Vertical stratification patterns of tropical forest vertebrates: a meta-analysis

Highs and Lows of Arboreal Life: Space use and Movement Strategies of Lion-Tailed Macaques (Macaca silenus) in the Western Ghats of India

Lion-tailed macaques (Macaca silenus), endemic to the Western Ghats of India, are increasingly threatened by habitat loss and degradation, and are vulnerable to environmental change. Insights into their spatial ecology can reveal the strategies that enable these macaques to navigate and use spatially complex heterogeneous spaces. This is crucial for conservation, given the increasing human disturbance in and around the Western Ghats. This study, conducted in Silent Valley National Park between January and June of 2019, 2022, and 2023, focused on two macaque troops occupying habitats with varying human presence-in the park's core (Sairandhri) and in the buffer (Keeripara). The observed group sizes of the Sairandhri and Keeripara troops were 51 and 21, respectively. We examined differences in the spatial ecology of these troops by assessing their vertical space use, two-dimensional (2D) and three-dimensional (3D) home ranges, and using an integrated step-selection function to understand movement-based habitat selection. We observed similarities in movement patterns across the two troops, with notable differences mainly in their vertical use of the forest. The Keeripara troop, resident in a more disturbed area, utilized a smaller home range (1.80 km²). They spent 94.2% of their time in mid-level canopy (6-20 m), descending rarely (1.1%) into lower strata (≤ 5 m), likely due to perceived high risk from predators and humans, and proximity to roads. The Sairandhri troop, resident in the less disturbed area, had a larger home range (3.05 km²) and exhibited greater terrestriality (11.3%), with 84.2% observed time in mid-canopies. Both troops preferred areas with canopy cover and fruiting trees, displaying similar slow movements (indicated through small step lengths and large turning angles) near these resources. Our findings suggest that lion-tailed macaques may be less strictly arboreal than previously believed, displaying more terrestriality in less disturbed habitats. Strategic use of 3D space based on local ecological and anthropogenic conditions highlights the need for conservation efforts that maintain canopy connectivity to support the ecological flexibility of this vulnerable species.

Vertical and diel niches modulate thermal selection by rainforest frogs

Thermoregulatory behaviour determines an organism's body temperature and therefore its physiological condition, and may differ for organisms situated across climate gradients. Species' preferred or selected temperatures may be higher in warmer locations-referred to as coadaptation-or lower in warmer temperatures-countergradient variation. Here, we tested if rainforest amphibians exhibited coadaptation or countergradient thermal selection across an underappreciated spatial climate gradient (vertical height from forest floor to canopy) and separating diel activity (diurnal versus nocturnal behaviour). We captured 2534 amphibians over 216 ground-to-canopy surveys, and conducted 282 thermal selection assays for 37 species while pairing microclimate measurements and mechanistic model predictions to understand vertical and daily thermal variation in the field. Amphibians exhibited countergradient thermal selection: species occupying cool nocturnal conditions in canopies selected warmer temperatures than species occupying hot diurnal conditions at the forest floor. Furthermore, amphibians selected warmer temperatures than the average conditions that they were exposed to when active, and this divergence was especially high for nocturnal arboreal species (8.68°C). This suggests that rainforest amphibians dramatically underfill the warm end of their thermal niches, a trend across local thermal gradients that reflects recent findings across elevational and latitudinal gradients. We show that considering multidimensional climate gradients is important to evaluate thermoregulatory behaviour, and its evolutionary underpinnings, for understanding species' niches and community assembly.

Bird communities across different levels of human settlement: A comparative analysis from two northern Amazonian ecoregions

Urban ecosystems are increasingly dominating landscapes globally, so it is critical to understand the effects of human settlements on biodiversity. Bird communities are effective indicators because they are impacted by the size and expansion of human settlements, exemplified by changes in their habitat use, breeding and foraging behaviours, as well as patterns of richness and abundance. Existing studies on bird community responses to human settlements have mainly focused on single ecoregions and large cities, leaving a gap in comparative research on how differently sized human settlements affect bird communities across various ecoregions. To address this gap, we examine species richness, bird abundances and community composition in human settlements, which exhibit variable sizes, populations, landscape configurations, and overall intensity of settlement in two tropical ecoregions in Guyana, Amazonia: forest and savannah. In each ecoregion we explored how different groupings of urban tolerance in birds responded to human settlements of differing population size and building densities. Overall, we found significant differences in bird communities across the varying levels of human settlement intensity in both ecoregions, with greater differences in bird community composition in the forest ecoregion than the savannah region. In both ecoregions, species richness and abundance were highest at the medium level of settlement of human settlement. Our findings suggest that bird tolerance to human settlements varies based on ecoregion and site-level factors. In the savannah, built features may be benefitting birds from all urban tolerance levels, but they have a negative impact on less urban-tolerant species in the forest ecoregion. Our comparative analysis reveals for the first time that the impact of human settlements on avian communities in northern Amazonia varies among ecoregions, indicating that species evolved to live in a savannah may be more tolerant to human settlements than those more evolved to a forest system.

Ecological patterns and processes in the vertical dimension of terrestrial ecosystems

Climatic gradients such as latitude and elevation are considered primary drivers of global biogeography. Yet, alongside these macro-gradients, the vertical space and structure generated by terrestrial plants form comparable climatic gradients but at a fraction of the distance. These vertical gradients provide a spectrum of ecological space for species to occur and coexist, increasing biodiversity. Furthermore, vertical gradients can serve as pathways for evolutionary adaptation of species traits, leading to a range of ecological specialisations. In this review, we explore the ecological evidence supporting the proposition that the vertical gradient serves as an engine driving the ecology and evolution of species and shaping larger biogeographical patterns in space and time akin to elevation and latitude. Focusing on vertebrate and invertebrate taxa, we synthesised how ecological patterns within the vertical dimension shape species composition, distribution and biotic interactions. We identify three key ecological mechanisms associated with species traits that facilitate persistence within the vertical environment and draw on empirical examples from the literature to explore these processes. Looking forward, we propose that the vertical dimension provides an excellent study template to explore timely ecological and evolutionary questions. We encourage future research to also consider how the vertical dimension will influence the resilience and response of animal taxa to global change.