Changes In Species Composition Research Articles

Past and present effects of habitat amount and fragmentation per se on plant species richness, composition and traits in a deforestation hotspot

Worldwide, human activities are rapidly changing land cover and its spatial configuration. While it is widely acknowledged that habitat loss is a major cause of biodiversity loss, there is less agreement on how biodiversity responds to changes in habitat configuration. We assessed the effects of forest amount and forest fragmentation per se (the number of patches for a given forest amount, an aspect of configuration) on woody species richness, composition, and traits in the Dry Chaco forest, a global deforestation hotspot. We sampled woody plants in 24 forest sites varying in forest amount and fragmentation per se in the surrounding landscapes. Using Generalized Linear Modeling we tested whether a model with just forest amount was at least as able to predict species richness as a model with either patch size or isolation or the combination of both. We also tested whether forest amount and fragmentation per se influenced species richness, composition, and the density of four species traits. Finally, we compared these responses to forest amount and fragmentation per se measured in the past (2009) vs. in the present (2017) to look for time-lagged responses. We found that: 1) in support of the habitat amount hypothesis, species richness was more strongly related to forest amount than to the size and/or isolation of the forest patch containing the sample plot; 2) the positive effect of forest amount on species richness was more important than the effect of fragmentation per se (also positive); 3) fragmentation per se changed species composition such that plots in landscapes with more fragmented forest had species with smaller leaves and seeds, and higher wood density; and 4) species richness showed a time-lagged response to forest amount but not to forest fragmentation per se. Our results suggest that preservation of native Dry Chaco forest should be prioritized regardless of its fragmentation level, for conserving woody plant species diversity.

Multiple responses of bryophytes in a chronosequence of burnt areas in non-fire prone subtropical cloud forests

In non-fire prone ecosystems, like some subtropical humid forests, fire produces habitat destruction and intensifies land degradation by inducing changes in native species composition, soil properties and erosive processes. Bryophytes are key components of the Macaronesian laurel forests playing an important role in regulating water cycling and microclimate. Ecological and taxonomical bryophytes groups have distinct ecological and physiological requirements and may respond in a different way to the same fire events. Therefore, analysing post fire recovery of bryophyte communities represents a key step towards a better understanding of forest fire drivers and post fire management. We investigated how species richness and composition of different ecological and taxonomical bryophyte groups varied in 1158 samples within a fire chronosequence from 5 to 57 years in the best-preserved laurel forest from Canary Islands (Garajonay National Park) analysing communities in terms of differences with comparable surrounding old growth unburnt stands. Epiphyte, terricolous and saxicolous bryophytes were sampled at each plot and the influence of the time since fire was analyzed together with environmental variables (temperature, precipitation, mist precipitation and elevation) and forest structure variables. Our results indicate that there is no general pattern of post fire recolonization, as recolonization varies depending on the ecological and phylogenetic groups considered. Climate and forest structure play an important role in post-fire recolonization, such that time since fire is not the most important variable influencing richness and composition. The results increase the understanding of the processes that shape compositional patterns in groups with high dispersal capacities and high microclimate dependence, such as mosses and liverworts.

Changes in Richness and Species Composition after Five Years of Grazing Exclusion in an Endemic Pasture of Northern Mexico

A well-managed grazing system improves the productivity and health, and it is important to promote sustainability. We analyzed the impact of grazing on the Sierra de Zapalinamé protected area in north Mexico. Our hypothesis was that grazing modifies species composition, richness, and nutrients after grazing exclusion for five years. In this area, eight plots were excluded from grazing, and species richness, evenness, and plant functional types for five years were monitored. This monitoring was also carried out on eight control plots adjacent to the excluded plots. Soil samples were collected from each plot in the fifth year of exclusion for nutrient content analysis. Grazing discriminated plant species composition after five years between excluded and control plots, but not species richness and evenness. In addition, exclusion increased grass cover and decreased forb cover. Indicator species for excluded and control sites were identified. It was concluded that part of the pastures can be excluded from grazing as a way to analyze changes in this protected area and promote greater plant diversity.

