distributions).     

The Influence of Habitat,Season, and Detectability on Abundance Estimates across an Amazonian Parrot Assemblage

The Amazon basin holds very high parrot species richness but almost nothing is known of parrot population densities in the region or how these vary between species, habitats, sites, and seasons. Such data are becoming important as humans impact on increasing areas of the region. Seventeen parrot species were surveyed using a line transect distance sampling method over 3 yr in floodplain and terra firme forests at two sites in the Tambopata region of southeast Peru. Density estimates for most species were in the range of 3.3–7.8/km², with Brotogeris cyanoptera and Amazona farinosa reaching densities of 22 and 23/km² in floodplain forest during the dry season. Parrot densities were higher in floodplain forest than in terra firme forest at both sites. The parrot communities of terra firme forests were similar across sites and seasons, but those in floodplain forests differed widely across sites and across seasons. Upper canopy birds are notoriously difficult to survey. We introduce a procedure to correct for the likely violation of the assumption that all birds on the transect line are detected (distance sampling assumption g(0) = 1). We correct g(0) based on calling rates of birds using a cue‐counting technique. Multipliers for g(0) differ across species and site, but not season. This method yielded density estimates on average 22 percent higher (6–40% higher in individual species) than those from the standard method.     

Plant-parasitic Nematode Communities and Their Associations with Soil Factors in Organically Farmed Fields in Minnesota

A survey was conducted to determine the assemblage and abundance of plant-parasitic nematodes and their associations with soil factors in organically farmed fields in Minnesota. A total of 31 soil samples were collected from southeast (SE), 26 samples from southwest (SW), 28 from west-central (WC), and 23 from northwest (NW) Minnesota. The assemblage and abundance of plant-parasitic nematodes varied among the four regions. The soybean cyst nematode, Heterodera glycines, the most destructive pathogen of soybean, was detected in 45.2, 88.5, 10.7, and 0% of organically farmed fields with relative prominence (RP) values of 10.3, 26.5, 0.6, and 0 in the SE, SW, WC, and NW regions, respectively. Across the four regions, other common genera of plant-parasitic nematodes were Helicotylenchus (42.6, RP value, same below), Pratylenchus (26.9), Tylenchorhynchus and related genera (9.4), Xiphinema (5.6), and Paratylenchus (5.3). Aphelenchoides, Meloidogyne, Hoplolaimus, Mesocriconema, and Trichodorus were also detected at low frequencies and/or low population densities. The similarity index of plant-parasitic nematodes between two regions ranged from 0.44 to 0.71 and the similarity increased with decreasing distance between regions. The densities of most plant-parasitic nematodes did not correlate with measured soil factors (organic matter, pH, texture). However, the densities of Pratylenchus correlated negatively with % sand, and Xiphinema was correlated negatively with soil pH.