Tropical ant communities are in long-term equilibrium

Communities change with time. Studying long-term change in community structure permits deeper understanding of community dynamics, and allows us to forecast community responses to perturbations at local (e.g. fire, secondary succession) and global (e.g. desertification, global warming) spatial scales. Monitoring efforts exploring the temporal dynamics of indicator taxa are therefore a critical part of conservation agendas. Here, the temporal dynamics of the Otongachi leaf litter ant community, occurring in a cloud forest in coastal Ecuador, were explored. By sampling this community six times over eleven years, I assessed how the ant fauna caught by Winkler traps (more diverse and cryptic fauna) and caught by pitfall traps (larger, more mobile fauna) changed over time. The Otongachi leaf litter ant community was dynamic. Although species richness in the community remained constant, temporal turnover of species was high: on average, 51% of the ant species in Winkler traps, and 56% of those in pitfall traps, were replaced with other ant species from one year to the other. Shifts in the rank abundance of species in the community were also large across the eleven years and, on average, shifts in the rank abundance of species collected by Winkler traps doubled those occurring in pitfall traps from one census to the other. In spite of these trends, the Otongachi ant fauna showed no (Winkler) or weak (pitfall) evidence of directional change (towards a new community). Thus, this tropical ant community can be divided in two community compartments. The Winkler compartment composed by a more diverse and cryptic ant fauna appears to be resilient and stable in time. The pitfall compartment composed by larger and more mobile ants may be prone to respond to disturbance. This study suggests that 1) species appearing/disappearing from a site may be rather the rule, difficult to separate from responses to ecological stress. 2) Conclusions made in short-term studies, or studies comparing two (e.g. before and after) snapshots of a community, should thus be revisited. Finally, 3) the ant fauna caught by pitfall traps (a rather simple and cheap survey method) is the most likely community compartment to indicate ecological perturbation. This study adds to the growing evidence that using ants as ecological indicators should incorporate long-term temporal dynamics.     

Cedrela nebulosa: A novel species for dendroclimatological studies in the montane tropics of South America

Up to now, the development of dendrochronological records from tropical regions in South America has been limited to the lowlands with emphasis in the Amazon basin. In this contribution, we present the first chronology of Cedrela nebulosa, a species that develops in the tropical mountainous regions of South America. We collected samples from trees in Monobamba district in Peru, analysed the anatomical features that determine the growth rings, and processed following the methods commonly used in dendrochronology. The 133-years chronology covering the 1883–2015 period, showed large correlation between series. In order to determine the climatic variables that control tree growth, we performed correlation analyses between tree-growth and local and regional precipitation and temperature records. We found that precipitation triggers tree growth at the beginning of the spring season but temperature seems to be the main control in annual growth. Also, C. nebulosa chronology present coherent variations with Multivariate Enso Index (MEI) and Pacific Ocean sea surface temperatures during summer months. This climate-sensitive tree-ring record indicates good potential for dendroclimatic studies and provides an opportunity to reconstruct climatic variations in montane forests of the tropical Andes.     

Distribution patterns and insular biogeography of South Asian raptor communities

Ten diurnal raptor communities (Falconiformes) were studied in continental and peninsular situations, and on landbridge and oceanic islands of various sizes, from Southern India to Southern Vietnam and from Sri Lanka to Java. An index of abundance was derived from 1-km² sample plots. A consistent decrease of species richness occurred from continent to peninsulas and to large landbridge islands, then more abruptly to oceanic islands. The impoverishment process was much faster for open habitat raptors than for forest species, and for rarest and most specialized raptors than for common and more generalist species. Large taxa survived on islands as well as smaller species. Specific habitat requirements, historical factors and forest fragmentation were probably more important determinants of community composition than land area itself. An insular syndrome was documented in forest species on islands, including significant examples of habitat niche expansion, interspecific segregation and density compensation. Some cases suggested that interspecific competition was involved. Such relaxation of habitat and density constraints may enhance the survival probability of these species on islands.     