Basic aspects determining dynamics of storage pests’ population in technocenoses of grain storage facilities of the Republic of Belarus

Nowadays the problem of storage pests is of current interest, as arthropods living in grain storage facilities and eating grain cause both direct and indirect damage. As a result of the research carried out in 2019–2020 in storehouses of Belarus, the species composition of stored grain pests including 17 species was specified. The paper focuses on the aspects affecting the change of species composition, dominance structure, dynamics of pests’ population when agricultural products are stored in grain storage facilities. It has been determined that the structure of fauna depended on the method of storage (floor storage, bin storage), purpose of products (seed or forage grain), construction and types of storage facilities (airproof, not airproof). In unfilled storehouses coleopterans dominated with a floor storage (84.4 % of the total number), and ticks at bin storage (56.3 %). In grain storage facilities for seeds grain ticks were additional species (27.5 %), and they were permanent in storage facilities for forage grain (52.9 %). The pests were not discovered in disinfected airproof grain storage facilities with seed grain. Abiotic factor (temperature and air humidity) is a key predictor regulating dynamics of the population of stored grain pests during winter and spring-summer periods. The reduction of sensitivity of lesser grain borer (death in 50 %) and ticks (death in 73.6 %) to insectoacaricide with pirimiphos methyl as well as rice weevil (50 %), rust-red grain beetle (20 %) and ticks (48.5 %) to the composition of bifenthrin and malathion was identified for the first time in Belarus. The data indicating obligatory after harvest treatment of grain (cleaning and drying) were obtained, as soon as the absence of these elements in the protection technology brings about the development of ticks during autumn-spring period. The findings can be used for the development of antiresistant and ecologically sound systems of protection against storage pests.

Seasonal change in species composition and target-site mutations in Anopheles gambiae s.l. in the severe drought area of Kandi, North-eastern Benin

The persistence of malaria transmission in areas with very arid environmental conditions remains enigmatic. The present study investigated seasonal variation of mosquito species composition and Kdr and Ace-1 mutations in Anopheles gambiae s.l. in the very arid district of Kandi in North-eastern Benin.Adult mosquitoes were sampled over 1 year using both human landing catches (HLC) and pyrethrum spray catches in 4 villages belonging to 2 areas of different levels of aridity. The collections were carried out on a bi-monthly basis in the wet season, and once every month in the dry season to better capture the entomological situation in drought period. Females An. gambiae sl specimens were kept aside and analysed by PCR for species identification. Presence of kdr and Ace-1 mutations was also assessed in the An. gambiae s.l. collection.A total of 2,211 host-seeking mosquitoes belonging to 15 species were collected in the study area. An. gambiae s.l. was the most abundant species and represented 67% of the collection. Other Anopheles species were found at very low frequency among which An. funestus, An. pharoensis, An. broheri and An. coustani. Molecular species identification showed in dry season a significantly higher frequency of An. coluzzii over An. gambiae s. s. in both less dry (70% vs 29% with p < 0.001) and driest (70% vs 30% and p = 0.034) areas of the district of Kandi. In the rainy season, there was similar frequency of An. coluzzii and An. gambiae s. s. in the less arid area (53% vs 45%; p = 0.153), while An. coluzzii remained significantly predominant (62% vs 38%; p = 0.012) in the driest zone. The frequency of kdr mutation was significantly higher in dry season than in rainy season (93% vs 84%; p

Pollution has negative effects on macrozoobenthic trait diversity in a large subtropical estuary.

Changes in species composition and relative abundance caused by pollution might have an impact on the community dynamics and ecosystem functioning. Macrobenthos are widely used as indicators of marine environmental health due to their sensitive to disturbance. The present study aims to evaluate spatial and temporal variability of functional diversity of macrobenthos of the Montevideo and Canelones coastal zone along a pre-established pollution gradient, based on Biological Traits Analysis, and functional diversity indices. Body-size", "Feeding-mode", "Habitat", and "Indicator-role" were useful proxies to detect changes in environmental conditions in organically enriched habitats. FRic, FEve and FDis detected temporal variations but only FRic registered spatial variations. Differences among surveys would mainly reflect environmental variability caused by the 2009-2010 El Niño-Southern Oscillation event. Finally, negative correlations between FEve and FDis with AMBI suggest both indices as useful proxies of benthic environmental health, with potential to be used in monitoring and quality assessment programs.

