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A Squirrel’s Guide to the Olive Galaxy: Tree-Level Determinants of Den-Site Selection in the Persian Squirrel within Traditional Mediterranean Olive Groves
by
, , , , , , and
Yiannis G. Zevgolis
1,*
,
Efstratios Kamatsos
1, 
Apostolos Christopoulos
2,
Christina Valeta
1,
Eleni Rekouti
3,
Christos Xagoraris
4,
George P. Mitsainas
3
,
Petros Lymberakis
5,
Dionisios Youlatos
6,7
and
Panayiotis G. Dimitrakopoulos
1
1
Biodiversity Conservation Laboratory, Department of Environment, University of the Aegean, GR-81132 Mytilene, Greece
2
Department of Zoology and Marine Biology, Faculty of Biology, National and Kapodistrian University of Athens, GR-15772 Athens, Greece
3
Section of Animal Biology, Department of Biology, University of Patras, GR-26504 Patras, Greece
4
Department of Geography, School of Environment, Geography and Applied Economics, Harokopio University, GR-17671 Athens, Greece
5
Natural History Museum of Crete, School of Sciences and Engineering, University of Crete, GR-71409 Irakleio, Greece
6
Laboratory of Marine and Terrestrial Animal Diversity, Department of Zoology, School of Biology, Aristotle University of Thessaloniki, GR-54124 Thessaloniki, Greece
7
International Center for Biodiversity and Primate Conservation, Dali University, Dali 671003, China
*
Author to whom correspondence should be addressed.
Biology 2025, 14(12), 1676; https://doi.org/10.3390/biology14121676
Submission received: 27 October 2025
/
Revised: 16 November 2025
/
Accepted: 22 November 2025
/
Published: 25 November 2025
(This article belongs to the Special Issue Young Researchers in Ecology)
Simple Summary
Traditional centennial olive groves represent ecologically complex agroecosystems that combine agricultural use with high conservation value across the Mediterranean Basin. On Lesvos Island, Greece, which is the westernmost limit of the Persian squirrel’s (Sciurus anomalus) natural range, these centennial olive trees provide essential nesting refuges. To identify the factors guiding den-site selection, we measured structural, physiological, and thermal traits of 288 olive trees, including 36 confirmed den trees. Squirrels consistently selected older and taller trees with extensive crowns, high leaf area, and elevated photosynthetic performance, traits that enhance canopy productivity and promote a more stable microclimate. Infrared thermography further revealed that den trees exhibited lower orientation-related temperature asymmetries, reflecting stronger thermal regulation at the trunk level. Integrative modeling identified crown development and trunk thermal stability as the most decisive predictors of den occupancy. These results demonstrate that centennial olive trees function as important biophysical refuges, reinforcing the need to preserve traditional olive landscapes as key habitats for arboreal mammals in Mediterranean ecosystems.
Abstract
Traditional centennial olive groves represent ecologically valuable agroecosystems that support both biodiversity and cultural heritage across Mediterranean landscapes. On Lesvos Island, Greece, which marks the westernmost limit of the Persian squirrel (Sciurus anomalus) distribution, these centennial olive trees serve as essential nesting resources for this regionally Vulnerable species. However, the tree-level mechanisms determining den-site suitability remain insufficiently understood. We examined 288 centennial olive trees, including 36 with confirmed dens, integrating structural, physiological, and thermal metrics to identify the attributes influencing den occupancy. Our results showed that squirrels consistently selected older and taller olives with broad crowns and high photosynthetic activity, indicating a preference for vigorous, architecturally complex trees that provide stable microclimatic conditions. Infrared thermography revealed that occupied trees exhibited lower trunk temperature asymmetries and stronger thermal buffering capacity, highlighting the role of microclimatic stability in den-site selection. Overall, our findings show that den-site selection in S. anomalus is shaped by the interplay of structural maturity, physiological performance, and thermal coherence. By linking tree function to den-site suitability, our work advances a mechanistic understanding of microhabitat selection and emphasizes the importance of centennial olive trees as biophysical refugia within traditional Mediterranean agroecosystems.