Growth response of Abies georgei to climate increases with elevation in the central Hengduan Mountains,southwestern China

Climatic harshness is expected to increase at higher elevations; however, elevational trends of tree radial growth response of high-elevation forests to climate change need to be investigated at different locations because of existing local variability in site-specific climatic conditions. We developed tree-ring width chronologies of Yunnan fir (Abies georgei) along elevation gradients at two sites in the central Hengduan Mountains (HM). High-elevation forests of A. georgei showed growth synchronicity and common growth signals along elevation gradients, indicating a common climatic forcing, although tree radial growth rates decreased with increasing elevation. Radial growth of Yunnan fir showed positive correlations with summer temperatures and February precipitation and moisture availability, but were negatively correlated with spring temperatures. The strongest positive relationship indicated summer (July) mean and minimum temperatures are the most important growth determining climatic factors for tree radial growth in the cold environment of HM, and this relationship revealed a clear elevational trend with stronger correlations at higher altitudes. In contrast, tree radial growth was negatively correlated with June precipitation and moisture availability. The whole study period 1954–2015 was split in two sub-periods of equal length. Comparing the early sub-period (1954–1984) to the later sub-period (1985–2015), tree growth response to the summer temperatures strongly increased, while it became weaker to June precipitation and moisture availability. High-elevation Yunnan fir forests in the HM currently benefit from elevated growing season temperatures under humid summer conditions. However, increasing temperatures may induce drought stress on tree radial growth if the observed decreasing trend in humidity and precipitation continues.     

Stronger dung removal in forests compared with grassland is driven by trait composition and biomass of dung beetles

1. Ecosystem processes depend on the biomass of the involved organisms, but their functional diversity may play an additional role. In particular, the exclusion of key functional groups through habitat disturbance may lead to the breakdown of ecosystem functions. Dung removal is an important process contributing to nutrient cycling and thus productivity in grazed ecosystems. 2. This study investigated the role of different functional groups of dung beetles in dung removal in different habitats within a wood-pasture in two different seasons. An experimental setting with 12 blocks and 108 dung pads was used to investigate short-term dung removal over 1 week of exposure. 3. Dung removal was most strongly affected by habitat type, with almost 40% lower levels in grassland than in adjacent forest and forest gaps. Of all assemblage characteristics, total biomass of tunneller species was the strongest predictor of dung removal, whereas functional diversity showed no significant effect. In accordance with the dung removal pattern at habitat type level, densities of large tunnellers were suppressed in grassland compared with forest. 4. It is concluded that dung removal is habitat-specific and large tunnellers play a disproportionate role in this important ecosystem function in temperate forests.     

Regulating Ecosystem Services of forests in ten Italian Metropolitan Cities: Air quality improvement by PM10 and O3 removal

Urban and periurban forests, which are integrated within the concept of Green Infrastructure, provide important Ecosystem Services, including air purification. In this study, we quantified the Ecosystem Service of particulate matter (PM₁₀) and Ozone (O₃) removal from urban and periurban forests in ten metropolitan cities in Italy, and its total monetary value. In order to gain a better understanding of how Ecosystem Services can be regulated on a wider scale, the vegetation ecosystem types were grouped into Physiognomic-Structural Categories of Vegetation according to morphofunctional criteria. The pollution removal was mapped using a remote sensing and GIS approach, by applying a deposition model and a stomatal flux model. We estimated, for the ten metropolitan cities, an overall pollution abatement of 7150 Mg of PM₁₀ and 30,014 Mg of O₃ in the year 2003, which was an extremely hot year. Our findings indicate that structural characteristics (i.e. Leaf Area Index) and functional diversity, linked to stomatal conductance, exert a marked influence on the provision of the regulating Ecosystem Services, whose total monetary value was estimated to be equal to 47 and 297 million USD for PM₁₀ and O₃ removal, respectively. This study represent the first national-scale assessment of the Ecosystem Services of air pollution removal in Europe, thus providing information that may be useful to stakeholders to manage Green Infrastructure more efficiently.