Relationship of woody species composition with edaphic characteristics in threatened riparian Atlantic Forest remnants in the upper Rio Doce basin, Brazil

Studies on the composition, richness and diversity of plant species in tropical communities are essential for understanding relevant ecological processes and for developing appropriate conservation policies. Considering that areas subject to direct impacts due to dam breach may in the long‐term present changes in species composition and in soil parameters, we evaluated the composition of the flora, described the current vegetation profile, and evaluated whether differences in species composition was influenced by soil variables of three areas along the Gualaxo River, in Minas Gerais State, Brazil. In addition, we identified important plant species through occurrence and phytosociological parameters for ecological restoration projects in the affected region, serving as reference areas. We sampled plant species with DBH ≥ 5 cm (diameter at breast height – measured 1.30 m above ground level) in 77 plots distributed in three riparian forest areas. We calculated phytosociological parameters and related them to edaphic factors. A total of 1579 individual plants belonging to 53 botanical families and 227 species were sampled in the three areas. The Fabaceae family was the most representative with 46 species. Species composition and diversity among the sampled areas was similar and was associated with edaphic factors. Furthermore, some species (e.g. Xylopia sericea, Cupania emarginata and Ocotea pulchalla) showed an important relation with soil variables. Some species of the genera (e.g. Byrsonima, Xylopia, Ocotea and Croton) and families (e.g. Fabaceae and Myrtaceae) found here, can be important species in the restauration process for the local and regional maintenance of floristic identity in the Rio Doce river.

Impacts of the Invasive Alien Carpobrotus spp. on Coastal Habitats on a Mediterranean Island (Giglio Island, Central Italy).

Carpobrotus acinaciformis and C. edulis are well-known invasive alien plants native to South Africa, whose detrimental effects on native communities are widely documented in the Mediterranean basin and thus largely managed in coastal ecosystems. Most of the literature on these species focuses on their impacts on habitats of sandy coastal dunes, while the effects of Carpobrotus spp. invasion on other habitats such as rocky cliffs and coastal scrubs and garrigues are almost neglected. We present a study case conducted on a small Mediterranean island where Carpobrotus spp. invaded three different natural habitats listed within the Habitat Directive 92/43/CEE (Natura 2000 codes 1240, 1430, and 5320). We surveyed the presence and abundance of native species and Carpobrotus spp. on 44 permanent square plots of 4 m2 in invaded and uninvaded areas in each of the three habitats. We found impacts on plant alpha diversity (intended as the species diversity within each sampled plot) in all the habitats investigated in terms of a decrease in species richness, Shannon index, and abundance. Invaded communities also showed a severe change in species composition with a strong homogenization of the floras of the three habitats. Finally, the negative effect of invasion emerged even through the analyses of beta diversity (expressing the species diversity among sampled plots of the same habitat type), with Carpobrotus spp. replacing a large set of native species.

A cross-sectional study of Simulium damnosum sensu lato breeding sites and species distribution in Sudan savanna, mixed savanna–forest and rainforest regions in Cameroon

BackgroundThe presence of breeding sites and distribution of species of Simulium damnosum sensu lato are critical in understanding the epidemiology of onchocerciasis and evaluating the impact of elimination interventions. Reports on breeding sites and species distribution of members of S. damnosum s.l. in Cameroon are scarce and the few ones available date back to more than three decades. The aim of this study is to provide information on S. damnosum breeding sites across the rainy (RS) and dry (DS) seasons and the species composition in three different regions in Cameroon: Southwest (SW), Northwest (NW) and North (N).MethodsA cross-sectional two-season study was carried out in three regions with different ecological characteristics (SW—rainforest; NW—mixed forest–Guinea savanna; N—Sudan savanna). Pre-control onchocerciasis endemicity, relief maps and historical entomological information were used to identify potential rivers for purposive sampling. Sampled larvae were fixed in Carnoy’s solution and sorted, and S. damnosum s.l. larvae were stored until identification by cytotaxonomy. Geographical coordinates of potential breeding sites were recorded to produce maps using ArcGIS, while Chi-square tests in SPSS were used to test for any differences between black fly seasonal breeding rates.ResultsA total of 237 potential breeding sites were sampled (RS = 81; DS = 156) and 72 were found positive for S. damnosum s.l. The SW had the most positive sites [67 (RS = 24; DS = 43)], with a significant difference in the rate of breeding between the seasons (P < 0.05). Among 68 sites visited in both seasons, 16 (23.5%) were positive in one of the two seasons with more sites positive in DS(11) than RS(05), 14 (20.6%) and 38 (55.9%) respectively positive and negative in both seasons. Simulium damnosum sensu stricto and S. sirbanum were the main species in the N, while S. squamosum and S. mengense were the predominant species in the NW and SW. Simulium soubrense and S. yahense were uniquely recorded in the SW.ConclusionsA comprehensive mapping of breeding sites requires rainy and dry seasons sampling. This study demonstrates that a breeding site survey of S. damnosum s.l. is achievable in forest as well as savanna zones. Not all potential breeding sites are actual breeding sites. Observation of S. soubrense in the SW indicates changes in species composition over time and could affect onchocerciasis epidemiology in this area.Graphical abstract

