Tropical rainforest bird community structure in relation to altitude, tree species composition, and null models in the Western Ghats, India

Studies of species distributions on elevational gradients are essential to understand principles of community organisation as well as to conserve species in montane regions. This study examined the patterns of species richness, abundance, composition, range sizes, and distribution of rainforest birds at 14 sites along an elevational gradient (500-1400 m) in the Kalakad-Mundanthurai Tiger Reserve (KMTR) of the Western Ghats, India. In contrast to theoretical expectation, resident bird species richness did not change significantly with elevation although the species composition changed substantially (<10% similarity) between the lowest and highest elevation sites. Constancy in species richness was possibly due to relative constancy in productivity and lack of elevational trends in vegetation structure. Elevational range size of birds, expected to increase with elevation according to Rapoport's rule, was found to show a contrasting inverse U-shaped pattern because species with narrow elevational distributions, including endemics, occurred at both ends of the gradient (below 800 m and above 1,200 m). Bird species composition also did not vary randomly along the gradient as assessed using a hierarchy of null models of community assembly, from completely unconstrained models to ones with species richness and range-size distribution restrictions. Instead, bird community composition was significantly correlated with elevation and tree species composition of sites, indicating the influence of deterministic factors on bird community structure. Conservation of low- and high-elevation areas and maintenance of tree species composition against habitat alteration are important for bird conservation in the southern Western Ghats rainforests.Comment: 36 pages, 5 figures, two tables (including one in the appendix) Submitted to the Journal of the Bombay Natural History Society (JBNHS

Germination responses to light of four Neotropical forest tree species along an elevational gradient in the southern Central Andes

Seed germination is a key part of plants' life cycle and is mostly affected by the genetic background, the environmental conditions experienced by the mother plant and the seedbed conditions. The germination response to light is essential to optimize germination and seedling establishment in space and time. In addition, the germination response to light is a trait often related to the response of the seeds to their position in the soil (uncovered/buried). Here, we studied the germination response to light of four key tree species of the Yungas forest (Anadenanthera colubrina, Enterolobium contortisiliquum, Jacaranda mimosifolia and Handroanthus impetiginosus) sampled along an elevational and environmental gradient with contrasting vegetation cover and disturbance. Relative light germination (RLG) and mean germination time (MGT) were determined. Final germination was tested under cycles of light (8 h) and darkness (16 h) versus complete darkness (24 h) and elevation, and MGT was tested as a function of elevation of the provenance. The RLG increased from smaller to larger-seeded species. The MGT of three of the studied species was affected by the elevation of the provenance. Complete darkness negatively affected final germination, while two species exhibited a significant interaction between the provenance and light. The variable germination responses to light along the elevational gradient highlights the influence of the environment on germination as a key factor that should be considered for forest management, conservation and restoration projects

Low temperatures impact species distributions of jumping spiders across a desert elevational cline.

Temperature is known to influence many aspects of organisms and is frequently linked to geographical species distributions. Despite the importance of a broad understanding of an animal's thermal biology, few studies incorporate more than one metric of thermal biology. Here we examined an elevational assemblage of Habronattus jumping spiders to measure different aspects of their thermal biology including thermal limits (CTmin, CTmax), thermal preference, V̇CO2 as proxy for metabolic rate, locomotor behavior and warming tolerance. We used these data to test whether thermal biology helped explain how species were distributed across elevation. Habronattus had high CTmax values, which did not differ among species across the elevational gradient. The highest-elevation species had a lower CTmin than any other species. All species had a strong thermal preference around 37 °C. With respect to performance, one of the middle elevation species was significantly less temperature-sensitive in metabolic rate. Differences between species with respect to locomotion (jump distance) were likely driven by differences in mass, with no differences in thermal performance across elevation. We suggest that Habronattus distributions follow Brett's rule, a rule that predicts more geographical variation in cold tolerance than heat. Additionally, we suggest that physiological tolerances interact with biotic factors, particularly those related to courtship and mate choice to influence species distributions. Habronattus also had very high warming tolerance values (&gt; 20 °C, on average). Taken together, these data suggest that Habronattus are resilient in the face of climate-change related shifts in temperature

The effect of elevation on species richness in tropical forests depends on the considered lifeform: results from an East African mountain forest

Elevation gradients in tropical forests have been studied but the analysis of patterns displayed by species richness and elevation have received little attention. We examined whether the effect of elevation on species richness varies according to forest lifeforms and the main plant families in the Kahuzi-Biega National Park, within the Albertine Rift. We established 20 1-ha plots from 810 to 2760 m asl. Inside each plot, species inventories were carried out within three nested sub-plots: the tree lifeform (i.e. species with a dbh ≥ 10 cm), the shrub lifeform (dbh < 10 cm) and the herbaceous lifeform. For trees and shrubs (woody lifeforms) abundance data (i.e. number of individuals per species) were taken into account whereas the herbaceous lifeform was surveyed using presence–absence data. We plotted species counts vs elevation for each of the ten richest families per forest lifeform and resorted to Poisson regression models to assess the statistical meanings of the displayed results. Hurdle models (truncated Poisson regression) were used to account for overdispersion in the data. For woody lifeforms, we observed a monotonic decrease of species richness, while species richness appeared to be increasing with elevation for the herbaceous lifeform. Woody lifeforms displayed various vegetation patterns according to the considered families, therefore, contrasting with the general pattern observed in the herbaceous lifeform. These findings suggest the existence of specific eco-physiological properties pertaining to each forest lifeform and the existence of family-specific elevation patterns of species richness

Parallel functional and stoichiometric trait shifts in South American and African forest communities with elevation

