Biology subjects

Vargas, F. H.

Publications and source records attributed to Vargas, F. H..

3 recordsLinked to original sources

bioRxiv2022

Prey resources are more important than climatic conditions for predicting the distribution of a broad-ranged apex predator

A current biogeographic paradigm states that climate regulates species distributions at continental scales and that biotic interactions are undetectable at coarse-grain extents. However, recent advances in spatial modelling show that incorporating food resource distributions are important for improving model predictions at large distribution scales. This is particularly relevant to understand the factors limiting distribution of widespread apex predators whose diets are likely to vary across their range. The harpy eagle (Harpia harpyja) is a large raptor, whose diet is largely comprised of arboreal mammals, such as sloths and primates, all with broad distributions across Neotropical lowland forest. Here, we used a hierarchical modelling approach to determine the relative importance of abiotic factors and prey resource distribution on harpy eagle range limits. Our hierarchical approach consisted of the following modelling sequence of explanatory variables: (a) abiotic covariates, (b) prey resource distributions predicted by an equivalent modelling for each prey, (c) the combination of (a) and (b), and (d) as in (c) but with prey resources considered as a single prediction equivalent to prey species richness. Incorporating prey distributions improved model predictions but using solely these biotic covariates still resulted in a high performing model. In the Abiotic model, Climatic Moisture Index (CMI) was the most important predictor, contributing 80 % to model prediction. Three-toed sloth (Bradypus spp.) was the most important prey resource, contributing 57 % in a combined Abiotic-Biotic model, followed by CMI contributing 29 %. Harpy eagle distribution had moderate to high environmental overlap across all prey distributions in geographic space when measured individually, but overlap was substantially lower in environmental space when prey distributions were combined. With strong reliance on prey distributions across its range, harpy eagle conservation programs must therefore consider its most important food resources as a key element in the protection of this threatened raptor.

ecology↗

bioRxiv2022

Habitat resource overlap in two broad-ranged sympatric Neotropical forest eagles

Quantifying resource partitioning between co-occurring species has important ecological and evolutionary implications. Yet, few studies compare resource overlap in both geographic and environmental space. We test whether the habitat requirements of two closely related Neotropical forest eagles, the crested eagle (Morphnus guianensis) and harpy eagle (Harpia harpyja), differ at fine and coarse resolutions across their shared geographic range. Using landcover and topographic covariates, we quantified resource overlap first using higher resolution (30 arc-sec data) generalized linear models (GLMs), and second using coarser-grain (2.5 arc-min data) environmental ordination. The distribution of both eagles was largely explained by canopy species richness and structural complexity with evergreen forest, but with differing responses to landcover and topography, particularly with the harpy eagle more likely in areas of dense evergreen forest. Both eagles were negatively associated with mosaic forest, with this relationship stronger for the crested eagle. Harpy eagle distribution was restricted by higher elevation and terrain roughness, compared to the crested eagle, whose distribution was more restricted by canopy species richness and structure. From the GLMs, resource overlap was > 92 % in geographical space but reduced to 64 % in environmental space. From ordination, resource overlap was 76 % in environmental space, with randomization tests supporting equivalent environmental space for both eagles. Our results suggest that at the biogeographical scale, crested and harpy eagles share environmental space, but there may be subtle differences in fine-scale habitat preference. We recommend habitat resource overlap be assessed in both geographical and environmental space at multiple resolutions to capture the inherent variability in environmental conditions available to co-occurring species.

ecology↗

bioRxiv2021

Range-wide habitat use and Key Biodiversity Area coverage for a lowland tropical forest raptor across an increasingly deforested landscape

Quantifying habitat use is important for understanding how animals meet their requirements for survival and provides useful information for conservation planning. Currently, assessments of range-wide habitat use that delimit species distributions are incomplete for many taxa. The harpy eagle (Harpia harpyja) is a raptor of conservation concern, widely distributed across Neotropical lowland forests, that currently faces threats from increasing habitat loss and fragmentation. Here, we use a logistic regression modelling framework to identify habitat resource selection and predict habitat suitability based on a new method developed from the International Union for the Conservation of Nature Area of Habitat range metric. From the habitat use model, we performed a gap analysis to identify areas of high habitat suitability in regions with limited coverage in the Key Biodiversity Area (KBA) network. Range-wide habitat use indicated that harpy eagles prefer areas of 70-75 % evergreen forest cover, low elevation, and high vegetation heterogeneity. Conversely, harpy eagles avoid areas of >10 % cultivated landcover and mosaic forest, and topographically complex areas. Our habitat use model identified a large continuous area across the pan-Amazonia region, and a habitat corridor from the Choco-Darien ecoregion of Colombia running north along the Caribbean coast of Central America. Little habitat was predicted across the Atlantic Forest biome, which is now severely degraded. The current KBA network covered [~]18 % of medium to high suitability harpy eagle habitat exceeding the target representation (10 %). Four major areas of high suitability habitat lacking coverage in the KBA network were identified in the Choco-Darien ecoregion of Colombia, western Guyana, and north-west Brazil. We recommend these multiple gaps of habitat as new KBAs for strengthening the current KBA network. Modelled area of habitat estimates as described here are a useful tool for large-scale conservation planning and can be readily applied to many taxa.

ecology↗