Species richness, resource availability, and disturbance are the primary factors considered in assessing the invasibility of plant communities. Nonetheless, the density of individuals in a community is a common and easy trait to measure. The ecological significance of the density of both native and invasive tree species was assessed using a systematic review and formal meta-analysis. The densities of recipient communities and invasive exotic tree species in novel ranges were identified in the published literature. In addition, we compared by means of a meta-analysis: (i) densities of invasive versus native species in invaded communities; (ii) densities of native species in invaded versus uninvaded communities; and (iii) densities of invasive species along distance gradients from initial locus of invasion. Invasive trees were found at higher densities than native species in recipient communities. Invasions by woody species were also recorded in communities with relatively low densities of natives suggesting that (i) low density forests may be more susceptible to invasion and/or (ii) density of the recipient community may be reduced during the invasion process. In addition, comparison of native species densities between invaded and uninvaded stands from the same community suggests that invasive trees negatively affect density of native trees once established. Therefore, the widely reported low density and often richness of native plants in invaded communities cannot be directly linked to ecosystem susceptibility to invasion without considering concomitant impacts. These findings suggest that density is a key preliminary determinant or factor which should be considered when assessing tree invasion dynamics.
One of the greatest concerns in community ecology is to find how species composition patterns are related to different environmental and spatial conditions. This approach is especially interesting when applied to high diversity heterogeneous forests such as the Brazilian Atlantic Rainforest sensu lato. The present study aims to verify the existence of indicator species in four southern Atlantic Rainforest formations and identify relationships among distributions of tree species with environmental and spatial variables. For that, tree species density data of 21 phytosociological surveys were collected from the literature. The data were analyzed using indicator species and partial canonical redundancy analysis (partial RDA). Sandy coastal formation contained the greatest number of indicator species (17), followed by Atlantic rainforest (10), cloud forest (4) and Araucaria forest (3). The partial RDA analysis explained 22% of total data variation, of which 11% was assigned to the environment, 5% to space, 6% to spatial component of environmental influence, and 78% remained undetermined. The forest formations present different sets of indicator species suggesting replacement of species along the forest formations. The largest and significant fraction of variation in the composition and abundance of tree species explained by environmental variables reflects the heterogeneity and complexity of habitats throughout the region of Atlantic Forest. The low spatial influence and the environmental results indicate a pattern of structured communities due to different requirements of niches by species (niche theory).
Authors:Eszter Laczkó-Zöld, Péter Forgó, István Zupkó, Eşianu Sigrid, and Judit Hohmann
Physalin D was isolated from the methanol extract of Physalis alkekengi L. fruits by combination of different chromatographic methods (CPC, TLC, HPLC). The structure was elucidated based on 1H and 13C NMR spectral analysis with the aid of 2D-correlation spectroscopy (1H, 1H-COSY, HSQC and HMBC) and comparison with literature data. The quantity of physalin D in mature and immature fruits and calyces was determined by RP-HPLC-UV method. Among the studied samples, immature calyx showed the highest content of physalin D (0.7880 ± 0.0612%), while mature calyx contained 4 times less amount (0.2028 ± 0.016%). The physalin D content of the fruit was much lower; immature fruits contained 0.0992 ± 0.0083% physalin D and mature fruits 0.0259 ± 0.0021%. The antiproliferative activity of the CHCl3 extract and its fractions was tested on three cancer cell lines (HeLa, MCF-7 and A431). The antiproliferative activity of physalin D is discussed with regard the published data.
Ponds contribute substantially to the maintenance of regional biodiversity. Despite a growing body of literature on biotic-abiotic relationships in ponds, only few generalizations have been made. The difficulty in identifying the main drivers of pond biodiversity has been typically attributed to the heterogeneity of the local and regional conditions characterizing ponds. However, little is known on how the use of different analytical approaches and community response variables affects the results of analysis of community patterns in ponds. Here, we used a range of methods to model the response of water beetle and plant community data (species richness and composition) to a set of 12 environmental and management variables in 45 farmland ponds. The strength of biotic-abiotic relationships and the contribution of each variable to the overall explained variance in the reduced models varied substantially, for both plants and beetles, depending on the method used to analyze the data. Models of species richness included a lower number of variables and explained a larger amount of variation compared to models of species composition, reflecting the higher complexity characterizing multispecies response matrices. Only two variables were never selected by any of the model, indicative of the heterogeneity characterizing pond ecosystems, while some models failed to select important variables. Based on our findings, we recommend the use of multiple modeling approaches when attempting to identify the principal determinants of biodiversity for each response variable, including at least a non-parametric approach, as well as the use of both species richness and composition as the response variables. The results of this modeling exercise are discussed in relation to their practical use in the formulation of conservation strategies.