Effects of drought-induced holm oak dieback on BVOCs emissions in a Mediterranean forest

Climate change is impairing tree physiology and growth, causing an increase in tree dieback in many Mediterranean forests. These desiccation phenomena are leading to changes in land cover and plant community composition. Mediterranean plants are capable to emit large amount of Biogenic Volatile Organic Compounds (BVOCs), whose emission and biosynthesis is strongly affected by environmental conditions. This study evaluates the seasonal changes in understory species composition in two forest stands in Southern Tuscany characterized by different levels of Quercus ilex L. crown defoliation (low and high defoliation, LD and HD) and the relationship with BVOCs emissions over three years. We found significant changes in the understory plant community following Q. ilex crown defoliation and mortality, observing an increment in the number of shrubs both in HD and LD stands. The environmental sampling of BVOCs fully reflected the changes in vegetation cover and composition, with a reduction in the amount of monoterpene emissions due to the increasing rates of defoliation and mortality of Q. ilex trees. Our results suggest that terpene emissions from Mediterranean forests would be modified by an increase of Q. ilex dieback, with important consequences for functioning of this forest ecosystem and its atmospheric chemistry.

The last millennium viewed from a fine-resolution freshwater diatom record from northwestern Patagonia

Little is known about the response of terrestrial and aquatic ecosystems to changes in climatic and human influences during the last millennium in northwestern Patagonia (NWP, 40°-44°S). By virtue of their sensitivity and specificity, diatoms are ideal for examining past changes in aquatic ecosystems and deciphering the ranges of variability under natural and human-induced conditions. To date, however, very few fossils diatom studies have examined in detail the environmental evolution during the last millennium throughout Patagonia. Here we present a fine-resolution diatom record from a lake-sediment core collected from Lago Pichilaguna (41°S), a closed-basin and shallow lake with a small catchment area located in the lowlands of the Chilean Lake District in NWP. The record spans the last millennium with a median time resolution of ∼12 years between samples, and shows abundant small Aulacoseira spp. between ∼1000-900 and ∼600-300 cal yr BP, which alternate in dominance with small fragilarioids and small raphid diatoms between ∼900-600 and ∼300-200 cal yr BP. A rapid shift to planktonic diatoms started at ∼200 cal yr BP and led to their modern dominance. We interpret centennial-scale changes in temperature, precipitation, and lake turbulence, with warm/dry/stratified phases between ∼1000-900 and ∼600-300 cal yr BP related to weak westerly winds, and intervals of cold/wet and mixed water column conditions between ∼900-600 and ∼300-200 cal yr BP, favored by stronger winds. The transition from periphytic to planktonic diatoms that started at ∼200 cal yr BP suggests juxtaposition of the warmest/driest phase of the last millennium and the onset of large-scale disturbance by Chilean/European settlers in NWP. Our results reveal that human disturbance during historical time surpassed the natural ranges of variability and resilience of aquatic and terrestrial ecosystems over the last millennium, generating abrupt changes in biodiversity, species composition, and community structure.

Hardwood regeneration in red pine plantations: Thinning and site quality effects on changes in density and species composition from edges to interiors

