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Modelling the nesting-habitat of threatened vulture species in the caucasus: An ecosystem approach to formalising environmental factors in species distribution models
Avian Research 2023, 14(4): 100131
Published: 28 August 2023
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Abiotic factors play an important role in species localisation, but biotic and anthropogenic predictors must also be considered in distribution modelling for models to be biologically meaningful. In this study, we formalised the biotic predictors of nesting sites for four threatened Caucasian vultures by including species distribution models (wild ungulates, nesting tree species) as biotic layers in the vulture Maxent models. Maxent was applied in the R dismo package and the best set of the model parameters were defined in the R ENMeval package. Performance metrics were continuous Boyce index, Akaike's information criterion, the area under receiver operating curve and true skill statistics. We also calculated and evaluated the null models. Kernel density estimation method was applied to assess the overlap of vulture ecological niches in the environmental space. The accessibility of anthropogenic food resources was estimated using the Path Distance measure that considers elevation gradient. The availability of pine forests (Scots Pine) and wild ungulates (Alpine Chamois and Caucasian Goat) contributed the most (29.6% and 34.3%) to Cinereous Vulture (Aegypius monachus) nesting site model. Wild ungulate distribution also contributed significantly (about 46%) to the Bearded Vulture (Gypaetus barbatus) model. This scavenger nests in the highlands of the Caucasus at a minimum distance of 5–10 ​km from anthropogenic facilities. In contrast, livestock as a food source was most important in colony distribution of Griffon Vulture (Gyps fulvus). The contribution of distances to settlements and agricultural facilities to the model was 45%. The optimal distance from Egyptian Vulture (Neophron percnopterus) nesting sites to settlements was only 3–10 ​km, to livestock facilities no more than 15 ​km with the factor contribution of about 57%. Excluding the wild ungulate availability, the ecological niches of studied vultures overlapped significantly. Despite similar foraging and nesting requirements, Caucasian vultures are not pronounced nesting and trophic competitors due to the abundance of nesting sites, anthropogenic food sources and successful niche sharing.

Open Access Research Article Issue
Ecological niche modeling of the main forest-forming species in the Caucasus
Forest Ecosystems 2022, 9(2): 100019
Published: 01 March 2022
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Background

Ecological niche modeling of the main forest-forming species within the same geographic range contributes significantly to understanding the coexistence of species and the regularities of formation of their current spatial distribution. The main abiotic and biotic environmental variables, as well as species dispersal capability, affecting the spatial distribution of the main forest-forming species in the Caucasus, have not been sufficiently studied.

Methods

We conducted studies within the physiographic boundaries of the Caucasus, including the Russian Federation, Georgia, Armenia, and Azerbaijan. Our studies focused on ecological niche modeling of pure fir, spruce, pine, beech, hornbeam, and birch forests through species distribution modeling and the concept of BAM (Biotic-Abiotic-Movement) diagram. We selected 648 geographic records of pure forests occurrence. ENVIREM and SoilGrids databases, statistical tools in R, Maxent were used to assess the influence of abiotic, biotic, and movement factors on the spatial distribution of the forest-forming species.

Results

Geographic expression of fundamental ecological niches of the main forest-forming species depended mainly on topographic conditions and water regime. Competitor influence reduced the potential ranges of the studied species by 1.2–1.7 times to the geographic expression of their realized niches and led to differences in the distribution of species with similar requirements for abiotic conditions. Movement factor significantly limited the areas suitable for pure forests (by 1.2–1.8 times compared with geographic expression of realized ecological niches), except for birch forests.

Conclusion

Distribution maps, constructed by abiotic, biotic, and movement factors, were the models of the occupied distributional area of the forest-forming species in the Caucasus. Biotic and movement factors should be considered in modeling studies of forest ecosystems if models are to have biological meaning and reality.

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