*4.2. Anthropogenic Gradients*

Beyond the prominent role of climate, land-use-related variables and human imprint emerged as weaker but significant determinants of the functional diversity and species richness of all examined taxa. Unsurprisingly, all taxa benefited from the land use diversity, as it reflects the habitat heterogeneity, that is, the availability of niches, which allows the coexistence of greater numbers of species with diverse functional traits [48,51]. Regarding human imprint, long-term human occupancy structures communities, with human pressures acting either as drivers or filters of functional diversity [24,25,33]. Amphibian (Rao's quadratic entropy) and reptile (functional richness) functional diversity decreased with the percentage of urban land area. Urbanization has a strong negative effect on amphibian and reptile assemblages, with few species having specific adaptations being able to secure their survival in urban areas [55], as in all fragmented and largely human-modified landscapes [11], and might result in the functional homogenization of communities [27]. Although amphibian functional diversity decreased with urban area, it increased with human population density, as has previously been shown for the species richness of different taxonomic groups [56,57]. Regarding the possible mechanisms for the positive richness, human population density invoking the suitability of climatic conditions, resource availability, and spatial heterogeneity [56] might explain the more functionally diverse amphibian communities in areas of higher human population density. On the other hand, agricultural area enhanced the richness (species and functional) of amphibians and disfavored reptiles. In a recent review [55], a non-significant, albeit negative, effect of agriculture on the species richness of these taxa was reported, but in the present study this was confirmed only for reptile functional diversity. Amphibians might benefit from the availability of water related to agriculture, or in some cases the matrix structure (e.g., possible landscape heterogeneity generated by the combination of agricultural and natural habitats) [55,58,59]. Inconsistent with recent research which reports that the trophic structure (an aspect of functional diversity) of communities highly exposed to human impacts is more simplified in terms of predicted structures with climate [60], here we found that mammalian richness and functional diversity were promoted by both the percentage of agricultural area and human population density. Low- to medium-intensity agriculture might conserve the diversity and functions of reptile communities [33,61], while the reported positive association between mammalian richness and human population density in Europe [56] seems to also apply to their functional diversity.

Although amphibians, reptiles, and mammals differ in their ecological roles, given the cross-taxon differentiations, these taxa shared some similarities in their responses and therefore in key functional roles [30]. Further investigation of mechanisms which drive functional diversity patterns considering data on different taxonomic groups could reveal further insights into how species functional roles can either complement or not respond to environmental variation. Climate, land uses, and other human-related factors influence species assemblages synergistically, making it difficult to decipher their individual effects on distribution patterns [33,62]; however, this might be related to the scale of the analysis. Here, we found that some human–landscape factors significantly affected diversity patterns at broad spatial scales. The consistency of the results was also extended to the different aspects of functional diversity (functional richness and Rao's quadratic entropy). Despite the acknowledged relationship between different functional diversity metrics [36,37], applying such analyses could help us to deepen our knowledge of how different aspects of functional diversity respond to environmental variation.

### **5. Conclusions**

Our study highlighted the roles of climate and variables related to land uses and human pressures on shaping the species richness and functional diversity of amphibians, reptiles, and mammals in Europe. We found a strong effect of climate, with the role of human imprint being significant but of lower impact. The effect of urban land area and human population density on functional diversity patterns reported here might have irreversible negative impacts on taxonomic groups such as amphibians, thus resulting in the impaired provision of ecosystem services. However, our study highlights the importance of some human-related factors (e.g., agricultural area) that could preserve communities' functions under specific circumstances. In the era of global change, neglecting human imprint may lead us to misinterpret the effects of environmental variation on the distribution of species and traits [25]. Functional diversity, a significant dimension of biodiversity, bridges ecosystem functioning and community responses to environmental change [32]. Biodiversity hotspots for terrestrial vertebrates may be extensively influenced by climate change, especially in the Mediterranean bioregion [63]. Traditional conservation practices should also implement new approaches (e.g., including research on functional traits and functional diversity) to optimize conservation planning, and thus preserve ecosystem functioning. Enhancing our understanding of the determinants and processes that govern functional diversity patterns is valuable for maintaining ecosystem resilience and stability under the prism of climate and land use change.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/ 10.3390/d13060275/s1, Table S1: Sources of information used to compile the trait databases of studied taxa.

**Author Contributions:** Conceptualization, M.A.T., M.L., A.A.-C. and A.S.K.; methodology, M.A.T., M.L. and D.E.-M.; software, M.A.T., M.L. and D.E.-M.; validation, M.A.T., M.L., D.E.-M., A.A.-C. and A.S.K.; formal analysis, M.A.T., M.L. and D.E.-M.; investigation, M.A.T. and M.L.; resources, A.S.K.; data curation, M.A.T., M.L. and D.E.-M.; writing—original draft preparation, M.A.T. and M.L.; writing—review and editing, M.A.T., M.L., D.E.-M., A.A.-C., S.P.S. and A.S.K.; visualization, M.L. and D.E.-M.; supervision, A.S.K.; project administration, A.S.K.; funding acquisition, A.S.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** Hellenic Foundation for Research and Innovation (H.F.R.I.) under the "First Call for H.F.R.I. Research Projects to support Faculty members and Researchers and the procurement of high-cost research equipment grant".

**Institutional Review Board Statement:** Not applicable.

**Data Availability Statement:** Publicly available datasets were analysed in this study. This data can be found here: http://na2re.ismai.pt/; https://www.european-mammals.org/php/mapmaker.php; https://worldclim.org/; https://www.pbl.nl/en/image/data; https://land.copernicus.eu/paneuropean/corine-land-cover/clc-2000.

**Acknowledgments:** This research work was supported by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the "First Call for H.F.R.I. Research Projects to support Faculty members and Researchers and the procurement of high-cost research equipment grant" (Project Number: HFRI-FM17-2024 Mapping Functional Diversity Drivers, Impacts and Threats-MAPFUN). The results presented in this work were produced using the Aristotle University of Thessaloniki (AUTh) High Performance Computing Infrastructure and Resources. The authors would like to acknowledge the support provided by the IT Center of the Aristotle University of Thessaloniki (AUTh) throughout the process of this research work. We would like to thank the anonymous reviewers for their helpful comments.

**Conflicts of Interest:** The authors declare no conflict of interest.