Red pine plantations may promote more desirable hardwood regeneration than hardwood stands because of differences in: 1) the composition and quantity of tree seeds available, and 2) abiotic and biotic properties of growth and establishment environments. However, information on how distance from hardwood edges, thinning of overstory pine, and site quality shapes hardwood regeneration properties in red pine plantations is scarce. Such information would aid in understanding and managing red pine plantation effects on hardwood regeneration processes and guide spatial and temporal rotations of such effects across landscapes. To elucidate relationships, we monitored hardwood seedlings and canopy openness across transitions from hardwood edges to red pine plantation interiors at 40 sites spanning a site quality gradient in northwestern-lower Michigan. Hardwood seedling density: 1) declined substantially from edges to interiors at all but low-quality sites before stabilizing 30-m into plantations, 2) was reduced, or not affected, by thinning despite positive effects on seedling light environments, and 3) was greater at intermediate than high- and low- quality sites. From edges to interiors, species composition shifted towards Acer rubrum, Quercus species, and Prunus serotina and away from Acer saccharum, Fagus grandifolia, Fraxinus americana, and Ostrya virginiana. Species increasing in relative abundance and/or density from edges to interiors were generally more drought-tolerant, shade-intolerant, large-seeded, and animal-dispersed than decreasing species. Shifts towards less shade-tolerant species from edges to interiors were consistent with increases in canopy openness and were most pronounced where changes in light were greatest (i.e., thinned plantations on high-quality sites). Changes in hardwood seedling density and composition were likely driven by differences across species in dispersal traits, seed characteristics, and relative adaptation to interior conditions (likely hotter, drier, and nutrient poor). To promote commercially valuable hardwoods, increase mast for wildlife, or improve climatic resiliency, the most suitable targets for conversion to hardwoods may be plantations with significant interiors (i.e., area > 30-m from hardwood edges) on higher quality sites adjacent to desirable seed sources (e.g., Quercus rubra, Prunus serotina, Acer saccharum). More desirable hardwood regeneration may result from reevaluating thinning timings and intensities originally designed to maximize red pine production. Our results also indicate that intentional management of surrounding hardwood forest composition (i.e., seed sources), within plantation retention of hardwood islands (e.g., mature oak stems), and greater control of Acer rubrum competition may further increase the desirability of hardwood regeneration in red pine plantations.

Rocky Mountain forests are poised to recover following bark beetle outbreaks but with altered composition

AbstractAmplified by warming temperatures and drought, recent outbreaks of native bark beetles (Curculionidae: Scolytinae) have caused extensive tree mortality throughout Europe and North America. Despite their ubiquitous nature and important effects on ecosystems, forest recovery following such disturbances is poorly understood, particularly across regions with varying abiotic conditions and outbreak effects.To better understand post‐outbreak recovery across a topographically complex region, we synthesized data from 16 field studies spanning subalpine forests in the Southern Rocky Mountains, USA. From 1997 to 2019, these forests were heavily affected by outbreaks of three native bark beetle species (Dendroctonus ponderosae,Dendroctonus rufipennisandDryocoetes confusus). We compared pre‐ and post‐outbreak forest conditions and developed region‐wide predictive maps of post‐outbreak (1) live basal areas, (2) juvenile densities and (3) height growth rates for the most abundant tree species – aspen (Populus tremuloides), Engelmann spruce (Picea engelmannii), lodgepole pine (Pinus contorta) and subalpine fir (Abies lasiocarpa).Beetle‐caused tree mortality reduced the average diameter of live trees by 28.4% (5.6 cm), and species dominance was altered on 27.8% of field plots with shifts away from pine and spruce. However, most plots (82.1%) were likely to recover towards pre‐outbreak tree densities without additional regeneration. Region‐wide maps indicated that fir and aspen, non‐host species for bark beetle species with the most severe effects (i.e.Dendroctonusspp.), will benefit from outbreaks through increased compositional dominance. After accounting for individual size, height growth for all conifer species was more rapid in sites with low winter precipitation, high winter temperatures and severe outbreaks.Synthesis. In subalpine forests of the US Rocky Mountains, recent bark beetle outbreaks have reduced tree size and altered species composition. While eventual recovery of the pre‐outbreakforest structureis likely in most places, changes inspecies compositionmay persist for decades. Still, forest communities following bark beetle outbreaks are widely variable due to differences in pre‐outbreak conditions, outbreak severity and abiotic gradients. This regional variability has critical implications for ecosystem services and susceptibility to future disturbances.

Species level mapping of a seagrass bed using an unmanned aerial vehicle and deep learning technique.

