Tracking Small Animals in Complex Landscapes: A Comparison of Localisation Workflows for Automated Radio Telemetry Systems

Automated radio telemetry systems (ARTS) have the potential to revolutionise our understanding of animal movement by providing a near-continuous record of individual locations in the wild. However, localisation errors in ARTS data can be very high, especially in natural landscapes with complex vegetation structure and topography. This curtails the research questions that may be addressed with this technology. We set up an ARTS grid in a valley with heterogeneous vegetation cover in the Colombian high Andes and applied an analytical pipeline to test the effectiveness of localisation methods. We performed calibration trials to simulate animal movement in high- or low-flight, or walking on the ground, and compared workflows with varying decisions related to signal cleaning, selection, smoothing, and interpretation, along with four multilateration approaches. We also quantified the influence of spatial features on the system's accuracy. Results showed large variation in localisation error, ranging between 0.4-43.4 m and 474-1929 m, depending on the localisation method used. We found that the selection of higher radio signal strengths and data smoothing based on the temporal autocorrelation are useful tools to improve accuracy. Moreover, terrain ruggedness, height of movement, vegetation type, and the location of animals inside or outside the grid area influence localisation error. In the case of our study system, thousands of location points were successfully estimated for two high-altitude hummingbird species that previously lacked movement data. Our case study on hummingbirds suggests ARTS grids can be used to estimate small animals' home ranges, associations with vegetation types, and seasonality in occurrence. We present a comparative localisation pipeline, highlighting the variety of possible decisions while processing radio signal data. Overall, this study provides guidance to improve the resolution of location estimates, broadening the application of this tracking technology in the study of the spatial ecology of wild populations.

Elevational and Seasonal Patterns of Plant-Hummingbird Interactions in a High Tropical Mountain

Tropical mountain ecosystems harbor diverse biological communities, making them valuable models for exploring the factors that shape ecological interactions along environmental gradients. We investigated the spatial and temporal drivers of plant-hummingbird interaction networks across three forest types (pine-oak, fir, and subalpine) along a tropical high mountain gradient in western Mexico (2400 to 3700 m.a.s.l.). We measured species abundance, diversity, morphology, and interaction frequencies. Plant diversity metrics significantly declined in the highest elevation subalpine forest, whereas hummingbird diversity remained consistent across elevations. Interaction networks were similarly nested across elevations, but they were more specialized in the subalpine forest, where lower plant species richness and higher floral abundance led to greater resource partitioning among hummingbirds. Plant-hummingbird networks were larger and less specialized during the dry season, driven by greater species diversity and abundance. Species turnover explained network variation along the elevational gradient, while interaction rewiring and the arrival of migratory hummingbirds explained changes between seasons. Phenological overlap was the most important driver of the observed variation in interaction frequencies across elevations and seasons. Flower abundance had a minor influence on interaction frequencies at low- and mid-elevation networks, and hummingbird abundance was significant for dry- and rainy-season networks. Morphological matching was significant in the low-elevation forest and in the dry season. Plant phylogenetic relatedness had negligible effects on interaction patterns, but hummingbird phylogeny influenced feeding preferences in high-elevation and rainy-season networks. Our findings highlight the role of species turnover, interaction rewiring, and phenological overlap in structuring plant-hummingbird networks, with specific effects of abundance, morphology, and phylogeny varying with elevation and season. High-elevation ecosystems play a crucial role as reservoirs of floral resources for both resident and migratory hummingbirds during resource-scarce periods, emphasizing their importance in maintaining biodiversity in tropical mountain gradients.

Using photogrammetry to create virtual permanent plots in rare and threatened plant communities

Premise

Many plant communities across the world are undergoing changes due to climate change, human disturbance, and other threats. These community-level changes are often tracked with the use of permanent vegetative plots, but this approach is not always feasible. As an alternative, we propose using photogrammetry, specifically photograph-based digital surface models (DSMs) developed using structure-from-motion, to establish virtual permanent plots in plant communities where the use of permanent structures may not be possible.