In the 19th century, it was found that attraction of bees to light was controlled by light intensity irrespective of colour, and a few critical entomologists inferred that vision of bees foraging on flowers was unlike human colour vision. Therefore, quite justly, Professor Carl von Hess concluded in his book on the Comparative Physiology of Vision (1912) that bees do not distinguish colours in the way that humans enjoy. Immediately, Karl von Frisch, an assistant in the Zoology Department of the same University of Münich, set to work to show that indeed bees have colour vision like humans, thereby initiating a new research tradition, and setting off a decade of controversy that ended only at the death of Hess in 1923. Until 1939, several researchers continued the tradition of trying to untangle the mechanism of bee vision by repeatedly testing trained bees, but made little progress, partly because von Frisch and his legacy dominated the scene. The theory of trichromatic colour vision further developed after three types of receptors sensitive to green, blue, and ultraviolet (UV), were demonstrated in 1964 in the bee. Then, until the end of the century, all data was interpreted in terms of trichromatic colour space. Anomalies were nothing new, but eventually after 1996 they led to the discovery that bees have a previously unknown type of colour vision based on a monochromatic measure and distribution of blue and measures of modulation in green and blue receptor pathways. Meanwhile, in the 20th century, search for a suitable rationalization, and explorations of sterile culs-de-sac had filled the literature of bee colour vision, but were based on the wrong theory.
Community patterns in species-by-site matrices provide valuable clues for inferring ecological processes at work. One such pattern is the occupancy frequency distribution (OFD) depicting the frequency distribution of row sums (i.e., occupancy) with a quarter OFDs of bimodal forms. Another pattern that also reflects the structure of row sums is the ranked species occupancy curve (RSOC), and has been shown to imply a 50% of bimodality in OFDs. The use of RSOCs has been advocated in literature over the OFD based on two conclusions from a 6-model inference using only 24 matrices: (i) RSOCs have two general forms, with half representing bimodal OFDs; (ii) there are no effects of spatial and study scales on RSOCs of different forms. Using a much more representative dataset of 289 matrices, I cast doubt on these two conclusions. A missing but dominant RSOC model (the truncated power law) is added. The number of species and the nestedness of the community differ significantly among matrices of different RSOC forms; however, the number of sites and the taxa in the studies do not differ among RSOC or OFD forms. The quarter OFDs of bimodal forms is reassured, with the least frequent occupancy consistent with Raunkiaer’s law of frequency. Importantly, a RSOC is mathematically transferrable to an OFD, with the derivative of the occupancy ranking curve being equal to the negative reciprocal of the occupancy frequency. Based on the type of the community (null versus interactive) and site environment (homogenous versus heterogeneous), four scenarios are needed to identify pre-inferring assemblage mechanisms. The results highlight the need for shifting research from the emphasis of marginal sums to the analysis of matrix structure for an in-depth understanding of the community assemblage patterns and mechanisms.
Authors:G. Bonanomi, G. Incerti, A. Stinca, F. Cartenì, F. Giannino, and S. Mazzoleni
Ring shaped patches of clonal plants fascinated plant ecologists since long time. In this work we review the reports on the occurrence of ring pattern in different environmental conditions, the growth forms of ring-forming plants, the mechanisms underlying ring formation, and the consequences for species diversity at community scale. Rings formed by 83 species of clonal vascular plants have been found in grasslands, deserts, bare substrates of lava flow, harvested peat lands, salt marshes, and sand dunes. Four causal hypotheses have been proposed for the emergence of ring patterns: i. occurrence of architectural constraints for ramets development; ii. induction by fire, drought, trampling or overgrazing; iii. nutrient and water depletion by competition inside the ring; and iv. onset of species-specific negative plant-soil feedback in the inner zone of the clone. Since almost all the available studies are observations of ring structure or modelling exercises, none of the putative mechanisms for ring formation emerged from the literature as either generally applicable or suitable for rejection. Therefore, long-term field experiments are needed to investigate the relative prevalence of different mechanisms in different environments. Ring formation bears important consequences at community scale, because ring forming plants often act as “nurses”, enhancing the recruitment and development of different plant species. In fact, ring establishment modifies above- and below-ground environmental conditions, providing specialized safe sites for beneficiaries in the inner zone of the clones. Such interspecific facilitation by ring forming plants, particularly in chronically stressed environments, contributes to increase plant species richness and can locally promote the successional dynamics.
Forest biomes have expanded and contracted in response to past climate fluctuations, but it is not clear how they will respond to human-induced atmospheric change. We provide a review of the literature, describing historical links between biogeographical and atmospheric patterns, comparing characteristics of forest biomes and describing expected changes in climate forcings from observed range shifts. Over the geological history, climate fluctuations prompted changes in forest distribution that, in turn, stabilized the atmosphere. Over the past century, warming-induced stress has caused widespread declines of mature forests, but new forests have expanded into open areas of boreal, tropical and temperate regions. Historically, forest expansion happened at much faster rates in cold than in warm regions. Across biomes, species interactions control the use of limiting resources, regulating community dynamics and expansion rates in response to climate variability. Modern impacts of land use change on the distribution of forest biomes are well understood, but the expansion of new forests and their role in stabilizing the atmosphere are yet to be accounted for in global models. Expansion of tropical and temperate forests would yield a negative climate forcing through increased carbon sequestration and evaporative cooling, but in the boreal region forest expansion could amplify climate warming due to changes in albedo. Although qualitative descriptions of forest-atmosphere interactions are possible based on existing records, the net climate forcing from forest range shifts remains uncertain. Three critical gaps in knowledge hinder rigorous evaluations of causality necessary to probe for linkages between climatic and biogeographical patterns: (i) reconstructions of vegetation dynamics have not sufficiently represented warm biomes; (ii) climate and vegetation dynamics are typically assessed at non-comparable scales; and (iii) single-proxies are normally used to simultaneously infer changes in climate and vegetation distribution, leading to redundancy in interpretation. Addressing these issues would improve our ability to decipher past and predict future outcomes of forest-atmosphere interactions.