BackgroundSeagrass beds are essential habitats in coastal ecosystems, providing valuable ecosystem services, but are threatened by various climate change and human activities. Seagrass monitoring by remote sensing have been conducted over past decades using satellite and aerial images, which have low resolution to analyze changes in the composition of different seagrass species in the meadows. Recently, unmanned aerial vehicles (UAVs) have allowed us to obtain much higher resolution images, which is promising in observing fine-scale changes in seagrass species composition. Furthermore, image processing techniques based on deep learning can be applied to the discrimination of seagrass species that were difficult based only on color variation. In this study, we conducted mapping of a multispecific seagrass bed in Saroma-ko Lagoon, Hokkaido, Japan, and compared the accuracy of the three discrimination methods of seagrass bed areas and species composition, i.e., pixel-based classification, object-based classification, and the application of deep neural network.MethodsWe set five benthic classes, two seagrass species (Zostera marina and Z. japonica), brown and green macroalgae, and no vegetation for creating a benthic cover map. High-resolution images by UAV photography enabled us to produce a map at fine scales (<1 cm resolution).ResultsThe application of a deep neural network successfully classified the two seagrass species. The accuracy of seagrass bed classification was the highest (82%) when the deep neural network was applied.ConclusionOur results highlighted that a combination of UAV mapping and deep learning could help monitor the spatial extent of seagrass beds and classify their species composition at very fine scales.

Recent insights into the use of invertebrates as indicators of habitat quality

Invertebrates are an important part of aquatic and terrestrial systems, and are, thus, useful as indicators of environmental changes. Habitat quality can be assessed by noting changes in species composition, and relative abundances, using various indices, and by alterations in physiology and morphology of what are known as indicator species. Research shows that invertebrates can be used to indicate if habitat conditions have changed, either worsened or improved. This is why identifying indicator species is crucial. This article covers some recent findings of how invertebrate organisms can be helpful in aquatic and terrestrial ecosystems in indicating ecosystem and habitat deterioration. We also discuss what makes a good indicator species and the types of taxa that have been used in this way.

Forest degradation in the Dry Chaco: A detection based on 3D canopy reconstruction from UAV-SfM techniques

Forest degradation is a gradual process through which the forest’s biomass declines, the species composition and vertical complexity change and the soil physicochemical properties degrade. Evaluating forest degradation is challenging, as it needs measurable indicators in order to compare different states of degraded forest with forests in optimal conditions. The UAV-SfM technique, combining imagery taken from unpiloted aerial vehicles (UAV) and Structure from Motion (SfM) algorithms, offers the opportunity to model forests in three dimensions and to derive ecological indicators describing forest conditions. The research objective of this paper is to evaluate to what extent information on forest degradation can be derived with UAV-SfM techniques.The Dry Chaco ecosystem in Argentina offers us the possibility to study the effects of a long history of anthropogenic disturbances on subtropical broadleaf dry forests. We surveyed a sample of 54 forest plots with different degradation histories with a UAV. Based on existing literature on forest ecology, two main degradation mechanisms were defined: loss of vertical integrity and vertical complexity. Multivariate statistical techniques were applied on structural indicators extracted from the 3D canopy model to classify the forest plots into groups or clusters with similar forest conditions. Next, the structural characteristics of the clusters were discussed in the light of a conceptual framework on forest degradation in the Dry Chaco. The results show that objective criteria derived from UAV-SfM 3D canopy models can be used to differentiate (1) forests in good condition from (2) forests that were subject to extensive processes of degradation, (3) forest with a dominance of shrubs and low trees, (4) forests intensively disturbed and (5) low vegetation dominated by bare soils with shrubs.

Coral community data Heron Island Great Barrier Reef 1962–2016

Here we describe benthic composition data derived from benthic photoquadrats collected over 41 surveys between 1962 and 2016 at four sites on Heron reef, at the southern end of Australia’s Great Barrier Reef, to assess change in coral composition over time. Surveys have often been annual, in a few years sub-annual, and the longest gap is six years. A subset of the data from two sites with the most complete records has been fully processed to allow the size of all individual colonies, and changes in species composition and cover, to be tracked over time. The taxonomy in these quadrats has been carefully checked for internal consistency, and is generally at the species level. A second subset has been processed, but has not been through full quality control, while a third subset exists as images only. This is the longest, 56 years, regular photographic record of coral cover in existence, and provides a valuable temporal contrast dating back in time to more recent studies of greater geographic extent and/or resolution.