Methods

In 2021 and 2022, we took iPhone photographs to record species presence in 1-m2 plots distributed across alpine communities in the northeastern United States. We then compared field estimates of percent coverage with coverage estimated using DSMs.

Results

Digital surface models can provide effective, minimally invasive, and permanent records of plant species presence and percent coverage, while also allowing managers to mark survey locations virtually for long-term monitoring. We found that percent coverage estimated from DSMs did not differ from field estimates for most species and substrates.

Discussion

In order to continue surveying efforts in areas where permanent structures or other surveying methods are not feasible, photogrammetry and structure-from-motion methods can provide a low-cost approach that allows agencies to accurately survey and record sensitive plant communities through time.

Opposing Patterns of Altitude-Driven Pollinator Turnover in the Tropical and Temperate Americas

AbstractAbiotic factors (e.g., temperature, precipitation) vary markedly along elevational gradients and differentially affect major groups of pollinators. Ectothermic bees, for example, are impeded in visiting flowers by cold and rainy conditions common at high elevations, while endothermic hummingbirds may continue foraging under such conditions. Despite the possibly far-reaching effects of the abiotic environment on plant-pollinator interactions, we know little about how these factors play out at broad ecogeographic scales. We address this knowledge gap by investigating how pollination systems vary across elevations in 26 plant clades from the Americas. Specifically, we explore Cruden's 1972 hypothesis that the harsh montane environment drives a turnover from insect to vertebrate pollination at higher elevations. We compared the elevational distribution and bioclimatic attributes for a total of 2,232 flowering plants and found that Cruden's hypothesis holds only in the tropics. Above 30°N and below 30°S, plants pollinated by vertebrates (mostly hummingbirds) tend to occur at lower elevations than those pollinated by insects. We hypothesize that this latitudinal transition is due to the distribution of moist, forested habitats favored by vertebrate pollinators, which are common at high elevations in the tropics but not in the temperate Americas.

Vegetation Assembly, Adaptive Strategies and Positive Interactions During Primary Succession in the Forefield of the Last Venezuelan Glacier

Glaciers are receding at unprecedented rates in the alpine tropics, opening-up new areas for ecosystem assembly. However, little is known about the patterns/mechanisms of primary succession during the last stages of glacier retreat in tropical mountains. Our aim was to analyze soil development and vegetation assembly during primary succession, and the role of changing adaptive strategies and facilitative interactions on these processes at the forefront of the last Venezuelan glacier (Humboldt Peak, 4,940 m asl). We established a chronosequence of four sites where the glacier retreated between 1910 and 2009. We compared soil organic matter (SOM), nutrients and temperatures inside vs. outside biological soil crusts (BSCs) at each site, estimated the cover of lichen, bryophyte and vascular plant species present, and analyzed changes in their growth-form abundance and species/functional turnover. We also evaluated local spatial associations between lichens/bryophytes and the dominant ruderal vascular plant (the grass Poa petrosa). We found a progressive increase in SOM during the first century of succession, while BSCs only had a positive buffering effect on superficial soil temperatures. Early seral stages were dominated by lichens and bryophytes, while vascular plant cover remained low during the first six decades, and was almost exclusively represented by wind dispersed/pollinated grasses. There was a general increase in species richness along the chronosequence, but it declined in late succession for lichens. Lichen and bryophyte communities exhibited a higher species turnover than vascular plants, resulting in the loss of some pioneer specialists as succession progressed. Lichen and bryophyte species were positively associated with safe-sites for the colonization of the dominant ruderal grass, suggesting a possible facilitation effect. Our results indicate that lichens and bryophytes play a key role as pioneers in these high tropical alpine environments. The limited initial colonization of vascular plants and the progressive accumulation of species and growth-forms (i.e., direct succession) could be linked to a combination of severe environmental filtering during early seral stages and limitations for zoochoric seed dispersal and entomophilic/ornithophilic pollination. This could potentially result in a slow successional response of these ecosystems to accelerated glacier loss and climate change.