The Amazon and Congo basins are the two largest continuous blocks of tropical forest with a central role for global biogeochemical cycles and ecology. However, both biomes differ in structure and species richness and composition. Understanding future directions of the response of both biomes to environmental change is paramount. We used one elevational gradient on both continents to investigate functional and stoichiometric trait shifts of tropical forest in South America and Africa. We measured community-weighted functional canopy traits and canopy and topsoil delta N-15 signatures. We found that the functional forest composition response along both transects was parallel, with a shift towards more nitrogen-conservative species at higher elevations. Moreover, canopy and topsoil delta N-15 signals decreased with increasing altitude, suggesting a more conservative N cycle at higher elevations. This cross-continental study provides empirical indications that both South American and African tropical forest show a parallel response with altitude, driven by nitrogen availability along the elevational gradients, which in turn induces a shift in the functional forest composition. More standardized research, and more research on other elevational gradients is needed to confirm our observations

Determination of Ellenberg’s indicator values along an elevational gradient in Central Black Sea Region of Turkey

The Central Black Sea Region has an unique vegetation because different vegetation types occurred. In the present study plant communities (from Mediterranean-type to temperate forests) in the Central Black Sea Region along an elevational gradient was evaluated on Ellenberg’s Indicator Values (EIVs). EIVs were calculated for nutrient availability, pH and temperature variables (nutrient availability (N), pH (R) and temperature (T)) with the help of weighted averages. Additionally, the vegetation of the study area was classified by using two way indicator species analyses (TWINSPAN) method and the interactions among plant species and EIVs were also studied by the help of Canonical Correspondence Analysis (CCA). We found some differences between our data and the previous data which were obtained from similar vegetation types with respect to EIV’s for nutrient availability, pH and temperature. Pteridium aquilinum, Fragaria vesca and Euphorbia amygdaloides var. amygdaloides may be used as an indicator of nutrient availability. There were significant differences among species regarding EIVs for temperature because the study area includes temperate and Mediterranean-type communities

Experimental salt marsh islands: a model system for novel metacommunity experiments

Shallow tidal coasts are characterised by shifting tidal flats and emerging or eroding islands above the high tide line. Salt marsh vegetation colonising new habitats distant from existing marshes are an ideal model to investigate metacommunity theory. We installed a set of 12 experimental salt marsh islands made from metal cages on a tidal flat in the German Wadden Sea to study the assembly of salt marsh communities in a metacommunity context. Experimental plots at the same elevation were established within the adjacent salt marsh on the island of Spiekeroog. For both, experimental islands and salt marsh enclosed plots, the same three elevational levels were realised while creating bare patches open for colonisation and vegetated patches with a defined transplanted community. One year into the experiment, the bare islands were colonised by plant species with high fecundity although with a lower frequency compared to the salt marsh enclosed bare plots. Initial plant community variations due to species sorting along the inundation gradient were evident in the transplanted vegetation. Competitive exclusion was not observed and is only expected to unfold in the coming years. Our study highlights that spatially and temporally explicit metacommunity dynamics should be considered in salt marsh plant community assembly and disassembly

Terrestrial camera traps: essential tool for the detection and future monitoring of the Critically Endangered Sira curassow Pauxi koepckeae

The only known population of Sira curassow Pauxi koepckeae resides within the Sira Communal Reserve, a chain of isolated and high-elevation outcrops of the Peruvian Andes. The species has previously been detected on just a handful of occasions, is thought to number less than 400 adult individuals and is Critically Endangered according to the International Union for Conservation of Nature Red List. As such, evaluating potential monitoring techniques to study the Sira curassow is of crucial importance to best inform future management strategies. We performed a preliminary assessment of camera traps to detect and collect novel ecological information on the Sira curassow. We used 17 cameras placed at regular altitudinal intervals (either 50 or 100 m) between 800 and 1800 m above sea level, 2 cameras placed at important habitat features, and 2 additional cameras placed on trails to assess hunting activity. Cameras were left in situ for 6 mo (March-September 2015). Sira curassows were detected at 26% of survey locations, totalling 19 independent detections. This resulted in an overall occupancy estimate of 0.25 across the whole transect and 0.55 across the current known elevational range. All records occurred between 1150 and 1500 m. Finally, we detail new ecological information obtained from the camera trap footage, readdress current threats to the species and provide recommendations regarding future monitoring

Connecting species’ geographical distributions to environmental variables: range maps versus observed points of occurrence

Connecting the geographical occurrence of a species with underlying environmental variables is fundamental for many analyses of life history evolution and for modeling species distributions for both basic and practical ends. However, raw distributional information comes principally in two forms: points of occurrence (specific geographical coordinates where a species has been observed), and expert-prepared range maps. Each form has potential short-comings: range maps tend to overestimate the true occurrence of a species, whereas occurrence points (because of their frequent non-random spatial distribution) tend to underestimate it. Whereas previous comparisons of the two forms have focused on how they may differ when estimating species richness, less attention has been paid to the extent to which the two forms actually differ in their representation of a species’ environmental associations. We assess such differences using the globally distributed avian order Galliformes (294 species). For each species we overlaid range maps obtained from IUCN and point-of-occurrence data obtained from GBIF on global maps of four climate variables and elevation. Over all species, the median difference in distribution centroids was 234 km, and median values of all five environmental variables were highly correlated, although there were a few species outliers for each variable. We also acquired species’ elevational distribution mid-points (mid-point between minimum and maximum elevational extent) from the literature; median elevations from point occurrences and ranges were consistently lower (median −420 m) than mid-points. We concluded that in most cases occurrence points were likely to produce better estimates of underlying environmental variables than range maps, although differences were often slight. We also concluded that elevational range mid-points were biased high, and that elevation distributions based on either points or range maps provided better estimates