BetaBayes—A Bayesian Approach for Comparing Ecological Communities

Ecological communities change because of both natural and human factors. Distinguishing between the two is critical to ecology and conservation science. One of the most common approaches for modelling species composition changes is calculating beta diversity indices and then relating index changes to environmental changes. The main difficulty with these analyses is that beta diversity indices are paired comparisons, which means indices calculated with the same community are not independent. Mantel tests and generalised dissimilarity modelling (GDM) are two of the most commonly used statistical procedures for analysing such data, employing randomisation tests to consider the data’s dependence. Here, we introduce a Bayesian model-based approach called BetaBayes that explicitly incorporates the data dependence. This approach is based on the Bradley–Terry model, which is a widely used approach for modelling paired comparisons that involves building a standard regression model containing two varying intercepts, one for each community involved in the beta diversity index, that capture their respective contributions. We used BetaBayes to analyse a famous dataset collected in Panama that contains information on multiple 1 ha plots from the rain forests of Panama. We calculated the Bray–Curtis index between all pairs of plots, analysed the relationship between the index and two covariates (geographic distance and elevation), and compared the results of BetaBayes with those from the Mantel test and GDM. BetaBayes has two distinctive features. The first is its flexibility, which allows the user to quickly change it to fit the data structure; namely, by adding varying effects, incorporating spatial autocorrelation, and modelling complex nonlinear relationships. The second is that it provides a clear path for performing model validation and model improvement. BetaBayes avoids hypothesis testing, instead focusing on recreating the data generating process and quantifying all the model configurations that are consistent with the observed data.

Carbohydrates and secondary compounds of alpine tundra shrubs in relation to experimental warming

BackgroundIt is critical to understand the sensitivity, response direction and magnitude of carbohydrates and secondary compounds to warming for predicting the structure and function of the tundra ecosystem towards future climate change.ResultsOpen-top chambers (OTCs) were used to passively increase air and soil temperatures on Changbai Mountain alpine tundra. After seven years’ continuous warming (+ 1.5 °C), the vegetation coverage, nonstructural carbohydrates (soluble sugars and starch) and secondary compounds (total phenols, flavonoids and triterpenes) of leaves and roots in three dominant dwarf shrubs, Dryas octopetala var. asiatica, Rhododendron confertissimum and Vaccinium uliginosum, were investigated during the growing season. Warming did not significantly affect the concentrations of carbohydrates but decreased total phenols for the three species. Carbohydrates and secondary compounds showed significantly seasonal pattern and species-specific variation. No significant trade-off or negative relationship between carbohydrates and secondary compounds was observed. Compared to Dr. octopetala var. asiatica, V. uliginosum allocated more carbon on secondary compounds. Warming significantly increased the coverage of Dr. octopetala var. asiatica, did not change it for V. uliginosum and decreased it for Rh. confertissimum. Rh. confertissimum had significantly lower carbohydrates and invested more carbon on secondary compounds than the other two species.ConclusionsEnhanced dominance and competitiveness of Dr. octopetala var. asiatica was companied by increased trend in carbohydrate concentrations and decreased ratio of secondary compounds to total carbon in the warming OTCs. We, therefore, predict that Dr. octopetala var. asiatica will continue to maintain dominant status, but the competition ability of V. uliginosum could gradually decrease with warming, leading to changes in species composition and community structure of the Changbai tundra ecosystem under future climate warming.

Pollen, macrofossils and sedaDNA reveal climate and land use impacts on Holocene mountain vegetation of the Lepontine Alps, Italy

Both climate change and anthropogenic disturbance affect vegetation composition, but it is difficult to separate these drivers of vegetation change from one another. A better understanding of past vegetation dynamics is necessary to disentangle the influence of different forcing factors and assess future vegetation change. Here we present the first multi-proxy palaeoecological study combining sedimentary ancient DNA (sedaDNA), pollen, spores, stomata, charcoal and plant macrofossils from the Alps. We reconstructed the Holocene vegetation dynamics and fire history at Lago Inferiore del Sangiatto (1980 m asl), a small lake in the subalpine belt of the Ossola region, Italian Lepontine Alps. Afforestation in response to climate warming started at 10,700 cal yr BP with Larix decidua and tree Betula, which formed open forests together with Pinus cembra from 10,500 cal yr BP onwards. Human impact on the regional vegetation started at 5100 cal yr BP, resulting in expansions of Picea abies and Alnus viridis and the collapse of Abies alba. Species response models and ordination analysis show that livestock grazing and fire were major drivers of vegetation change at Lago Inferiore del Sangiatto during the late Holocene. Finally, increasing human impact during the Bronze (ca. 4200–2900 cal yr BP) and Iron Age (ca. 2900–2000 cal yr BP) led to the formation of species-rich larch meadows and alpine pastures that are still dominant today. The palaeoecological data suggest that under projected climate change and land abandonment, the treeline ecotone will likely shift to higher altitudes, leading to important changes in species composition and increasing the risk of biodiversity loss.